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Show 436 DARWINISM CHAP. will even then not equal, in each generation, the amount of the fortuitous variations of the same part. If it be urged that the effects of use would modify all the individuals of a species, while the fortuitous variations to the amount named only apply to a portion of them, it may be replied, that that portion is sufficiently large to afford ample materials for selection, since it often equals the numbers that can annually survive; while the recurrence in each successive generation of a like amount of variation would render possible such a rapid adjustment to new conditions that the efl'ccts of u. e or disuse would be as nothing in comparison. It follows, that even admitting the modifying effects of the environment, and that such modifications are inherited, they would yet be entirely swamped by the greater effects of fortuitous variation, and the far more rapid cumulative results of the selection of such variations. Supposed Action of the Environme1·~t in Initiating Vct1'iGdions. It is, however, urged that the reaction of the environment initiates variation , which without it would never arise; such, for instance, as the origin of horns through the pressures and irritations caused by butting, or otherwi e using the head as a weapon or for defence. Admitting, for the sake of argument, that this is so, all the evidence we possess shows that, from the very first appearance of the rudiment of such an organ, it would vary to a greater extent than the amount of growth directly produced by usc; and these variations would be subject to selection, an<l would thus modify the organ in ways which usc alone would never bring about. \Ve have seen that this h<tH been the case with the branching antlers of the stag, which have been modified by selection, so as to become uscfnl in other ways than as a mere weapon ; and the same ha,R almost certainly been the case with the variously cnrve<l and twisted horns of antelopes. In like manner, every conceivable rudiment would, from its first appearance, be subject to the law of variation and selection, to which, thenceforth, the direct effect of the environment would be altogether subordinate. A very similar mode of reasoning will apply to the other branch of the subject-the initiation of structures and organs XIV FUNDAMENTAL PROBLEMS 437 by the action of the fundamental laws of growth. Admitting that such laws have determined some of the main divisions of ~he animal an<l vegetable kingdom, have originated certain Important organs, and have been the fundamental cause of certain lines of development, yet at every step of the process these laws mu. t have acted in entire subordination to the law of natural selection. No modification thi1s initiated could have aclv<tnccd a single step, unless it were, on the whole, a useful mo~ification; while its entire future course would be necessarily subJ ect to the laws of variation and selection, by which it would be sometimes checked, sometimes hastened on, sometimes diverted to one purp~se, sometimes to another, according as the need. of the orgamsm, un<ler the special conditions of its exi. tcncc, required such modi fica,tion. \V c need not deny that such laws and influences may ha,ve acted in the manner suggcstccl, but what we do deny is that they could possibly csca.pe from the ever-present and all-powerful modifyino- effects of varia,tion and natural selection.! b JVeismann' s Theo1'y of 1Ie1·edity. Professor August \V cismann has put forth a new theory of heredity fonndecl upon the "continuity of the germ-ph m," one of the logical consequences of which is, that acquired characters of whatever kind arc not transmitted from parent to off: pring. As this i. a matter of vita,l importance to the theory of natnrn.l selection, a,nd a , if well founded, it strikes away the foundations of most of the theories discnssed in the present ·Ch<.tpter, a brief outline of \V cismann's views must be attempted, 1 In an es ay on "The Duration of Lif , " forming part of the translation ·Of Dr. Weismann's papers alrea<ly referred to, the author sti ll further extends the . phere of natural selection by showing that the averag0 duration of life in each .. pecies has been u..termined by it. A certain length of life is cs. ential in order that the species may produce offspring ·ufficient to ervure its ·ontinuance under the most unfavourable conditions ; and it is shown that the remarkable inequalities of longevity in difl'erent species and groups may be thus accounted for. Yet more, the occurrence of death in the higher organ ism., in place of the continued survival of the uni cellular orgaui. ms how- ever much they may increase by subdivi ion, may be traced to the ~ame great law of utility for the race and su rvival of the fittest. The whole essay is of ·exceeding intere ·t, and will repay a careful peru ·al. A similar idea occurred to the present wriU>r about twenty years back, and was brielly noted down at the time, but subsequently forgotten. |