THEORY OF NATURAL SELECTION. 189 



I can discover, inhabiting distinct stations, such as high 

 land or low land, dry or moist districts. Moreover, in the 

 case of animals which wander much about and cross freely, 

 their varieties seem to be generally confined to distinct 

 regions. 



Bronn also insists that distinct species never differ 

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

 and he asks, how it always comes that many parts of the 

 organization 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 varia- 

 tions, if slight, first in one part and then in another ; and 

 as they would be transmitted all together, they would ap- 

 pear 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 char- 

 acteristics, have been modified ; but if we could trace each 

 step in the history of their transformation — and the latter 

 steps can be traced — we should not see great and simulta- 

 neous changes, but first one part and then another slightly 

 modified and improved. Even when selection has been ap- 

 plied 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 attributed partly to the principle of correlated growth, 

 ani partly to so-called spontaneous variation. 



A much more serious objection has been urged by Bronn, 

 and recently by Broca, namely, that many characters 

 appear to be of no service whatever to their possessors, and 

 therefore cannot have been influenced through natural 

 selection. Bronn adduces the length of the ears and tails 

 in the different species of hares and mice — the complex 

 folds of enamel in the teeth of many animals, and a multi- 

 tude of analogous cases. With respect to plants, this sub- 

 ject has been discussed by Nageli in an admirable essay. 

 He admits that natural selection has effected much ; but b$ 



