228 ZOOLOGK AL A( CEPTA1ION OF 



ralists to seek for a criterion of speeies in breeding *. They 

 established the rule, that those animals which copulate to- 

 gether, and produce an offspring equally prolific with them- 

 selves, belong to one and the same species, ascribing the 

 differences which may exist between them to adventitious 

 causes. The high authority of Buffon and Hunter, who 

 adoptv'd this opinion, occasioned the criterion of breeding to 

 be very generally relied on. 



If we admit this, the question respecting the human 

 species would be immediately solved . for all the races breed 

 together; and their offspring is prolific, either with each 

 other, or with any of the original races. Indeed, we know 

 no difference in productiveness between such unions and 

 those of the same race. 



This rule, however, involves a petitio principii, in assuming 

 that animals of distinct species never produce together a 

 ])roiific offspring. Generally, indeed, hybrid animals, or the 

 offspring of any two species, are incapable of generation ; 

 and this is a powerful additional provision for preserving 

 uniformity of species. There are, however, instances, both 

 among the mammalia and birds, of individuals belonging to 

 species universally held to be distinct, uniting and producing 

 young, which were again prolific. Tliat the mule can en- 

 gender with the mare, and that the she mule can conceive, 

 was known to Aristotle. The circumstance is said to 

 occur most frequently In warm countries ; but it has taken 

 place in Scotland f. Buffon states that the offspring of 

 the he-goat and ewe possesses perfect powers of reproduc- 

 tion. We migiit expect these animals, with the addition 

 also of the chamois (antelope rupicapra), to copulate to- 

 getlier easily, because they are nearly of the same size, very 

 similar in internal structure, accustomed to artificial domes- 

 tic life, and to the society of each other from birth up- 

 wards. There is a similar facility in some birds belonging 



♦ Tiie principle has not escaped common observation : it is t Apressed in 

 the English word breed, and in the German gattung (species), which signifies 

 copulation. 



f Biiii ON, by Wood ; v. 4. p. 200, 205. 



