Thus much, we believe, will be generally admitted as a very moderate claim. Evolution is certainly a legitimate induction from the facts of biology. But we are prepared to go much further. We are confident that evolution isabsolutely certain. Not, indeed, evolution as a special theory—Lamarckian, Darwinian, Spencerian—for these are all more or less successful modes of explaining evolution; nor evolution as a school of thought, with its following of disciples—for in this sense it is still in the field of discussion—but evolution as a law of derivation of forms from previous forms; evolution as a law of continuity, as a universal law of becoming. In this sense it is not only certain, it is axiomatic. It is only necessary to conceive it clearly, to see that it is a necessary truth. This may seem paradoxical to some. I stop to justify it.
Physical phenomena we all admit follow one another in unbroken succession, each derived from a preceding, and giving origin to a succeeding. We call this the law of causation, and say that it is axiomatic. We might call it a law of derivation. So also organicformsfollow one another in continuous chain, each derived from a preceding and giving origin to a succeeding. We call this a law of derivation. We might call it alaw of causation, and say that it too is axiomatic. The origins of new phenomena are often obscure, even inexplicable, but we never think to doubt that they have a naturalcause; for so to doubt is to doubt the validity of reason, and the rational constitution of Nature. So also the origins of new organicformsmay be obscure or even inexplicable, but we ought not on that account to doubt that they had a natural cause, and came by a natural process; for so to doubt is also to doubt the validity of reason, and the rational constitution of organic Nature. The law of evolution is naught else than the scientific or, indeed, the rational mode of thinking about the origin of things in every department of Nature. In a word, it is naught else than the law of necessary causation applied toformsinstead of phenomena. Evolution, therefore, is no longer a school of thought. The wordsevolutionismandevolutionistought not any longer to be used, any more thangravitationismandgravitationist; for the law of evolution is as certain as the law of gravitation. Nay, it is far more certain. The nexus betweensuccessive events in time(causation) is far more certain than the nexus betweencoexistent objects in space(gravitation). The formeris a necessary truth, the latter is usually classed as a contingent truth. I have used and may continue to use the term evolutionist, but if so it is only in deference to the views of many intelligent persons, who do not yet see the certainty of the law.
It will be seen from the preceding chapter that we regard the law of evolution in its wider sense, viz., the derivative origin of all forms, organic or other, as axiomatic, and therefore requiring no further proof. Among scientific men there is no longer any discussion of the truth of this law, but only of the theories of the causes of the law. We believe that to the scientific mind there is no other rational mode of looking at the subject of origin of organic forms. To such a mind, therefore, all that follows is but the deductive application of that law in the explanation of the phenomena of organic Nature. But it takes time for the popular mind to readjust itself to new and revolutionary truth. Many minds, even among the most intelligent, have not yet accepted this as the only rational mode of thought. Many men require furtherspecial proofsof the derivative origin of organic forms. Even to those who accept evolution, these proofs will be interesting as illustrations of such origin. Wewill attempt to bring out these proofs under several heads, the most important of which are: 1. Proofs from morphology, or the general laws of animal structure; 2. Proofs from embryology; 3. Proofs from geographical distribution of organic forms; and, 4. Proofs from artificial breeding. The subject is so vast that all we can do is to touch lightly only the most salient points under each of these heads; for, as we have already said, the evidence is really nothing less than the whole science of biology. Preparatory to this, however, it is necessary to bring out a little more fully than before (page 29), though still only in outline, the two antagonistic views, which may be called the old and the new, or the natural and the supernatural, of the origin of new organic forms, especially species.
Origin of New Organic Forms; the Old View briefly stated.—According to the old-school naturalists, species are the ultimate elements of taxonomy: genera, families, orders, etc., may gradually change their character from age to age, by the introduction of new species; but species were supposed to be substantiallypermanent. It was necessary to have some unit for convenience of description and classification, and this was found to be the best because most stable. As in nearly all cases of beliefs, this doctrine was held at first somewhat loosely, as a provisional and convenient view—as a good working hypothesis—but gradually, under pressure of controversy, became more strictly formulated, and, as it were, hardened into a scientific dogma, especially in the hands ofAgassiz. According to this view, the first pair or pairs of each specific kind originated we know not how, but certainlyat once in its present formin full perfection, and, therefore, presumably bydirect creativeact of Deity; and then afterward by the law of generation continued to produce others of the same pattern indefinitely. Moreover, the first one or more pairs of each kind multiplied and spread abroad in every direction,each from its own center of origin, as far as physical conditions and struggle for life with other species would allow. This idea explains tolerably well the geographical distribution of species as we now find it. For example, species on different continents are widely different, because those on each have originated independently where we now find them, and spread in all directions as far as physical conditions would allow, but could not reach other continents because of the ocean-barrier. That this is the only reason they are not there, is shown by the fact that, if they are carried there, they usually do perfectly well. Even on the same continent, for the same reason, species may be very different if separated by impassable barriers such as high mountain-chains or by climate. But wherever one group of species, originating in one place, comes in contact on the margin of their range with another group of species originating in another place, we see no evidence oftransmutationof one formintoanother, but onlysubstitutionof one fully-formed speciesforanother equally fully formed. Therefore, we must conclude that physical conditions may limit therange of a species, but can not transmute it into another. Thus, to say the least, many of the facts of geographical distribution are well explained by this idea of creative origin in specific centers and subsequent permanence of specific form. We saymanyof the facts; we will show hereafter thatnot allcan be thus explained.
But the main question is not of geographical but of geological distribution; not distribution in space, but succession in time. Species do not continue forever. On the contrary, they have changed many times in the course of geological history. As conditions become unfavorable, species die out or become extinct, and others take their place and carry forward the life and development of the organic kingdom. Now, how do they change? According to this school of thought, here also, as in geographical distribution, they are not transmuted but replaced; here also physical conditions may destroy a species, but can not transform it into another. As species die out, others are created at once, out of hand and fully formed in their place; but in accordance with a preordained plan consistently carried out and working ever toward higher and higher conditions. Thus, life is continued on the earth by the alternation of supernatural and natural processes; by the alternate use of direct and indirect action of Deity: direct in the introduction of first pairs, indirect through the natural process of reproduction in the continuance and multiplication of the species. Each species is made according to a pattern in the Divine mind, on a sort of intellectual die, and thencontinues to reproduce a succession of individuals of the same pattern as if struck from the same die until the die is broken or worn out. Another die is made, of another pattern, and individuals are struck from this; and so on, throughout the whole geological history of the organic kingdom. Only, we must add that the successive dies are made to follow one another according to a plan which is expressed by the three laws already given onpage 11. Thus, the origin of individuals is natural, the origin of species supernatural; the making of dies is supernatural, the coinage is natural.
We have stated this view in a too extreme form, in order to make it clearer. We now, therefore, proceed to qualify somewhat. Specific types were held, by writers of this school of thought, to besubstantiallybut not absolutely unchangeable. Successive individuals of the same species were admitted to be not exactly alike. Such slight differences were calledvarieties. It was admitted, indeed, that species varied, but it was believed that such variations in any direction were strictly limited in amount. A species may be compared to a right cylinder standing on end. As such a cylinder may be tilted slightly in one direction or another, without overthrowing its equilibrium, the cylinder tending ever to right itself and return to its original position, so a species may be varied slightly in one direction or another without destroying its integrity, the species tending ever to return to its normal or typical form. But as the cylinder, if pushed too far from its normal position, is overthrown,so also a species, if pressed too far in the way of variation from its typical form, is destroyed, but not changed into another species. As cylinders may be more or less rigid, depending upon the breadth of their bases, so also some species are more rigidly set in their typical form, and some are more plastic to influences causing variations, but in all cases there is a limit to the amount of oscillation consistent with integrity.
The New View briefly stated.—According to Darwin, and all biologists of the present day, species are variablewithout limit, if only the causes of change are constant and slow enough in their operation, and the time long enough. A species must be in harmony with its environment, for this is the condition of its existence. Now, if the environment change, the species musttendto change slowly from generation to generation, so as to readjust its relations in harmony with the changing environment. If the change of environment be slow, the readjustment may be successful, and the species will change gradually into another form, so different that it will be called a different species, especially if the intermediate gradations be destroyed. If the change in the environment be too rapid, many species, especially the more rigid, will be destroyed, while the more plastic may survive by modification. Thus, at every step in the evolution of the organic kingdom, some species have died without issue, while others have saved themselves by changing into new forms in harmony with the new environment. Comparing to a growing tree, some branches overshadowed die,while others push on for light, forming new lateral buds, and dividing as they grow. By continued divergent change species gradually become genera, genera families, etc. Thus, varieties, species, genera, families, orders, classes, etc., are only different degrees of differences formed all in the same way. Varieties are only commencing species, species commencing genera, and so on. There is no making and wearing out of dies, and making of new ones; the whole process is a natural one—the whole series is genetically connected. In a perfect classification varieties, species, genera, families, orders, classes, etc., are only differentdegrees of blood-kinship.
So much may be regarded as certain, and out of the field of discussion among biologists of the present day. It is only in defining this process more accurately, and especially in thetheory of the causesorfactorsof evolution, that there are still difference and discussion. The most probable view on this subject we now proceed to give.
Factors of Evolution.—The causes of change or adaptive modification, or the factors of evolution, are at leastfourwell known, and probably many more still unknown: 1. The physical environment—heat and cold, dryness and moisture—affects function of organs, and function affects structure, and both changed function and changed structure are inherited by offspring, and so increased from generation to generation, becoming greater without limit. 2. Increaseduseordisuseof organs enforced or permitted by change in the environment,physical or organic, or both, induces change in form, size, and structure of the organs; and this change is inherited by the offspring, and so from generation to generation small differences are integrated until they become great without limit. These two factors were recognized by Lamarck. 3. “Natural selection,” or “survival of the fittest,” among divergent varieties of offspring. This is the distinctive Darwinian factor. In the two preceding factors the change is during theindividual lifetime, and reproduction is supposed to transmit it unchanged to the offspring. In this factor, on the contrary, the form and structure are supposed to remain unchanged during the individual life, but for some unknown cause there are slight variations in different directions (divergent) in the offspring from the same parents. Now, when we remember that by reproduction the number of individuals tends to increase by geometrical progression, and that in each generation only a very few (on an average only two from all the offspring of one pair) can survive, it is evident that among these divergent varieties those will most likely survive which are most in harmony with the external environment, and which possess the most efficient organs of defense or of escape, or for food-taking. The surviving offspring, therefore, will be on the average better in these respects than their parents. It matters not how little better, for the integration of even infinitesimal improvements from generation to generation will eventually produce any required amount of change. 4. To the above Darwin has added also“sexual selection.” Innaturalselection there is struggle ofallforfood, ormeans of living. In sexual selection there is a struggle among themalesfor possession of thefemale, and themeans of procreation. The one is connected with the nutritive appetite, the other with the reproductive appetite. This mode of selection acts in two ways, by the law of battle and the law of attractiveness. The strongest or the most attractive males alone, or mainly, leave offspring, which, of course, inherit their peculiarities; and these are increased indefinitely by integration through successive generations, thus increasing the strength or the beauty. Of these two laws, the law of battle is most conspicuous among mammals, and the law of attractiveness among birds. It is evident that this factor can not operate among many lower animals which are hermaphroditic, nor among plants.
Of these acknowledged factors of evolution, the first two were known to Lamarck and the older evolutionists. The third and fourth are distinctively Darwinian. According to Darwin, while all these are operative, the third is the most powerful; but Spencer accords this distinction to the Lamarckian factors. Many American zoölogists take the same view.
Such until very recently were all the recognized factors of evolution. But, within the past year (1886) has taken place, it seems to us, the most important advance in the theory of evolution since Darwin. It is the suggestion by Mr.Catchpool,14and afterward the more full elaborationby Dr. Romanes, of another factor, which he calls “physiological selection.”15
The great objections to the sufficiency of the theory of evolution, as left by Darwin, were twofold: 1. While natural selection accounts completely for the formation ofusefulstructures or adaptive modifications, and therefore for differences characterizing classes, orders, families, and even genera—for these are all adaptive—it can not so completely account for those constituting species; for these consist mostly oftrivialdifferences in coloration, relative proportion of parts, which are ofno perceivable usein the struggle for life, and therefore could not be preserved and integrated by natural selection. Therefore, according to Romanes, natural selection is a theory of origin of adaptive structures rather than of origin of species. Comparing to a growing tree, once admit lateral buds started, and natural selection completely accounts for the growth in different directions, and therefore for the profuse ramification; but the origin of the lateral buds is not explained.
2. The second difficulty is as follows: Such commencing differences as constitute varieties and species not only would not be preserved and integrated by natural selection unless useful, but would immediately beswamped by cross-breedingwith the parental form. But, as the whole divergence commences in varieties, evidentlyit could not commence at all unless this cross-breeding be in some way prevented. This may, indeed, be done, without the assumption of any new factor of evolution, bymigration; and, hence, migration must be regarded as an important agent in the creation of new forms, not only by the effect of a new environment, but also by prevention of the swamping of commencing species by cross-breeding with the parental form; but in a crowded locality, without outlet for migration (the very conditions most favorable for severe competitive struggle, and therefore for most potent operation of natural selection; and therefore, also, according to Darwin, for profuse diversification), commencing varieties could not pass into species, because swamped by cross-breeding. Once the divergence reaches the point of cross-sterility—i. e., of species—then, indeed, by true breeding, characters, even though not useful, may be preserved. But how is it to commence?
This difficulty has been severely felt by all Darwinists. It seems to us that it is largely met by Dr. Romanes. According to Romanes, no organ is so subject to varietal changes as thereproductive, and these in no respect so much as in degrees of fertility. Unfortunately, these changes are not visible, and must be judged of only by the results. It is not uncommon, for example, to find sterility between individuals (sexual incompatibility) who are both of them perfectly fertile with other individuals. Similarly, cross-sterility, partial or complete, is not uncommon between varieties or races, as Mr. Darwinhas long ago noticed. It very generally, as we know, occurs between, and, in fact, is constantly used as a test of, species. Now, this cross-sterility with parent stock, which we find so constant a character of species, and which, therefore, musthave commenced as a partial cross-sterilityin varieties, is itantecedent or consequent to other variations? It has been usual to suppose it consequent to a certain amount of divergence, viz., that which constitutes, or at least approaches, species. But, according to Romanes, it isantecedent. Among many other variations, this is that one which originates species, because it prevents reversion by cross-breeding with the parent stock, and insures true breeding with its own kind. In a word, it sexually isolates the species. Suppose, then, a species multiplying indefinitely in one locality: trivial variations of many kinds, and in many directions, occur among the offspring. These are merged by cross-breeding into the original type, which, therefore, remains unchanged. But, from time to time, among these variations there occur some affecting the reproductive organs in such wise as to produce partial or complete cross-sterility with the parent form. This is the beginning of a new species. It breeds true with its own kind, and therefore all the associated variations external and visible, and therefore constituting species, although trivial and of no use in the struggle for life, are preserved.
This view completely accounts for the cross-fertility of artificial breeds equivalent in other respects to species; for cross-sterility is not an end aimed at by the breeder,it being easy to prevent cross-breeding, if desired, by artificial isolation. But, if this view be true, species from widely-different geographical regions ought also to be often cross-fertile, because, having been formed by geographical isolation, sexual isolation was not a necessary factor in their formation. This point deserves testing by careful observation.
It may be, and has been, objected to Dr. Romanes’s claims, that this is no new factor; that physiological selection is only a form of natural selection. This objection, it seems to us, is little more than a play upon words. It certainly is selection, and by anaturalprocess, and therefore in some sense a natural selection, but not in the sense of Darwin. It is not a selection of individualsfittest to survive; for cross-fertile individuals are as fit to survive as individuals, though not as species, as are cross-sterile. Natural selection is intent only on preserving the best individuals; physiological selection on preserving the kind. Natural selection continues the direction of progress unchanged; physiological makes new directions.
In addition to all these factors oforganicevolution, there is still another far higher factor characteristic of man alone. This is theconscious, voluntary co-operation of the thing evolving—the spirit of man—in the work of its own evolution. This may be called therational factor. This, the most important factor of human evolution, is usually ignored by writers on evolution—either as non-existent, or else as lying beyond the domain of science.We will emphasize its importance by taking it up more fully in the next chapter.
It will be observed that Darwin and his followers take divergent variations of offspring simply as a known fact, upon which natural selection operates to produce progressive modification; and, as the cause of variation in offspring is wholly unknown, such variations are often spoken of as fortuitous. But, of course, it is well understood that nothing in Nature is really fortuitous. They may, however, for all purposes of natural selection be thus regarded until we know their cause. It is evident, then, that if we, with Darwin, take natural selection, as the most important known factor, the really most important cause of evolution is thecauseof varieties. This is theunknownfundamental factor. As Darwin reduced Agassiz’s three formal laws of succession to more general laws of life, and thus made one important step in the advance of biological science, so he who shall explain thecauseof divergent variation will make another important step by reducing the phenomena to still more general and fundamental laws of life.
In conclusion, let me again impress upon the reader that all the doubt and discussion, above described, as to the factors of evolution, is entirely aside from the truth of evolution itself, concerning which there is no difference of opinion among thinkers.
We have given in the previous chapter six factors of evolution—viz.: 1.Pressure of the environment.2.Use and disuse of parts.3.Natural selection.4.Sexual selection.5.Physiological selection.6.Reason.Let us now compare these as to their grade in the scale of energy and as to the order of their introduction.
The first two or the Lamarckian factors are the lowest in position, the most fundamental and universal, and therefore the first in the order of appearance. They precede all other factors, and were doubtless for a long timethe only ones in operation. For, observe, all the selective factors—i. e., those of Darwin and Romanes—are conditioned on reproduction; for the changes produced by these are not in the individual during life, but in the offspring at birth. And not only so, but the operations of these factors are further conditioned onsexual modesof reproduction; for all the non-sexual modes of reproduction—as, for example, by fissure and by budding—are but slight modifications of growth, and the resulting multitude oforganisms may be regarded as in some senseonly an extension of the first individual. Of course, therefore, the identical characters of the first individual are continued indefinitely, except in so far as they are modified in successive generations by the effect of the environment and by use and disuse—i. e., by the Lamarckian factors. In sexual generation, on the contrary, the characters of two diverse individuals are funded in a common offspring; and the same continuing through successive generations, it is evident that the inheritance in each individual offspring is infinitely multiple. Now, thetendency to variationin offspringis in proportion to the multiplicity of the inheritance: for among the infinite number of slightly differing characters, as it were, offered for inheritance in each generation, some individuals will inherit more of one and some more of another character. In a word, sexual reproduction by multiple inheritancetends to variation of offspring, and thus furnishes material for natural selection.16
Thus, then, I repeat, all the selective factors are absolutely dependent on sexual modes of reproduction. But there was a time when this mode of reproduction did not yetexist.17The sexual modes developed out of non-sexual modes. If these non-sexual preceded sexual modes of reproduction, it is evident that at first only Lamarckian factors could operate. Evolution was thencarried forward wholly by changes in the individual produced by environment and by use and disuse (acquired characters), inherited and increased by integration through successive generations indefinitely. It is probable, therefore, that therateof evolution was at first comparatively slow; unless, indeed, as seems probable, theearliestformswere thenand thelowestformsare nowmore plastic under the influence of physical conditions than are the present higher forms. Doubtless, now, in the higher animals and plants, the Darwinian factors are by far the most potent; for, among plants, where we can use these factors separately, if we wish tomakevarieties, we propagate by seeds (sexual reproduction); but, if we wish to preserve varieties, we propagate by buds and cuttings (non-sexual reproduction).
I have taken the two Lamarckian factors together, and showed that they preceded the Darwinian. But even in the two Lamarckian factors there is a difference in grade. Undoubtedly the lowest, the most fundamental, and therefore the first introduced, waspressure of the physical environment. For use and disuse of organs implies some degree of volition and voluntary motion, and therefore already some advance in the scale of evolution.
With the introduction of sex another entirely different and higher factor was introduced, viz.,natural selection, or selection of the fittest individuals of a varying progeny. We have already seen how sexual generation produces variation of offspring, and how this furnishesmaterials for natural selection. As soon, therefore, as this form of generation was evolved, this higher factor came into operation and immediately assumed control; while the previous factors became subordinate, though still underlying, conditioning, and modifying the activity of the higher. The result was an immediate increase in the rate of evolution. It is very worthy of note that it is in the higher animals, such as birds and mammals, in which we have only the highest forms of sexual reproduction, where the diversity of characters of the two sexes funded in the offspring is the greatest, and where, therefore, the variation in offspring is also greatest and natural selection most active; it is precisely among these that the Lamarckian factors are most feeble, because, during the most plastic period of life, the offspring is removed from the influence of the physical environment, and from use and disuse by its inclosure within the womb, or within a large egg surrounded with abundant nutriment. Development is already well advanced before Lamarckian factors can operate at all.
Next, I suppose, physiological selection, or Romanes’s factor, came into operation. After the introduction of sex, it became necessary that the individuals of some varieties should be isolated in some way, so as to prevent the swamping of varietal characters, as fast as formed, in a common stock, bycross-breeding. In very low forms, with slow locomotion, such isolation might easily take place accidentally. Even in higher forms, changes in physical geography or accidental dispersion by winds andcurrents would often produce geographical isolation, and thus, by preventing crossing with the parent stock, secure the formation of new species from such isolated varieties. But, in order to insure in all cases the preservation of commencing species,sexual isolation, or partial or complete infertility of some varieties with other varieties and with the parent stock, was introduced, as I suppose, later. The process by which this takes place has already been explained. According to Romanes, natural selection alone, with cross-breeding, tends tomonotypalevolution; isolation of some kind is necessary for polytypal evolution. The tree of evolution, under the influence of natural selection alone, grows, palm-like, from itsterminal bud; isolation of varieties was necessary for the starting oflateral buds, and thus for the profuse ramification which is its most conspicuous character.
Next, I suppose, was introducedsexual selection, or contest among the males, by battle or by display, for possession of the females, and the success of the strongest or the most attractive; and the perpetuation and increase of these superior qualities of strength and beauty in the next generation. This, I suppose, was later, because connected with a higher development of the psychical nature. This is especially true where splendor of color or beauty of song determines the selection. As might be supposed, therefore, this factor is operative only among the highest animals, especially birds andmammals.18
Next and last, and only with the appearance ofMan, another entirely different and far higher factor was introduced, viz.,conscious, voluntary co-operationin the work of his own evolution—a conscious, voluntary striving toattain an ideal. We have called this a factor, but it is much more than a mere factor, co-ordinate with other factors. It is, rather, a different kind of evolution. It is evolution on a higher plane and by another nature. AsphysicalNature worksunconsciously, using certain factors, sospiritualnature worksconsciously, co-operating and using the same factors. At first this factor, if we still call it so, was extremely feeble. In the early stages of his progress, man, like other animals, was largely urged on by forces of organic evolution, unknowing and uncaring whither he tended. But more and more, as civilization advances, this higher and distinctively human factor becomes more and more dominant, until now, in civilized communities, it takes control of evolution. Reason, instead of Nature, now assumes control, though still using the methods and factors of Nature. Thisfree, self-determined evolution of the race, in order to distinguish it from thenecessaryevolution of the organic kingdom, we call progress.
Now, in this whole process we observe two strikingstages. The one is the introduction of sex, the other is the introduction ofreason.19They may be compared to two equally striking stages in the development of theindividual. As theontogenicevolution receives fresh impulse at the moment of fertilization, so the evolution of the organic kingdom receives fresh impulse at the moment of introduction of sex. As in ontogenic evolution the individual at birth enters upon a new and higher plane, in which it co-operates in its ownphysicalgrowth, so the organic kingdom, with the introduction of man, enters upon a new and higher plane, in which man co-operates in the physical andspiritualgrowth of the race. With sex three new and higher factors were introduced, and these immediately assumed control and quickened the rate of evolution. With reason another and infinitely higher factor is introduced, which, in its turn, assumes control, and not only again quickens the rate, but elevates the whole plane of evolution. Moreover, this voluntary, rational factor not only takes control itself, but transforms all other factors and uses them in a new way and for its own higher purposes.
This last is by far the greatest change which has ever occurred in the history of evolution. In organic evolutionNature operates by necessary law without the conscious voluntary co-operation of the thing evolving. In human progress man voluntarily co-operates with Nature in the work of evolution, and even assumes to take the process mainly into his own hands. Organic evolution is bynecessarylaw, human progress byfreeor at least by freer law. Organic evolution is by apushingupward and onward frombelowandbehind, human progress by adrawingupward and onward from above and in front by the attractive force of ideals. In a word, organic evolution is by the law offorce, human evolution by the law oflove.
It may be well to stop a moment and show briefly some of the differences between organic and human evolution—differences which are, of course, wholly the result of the introduction of this new factor:
1. In organic evolution “the fittest” are those most in harmony with the physical environment, and therefore they survive. In human evolutionthe fittestare those most in harmony withthe ideal, and often, especially in the early stages, when the race is still largely under the dominion of organic factors, they do not survive, because not in harmony with the social environment. But, although the fittest individuals may indeed perish, theidealsurvives in the race and will eventually triumph.
2. In organic evolution the weak, the sick, the helpless, the unfit in any way perish andought to perish, because this is the most efficient way of strengthening thebloodorphysical natureof the species, and thus of carrying forward evolution. In human evolution the weak,the helpless, the sick, the old, the unfit in any way are sustained andought to be sustained, because sympathy, love, pity, strengthen thespiritormoral natureof the race. But let us remember that in this material world of ours and during this earthly life the spirit or moral nature is conditioned on the physical nature; and, therefore, in all our attempts to help the weak we must be careful to avoid poisoning the blood and weakening the physical vigor of the race by inheritance. This gravest of social problems, viz., How shall we obey the higher law of love and mutual help without weakening thebloodof the race by inheritance and the spirit of the race by removing the necessity of self-help?—this problem, I believe, can and will be solved by arational education, physical, mental, and moral. I only allude to this. It is too wide a field to follow up here.
3. In organic evolution the bodilyformandstructuremust continually change in order to keep in harmony with the ever-changing environment. In other words, organic evolution is by continual change of species, genera, families, etc. There must be continual evolution of new forms by modification. In human evolution, on the contrary, and more and more as civilization advances, man modifies the environment so as to bring it into harmony with himself and his wants, and therefore there is no necessity of change of bodily form and structure or making of new species of man. Human evolution is not by modification ofform—new species; but by modification of spirit—new planes of activity,higher character. And thespirit is modified and character elevated, not bypressureof anexternal physical environment, but by theattractiveforce of aninternal spiritual ideal.
4. The way of evolution toward the highest—i. e., from protozoan to man and from lowest man to the ideal, the divine man—is a verystraight and narrow way, and few there be that find it. In the case of organic evolution it is so straight and so narrow that any divergence therefrom is fatal to upward movement toward man. Once get off the track, and it isimpossibleto get on again. No living form of animal is on its waymanward, or can by any possibility develop into man. They are all gone out of the way. There is none going right; no, not one. The organic kingdom developing through all geological times may be compared to a tree whose trunk is deeply buried in the lowest strata, whose great limbs were separated in early geological times, whose secondary branches diverged in middle geological times, and whose extreme twiglets, and also its graceful foliage, its beautiful flowers, and luscious fruits, are the fauna and flora of the present day. But this tree of evolution is anexcurrent stem, continuous through the clustering branches to the terminal shoot—man. Once leave the stem as a branch, and it is easy to continue growing in the direction chosen, but impossible to get back on the straight upward way to the highest. In human evolution, whether individual or racial, the same law holds, but with a difference. If individual or race gets off the straight, narrow way toward the highest—the divine ideal—it is hard, very hard to get back onthe track. Hard, I say, butnotimpossible, because man’s conscious voluntary effort is the chief factor in his own evolution. By virtue of self-activity, through the use of reason and co-operation in the work of evolution, man alone of all created things is able to rectify an error of direction and return again to the deserted way.
5. In organic evolution, when a higher factor appears, it immediately assumes control, and previous lower factors sink into a subordinate position, though still underlying and conditioning the higher. But in human evolution, the higher rational factor, when it comes in with man, not only assumes control, but transforms all other factors and uses them in a new way and for its own higher purposes. In fact, as already said, it is much more than a mere factor. It determines a new kind of evolution—evolution on a new and higher plane though, indeed, underlaid and conditioned by the laws of organic evolution. Asexternal physicalNature uses many factors to carry forward organic evolution, so theinternal spiritualnature, characteristic of man alone, uses these same factors in a new way to carry forward human evolution or progress. Thus, for example, one organic factor—the environment—is modified or even totally changed so as to effect suitably the human organism. This ishygiene. Again, use and disuse—another factor—is similarly transformed. The various organs of the body and faculties of the mind are deliberately used in such wise and degree (determined by reason) as to produce the highest efficiency of each part and the greatest strength and beauty of the whole.This iseducation—physical, mental, moral. So also the selective factors are similarly transformed, andnaturalselection becomesrationalselection. We all know how this method is applied to domestic animals and cultivated plants in the formation of useful or beautiful varieties. Why should it not be applied also to the improvement of our race in the selection of our mates in marriage, or in the selection of our teachers, our law-makers, our rulers? Alas! how little even yet does reason control our selection in these matters! How largely are we yet under the law of organic evolution!
Application of these principles to some questions of the day:
I. Evolution, as a law of derivation of organic forms from previous forms by descent with modifications, as already shown, is as certain as the law of gravitation. This question has passed beyond the realm of doubtful discussion; but the causes, the factors, the details of the process of evolution are still under discussion. Both Darwin and Spencer, the two great founders of the theory of evolution in its modern form, acknowledge and insist on at least four factors, viz., the two Lamarckian and the two distinctively Darwinian. The only difference between them is in the relative importance of the two sets: Spencer regarding the former and Darwin the latter as the more potent. But in these latest times there has arisen a class of biologists, including some of highest rank, such as Wallace, Weismann, and Lankester, who out-Darwin Darwin himself in theirexaltation of the most distinctive Darwinian factor, viz., natural selection. They try to show that natural selection is the sole and sufficient cause of evolution; that changes in the individual, whether as the effect of the environment or by use and disuse of organs, are not inherited at all; that Lamarck was wholly wrong; that Darwin (in connection with Wallace) was the sole founder of the true theory of evolution; and, finally, that Darwin himself was wrong only in making any terms whatever with Lamarck. This view has been calledNeo-Darwinism.
Perhaps the reasons for this view have been most strongly put by Weismann, and are based partly on experiments, but mainly on his ingenious and now celebrated theory of the immortality of germ-plasm. The animal body consists of two kinds of cells wholly different in function—somatic cells and germ-cells, including in this last the sexual elements both male and female. Somatic cells are specially modified for the various functions of the body; germ-cells are wholly unmodified. The somatic cells are for the conservation of theindividuallife, the germ-cells for the conservation of thespecies. In the development of the egg the germ-cell multiplies itself into a cell-aggregate, and then most of the resulting multitude of cells are modified in various ways to form the tissues and organs of the body—somatic cells; but a few are reserved and put aside in an unmodified form in the sexual organs as germ-cells, to again produce ova which again divide into somatic and germ-cells, and so on indefinitely.Now, according to Weismann, inheritance is only throughgerm-cells, while the environment affects only thesomatic cells. Therefore changes produced by the environment can not be inherited. Sexual modes of generation were introduced for the purpose of producing variability in progeny, and thus furnishing material for natural selection, as this was the only means of evolutionary advance. Weismann made many experiments on animals, especially by mutilation, to show that somatic changes are not inherited.
A full discussion of this question would be unsuitable in a work like this. We will therefore content ourselves with making three brief remarks:
a.If the views presented in the early part of this chapter are true, then the Lamarckian factors must be true factors,because there was a time when there were no others. They were therefore necessary, at least to start the process, even if no longer necessary at present.
b.But if these factors were ever operative,they must be so still, though possibly in a subordinate degree. A lower factor is not abolished, but only becomes subordinate to a higher when the latter is introduced. Thus it may well be that Lamarckian factors are comparatively feeble at the present time and among living species, especially of the higher animals, and yet not absent altogether. In the earliest stages of evolution there was acomplete identification of germ-cells and somatic cells—of the individual with the species. In such cases, of course, any effect of the environment must be inherited and increasedfrom generation to generation. But the differentiation of the germ and somatic cells was not all at once, nor is their sympathetic relation completely severed. It was agradual process, and therefore the effect of the environmenton the germ-cells through the somatic cellscontinued, though in decreasing degree, and still continues. The differentiation in the higher animals is now so complete that germ-cells are probably not at all affected by changes in somatic cells, unless these changes arelong continued in the same direction, and are not antagonized by natural selection.
c.It is a general principle of evolution that thelaw of the whole is repeated with modifications in the part. This is a necessary consequence of the unity of Nature. We ought to expect, therefore, and do find, that the order of the use of the factors of evolution is the same in the evolution of theorganic kingdom, in the evolution ofeach species, and in the evolution ofeach individual. In all these the physical factors are at first powerfully operative; these become subordinate to organic factors, and these, in their turn, to psychical and rational factors. Therefore, as the individual in its early stages—i. e., in embryo and infancy—is peculiarly plastic under the influence of the physical environment, and afterward becomes more and more independent of these; so a species when first formed is more plastic under the influences of Lamarckian factors, and afterward becomes more rigid to the same. And so also the organic kingdom was at first more plastic under Lamarckian factors, and has becomeless so in the present species, especially in the higher animals. The principal reason of this, as we have already seen, is the increasing differentiation of germ and somatic cells, and the removal of the former to the interior, where they are more and more protected from external influence.
II. Some evolutionists—the materialistic—insist on making human evolution identical in all respects with organic evolution. This, we have shown, is not true. The very least that can be said is that a new and far more potent factor is introduced with man, which modifies greatly the process. But we may claim much more, viz., that evolution is here on a different and higher plane. The factors of organic evolution are, indeed, still present, and condition the whole process; but they are not left to be used by Nature alone. On the contrary, they are used in a new way and for higher purposes—by reason.
But by a revulsion from the materialistic extreme some have gone to the opposite extreme. They would place human progress and organic evolution in violent antagonism, as if subject to entirely different and even opposite laws; but we have also shown that, although the distinctive human factor is indeed dominant, yet it is underlaid and conditioned by all the lower factors; that these lower factors are still necessary as the agents used by reason.
III. We have already given the views of Weismann and Wallace, and some reasons for not accepting them;but there is one important aspect not yet touched. There are some logical consequences of these views when applied to human evolution which seem to us nothing less than areductio ad absurdum. This brings into view still another contrast between organic evolution and human progress.
In organic evolution, when the struggle for life is fierce and pitiless as it is now among the higher animals, natural selection is undoubtedly by far the most potent factor. It is at least conceivable (though not probable) that at the present time organic evolution might be carried on mainly or even wholly by this factor alone; but in human evolution, especially in civilized communities, this is impossible. If Weismann and Wallace be right, then alas for all our hopes of race improvement—physical, mental, and moral!—for natural selection will never be applied by man to himself as it is by Nature to organisms. His spiritual nature forbids. Reason may freely use the Lamarckian factors of environment and of use and disuse, but is debarred the unscrupulous use of natural selectionas its only method. As this is an important point, we must explain.
All enlightened schemes of physical culture and hygiene, although directed primarily to secure the strength, the health, and the happiness of thepresent generation, yet are sustained and ennobled by the conviction that the improvement of the individuals of each generation enters by inheritance into the gradual physical improvement of the race. All our schemes of education, intellectual and moral, though certainly intended mainly for the improvementof the individual, are glorified by the hope that the race also is thereby gradually elevated. It is true that these hopes are usually extravagant; it is true that thewholeimprovement of one generation is not carried over by inheritance into the next; it is true, therefore, that we can not by education raise a lower race up to the plane of a higher in a few generations or even in a few centuries: but there must be at least a small residuum, be it ever so small, carried forward from each generation to the next, which, accumulating from age to age, determines the slow evolution of the race. Such are the hopes on which all noble efforts for race-improvement are founded. Are all these hopes baseless? They are so if Weismann and Wallace are right. If it be true that reason must direct the course of human progress, and if it be true also that selection of the fittest in the organic sense is the only method which can be used by reason, then the dreadful law of pitiless destruction of the weak, the helpless, the sick, the old, must with Spartan firmness be voluntarily and deliberately carried out. Against such a course we instinctively revolt with horror, because contrary to the law of our spiritual nature.
But the use by reason of the Lamarckian factors is not attended with any such revolting consequences. All our hopes of race-improvement, therefore, are strictly conditioned on the efficacy of these factors—i. e., on the fact that useful changes, determined by education in each generation, are to some extent inherited and accumulated in the race.
Analogy and Homology.—In biology those organs or parts in different animals are said to beanalogouswhich, however different their origin, have a general similarity of form and especially of function; while those are calledhomologouswhich, however different their general appearance, and however different their function, yet may, by close examination and extensive comparison, be shown to be modifications of one another—to be, in fact, originally the same part modified for different purposes. In the former the parts compared look and behave as if they were the same, but are not; in the latter they look and behave entirely differently, but are, in fact, the same part in disguise.
We can best make this plain by examples. The wing of a bird and the wing of a butterfly are analogous organs. They have the same function—i. e., flying; and this function necessitates the same general form of a flatplane. But they are not at all homologous; they are not at all the same organ or part. They certainly have never been formed one out of the other by modification. But the wing of a bird, the fore-paw of a reptile or mammal, the wing of a bat, and the arm and hand of a man, though so different in form and function, are homologous parts. On close examination they are found to have the same general structure, to be composed of essentially the same pieces, although they are so greatly modified in order to adapt them to different functions, that the general or superficial resemblance is now lost. Their structure is precisely such as it would be if they had all originated from some archetypal fore-limb by modifications in different directions of its several parts. By extensive comparison in the taxonomic and ontogenic series, all the intermediate gradations between these extreme modifications may be picked up.