24 GENERAL EVOLUTION. 



the wolf, the red fox, the red-tailed hawk, the garter-snake, the 

 tiger, salamander, etc. 



That the yariability depends on a peculiar condition of the ani- 

 mals themselves, and not on domestication, excepting in so far as 

 it produces these conditions, is plain, not only from the above 

 facts, but from those observed in domestication. It is well known 

 that while pigeons, fowls, cattle, dogs, etc., are variable, or '^ pro- 

 tean," the peafowl (Pavo) has maintained its specific characters 

 with great accuracy during a period of domestication as long as 

 that of the other species named. The same may be said of the 

 guinea {Numida) and the turkey {Meleagris). These facts show 

 that domestication is only a remote cause of variability. 



5. On the Location of Growth-Force. 



With the fact of increase of general growth-force before us, 

 have we any others which can guide us in fixing on a cause for its 

 special location ? It is plain that the useful additions which have 

 constituted certain genera, families, orders, etc., what they are, 

 must have been produced as a consequence of the existence of a 

 need for them ; or, on the other hand, being created first, they 

 must have sought for use, and found it. But what are the rela- 

 tive chances of truth for these two propositions ? In the second 

 case, admitting evolution as proved (see Part I), we perceive that 

 an almost infinite chance exists against any usual amount of 

 variation, as observed, producing a structure which shall be fit to 

 survive in consequence of its superior adaptation to external cir- 

 cumstances. It would be incredible that a blind or undirected 

 variation should not fail in avast majority of instances to produce 

 a single case of the beautiful adaptation to means and ends which 

 we see so abundantly around us. The amount of attemjot, failure, 

 and consequent destruction, would be preposterously large, and 

 in no wise consistent with the facts of teleology as we behold 

 them. 



What of the opposite view ? We have in its support the well- 

 known facts of determination of nutritive fluid during use of 

 parts, not only for supplying fuel for the motions of use, but also 

 for growth-force and material for the increase in bulk of the part 

 used. Who has not remarked the large size of the hands of the 

 laborer, and of the nails of the working-woman ? Who can not 

 remember some of the countless examj)les of certain modifications 

 of form being associated with special excellence of use of the parts 



