1899] E WART'S PENYCUIK EXPERIMENTS 207 



genetically) older species is usually dominant, a recently-formed aberra- 

 tion may be prepotent over the type from which it has but recently 

 arisen [Trans. Entom. Soc. London, 1898, pp. 17-42]. Mr. Galton 

 holds a similar view, and regards prepotency as itself " a heritable 

 sport or aberrant variation." 



While in no way overlooking or combating this position, Prof. 

 Ewart lays emphasis on the second, and probably more frequent origin 

 of prepotency, as the result of inbreeding. " Some breeders say that 

 they can produce a horse so prepotent, so fixed by interbreeding, that 

 it will produce its like however mated " ; and there is much evidence 

 to show that, of two parents, the more inbred — up to a certain limit of 

 stability — is likely to have the greater influence on the offspring. 



A few examples will suffice. An inbred Dalmatian dog is likely 

 to be prepotent over a collie, a Basset hound over the ancestral blood- 

 hound, an inbred hornless Galloway over one of the long-horned High- 

 land cattle, and Semitic over English blood. 



As inbreeding is frequent in nature, 'especially among gregarious 

 and isolated groups, and as it tends to develop prepotency, we are able 

 to understand better how new variations may have persisted in the 

 course of evolution. The old difficulty that new variations would tend 

 to be swamped or levelled down by intercrossing was met by Eomanes 

 and Gulick in their theory of Isolation, some form of which was sup- 

 posed to limit the range of effective intercrossing. But as this theory 

 has not been sufficiently demonstrated, Prof. Ewart justly insists on 

 the importance of prepotency as an evolutionary factor. But may it 

 not be said that the prepotency which results from inbreeding is itself 

 the result of some form of Isolation ? Even preferential mating is a 

 form of Isolation in the wide sense. 



Just as in connection with the determination of the sex of the 

 offspring, which may be the resultant of many factors, so in the case 

 of prepotency the result which may be reasonably predicted does not 

 always come off, the natural prepotency being counteracted by other 

 influences due to vigour, age, nutrition, and environment. 



The unpredictable nature of the results is well illustrated in Prof. 

 Ewart's observations on crossing wild and tame forms. When white 

 doe-rabbits were paired with wild brown bucks, the progeny resembled 

 the wild form ; but of the nine zebra-horse hybrids only two take 

 predominantly after the wild parent. The experiments which others 

 have made on butterllies suggest the conclusion that the older form 

 will tend to be dominant, but this may simply mean that the hybrid- 

 isation has evoked reversion. We seem to have securer evidence as 

 to prepotency in such a case as the Basset predominant over the 

 bloodhound from which it is derived. 



The experiments of Standfuss tended to the conclusion that in 

 hybridising the male parent was prepotent over ( the female; the young- 

 forms were at first liker the female (which may be in part due to the 



