284 LAWS GOVERNING THE STERILITY 



fact we must conclude either that the aboriginal parent- 

 species at 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 moso 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 in- 

 digenous 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 evidence that the 

 crossed offspring from the Indian humped and common 

 cattle are intei' se perfectly fertile; and from the observa- 

 tions by Riitimeyer on their important osteological differ- 

 ences, as well as from those by Mr. Bly th on their differences 

 in habits, voice, constitution, etc., these two forms must 

 be regarded as good and distinct species. The same remarks 

 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 GOVERIS'IKG THE STERILITY OF FIRST CROSSES AKD 



OF HYBltlDS. 



We will now consider a little more in detail the laws 

 governing 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 confusion. The following conclusions are drawn up 

 chiefly from Gartner's admirabb work on the hybridization 

 of plants. I have taken much pains to ascertain how far 

 they apply to animals, and, considering how scanty our 



