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rated regions take no account of the lapse of time since the separation occurred, but only of the amount of difference in soil, climate, and other circumstances which had come about after the separation.
3. The inhabitants of oceanic islands should, if specially created in them (as every species peculiar to an island or to a group must have been, according to the special creation theory), be found established where they are best fitted to flourish. Toads and frogs should be as much more numerous than lizards as they are on mainlands. Mammals, too, where the conditions are as well adapted for them as is often the case (for instance, at Porto Santo), should abound.
It will already have been seen that the above conclusions, which would be unavoidable if the special creation theory were true, exactly reverse the known facts in regard to distribution. Is it, then, strange, that, since the death of Professor Agassiz, there has been no celebrated thinker on the subject of distribution who is not also a believer in the theory of descent?
1 In 1873.
THE ORIGIN AND ANTIQUITY OF MAN.
has been done toward illustrating the way in which animals might gain by improvement or specialization of their physical constitution, there has been no consideration of the advantages that might be derived from a more fully developed brain and the increase of mental power which it would bring. Yet, even were there no evidence for or against such a supposition, who could doubt that a gain in mind might serve species in the struggle for existence not less surely than a gain in body? As we should expect to find the facts in this regard, so they actually present themselves. Pursuing the animal life-history of the earth from the Cambrian age to the age of man, the student may read the story of the acquisition of a nervous system, then of a brain, and, after that, a continued progress in brain-development.
Or again, if we consider the case of the vertebrate animals by themselves, the same general truth is strikingly exemplified ; since the first type to appear, that of the fishes, is lowest in brain-development, while the last type, that of mammals, is the highest in this respect. Even within the class of main mals, the same law holds good, as is most strikingly illustrated by Professor Marsh's comparison of the brain of the Brontotherium (a quadruped of the middle part of the mammalian age) with the brain of a related animal, the modern horse. Now, it is a well-recognized fact, that the most extensive and profitable variations among animals are likely to occur in those organs which are already highly developed, or, in other words, that specialization appears to make the most rapid progress in parts which have before become much specialized. Out of the hundreds of examples that might be quoted in illustration of this, one must suffice. Among pigeons the fantail variety is valued solely for the wide-spread tail. This has varied greatly in size, form, and number of feathers from that of the wild parent species. And it is among fan-tails that we still ineet with more differences in the development
1 Dana's Manual of Geology, p». 508.
of the tail in individual birds than can be found in any other variety of pigeon.
Following up the history of brain-development as recorded in the fossils of vertebrate animals, from the fishes of the silurian to the mammals of the mesozoic, the decided superiority of the mammalian brain is manifest enough.
Evidently there was no previous group with brain enough to outstrip other animals in the struggle for existence, solely by reason of its suiperior mental powers. Scaly coats of mail, formidable teeth, or tremendous muscular power, had characterized some of the vertebrates from the beginning. But it was not until mammals appeared, that intelligence became so important a factor in the struggle for existence that we might naturally expect as a result rapid and unusual variations in brain-development. We must keep constantly in mind the principle already stated, that the most variation is found occurring in those parts which are already highly specialized.
Man, as Professor Cope has well argued, though the highest of animals, and therefore of mammals, is not the highest as a mammal in any other respect saye that of possessing a superior brain.
“ In all general points his limbs are those of the primitive type so common in the eocene. He is plantigrade, 2 has five toes, separate carpals 3 and tarsals,4 short heel, rather flat astragalus,5 and neither hoofs nor claws, but something between the two: the bones of the fore-arm and leg are not so unequal as in the higher types, and remain entirely distinct from each other, and the ankle-joint is not so perfect as in many of them. In his teeth his character is thoroughly primitive. . . . His structural superiority consists solely in the complexity and size of his brain.
: . A very important lesson is derived from these and kindred facts. The monkeys were anticipated in the greater fields of the world's activity by more powerful rivals. The ancestors of the ungulates 6 held the fields and the swamps; and the carnivora, driven by hunger, learned the arts and cruelties of the chase. The weaker ancestors of the Quadrumana possessed neither speed, nor weapons of offence and defence; and nothing but an arboreal life was left them, where they developed the prehensile powers of the feet. Their digestive system unspecialized, their food various, their life the price of ceaseless vigilance, no wonder that that inquisitiveness and wakefulness was stimulated and developed which is the condition of progressive intelligence. "T
1 The first period of the tertiary age.
7 Professor Edward D. Cope, The Origin of the Fittest, pp. 279, 280.