Accordingly if we are compelled to maintain the fluent and conventional character of the idea of species, if we must grant that there is in nature only less and greater differences, but in such abundant gradations that from the least noticeable individual shade of difference to the extreme difference between the higher and the lower organisms there takes place a transition by small stages unnoticeable by us (comp. Wallace’s “Contributions to Natural Selection”), then neither in the idea of Species nor in a similar narrower or wider notion can there exist a compulsion for the Unconscious, regulating the minimum interval of its steps in the progressive development of the organisation, but the smallest extent of the leaps of heterogeneous generation will still only have to be sought in the magnitude of the modifying resistances and the ends pursued by the Unconscious (e.g., attainment of certain stages of organisation in certain intervals of time). But now, as we know, not perfect similarity, but only general resemblance, is found between parents and children, for the various material circumstances bring about in generation individual variations from the ideal normal type, which perfectly to level would require an altogether useless expenditure of force on the part of the Unconscious, since these individual variations usually and in the main are neutralised of themselves by the inter-mixture of families. Accordingly one has not to wonder at the unlikeness, but rather at the likeness of parents and child; for if the Unconscious should behave in all generation within the same species in the same way, and save itself the labour of a continually neutralising interposition, the differences between begetters and begotten which would arise through the diversity of the material circumstances would be still far greater than experience now shows us. Nevertheless, we see cases occur in which the Unconscious prefers to send monsters into the world to endeavouring to overcome the existing material difficulties.—The remaining individual differences are undoubtedly great enough to lead quickly to an essential alteration of the type, and the Unconscious need only hinder the neutralising of these differences by crossing in those cases in which the variations answer to its progressive plan, either by directly retaining them or by an external mechanism; thus, again, a large part of the expenditure of energy is in this manner saved.
That such origins of species by the summation of individual variations have actually occurred, numerous animal classes in our geological collections prove, when the collectors do not discard the inconvenient intermediate stages, which will not fit into any artificial division. “Numberless are the species of ammonites that have been described; annually new ones are added to the old, and whole cases are filled with books on ammonites. If we arrange them in a series, the differences between any two specimens are in fact so inconsiderable that everybody must undoubtedly regard them as individual peculiarities. In a dozen, however, the small differences amount to something considerable, and in two dozen the amount of the differences has become so large that no resemblance at all can any longer be observed between the first and the last. Here no specific difference any longer holds water, as soon as one has only specimens enough to illustrate the transitions” (Fraas, “Vor der Sündfluth,” p. 269). Very much the same may be said of the Trilobites, and many other classes. One other quotation concerning snails. “At Steinheim (Würtemberg) there is a hill of tertiary date, which more than half consists of snow-white shells of Valvata multiformis. One end of this snail is extremely turreted, like a Paludina (twice as high as thick), the other has a quite flat umbilicus (discoid, its length one-fourth of its thickness). Even the most cautious savant, who employs all sorts of distinctions for establishing a species, stands puzzled before the Klosterberg of Steinheim, and must confess that all the million forms on which his foot treads pass so easily and imperceptibly into one another, that he can only speak of one species” (Fraas, p. 30). At the lower part of the hill lie the flattest, at the upper part the most turreted forms. In the thousands of years that this hill was in process of formation the species has in this manner changed. In the same calcareous sand of Steinheim one may quite distinctly trace in the superposed strata the gradual severance of one stem-form into diverging, subsequently sharply separated species (comp. Hilgendorf’s Communication in the Monthly Report of the Berl. Acad. of Sc., July 1866).
If, therefore, we may look upon it as established that the Unconscious will frequently be able to employ for the production of a new species a sum of accidental individual variations, that by no means implies that these are always offered to the Unconscious in all those directions which it intends to adopt; there always remains the possibility, that just the most important advance of all can not be comprehended as accidental variations, but only as systematically varying formative processes. I think we must even assume that all the elevations to essentially higher stages, which presuppose the formation of organs not previously in existence, cannot be explained by accidental individual variations, although the latter may have performed the main work in the thorough elaboration of an existing type in all directions.
How can a change simultaneously occurring at different parts of the body, which exhibits a systematic correlation in its different parts, be sufficiently understood by accidental variations, e.g., the formation of the udder in the first marsupial, which must necessarily go hand in hand with bearing alive if the young are not to perish miserably after birth, or the correlated change of the male and female sexual parts if copulation is to remain possible? Just as little can the principle of accidental variation be regarded as sufficient where certain animal forms exhibit peculiarities of anatomical structure, which, valueless for themselves, have a significance only as intermediate transitional forms for more highly developed stages, where accordingly one clearly sees the existence anticipated for the sake of the future purpose, e.g., the first formation of a cartilaginous spinal cord in those primitive fish-forms, which by their exo-skeleton possessed perfect solidity like the Crustacea, whence they are derived, so that the primitive endo-skeleton had an importance not for themselves, but only for their later descendants, which converted the shell – cuirass into a scaly coat; or, e.g., the brain of the lowest savages and primitive men, which is five-sixths as large as the brain of the most advanced races, whilst for the functions it subserves the brain of the anthropoid apes would quite well suffice, that only amounts to one-third of that of civilised man. Even Wallace literally says: “Natural selection could endow the savage only with a brain which surpasses slightly that of the ape, whilst he actually possesses one which stands a little below that of a philosopher.” This circumstance, combined with the fact that hair is absent from the back of man; that hand and foot seem needlessly perfect organs for the savage, and that the human vocal organs, especially the soft palate, contain such wonderful, and, for the savage, useless latent capabilities, which only find application with higher civilisation,—all these circumstances cause Wallace to draw the conclusion “that a superior intelligence guided the development of man in a particular direction and to a definite end, precisely as man guides the evolution of many animal and vegetable forms.”
The Darwinian theory has the merit of having pointed to the summation of individual variations in a particular direction, and the change of a type thereby rendered possible into that of another species, and of having proved the same by copious examples. It is very pardonable for a new and meritorious view when it exaggerates its range and thinks to explain everything, when in reality it explains only some, perhaps even most facts, and the more interesting is the above testimony of Darwin’s rival Wallace, which openly confesses the insufficiency of this theory for the explanation of the origin of Man.—
Let us now consider what expedients the Unconscious employs in the cases to which its sole remaining task is limited—to retain the accidentally arisen individual variations, and to prevent their normal neutralisation and obliteration by crossing.
The sole expedient already familiar to us is the instinct of individual selection in the gratification of the sexual impulse. In Chap. v. B. we saw how beauty is increa
sed and enhanced in the animal kingdom by this means; in Chap. ii. B. we perceived the value of the same for the improvement of the human race in every respect, and cast a side glance at the possibility of similar processes in the higher classes of the animal kingdom. If this aid is almost without significance in the lower classes of animals, it increases in importance with the progress of development, acts, however, certainly always more for the fixing and improvement of a species in itself than for the passage into another. Frequently, in place of the active selection of the male, occurs a passive selection of the female, in that the inflamed males, animated by a special fighting instinct, contend for the possession of the female, when of course the most powerful and most active carry off the victory.
Much more thoroughly operates for the change of a species another circumstance, the which to have made good is the most signal merit of the Darwinian theory—natural selection in the struggle for existence.
Every plant, every animal, has in two respects to carry on a struggle for existence: first, negatively to defend itself against the enemies threatening to destroy it, as, e.g., the elements, and the robbers and parasites, who would prey upon it; and, secondly, positively to compete in acquiring or retaining what is necessary for the continuance of life, as food, air, light, soil, &c. The fleetest animals, those which know best how to conceal themselves, or least attract notice by their colour and form, will most easily be able to elude the persecutions of their enemies. Of animals and plants, those will least fall a sacrifice to the injuries of the weather, storm, frost, heat, wet, dryness, &c., which are most capable of resistance to these circumstances by their external or internal organisation. Of beasts of prey, only the most active, quickest, most powerful and craftiest will be able to escape hunger when there is dearth of food; of plants, those which maintain themselves most vigorously under like circumstances will become more luxuriant in growth than others, and, as regards the enjoyment of light, air, and rain, will attain so decided an advantage as to stifle those lagging behind. We see this struggle for existence most frequently entered upon between different species, and end with the perfect annihilation of one, e.g., the domestic rat by the migratory rat. Less noticed but far more general is that among different individuals of the same species. The latter naturally causes an improvement of the species, for it is in all cases the feeblest individuals which are excluded by premature annihilation from the office of propagation, which is accordingly exercised by the cleverest and most powerful individuals for the longest period. Besides improvement, however, such a variation of the species can also take place that varieties and races, and finally new species, arise. This case can of course only occur if the external relations of life become different; then will natural selection favour in reproduction those individual characters which especially in the new circumstances show special vital force. The consequence will thus always be an accommodation to the external conditions of life. As now the Unconscious likewise wills this accommodation, so has it only to leave natural selection in the struggle for existence perfectly unchecked in order to see this end attained without trouble, without any special interposition.
Such changes of the outward conditions of life may take place in very different ways. In the first place, the plant or the animal may seek the same by wandering, and thus by local separation or formation of colonies protect the variety about to be formed from the threatened reversion to the ancient stock; secondly, their own homes may be sought out by strange plants and species of animals on their wanderings, and they may be compelled to test and strengthen their powers in contest with these; in the third place, by elevations or depressions the situation of the ground and height above the sea may be altered, mountains may become a table-land, plains mountain-ridges, sea-bottoms plains, coasts continents, severed lands be united, united lands be separated, &c.; in the fourth place, changes of climate, even apart from the already mentioned causes, may occur; and finally, in the fifth place, changes in the vegetable kingdom are altered conditions of life for the animal kingdom, and conversely. These relations offer a rich variety, and in most geographical districts such changes in the course of the geological development of the earth’s surface have not taken place once but innumerable times.
If a plant migrates to a more uniformly moist soil, its leaves generally become less divided, more glabrous and grass-green, the flowers smaller and darker. Conversely, if a plant settles on a more porous and dry soil, its leaves become bluer, more procumbent, more divided or separated into fibres, the flowers larger and brighter, and it is enveloped in a thick hairy covering. Thus on a dry calcareous soil Hutchinsia brevicaulis passes into H. alpina, Arabis cœrulea into bellidifolia, Alchemilla fissa into vulgaris, Betula pubescens into alba; on a damp soil devoid of lime Dianthus alpinus is transformed into deltoides (according to A. Kerner in the Austr. Bot. Journal). In the animal kingdom, where the altered outward circumstances do not lie so close together as the different soils for the plant, owing to the present average constancy of the geographical and climatic relations, specific variation by natural selection has not yet been observed, but certainly formation of strongly marked varieties, especially under the unintentional influence of man, e.g., origination of very different races of domestic animals (dogs, cattle, sheep, horses); and bearing in mind the above-mentioned facility of the transition from the race to the variety, it may justly be assumed that in former times, when not seldom a more rapid transformation of the external circumstances may have occurred than the human race has historically recorded, that in these earlier times many formations of new species may have come about by natural selection in the struggle for existence.—In opposition to this it is maintained that then the infinitely many intermediate forms through which one species passes into the other must be capable of demonstration in the strata, whilst yet the fossil species for the most part are just as sharply, and still more sharply, distinguishable from one another than the living. This proves nothing at all; for it lies in the nature of the case that that form must be the final form which is more capable of life than all the preceding phases, which therefore conquers, i.e., eradicates, all these in the struggle for existence; but if they are soon thrust on one side by the final form, they have only had a brief existence as compared with the final form, which now, as the best adapted to the circumstances, persists at least as long as these circumstances; acordingly one cannot wonder if hitherto so few transitional forms have been found between different species. That none of these have ever been found is not true; on the contrary, both among higher, and quite specially among lower animals, an astonishing number of transitional forms are found.
In addition to the examples mentioned above (pp. 304–307) the following may be instanced. Passing from the radiate to the bilateral type, we are acquainted with two series. (1) Star-fish, sea-urchins, holothuriæ; in the latter, what was tipper and under has become back and front, and as by the arrangement of the so-called ambulacra a new upper and under side has been formed, at the same time a right and left side has arisen. (2) Corals, Rugosa, slipper-shells; in the palæozoic Rugosa, the dividing walls of the calcareous shell answering to the septa of the bodily cavity are no longer arranged regularly as in the other corals, but at least in the interposed after-growth always at the side of a primary dividing-wall, so that in respect of the latter a bilateral type arises. When the Rugosa develop an operculum in addition, there arises the slipper-shell, hitherto reckoned to the Conchifera.
As the Australian and New Zealand fauna is in general to be regarded as an arrested representative of an older geological period, it has recently furnished us in the New Zealand bridge-lizard with an animal which, in certain characters (biconcave vertebral axis after the fashion of the Saurians, sexual apparatus without male organ), has remained at the stage of the fish-salamanders, but in other respects has developed into the external form of a lizard, which, in a remarkable manner, unites the normal characters of the tortoises (absence of teeth), crocodiles (immobility of the four legs), and
snakes (movable rami of the lower jaw united by a ligament, and participation of the ribs in locomotion).
Huxley traces back the pedigree of the horse of the modern period step by step through the horses of older times, through Hipparion and Hipparitherium to Plagiolophus, which latter is already a species of the genus Palæotherium (the common ancestor of the hoof-horses and pachyderms), and in a similar manner the musk animals of the present day through the Cainotherium of the Miocene to Dichobune from the Eocene as primitive form. Gaudry has found in the Miocene strata of Pikermi in Greece “the group of the Limocyonidœ, which is intermediate between bears and wolves; the genus Hyœnictis, which unites the hyenas with the civet cats; the Ancylotherium, which is related both to the extinct mastodon and to the living pangolin or scaly ant-eater, and the Helladotherium, which unites the now isolated giraffe with the stag and the antelope” (Wallace).—A rich world of forms reveals itself to us in the contemplation of the genus Crocodile. The crocodiles of the cretaceous period are different from those of the older tertiary period, and these again are just as different from the crocodiles of the younger tertiary strata as from those of the present day. Nevertheless, the differences between one form of the series and another are so slight that they are only discernible by the eye of the connoisseur.—Reptiles and birds seem to be two of the most widely separated orders, and yet the Soolenhofen slates have, on the one hand, yielded a bird (Archœopteryx) which by its elongated form, unfused bones between the hands, and strong claws on the wing-fingers, far more closely approaches the reptiles than the ostrich-like birds of the present day; and, on the other hand, laid bare a reptile (Compsognathus longipes), that not only (as probably most Dinosauria did) went exclusively on its hind-legs, but also in the parts found is remarkably similar to the Archæopteryx. The footprints of reptiles and birds of that time, interconnected through all conceivable shades, lead us to expect that we shall yet find more remains of intermediate forms, which will bridge over the hitherto existing differences.
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