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Show 408 RECAPITULATION. [CHAP. XIV tion, the slight differences character~stic of varieties o~ the same species, tend to be augmented Into the greater differences characteristic of species of the same genus. New and improved varieties will inevitably ~upplant .and ext~rminate the older, less improved and Intermediate vaneties; and thus species. are render~d to a la:ge extent defined and distinct obJects. Dominant species belonging to the larger groups tend to give birth to new and dominant forms; so that each large group tends to become still larger, and at the same time more divergent in character. But as all groups cannot thus succeed in increasing in size, for the world would not hold them, the 1nore dominant groups beat the less dominant. This tendency in the large groups · to go on increasing in size and diverging in character, together with the almost inevitable contingency of much extinction, explains the arrangement of all the forms of life, in groups subordinate to groups, all within a few great classes, which we now see everywhere around us, and which has prevailed throughout all time. This grand fact of the grouping of all organic beings seems to me utterly inexplicable on the theory of creation. As natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modification; it can act only by very short and slow steps. l-Ienee the canon of " Natura non facit saltum," which every fresh addition to our knowledge tends to make more strictly correct, is on this theory silnply intelligible. We can plainly see why nature is prod- . igal in variety, though niggard in innovation. But whythis should be a law of nature if each species has been independently created, no 1nan can explain. Many other facts are, as it seems to me, explicable on this theory. I-Iow strange it is that a bird, under the form of a woodpecker, should have been created to prey on insects on the ground; that upland geese, which never or rarely swim, should have been created with webbed feet; that a thrush should have been created to dive and feed on sub-aquatic insects; and that a l?etrel should have been created with habits and structure fitting it for the life of an auk or grebe ! and so on in endless other cases. But CHAP. XIV.] RECAPITULATION. 409 o. n the vbi ew o.f each sp em·e s co?stant1 y try1· ng to I· ncrease 1h n~m tr, Wit~ natural selection always ready to adapt t e .~1 ow Y ':arying des?endants of each to any unoccupied or 1 -occup1ed place 1n nature, these facts cease to be strange, or perhaps ~ight even have been anticipated. . .A.~ natural selection acts by competition, it adapts the Inhabltan~s of each .country only in relation to the degree of pe~fectlon of ~hmr associates ; so that we need feel no surpr1se at .the 1nh~bitants of any one country, although on the ord1nary view supposed to have been specially created and adapted for t~at country, being beaten and supplanted by the naturalised productions from another land. Nor ought we to marvel if all the contrivances in natu:e be not, as far as we can judge, absolutely perfect; and If some of them be abhorrent to our ideas of fitness. We, need not marvel at the sting of the bee causing the bees own death ; . at drones being produced in such vast nu~bers ~or ~ne Single act, and being then slaughtered by their sterile ~1sters ; a~ th~ as~onishing waste of pollen by our fir-trees , at . the 1nstlnct1ve hatred of the queen bee fo! ~er ow~ fert1le daughters; at ichneumonidre feeding Within the hve bodies of caterpillars· and at other such cases.. The wonder indeed is, on th~ theory of natural s~lectlon, that more cases of the want of absolute perfectJon have not been observed. . The complex and little known laws governing variatw~ are the same, as far as we can see, with the laws whiCh have governed the production of so-called specific forms. In bot}'! cas~s physical conditions seem to have produced but httle direct effect; yet when varieties enter any zone, tp.ey occasionally assume some of the characters of t~e spemes proper to that zone. In both varieties and spe~Ie~, us~ and disuse seem to have produced some effect; for ~t IS drfficult to resist this conclusion when we look, for 1:nstance, a~ the ~ogger-headed duck, which has wings, Incapa~le of fhght, 1n nearly the same condition as in the domestic ~uc~; or w~en we look at th~ burrowing tucutucu, whi_ch 1s occas~onally blind, a:p.d th~n ~t certain moles, wh1cl}. are habitu~lly l:>lind and. l:l~ve their eyes covered with skin ; or whe~ we 'look at' the blind. animals 18 .. |