LAWS GOVERNING THE STERILITY 305 



first produced perfectly fertile hybrids, or that the hybrids 

 subsequently reared under domestication became quite fertile. 

 This latter alternative, which was first propounded by Pallas, 

 seems by far the most probable, and can, indeed, hardly be 

 doubted. It is, for instance, almost certain that our dogs are 

 descended from several wild stocks; yet, with perhaps the 

 exception of certain indigenous domestic dogs of South 

 America, all are quite fertile together; but analogy makes 

 me greatly doubt, whether the several aboriginal species would 

 at first have freely bred together and have produced quite 

 fertile hybrids. So again I have lately acquired decisive evi- 

 dence that the crossed offspring from the Indian humped and 

 common cattle are inter se perfectly fertile; and from the 

 observations by Riitimeyer on their important osteological 

 differences, as well as from those by Mr. Bl}'lh on their dif- 

 ferences in habits, voice, constitution, &c., these two forms 

 must be regarded as good and distinct species. The same re- 

 marks may be extended to the two chief races of the pig. 

 We must, therefore, either give up the belief of the universal 

 sterility of species when crossed; or we must look at this 

 sterility in animals, not as an indelible characteristic, but as 

 one capable of being removed by domestication. 



Finally, considering all the ascertained facts on the inter- 

 crossing of plants and animals, it may be concluded that some 

 degree of sterility, both in first crosses and in hybrids, is an 

 extremely general result ; but that it cannot, under our present 

 state of knowledge, be considered as absolutely universal. 



LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF 



HYBRIDS. 



We will now consider a little more in detail the laws gov- 

 erning the sterility of first crosses and of hybrids. Our chief 

 object will be to see whether or not these laws indicate that 

 species have been specially endowed with this quality, in order 

 to prevent their crossing and blending together in utter con- 

 fusion. The following conclusions are drawn up chiefly from 

 Gartner's admirable work on the hybridisation of plants. I 

 have taken much pains to ascertain how far they apply to 

 animals, and, considering how scanty our knowledge is in re- 



