THE ORIGIN OF LIFE

It is said to be a great merit of canon law that it was the first to extend legal protection to the human embryo, and punished abortion with death as a mortal sin. But as this mystical theory of the entrance of the soul is now scientifically untenable, we should expect them consistently to extend this protection to the fœtus in its earlier stages, if not to the ovum itself. The ovary of a mature maid contains about 70,000 ova; each of these might be developed into a human being under favorable circumstances if it united with a male spermium after its release from the ovary. If the state is so eager for the multiplication of its citizens in the general interest, and regards prolific reproduction as a "duty" of its members, this is certainly a "sin ofomission." It punishes abortion with several years' imprisonment. But while civil law thus takes its inspiration from canon law, it overlooks the physiological fact that the ovum is a part of the mother's body over which she has full right of control; and that the embryo that develops from it, as well as the new-born child, is quite unconscious, or is a purely "reflex machine," like any other vertebrate. There is no mind in it as yet; it only appears after the first year, when its organ, the phronema in the cortex, is differentiated. This interesting fact is explained by the biogenetic law, which shows that the ontogeny of the brain is a condensed recapitulation of its phylogeny in virtue of the laws of heredity.The biogenetic law applies just as much to the brain, the organ of mind, as to any other organ of the human body. On the strength of the ontogenetic facts, which fall under direct observation, we infer that there was a corresponding development in the phylogenetic series of our animal ancestors. A significant confirmation of this inference is found in comparative anatomy. It shows that in all the skull-animals (craniota)—from the fishes and amphibia up to the apes and man—the brain is developed in the same way, as a vesicular distension of the ectodermal medullary tube. This simple oval cerebral vesicle first divides into three and afterwards five successive vesicles by transverse constriction (Anthropogeny, chapter xxiv., plate 24). It is the first of these vesicles, the cerebrum, that afterwards becomes the chemical laboratory of the mind. In the lower craniota (fishes and amphibia) the cerebrum remains very small and simple. It only reaches a notably higher stage in the three chief classes of the vertebrates, the amniotes. As these land-dwelling and air-breathing craniota have more difficult work to do in the struggle for life than their lower aquatic ancestors, we find much more variedand complex habits among them. These hereditary habits are gradually converted into instincts by functional adaptation and progressive heredity; and with the further development of consciousness in the higher mammals we have at last the appearance of reason. The gradual unfolding of the mental life is accompanied step by step with the advance of its anatomic organ, the phronema in the cortex. Recent careful investigations of the ontogeny and histology of the origin of mind (by Flechsig, Hitzig, Edinger, Ziehen, Oscar Vogt, etc.) have given us an interesting insight into the mysterious processes of its phylogeny.While the comparative anatomy of the cortex gives us a good idea of the gradual historical development of the mind in the higher classes of vertebrates, we get at the same time from their fossilized remains positive indications as to the period of time in which this phylogenesis has slowly taken place. The historical series in which the classes of vertebrates have succeeded each other in the great periods of the organic history of the earth is directly demonstrated by their fossil remains—the real commemorative medals of natural creation—and gives us a most valuable record of the ancestral history of our race and of the mind. The oldest strata that contain vertebrate remains form the huge Silurian System, which were, on the latest calculations, formed more than a hundred million years ago. They contain a few fossil fishes. In the succeeding Devonian System these are followed by the dipneusta, transitional forms between the fishes and the amphibia. The latter, the oldest four-footed and five-toed vertebrates, appear in the Carboniferous Period. They are succeeded in the Permian, the next system, by the oldest amniotes, the primitive reptiles (tocosauria). It is not until the next period (the Triassic) that the oldest mammals are found, small primitive monotremes (pantotheria), then marsupials inthe Jurassic, and the first placentals in the Cretaceans. The great wealth of varied and highly organized forms which are contained in this third and last sub-class of the mammals appear only in the succeeding Tertiary Period. The numbers of well-preserved skulls which these placentals have left behind in fossil form are particularly important, because they give us an idea of the quantitative and qualitative formation of the brain within the various orders; thus, for instance, in the modern carnivora the brain is from two to four times, and in the modern ungulates from six to eight times, as large (in proportion to the size of the body) as in their earliest Tertiary ancestors. It is also found that the cortex (the real organ of mind) has developed in the Tertiary Period at the expense of the other parts of the brain. The duration of this Cænozoic Period has lately been calculated at three million years (according to other geologists twelve to fourteen or more million years). It was, at all events, sufficient to make possible the gradual development of the human mind from the lower intelligence of our ape-ancestors and the instincts of the older placentalia.We have given the physiological name of the "phronema," as the real organ of mind or the instrument of reason, to that part of the cortex on the normal anatomic condition of which the action of the human mind depends. The remarkable investigations during the last few decades of the finer texture of the grey cortex (or cortical substance of the cerebrum) have shown that its structure—a real anatomic "wonder of life"—represents the most perfect morphological product of plasm; and its physiological function—mind—is the most perfect action of a "dynamo-machine," the highest achievement that we know anywhere in nature. Millions of psychic cells or neurona—each of them of an extremely elaborate fibril molecular structure—are associated asspecial thought-organs (phroneta) at certain parts of the cortex, and these again are built up into a large harmonious system of wonderful regularity and capacity. Each phronetal cell is a small chemical laboratory, contributing its share to the unified central function of the mind, the conscious action of reason. Scientists are still very far from agreement as to the extent of the phronema in the cortex and its delimitation from the neighboring sense-centres (sensoria). But they are all agreed that there is such a central organ of mind, and that its normal anatomic and chemical condition is the first requisite for the life of the human mind. This belief—one of the foundations of monistic psychology—is confirmed by the study of psychiatry.The study of the diseased organism has greatly furthered our knowledge of the normal frame. Diseases are so many physiological experiments made by nature herself under special conditions, which experimental physiology would often be unable to arrange artificially. The thoughtful physician or pathologist can often obtain most important knowledge of the function of organs by carefully observing them during disease. This is especially true of diseases of the mind, which always have their immediate foundation in an anatomical or chemical modification of certain parts of the brain. Our advancing knowledge of the localization of mental functions, or of their connection with special phroneta or organs of thought, is for the most part based on the experience that the destruction of the one is followed by the extinction of the other. Modern psychiatry, the empirical science of mental disease, has thus become an important element of our monistic psychology. If Immanuel Kant had studied it and had visited the asylum wards for a few months, he would certainly have escaped the dualist errors of his philosophy. We may say the same of the modern metaphysical psychologists who built up a mystictheory of an immortal soul without knowing the anatomy, physiology, and pathology of the brain.The comparative anatomy, physiology, and pathology of the brain, in concurrence with the results of ontogeny and phylogeny, have led us to form the sound monistic principle that the human mind is a function of the phronema, and that the neurona of the latter, or the phronetal cells, are the real elementary organs of mental life. Hence modern energism is perfectly justified in regarding mental energy (in all its forms) from the same point of view as all other forms of nervous energy, and in fact all manifestations of energy in organic or inorganic nature. Fechner's psychophysics had already shown that a part of this nervous energy is measurable and mathematically reducible to the mechanical laws of physics (Riddle, chapter vi.) Ostwald has, in hisNatural Philosophy, lately emphasized the fact that all the manifestations of mental life, not only sensation and will, but even thought and consciousness, can be reduced to nervous energy. Hence we may distinguish what are called mental forces from the other expressions of nervous energy asphronetic energy. The monistic research of Ostwald on the energy-processes in mental life (chapter xviii.), consciousness (chapter xix.), and will (chapter xx.) is very notable, and confirms the views I advanced in the second part of theRiddle(chapters vi., x., and xi.). Ostwald has, however, caused some misunderstanding by insisting on substituting his idea of energy for the pure notion of substance (as Spinoza had formulated it), and by rejecting the other attribute of substance, matter. His supposed "Refutation of Materialism" is a mere attack on windmills; his energism (the consistent dynamism of Leibnitz, etc.) is just as one-sided as its apparent opposite, the consistent materialism of Democritus, Holbach, etc. The latter makes matter precede force; the former regards matter asthe product of force. Monism escapes the one-sidedness of both systems, and, as hylozoism, refuses to separate the two attributes of substance, space-filling matter and active energy. This applies to mental life just as to any other natural process; our mental forces or phronetic energies are just as much bound up with the neuroplasm, the living plasm of the neurona in the cortex, as the mechanical energy of our muscles is with the contractile myoplasm, the living muscular substance.In the exhaustive study of consciousness which I gave in the tenth chapter of theRiddleI sought to show that this enigmatic function—the central mystery of psychology—is not a transcendental problem, but a natural phenomenon, subject to the law of substance, as much as any other psychic power. The child's consciousness only develops long after its first year, and grows as gradually as any other psychic function; like these, it is bound up with the normal anatomic and chemical condition of its organs, the phroneta in the cortex. Consciousness develops originally out of unconscious functions (as an "inner view," or mirroring, of the action of the phronema); and at any time an unconscious process in the cortex may come within the sphere of consciousness by having the attention directed to it. On the other hand, conscious actions, which need a good deal of attention when they are first learned (such as playing the piano), may become unconscious through frequent repetition and practice. The fact that chemical energy is converted in the phronetal cells during any of these actions is proved by the fatigue and exhaustion which prolonged mental work causes in the brain, just as mechanical work does in the muscles. Fresh matter has to be supplied by the food before the mental work can be continued. Moreover, it is well known that various drinks have a considerable influence on consciousness (coffee and tea, beer and wine); and the temporaryextinction of it under chloroform or ether is an analogous fact. Again, the familiar phenomena of the dream, the deviations from normal consciousness, hallucinations, delusions, etc., must convince every impartial thinker that these mental functions are not of a metaphysical character, but physical processes in the neuroplasm of the brain, and thoroughly dependent on the law of substance.In complete contrast to this natural monistic conception of the human mind, which is, in my opinion, definitely established by nineteenth-century science, we have the older dualistic estimate of it which is still widely accepted both by unlearned and learned, especially metaphysicians and theologians. I have already dealt in theRiddle(chapter xi.) with the grounds for this belief in an immaterial soul, and expressed my conviction that "the belief in the immortality of the human soul is in flagrant contradiction to the soundest empirical principles of modern science." I must refer the reader to what I said there about thanatism and athanatism, only reminding him once more of the immense influence of the Kantist philosophy in maintaining this belief in the spirituality of the soul. Kant derived from the introspective study of his own gifted mind an extremely high estimate of human reason, and he fallaciously transferred this estimate to the human mind generally. He did not perceive that it is either wholly wanting in the savage, or does not rise much above the stage which has been reached by the intelligence of the dog, horse, elephant, and other advanced animals.Modern anthropogeny has raised the theory of evolution to the rank of an historical fact. All the various organs of our body resemble those of our nearest relatives, the anthropoid apes, in their structure and composition. They only differ from them in details of form and size, which are determined by inherited variationsof growth. But the functions as well as the organs have been inherited by man from his primate ancestors. This applies to the mind also, which is merely the collective function of the phronema, the central organ of thought. An impartial comparison of mental life in the anthropoid ape and the savage shows that the differences between the two are not more considerable than the differences in the structure of their brains. Hence, if one accepts the dualistic theory of the soul formulated by Plato and Kant and accepted by so many modern psychologists, it is necessary to attribute an immortal soul to the anthropoid apes and the higher mammals (especially to domestic dogs) just as well as to savage or civilized man (cf.chapter xi. of theRiddle).The thorough and careful study of the mental life of the savage, supported by the results of anthropogeny and ethnography, has in the course of the last forty years decided the issue of this struggle between the conflicting theories of the origin of civilization. The older theory of degeneration, based on religious beliefs, and so preferred by theologians and theosophists, declared that man—the "image of God"—was created originally with perfect bodily and mental powers, and only fell away from his high estate after the original sin. On this view the present savages are degenerate descendants of the first godlike men. (In tropical lands the anthropoid apes are in similar fashion regarded by the natives as degenerate branches of their own stem!) Although this Biblical degeneration theory is still taught in most of our schools, and even supported by a few mystic philosophers, it had lost all scientific countenance before the end of the nineteenth century. It is now replaced by the modern theory of evolution, which was represented by Lamarck, Goethe, and Herder a century ago, and raised to a predominant position in ethnography by Darwin and Lubbock. It has taughtus that human civilization is the outcome of a long and gradual process of evolution, covering thousands of years. The civilized races of our time have arisen from less civilized races, and these in turn from lower, until we reach the savage races which show no trace of civilization.Ethnologists distinguish as a separate class the races which are found midway between the civilized peoples and the savages. We shall deal with their classification and characteristics later on (chapter xvii.). These races show some advance on the artistic instinct which we find in a slight degree even among the savages at times; moreover, their animal curiosity develops into human curiosity, and raises the question of the causes of phenomena, the germ of all science.Civilized races, which occupy the next stage to these, are raised above them by the formation of larger states and a greater division of labor. The specialization of the various groups of workers and the greater ease of maintenance permit a further development of art and science. To these groups belong, of living races, the majority of the Mongolians, and the greater part of the inhabitants of Europe and Asia in ancient and mediæval times. The great ancient civilizations of China, Southern India, Asia Minor, Egypt, and afterwards of Greece and Italy, show not only a great development of art and science, but also a concern for legislation, religious worship, education of the young, and the spread of knowledge by written books.Civilization in the narrower sense, characterized by a high development of art and science and the manifold application of them to practical life in legislation, education, etc., was greatly advanced even in antiquity among several nations—in Asia by the Chinese, Southern Indians, Babylonians, and Egyptians; in Europe by the Greeks and Romans of the classic age. However, theirresults were at first restricted to narrow fields, and were mostly lost during the Middle Ages. Modern civilization rose to importance about the end of the fifteenth century, when the invention of printing had made possible the spread of knowledge far and wide, the discovery of America and circumnavigation of the globe had widened the horizon, and the Copernican system had demolished the error of geocentricism. Then began the many-sided growth of civilization which has reached so marvellous a height in the nineteenth century through the extraordinary development of science. Then at last free reason could triumph over the prevailing mediæval superstition.XVTHE ORIGIN OF LIFEThe miracle of the origin of life—Creation of species: Moses and Agassiz—Creation of the first cells: Wigand and Reinke—Agnostic position: resignation—Eternity hypothesis (dualistic, Helmholtz; monistic, Preyer)—Archigony hypothesis (autogony hypothesis, Haeckel, Nägeli; cyanic hypothesis, Pflüger, Verworn)—Spontaneous generation—Saprobiosis or necrobiosis—Experiments in spontaneous generation—Pasteur—Stages of archigony—Observation of archigony—Synthesis of plasma—Value of the unsuccessful experiments to produce plasm artificially—The logic of modern experimental biology.The question of the origin of life is one of the most important and interesting, but one of the most difficult and complicated, problems with which the mind of man has been occupied for thousands of years. There are few other questions (such as the freedom of the will or personal immortality) on which such different and contradictory views have been expressed, and few that remain so far from being closed at the present day. There are, moreover, few problems on which the opinions of even distinguished thinkers diverge so much, and have degenerated so much into fantastic hypotheses. This is partly due to the extreme difficulty of giving a strictly scientific solution of the problem and partly to the confusion of ideas which is so great in this controversy, the lack of clear rational insight, and the powerful authority of the prevailing religious faith and other venerable dogmas.The easiest and quickest thing to do is to cut the Gordian knot of the question with the sword of faith, or answer it with a belief in a supernatural creation. The first article of the creed was given to us in childhood as the foundation of all cosmic philosophy. It is based on the Mosaic account of creation in the first chapter of Genesis. As I have fully examined its scientific value in the second chapter of myHistory of Creation, I may refer the reader thereto. It is unquestionable that this myth still has a very great practical influence; the great majority of the clergy cling to it because it is found in the infallible "word of God." Most governments, which hold blind faith to be an important element of education, include it in the code for the elementary school. On the other hand, it is difficult to find a man of science who will uphold it to-day. The gifted Louis Agassiz made one of the most remarkable attempts to do this in hisEssay on Classification(1858), a book that appeared almost contemporaneously with Darwin's epoch-makingOrigin of Species, and dealt with the general problems of biology from the directly opposite, the mystic, point of view. According to Agassiz, each species of animal or plant is an "incarnate thought of the Creator."Differing from this Biblical fancy of the supernatural creation of each species, two botanists, Wigand of Marburg and Reinke of Kiel, have lately restricted the action of the celestial architect very considerably; they have ascribed to him only the creation of the primitive cells, which he is supposed to have endowed with the power to develop into the higher organisms. Wigand assumed for the origin of each species a special primitive cell and a long phylogenetic development of this; Reinke prefers a stem, composed of a number of species. These modern creative theories have no more scientific value than that of Agassiz; they are equally based on pure superstition (cf.chapters i.-iii.).A different attitude from this irrational positive superstition is the sceptical view of those scientists who regard the question of the origin of life as insoluble or transcendental. Darwin and Virchow are representatives of this agnostic position; they held that we know nothing, and can know nothing, about the origin of the first organisms. Darwin, for instance, explains in his chief work that he "has nothing to do with the origin of the fundamental spiritual forces, or with that of life itself." This is a complete abandonment of the task of solving a scientific problem which must present as definite a subject of inquiry to modern research as any other evolutionary problem. The origin of life on our planet represents a fixed point in its history. However, there is nothing to be said if a scientist chooses to make no inquiry into it. A number of distinguished modern scientists maintain this agnostic attitude; they are more or less convinced that the origin of life is a natural process, but believe we have not as yet the means to explain it.Different, again, is a third attitude which regards the problem of the origin of life as extremely difficult, yet capable of solution. This is the position of Dubois-Reymond, for instance, who counts the origin of life as the third great cosmic problem. Most of the modern scientists who have worked on the problem are of this opinion, although their views as to the way of solving it differ very much. We are confronted, in the first place, with two essentially different views which we may call the eternity-hypothesis and the theory of archigony (or spontaneous generation). According to the first view, organic life is eternal; according to the second, it began at a definite point of time. The eternity-hypothesis has assumed two very different forms, one of which has a dualistic and the other a monistic base. Helmholtz is a representative of the former theory, and Preyer of the latter.Hermann Eberhard Richter put forward, in 1865, the hypothesis that infinite space is full throughout of the germs of living things, just as it is of inorganic bodies; both of them are in a condition of eternal development. When the ubiquitous germs reach a mature and habitable cosmic body, which possesses heat and moisture in the proper degrees for their development, they break into life, and may lead to the formation of a whole world of living things. Richter conceives these ubiquitous germs as living cells, and formulates the principle:Omne vivum ab æternitate e cellula(Every living thing is eternal and from a cell). In much the same way the botanist Anton Kerner postulates the eternity of organic life and its complete independence of the inorganic world. But the difficulties encountered by this hypothesis, in the indefinite form that Kerner gives it, are so great and so obvious that his theory has won no recognition.However, the "cosmozoic hypothesis" attained a great popularity when it was afterwards taken up by two of the most distinguished physicists, Hermann Helmholtz and Sir W. Thomson (Lord Kelvin). Helmholtz formulated the alternative thus (in 1884): "Organic life either came into existence at a certain period, or it is eternal." He declared for the latter view, on the ground that we have not succeeded in producing living organisms by artificial means. He supposes that the meteors that roam about the universe might contain the germs of organisms, and, under favorable conditions, these might reach the earth or other planets and develop thereon. This cosmozoic hypothesis of Helmholtz is untenable, because the physical features of space (the extreme temperatures, the absolute dryness, the absence of atmosphere, etc.) exclude the lasting existence of plasm on meteorites in the form of organic germs with a capacity to live. The hypothesis is, moreover, logically useless,since it does not solve, but postpones, the question of the origin of organic life. If it is consistently worked out, it leads to pure cosmological dualism.Another and very different theory of the eternity of life has been elaborated by Theodor Fechner (1873) and Wilhelm Preyer (1880). Both these scientists extend the idea of life to the whole cosmos, and reject the distinction that is usually drawn between the organic and the inorganic. Fechner goes so far as to ascribe consciousness to the whole universe and every single body in it, and regards individual organisms merely as parts of one vast universal organism. His system is, therefore, panpsychistic, and, at the same time, pantheistic, as he somewhat mystically connects the idea of a conscious God with that of a living universe. Preyer generally agrees with him in extending the idea of life to the whole universe, and conceiving it as an organism. He applies his theory in the symbolic sense which I alluded to on page 38, and described as impracticable. The fiery mass of the forming earth is the gigantic organism, and Preyer gives the name of "life" to its rotatory movement (or gravitational energy). As it cooled down, the heavier metals (the dead inorganic masses) separated from it; from the rest of it were formed first simple and afterwards complex carbon-combinations, and finally albumin and plasm. This extension of the word "organism" has very properly met with little approval in biology. It only increases the confusion, and the difficulty of marking off biological from abiological science, which is both practically necessary and theoretically justified.If, then, in our opinion, the eternity-hypotheses are of no more value than the creation-hypotheses, we have left, for the purpose of answering the great question of the origin of life, only the third group of scientific theories which I have combined under the general heador archigony. They start from the following points: 1. Organic life is everywhere bound up with the plasm (or protoplasm), a chemical substance of a viscous character, having albuminous matter and water as its chief constituents. 2. The characteristic movements of this living substance, to which we give the name of organic life, are physical and chemical processes, that can only take place within certain limits of temperature (between the freezing-point and boiling-point of water). 3. Beyond these limits organic life may in certain circumstances be maintained for a time in a latent condition (apparent death, potential life); but this latent condition is restricted to a certain (and generally short) period. 4. As the earth, like all the other planets, was for a long time in a state of incandescence, at a temperature of several thousand degrees, living organisms (viscous albuminoids) cannot possibly have existed on it, and so cannot be eternal. 5. Fluid water, the first condition for the appearance of organic life, cannot have formed on it until the crust at the surface had fallen below boiling-point. 6. The chemical processes which first set in at this stage of development must have been catalyses, which led to the formation of albuminous combinations, and eventually of plasm. 7. The earliest organisms to be thus formed can only have been plasmodomous monera, structureless organisms without organs; the first forms in which the living matter individualized were probably homogeneous globules of plasm, like certain of the actual chromacea (chroococcus). 8. The first cells were developed secondarily from these primitive monera, by separation of the central caryoplasm (nucleus) and peripheral cytoplasm (cell-body).The monistic hypothesis of abiogenesis, or autogony (= self-development) in the strictly scientific sense of the word, was first formulated by me in 1866 in the second book of theGeneral Morphology. The solidfoundation for it was found in the monera I had described, the very simple organisms without organs that had up to that time been overlooked or thrust aside. It is of radical importance, in giving a naturalistic solution of the problem of the origin of life, to start from these structureless granules of living matter, and not—as still generally happens—from the cell; these nucleated elementary organisms could not be the earliest archigonous living things, but must have been evolved secondarily from the unnucleated monera. Hence, I made a very thorough study of these rudimentary organisms in myMonograph on the Monera(1870), and endeavored to formulate it more clearly later on (in the first volume of theSystematic Phylogeny). In regard to the chemical question of the first formation of plasm and its inorganic preparation, Edward Pflüger conducted some valuable investigations, and recognized that the radical of cyanogen was the chief element of the living plasm. I may therefore distinguish two different stages of the theory—my own older autogony-hypothesis and the later cyanogen-hypothesis.The theory of abiogenesis, or archigony, which I advanced in 1866, and have developed in later writings, appeals directly to the biochemical facts that modern vegetal physiology has firmly established. The chief of these facts is that even the living green plant-cell has the synthetic faculty of plasmodomism or carbon-assimilation; that is to say, it is able to build up, by a chemical synthesis and reduction, from simple inorganic compounds (water, carbonic acid, nitric acid, and ammonia), the complex albuminous compounds which we call plasm or protoplasm, and which we regard as the active living substance and the true material basis of all vital function (cf.chapter vi.). All botanists are now agreed that this most important process of vegetal life, the fundamental process of all organic life and all organization,is a purely chemical (or, in the wider sense, physical) process, and that there is no question of a specific vital force or a mystic constructor (like the famous "mechanical engineer of life"), or any other transcendental agency, in connection with it. The tiny chemical laboratory in which this remarkable organoplastic process takes place under the influence of sunlight is, in the simplest plants, the chromacea, either the whole homogeneous globule of plasm (chroococcus) or its bluish-green surface-layer, which is active as a chromatic principle (chromatophore). But in most plants these reduction-laboratories are the chromatella or chromatophora, which have been differentiated from the rest of the plasm of the cell, and are colorless globular leucoplasts within its dark interior, or green chromoplasts (or granules of chlorophyll) at its illumined surface. My theory of archigony only assumes that this chemical process of plasmodomism which we find repeated every second in every plant-cell exposed to the sunlight, and which has become an "inherited habit" of the green plant-cell, developed of itself at the beginning of organic life; in other words, it is a catalytic process (or one analogous to catalysis), the physical and chemical conditions of which were present in the condition of organic nature at that time.My hypothesis was very strongly confirmed twenty years ago by the adhesion of the able botanist, Carl Nägeli. In his instructive work,A Mechanical-physiological Theory of Evolution(1884), he supported all the principal ideas as to the natural origin of life which I had advanced in 1866. He formulates the chief part of them in this admirable principle:The origin of the organic from the inorganic is, in the first place, not a question of experience and experiment, but a fact deduced from the law of the constancy of matter and force. If all things in the material world are causally related, if allphenomena proceed on natural principles, organisms, which are formed of and decay into the same matter, must have been derived originally from inorganic compounds.This excellent and clear declaration of a distinguished scientist and profound thinker might be taken to heart by the "exact" scientists who are always attacking the monistic theory of archigony as an unproved hypothesis, or regard the whole problem as insoluble. Nägeli has, moreover, proceeded to make a thorough study of the molecular processes involved, and embodied the results in his idioplasm theory. He believes that at the beginning of organization the definite autonomous arrangement of the smallest homogeneous parts of the plasm was a matter of the greatest importance. In his opinion these "micella" are crystalline groups of molecules, arranged multifariously in strings and parallel rows.A similar and more elaborate attempt to give a physical explanation of the processes of archigony and trace them to mechanical molecular structures was made by Ludwig Zehnder in 1899 in his work onThe Origin of Life. He believes that the smallest and lowest life-unities (the micellar strings of Nägeli and the biophora of Weismann, corresponding to my plastidules) have a tubular shape, and so he calls them "fistella." He supposes that these invisible molecular structures are regularly arranged in millions in the plasma of the cell, and differentiated in such a way that some will effect endosmosis, others contraction, others the conduction of stimuli, and so on. As in the similar work of Nägeli and others, the value of this molecular hypothesis is that it stimulates us to attempt to conceive the mode of the arrangement and movement of the molecules of plasm in the process of archigony on physical principles.A more interesting and notable attempt to penetrate into the mysterious obscurity of the chemical processesin archigony was made in 1875 by the distinguished physiologist, Edward Pflüger, in his essay onPhysiological Combustion in the Living Organism. He starts from the fact that the plasm (or protoplasm) is the material basis of all vital phenomena, and that this living matter owes its properties to the chemical properties of the albumin (whether we regard this as a chemical unity, protein or protalbumin, or as a mixture of different compounds). However, Pflüger sharply distinguishes between the living albumin of the plasm out of which all organisms are built, and the dead albumin, such as we find it, for instance, in the glairy albumin of the hen's egg. Only the living albumin (plasm) decomposes of itself in a slight degree, and to a greater extent under the influence of external excitation; the dead albumin will remain intact for a long time under favorable conditions. The cause of the extraordinary instability of the living albumin is its intramolecular oxygen—that is to say, the oxygen that is taken into the interior of the plasma-molecules in breathing, and effects there a disassociation, surrounding the atoms and breaking up the new-formed groups.The real cause of this rapid decomposability of the plasm, and of the accompanying formation of carbonic acid, is found in the cyanogen, a remarkable body composed of an atom of carbon and an atom of nitrogen, which, in conjunction with potassium, forms the well-known and very virulent poison, cyanide of potassium. The non-nitrogenous decomposition-products of the dead and the living albumin agree in the main, but their nitrogenous products are totally different. Uric acid, creotin, guanine, and the other decomposition products of plasm contain the cyanogen-radical, and the most important of all, urea, can be artificially produced from cyanic compounds, as Wöhler showed in 1828. From this we may infer that the living albumin always containsthe cyanogen-radical, and that dead nutritive albumin does not. The belief that it is cyanogen which gives its characteristic vital properties to the plasm is supported by a number of analogies that we find to exist between cyanide compounds, especially cyanic acid (C N O H.) and the living albumin. Both bodies are fluid and transparent at a low temperature, while they set at a higher; both of them break up in the presence of water into carbonic acid and ammonia; both produce urea by disassociation (by the intramolecular surrounding of the atoms, not by direct oxydation). "The similarity of the two substances is so great," says Pflüger, "that I might describe cyanic acid as a semi-living molecule." Both substances grow in the same way by concatenation of the atoms, homogeneous groups of atoms joining together chainwise in large masses.There is an especial interest in connection with the theory of archigony and its physical basis in the chemical fact that cyanogen and its compounds—cyanide of potassium, cyanic acid, cyanide of hydrogen, etc.—are only formed at incandescent heat; that is to say, when the requisite inorganic nitrogenous compounds are put with glowing coals, or the mixture is heated to incandescence. Other essential constituents of albumin, such as carburetted hydrogen or alcohol-radical, can be formed synthetically in heat. "Thus," says Pflüger, "nothing is clearer than the possibility of the formation of cyanic compounds when the earth was entirely or partially in a state of incandescence or great heat. We see how extraordinarily all the facts of chemistry point to fire as the force that has produced the constituents of albumin by synthesis. Hence life was born from fire, and the chief conditions of its appearance are associated with a time when the earth was a glowing ball of fire. When we remember the incalculably long period in which the surface of the earth was slowly cooling,we see that cyanogen, and the compounds that contained cyanogen, and carburetted hydrogen, had plenty of time and opportunity to follow out to any extent their great tendency to the transposition and formation of polymeria (chains of atoms), and, with the co-operation of oxygen and afterwards of water and salts, to evolve into the self-decomposable albumin which is living matter." In regard to the latter feature, it is well to emphasize the fact that, as will be understood, there must have been a long series of chemical intermediary stages between the incandescent formation of cyanogen and the appearance of the aqueous living plasm.Pflüger's cyanogen theory does not conflict with my monera theory, but rather supplements it, by its careful and thoroughly scientific study of a much earlier stage of primitive biogenesis—in a sense, the first period of preparation for the formation of albumin. This must be well borne in mind in view of the attacks which have lately been made on it by Neumeister and other vitalists; it is supposed to be untenable, because "there is an impassable gulf between cyanic compounds and proteids." This criticism is answered by the living albumin itself, which always contains in its nitrogenous decomposition products the radical of cyanide or other substances (urea) that can be artificially produced from cyanic compounds. Another objection is that "the cyanic compounds which were formed in the heat must have very quickly perished on the subsequent appearance of water." The objection has no weight, since we can form no definite idea as to the special conditions of chemical activity in those times. We can only say that the conditions during this long period (embracing millions of years) were totally different from those of chemical action at the surface of the earth to-day. The real ground of the opposition of Neumeister and other vitalists is their dualistic conception of nature, which willmaintain at all costs the deep gulf between the organic and inorganic worlds.Max Verworn, in hisGeneral Physiology, has fully described and criticised the various theories of the appearance of life on the earth. He rightly attributes a great value to Pflüger's cyanogen theory, because "it makes a strictly scientific study of the problem in close relation to the facts of physiological chemistry, and goes thoroughly into detail." He agrees with Pflüger when he expresses himself as follows: "I would say, therefore, that the first albumin to be formed was in point of fact living matter, endued with the property in all its radicals of attracting especially homogeneous parts with great force and preference, in order to build them chemically into the molecule, and so grow indefinitely. On this view the living albumin need not have a constant molecular weight, because it is a huge molecule in an unceasing process of formation and decomposition, probably acting on the ordinary chemical molecules as a sun does on a small meteor." This theory, which I believe to be correct, is also maintained by many other modern scientists who have made a particular study of the difficult question of the nature and origin of the albuminoids.Now that we have described the various modern theories of archigony that are worth considering, and recognized with Nägeli that the original development of the organic from the inorganic is a fact, we may glance at the older theories which, under the name of "spontaneous generation," afforded matter for a good deal of controversy. It is true that they are now almost entirely abandoned, but the experiments in connection with them excited a good deal of interest and led to many misunderstandings.The older hypotheses of "spontaneous generation" do not bear on our problem of archigony (or the firstdevelopment of living matter from lifeless inorganic carbon compounds) but relate to the formation of lower organisms out of the putrid and decomposing organic elements of higher organisms. In order to distinguish these hypotheses from the totally different theory of archigony, it is better to give them the name of saprobiosis (an earlier name was necrobiosis), which means the birth of living from dead (nekron) or putrid (sapron) organic matter. Saprobiosis is preferable, because necrobiosis is better used in a different sense, for the dead organic parts which gradually bring about the death of the living body (see p. 106). It was believed in ancient times that lower organisms could arise from the dead remains of higher organisms, such as fleas from manure, lice from morbid pustules in the skin, moths from old furs, and mussels from slime in the water. As these stories were supported by the authority of Aristotle, and on that account believed by St. Augustine and other fathers, and reconciled with the faith, they were held until the beginning of the eighteenth century. Even in the year 1713 the botanist Heucherus stated that the green duck-weed (lemna) is only condensed grease from the surface of foul standing water, and that water-cress was formed from it in fresh running water.The first scientific refutation of these old stories was made by the Italian physician, Francisco Redi, in 1674, on the basis of very careful experiment: he was persecuted for "unbelief" on that account. He showed that all these animals arose from eggs that had been deposited by female animals in dung, skin, fur, slime, etc. But at that time the proof could not be extended to the tape-worms, maw-worms, and other intestinal animals (entozoa), which live inside other animals (in the bowels, blood, brain, or liver). It was still believed that these arise from diseased parts of the host-animals in which they live, until about the middle of the nineteenth century.It was not until 1840-1860 that it was shown by the experiments of Siebold, Leuckart, Van Beneden, Virchow, and other famous biologists, that all these intestinal animals have come from without into the animals they live in, and propagate there by eggs. Of late years the proof has been applied all round.On the other hand, the hypothesis of saprobiosis retained its position until quite recently for one section of the smallest and lowest organisms, the microscopic forms of life, invisible to the naked eye, which were formerly called infusoria, and which we now call by the wider name of protists or unicellulars. When Leeuwenhoek discovered the infusoria in 1675 with the newly invented microscope, and showed that they arise in great quantities in infusions of hay, moss, flesh, and other putrid organic substances, it was generally believed that they were spontaneously generated there. The Abbé Spallanzani showed in 1687 that no infusoria appear in these infusions if they are well boiled and the vessel is carefully closed; the boiling kills the germs in them, and the exclusion of air prevents the entrance of fresh germs. In spite of this, many microscopists still believed that certain infusoria, particularly the very small and simple bacteria, could be born directly from putrid or diseased tissues of organisms, or from decomposing organic fluids; the opinion was maintained by Pouchet at Paris in 1858, and afterwards by Charlton Bastian. The controversy about the subject moved the Paris Academy in 1858 to offer a prize for "careful research that would throw new light on the question of spontaneous generation." It fell to the famous Louis Pasteur, who proved, by a series of ingenious experiments, that there are everywhere in the atmosphere numbers of germs of microbes or microscopic organisms floating among the dust particles, and that these grow and reproduce when they reach water. Not only infusoria,but also small highly organized plants and animals—such as lichens, mosses, rotifers, and tardigrades—can live for months in a desiccated condition, be carried in all directions by the wind, and reawaken into life when they reach water. On the other hand, Pasteur showed convincingly that organisms never appear in infusions of organic substances when they are sufficiently boiled and the atmosphere that reaches them has been chemically purified. He summed up the results of his rigorous experiments, which were confirmed by Robert Koch and other bacteriologists, and gave rise to the modern precautions as to disinfection, in the maxim: "Spontaneous or equivocal generation is a myth."The famous experiments of Pasteur and his successors had destroyed the myth of saprobiosis, but not the theory of archigony. These entirely different hypotheses are still very frequently confused, because the old title of "spontaneous generation" is used for both. We still read sometimes that the "unscientific" belief in abiogenesis has been definitely refuted by these experiments, and that the question of the origin of life has thus become an insoluble enigma. There is an astonishing superficiality and lack of discernment in such remarks; they would hardly be possible in any other branch of science. But in biology—many of its distinguished representatives continue to say—we have only to observe and correctly describe facts; the formation of clear ideas and the indulgence in reflection on the facts are unnecessary and dangerous, and, therefore, to be avoided! It is due to this pitiable condition of biological methods of research that our hypothesis of archigony is still attacked, or else ignored. Why? Because the false hypothesis of saprobiosis, which has absolutely nothing in common with it but the name "spontaneous generation," has been refuted by theexperiments of Pasteur and his colleagues![9]These experiments prove nothing whatever beyond the fact that new organisms are not formed in certain infusions of organic matter—under definite, artificial conditions. They do not even touch the important and pressing question, which alone interests us: "How did the earliest organic inhabitants of our earth, the primitive organisms, arise from inorganic compounds?"The great popularity of the famous experiments of Pasteur on spontaneous generation, and the unfortunate confusion of ideas which was caused by the false interpretation of his results, make it necessary for me to say a word on the general value of scientific experiments in many questions. Since Bacon introduced experiment into science three hundred years ago, and gave it a logical basis, both our speculative knowledge of nature and the practical application of our knowledge made remarkable progress. New methods of research made it possible for modern workers to penetrate far more deeply into the nature of phenomena than the older thinkers had done, who had no knowledge of experiment. Especially in the nineteenth century the development of the experimental method, or the putting of a question to nature, led to enormous advances in the various sciences.In the subject we are considering the question to be put to nature is: "Under what conditions and in what manner is living matter (or plasm) formed from lifeless inorganic compounds?" We may confidently assume that in the period when archigony took place—the time when organic life first appeared on the cooled surface of the earth, at the beginning of the Laurentian Age—the conditions of existence were totally differentfrom what they are now; but we are very far from having a clear idea of what they were, or from being able to reproduce them artificially. We are just as far from having a thorough chemical acquaintance with the albuminous compounds to which plasm belongs. We can only assume that the plasma-molecule is extremely large, and made up of more than a thousand atoms, and that the arrangement and connection of the atoms in the molecule are very complicated and unstable. But of the real features of this intricate structure we have as yet no conception. As long as we are ignorant of this complex molecular structure of albumin, it is useless to attempt to produce it artificially. Yet in this position of the matter we would seek to produce that great wonder of life, the plasm, artificially, and when the experiment miscarries (as we should expect) we cry out: "Spontaneous generation is impossible."When we carefully consider the intelligent experiments that have been made in regard to archigony in the light of these facts, it is clear that their negative result does not in the slightest degree affect our question. The much-admired experiments of Pasteur and his colleagues prove merely that in certain artificial conditions infusoria are not formed in decomposing organic compounds (or the dead tissues of highly organized histona); they cannot possibly prove that saprobioses of this kind do not take place under other conditions. They tell us nothing whatever about the possibility or reality of archigony; in the form in which I put the scientific hypothesis in 1866 it is completely untouched by all these experiments. It remains intact as the first attempt to give a provisional reply—if only in the form of a temporary hypothesis—on the basis of modern science to one of the chief questions of natural philosophy.In myGeneral Morphology(1866), and afterwards in myBiological Studies on the Monera and other Protists,and the first volume of mySystematic Phylogeny(1894), I attempted to sketch in detail the stages of the process to which I give the name of archigony. I distinguished two principal stages—autogony(the formation of the first living matter from inorganic nitrogenous carbon-compounds) andplasmogony(the formation of the first individualized plasm; the earliest organic individuals in the form of monera). In more recent efforts I have made use of the important results reached by Nägeli (1884) in his investigations of the same subject. In regard to some important points relating to the chemico-physical part of the question, Nägeli has, in hisMechanico-physiological Theory of Evolution(chapter ii.), gone more into the details of the process of archigony. To the earliest living things, which were formed by "unicellular organization" of the plasm out of simple inorganic compounds, he gives the name ofprobiaorprobionta, and thinks that these had an even simpler structure than my monera. This view seems to rest on a misunderstanding. Nägeli does not strictly follow my definition, "organisms without organs" (that is to say, structureless living particles of plasm without morphological differentiation), but he has in mind the individual rhizopod-like organisms which I had at first described as monera—protamœba,protogenes,protomyxa, etc. In my present view the chromacea, or plasmodomous phytomonera, are much more important than these plasmophagous zoomonera. It is curious that Nägeli does not make thorough use of their primitive organization for the establishment of his theory, although he has had the great merit of describing these most primitive of all living organisms as unicellular algæ (1842). As a matter of fact, the simplest chromacea (chroococcus and related forms) approach so closely to his hypothetical probia or probionta that the only things we can regard as the rudiments of organization in the chroococcacea are thesecretion of a protective membrane about the homogeneous plasma-globule and the separation of the blueish-green cortical zone from the colorless central granule. The more important of the further conclusions of Nägeli are those which relate to the mode of the primitive abiogenesis and the frequent repetition of this physical process.Recently Max Kassowitz, in the second volume of hisGeneral Biology(1899), has gone fully into the various stages of the process of archigony, as a sequel to his metabolic theory of the building up and decay of plasm, from the point of view of physiological chemistry. He says very truly that the development of living from lifeless matter must not be conceived as a sudden leap; the very complicated chemical unities which now form the basis of life have been slowly and gradually evolved during an incalculably long period by the way of substitution for simpler compounds. We may join these views—which generally accord with my earlier deductions—with Pflüger's cyanogen theory, and so draw up the following theses:1. A preliminary stage to archigony is the formation of certain nitrogenous carbon-compounds which may be classed in the cyanic group (cyanic acid, etc.). 2. When the crust of the earth stiffened, water was formed in the fluid condition; under its influence, and in consequence of the great changes in the carbonic-acid laden atmosphere, a series of complicated nitrogenous carbon-compounds were formed from these simple cyanic compounds, and these first produced albumin (or protein). 3. The molecules of albumin arranged themselves in a certain way, according to their unstable chemical attractions, in larger groups of molecules (pleona or micella). 4. The albumin-micella combined to form larger aggregations, and produced homogeneous plasma-granules (plassonella). 5. As they grew the plassonelladivided, and formed larger plasma-granules of a homogeneous character: monera (= probionta). 6. In consequence of surface-strain or of chemical differentiation, there took place a separation of the firmer cortical layer (membrane) from the softer marrow layer (central granule), as in many of the chromacea. 7. Afterwards the simplest (nucleated) cells were formed from these unnucleated cytodes, the hereditary mass of the plasm gathering within the monera and condensing into a firm nucleus.It is an interesting, but at present unanswered, question whether the process of archigony only occurred once in the course of time or was frequently repeated. Reasons can be given for both views. Pflüger says: "In the plant the living albumin only continues to do what it has done ever since its origin—constantly to regenerate itself or to grow; hence I believe that all the albumin in the world comes from that source. On that account I doubt if spontaneous generation takes place in our time. Moreover, comparative biology directly shows that all life has come from one single root." However, this view does not exclude the possibility of the chemical process of spontaneous plasmodomism having been frequently repeated—under like conditions—in the same form in primordial times.On the other side, Nägeli especially has pointed out that there is no reason to prevent us from thinking that archigony was repeated several times, even down to our own day. Whenever the physical conditions for the chemical process of plasmodomism were given, it might be repeated anywhere at any time. As to locality, the sea-shore probably affords the most favorable conditions; as, for instance, on the surface of fine moist sand the molecular forces of matter in all its conditions—gaseous, fluid, viscous, and solid—find the best conditions for acting on each other. It is a fact that to-day all thevarious evolutionary forms of living matter—from the simplest moneron (chroococcus) to the plain nucleated cell, from this to the highly organized cell of the radiolaria and infusoria, from the simple ovum to the most elaborate tissue-structure in the higher plants and animals, from the amphioxus to man—come in an order of succession. There are only two ways of explaining this fact: either the simplest living organisms, the chromacea and bacteria, the palmella and amœbæ, have remained unchanged or made very little advance in organization since the beginning of life—more than a hundred million years; or else the phylogenetic process of their transformation has been frequently repeated in the course of this period, and is being repeated to-day. Even if the latter were the case, we should hardly be in a position to learn it by direct observation.Assuming that the simplest organisms are still formed by abiogenesis, the direct observation of the process would probably be impossible, or at least extremely difficult, for the following reasons: 1. The earliest and simplest organisms are most probably globular particles of plasm, without any visible structure, like the simplest living chromacea (chroococcus). 2. These plasmodomous monera cannot be distinguished from the chromoplasts (chlorophyll-granules), which live inside plant-cells, and may continue after the death of the cells to multiply independently by cleavage. 3. We must admit with Nägeli that the original size of these probionta (in spite of the relatively colossal size of their molecules) is very small—much too small to come within the range of the best microscope. 4. In the same way the primitive metabolism and the slow, simple growth of these monera would not come within direct observation. 5. As a matter of fact, we do often find in stagnant water, and in the sea, tiny granules which consist, or seem to consist, of plasm. We usually regard them asdetached portions of dead animals or plants; little isolated chlorophyll-granules that may be found everywhere are looked upon as rejected products of vegetal cells. But who could refute the assumption that they are really plassonella or young monera, which grow slowly and unite with similar particles to form larger plasmic bodies?It is often objected to our naturalistic and monistic conception of archigony that we have not yet succeeded in forming albuminous bodies, and especially plasm, in our chemical laboratories by artificial synthesis; from this the perverse dualistic conclusion is drawn that it is only supernatural vital forces that can do this. It is forgotten that we do not yet know the complicated structure of albuminous bodies, and that we do not yet know what really happens inside the green chlorophyll-granules which in every plant-cell convert the radiant energy of sunlight into the virtual energy of the new-formed plasm. How can we be expected to reproduce synthetically, with the imperfect and crude methods of present chemistry, an elaborate chemical process the nature of which is not analytically known to us? However, the worthlessness of this sceptical objection is obvious: we can never claim that a natural process is supernatural because we cannot artificially reproduce it.XVITHE EVOLUTION OF LIFEInorganic and organic evolution—Biogenesis and cosmogenesis—Mechanical evolution—Mechanics of phylogenesis—Theory of selection—Theory of idioplasm—Phyletic vital force—Theory of germ-plasm—Progressive heredity—Comparative morphology—Germ-plasm and hereditary matter—Theory of mutation—Zoological and botanical transformism—Neo-Lamarckism and Neo-Darwinism—Mechanics of ontogenesis—Biogenetic law—Tectogenetic ontogeny—Experimental evolution—Monism and biogeny.I fully explained in myGeneral Morphology(1866) the profound importance of the science of evolution in relation to our monistic philosophy. A popular synopsis of this is given in myHistory of Creation, and is briefly repeated in the thirteenth chapter of theRiddle. I must refer the reader to these works, especially the latter, and confine myself here to a consideration of some of the principal general questions of evolution in the light of modern science. The first thing to do is to compare the conflicting views on the nature and significance of biogenesis which still face each other at the beginning of the twentieth century.The essential unity of inorganic and organic nature, which I endeavored to establish in the second book of theGeneral Morphology, and the significance of which I explained in the fourteenth chapter of theRiddle, is found through the whole course of its development, in the causes of phenomena and their laws. Hence, indealing with the evolution of organisms, we reject vitalism and dualism, and maintain our conviction that it can always be traced to physical forces (and especially chemical energy). As we regard plasm as the basis of it (chapter vi.), we may say that organic evolution depends on the mechanics and chemistry of the plasm. We postulate no supernatural vital force for the explanation of physiological functions, and we are just as far from admitting it as regulator or agency of the biogenetic process.If we understand by biogeny the sum total of the organic evolutionary processes on our planet, by geogeny the processes at work in the formation of the earth itself, and by cosmogony those that produced the whole world, biogeny is clearly only a small part of geogeny, and this in turn only a small section of the vast science of cosmogony. This important relation is evident enough, yet often overlooked; it holds both of time and space. Even if we suppose that the biogenetic process occupied more than a hundred million years, this period is probably much shorter than that which our planet has needed for its development as a cosmic body—from the first detachment of the nebular ring from the shrinking body of the sun to its condensation into a rotating sphere of gas, and from this to the formation of the incandescent globe, the stiffening of the crust at its surface, and finally the downpour of fluid water. It was not until this last stage that carbon could begin its organogenetic activity and proceed to the formation of plasm. But even this long geogenetic process is, as regards space and time, only a very small part of the illimitable history of the world. If we further assume that organic life develops on other cosmic bodies (Riddle, chapter xx.) in the same way as on our earth under like conditions, the whole sum of all these biogenetic processes is only a small part of the all-embracing cosmogenetic process. The vitalistic belief that itsmechanical course was interrupted from time to time by the supernatural creation of organisms is opposed to pure reason, the unity of nature, and the law of substance. We must, therefore, hold fast above all to the conviction that all biogenetic processes are just as reducible to the mechanics of substance as all other natural phenomena.The mechanical and natural character of the development of inorganic nature, the earth and the whole material world, was established mathematically at the end of the eighteenth century by the great atheist Laplace in hisMécanique Céleste(1799). The similar cosmogony which Kant had expounded in 1755 in hisGeneral Natural History and Theory of the Heavensonly obtained recognition at a later date (Riddle, chapter xiii.). But the possibility of giving a mechanical explanation of organic nature was not seen until Darwin provided a solid foundation for the theory of descent by his theory of selection in 1859. I made the first comprehensive attempt to do this in 1866 in myGeneral Morphology, the aim of which is expressed in the title: "General outlines of the science of organic forms, mechanically grounded on Darwin's improvement of the theory of descent." Especially in the second volume of the work, the "General Evolution of Organisms," I endeavored to show that both sections of the science, ontogeny (or embryology) and phylogeny, can be reduced to physiological activities of the plasm, and so explained mechanically, in the wider meaning of the word.When I stated the nature and the aim of phylogeny in 1866, most biologists regarded my attempt as unjustifiable, as they did Darwinism itself, of which it was a natural consequence. Even the famous Émil Dubois-Reymond, to whom as a physiologist it should have been welcome, described it as "a poor romance"; he compared my first attempts to construct the genealogical tree of the organic classes, on the evidence of paleontology,comparative anatomy, and ontogeny, to the hypothetical labors of philologists to draw up the genealogical tree of the legendary Homeric heroes. As a matter of fact, I had myself described my imperfect effort as merely a provisional sketch, as a temporary hypothesis that would open the way for later and better research. A single glance at the immense literature of phylogeny to-day shows how much has been done since in this province, and how far we have advanced in the establishment of the features of evolution by means of the united labors of numbers of able paleontologists, anatomists, and embryologists. Ten years ago I attempted, in the three volumes of mySystematic Phylogeny, to give a comprehensive statement of the results attained. My chief aim was, on the one hand, to construct a natural system of organisms on the basis of their ancestral history, and on the other hand to prove the mechanical character of the phylogenetic process. All the activities of organisms which are at work in the transformation of species and the production of new ones in the struggle for existence may be reduced to their physiological functions—to growth, nutrition, adaptation, and heredity; and these again to the mechanics and chemistry of the plasm. The struggle for life is itself a mechanical process, in which natural selection uses the disproportion between the excess of germs and the restricted means of existence, in conjunction with the variability of species, in order to produce new purposive structures mechanically and without any preconceived design. This teleological mechanicism has no need of a mysterious design or finality; it takes its place in the general order of mechanical causality which controls all the processes in the universe. Natural finality is only a special instance of mechanical causality. The one is subordinate to the other, not opposed to it, as Kant would have it.The effort that the great Lamarck made in 1809, in hisPhilosophie Zoologique, to establish transformism deserves high appreciation from monists, because it was the first attempt to give a natural explanation of the origin of the countless species of organic forms which inhabit our planet. Up to that time it had been the fashion to attribute their origin to a miraculous intervention of the Creator. This metaphysical creationism had now to face physical evolutionism. Lamarck explained the gradual formation of organic species by the interaction of two physiological functions—adaptation and heredity. Adaptation consists in the improvement of organs by use, and degeneration by disuse; heredity acts by transmitting the features thus acquired to posterity. New species arise by physiological transformation from older species. The fact that this great thought was overlooked for half a century does not detract from its profound significance. But it only obtained general recognition when Darwin had supplemented it and filled up its causal gaps by the theory of selection in 1859. Apart from this specifically Darwinian feature (whether it be true or not), the fundamental idea of transformism is now generally received; it is admitted to-day even by metaphysicians who maintained a spirited opposition to it thirty years ago. The fact of the progressive modification of species is only intelligible on Lamarck's theory that the actual species are the transformed descendants of older species. In spite of all the learning and zeal with which the theory has been attacked, it has proved irrefutable; nor can any one suggest a better theory to replace it. This may be said particularly of its chief consequence—the descent of man from a series of other mammals (proximately from the apes).The high value of Darwin's theory of selection for the monistic biology is now acknowledged by all competentand impartial authorities on the science. In the course of the forty-four years since it found its way into every branch of biology, it has been employed in more than a hundred large works and several thousand essays in explaining biological phenomena. This alone is enough to show its profound importance. Hence it is mere ignorance of the subject and its literature to say, as has been done several times of late, that Darwinism is in decay, or even "dead and buried." However, absurd writings of this kind (such as Dennert'sAt the Death-bed of Darwinism) have a certain practical influence, because they fall in with the prevailing superstition in theology and metaphysics. Unfortunately, they also seem to obtain notice from the circumstance that a few botanists persistently attack the Darwinian theory. One of the most conspicuous of these is Hans Driesch, who affirms that all Darwinists (and therefore the great majority of modern biologists) have softening of the brain, and that Darwinism is (like Hegel's philosophy) the delusion of a generation. The arrogance of this conceited writer is about equal to the obscurity of his biological opinions, the confusion of which is covered by a series of most extravagant metaphysical speculations. All these attacks have lately been met very ably by Plate in his work,On the Significance of the Darwinian Principle of Selection and the Problem of the Foundation of Species(second edition, 1903). The most thorough of recent defences of Darwinism is that made by August Weismann in hisLectures on the Theory of Descent(1902) and other works. But the distinguished zoologist goes too far when he seeks to prove the omnipotence of selection and wishes to ground it on an untenable molecular hypothesis—the theory of germ-plasm, which we will consider presently. Apart from these or other exaggerations, we may say with Weismann that Lamarck's theory of descent received a sound causal basisby Darwin's theory of selection. Its real foundations are these three phenomena: heredity, adaptation, and the struggle for existence. All three are, as I have often said, of a purely mechanical and not a teleological nature. Heredity is closely bound up with the physiological function of reproduction, and adaptation with nutrition; the struggle for life follows logically and mathematically from the disproportion between the number of potential individuals (germs) and of actual individuals that grow to maturity and propagate the species.When I had, in myGeneral Morphology, endeavored to gain acceptance for Darwin's theory of selection, and had presented evolution as a comprehensive theory from the point of view of the monistic philosophy, a number of works, sometimes of value, appeared, which made special studies of the various parts of the immense province. Eighteen years afterwards a greater work was published, which started from the same monistic principles, but reached the same conclusion by a different way. In 1884 Carl Nägeli, one of our ablest and most philosophic botanists, issued hisMechanical-physiological Theory of Evolution. This interesting book consists of various parts. It is especially notable that evolution is presented in it as the one possible and natural theory of the origin of species; even morphology and classification are treated explicitly as "phylogenetic sciences." The chapter on archigony—a dark and dangerous problem that is generally avoided by scientists!—is one of the best that has been written on the subject. On the other hand, Nägeli rejects Darwin's theory of selection altogether, and would explain the origin of species by an inner "definitely directed variation," independently of the conditions of existence in the outer world. As Weismann has properly observed, this internal principle of evolution, which dispenses with adaptation in the truesense of the word, is at the bottom merely a "phyletic vital force." It is not made more acceptable by Nägeli when he builds up a subtle metaphysical system on it and postulates a special "principle of isagitation." But the idioplasm theory he connects with it is of some value, since it goes more fully into the differentiation of the cell-plasm into two physiologically different parts—the idioplasm of the hereditary matter and the trophoplasm as nutritive matter of the cell.

It is said to be a great merit of canon law that it was the first to extend legal protection to the human embryo, and punished abortion with death as a mortal sin. But as this mystical theory of the entrance of the soul is now scientifically untenable, we should expect them consistently to extend this protection to the fœtus in its earlier stages, if not to the ovum itself. The ovary of a mature maid contains about 70,000 ova; each of these might be developed into a human being under favorable circumstances if it united with a male spermium after its release from the ovary. If the state is so eager for the multiplication of its citizens in the general interest, and regards prolific reproduction as a "duty" of its members, this is certainly a "sin ofomission." It punishes abortion with several years' imprisonment. But while civil law thus takes its inspiration from canon law, it overlooks the physiological fact that the ovum is a part of the mother's body over which she has full right of control; and that the embryo that develops from it, as well as the new-born child, is quite unconscious, or is a purely "reflex machine," like any other vertebrate. There is no mind in it as yet; it only appears after the first year, when its organ, the phronema in the cortex, is differentiated. This interesting fact is explained by the biogenetic law, which shows that the ontogeny of the brain is a condensed recapitulation of its phylogeny in virtue of the laws of heredity.

The biogenetic law applies just as much to the brain, the organ of mind, as to any other organ of the human body. On the strength of the ontogenetic facts, which fall under direct observation, we infer that there was a corresponding development in the phylogenetic series of our animal ancestors. A significant confirmation of this inference is found in comparative anatomy. It shows that in all the skull-animals (craniota)—from the fishes and amphibia up to the apes and man—the brain is developed in the same way, as a vesicular distension of the ectodermal medullary tube. This simple oval cerebral vesicle first divides into three and afterwards five successive vesicles by transverse constriction (Anthropogeny, chapter xxiv., plate 24). It is the first of these vesicles, the cerebrum, that afterwards becomes the chemical laboratory of the mind. In the lower craniota (fishes and amphibia) the cerebrum remains very small and simple. It only reaches a notably higher stage in the three chief classes of the vertebrates, the amniotes. As these land-dwelling and air-breathing craniota have more difficult work to do in the struggle for life than their lower aquatic ancestors, we find much more variedand complex habits among them. These hereditary habits are gradually converted into instincts by functional adaptation and progressive heredity; and with the further development of consciousness in the higher mammals we have at last the appearance of reason. The gradual unfolding of the mental life is accompanied step by step with the advance of its anatomic organ, the phronema in the cortex. Recent careful investigations of the ontogeny and histology of the origin of mind (by Flechsig, Hitzig, Edinger, Ziehen, Oscar Vogt, etc.) have given us an interesting insight into the mysterious processes of its phylogeny.

While the comparative anatomy of the cortex gives us a good idea of the gradual historical development of the mind in the higher classes of vertebrates, we get at the same time from their fossilized remains positive indications as to the period of time in which this phylogenesis has slowly taken place. The historical series in which the classes of vertebrates have succeeded each other in the great periods of the organic history of the earth is directly demonstrated by their fossil remains—the real commemorative medals of natural creation—and gives us a most valuable record of the ancestral history of our race and of the mind. The oldest strata that contain vertebrate remains form the huge Silurian System, which were, on the latest calculations, formed more than a hundred million years ago. They contain a few fossil fishes. In the succeeding Devonian System these are followed by the dipneusta, transitional forms between the fishes and the amphibia. The latter, the oldest four-footed and five-toed vertebrates, appear in the Carboniferous Period. They are succeeded in the Permian, the next system, by the oldest amniotes, the primitive reptiles (tocosauria). It is not until the next period (the Triassic) that the oldest mammals are found, small primitive monotremes (pantotheria), then marsupials inthe Jurassic, and the first placentals in the Cretaceans. The great wealth of varied and highly organized forms which are contained in this third and last sub-class of the mammals appear only in the succeeding Tertiary Period. The numbers of well-preserved skulls which these placentals have left behind in fossil form are particularly important, because they give us an idea of the quantitative and qualitative formation of the brain within the various orders; thus, for instance, in the modern carnivora the brain is from two to four times, and in the modern ungulates from six to eight times, as large (in proportion to the size of the body) as in their earliest Tertiary ancestors. It is also found that the cortex (the real organ of mind) has developed in the Tertiary Period at the expense of the other parts of the brain. The duration of this Cænozoic Period has lately been calculated at three million years (according to other geologists twelve to fourteen or more million years). It was, at all events, sufficient to make possible the gradual development of the human mind from the lower intelligence of our ape-ancestors and the instincts of the older placentalia.

We have given the physiological name of the "phronema," as the real organ of mind or the instrument of reason, to that part of the cortex on the normal anatomic condition of which the action of the human mind depends. The remarkable investigations during the last few decades of the finer texture of the grey cortex (or cortical substance of the cerebrum) have shown that its structure—a real anatomic "wonder of life"—represents the most perfect morphological product of plasm; and its physiological function—mind—is the most perfect action of a "dynamo-machine," the highest achievement that we know anywhere in nature. Millions of psychic cells or neurona—each of them of an extremely elaborate fibril molecular structure—are associated asspecial thought-organs (phroneta) at certain parts of the cortex, and these again are built up into a large harmonious system of wonderful regularity and capacity. Each phronetal cell is a small chemical laboratory, contributing its share to the unified central function of the mind, the conscious action of reason. Scientists are still very far from agreement as to the extent of the phronema in the cortex and its delimitation from the neighboring sense-centres (sensoria). But they are all agreed that there is such a central organ of mind, and that its normal anatomic and chemical condition is the first requisite for the life of the human mind. This belief—one of the foundations of monistic psychology—is confirmed by the study of psychiatry.

The study of the diseased organism has greatly furthered our knowledge of the normal frame. Diseases are so many physiological experiments made by nature herself under special conditions, which experimental physiology would often be unable to arrange artificially. The thoughtful physician or pathologist can often obtain most important knowledge of the function of organs by carefully observing them during disease. This is especially true of diseases of the mind, which always have their immediate foundation in an anatomical or chemical modification of certain parts of the brain. Our advancing knowledge of the localization of mental functions, or of their connection with special phroneta or organs of thought, is for the most part based on the experience that the destruction of the one is followed by the extinction of the other. Modern psychiatry, the empirical science of mental disease, has thus become an important element of our monistic psychology. If Immanuel Kant had studied it and had visited the asylum wards for a few months, he would certainly have escaped the dualist errors of his philosophy. We may say the same of the modern metaphysical psychologists who built up a mystictheory of an immortal soul without knowing the anatomy, physiology, and pathology of the brain.

The comparative anatomy, physiology, and pathology of the brain, in concurrence with the results of ontogeny and phylogeny, have led us to form the sound monistic principle that the human mind is a function of the phronema, and that the neurona of the latter, or the phronetal cells, are the real elementary organs of mental life. Hence modern energism is perfectly justified in regarding mental energy (in all its forms) from the same point of view as all other forms of nervous energy, and in fact all manifestations of energy in organic or inorganic nature. Fechner's psychophysics had already shown that a part of this nervous energy is measurable and mathematically reducible to the mechanical laws of physics (Riddle, chapter vi.) Ostwald has, in hisNatural Philosophy, lately emphasized the fact that all the manifestations of mental life, not only sensation and will, but even thought and consciousness, can be reduced to nervous energy. Hence we may distinguish what are called mental forces from the other expressions of nervous energy asphronetic energy. The monistic research of Ostwald on the energy-processes in mental life (chapter xviii.), consciousness (chapter xix.), and will (chapter xx.) is very notable, and confirms the views I advanced in the second part of theRiddle(chapters vi., x., and xi.). Ostwald has, however, caused some misunderstanding by insisting on substituting his idea of energy for the pure notion of substance (as Spinoza had formulated it), and by rejecting the other attribute of substance, matter. His supposed "Refutation of Materialism" is a mere attack on windmills; his energism (the consistent dynamism of Leibnitz, etc.) is just as one-sided as its apparent opposite, the consistent materialism of Democritus, Holbach, etc. The latter makes matter precede force; the former regards matter asthe product of force. Monism escapes the one-sidedness of both systems, and, as hylozoism, refuses to separate the two attributes of substance, space-filling matter and active energy. This applies to mental life just as to any other natural process; our mental forces or phronetic energies are just as much bound up with the neuroplasm, the living plasm of the neurona in the cortex, as the mechanical energy of our muscles is with the contractile myoplasm, the living muscular substance.

In the exhaustive study of consciousness which I gave in the tenth chapter of theRiddleI sought to show that this enigmatic function—the central mystery of psychology—is not a transcendental problem, but a natural phenomenon, subject to the law of substance, as much as any other psychic power. The child's consciousness only develops long after its first year, and grows as gradually as any other psychic function; like these, it is bound up with the normal anatomic and chemical condition of its organs, the phroneta in the cortex. Consciousness develops originally out of unconscious functions (as an "inner view," or mirroring, of the action of the phronema); and at any time an unconscious process in the cortex may come within the sphere of consciousness by having the attention directed to it. On the other hand, conscious actions, which need a good deal of attention when they are first learned (such as playing the piano), may become unconscious through frequent repetition and practice. The fact that chemical energy is converted in the phronetal cells during any of these actions is proved by the fatigue and exhaustion which prolonged mental work causes in the brain, just as mechanical work does in the muscles. Fresh matter has to be supplied by the food before the mental work can be continued. Moreover, it is well known that various drinks have a considerable influence on consciousness (coffee and tea, beer and wine); and the temporaryextinction of it under chloroform or ether is an analogous fact. Again, the familiar phenomena of the dream, the deviations from normal consciousness, hallucinations, delusions, etc., must convince every impartial thinker that these mental functions are not of a metaphysical character, but physical processes in the neuroplasm of the brain, and thoroughly dependent on the law of substance.

In complete contrast to this natural monistic conception of the human mind, which is, in my opinion, definitely established by nineteenth-century science, we have the older dualistic estimate of it which is still widely accepted both by unlearned and learned, especially metaphysicians and theologians. I have already dealt in theRiddle(chapter xi.) with the grounds for this belief in an immaterial soul, and expressed my conviction that "the belief in the immortality of the human soul is in flagrant contradiction to the soundest empirical principles of modern science." I must refer the reader to what I said there about thanatism and athanatism, only reminding him once more of the immense influence of the Kantist philosophy in maintaining this belief in the spirituality of the soul. Kant derived from the introspective study of his own gifted mind an extremely high estimate of human reason, and he fallaciously transferred this estimate to the human mind generally. He did not perceive that it is either wholly wanting in the savage, or does not rise much above the stage which has been reached by the intelligence of the dog, horse, elephant, and other advanced animals.

Modern anthropogeny has raised the theory of evolution to the rank of an historical fact. All the various organs of our body resemble those of our nearest relatives, the anthropoid apes, in their structure and composition. They only differ from them in details of form and size, which are determined by inherited variationsof growth. But the functions as well as the organs have been inherited by man from his primate ancestors. This applies to the mind also, which is merely the collective function of the phronema, the central organ of thought. An impartial comparison of mental life in the anthropoid ape and the savage shows that the differences between the two are not more considerable than the differences in the structure of their brains. Hence, if one accepts the dualistic theory of the soul formulated by Plato and Kant and accepted by so many modern psychologists, it is necessary to attribute an immortal soul to the anthropoid apes and the higher mammals (especially to domestic dogs) just as well as to savage or civilized man (cf.chapter xi. of theRiddle).

The thorough and careful study of the mental life of the savage, supported by the results of anthropogeny and ethnography, has in the course of the last forty years decided the issue of this struggle between the conflicting theories of the origin of civilization. The older theory of degeneration, based on religious beliefs, and so preferred by theologians and theosophists, declared that man—the "image of God"—was created originally with perfect bodily and mental powers, and only fell away from his high estate after the original sin. On this view the present savages are degenerate descendants of the first godlike men. (In tropical lands the anthropoid apes are in similar fashion regarded by the natives as degenerate branches of their own stem!) Although this Biblical degeneration theory is still taught in most of our schools, and even supported by a few mystic philosophers, it had lost all scientific countenance before the end of the nineteenth century. It is now replaced by the modern theory of evolution, which was represented by Lamarck, Goethe, and Herder a century ago, and raised to a predominant position in ethnography by Darwin and Lubbock. It has taughtus that human civilization is the outcome of a long and gradual process of evolution, covering thousands of years. The civilized races of our time have arisen from less civilized races, and these in turn from lower, until we reach the savage races which show no trace of civilization.

Ethnologists distinguish as a separate class the races which are found midway between the civilized peoples and the savages. We shall deal with their classification and characteristics later on (chapter xvii.). These races show some advance on the artistic instinct which we find in a slight degree even among the savages at times; moreover, their animal curiosity develops into human curiosity, and raises the question of the causes of phenomena, the germ of all science.

Civilized races, which occupy the next stage to these, are raised above them by the formation of larger states and a greater division of labor. The specialization of the various groups of workers and the greater ease of maintenance permit a further development of art and science. To these groups belong, of living races, the majority of the Mongolians, and the greater part of the inhabitants of Europe and Asia in ancient and mediæval times. The great ancient civilizations of China, Southern India, Asia Minor, Egypt, and afterwards of Greece and Italy, show not only a great development of art and science, but also a concern for legislation, religious worship, education of the young, and the spread of knowledge by written books.

Civilization in the narrower sense, characterized by a high development of art and science and the manifold application of them to practical life in legislation, education, etc., was greatly advanced even in antiquity among several nations—in Asia by the Chinese, Southern Indians, Babylonians, and Egyptians; in Europe by the Greeks and Romans of the classic age. However, theirresults were at first restricted to narrow fields, and were mostly lost during the Middle Ages. Modern civilization rose to importance about the end of the fifteenth century, when the invention of printing had made possible the spread of knowledge far and wide, the discovery of America and circumnavigation of the globe had widened the horizon, and the Copernican system had demolished the error of geocentricism. Then began the many-sided growth of civilization which has reached so marvellous a height in the nineteenth century through the extraordinary development of science. Then at last free reason could triumph over the prevailing mediæval superstition.

XV

The miracle of the origin of life—Creation of species: Moses and Agassiz—Creation of the first cells: Wigand and Reinke—Agnostic position: resignation—Eternity hypothesis (dualistic, Helmholtz; monistic, Preyer)—Archigony hypothesis (autogony hypothesis, Haeckel, Nägeli; cyanic hypothesis, Pflüger, Verworn)—Spontaneous generation—Saprobiosis or necrobiosis—Experiments in spontaneous generation—Pasteur—Stages of archigony—Observation of archigony—Synthesis of plasma—Value of the unsuccessful experiments to produce plasm artificially—The logic of modern experimental biology.

The question of the origin of life is one of the most important and interesting, but one of the most difficult and complicated, problems with which the mind of man has been occupied for thousands of years. There are few other questions (such as the freedom of the will or personal immortality) on which such different and contradictory views have been expressed, and few that remain so far from being closed at the present day. There are, moreover, few problems on which the opinions of even distinguished thinkers diverge so much, and have degenerated so much into fantastic hypotheses. This is partly due to the extreme difficulty of giving a strictly scientific solution of the problem and partly to the confusion of ideas which is so great in this controversy, the lack of clear rational insight, and the powerful authority of the prevailing religious faith and other venerable dogmas.

The easiest and quickest thing to do is to cut the Gordian knot of the question with the sword of faith, or answer it with a belief in a supernatural creation. The first article of the creed was given to us in childhood as the foundation of all cosmic philosophy. It is based on the Mosaic account of creation in the first chapter of Genesis. As I have fully examined its scientific value in the second chapter of myHistory of Creation, I may refer the reader thereto. It is unquestionable that this myth still has a very great practical influence; the great majority of the clergy cling to it because it is found in the infallible "word of God." Most governments, which hold blind faith to be an important element of education, include it in the code for the elementary school. On the other hand, it is difficult to find a man of science who will uphold it to-day. The gifted Louis Agassiz made one of the most remarkable attempts to do this in hisEssay on Classification(1858), a book that appeared almost contemporaneously with Darwin's epoch-makingOrigin of Species, and dealt with the general problems of biology from the directly opposite, the mystic, point of view. According to Agassiz, each species of animal or plant is an "incarnate thought of the Creator."

Differing from this Biblical fancy of the supernatural creation of each species, two botanists, Wigand of Marburg and Reinke of Kiel, have lately restricted the action of the celestial architect very considerably; they have ascribed to him only the creation of the primitive cells, which he is supposed to have endowed with the power to develop into the higher organisms. Wigand assumed for the origin of each species a special primitive cell and a long phylogenetic development of this; Reinke prefers a stem, composed of a number of species. These modern creative theories have no more scientific value than that of Agassiz; they are equally based on pure superstition (cf.chapters i.-iii.).

A different attitude from this irrational positive superstition is the sceptical view of those scientists who regard the question of the origin of life as insoluble or transcendental. Darwin and Virchow are representatives of this agnostic position; they held that we know nothing, and can know nothing, about the origin of the first organisms. Darwin, for instance, explains in his chief work that he "has nothing to do with the origin of the fundamental spiritual forces, or with that of life itself." This is a complete abandonment of the task of solving a scientific problem which must present as definite a subject of inquiry to modern research as any other evolutionary problem. The origin of life on our planet represents a fixed point in its history. However, there is nothing to be said if a scientist chooses to make no inquiry into it. A number of distinguished modern scientists maintain this agnostic attitude; they are more or less convinced that the origin of life is a natural process, but believe we have not as yet the means to explain it.

Different, again, is a third attitude which regards the problem of the origin of life as extremely difficult, yet capable of solution. This is the position of Dubois-Reymond, for instance, who counts the origin of life as the third great cosmic problem. Most of the modern scientists who have worked on the problem are of this opinion, although their views as to the way of solving it differ very much. We are confronted, in the first place, with two essentially different views which we may call the eternity-hypothesis and the theory of archigony (or spontaneous generation). According to the first view, organic life is eternal; according to the second, it began at a definite point of time. The eternity-hypothesis has assumed two very different forms, one of which has a dualistic and the other a monistic base. Helmholtz is a representative of the former theory, and Preyer of the latter.

Hermann Eberhard Richter put forward, in 1865, the hypothesis that infinite space is full throughout of the germs of living things, just as it is of inorganic bodies; both of them are in a condition of eternal development. When the ubiquitous germs reach a mature and habitable cosmic body, which possesses heat and moisture in the proper degrees for their development, they break into life, and may lead to the formation of a whole world of living things. Richter conceives these ubiquitous germs as living cells, and formulates the principle:Omne vivum ab æternitate e cellula(Every living thing is eternal and from a cell). In much the same way the botanist Anton Kerner postulates the eternity of organic life and its complete independence of the inorganic world. But the difficulties encountered by this hypothesis, in the indefinite form that Kerner gives it, are so great and so obvious that his theory has won no recognition.

However, the "cosmozoic hypothesis" attained a great popularity when it was afterwards taken up by two of the most distinguished physicists, Hermann Helmholtz and Sir W. Thomson (Lord Kelvin). Helmholtz formulated the alternative thus (in 1884): "Organic life either came into existence at a certain period, or it is eternal." He declared for the latter view, on the ground that we have not succeeded in producing living organisms by artificial means. He supposes that the meteors that roam about the universe might contain the germs of organisms, and, under favorable conditions, these might reach the earth or other planets and develop thereon. This cosmozoic hypothesis of Helmholtz is untenable, because the physical features of space (the extreme temperatures, the absolute dryness, the absence of atmosphere, etc.) exclude the lasting existence of plasm on meteorites in the form of organic germs with a capacity to live. The hypothesis is, moreover, logically useless,since it does not solve, but postpones, the question of the origin of organic life. If it is consistently worked out, it leads to pure cosmological dualism.

Another and very different theory of the eternity of life has been elaborated by Theodor Fechner (1873) and Wilhelm Preyer (1880). Both these scientists extend the idea of life to the whole cosmos, and reject the distinction that is usually drawn between the organic and the inorganic. Fechner goes so far as to ascribe consciousness to the whole universe and every single body in it, and regards individual organisms merely as parts of one vast universal organism. His system is, therefore, panpsychistic, and, at the same time, pantheistic, as he somewhat mystically connects the idea of a conscious God with that of a living universe. Preyer generally agrees with him in extending the idea of life to the whole universe, and conceiving it as an organism. He applies his theory in the symbolic sense which I alluded to on page 38, and described as impracticable. The fiery mass of the forming earth is the gigantic organism, and Preyer gives the name of "life" to its rotatory movement (or gravitational energy). As it cooled down, the heavier metals (the dead inorganic masses) separated from it; from the rest of it were formed first simple and afterwards complex carbon-combinations, and finally albumin and plasm. This extension of the word "organism" has very properly met with little approval in biology. It only increases the confusion, and the difficulty of marking off biological from abiological science, which is both practically necessary and theoretically justified.

If, then, in our opinion, the eternity-hypotheses are of no more value than the creation-hypotheses, we have left, for the purpose of answering the great question of the origin of life, only the third group of scientific theories which I have combined under the general heador archigony. They start from the following points: 1. Organic life is everywhere bound up with the plasm (or protoplasm), a chemical substance of a viscous character, having albuminous matter and water as its chief constituents. 2. The characteristic movements of this living substance, to which we give the name of organic life, are physical and chemical processes, that can only take place within certain limits of temperature (between the freezing-point and boiling-point of water). 3. Beyond these limits organic life may in certain circumstances be maintained for a time in a latent condition (apparent death, potential life); but this latent condition is restricted to a certain (and generally short) period. 4. As the earth, like all the other planets, was for a long time in a state of incandescence, at a temperature of several thousand degrees, living organisms (viscous albuminoids) cannot possibly have existed on it, and so cannot be eternal. 5. Fluid water, the first condition for the appearance of organic life, cannot have formed on it until the crust at the surface had fallen below boiling-point. 6. The chemical processes which first set in at this stage of development must have been catalyses, which led to the formation of albuminous combinations, and eventually of plasm. 7. The earliest organisms to be thus formed can only have been plasmodomous monera, structureless organisms without organs; the first forms in which the living matter individualized were probably homogeneous globules of plasm, like certain of the actual chromacea (chroococcus). 8. The first cells were developed secondarily from these primitive monera, by separation of the central caryoplasm (nucleus) and peripheral cytoplasm (cell-body).

The monistic hypothesis of abiogenesis, or autogony (= self-development) in the strictly scientific sense of the word, was first formulated by me in 1866 in the second book of theGeneral Morphology. The solidfoundation for it was found in the monera I had described, the very simple organisms without organs that had up to that time been overlooked or thrust aside. It is of radical importance, in giving a naturalistic solution of the problem of the origin of life, to start from these structureless granules of living matter, and not—as still generally happens—from the cell; these nucleated elementary organisms could not be the earliest archigonous living things, but must have been evolved secondarily from the unnucleated monera. Hence, I made a very thorough study of these rudimentary organisms in myMonograph on the Monera(1870), and endeavored to formulate it more clearly later on (in the first volume of theSystematic Phylogeny). In regard to the chemical question of the first formation of plasm and its inorganic preparation, Edward Pflüger conducted some valuable investigations, and recognized that the radical of cyanogen was the chief element of the living plasm. I may therefore distinguish two different stages of the theory—my own older autogony-hypothesis and the later cyanogen-hypothesis.

The theory of abiogenesis, or archigony, which I advanced in 1866, and have developed in later writings, appeals directly to the biochemical facts that modern vegetal physiology has firmly established. The chief of these facts is that even the living green plant-cell has the synthetic faculty of plasmodomism or carbon-assimilation; that is to say, it is able to build up, by a chemical synthesis and reduction, from simple inorganic compounds (water, carbonic acid, nitric acid, and ammonia), the complex albuminous compounds which we call plasm or protoplasm, and which we regard as the active living substance and the true material basis of all vital function (cf.chapter vi.). All botanists are now agreed that this most important process of vegetal life, the fundamental process of all organic life and all organization,is a purely chemical (or, in the wider sense, physical) process, and that there is no question of a specific vital force or a mystic constructor (like the famous "mechanical engineer of life"), or any other transcendental agency, in connection with it. The tiny chemical laboratory in which this remarkable organoplastic process takes place under the influence of sunlight is, in the simplest plants, the chromacea, either the whole homogeneous globule of plasm (chroococcus) or its bluish-green surface-layer, which is active as a chromatic principle (chromatophore). But in most plants these reduction-laboratories are the chromatella or chromatophora, which have been differentiated from the rest of the plasm of the cell, and are colorless globular leucoplasts within its dark interior, or green chromoplasts (or granules of chlorophyll) at its illumined surface. My theory of archigony only assumes that this chemical process of plasmodomism which we find repeated every second in every plant-cell exposed to the sunlight, and which has become an "inherited habit" of the green plant-cell, developed of itself at the beginning of organic life; in other words, it is a catalytic process (or one analogous to catalysis), the physical and chemical conditions of which were present in the condition of organic nature at that time.

My hypothesis was very strongly confirmed twenty years ago by the adhesion of the able botanist, Carl Nägeli. In his instructive work,A Mechanical-physiological Theory of Evolution(1884), he supported all the principal ideas as to the natural origin of life which I had advanced in 1866. He formulates the chief part of them in this admirable principle:

The origin of the organic from the inorganic is, in the first place, not a question of experience and experiment, but a fact deduced from the law of the constancy of matter and force. If all things in the material world are causally related, if allphenomena proceed on natural principles, organisms, which are formed of and decay into the same matter, must have been derived originally from inorganic compounds.

This excellent and clear declaration of a distinguished scientist and profound thinker might be taken to heart by the "exact" scientists who are always attacking the monistic theory of archigony as an unproved hypothesis, or regard the whole problem as insoluble. Nägeli has, moreover, proceeded to make a thorough study of the molecular processes involved, and embodied the results in his idioplasm theory. He believes that at the beginning of organization the definite autonomous arrangement of the smallest homogeneous parts of the plasm was a matter of the greatest importance. In his opinion these "micella" are crystalline groups of molecules, arranged multifariously in strings and parallel rows.

A similar and more elaborate attempt to give a physical explanation of the processes of archigony and trace them to mechanical molecular structures was made by Ludwig Zehnder in 1899 in his work onThe Origin of Life. He believes that the smallest and lowest life-unities (the micellar strings of Nägeli and the biophora of Weismann, corresponding to my plastidules) have a tubular shape, and so he calls them "fistella." He supposes that these invisible molecular structures are regularly arranged in millions in the plasma of the cell, and differentiated in such a way that some will effect endosmosis, others contraction, others the conduction of stimuli, and so on. As in the similar work of Nägeli and others, the value of this molecular hypothesis is that it stimulates us to attempt to conceive the mode of the arrangement and movement of the molecules of plasm in the process of archigony on physical principles.

A more interesting and notable attempt to penetrate into the mysterious obscurity of the chemical processesin archigony was made in 1875 by the distinguished physiologist, Edward Pflüger, in his essay onPhysiological Combustion in the Living Organism. He starts from the fact that the plasm (or protoplasm) is the material basis of all vital phenomena, and that this living matter owes its properties to the chemical properties of the albumin (whether we regard this as a chemical unity, protein or protalbumin, or as a mixture of different compounds). However, Pflüger sharply distinguishes between the living albumin of the plasm out of which all organisms are built, and the dead albumin, such as we find it, for instance, in the glairy albumin of the hen's egg. Only the living albumin (plasm) decomposes of itself in a slight degree, and to a greater extent under the influence of external excitation; the dead albumin will remain intact for a long time under favorable conditions. The cause of the extraordinary instability of the living albumin is its intramolecular oxygen—that is to say, the oxygen that is taken into the interior of the plasma-molecules in breathing, and effects there a disassociation, surrounding the atoms and breaking up the new-formed groups.

The real cause of this rapid decomposability of the plasm, and of the accompanying formation of carbonic acid, is found in the cyanogen, a remarkable body composed of an atom of carbon and an atom of nitrogen, which, in conjunction with potassium, forms the well-known and very virulent poison, cyanide of potassium. The non-nitrogenous decomposition-products of the dead and the living albumin agree in the main, but their nitrogenous products are totally different. Uric acid, creotin, guanine, and the other decomposition products of plasm contain the cyanogen-radical, and the most important of all, urea, can be artificially produced from cyanic compounds, as Wöhler showed in 1828. From this we may infer that the living albumin always containsthe cyanogen-radical, and that dead nutritive albumin does not. The belief that it is cyanogen which gives its characteristic vital properties to the plasm is supported by a number of analogies that we find to exist between cyanide compounds, especially cyanic acid (C N O H.) and the living albumin. Both bodies are fluid and transparent at a low temperature, while they set at a higher; both of them break up in the presence of water into carbonic acid and ammonia; both produce urea by disassociation (by the intramolecular surrounding of the atoms, not by direct oxydation). "The similarity of the two substances is so great," says Pflüger, "that I might describe cyanic acid as a semi-living molecule." Both substances grow in the same way by concatenation of the atoms, homogeneous groups of atoms joining together chainwise in large masses.

There is an especial interest in connection with the theory of archigony and its physical basis in the chemical fact that cyanogen and its compounds—cyanide of potassium, cyanic acid, cyanide of hydrogen, etc.—are only formed at incandescent heat; that is to say, when the requisite inorganic nitrogenous compounds are put with glowing coals, or the mixture is heated to incandescence. Other essential constituents of albumin, such as carburetted hydrogen or alcohol-radical, can be formed synthetically in heat. "Thus," says Pflüger, "nothing is clearer than the possibility of the formation of cyanic compounds when the earth was entirely or partially in a state of incandescence or great heat. We see how extraordinarily all the facts of chemistry point to fire as the force that has produced the constituents of albumin by synthesis. Hence life was born from fire, and the chief conditions of its appearance are associated with a time when the earth was a glowing ball of fire. When we remember the incalculably long period in which the surface of the earth was slowly cooling,we see that cyanogen, and the compounds that contained cyanogen, and carburetted hydrogen, had plenty of time and opportunity to follow out to any extent their great tendency to the transposition and formation of polymeria (chains of atoms), and, with the co-operation of oxygen and afterwards of water and salts, to evolve into the self-decomposable albumin which is living matter." In regard to the latter feature, it is well to emphasize the fact that, as will be understood, there must have been a long series of chemical intermediary stages between the incandescent formation of cyanogen and the appearance of the aqueous living plasm.

Pflüger's cyanogen theory does not conflict with my monera theory, but rather supplements it, by its careful and thoroughly scientific study of a much earlier stage of primitive biogenesis—in a sense, the first period of preparation for the formation of albumin. This must be well borne in mind in view of the attacks which have lately been made on it by Neumeister and other vitalists; it is supposed to be untenable, because "there is an impassable gulf between cyanic compounds and proteids." This criticism is answered by the living albumin itself, which always contains in its nitrogenous decomposition products the radical of cyanide or other substances (urea) that can be artificially produced from cyanic compounds. Another objection is that "the cyanic compounds which were formed in the heat must have very quickly perished on the subsequent appearance of water." The objection has no weight, since we can form no definite idea as to the special conditions of chemical activity in those times. We can only say that the conditions during this long period (embracing millions of years) were totally different from those of chemical action at the surface of the earth to-day. The real ground of the opposition of Neumeister and other vitalists is their dualistic conception of nature, which willmaintain at all costs the deep gulf between the organic and inorganic worlds.

Max Verworn, in hisGeneral Physiology, has fully described and criticised the various theories of the appearance of life on the earth. He rightly attributes a great value to Pflüger's cyanogen theory, because "it makes a strictly scientific study of the problem in close relation to the facts of physiological chemistry, and goes thoroughly into detail." He agrees with Pflüger when he expresses himself as follows: "I would say, therefore, that the first albumin to be formed was in point of fact living matter, endued with the property in all its radicals of attracting especially homogeneous parts with great force and preference, in order to build them chemically into the molecule, and so grow indefinitely. On this view the living albumin need not have a constant molecular weight, because it is a huge molecule in an unceasing process of formation and decomposition, probably acting on the ordinary chemical molecules as a sun does on a small meteor." This theory, which I believe to be correct, is also maintained by many other modern scientists who have made a particular study of the difficult question of the nature and origin of the albuminoids.

Now that we have described the various modern theories of archigony that are worth considering, and recognized with Nägeli that the original development of the organic from the inorganic is a fact, we may glance at the older theories which, under the name of "spontaneous generation," afforded matter for a good deal of controversy. It is true that they are now almost entirely abandoned, but the experiments in connection with them excited a good deal of interest and led to many misunderstandings.

The older hypotheses of "spontaneous generation" do not bear on our problem of archigony (or the firstdevelopment of living matter from lifeless inorganic carbon compounds) but relate to the formation of lower organisms out of the putrid and decomposing organic elements of higher organisms. In order to distinguish these hypotheses from the totally different theory of archigony, it is better to give them the name of saprobiosis (an earlier name was necrobiosis), which means the birth of living from dead (nekron) or putrid (sapron) organic matter. Saprobiosis is preferable, because necrobiosis is better used in a different sense, for the dead organic parts which gradually bring about the death of the living body (see p. 106). It was believed in ancient times that lower organisms could arise from the dead remains of higher organisms, such as fleas from manure, lice from morbid pustules in the skin, moths from old furs, and mussels from slime in the water. As these stories were supported by the authority of Aristotle, and on that account believed by St. Augustine and other fathers, and reconciled with the faith, they were held until the beginning of the eighteenth century. Even in the year 1713 the botanist Heucherus stated that the green duck-weed (lemna) is only condensed grease from the surface of foul standing water, and that water-cress was formed from it in fresh running water.

The first scientific refutation of these old stories was made by the Italian physician, Francisco Redi, in 1674, on the basis of very careful experiment: he was persecuted for "unbelief" on that account. He showed that all these animals arose from eggs that had been deposited by female animals in dung, skin, fur, slime, etc. But at that time the proof could not be extended to the tape-worms, maw-worms, and other intestinal animals (entozoa), which live inside other animals (in the bowels, blood, brain, or liver). It was still believed that these arise from diseased parts of the host-animals in which they live, until about the middle of the nineteenth century.It was not until 1840-1860 that it was shown by the experiments of Siebold, Leuckart, Van Beneden, Virchow, and other famous biologists, that all these intestinal animals have come from without into the animals they live in, and propagate there by eggs. Of late years the proof has been applied all round.

On the other hand, the hypothesis of saprobiosis retained its position until quite recently for one section of the smallest and lowest organisms, the microscopic forms of life, invisible to the naked eye, which were formerly called infusoria, and which we now call by the wider name of protists or unicellulars. When Leeuwenhoek discovered the infusoria in 1675 with the newly invented microscope, and showed that they arise in great quantities in infusions of hay, moss, flesh, and other putrid organic substances, it was generally believed that they were spontaneously generated there. The Abbé Spallanzani showed in 1687 that no infusoria appear in these infusions if they are well boiled and the vessel is carefully closed; the boiling kills the germs in them, and the exclusion of air prevents the entrance of fresh germs. In spite of this, many microscopists still believed that certain infusoria, particularly the very small and simple bacteria, could be born directly from putrid or diseased tissues of organisms, or from decomposing organic fluids; the opinion was maintained by Pouchet at Paris in 1858, and afterwards by Charlton Bastian. The controversy about the subject moved the Paris Academy in 1858 to offer a prize for "careful research that would throw new light on the question of spontaneous generation." It fell to the famous Louis Pasteur, who proved, by a series of ingenious experiments, that there are everywhere in the atmosphere numbers of germs of microbes or microscopic organisms floating among the dust particles, and that these grow and reproduce when they reach water. Not only infusoria,but also small highly organized plants and animals—such as lichens, mosses, rotifers, and tardigrades—can live for months in a desiccated condition, be carried in all directions by the wind, and reawaken into life when they reach water. On the other hand, Pasteur showed convincingly that organisms never appear in infusions of organic substances when they are sufficiently boiled and the atmosphere that reaches them has been chemically purified. He summed up the results of his rigorous experiments, which were confirmed by Robert Koch and other bacteriologists, and gave rise to the modern precautions as to disinfection, in the maxim: "Spontaneous or equivocal generation is a myth."

The famous experiments of Pasteur and his successors had destroyed the myth of saprobiosis, but not the theory of archigony. These entirely different hypotheses are still very frequently confused, because the old title of "spontaneous generation" is used for both. We still read sometimes that the "unscientific" belief in abiogenesis has been definitely refuted by these experiments, and that the question of the origin of life has thus become an insoluble enigma. There is an astonishing superficiality and lack of discernment in such remarks; they would hardly be possible in any other branch of science. But in biology—many of its distinguished representatives continue to say—we have only to observe and correctly describe facts; the formation of clear ideas and the indulgence in reflection on the facts are unnecessary and dangerous, and, therefore, to be avoided! It is due to this pitiable condition of biological methods of research that our hypothesis of archigony is still attacked, or else ignored. Why? Because the false hypothesis of saprobiosis, which has absolutely nothing in common with it but the name "spontaneous generation," has been refuted by theexperiments of Pasteur and his colleagues![9]These experiments prove nothing whatever beyond the fact that new organisms are not formed in certain infusions of organic matter—under definite, artificial conditions. They do not even touch the important and pressing question, which alone interests us: "How did the earliest organic inhabitants of our earth, the primitive organisms, arise from inorganic compounds?"

The great popularity of the famous experiments of Pasteur on spontaneous generation, and the unfortunate confusion of ideas which was caused by the false interpretation of his results, make it necessary for me to say a word on the general value of scientific experiments in many questions. Since Bacon introduced experiment into science three hundred years ago, and gave it a logical basis, both our speculative knowledge of nature and the practical application of our knowledge made remarkable progress. New methods of research made it possible for modern workers to penetrate far more deeply into the nature of phenomena than the older thinkers had done, who had no knowledge of experiment. Especially in the nineteenth century the development of the experimental method, or the putting of a question to nature, led to enormous advances in the various sciences.

In the subject we are considering the question to be put to nature is: "Under what conditions and in what manner is living matter (or plasm) formed from lifeless inorganic compounds?" We may confidently assume that in the period when archigony took place—the time when organic life first appeared on the cooled surface of the earth, at the beginning of the Laurentian Age—the conditions of existence were totally differentfrom what they are now; but we are very far from having a clear idea of what they were, or from being able to reproduce them artificially. We are just as far from having a thorough chemical acquaintance with the albuminous compounds to which plasm belongs. We can only assume that the plasma-molecule is extremely large, and made up of more than a thousand atoms, and that the arrangement and connection of the atoms in the molecule are very complicated and unstable. But of the real features of this intricate structure we have as yet no conception. As long as we are ignorant of this complex molecular structure of albumin, it is useless to attempt to produce it artificially. Yet in this position of the matter we would seek to produce that great wonder of life, the plasm, artificially, and when the experiment miscarries (as we should expect) we cry out: "Spontaneous generation is impossible."

When we carefully consider the intelligent experiments that have been made in regard to archigony in the light of these facts, it is clear that their negative result does not in the slightest degree affect our question. The much-admired experiments of Pasteur and his colleagues prove merely that in certain artificial conditions infusoria are not formed in decomposing organic compounds (or the dead tissues of highly organized histona); they cannot possibly prove that saprobioses of this kind do not take place under other conditions. They tell us nothing whatever about the possibility or reality of archigony; in the form in which I put the scientific hypothesis in 1866 it is completely untouched by all these experiments. It remains intact as the first attempt to give a provisional reply—if only in the form of a temporary hypothesis—on the basis of modern science to one of the chief questions of natural philosophy.

In myGeneral Morphology(1866), and afterwards in myBiological Studies on the Monera and other Protists,and the first volume of mySystematic Phylogeny(1894), I attempted to sketch in detail the stages of the process to which I give the name of archigony. I distinguished two principal stages—autogony(the formation of the first living matter from inorganic nitrogenous carbon-compounds) andplasmogony(the formation of the first individualized plasm; the earliest organic individuals in the form of monera). In more recent efforts I have made use of the important results reached by Nägeli (1884) in his investigations of the same subject. In regard to some important points relating to the chemico-physical part of the question, Nägeli has, in hisMechanico-physiological Theory of Evolution(chapter ii.), gone more into the details of the process of archigony. To the earliest living things, which were formed by "unicellular organization" of the plasm out of simple inorganic compounds, he gives the name ofprobiaorprobionta, and thinks that these had an even simpler structure than my monera. This view seems to rest on a misunderstanding. Nägeli does not strictly follow my definition, "organisms without organs" (that is to say, structureless living particles of plasm without morphological differentiation), but he has in mind the individual rhizopod-like organisms which I had at first described as monera—protamœba,protogenes,protomyxa, etc. In my present view the chromacea, or plasmodomous phytomonera, are much more important than these plasmophagous zoomonera. It is curious that Nägeli does not make thorough use of their primitive organization for the establishment of his theory, although he has had the great merit of describing these most primitive of all living organisms as unicellular algæ (1842). As a matter of fact, the simplest chromacea (chroococcus and related forms) approach so closely to his hypothetical probia or probionta that the only things we can regard as the rudiments of organization in the chroococcacea are thesecretion of a protective membrane about the homogeneous plasma-globule and the separation of the blueish-green cortical zone from the colorless central granule. The more important of the further conclusions of Nägeli are those which relate to the mode of the primitive abiogenesis and the frequent repetition of this physical process.

Recently Max Kassowitz, in the second volume of hisGeneral Biology(1899), has gone fully into the various stages of the process of archigony, as a sequel to his metabolic theory of the building up and decay of plasm, from the point of view of physiological chemistry. He says very truly that the development of living from lifeless matter must not be conceived as a sudden leap; the very complicated chemical unities which now form the basis of life have been slowly and gradually evolved during an incalculably long period by the way of substitution for simpler compounds. We may join these views—which generally accord with my earlier deductions—with Pflüger's cyanogen theory, and so draw up the following theses:

1. A preliminary stage to archigony is the formation of certain nitrogenous carbon-compounds which may be classed in the cyanic group (cyanic acid, etc.). 2. When the crust of the earth stiffened, water was formed in the fluid condition; under its influence, and in consequence of the great changes in the carbonic-acid laden atmosphere, a series of complicated nitrogenous carbon-compounds were formed from these simple cyanic compounds, and these first produced albumin (or protein). 3. The molecules of albumin arranged themselves in a certain way, according to their unstable chemical attractions, in larger groups of molecules (pleona or micella). 4. The albumin-micella combined to form larger aggregations, and produced homogeneous plasma-granules (plassonella). 5. As they grew the plassonelladivided, and formed larger plasma-granules of a homogeneous character: monera (= probionta). 6. In consequence of surface-strain or of chemical differentiation, there took place a separation of the firmer cortical layer (membrane) from the softer marrow layer (central granule), as in many of the chromacea. 7. Afterwards the simplest (nucleated) cells were formed from these unnucleated cytodes, the hereditary mass of the plasm gathering within the monera and condensing into a firm nucleus.

It is an interesting, but at present unanswered, question whether the process of archigony only occurred once in the course of time or was frequently repeated. Reasons can be given for both views. Pflüger says: "In the plant the living albumin only continues to do what it has done ever since its origin—constantly to regenerate itself or to grow; hence I believe that all the albumin in the world comes from that source. On that account I doubt if spontaneous generation takes place in our time. Moreover, comparative biology directly shows that all life has come from one single root." However, this view does not exclude the possibility of the chemical process of spontaneous plasmodomism having been frequently repeated—under like conditions—in the same form in primordial times.

On the other side, Nägeli especially has pointed out that there is no reason to prevent us from thinking that archigony was repeated several times, even down to our own day. Whenever the physical conditions for the chemical process of plasmodomism were given, it might be repeated anywhere at any time. As to locality, the sea-shore probably affords the most favorable conditions; as, for instance, on the surface of fine moist sand the molecular forces of matter in all its conditions—gaseous, fluid, viscous, and solid—find the best conditions for acting on each other. It is a fact that to-day all thevarious evolutionary forms of living matter—from the simplest moneron (chroococcus) to the plain nucleated cell, from this to the highly organized cell of the radiolaria and infusoria, from the simple ovum to the most elaborate tissue-structure in the higher plants and animals, from the amphioxus to man—come in an order of succession. There are only two ways of explaining this fact: either the simplest living organisms, the chromacea and bacteria, the palmella and amœbæ, have remained unchanged or made very little advance in organization since the beginning of life—more than a hundred million years; or else the phylogenetic process of their transformation has been frequently repeated in the course of this period, and is being repeated to-day. Even if the latter were the case, we should hardly be in a position to learn it by direct observation.

Assuming that the simplest organisms are still formed by abiogenesis, the direct observation of the process would probably be impossible, or at least extremely difficult, for the following reasons: 1. The earliest and simplest organisms are most probably globular particles of plasm, without any visible structure, like the simplest living chromacea (chroococcus). 2. These plasmodomous monera cannot be distinguished from the chromoplasts (chlorophyll-granules), which live inside plant-cells, and may continue after the death of the cells to multiply independently by cleavage. 3. We must admit with Nägeli that the original size of these probionta (in spite of the relatively colossal size of their molecules) is very small—much too small to come within the range of the best microscope. 4. In the same way the primitive metabolism and the slow, simple growth of these monera would not come within direct observation. 5. As a matter of fact, we do often find in stagnant water, and in the sea, tiny granules which consist, or seem to consist, of plasm. We usually regard them asdetached portions of dead animals or plants; little isolated chlorophyll-granules that may be found everywhere are looked upon as rejected products of vegetal cells. But who could refute the assumption that they are really plassonella or young monera, which grow slowly and unite with similar particles to form larger plasmic bodies?

It is often objected to our naturalistic and monistic conception of archigony that we have not yet succeeded in forming albuminous bodies, and especially plasm, in our chemical laboratories by artificial synthesis; from this the perverse dualistic conclusion is drawn that it is only supernatural vital forces that can do this. It is forgotten that we do not yet know the complicated structure of albuminous bodies, and that we do not yet know what really happens inside the green chlorophyll-granules which in every plant-cell convert the radiant energy of sunlight into the virtual energy of the new-formed plasm. How can we be expected to reproduce synthetically, with the imperfect and crude methods of present chemistry, an elaborate chemical process the nature of which is not analytically known to us? However, the worthlessness of this sceptical objection is obvious: we can never claim that a natural process is supernatural because we cannot artificially reproduce it.

XVI

Inorganic and organic evolution—Biogenesis and cosmogenesis—Mechanical evolution—Mechanics of phylogenesis—Theory of selection—Theory of idioplasm—Phyletic vital force—Theory of germ-plasm—Progressive heredity—Comparative morphology—Germ-plasm and hereditary matter—Theory of mutation—Zoological and botanical transformism—Neo-Lamarckism and Neo-Darwinism—Mechanics of ontogenesis—Biogenetic law—Tectogenetic ontogeny—Experimental evolution—Monism and biogeny.

I fully explained in myGeneral Morphology(1866) the profound importance of the science of evolution in relation to our monistic philosophy. A popular synopsis of this is given in myHistory of Creation, and is briefly repeated in the thirteenth chapter of theRiddle. I must refer the reader to these works, especially the latter, and confine myself here to a consideration of some of the principal general questions of evolution in the light of modern science. The first thing to do is to compare the conflicting views on the nature and significance of biogenesis which still face each other at the beginning of the twentieth century.

The essential unity of inorganic and organic nature, which I endeavored to establish in the second book of theGeneral Morphology, and the significance of which I explained in the fourteenth chapter of theRiddle, is found through the whole course of its development, in the causes of phenomena and their laws. Hence, indealing with the evolution of organisms, we reject vitalism and dualism, and maintain our conviction that it can always be traced to physical forces (and especially chemical energy). As we regard plasm as the basis of it (chapter vi.), we may say that organic evolution depends on the mechanics and chemistry of the plasm. We postulate no supernatural vital force for the explanation of physiological functions, and we are just as far from admitting it as regulator or agency of the biogenetic process.

If we understand by biogeny the sum total of the organic evolutionary processes on our planet, by geogeny the processes at work in the formation of the earth itself, and by cosmogony those that produced the whole world, biogeny is clearly only a small part of geogeny, and this in turn only a small section of the vast science of cosmogony. This important relation is evident enough, yet often overlooked; it holds both of time and space. Even if we suppose that the biogenetic process occupied more than a hundred million years, this period is probably much shorter than that which our planet has needed for its development as a cosmic body—from the first detachment of the nebular ring from the shrinking body of the sun to its condensation into a rotating sphere of gas, and from this to the formation of the incandescent globe, the stiffening of the crust at its surface, and finally the downpour of fluid water. It was not until this last stage that carbon could begin its organogenetic activity and proceed to the formation of plasm. But even this long geogenetic process is, as regards space and time, only a very small part of the illimitable history of the world. If we further assume that organic life develops on other cosmic bodies (Riddle, chapter xx.) in the same way as on our earth under like conditions, the whole sum of all these biogenetic processes is only a small part of the all-embracing cosmogenetic process. The vitalistic belief that itsmechanical course was interrupted from time to time by the supernatural creation of organisms is opposed to pure reason, the unity of nature, and the law of substance. We must, therefore, hold fast above all to the conviction that all biogenetic processes are just as reducible to the mechanics of substance as all other natural phenomena.

The mechanical and natural character of the development of inorganic nature, the earth and the whole material world, was established mathematically at the end of the eighteenth century by the great atheist Laplace in hisMécanique Céleste(1799). The similar cosmogony which Kant had expounded in 1755 in hisGeneral Natural History and Theory of the Heavensonly obtained recognition at a later date (Riddle, chapter xiii.). But the possibility of giving a mechanical explanation of organic nature was not seen until Darwin provided a solid foundation for the theory of descent by his theory of selection in 1859. I made the first comprehensive attempt to do this in 1866 in myGeneral Morphology, the aim of which is expressed in the title: "General outlines of the science of organic forms, mechanically grounded on Darwin's improvement of the theory of descent." Especially in the second volume of the work, the "General Evolution of Organisms," I endeavored to show that both sections of the science, ontogeny (or embryology) and phylogeny, can be reduced to physiological activities of the plasm, and so explained mechanically, in the wider meaning of the word.

When I stated the nature and the aim of phylogeny in 1866, most biologists regarded my attempt as unjustifiable, as they did Darwinism itself, of which it was a natural consequence. Even the famous Émil Dubois-Reymond, to whom as a physiologist it should have been welcome, described it as "a poor romance"; he compared my first attempts to construct the genealogical tree of the organic classes, on the evidence of paleontology,comparative anatomy, and ontogeny, to the hypothetical labors of philologists to draw up the genealogical tree of the legendary Homeric heroes. As a matter of fact, I had myself described my imperfect effort as merely a provisional sketch, as a temporary hypothesis that would open the way for later and better research. A single glance at the immense literature of phylogeny to-day shows how much has been done since in this province, and how far we have advanced in the establishment of the features of evolution by means of the united labors of numbers of able paleontologists, anatomists, and embryologists. Ten years ago I attempted, in the three volumes of mySystematic Phylogeny, to give a comprehensive statement of the results attained. My chief aim was, on the one hand, to construct a natural system of organisms on the basis of their ancestral history, and on the other hand to prove the mechanical character of the phylogenetic process. All the activities of organisms which are at work in the transformation of species and the production of new ones in the struggle for existence may be reduced to their physiological functions—to growth, nutrition, adaptation, and heredity; and these again to the mechanics and chemistry of the plasm. The struggle for life is itself a mechanical process, in which natural selection uses the disproportion between the excess of germs and the restricted means of existence, in conjunction with the variability of species, in order to produce new purposive structures mechanically and without any preconceived design. This teleological mechanicism has no need of a mysterious design or finality; it takes its place in the general order of mechanical causality which controls all the processes in the universe. Natural finality is only a special instance of mechanical causality. The one is subordinate to the other, not opposed to it, as Kant would have it.

The effort that the great Lamarck made in 1809, in hisPhilosophie Zoologique, to establish transformism deserves high appreciation from monists, because it was the first attempt to give a natural explanation of the origin of the countless species of organic forms which inhabit our planet. Up to that time it had been the fashion to attribute their origin to a miraculous intervention of the Creator. This metaphysical creationism had now to face physical evolutionism. Lamarck explained the gradual formation of organic species by the interaction of two physiological functions—adaptation and heredity. Adaptation consists in the improvement of organs by use, and degeneration by disuse; heredity acts by transmitting the features thus acquired to posterity. New species arise by physiological transformation from older species. The fact that this great thought was overlooked for half a century does not detract from its profound significance. But it only obtained general recognition when Darwin had supplemented it and filled up its causal gaps by the theory of selection in 1859. Apart from this specifically Darwinian feature (whether it be true or not), the fundamental idea of transformism is now generally received; it is admitted to-day even by metaphysicians who maintained a spirited opposition to it thirty years ago. The fact of the progressive modification of species is only intelligible on Lamarck's theory that the actual species are the transformed descendants of older species. In spite of all the learning and zeal with which the theory has been attacked, it has proved irrefutable; nor can any one suggest a better theory to replace it. This may be said particularly of its chief consequence—the descent of man from a series of other mammals (proximately from the apes).

The high value of Darwin's theory of selection for the monistic biology is now acknowledged by all competentand impartial authorities on the science. In the course of the forty-four years since it found its way into every branch of biology, it has been employed in more than a hundred large works and several thousand essays in explaining biological phenomena. This alone is enough to show its profound importance. Hence it is mere ignorance of the subject and its literature to say, as has been done several times of late, that Darwinism is in decay, or even "dead and buried." However, absurd writings of this kind (such as Dennert'sAt the Death-bed of Darwinism) have a certain practical influence, because they fall in with the prevailing superstition in theology and metaphysics. Unfortunately, they also seem to obtain notice from the circumstance that a few botanists persistently attack the Darwinian theory. One of the most conspicuous of these is Hans Driesch, who affirms that all Darwinists (and therefore the great majority of modern biologists) have softening of the brain, and that Darwinism is (like Hegel's philosophy) the delusion of a generation. The arrogance of this conceited writer is about equal to the obscurity of his biological opinions, the confusion of which is covered by a series of most extravagant metaphysical speculations. All these attacks have lately been met very ably by Plate in his work,On the Significance of the Darwinian Principle of Selection and the Problem of the Foundation of Species(second edition, 1903). The most thorough of recent defences of Darwinism is that made by August Weismann in hisLectures on the Theory of Descent(1902) and other works. But the distinguished zoologist goes too far when he seeks to prove the omnipotence of selection and wishes to ground it on an untenable molecular hypothesis—the theory of germ-plasm, which we will consider presently. Apart from these or other exaggerations, we may say with Weismann that Lamarck's theory of descent received a sound causal basisby Darwin's theory of selection. Its real foundations are these three phenomena: heredity, adaptation, and the struggle for existence. All three are, as I have often said, of a purely mechanical and not a teleological nature. Heredity is closely bound up with the physiological function of reproduction, and adaptation with nutrition; the struggle for life follows logically and mathematically from the disproportion between the number of potential individuals (germs) and of actual individuals that grow to maturity and propagate the species.

When I had, in myGeneral Morphology, endeavored to gain acceptance for Darwin's theory of selection, and had presented evolution as a comprehensive theory from the point of view of the monistic philosophy, a number of works, sometimes of value, appeared, which made special studies of the various parts of the immense province. Eighteen years afterwards a greater work was published, which started from the same monistic principles, but reached the same conclusion by a different way. In 1884 Carl Nägeli, one of our ablest and most philosophic botanists, issued hisMechanical-physiological Theory of Evolution. This interesting book consists of various parts. It is especially notable that evolution is presented in it as the one possible and natural theory of the origin of species; even morphology and classification are treated explicitly as "phylogenetic sciences." The chapter on archigony—a dark and dangerous problem that is generally avoided by scientists!—is one of the best that has been written on the subject. On the other hand, Nägeli rejects Darwin's theory of selection altogether, and would explain the origin of species by an inner "definitely directed variation," independently of the conditions of existence in the outer world. As Weismann has properly observed, this internal principle of evolution, which dispenses with adaptation in the truesense of the word, is at the bottom merely a "phyletic vital force." It is not made more acceptable by Nägeli when he builds up a subtle metaphysical system on it and postulates a special "principle of isagitation." But the idioplasm theory he connects with it is of some value, since it goes more fully into the differentiation of the cell-plasm into two physiologically different parts—the idioplasm of the hereditary matter and the trophoplasm as nutritive matter of the cell.

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