Chap. XXIII. CONDITIONS OF LIFE. 279 



believe that this is in any way related to the nature of the climate to which 

 they have been exposed. 36 



It appears at first sight probable that the increased size, the tendency to 

 fatten, the early maturity and altered forms of our improved cattle, sheep, 

 and pigs, have directly resulted from their abundant supply of food. This 

 is the opinion of many competent judges, and probably is to a great extent 

 true. But as far as form is concerned, we must not overlook the equal 

 or more potent influence of lessened use on the limbs and lungs. We see, 

 moreover, as far as size is concerned, that selection is apparently a more 

 powerful agent than a large supply of food, for we can thus only account 

 for the existence, as remarked to me by Mr. Blyth, of the largest and 

 smallest breeds of sheep in the same country, of Cochin-China fowls and 

 Bantams, of small Tumbler and large Bunt pigeons, all kept together and 

 supplied with abundant nourishment. Nevertheless there can be little 

 doubt that our domesticated animals have been modified, independently 

 of the increased or lessened use of parts, by the conditions to which 

 they have been subjected, without the aid of selection. For instance, Prof. 

 Eiitimeyer 87 shows that the bones of all domesticated quadrupeds can be 

 distinguished from those of wild animals by the state of their surface 

 and general appearance. It is scarcely possible to read Nathusius's excel- 

 lent ' Vorstudien/ 38 and doubt that, with the highly improved races of 

 the pig, abundant food has produced a conspicuous effect on the general 

 form of the body, on the breadth of the head and face, and even on the 

 teeth. Nathusius rests much on the case of a purely bred Berkshire pig, 

 which when two months old became diseased in its digestive organs, and 

 was preserved for observation until nineteen months old ; at this age it had 

 lost several characteristic features of the breed, and had acquired a long, 

 narrow head, of large size relatively to its small body, and elongated legs. 

 But in this case and in some others we ought not to assume that, because 

 certain characters are lost, perhaps through reversion, under one course 

 of treatment, therefore that they had been at first directly produced by an 

 opposite course. 



In the case of the rabbit, which has become feral on the island of Porto 

 Santo, we are at first strongly tempted to attribute the whole change — 

 the greatly reduced size, the altered tints of the fur, and the loss of certain 

 characteristic marks — to the definite action of the new conditions to which 

 it has been exposed. But in all such cases we have to consider in addition 

 the tendency to reversion to progenitors more or less remote, and the 

 natural selection of the finest shades of difference. 



The nature of the food sometimes either definitely induces certain pecu- 

 liarities, or stands in some close relation with them. Pallas long ago 

 asserted that the fat-tailed sheep of Siberia degenerated and lost their enor- 

 mous tails when removed from certain saline pastures; and recently 



36 Azara has made some good remarks Soc.,' 1856, p. 38. 



on this subject, ' Quadruples du . 3 7 ' Die Fauna der Pfahlbauten,' 1861, 



Paraguay,' torn. ii. p. 337. See an s. 15. 



account of a family of naked mice ss t Schweinschasdel,' 1864, s. 99. 

 produced in England, ' Proc. Zoolog. 



