ARE SPECIES STABLE? 35 



authenticated case of domestic races being sterile 

 when crossed, a fact which he considers extraordi- 

 nary, considering the great difference between do- 

 mestic breeds of dogs, fowls, pigs, etc., and the very 

 slight differences between natural species which are 

 sterile inter se. So far, then, as experiments on do- 

 mestic animals are concerned, the evidence seems 

 to indicate that no amount of ordinary accumula- 

 tion of variations is able to produce forms so differ- 

 ent as to be infertile when crossed. If, then, this be 

 accepted as a criterion for specific distinction, there 

 is no case on record where there has been even an 

 approximation toward the production of a new 

 species. 



Possibly the human race may be a partial case in 

 hand. The races of men are to-day pretty univer- 

 sally admitted to be simple varieties of a single 

 species. The different races are well known to be 

 fertile when crossed, a fact attested by half-breeds 

 of all sorts. But it frequently appears that half- 

 breeds form a somewhat weak race, having lost the 

 vigor of either parent. Particularly is this true 

 when half-breeds intermarry. It is stated by Broca 

 that in some cases the fertility is not kept up for 

 many generations, unless the pure blood of one of 

 the parents is introduced. This is true he says of 

 the cross between the Australian and European 

 races. It is frequently stated that mulattoes are 

 not very fertile, and soon become sterile unless the 

 pure blood of one of the races is once more intro- 

 duced. But all of these statements are denied. 

 Others who have studied the matter claim that all 



