Chapter III: Present State of the Darwinian Theories (1)

§ 1. _The Theory of Descent._

The historical retrospect of the Darwinian theories, from their purely scientific side, leads us of itself to a critical review of their present state. We can briefly indicate in advance the result to which it will lead us, viz.: that the descent theory has gained, the selection theory has lost ground, the theory of development oscillates between both; but that all three theories have not yet passed beyond the rank of hypotheses, although they have very unequal hypothetical value. We can best arrange our review by beginning with that theory which is the most common, and which perhaps may still have value when both the others find their value diminished or lost: _the theory of descent_. From that we proceed to the _theory of evolution_, and from this to that of _selection_.

The theory of descent is indeed at first sight exceedingly plausible, and will probably always be the _directive_ for all future investigations as to the origin of species. The organic species show, besides the great variety of their characteristics and the unchangeable nature of these characteristics, many other qualities which are common to them; and these common characteristics are precisely those which are most essential. {62} Moreover the higher the structure of the organisms which are differentiated, the more numerous and more valuable will become the evidences of similarity, and the greater also will be their distance from the inorganic and from the lowest organisms of their class, their type, or their kingdom. For instance, rose and apple-tree, elder and ash, wolf and dog, goat and sheep, ape and man, are not only a great deal farther removed from the mode of existence of inorganic bodies than the algæ, the monera, and other low organisms, but they have also, in spite of the great interval which separates them from one another and especially which separates man from every animal, much more numerous and important points of contact than, for instance, two families or genera of algæ or of mosses, of polyps or of infusoria, have among one another. Now our imagination refuses to accept the theory that the Creator, or nature, or whatever we wish to call the principle generating the species, in producing the new species, laid aside all those points of contact which are continually becoming more numerous and more important, and produced instead, by ever widening leaps, the new and higher species from the inorganic, which lies farther and farther from them. On the other hand, the theory appears to us all the more plausible, that every new species came into existence on that stage which is the most nearly related to it, and which was already in existence. If we add further, that the two old maxims of the natural scientists, _omne vivum ex ovo_ and _omne ovum ex ovario_, have not been invalidated, in spite of all the searching for a _generatio æquivoca_, and that, even if the origination of the lowest organisms out of the inorganic could in future be {63} proved, yet the truth of these maxims for all the higher organized individuals is established as a fact without exception. Moreover, if we take into consideration the fact that we can not at all imagine either the origin or the first development of a higher animal or a human organism without the protecting integument and the nourishing help of a mother's womb, we may venture to say that each and every attempt to render the origin of the first individuals of the higher species conceivable, leads of necessity to the descent theory. We have either to reject, once for all, such an attempt, as an unscientific playing with impossibilities, or to accept the idea of descent. It is certainly the lasting merit of Darwin, even if his whole structure of proofs should in the course of time show itself weak, that he not only had the courage (as others had before him), but also inspired scientists with the courage to trace the idea of a descent of species in a scientific way.

To be sure, so long as we have no other proof of the descent theory than the circumstance that we can imagine it, it will continue to be nothing more than an ingenious hypothesis. We have, therefore, to look to the realm of nature for more direct proofs; and we are there furnished with them. They are presented to us by geology in connection with the botanical and zoölogical systems, by geology in connection with vegetable and animal geography, by comparative anatomy, and by the history of the embryonic development of animals.

_Geology_ finds in the strata of the crust of the globe a large number of extinct plants and animals of extraordinary variety; but all of them, however much they {64} may differ from the organisms of to-day, are completely in harmony with the _botanical_ and _zoölogical systems_ in which we divide the still living organisms. Not only have by far the most of the now extinct genera and species their family and stem-companions, and many even their genera and species companions, in the living world, but also those genera whose nearer relations are now extinct--as, for instance, the club-moss-trees, the trilobites, the ammonites, the belemnites, the sauria, the nummulites,--show still a very perceptible relationship with living genera, and can be quite accurately included in the botanical and zoölogical systems; nay, they even fill up gaps in it. The anatomical, morphological, and, so far as we can judge, the physiological and biological relationship of the fossil with living organisms, is so great and comprehensive that in the present state of science a systematic botany or zoölogy, that should only treat of the fossils or of living organisms alone, would be imperfect. But the relationship of the fossil organisms with the natural systems of botany and zoölogy is apparent not only in this respect, but also in the fact that the single species during the long periods of time which are shown by geology to have elapsed, came into existence in a series, which again pretty closely corresponds to the natural system of the organic kingdoms; and that the fossil representatives of all classes and families, the nearer they come to the present world, appear the more nearly related to the living organisms, so that the fauna and flora of the ante-human time are lost in those of the human period by transitions gliding from the one to the other. For instance, in the Miocene formation of the tertiary epoch {65} we find thirty per cent. of species still living to-day; in the Pliocene, even sixty to eighty per cent., and toward its end even about ninety-six per cent. of species which are identical with those now living.

A brief glance may still more closely illustrate this analogy between the geological series and the organic systems. Plants and animals seem to have appeared nearly at the same time, and at first in the form of the very lowest organisms. The earliest plants found by geology belong also to the lowest stage of the vegetable kingdom; they are the algæ. They are followed again by higher cryptogamous plants, especially ferns and club-mosses. Only at a later period flowering plants appear, among them being first the plants with naked seeds standing lower in the systems, as the cycad-trees and pine-forests; later, those with enclosed seeds, among them being again first the monocotyledons, last the dicotyledons,--all of them precisely corresponding to the botanical system. The same thing is true in the animal kingdom. If the eozoon Canadense, found in the laurentian slate of the Cambrian formation in North America, is really an organism and not an inorganic form, the earliest vestiges of animal life we can find are the rhizopodes or foraminifera; and these organisms belong to the lowest stage of life--to that stage which forms a kind of undeveloped intermediate member between the vegetable and animal kingdom, Häckel's kingdom of the protista. The next oldest animal organisms found in the Cambrian formation are the zoöphytes, and immediately above them the mollusca and the crustacea. In the following Silurian period we find corals, radiata, worms, mollusca, and crustacea, in {66} great number, also all the main-types of the invertebrates; and in the highest Silurian strata there are also to be found representatives of the lowest class of vertebrates, of fish, but still of very low organization and little differentiated. That the five main-types of the invertebrates seem to have appeared quite contemporaneously, yet that the zoöphytes really appeared first, does not contradict the before-mentioned law of a progress in the appearance of the organisms from the lower to the higher. For in the zoölogical system also these main-types of the invertebrates do not stand one above the other, but by the side of each other: at most, the radiata, the worms, the mollusca, and the articulata, take their places above the zoöphytes. Only within the main-types, in the classes, orders, etc., do differences in rank take effect; and even here, not without exception. What difference in rank, for instance, is there between an oyster and a cuttle-fish? between a cochineal and a bee or ant? and yet the first two belong to one and the same type--the type of mollusca; and the last three to one and the same class--the class of insects. The vertebrates rank decidedly above the invertebrates; and in a manner wholly corresponding to this, the vertebrates also appear after the invertebrates. Just as decidedly as to their rank, the main classes of the vertebrates do not stand beside, but above one another: above the fish stand the amphibia, above them the reptiles, next the birds, and above them the mammalia. To this series of succession also the geological facts seem to correspond pretty closely; only long after the fish do the first amphibia and reptilia appear--although it can not yet be decided which of these {67} two classes has left its earliest traces. If the interpretation of the gigantic foot-steps in the colored sandstone of North America, as belonging to the cursorial birds, is correct, the first appearance of birds falls in the time between the reptilia and mammalia; otherwise the first mammalia would have appeared before the first birds. For if we find the first real bones of birds only in the Jura and in the Chalk-formation, they are birds with tail-spines and with teeth in the beak--hence still related to the reptilia or the sauria. The first traces of mammalia to be found in the Upper Keuper formation, and in the Jura, belong to the order of opossums or marsupialia; _i.e._, to that order which (excepting the echidna and the ornithorhynchus that, as so-called monotremeta, stand the very lowest in the class of the mammalia, but are very scarce) occupies the lowest stage among the multitude of mammalia. Only after them do the higher orders of mammalia appear; and last of all organisms, man.

If we follow more in detail the appearance of the single organisms, some remarkable modifications show themselves in the course of their appearance and growth. We have heretofore mentioned the possibility of the appearance of the mammalia before the bird. Another fact which deserves attention is, that frequently the lowest representatives of a class or an order do not at first appear where the highest representatives of the next lower class or order are in existence, but with lower representatives of a preceding class or order, viz.: such representatives of the same as are still less differentiated and unite in themselves comparatively still more generic and less specific characteristics--as for instance, the lowest and {68} earliest amphibia, which do not appear at the same time and place with the most highly organized fishes, but with fishes of still lower organization. Moreover many groups of organisms show in earlier geological periods a richness of development from which they have now fallen far away. For instance, among the mammalia the pachydermata, among the reptilia the salamander and newt, among the articulata the cephalopoda, are at present remarkably reduced;--compare with the legions of ammonites and belemnites of the secondary period the small number of nautilus and cuttle-fish of the seas at the present day. A similar fortune was experienced by the ferns and club-mosses which formed whole forests in the carboniferous period. Other groups which once played a great _rôle_, are now wholly extinct; for instance, the trilobites of the primary, the sauria of the secondary, the nummulites of the tertiary periods. Now, all these modifications of geological progress would entirely correspond to the idea of a pedigree to which the descent theory traces back the whole abundance of forms of organisms. As soon as we seriously accept the idea of a pedigree, each of the two organic kingdoms would throughout form for its classes and species not only one single straight line of descent, but a tree, the branches of which are again ramified in a manifold way; a tree on which single branches--as perhaps that of the class of birds--may leave the main-stem or a main-branch, possibly being a branch destined to a higher development, and on that account held back in the process of development; a tree, finally, on which also branches and twigs can wholly or partly die off, as those of the extinct or reduced groups of organisms. {69}

From the point where the geological formations approach the present time, _plant_ and _animal geography_ also assists _geology_ in increasing the weight of the reasons for an origin of organisms through descent. With the tertiary period, the fauna and flora of the globe, which in former periods had a nearly uniform character all over the earth and showed no climatic differences, begin to separate according to climate, zones, and greater continents. This separation becomes distinctly evident in the middle tertiary formations, the Miocene, and much more distinctly in the higher tertiary formations, the Pliocene. The animals, especially the higher vertebrates, of the Pliocene formation on each continent or each larger group of islands, correspond very closely to the now living animals of the same geographical limit, with the exception of being generally of a much larger size. The Pliocene animal world of mammalia of the three old continents, for instance, corresponds exactly, through all its orders, to the present fauna of Europe, Asia and Africa; and that on an average it was built up more stupendously than that of to-day, we can see from the cave-bear and the mammoth. South America is the home of a peculiar order of mammalia--of the edentata, to which belong the sloth, the armadillo, and the like. All its predecessors are to be found also in the Pliocene strata of South America, and only there; and mostly in gigantic, but otherwise completely related, forms. New Zealand has no indigenous mammalia, but in their place great cursorial birds with but rudimentary wings. Exactly the same thing is found by geology in its tertiary and post-tertiary strata: nowhere a mammal, but gigantic birds with rudimentary {70} wings, down to the dinornis, which probably died out in man's time. New Holland has merely marsupial and some monotrematous, but no placental, mammalia; even its tertiary strata give no placental mammalia, but marsupialia, in analogy with all living genera, herbivorous, and carnivorous. Indeed, the analogy goes so far that the same line which through the Indian Archipelago separates the present Australian animal and plant world from the Asiatic, forms also the separating line for the geological zones of the Pliocene epoch. All these are facts which render quite inevitable the idea of an origin of the higher organic species of to-day through descent.

But still, from another side, animal geography, though it does not yet speak for a common pedigree of the whole animal world, as the facts just mentioned also do not, still at least speaks for a descent of related, though at present separated, genera and species from common forefathers. The continents of the Old and New World are so constructed that toward the North Pole they approach one another very closely, and toward the South Pole they withdraw from one another. Without doubt there existed in the North, through long periods of time, a land-connection of America with Asia and with Europe. Now, both continents have their more or less characteristic animal world, and these characteristics are distributed over the two halves of the globe in the following extremely remarkable way: The fauna of the Old and the New World, in those groups of animal genera which live only in the warmer or tropic zones or only south of the equator, and have no associates of genera or families in the higher North, is in each hemisphere entirely characteristic, and differs in a {71} marked way from the fauna of the other half of the globe. For instance, the rhinoceros, the hippopotamus, the giraffe, the antelope with undivided horns, the hedgehog, the mole proper, are only inhabitants of the Old World, whence also the horse originally came, the striped ones in Africa and the non-striped in Asia; on the other hand, the lemur, the ant-eater, the armadillo, and others, are limited to South America. The apes of the Old World have five molar teeth on each side of the jaw, narrow noses, tails usually short and never prehensile, and fleshy protuberances for sitting; the apes of the New World have six molar teeth, flat noses, and long prehensile tails. And on the contrary, where closely related species are found on both parts of the globe, they belong only to genera of which single species live or have lived in the far North; as, for instance, the rein-deer, still common to the Old and the New World in this very North which once formed a bridge between the two halves of the earth. The same is true in regard to cattle, the deer, the cat, the dog, the hare. Similar facts can also be shown of other animal classes. The farther the different species of these genera withdraw from the North Pole, the greater become the differences between the species on the one half of the globe and the analogous species of the other. Compare on this point K. E. von Baer's "Studien aus dem Gebiete der Naturwissenchaften, über Darwin's Lehre," ("Studies from the Realm of Natural Science upon Darwin's Teachings"), p. 356 f. If we add, further, the before mentioned fact, that those genera which are exclusively peculiar to one or the other continent, have their related predecessors in the tertiary strata of these continents, {72} the hypothesis of a separate origin for each single species, without genealogical connection with the anatomically and physiologically related species, becomes neither more nor less than a scientific impossibility.

Moreover, there are several facts of _comparative anatomy_ which have long been the joy of all zoölogists and have rewarded the toilsome labors of detailed investigations by a delightful view over the whole realm of the organic world, but which find a scientific explanation only in the descent theory. They are the _homology of the organs_, and to a certain degree also the so-called _rudimentary organs_. By homology of organs we mean the fact that within one and the same class-group of organisms all the organs, and especially the organs in their most solid constituents, in the skeleton, are built after one and the same fundamental plan, and therefore are even in their most widely separated modifications varied after this one and the same plan. This is especially true of the vertebræ and the limbs. This homology goes so far within one class, particularly within the class of mammalia, that, for instance, the hands and feet of man, the hands of the ape, the paws of the beast of prey, the hoof of the horse and of the ox, the paws of the mole, the fins of the seal and of the whale, the wing-membranes of the flying-squirrel, correspond to one another in their smallest parts and ossicles, and can all be registered with the same numbers and letters; _i.e._, they are homologous to one another even to the minutest detail. The _ideal_ plan and connection in the organisms, disclosed by these facts, and long ago acknowledged and admired, receives at the same time its simple _material_ basis through the acceptance of a common descent. {73}

A similar relation is observed in _rudimentary organs_.

Many of them, as the nipples of males, point, if not to a common descent from a lower form, at least to a common plan of the sexes. But when the embryo of the whale still has its teeth in the jaw, the grown up whale its hip-bones, when the eye of man still has its winking membrane, the ear and many portions of the skin their rudimentary muscles of motion, the end of the vertebral column its rudimentary tail, the intestinal canal its blind intestine; when sightless animals, living in the dark, still have their rudimentary eyes, blind worms their shoulder-blades; when in like manner the plants, especially in their parts of fecundation, show in great number such rudimentary organs as are entirely useless for the functions of life, but which are never misleading in determining their relationship with other plants:--how simply are all these facts explained by the descent theory, how not at all without it!

Finally, if we now mention the _history of the development of animals_, we shall have to postpone to the next section the consideration of the most essential facts furnished by this science; for the individual development of animals is a process which could speak not only for a descent of the species, but also for a descent of them through gradual development. But where, as in the present section, we treat the descent theory apart from the evolution theory, we have also to think of the possibility that the species or groups of species are not originated through gradual development, but nevertheless do originate through descent--namely, in leaps through metamorphosis of germs or a heterogenetic generation; and for such an idea we find confirmation in the {74} observation of the history of development of animals, which we call _change of generation_ or _metagenesis_.[4] By this is meant the following phenomenon: Certain animals, as the salpa and doliolum of the order of the tunicata, as well as certain mites and many tape-worms, produce offspring which are wholly dissimilar to the mother stock. These offspring have the capacity of reproducing themselves--if not by sexual means, as at the first generation, still by the formation of sprouts; and it is only the animals originated by the second generation (with many species, even those by the third) which return again to the form of the first generation. The plant-lice transmit themselves through six, seven, even ten generations by means of sprouts, until a generation appears which lays eggs. Now it is indeed true that the change of generation forms a circle in which the form of the last generation always returns to that of the first, and therefore leaves the species, as species, wholly unchanged. But it is nevertheless a process which shows that the natural law of an identity between generator and product, observed in other relations, is not without exception; and if we once have reason to suppose that the generation of new species took place in past periods of the globe, but has ceased in the present, such processes in the single period open to our direct observation--namely, the present (in which, however, according to our knowledge, the species remain constant)--are {75} nevertheless hints worthy of notice. For they refer us to ways in which in those former times, when certainly new species did originate, this formation of species might possibly have taken place.

This consideration leads us to treat of the main objection raised to every descent theory: namely, that never yet has the origin of one species from another been observed, but that, on the contrary, _all species_--so far as our experience goes, stretching over thousands of years--_remain constant_. We will give no weight to the fact that the constancy of species seems by no means to be absolutely without exception; for on the whole, they certainly remain constant. The only example which goes to prove such an evolution of species as taking place to-day--viz: the natural history of sponges--seems not to have this bearing. The transitions of form, proven by O. Schmidt in the siliceous sponges and by Häckel in the chalk-sponges, seem to show, not the genetic coming forth of a new species out of another, and especially not the evolution of a higher species out of a lower, but rather the uncertainty of the idea of species in general and the worthlessness of the skeleton-forms, for this idea, in such low organizations as the sponges. But that objection already loses its chief force from the consideration that we have not only never observed the origin of one species from another, but never even the origin of a species itself; and that nevertheless all species have successively originated in time. If we, therefore, are not able to observe directly their origination, we have a right to make all possible attempts at approaching the knowledge of it in an indirect way. But we see this objection invalidated by still another {76} fact. From all observations, it seems to be evident that those agencies which originated the species in general have ceased since man appeared. Now this fact is inconvenient for all those who, on metaphysical grounds, reject aim and purpose in the world and accept an aimless motion in the universe, a circle in which only identical powers are ever active to all eternity. From this standpoint, the scientists cannot, except by very artificial hypotheses, escape the conclusion that, if new species once originated through descent, new species ought still to originate through descent. In like manner, it is true, they are also obliged to accept the other conclusion: that if new species once originated through primitive generation, new species ought still to originate through primitive generation. On the other hand, those scientists who recognize aims in the world for which the world and each part of it is destined, and which are attained in the world through the processes of coming into existence, have to expect in advance that the organic kingdoms are also planned with reference to those aims. They naturally see the aim of the origin of species attained, where in the organic world beings appear who combine with the highest physical organization a self-conscious and responsible spiritual life, and who are capable of conceiving the ideal, even the idea of God. For, with the appearance of these beings, there enter upon the theatre of the world beings who go beyond the value of a purely physical organism and of a purely somato-psychical life, and in like manner represent again a higher order of beings; just as the first appearance of organic life on earth once introduced a new and higher stage of {77} existence in contrast to the inorganic world. Scientists who take this standpoint can readily adopt the fact that we do not now observe the origination of new species; for it is in full harmony with their metaphysical doctrines, without the same being on that account essentially dependent upon the confirmation or rejection of the hypothesis of the present constancy of species. With this very fact, the maxim that if new species once originated through descent, new species must still originate through descent, has lost for them its truth, and therefore its power of demonstration. So we see even here, while in the midst of the discussion of a purely scientific problem, in what close correlation metaphysics and natural science stand, and moreover--since the metaphysical view is most closely connected with the religious--in what close relationship religion and natural science stand. At the same time we also see how little the metaphysical interest, and much more how little the religious interest, has reason to avoid the investigation of facts in nature.

§ 4. _The Theory of Evolution--Archæology, Ethnography, Philology._

The evolution theory teaches that the species have developed themselves one from another in gradual transitions, each of which was as small as the individual differences still observed to-day among the individuals of the same species. It is not without support, especially in the _history of the development of plants and animals_.

Each organic being becomes what it is by means of organic development. Each plant, even the highest organized, begins in its seed-germ with a simple cell, {78} and is differentiated in constant development up to the fully perfected individual. Each animal, even the most highly organized (man included), begins the course of its existence as an egg; and each egg has no greater value of form than that of a single cell. This egg-cell is differentiated, after fecundation, in gradual and imperceptible transitions, farther and farther, higher and higher, until the individual has reached its perfect organization. No organ, no function of the body, no power or function of the soul or of the mind, appears suddenly, but all in gradual development. Since we see all individuals thus originating by means of gradual development, the possibility lies very near that the different organic formations of all the organic kingdoms could also have been originated by the same means.

In still another direction does the history of the development of single plants and animals make this possibility plausible to us. In the animal world, and partly also in the plant world, the single individuals of higher species in their embryonic development pass through states of development, in the former stages of which not only the individuals of the most different species look confusingly similar to one another, but also the embryos in their organization remind us of the perfected state of much lower classes of beings. In order to give a clear idea of the first mentioned facts, Häckel, for instance, in his "Natural History of Creation" and in his "Anthropogeny," represents by engravings the embryos of different vertebrates and also of man; representations which--although, according to the judgment of competent scientists, unfortunately not exact, but modified, after the manner of stencil plates, in favor of {79} greater similarity--yet make it quite clear that the similarity of the different embryos must be very great. We see, for instance, on one table the embryos of a fish, a salamander, a turtle, a fowl; on a second, those of a pig, an ox, a rabbit, a man; on a third, those of a turtle, a fowl, a man; and we find the similarity really great. Examples of the second fact--that individuals of higher classes or orders in former states of their embryonic development represent an organization which corresponds to the full-grown individuals of the lower classes--are: the tail of the human embryo, the gill-arches of the embryos of reptilia, of birds, of mammalia, and of man. Now Häckel here takes up again an idea first suggested by Fritz Müller, and derives from these observations the "biogenetic maxim," as he calls it: "The history of the germ is an epitome of the history of the descent; or, in other words, ontogeny (the history of the germs or the individuals) is a recapitulation of phylogeny (the history of the tribe); or, somewhat more explicitly: that the series of forms through which the individual organism passes during its progress from the egg-cell to its fully developed state, is a brief, compressed reproduction of the long series of forms through which the animal ancestors of that organism (or the ancestral forms of its species) have passed from the earliest periods of so-called organic creation down to the present time." In his latest publication, "Ziele und Wege der heutigen Entwicklungsgeschichte," ("Aims and Methods of the Present History of Evolution"), he admits into the formulation of his biogenetic maxim also the consideration of those phenomena in the ontogenetic development which are no recapitulation of the history {80} of the stem, but originated by adapting the embryo to its surroundings. In the description and explanation of this theory, he uses a term which throws upon nature a peculiar reproach, never before made, namely: cenogeny, or history of falsifications, in contrast to palingeny, or history of abridgments. This amended formula now reads: The development of germs is an abridgment of the development of stems, and is the more complete according as the development of the abridgment is continued by inheritance, the less complete according as the development of the false is introduced by adaptation.

Now, we ask: Is this biogenetic maxim correct? and moreover, from the fact of the organic individuals originating through development, are we entitled to draw the conclusion that even the species must have originated through development? To this question we can no longer get an answer from the life-processes of living organisms; for we have already mentioned the fact that, according to the present state of our knowledge, we can no longer observe the origination of a new species. Moreover, the embryonic states of development show also, in all their similarity, even in the very first stages, and with especial distinctness in these first stages, many differences between the single species; and this is true especially of those species which, according to the followers of this so-called biogenetic maxim, should lie in the same stem-line,--so that the direct scientific value of the embryological results to the palæontological investigation, or of the latter to the former, is so far very slight. Such a problem, however, as the one contained in that biogenetic maxim, which only gives to investigators the _direction_ in which possibly an {81} interesting and profitable path can be opened, does not at all deserve the name of a "_law_." K. E. von Baer, the founder of the whole present science of the history of development, has certainly a most competent judgment of the correctness of this so-called biogenetic maxim; and he convincingly shows, in his essay on "Darwin's Doctrine," that the embryos never represent a former animalic form, but that their development follows the principle of representing first the common characteristics of the class, then those of the order, etc., until finally the individual characteristics appear in the formation. Those who wish more information about embryology can find it in Heinrich Rathke's "Entwicklungsgeschichte der Wirbelthiere" ("History of the Development of Vertebrates"), edited by A. Kölliker, Leipzig, Engelmann, 1861; and those who wish to inform themselves as to the influence of the ontogenetic results of the solution of the phylogenetic problems, will find, besides the before-mentioned work of Wigand, rich and clearly elaborated material in the publication of Wilhelm His--"Unsere Körperform und das physiologische Problem ihrer Entstehung, Briefe an einen befreundeten Naturforscher" ("The Form of our Body and the Physiological Problem of its Origin; Letters to an Associate Scientist"), Leipzig, Vogel, 1875. The latter writer, although he advocates the descent theory, rejects the hasty assertions of Häckel with direct and convincing arguments.

Thus embryology, having from the simple fact of an origin of single plants and animals through descent at least confirmed the idea of the _possibility_ of an origin also of species through development, forsakes us in the {82} inquiry as to the _reality_ of such a genealogy of development, and refers us to other sciences.

Such a science, from which we certainly are entitled to expect a decided answer, is _geology_. For if the evolution theory is right, those periods of the history of our globe in which new species originated--namely, the periods of geology--_must_ show us also the _forms of transition_ between the different species. And, indeed, geology gives us an answer; but it reads contradictorily: It says yes, and it says no.

Geology does show us forms of transition, and, indeed, most frequently in the lower classes of animals. Who that has once studied petrifactions, does not know the mass of forms of the terebratulæ, the belemnites, and the ammonites, in the Jura formation? Würtemberger has brought light into the perplexing division of species of the ammonites by simply showing their temporary and systematic transitions into one another. In the fresh water chalk formation of Steinheim, near Heidenheim, in Würtemberg, scientists have found, on the same place, in an uninterrupted series of strata, the snail valvata or paludina multiformis in all imaginable transitions--from the flat winding, showing the form of a chess-board, up to the sharp form of a tower. And it was not, as Hilgendorf thought, in a series which can be traced in the strata according to time, but, as Sandberger says, in quite a varied mixture, yet in all imaginable modifications. But even among the higher and the highest classes of animals, we can trace the transitions. The flying sauria, if not in their organs of flying, which remind us more of the bat, at least in head, neck, and toes, are closely connected with the {83} birds--the oldest birds of the Jura and chalk formations, with their tail-spines similar to the reptilia and their teeth in the beak to the sauria. The tertiary formations especially show the primitive history of many vertebrates in very instructive forms of transitions--which, for instance, Rütimeyer, a scientist who is very cautious in his conclusions, very distinctly traced to the horse, to the ruminating animals, and lately also to the turtles. Still more in detail, W. Kowalewsky has lately shown us the primitive history of the horse, and Leidy and Marsh have further completed it by the addition of American forms, the former having at the same time described the forms which have led to the tapir.

But to such facts there are, on the other hand, experiences directly contradictory. Many lower and higher forms of animals and plants appear in the geological strata, so far as they have been explored, in a wholly independent way. We have mentioned, in the foregoing section, that the main types of the invertebrates appear somewhat contemporaneously and without any traceable intermediate form. The trilobites, a quite highly organized order of crustacea, appear in the strata of the silurian epoch almost suddenly, in very many and very distinctly marked species. The uncertainty of our knowledge shows itself most clearly when we ask for the geneologic relationship of the vertebrates. In Chap. II, § 1 and § 2 we have already referred to the value which Darwin, and more especially Häckel, lays on the relationship of the larva of the ascidia to the lancelet fish. Now the important testimony of K. E. von Baer, in his "Mémoires de l'Académie de St. Pétersbourg," Ser. vii, Vol. 19, No. 2, tells us that the nerve-ganglion {84} of the ascidia lies on the side of the stomach, and on that account can not be homologous with the spine of the vertebrates, but that the cord in the larva of the ascidia is nothing more than a support for the tail in swimming, which afterwards disappears, as with many other larvæ. As to the course of reasoning in reaching these genealogical conclusions, he says: "The hypothesis is indeed flexible. According to common reasoning, that which shows itself early in the development is an inheritance of the first progenitors. Therefore the ascidæ ought to descend from the vertebrates, and not the reverse. But it was necessary to show the descent of the vertebrates from the lower forms. In order to respond to such a necessity, men sometimes reverse their conclusions. Although favorably disposed to the doctrine of the transmutation of the animalic forms, I want a complete proof before I can believe in a transformation of the vertebrate type into that of the mollusca." Moreover, the zoölogists Semper and Dohrn find in the embryonic development of the sharks, the scates, and other cartilaginous fishes, organs which would bring them rather into a nearer relationship with the ringed worms than with the crustacea. When, on the other hand, we look around in palæontology, the oldest fossil fishes remind us neither of the crustacea nor of the ringed worms, but of the crabs: a class of animals which lies entirely outside of Häckel's stem-line of vertebrates. Also the first appearance of mammalia does not show transitions. Thus far we have not found in the geological strata any vestiges of the half-apes, which, according to the hypothesis of the evolutionists, as a common stem-line for the lines of ape and man development, once played such an {85} important _rôle_, and which have quite numerous representatives.

But the answer which geology gives to our questions as to the probable confirmation of the evolution theory, naturally becomes most interesting where the _origin of man_ is treated of. Our attention is, therefore, especially directed to the most recent formations of the globe which show us the oldest remains of man. The most instructive are those parts of the skeleton which allow us to draw the most convincing conclusions as to the degree of mental development of an individual, namely: the parts of the skull. Although human bones seem to have been less easily preserved than those of animals, and are, comparatively speaking, very scarce, especially more so than prehistoric implements, still there are not wanting such remains, which go back far beyond historical time. The oldest known skull is the celebrated one of the Neander cave near Düsseldorf, with its large vault of the forehead, and its low height. Although Virchow finds on it evidences of rachitis in youth and of gout in old age, as well as of injuries, it nevertheless can not have been changed in its _fundamental form_ by any sickness, even according to Virchow. This very skull now indisputably shows a still lower formation, which, although quite essentially different from the type of the ape, stands nearer to it than is the case with the skulls of men in later times. Of a later date, and of a correspondingly higher form, are the skull of Engis, of Cannstatt, the skulls of the Belgian caves (especially Chauvaux), of France, and of Gibraltar. According to the weighty authority of Schaaffhausen (note his opening address at the Wiesbaden Congress of the {86} Anthropological Society, 1873), the skulls and the remaining parts of the skeleton show more indications of a lower formation the older they are. He especially calls attention to a certain bone of the roof of the skull--the _Os interparietale_ or the so-called _Os Incæ_--which has only recently been recognized as a characteristic of a lower formation of skulls, standing nearer to that of animals. As late as the summer of 1873, two human skeletons were found at Coblenz in a volcanic sand, of which Schaaffhausen says: "No less than eight anatomic marks of a lower formation, which probably have not heretofore been found together, indicate the great age of these remains." With all these traces of a difference between the former and the present state of the physical condition of man, the differences between the type of man and that of the animal are still great enough to leave wide open the possibility of the origin of man through some other means than that of gradual development. On the other hand, it is more or less in favor of the evolution idea, that so far such old remains of man have been found in places which certainly can not have been the cradle of mankind, and that those parts of the earth which we would naturally suppose to be the first dwelling place of the earliest human genera have been little or not at all investigated. And also the hypothesis of Häckel, that the cradle of mankind was a land between Africa and Asia, now sunk in the sea, and called Lemuria, can be neither proved nor denied. Such vague possibilities have indeed not the least scientific value.

In considering these contradictory results of geological investigation, we dare not overlook three points: First, our knowledge of the crust of the globe is still {87} very fragmentary, and does not yet extend over the whole globe. Further, it lies in the nature of the case that the strata in mountain formations can only give a very incomplete picture of the whole variety of the real organic life which may have populated the earth and the sea. What a poor picture of the present plant and animal life would be offered, for instance, by the soil of our continents, the slime, sand, and pebbles of our coasts and of the bottoms of our lakes and seas, if we had to construct from them alone the fauna and flora of the present! A third, but purely hypothetical, consideration is rendered of importance particularly by Darwin and Häckel; namely, that the forms of transition without doubt existed for a shorter period than those forms whose organization has established itself in fully developed species.

Thus far we have directed our attention to inquiring how the organic individuals were originated--and have throughout observed a successive development; next, we have questioned geology--and here also have observed a progress in the appearance of the species, but have received at the same time contradictory answers to the question whether this progress presents itself as a gradual development of one species from another or as a sudden appearance. So the reasons for and against the evolution theory almost balance one another; and it is not improbable that the hypothesis of an origin of species through development will have to share its authority with the hypothesis of a descent of species through heterogenetic generation, as well as with the hypothesis of a primitive generation of lower organisms, still repeating itself at a later time. Thus for the origination of {88} groups lying nearer together, we have the evolution theory; for the other groups, and especially for the origination of types where no transitions to other types can be traced, the theory of the heterogenetic or primitive generation recommends itself; and both theories thus far are of a purely hypothetical nature.

But there is still a third realm, which is just as open to our observation as the history of the development of organisms and as geology, and of which we can also ask, whether it does not open for us an indirect way to the knowledge of the origin of species, and especially of man--a knowledge which we can no longer approach in the direct way of observation. This realm is _natural history_ and the _history of the development of the human race_. For mankind also is engaged in a process of development, and its present members do not stand on the same height. Now the question is, to what beginning can we trace backward the development of mankind, and to what succeeding stages of development from this present condition? And do we find in these earliest periods, and on these lowest stages, points that are connected with still earlier conditions and organizations, and especially points which could genealogically join together mankind and the animal kingdom? Three sciences, still young, favorite children of the present generation, participate in investigating this realm, namely, _archæology_, _comparative ethnology_, and _comparative philology_.

_Archæology_ leads us back to far-off times. It is a fact that, chronologically speaking, man lived in the glacial period--according to French scientists, even before it; and that, palæontologically speaking, man and {89} mammoth lived at the same time, and, according to a discovery made some thirty years ago at Denise in Middle France, probably even man and another older and defunct form of pachydermata, the elephas meridionalis, in North America man and the mastodon. The reader may compare the discoveries regarding the age of mankind, as they are described most recently by Sir Charles Lyell in his work upon this subject, in the publications of the Anthropological Congress at Brussels in the year 1873, and in those of the fourth General Assembly of the German Society for Anthropology, Ethnology and Primitive History, at Wiesbaden, in the year 1873.

Now, to be sure, from the oldest human _tools_ and _utensils_ that are found, we can expect still less than from the oldest human bones that they will throw direct light upon the answer to the question of the _origin_ of man. For where man not only uses tools, but _manufactures_ the same for use, a wide breach already exists between man and animal. Manufactured articles, therefore, can only throw some light on the history of the development of the already existing human race. And even this light is less clear than we perhaps expected in view of the first interesting prehistorical discoveries. It is true, all these discoveries show us an ascent from the simplest and roughest forms to the more perfect; from the split but unpolished stone to the polished, and from stone to bronze and iron. But a progress of the human races in manufacturing and using articles, from the simple and rough form to the more artificial, lies so much in the nature of the case, and is so taken for granted with every conception of the origin of man, even with that contradictory to Darwinism, that from this simplicity of {90} the earliest tools we can not at all conclude that there was a condition of mankind lying near that of animals; and especially we can draw only general and uncertain conclusions as to that which makes man _man_, as to the spiritual and moral qualities of those prehistoric men. Moreover, in discoveries belonging to the very oldest, we come upon drawings and engravings from which we recognize the man of those primitive times as a creature whose life was not entirely taken up in the animalic struggle for existence, but was already adorned with those ideal pursuits and enjoyments which we are accustomed to ascribe to the height of civilization. Examine, for instance, the drawing of a mammoth on a mammoth tooth of Dordogne, which the French scientists Lartet and Christy have reprinted in their Reliquiæ Aquitanicæ (1868), and which Sir Charles Lyell has copied in his "Age of the Human Race." How much spirit and life in this primitive work of art! Or read what Fraas, in the "Journal of the German Society for Anthropology," March, 1874, reports about the picture of a grazing reindeer, engraved on a knife handle made of the horns of a reindeer, which was lately found in the cave of Thayngen near Schaffhausen, and which surpasses in beauty all rough drawings thus far found. The whole bearing of the animal--the muscles of the legs and the head, the form of the many-branched antlers, with the wide-spread eyes, the representation of the hair upon the body and under-jaw--all disclose a real artist among those savages.

This is also to be taken into consideration: that those men, whose traces we find, could possibly have been the descendants of more noble predecessors, driven {91} off and degenerated, just as well as they could have been representatives of the whole former condition of culture of mankind. In England, where the questions of the first condition of culture of mankind are very warmly discussed, the Duke of Argyll particularly, in his "Primeval Man," advocates these views, and very forcibly calls attention to the fact that thus far the places of the discovery of the earliest traces of man undoubtedly lie very far from the original home of the human race; while Sir John Lubbock, in his "Origin of Civilization" and in his "Prehistoric Times," and also Tylor in his "Beginning of Culture" and in his "Early History of Mankind," take the opposite view of a progress of mankind from the most uncultivated beginnings.

Archæology, as a whole, seems to do no more than admit that its results can be incorporated into the theory of an origin of the human race through gradual development, _if_ this theory can be shown to be correct in some other way, and that its results can just as well be brought into harmony with a contradictory theory.

_Comparative ethnology_ gives us quite a similar result. It is true, there are races of mankind in the lowest grades of human existence. It is well known how Darwin, in his voyage on board the "Beagle," got one of his first vivid impressions of the possibility of an evolution of man from the animal world, by seeing the inhabitants of Tierra del Fuego; and it is remarkable that the arms, tools, and furniture, used by the lowest savages, are very similar to the earliest remains of civilized races found on earth. The conclusion lies extremely near, that the savages simply remained in earlier stages of human culture; and an ethnographic picture of mankind {92} at present would in a similar way give an approximately correct view of its former development, as the natural zoölogical and botanical system of the present fauna and flora must give us at the same time the key to their pedigree; supposing the Darwinian theory to be correct.

If it were so, ethnology would be an altogether inestimable help for the exploration of the descent and development of the human race. For the extremely few and rare fossil remains of man--which, moreover, do not give us any answer to the most important questions in regard to the mental and moral quality of the primitive man--would be rendered complete by living examples of the kind, which remained at the old stages of development.