CHAP. VI.] AFFECTED BY NATURAL SELECTION. 149 



countries often have to struggle for their own subsistence, and are 

 exposed to a certain extent to natural selection, and individuals 

 with slightly different constitutions would succeed best under 

 different climates. With cattle susceptibility to the attacks of 

 flies is correlated with colour, as is the liability to be poisoned by 

 certain plants; so that even colour would be thus subjected to the 

 action of natural selection. Some observers are convinced that a 

 damp climate affects the growth of the hair, and that with the hair 

 the horns are correlated. Mountain breeds always differ from 

 lowland breeds ; and a mountainous country would probably affect 

 the hind limbs from exercising them more, and possibly even the 

 form of the pelvis ; and then by the law of homologous variation, 

 the front limbs and the head would probably be affected. The 

 shape, also, of the pelvis might affect by pressure the shape of 

 certain parts of the young in the womb. The laborious breathing 

 necessary in high regions tends, as we have good reason to believe, 

 to increase the size of the chest ; and again correlation would come 

 into play. The effects of lessened exercise together with abundant 

 food on the whole organisation is probably still more important ; 

 and this, as H. von Nathusius has lately shown in his excellent 

 Treatise, is apparently one chief cause of the great modification 

 which the breeds of swine have undergone. But we are far too 

 ignorant to speculate on the relative importance of the several 

 known and unknown causes of variation ; and I have made these 

 remarks only to show that, if we are unable to account for the 

 characteristic differences of our several domestic breeds, which 

 nevertheless are generally admitted to have arisen through 

 ordinary generation from one or a few parent-stocks, we ought 

 not to lay too much stress on our ignorance of the precise cause 

 of the slight analogous differences between true species. 



Utilitarian Doctrine, how far true : Beauty, how acquired. 



The foregoing remarks lead me to say a few words on the protest 

 lately made by some naturalists, against the utilitarian doctrine 

 that every detail of structure has been produced for the good of 

 its possessor. They believe that many structures have been 

 created for the sake of beauty, to delight man or the Creator (but 

 this latter point is beyond the scope of scientific discussion), or for 

 the sake of mere variety, a view already discussed. Such doctrines, 

 if true, would be absolutely fatal to my theory. I fully admit 

 that many structures are now of no direct use to their possessors, 

 and may never have been of any use to their progenitors ; but this 

 does not prove that they were formed solely for beauty or variety- 

 No doubt the definite action of changed conditions, and the 

 various causes of modifications, lately specified, have all produced 

 ao effect, probably a great effect, independently of any advantage 



