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Show 406 RECAPITULATION. [CnAP. XIV. females. The most vigorous individuals, or those which have most successfully struggled with their conditions ?f life, will generally leave most yrogeny. But success wrll often depend on having specia weapons or means of defence ' or on the charms. of the males ; and the slightest advantage will lead tQ vrctory. As geology plainly proclaims that each land has undergone great physical changes, we :n;tight have expected that organic beings would have varied under nature, in the smne way as they generally have varied under the changed conditions of d01nestication. And if there be any variability under nature, it would be an unaccountable fact if natural selection had not come into play. It has often been asserted, but the assertion is quite incapable of proof, that the an1ount of variation under nature is a str~ctly limited quantity. Man, thou~h acting on external characters alone and often caprimously, can produce within a short period a great result by adding up mere individual differences in his domestic productions ; and every one admits that there are at least individual differences in species under nature. But, besides such differences, all naturalists have admitted the existence of varieties, which they think sufficiently distinct to be worthy of record in systematic works. No one can draw any clear distinction between individual differences and slight varieties; or between more plainly marked varieties and subspecies, and species. Let it b~ observed how naturalists differ in the rank which they assign to the many representative forms in Europe and North America. If then we have under nature variability and a powerful agent always ready to act and select, why should we doubt that variations in any way useful to beings, under their excessively complex relations of life, would be preserved, accumulated, and inherited? Why, if man can by patience select variations most useful to himself, should nature fail in selecting variations useful, under changing conditions of life, to her living products? What lin1it can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature,-favouring the good and rejecting OnAP. XIV.] RECAPITULATION. 407 the b~d? I can ~ee no limit to this power, in slowl and ~eautlful~y adaptrng each form to the most complefrela-tlons of hfe. The theory of natural selectr'on 'f 1 k f th th h . , even 1 we oo no ur er ant 1s, seems to me to be in itself prob-able. I have already recapitulated as fairly as I ld th e opp~se d d1'f fi cul t1' es and objection' s; now iet us tucornu to' the special acts and arguments in favour of the theor On the vie'Y t~a~ species are only strongl;y marke/ ~nd perm~nent vaneties, and that each species first existed a. vanety, we can see why it is that no line of demarc~~ twn can be drawn between s;pecies, commonly supposed to I:ave b~en produced by spemal acts of creation, and varieties whwh are acknowledged to have been produced b secon.da~y laws.. On this same view we can understan~ how It IS that In each region where many species of a . genus have been. produced, and where they now flourish, these same species should pres~nt many varieties ; for w~1ere the manufactory of spemes has been active we m1ght expect, as a general rule, to find it still in action· and this is the pase if varieties be incipient species. More~ over, the species of the larger genera, which afford the greate~ number of varieties or incipient species retain to a certain degree the character of varieties · for they differ from ea~h other by a less amount of difference t'han do the species of smaller genera. The closely allied species also of t~e larger gener~ a~parently have restricted ranges, an~ theJ. are clustered In httle groups round other species -In which respect they resemble varieties. Those are ~trange relations on the view of each species having been ~dependently created, but are intelligible if all species first existed as varieties. 4-s each species tends by its geometrical ratio of reproduct~ on to increase inordinately in number; and as the modrfied descendants of each species will be enabled to increa~ e by S? much the more as they become n1ore diversified In habits and structure, so as to be enabled to seize on many and w~dely different places in t~e economy of nature, there Will be a constant tendency 1n natural selection t? preserve the ~ost divergent ?ffspring of any one speCies. Hence dur1ng a long-contmued course of modifica- |