GENERAL INTRODUCTION, xlv 



slowly induced by inbreeding-, but I doubt if prepotency 

 can be rapidly produced artificially apart from inbreeding. 

 It may therefore be taken for granted that interbreeding 

 (1) induces prepotency by fixing the characters of the 

 particular variety selected ; (2) in as far as it prevents or 

 at least limits intercrossing it diminishes the chance of 

 reversion on the one hand, and restricts the range of 

 variation on the other, thus tending to maintain un- 

 diluted the distinctive characters of the type. But it must 

 be added, inbreeding, while keeping the " blood '' pure, 

 tends to weaken it by diminishing the vitality of the breed. 

 Prepotency, on the other hand, however acquired, alike 

 in nature, on the farm, or in the dovecote, tends to arrest 

 or neutralise the swamping effects of intercrossing. 

 Some breeders say they can produce a horse so pre- 

 potent, so fixed by interbreeding, that it will produce its 

 like however mated. A famous breeder of high-class 

 ponies once Ijoasted that he had a filly so prepotent 

 through inbreeding that though she was sent to the best 

 Clydesdale stallion in Scotland she would throw a colt 

 showing no cart blood — provided the Clydesdale was not 

 also the product of inbreeding. Nature might make a 

 similar boast, the essential difference being that while in 

 the one case misfits and " weeds " are usually preserved, 

 in the other they are ruthlessly destroyed and buried out 

 of sight — in the struggle for existence the inbred 

 " weeds " go to the wall. 



The careful observer soon recognises that all through 

 animated nature the greatest effort is made to secure 

 rejuvenescence. In the animal kingdom, and largely in 

 the vegetable also, this renewal of youth, without which 

 vigorous life is impossible, is secured by intercrossing or 

 cross-fertilisation."^ The ingenuity displayed by plants 

 and animals to secure cross-fertilisation is simply mar- 



* Tliere is obviously no real difference between cross-fertilisation and 

 intercrossing. Whether we interbreed or intercross, engage in " line " 

 breeding or "cross" breeding, we are making use of cross-fertilisation. 

 Further, I may add the difference between intercrossing and hybridising 

 is one of degree, not of kind. 



