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Show 128 NATURAL SELECTION. CHAP. IV. 1' . beings can be supported on character; for more IV~~g diverge in structure, habits, the same area the more . ey f by lookino- at , . f whwh we see proo o and constitutiOn, o 11 ot or at naturalised pro-the inhabitants of any ~m~ spthe modification of the ductions. Therefore uri~g nd during the incessant descendants of any one species, a . 1 struggle of all species to in~~::::en~:eb~:~t:r1:i~o~: diversified these descend~ant. th b~ttle of life. Thus their chance of succee Ing In e . the small differences distinguishing varie~Ies of the same . . ill steadily tend to increase till the.y come to spe~~sth: g. reater differences between species of the equ . . t a enus or even of distinc . gener . . sa; eg hav~ seen that it is the ~ommon, t~e Wld~l~ diffused, and widely-ranging species, belongi~g to larger genera, wh I.C h vary most .' and these will t~.n d .t t o transmi' t t o their modified o.f fsprin·g thh a·t supenorl ny-which now makes them dominan~ In t eu own cou tries Natural selection, as has JUst beenh re~ar~~d, lead~ to divergence of character and to muc e~ Inc wn of the less improved and intermediate forms of l:rl': 't?n these principles, I believe, the nature dof thlte . a nti Ileys of all organi.c be~. ngs may b e exp1 a ~' ne . IS a rtu t wonderful fact-th e won d er 0 f which w. e are adp 101 overlook from familiarity-that all animals an a plants throughout all time and space should be r.ela:~d to each other in group. subordinate to group, In rt Whi.ch we everywhere behold-namely, va - manner ] d t ther eties of the same species most closely re ate oge 11 ' species of the same genus less closely and unequa y related together, forming sections and sub-gener~, :ed cies of distinct genera much less closely. relate f ._ genera related in different degrees, forming sub- a; lies families orders, sub-classes, and classes. be sev'e ral subo'r dinate groups I· n any c1 a ss cannot e CHAP. IV. SUMMARY. 129 ranked in a single file, but seem rather to be clustered round points, and these round other points, and so on in almost endless cycles. On the view that each species has been independently created, I can see no explanation of this great fact in the classification of all organic beings; but, to the best of my judgment, it is explained through inheritance and the complex action of natural selection, entailing extinction and divergence of character, as we have seen illustrated in the diagram. The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs ; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches ; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and G3 |