These disturbing or distorting newly introduced features or factors show themselves chiefly in connection with the embryonic conditions of growth—for example, yolk-sac, placenta, amnion. They all come within the category ofcænogenesis: they are cænogenetic, while the true, undisturbed recapitulation ispalingenetic.
Lastly, some features, so-called rudimentary or vestigial organs, instead of disappearing, are most tenacious in their recurrence, while others of originally fundamental importance scarcely leave recognisable traces, and are, so to speak, only hinted at during the embryonic growth of the creature we happen to study. Hence arises the philosophical study of 'Dysteleology.'
Among other terms invented by Haeckel, and now in general use, areMetamere,Metamerism,Cœlom,Gonochorism,Gastrula,Metazoa,Gnathostomata,Acrania,Craniota, andAmniota.
Hitherto we have dealt with his general work only, a résumé of which he gave for many years in a course of thirty lectures before an audience composed of 'all sorts and conditions of men.' Students of biology and of medicine side by side with theologians, incipient and ordained, jurists, political economists, and philosophers, crowded his lecture-room during the 'seventies to hear the master explaining the 'natural history of creation' or the mysteries of anthropogenesis. Another course of eighty lectures during the winter semester was, and still is, devoted to a systematic treatment of zoology, while practical classes are reserved for the more select.
His winning personality and fascinating eloquence, combined with a clear and concise delivery, have gained the enthusiastic admiration of many a student who went to the quiet University town in order to learn with his own ears and eyes.
List of Separate Publications by Professor Haeckel.
'Biologische Studien. I.: Studien ueber die Moneren und andere Protisten.' Leipzig, 1870 (out of print). He was the first to make observations on the natural history of the Monera, living bits of protoplasm, devoid even of a nucleus—e.g.,Protogenes primordialis,Protomyxa aurantiaca.
'Monographie der Radiolarien.' Berlin, 1862-88. With 171 plates.
'Entwicklungsgeschichte der Siphonophoren.' Utrecht, 1869.
'Plankton-Studien. Vergleichende Untersuchungen ueber die Bedeutung und Zusammensetzung der pelagischen Fauna und Flora.' Jena, 1880.
'Metagenesis und Hypogenesis von Aurelia aurita.' Jena, 1881.
'Monographie der Geryoniden oder Ruesselquallen.' Leipzig, 1865.
'Generelle Morphologie der Organismen.' 2 vols. Berlin, 1866.
'Anthropogenie oder Entwicklungsgeschichte des Menschen,' 1874; 4th edition, 1891.
'Natuerliche Schoepfungs-Geschichte.' 2 vols. Berlin, 1st edition, 1868; 9th edition, 1898. This work has been translated into most European languages (the first edition in English, under the title 'Natural History of Creation' in 1873; the eighth in 1892).
'Monographie der Kalkschwaemme.' 3 vols. Berlin, 1872 (out of print). With the subtitle, 'An Attempt to solve analytically the Problem of the Origin of Species.' In this work, illustrated by sixty plates, he showed that the Calcispongia are individually so yielding, so adaptive to external influences, that it is practically impossible to break up the whole group into anything like satisfactory species or genera. According to predilection, we can distinguish either 1 genus with only 3 species, or 3, 21, 43 genera, with 21, 111, 181, or 289 species respectively.
In this work, in 1872, Haeckel establishedthe homology of the two primary layers, ecto- and endoderm, throughout the Metazoa. The attempt to do the same for the four secondary layers, as made in the second part of his 'Gastræa-theory,' failed. It caused an enormous amount of research, hitherto without a satisfactory solution of the problem.
'Studien zur Gastræa-Theorie.' Jena, 1874. The transformation of the single primitive egg-cell by cleavage into a globular mass of cells (Morula)—which latter, becoming hollow (and then known as the Blastula), turns ultimately by invagination or by delamination into the Gastrula—is a series of processes which applies to all Metazoa. The Gastrula is, therefore, the ancestral form of the Metazoa; and the Gastræa-theory, founded by Haeckel, throws light, on the one hand, upon the mystery of the phyletic connection of the various animal groups, while, on the other hand, it connects the Metazoa, or multicellular organisms, with the lowest Protozoa. We come to this conclusion becausethe Gastrula arises from and passes through stages which exist as independent, permanent organisms among the Protozoa.
Needless to say this Gastræa-theory has been violently attacked in detail, with the result that various modifications of the Gastrula, until then undreamed of, have become known.
'Monographie der Medusen.' Jena, 1879-81. With 72 coloured plates.
'Reports on the Scientific Results of the Voyage of H.M.S.Challenger.' With 230 plates:
1. Deep-sea Medusæ. 1881.2. Radiolaria. 1887.3. Siphonophoræ. 1888.4. Deep-sea Keratosa. 1889.
1. Deep-sea Medusæ. 1881.2. Radiolaria. 1887.3. Siphonophoræ. 1888.4. Deep-sea Keratosa. 1889.
A short holiday spent on the coasts of the Red Sea produced the volume 'Arabische Korallen' (Berlin, 1876); and a longer trip to Ceylon has been described in 'Indische Reisebriefe,' of which the third editionappeared in 1893. The English translation (1883) is entitled 'A Visit to Ceylon.'
'Monism as connecting Religion and Science: the Confession of Faith of a Man of Science.' 1894.
Haeckels latest work is the 'Systematische Phylogenie' (Berlin, 1896), three volumes dealing with Protistæ and Plants, Invertebrata and Vertebrata. They contain the author's views on the natural system of the organic world, both living and extinct. Notable in the work are the many reconstructions of ancestral forms which, provided Evolution is true, must have existed—hypothetical until they, or something like them, are found in a fossil state. Everybody who works systematically, and upon the basis of Evolution, does, sometimes unconsciously, reconstruct such links, although he may perhaps not see the necessity, or have the courage to fix his vision, by assigning to it all those attributes or characters which are indicated by deductions from comparative anatomy, palæontology, and embryology.
The vegetable cell was discovered bySchleiden, Professor of Botany at Jena, in 1838. Next yearSchwannfound the animal cell.
In 1844Koellikerdiscovered that the egg cell, by division and multiplication, becomes an aggregation—a heap of new cells.
In 1849Huxleyfound the two primary layers (observed long before byPanderandBaerin the chick) also in certain Invertebrata, the Medusæ; and he called these layers 'ectoderm' and 'endoderm' respectively.
In 1851Remak, in his 'Untersuchungen über die Entwicklung der Thiere,' showed the egg to be a simple cell, and that from it, by repeated division or multiplication, arisethe germinal layers, and that by differentiation of the cells of these layers are formed all the tissues of the body.
Kowalevsky, of St. Petersburg, found the two primary germinal layers also in Worms, Echinoderms, Articulata, and other animals.
Haeckel, in 1872, found the same in the Sponges. He stated that these two germinal layers occur in all animals, except in the Protozoa; and that they are homologous, or equivalent, in all the groups of animals, from the Sponges up to Man. In 1873, in his 'Gastræa-theorie,' he explained the phylogenetic significance, and tried to show the homology, of the four secondary germinal layers.
An organism, as living matter, does not stand in opposition to, or outside of, the rest of the world. It is part of the world. It receives matter from its surroundings, and gives some back; therefore it is influenced by its surroundings. It is acted upon, and it reacts upon the latter, and if these change (and they are nowhere and never strictly the same) the organism alsovaries. Itadaptsitself, and if it does not, or, rather, cannot, do so, it dies, because it is unfit to live in the world, or, rather, in those particular surroundings and conditions in which it happens to be. That organism which yields most easily, accommodates itself most quickly, has the best chance of existence—survival of the fittest.'Fitness' in this case does not mean fitness to live, but rather a particular condition which happens to fit into the new circumstances.
Adaptation and variation are simultaneous: they are fundamentally the same. If there were no adaptability and no variability, those simplest of organisms which we suppose to have sprung into existence in the pre-Cambrian period would long ago have ceased to exist.
It is the physiological momentum which models the organism, and, by causing its adaptations, has produced its organs by change of function. Gegenbaur illustrates this most important fundamental truth by an excellent example. Suppose that, in an absolutely simple organism, all the parts of its exterior are under the same functional conditions, so that each part of the surface can take in food, and that this is digested, assimilated, in the interior. There is, in this condition, not yet any definite organ. If this organism sinks to the bottom andbecomes sessile, this part is excluded from taking in nourishing matter, while the opposite surface alone remains, or becomes more, fit for this function. Thus, a simple variation and adaptation has been produced, and if the same organism continues in this position, its bottom cells will estrange themselves from their original function, while those on the top will convey the food into the interior, where a cavity will be formed, ultimately with a permanent opening, the primitive gut and mouth, both very different from the 'foot.'
Thus, by adaptation and variation the organism acquires new functions, organs, features, and it gives up and eventually loses others. Its offspring is like it. Like produces like. This is the principle ofheredity. Adaptation, when going on generation after generation on the same lines in the same direction, becomes continuous, and has an intensifying,cumulativeeffect. By always weeding out from a flock of pigeons those birdswhich possess more dark feathers than the rest, we ultimately produce an entirely white race. We hurry on what Nature does slowly.
The inheritance of acquired characters becomes very obvious in the following example: The Monera are the lowest living organisms known; they consist of a mass of protoplasm, and are still devoid of even a nucleus. They multiply simply by division; each half is like the other, and like the parent (which by this process has ceased to exist), except that each is smaller and has to grow. A certain Moneron,Protomyxa aurantiaca, is orange-coloured, and its offspring is from the beginning of the same colour, and this colour has been acquired by that kind of Monera-like protoplasm which thereby has become the species called Aurantiaca. We have no reason for assuming that there existed from the beginning of life not only colourless, but also red, orange, and other kinds of protoplasm. In these simplest of organisms the whole process of heredityseems very obvious; but in the higher ones, in those which propagate by eggs, the problem is infinitely more complicated. It is true that the egg is, strictly, nothing but a small part of the parental organism, and we know from everyday experience that this single egg-cell has in it all the attributes and characteristics of the parent; but these attributes and characteristics make their appearance successively, just as the egg cell of a chick has neither wings nor feathers, not even a backbone, but develops these organs because its parents have them.
The theory that acquired characters are hereditary has often been vigorously attacked; but the champions of the negative position have not given us anything satisfactory instead. They question, also, the principle of adaptation as a factor in Evolution, and substitute 'variation,' coupled with 'natural selection.'
They point to Darwin's argument: (1) It is a fact that animals and plants produce amuch greater number of young than in their turn grow up to propagate the race; (2) no two of the frequently many individuals of the same breed are exactly alike, although the differences may be hidden to our perception (this is quite true, because no two entities can live in absolutely the same place and conditions); (3) through heredity the offspring takes over the faculties and features of the parents; (4) what decides which of the many individuals (each one possessing some aberration or variation) are to live and to propagate the race?—obviously those individual variations which happen to make the lucky possessors most fit for the struggle for life.
So far, well; but the 'Neo-Darwinians' imagine that 'adaptation' is not the cause, but the result, the effect, of the formation of species. According to them, the species are neither adapted by, nor do they adapt themselves to, their surroundings. Adaptation is to them an accomplished fact, a condition which aspecies happens to be in because its particular variation is the one which, to the exclusion of others, suits or fits into its surroundings. Such a view simply takes variation for granted, and stipulates it as a somethinga priori, without raising the further necessary question, why there should be any variations at all. Why, indeed, unless they are caused by external influences? Haeckel elucidated this by the conception of adaptation as explained in the foregoing pages.
These and kindred speculations have produced some rather curious discussions, which not infrequently end in conundrums. If we speak of a case of adaptation as a condition, a fact, we easily run the risk of getting into confusion about cause and effect. For example: Is the stag swift because he has long and slender legs, or are his legs long because he is swift? In reality, swiftness and length of legs are cause and effect in one. His legs have been so modified as to make him swift, because he has put them continuously to whatever washis full speed, which in his thick-footed ancestors was probably a very slow one. The above question reads, therefore, more sensibly as follows: Has the stag become swift because his legs have become long and slender, or have his legs become long and slender because he has attained swiftness? Now, we see that both halves of the double question are practically the same and instantly suggest the answer.
A fundamental difference between artificial machines and living organisms is that the former are worn out by use, while the latter not only repair the loss caused by use, but are also stimulated to further increase. On the other hand, organs which are not put into function, or are not used,degenerate. The various cells of the organ react upon external stimuli by increased activity. Why this should be so is another question—perhaps because those which do not would soon be not fit to survive. Each cell has a function; the more specialized the more intense it is. Everyexternal stimulus, every contact with the outer surroundings, is an insult, necessarily of detrimental effect, as it disturbs the equilibrium of the cell body. It must, therefore, be of advantage to the cells' well-being to return as soon as possible to thestatus quo ante, and this can only be done by increased activity.
In the present state of our knowledge, we can approach only the simplest cases of acquisition of characteristics. Mostly they are so complicated, subject to so many unthought-of conditions, that we do not know from which end to approach the problem. Frequently the supposed use of certain obvious features is the merest guesswork. This applies especially to features to which we are not accustomed (although wrongly so) to assign a function—for example, coloration. A green tree-frog will with predilection rest on green leaves. The advantages of concealment are obvious, and in this case he 'adapts himself' to the surroundings bymaking for green localities: if he did not he would be eaten up sooner than his more circumspect comrades. But this making for, and sitting in, the green has notnecessarilymade him of that colour. Extreme advocates of one view would argue as follows: Once upon a time there were among the offspring of ancestral tree-frogs some which, among other colours, exhibited green, not much, perhaps not even perceptible to our eyes. The occurrence of this colour, according to them, was spontaneous, a freak—as if in reality there were anything spontaneous in the sense of being causeless. The descendants of these more greenish creatures, provided they did not pair with frogs of the ordinary set, became still greener (by accumulative inheritance), and so on, until the green was pronounced sufficient to be of advantage when competition could set in.
With this view there is always the difficulty of understanding how the initial very small changes can be useful, unless we haveto deal with extremely simple organisms. Is it likely in the case of our frogs that an almost imperceptible variation in colour makes them more fit to live? We have to assume that 'luck' or chance kept them for generations out of harm's reach, until the accumulation of green, hitherto quite ineffective, neither harmful nor useful, became strong enough to be effective. Such cases undoubtedly happen.
But we can also argue out this problem in a somewhat different way, which goes nearer to the root of the whole process. The original slight, imperceptible change in pigmentation is not a spontaneous freak; it was caused by the direct influence of the surroundings in which the particular frogs happened to live, be this factor light or temperature or food. Thus it stands to reason that the offspring, living under similar conditions, will be acted upon in the same way. That factor which has added green to the parents will add green to the children,until by accumulative inheritance a more decidedly green race is produced.
The offspring of green plants do not become green when grown in the dark; the young plants inherit not the green, but the capacity of becoming green when acted upon by sunlight. This as an instance of direct influence of the surroundings on a substance (chlorophyll), which has not yet performed a function. But the kittens of a pair of black cats produce black hair before they are born, and we have no reason to doubt that the black pigment in their tegumentary structures is ultimately referable to the action of the sunlight. In many instances creatures living for generations in darkness become white, pigmentless, and they regain it when exposed to light. For example, the white, colourless Proteus from the caves of Adelsberg becomes clouded grey, and ultimately jet black, when kept in a tank whence light is not strictly excluded.
Blindness is a very general characteristicof creatures which dwell in darkness. There are all stages between total blindness and weak eyes. Now, do these blind creatures live in darkness because they are blind, or have they become first weak-eyed and then blind because of the continuous disuse of their eyes? The former explanation has actually been suggested! Individuals not smitten, but spontaneously, as a freak, born with sore eyes, have crept into the darkness for relief and have produced a blind race! To carry such a notion to the bitter end leads to absurdities. Anyhow, it is not understandable where the benefit of losing the eyesight arises. It can be explained only by continued disuse: witnessSpalax typhlus, the blind mole, and, above all, the Endoparasites.
Let us now take an example to explain the influence of a tangible external stimulus. Repeated pressure produces callosities. Although they are not exactly beneficial in the shape of corns on our toes, they areso on our hands. At any rate, the morphologist can trace the development of the footpads, nails, hoofs, and horns, step by step from small beginnings. The cells of the Malpighian stratum, of the inner, active portion of our epidermis, are excited to extra activity, and by continually producing more horn cells than peel off the surface of the skin in the normal process of wear and tear cause the formation of the pad. It need scarcely be mentioned that hypertrophic growths are not necessarily useful; they are often harmful, and in that case pathological.
Lastly, a few words about the very difficult question ofteleology. In trying to explain Evolution in a mechanical—sometimes called monistic, but in reality natural—way, we exclude anything like a set purpose, a goal, or ideal, a final condition which the organism strives to attain. Unknown, however, to many morphologists, especially embryologists, their writings are full of this teleological notion. Indeed, there are many casesin which an organism becomes changed, and quickly, too, in a way which cannot but be called reasonable. It starts modifications, be they outgrowths, alterations in shape or colour, or the making good of injuries received, which by 'short-cuts' produce the only advantageous result that can reasonably satisfy the new requirement or altered circumstances.
Trees growing in precarious positions, after part of the supporting rock has slipped away, throw out new roots, and rearrange some of the old ones in the only way which could save the tree. In animals which have lost part of a limb the wound closes up, and what is left is turned into a serviceable stump—for example, in water-tortoises (creatures in which reproduction of lost limbs does not happen). In frogs and newts the lost part is reproduced, not correctly, but in a good semblance. Tortoises which have had their shell smashed can throw off an astonishingly large portion and renew the bone as well as the overlapping scutes; but this mending is not neatly done. It serves the requirement, but it is patchwork; the new shell is such as no tortoise ever possessed before.
Mammals transported into colder countries, or subjected to continued exposure, grow a thicker coat; and the same kind of tree which in a sheltered valley is tall, large-leaved, and soft-wooded, assumes a very different aspect, although perhaps growing into a healthy specimen, when planted on a wind-exposed hill.
There is no room, or, rather, no time, to apply to these cases the principle of many variations or the long-continued accumulation of infinitely small changes. The thing is to be done quickly, or not at all. Nor can we explain the mending of a wound, which implies an activity of countless cells, simply as a case of, or similar to, the reproduction of a lost part; against such an explanation militates the almost absolute unlikelihood of that precise injury havinghappened before to any of the creature's ancestors.
Still, I think we are brought near the solution of the mystery by such considerations. We see no difficulty in the regeneration of a few cells, or in the making good of the disturbance suffered by one of the most simple organisms; but we become suspicious when we see that countless cells, not of one kind, but of the most varied tissues and parts of the body, make common cause in remedying a defect in a serviceable way.
We must assume that since the beginning of life organisms have been subjected to countless insults. We can scarcely speak of a wound in an Amæba; but these insults have always been made good, and whenever this was not the case, that particular organism came to an end. As these organisms developed into more complicated ones, the possible insults became more serious, more complicated; and the organisms took adaptive measures so as to be superior to them. Thisaction, I have no hesitation in declaring, became by heredity a habit. The whole creature became so thoroughly 'imbued' (for want of a better word) with the finding of ways and means for meeting sudden, serious conditions, that it now acts directly, and produces by a short-cut, with the least amount of time and with the smallest possible waste of material, that which meets the occasion, thereby saving the life of the individual and that of the race. This we cannot but call reasonable and to the purpose, although it is all carried out bycausæ efficienteswithout there being anycausæ finales.
One million years is a stretch of time beyond our conception. We can arrive at a more or less adequate understanding of what a million individuals or concrete things means. Several Continental nations can put more than a million men into the field. We can gaze at a building which contains as many bricks; and we know that our own body is composed of millions of millions of cells. No such help applies to time, because that itself is an entirely relative, abstract conception. We can imagine what one hundred years are like—a span of time seemingly short to the hale and hearty octogenarian, enormous to the child, totally inapplicable to certainanimals whose whole life is crowded into one single day.
Astronomers have long ceased to reckon distances by miles or any other understandable unit. They express the distances between us and the stars and nebulæ by 'years of light.' Try to imagine a unit of length equal to that which is passed through by light (186,000 miles per second) in one year. Not so very long ago the enormous distances resulting from astronomical calculations were looked upon as the most serious objection to the correctness of the astronomers' views as to the distances which separate our globe from the nearest fixed stars. We have not yet accustomed ourselves to reckoning time by some similar broadly-conceived standard—say æons of so many thousand years each.
Unfortunately, we possess no data whatever for calculating the age of the successive geological strata. Thanks to Lyell, the theory of violent universal cataclysms hasbeen done away with. It is more probable that the same agencies have acted which are now changing the aspect of the globe; and these changes are slow, as far as we know them—at least, as far as the formation of sedimentary strata is concerned, and these alone we have to deal with. Various calculations have been made, based upon the denudation of the mountains, the filling up of the valleys by the débris, the formation of deltas, etc. The results give enormous stretches of time, but all of them unsatisfactory, because the methods are so very local in their application.
The least objectionable attempt is that which, based upon astronomical calculations, tried to fix the height of the last Glacial epoch[27]at about 200,000 years ago, and asserted that since its beginning in the Pliocene epoch as many as 270,000 years have elapsed. The duration of the wholeTertiary period has by the same authorities been fixed approximately at 3,000,000 to 4,000,000 years. Beyond this we cannot venture without the wildest speculation; but we know to a certain extent the thickness of the various sedimentary strata, which amount in all to from 100,000 to 175,000 feet—on the average perhaps 130,000 feet, or about twenty miles.
Unless we prefer giving up all attempt at calculation as absolutely hopeless, and thus resign the whole problem, we must at least try to arrive at some results, and then see if these cannot reasonably be made use of.
Neither geologist nor physicist, and no zoologist, would accept the suggestion that these 130,000 feet of stratified rocks have been deposited within only as many years, although the average rate of deposit would in that case be not more than 1 foot per year. On the other hand, an indignant protest is raised against the assumption of 1,000,000,000 years.
Lord Kelvin[28]has come to the conclusion (from data which various other authorities regard as very unsatisfactory) that not much more than 100,000,000 years can have elapsed since the molten globe acquired a consolidated crust. Further time must have passed before the surface had become stable and cool enough to allow the temperature of the collecting oceans to fall below boiling-point, and it is obvious that life cannot possibly have begun until after this had happened.
Wallace, in his 'Island Life,' by making use of Professor A. Geikie's results as to the rate of denudation of matter by rivers from the area of their basins, and estimating the average rate of deposition, concludes that 'the time required to produce this thickness of rock [Professor Haughton's maximum of 177,000 feet] at the present rate of denudation and deposition is only 28,000,000 years.'Our lower assumption of 130,000 feet thickness would give only 20,000,000 years—a rate of 1 foot in 154 years.
Again, if we prefer round numbers to start with, we have only to assume that the age of the whole Tertiary period, with its 3,000 feet thickness, is 3,000,000 years (i.e., 1,000 feet in 1,000,000 years, or 1 foot in 1,000 years, surely an excessively slow rate); then 130,000,000 years would bring us to the bottom of the Laurentian or pre-Cambrian deposits. Of course, it is a pure assumption that the same rate of destruction and sedimentation applies to the whole of the strata; but we know nothing to the contrary, especially if we consider the average periods, the quick periods of extra activity, taken with the slow periods or those of standstill.
Dana estimated the length of the whole Tertiary period at one-fifteenth of the Mesozoic and Palæozoic combined. If we take the duration of the Tertiary period, as before, as 3,000,000 to 4,000,000 years, the totalwill amount to from 45,000,000 to 60,000,000 years.
Lastly, Walcott[29]has estimated the duration of the Palæozoic, Mesozoic, and Cænozoic or Tertiary epochs at about 17,000,000, 7,000,000 and 3,000,000 years respectively, giving 27,700,000 years from the beginning of the Cambrian; and Williams[30]has calculated the relative duration of the smaller epochs. See the table on p. 149.
The results of all these calculations fall surprisingly well within the limits of Lord Kelvin's allowance. Of course they are based upon assumptions, but none of them is inherently unreasonable; and it was my purpose to draw attention to the surprising coincidence in the closeness of these results, perhaps too good to be true. Such calculations are considered close enough if they range within a few multiples of each other.
Zoologists have fallen into the habit of requiring enormous lengths of time for the evolution of the animal kingdom. We know that Evolution is at best a slow process, and the conception of the changes necessary to evolve man from monkey-like creatures, these from the lowest imaginary mammals, these from some reptilian stock, thence descending to Dipnoan fish-like creatures, and so on back into Invertebrata, down to the simple Monera—this conception is indeed gigantic. Innumerable, almost endless, slow changes require seemingly unlimited time, and as time is endless, why not draw upon itad libitum?
Huxley pointed out that it took nearly the whole of the Tertiary epoch to produce the horse out of the four-toed Eohippos, and that, if we apply this rate to the rest of its pedigree, enormous times would be required. This is, however, a very misleading statement, which necessitates considerable reduction, in conformity with our increased palæontological knowledge. Animals of thegenus Equus—namely, Ungulata, with one toe, and with a certain tooth pattern—from the Upper Miocene of India are now known. Moreover, it is not simply a question of the gradual loss of the side-toes. The change from the fox-sized little Eohippos and Hyracotherium, so far as skull, teeth, vertebral column, and limbs are concerned (about the soft parts we know next to nothing), is a very great one indeed.
Elephants and mammoths seem to have developed very rapidly. None are known from Eocene strata; but towards the end of the Miocene they had spread over Asia, Europe, and North America, and that in great numbers. The Eocene Amblypoda are still so different that we hesitate to connect them ancestrally with the elephants.
The Pinnipedia (seals and walruses) are strongly modified fissiped Carnivora, and have existed since at least the Upper Miocene; the transformation must have been accomplished within the Miocene period.
We cannot shut our eyes to the fact that various groups have from the time of their first appearance burst out into an exuberant growth of modifications in form, size, and numbers, into all possible—and one might almost say impossible—shapes; and they have done this within comparatively short periods, after which they have died out not less rapidly. It seems almost as if these go-ahead creatures had, by accepting every possible modification and carrying the same to the extreme, too quickly exhausted their plasticity—which, after all, must have limits—thereby becoming unable to meet successfully the requirements of further changes in their surroundings. The slowly developing groups, keeping within main lines of Evolution, and not being tempted into aberrant side-issues, had, after all, a much better chance of onward evolution.
A good example of the former are the Dinosaurs. We do not know their ancestors; but we have here to deal only with theirrange of transformation. The oldest known forms occur in the Upper Trias; they attain their most stupendous development in the Upper Jurassic and in the Wealden; and they have died out with the Cretaceous epoch. But already some of their earliest forms had assumed bipedal gait, and the Oolitic Compsognathus had developed almost bird-like hind-limbs.
On the other hand, there are many instances of extremely slow development—facts which raise the difficult question of 'persistent types.' Are these due to a state of perfection which cannot be improved upon? Or are they due to a kind of morphological consolidation (not necessarily specialization) which can no longer yield easily, so that therefore through changes in their surroundings they may come to an end sooner than more plastic groups?
Struthio, the ostrich; Orycteropus, the Cape ant-eater; Tapirus, and many others, existed in the Miocene age practically asthey are now; but pre-Pliocene dolphins, cats, monkeys, stags, all belong to closely-allied and well-defined 'genera,' but different from the living forms.
Alligators and crocodiles are known from the Upper Chalk; Tomistoma since the Miocene; Gavialis since the Pliocene.
The oldest surviving reptile is Sphenodon, the Hatteria of New Zealand, a fair representative of what generalized reptiles of the later Triassic period seem to have been like; and to the same period belongs Ceratodus, the Australian mud-fish, hitherto the oldest known surviving genus of a very ancient and low type so far as Vertebrata are concerned.
Now let us see if the above estimates of geological time are so utterly inapplicable to animal evolution. On purpose we take one of the lowest estimates, about 28,000,000 years, and apportion them equally to the various strata or epochs.
The original owner of the famous Trinil skull, aPithecanthropus erectus, lived,according to some, in the Late Pliocene, according to others in the Early Plistocene, period—that is to say, somewhere about the beginning of our last Glacial epoch, some 270,000 years ago. Assuming that he and his like reached puberty at sixteen to twenty years of age, about 17,000 generations would lie between him and ourselves, or, to put it more forcibly, between him and the lowest living human races—say the Ceylonese Veddahs. Only 250 generations, at twenty years, carry us back to 3000B.C.(i.e., beyond the ken of history); and if it be objected that the differences between the oldest inhabitants of Egypt, the Naquada, and the present Fellahin are very slight, we are welcome to multiply these differences sixty or seventy fold, in order to arrive at the Pithecanthropus level. But these Naquada had no metal implements, and there cannot be the slightest doubt that the development of the human race went on by leaps and bounds after certain discoveries had been made—towit, the use of implements and that of fire. That creature which first took up a stone or a branch and wielded it thereby got such an enormous advantage over his fellow-creatures that his mental and bodily development went on apace. The same applies to the improvement of speech. We assume the single, monophyletic origin of mankind at one place, in one district; and the differences between some of the races of man are great enough to constitute what we might call species. Compare the Venus of Milo, that noble expression of the ancient Greeks' notion of female beauty, with the 'products of art' of the Veddahs or the dwarfs of Central Africa, or think of the beau-idéal which a Michael Angelo could possibly have evolved if he had never seen any but such people.
I.II.III.IV.V.VII.VII.Recent}Adam and Eve250Plistocene} 5}}Man, contemp-3,500}}} 270,000orary with Reindeer}}in FrancePliocene -}} 3,000,000Pithecanthropus1617.000}}} 600,000erectusMiocene -}10}Anthropoid1060,000}}} 2,100,000ApesEocene -}}Lemurs5420,000Cretaceous -10}3,600,000Jurassic -5}1,800,000Rhætic -}}}Prototheria, or31,800,000}}}first Mammalia}} 7,200,000}Keuper -} 5}}1,800,000Muschelkalk -}}}New Red}}}Theomorpha4425,000SandstoneMagnesian}}}Limestone}}}Lower Red}}}Proreptilia4250,000Sandstone}15}}4,000,000Coal-measures}}}Eotetrapoda4500,000Mountain}}}Limestone}}17,500,000}Devonian -15}4,000,000Dipnoi and51,000,000}CrossopterygiiSilurian -10}2,700,000First fishlike3900,000}}creaturesOrdovician -10}2,700,000Cambrian -15}4,000,000Sum total ofLaurentian -generations————Archean or(about)5,375,000Metamorphic
Explanation of the Table on p. 149.
Column I. contains the names of the successive sedimentary strata." II. contains the percentage of the duration of the various epochs, according toWilliams, the time from the Cambrian until recent times being taken as 100." III. gives the estimated duration in years of the Palæozoic, Mesozoic, and Cænozoic periods, according toWalcott." IV. gives in years the duration of the various smaller epochs, as computed from Walcott and Williams' statements." V. Representatives of stages of the ancestral line of man. The names stand in the level of the stratum in which they have made their first appearance." VI. contains the number of years which, in the present calculation, have been assumed necessary for the animal to reach puberty." VII. contains the number of generations which can have elapsed from stage to stage. For example, 60,000 generations separate the earliest known anthropoid apes from Pithecanthropus.
Column I. contains the names of the successive sedimentary strata.
" II. contains the percentage of the duration of the various epochs, according toWilliams, the time from the Cambrian until recent times being taken as 100.
" III. gives the estimated duration in years of the Palæozoic, Mesozoic, and Cænozoic periods, according toWalcott.
" IV. gives in years the duration of the various smaller epochs, as computed from Walcott and Williams' statements.
" V. Representatives of stages of the ancestral line of man. The names stand in the level of the stratum in which they have made their first appearance.
" VI. contains the number of years which, in the present calculation, have been assumed necessary for the animal to reach puberty.
" VII. contains the number of generations which can have elapsed from stage to stage. For example, 60,000 generations separate the earliest known anthropoid apes from Pithecanthropus.
Let us follow the descent of man further back. The next stage, reckoning backwards, is that from Pithecanthropus tobonâ-fideanthropoid apes. They are represented in the Miocene by various genera—e.g., Pliopithecus and Dryopithecus. According to Croll and Wallace, 850,000 years ago carry usinto the Miocene epoch. Assuming that these apes lived about 600,000 years before Pithecanthropus, namely, in the later half of the Miocene, and taking puberty at ten years of age, a high estimate, we get not less than 60,000 generations.
2. From Apes back to lowest Lemurs in the lowest Eocene. The date of Eocene being fixed at 3,000,000, we have about 2,100,000 years for this stage; assuming as much as five years for puberty, this results in 420,000 generations.
3. From Lemures to Prototheria. The earliest known mammalian remains come from the Rhætic, or top formation of the Triassic epoch; allowing for the Rhætic only 100,000 years, we have to add the whole of the Jurassic and Cretaceous, in all about 5,500,000 years. Assuming three years for a generation, we get 1,800,000 generations.
4. From Prototheria to something like the Theromorpha at the bottom of the Triassicstrata. A duration of 1,700,000 years divided by four gives 425,000 generations.
5. From Theromorpha to Proreptilia, represented by Eryops and Cricotus from the Lower Permian of Texas. Allowing 1,000,000 years, each generation at four years, we obtain 250,000 generations.
6. From Proreptilia to Eotetrapoda, the first terrestrial Vertebrata, represented by something like the Stegocephali, the earliest of which are known from the Coal-measures. Assuming them to have come into existence at the bottom of the Coal-measures, for the duration of which we may guess 2,000,000 years, we get, with four years' allowance for puberty, 500,000 generations.
7. From Eotetrapoda to a not yet separated or differentiated group of Crossopterygian and Dipnoan fishes, both of which are known from Devonian strata. The duration of the latter has been computed at 4,000,000 years, which, with 1,000,000 for the Mountain Limestone formation, gives us5,000,000 for this stage. Assuming, for the sake of round numbers, as much as five years for a generation, we get 1,000,000 generations.
8. Earliest stage, down to the first fish-like creatures. Teeth and spines indicating the existence of fishes are known from the Upper Silurian. By carrying the earliest fishes down to the bottom of the Silurian, with 2,700,000 years' duration, and allowing three years for attaining puberty, the calculation results in 900,000 generations.
Further back we cannot go. We do not know of any Vertebrate remains from the Ordovician and Cambrian, which together represent 6,700,000 years, enough for at least half as many generations of Prochordate creatures. The pre-Cambrian or Laurentian epoch lies quite beyond the reach of calculation, nor have we any trustworthy fossil remains of living matter from these strata, to which, however, Haeckel and others refer the first beginnings of life.
All the above calculations are, of course, only approximate. What we do know is the existence of representatives of the stages, our proofs being the fossils; but when we refer the origin of the Eotetrapoda, for example, to the bottom and not somewhere to the middle of the Coal-measures, we are guessing merely. Alterations in the levels assumed for the various stage-representatives will, of course, alter the result of the number of generations; but the leading idea, as a whole, is not thereby upset. The fact remains that in the Upper Silurian we have fishes; from the Coal-measures onwards, fishes and Amphibia; since the Permian, fishes, Amphibia, and reptiles; since the end of the Trias these three classes and the Mammalia; and lastly, at least since the Plistocene, man himself. If Evolution is true at all, the transformation from early fish-like creatures to man has come about within these epochs. Being able to assign a time of duration to each of them, with an approximate total of21,000,000 years, we are also able to put the whole ancestral series to a test by expressing each great stage in generations. The result is very satisfactory. The whole enormous stretch from the lowest fish-like creatures to man has been resolved into more than 5,000,000 successive generations, and each of these means a little step forwards in onward Evolution.
Nothing is to be gained for the understanding of our problem of Evolution if we multiply this enormous number of generations by ten or any other multiple. We are not able to conceive changes so small as those which necessarily have existed between Pithecanthropus and man if the whole striking difference is analysed into 17,000 steps. Every one of these stages in the modifications of the muscles, the skeletal framework, increase of brain, shortening of the trunk, lengthening of the legs, improvement of the hands, loss of the hairy coat, etc., is truly microscopical, imperceptible, just asthe Evolutionist imagines the whole process to have been. Again, where is the difficulty implied by the change from an air-breathing, in many structural points half-amphibian, fish into a primitive land-crawling four-footed creature, if we are allowed to resolve the transformation into 1,000,000 stages? So far from there being any difficulty, rather does it appear questionable if so many infinitely small changes have been necessary to bring about this result.
One thousand years make apparently no difference in the evolution of animals, nor does one second change the aspect of the hands on the face of a clock, nor did Julius Cæsar's commission of scientific men appreciate the error of about eleven minutes in the length of the year beyond its real value; but now the Russians are, owing to this neglect, nearly two weeks behind the civilized nations.
THE END.BILLING AND SONS, PRINTERS, GUILDFORD.