HYBRIDISM 245 



where neither pure parent-species exists, they must certainly be 

 highly or perfectly fertile. 



With our domesticated animals, the various races when crossed 

 together are quite fertile; yet in many cases they are descended 

 from two or more wild species. From this fact we must conclude 

 either that the aboriginal patent-species at first produced per- 

 fectly 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 

 stock; 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 aborig- 

 inal 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 inter se perfectly fertile ; and from 

 the observations by Riitimeyer on their important osteological 

 differences, as well as from those by Mr. Blyth on their differences 

 in habits, voice, constitution, etc., these two forms must be re- 

 garded 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 steriHty 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 intercross- 

 ing 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 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 admirable work 

 on the hybridization of plants. I have taken much pains to as- 



