xliv GENERAL INTRODUCTION. 



potent, while animals that are the offspinng of more or 

 less intimately related parents are interbred, — when the 

 parents have been closely related for several generations 

 they g.re said to be grossly inbred. There is, however, 

 nothing absolute about either prepotency or inbreeding, 

 they ai'e relative terms. An animal (male or female) may 

 be prepotent in some respects and not in others (and this 

 whether the prepotency has been acquired by inbreeding 

 or through a " sport '^), or prepotent with one mate and 

 not with another, prepotent one year but not the next, 

 because pi'epotency is of necessity subject to the influence 

 of variation and reversion, and also doubtless to nutrition 

 — more especially of the germ-plasm prior to fertilisation. 

 Prepotency, when associated with useful chai-acters, is 

 highly beneficial, while inbreeding is often a doubtful 

 heritage. Nature only tolerates inbreeding up to a cer- 

 tain point, for while it may assist in perpetuating useful 

 characters by inducing prepotency, it often does this at 

 the expense of vitality — it may be of fertility as well. 

 It is conceivable that inbreeding has played an important 

 part in the extinction of species ; it has undoubtedly been 

 the means of deteriorating, if not actually destroying, 

 many of the breeds and varieties artificially produced. 

 A carefully conducted series of experiments, showing the 

 effects of inbreeding on various kinds of animals, is still 

 greatly needed. When such a series is forthcoming it 

 will be time enough to discuss at length the physiology 

 of inbreeding. Still, something further may well, at this 

 stage, be said about inbreeding and prepotency. It will, 

 I think, be admitted that prepotency may be due to 

 either natural or artificial causes, or be partly due to 

 both. In nature, prepotency may (1) arise spontaneously 

 and abruptly along with sports in one or more directions, 

 or gradually with the help of natural selection — whether 

 it may arise as a special variation apart from a sport, as 

 Mr. Gal ton seems to think, I am not prepared to say ; 

 (2) it may be gradually acquired when a few individuals 

 of any given species or variety are so isolated that in- 

 breeding is inevitable. Artificial prepotency may be 



