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Show 122 NATURAL SELECTION. CHAP. IV. modl.f ie d 0J1!i!1. spr•i ng of a species get into some d. istinct countr ' or become quickly adapted to some quite ~ew stati.o ny, I. n wh I'C h child and parent .d o not come Into competition, both may continue to exist. If then our diagram be assumed to .represent a considerable amount of modification, species (A) . and II the earlier varieties will have become extinct, a . ( 14 t 14) • having been replaced by eight new species a om ' and (I) will have been replaced by six (n 14 to z 14) new species. · · 1 · But we may go further than this. The ong1na speCI~s of our genus were supposed to resemble eac~ other. I~ unequal degrees, as is so generally the case In nature, species (A) being more nearly rela~ed to B, C, and D, than to the other species; and species (I) more toG, H, K, L, than to the others. These two species (A! and(~), were also supposed to be very common and widely diffused species, so that they must originally ~ave had some advantage over most of the other spe~Ies of the genus. Their modified descendants, fourteen In number at the fourteen-thousandth generation, will probably have inherited some of the same advantages : they have also been modified and improved in a diversified manner at each stage of descent, so .as to have become adapted to many related places in the natural economy of their country. It seems, therefore, to me extremely probable that they will have taken the places of, and thus exterminated, not only their parents (A) and (I), but likewise some of the original species which were most nearly related to their parents. Hence very few of the original species will have transmitted offspring to the fourteen-thousandth generation. We may suppose that only one (F), of the two species which were least cl~sely related to the other nine original species, has transmitted descendants to this late stage of descent. CHAP. IV. DIVERGENCE OF CHARACTER. 123 .T~e new species in our diagram descended from the on~Inal eleven species, will now be fifteen in number. Owing to the divergent tendency of natural selection, the extreme amount of difference in character between species a 14 and z 14 will be much greater than that between the ~ost different of the original eleven species. The new speCies, moreover, will be allied to each other in a widely different manner. Of the eight descendants from (A) the thr~e marked a 14, q 14, p 14, will be nearly related from having recently branched off from a 10. b 14 a~df 14, fro~ having diverged at an earlier period from a , Will be In some degree distinct from the three firstnamed species ; and lastly, o 14, e 14, and m 1\ will be nearly related one to the other, but from having diverg~ d a~ the .first commencement of the process of modification, will be widely different from the other five species, and may constitute a sub-genus or even a distinct genus. The six descendants from (I) will form two subg~ nera or even genera. But as the original species (I) di~ered largely from (A), standing nearly at the extreme points of the original genus, the six descendants from (I) will, owing to inheritance, differ considerably from the eight descendants from (A); the two groups, more•:~ ver, ar~ su~posed to have gone on diverging in diffe~ e~t duect1?ns. The intermediate species, also (and this Is a very Important consideration), which connected the ?riginal spec~es (A) and (I), have all become, excepting (F), extinct, and have left no descendants. ~ence the six new species descended from (I), and the eight descended from (A), will have to be ranked as very distinct genera, or even as distinct sub-families. Thus it is, as I believe, that two or more genera are produced by descent, with modification, from two or more species of the same genus. And the two or G2 |