Chap. VIL] THEORY OF NATURAL SELECTION. 265 



from each other in single characters, but in many parts ; 

 and he asks, how it always comes that many parts 

 of the organisation should have been modified at the 

 same time through variation and natural selection ? But 

 there is no necessity for supposing that all the parts of 

 any being have been simultaneously modified. The 

 most striking modifications, excellently adapted for 

 some purpose, might, as was formerly remarked, be 

 acquired by successive variations, if slight, first in one 

 part and then in another ; and as they would be trans- 

 mitted all together, they would appear to us as if they 

 had been simultaneously developed. The best answer, 

 however, to the above objection is afforded by those 

 domestic races which have been modified, chiefly through 

 man's power of selection, for some special purpose. Look 

 at the race and dray horse, or at the greyhound and 

 mastiff. Their whole frames and even their mental 

 characteristics have been modified; but if we could 

 trace each step in the history of their transformation, 

 — and the latter stens can be traced, — we should not 

 see great and simultaneous changes, but first one part 

 and then another slightly modified and improved. Even 

 when selection has been applied by man to some one 

 character alone, — of which our cultivated plants offer 

 the best instances, — it will invariably be found that 

 although this one part, whether it be the flower, fruit, 

 or leaves, has been greatly changed, almost all the other 

 parts have been slightly modified. This may be attri- 

 buted partly to the principle of correlated growth, and 

 partly to so-called spontaneous variation. 



A much more serious objection has been urged by 

 Bronn, and recently by Broca, namely, that many cha- 

 racters appear to be of no service whatever to their 



