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Show 422 DARWINISM CHAP. these ~merican evolutionists have departed very widely from the views of Mr. Darwin, and in place of the well-established causes and admitted laws to which he appeals have introduced theoretical conceptions which have not yet been tested by experiments or facts, as well as metaphysical conceptions which arc incapable of proof. And when they come to illustrate these views by an appeal to palroontology or morphology, we :find that a far simpler and more complcL ' explanation of the facts is afforded by the established principle~ of variation and natural selection. The confidence with which these new ideas are enunciated, and the repeated assertion that without them Darwinism is powerless to explain the origin of organic forms, renders it necessary to bestow a little more time on the explanations they give us of well-known phe!Jomena with which, they assert, other theories arc incompetent to grapple. As examples of usc producing structural change, Mr. Cope adduces the hooked and toothed beaks of the falcons nn<l the butcher-birds, and he argues that the fact of these birds belowring to widely different groups proves that similarity of u e h~s produced a similar structural result. But no attempt is made to show any direct causal connection between the use of <L hill to cut or tear flesh and the development of a tooth on the mandible. Such use might conceivably strenathcn the hill . . . b or mcrease Its s1zc, but not cause a special tooth-like out()'rowth which was not present in the ancestral thrush-like fo~·ms of the. b~tcher-bird. . On ~he other hand, it is clear thnt any vanatwns of the b1ll tendmg towards a hook or tooth woultl (J'i vc the possessor some ad vantage in seizing and tearing its p7('y, and would thus be preserved and increased by natural selectio11. Again, Mr. Cope urges the effects of a supposed "law of polar or centrifugal growth" to counteract a tendency to unsymmetrical growth, where one side of the body is u ed more than the other. But the undoubted hurtfulness of want of symmetry in many important actions or functions would rapidly eliminate any such tendency. When, however, it has dress, ,nn:r~ely, what is the. meaning and importance of I rofessors Cope a1Hl Hyatt s views on acceleration and retardation 1 1 have endeavoun·d and given up in despair, the attempt to grasp their meaning" (L1j e and Lt:tlers vol. iii. p. 233). • XlV FUNDAMENTAL PROBLEMS 423 hccome useful, as in the ca e of the single enlarged claw of mrmy crustacea, it has been preserved by natural selection. Or·igin of the Feet of the Ung1.tlates. Perhaps the most ori()'innJ and suggestive of Mr. iop 's applications of the th ory of u c and effort in modifying structure arc, his chapters "On the Origin of the Foot-Structure of the Ungulates ; " and that " On the Effect of Impacts and ~trains on the Feet of Mammalia ; " and they will crvc also to show the comparative merits of thi · theory an l that of naturu,l selection in explaining a difficult ca e of modification, especially as it i an explanation claimed u lJCW and origina.l when first cnuncia,ted in 1 81. Let u , then, . ee how he deals with the problem. The r markahle progrcs. ivc change of a four or five -toed ancestor into the onc-toccl hor. c, and the equally remarkable division of the whole group of ungulate animal. into the oddtoed and even-toed clivi ions, Mr. Cope attempts to expbin by the effects of impact and use among animal which frequented hard or swampy ground respectively. On hard ground, it is urged, the long middle toe would be mo t used and subjected to the greatest train , and wonld therefore acquire both strength and development. It would then be still more exclusively u eel, and the extra nonri hmcnt required by it would be dru.wn from the a,cljacent lessused toes, which would accordingly diminish in size, till, after a long series of ch;wgc ·, the r cconls of which arc so well preserved in the American tcrti<try rocks, the true one-toed horse w:ts developed. In soft or swampy ground, on the other hand, the tendency would be to spren.cl out the foot so that there were two toes on c:teh ide. The two middle toes would thu be most used and mo t subj ect to strain , and would, therefore, illcrcasc at the expen c of the htteral toes. There would be, no donht, a,n advantage in the c two fun ctional toes being of equal size, so a to prevent twi:tinO' of the foot while walking; and vn,riation tending to bring thi about would be advantageous, and would therefore he pre crved. Thus, by a parallel cries of changes in another direction, adapted to a distinct ·et of conditions, we . honl(l arri vc at the symmetrical divided hoof of our deer and cattle. The fact |
