Chap, vi. affected by Natural Selection. 1 5 9 



or individual difference ; and we are immediately made conscious 

 of this by reflecting on the differences between the breeds of our 

 domesticated animals in different countries,— more especially in the 

 less civilised countries where there has been but little methodical 

 selection. Animals kept by savages in different 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 specu- 

 late 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, Jioiufar 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 



