Organic Evolution. 2 1 3 



of the hind limbs sharing in the general modification. 

 Mr. Spencer, therefore, argues that it is difficult to believe 

 that these multitudinous co-ordinated modifications are the 

 result of fortuitous variations seized upon by natural selec- 

 tion. For natural selection would have to wait for the 

 fortunate coincidence of a great number of distinct parts, 

 all happening to vary just in the particular way required. 

 That natural selection should seize upon the favourable 

 modification of a particular part is comprehensible enough ; 

 that two organs should coincidently vary in favourable 

 directions we can understand ; that half a dozen parts 

 should, in a few individuals among the thousands born, by 

 a happy coincidence, vary each independently in the right 

 way is conceivable ; but that the whole organization should 

 be remodelled by fortunately coincident and fortuitously 

 favourable variations is not readily comprehensible. It 

 may be answered — -Notwithstanding all this, we know that 

 such happy coincidences have occurred, for there is the 

 resulting giraffe. The question, however, is not whether 

 these modifications have occurred or not, but whether they 

 are due to fortuitous variation alone, or have been guided 

 by functional use. The argument seems to me to have 

 weight.* 



Still, we should remember that among neuter ants — 

 for example, in the Sauba ant of South America (Oecodoma 

 cephcdotes) — there are certain so-called soldiers with rela- 

 tively enormous heads and mandibles. The possession of 

 these parts so inordinately developed must necessitate 

 many correlated changes. But these cannot be due to 

 inherited use, since such soldiers are sterile. 



Furthermore, according to Professor Weismann, natural 

 selection is really working, not on the organism at large, 

 but on the germ-plasm which produces it ; and it is con- 



* Mr. Darwin, while contending that the modifications need not all have 

 been simultaneous, says, " Although natural selection would thus tend to give 

 the male elk its present structure, yet it is probable that the inherited effects 

 of use, and of the mutual action of part on part, have been equally or more 

 important " (" Animals and Plants under Domestication," vol. ii. p. 328). 



