GENERAL INTRODUCTION. XXI 



less be useful. On the great and all-important subject 

 of " variation " my experiments have no direct bearing, 

 but they justify my referring shortly to reversion, pre- 

 potency, and inbreeding. 



1. Reversion. — Nearly ten years have elapsed since Mr. 

 Galton's work on 'Natural Inheritance' appeared, and 

 yet but few breeders seem to fully realise that the off- 

 spring often take not so much after their immediate as 

 after their less remote ancestors, that probably in all 

 cases there is more or less marked " regression towards 

 mediocrity." If there is any truth in evolution, it is 

 extremely probable that the protoplasmic units of which 

 any given individual is composed have to encounter and 

 overcome during development countless numbers of cor- 

 responding units representing the component parts of a 

 long series of lost ancestors. If for any reason units 

 representing the latest development of the race or variety 

 — the latest variations, mental or physical — are unable to 

 assert themselves, are lacking in power or stability, 

 older and more potent units will take their place, and thus 

 lead to regression or reversion. The reversion may be 

 to recent, remote, or intermediate ancestors, and the 

 tendency will in most cases be to revert to "sports'' 

 that here and there mark the route along which the 

 development has proceeded. 



Any two individuals ma,y be likened to two pictures. 

 Even if portraits by the same artist of two members of 

 the same family, they would differ in form as well as in 

 colour. Were it possible to blend two such pictures into 

 one, the result would be a picture differing from the 

 originals, but not necessarily intermediate between them. 

 Some of the pigments (having been differently made up) 

 might neutralise each other, and latent colours — colours 

 which, for some reason or other, had been obscured in 

 one or both of the originals — might come to the surface. 

 There would be a loss of the characters which served to 

 distinguish the individuals from each other and the rest 

 of their relations, but yet there would doubtless be hints 

 here and there of the originals, and, because of the blend- 



