GENERAL INTRODUCTION. xH 



of new forms which were either sports or the product of 

 discontinuous variation, it does not follow reversion never 

 occurs. I think it must be admitted the pigeon and 

 rabbit experiments go a long way towards proving the 

 fact of reversion, and the more I contemplate my zebra 

 hybrids the more convinced I am that they are neither 

 new creations in the strict sense of the terra, nor yet 

 intermediate forms ; and if they are neither the one nor 

 the other, they must be more or less accurate restorations 

 of their comparatively remote ancestors. The heredity 

 problem is sufficiently difficult as it is, but if we are 

 debarred from invoking the assistance of the reversion 

 hypothesis it will become hopelessly incomprehensible. 

 In conclusion, I may point out that even from a practical 

 point of view reversion is of extreme importance, for it 

 indicates how in some cases varieties and breeds which 

 have through inbreeding undergone senile degeneration 

 may be regenerated without the loss of their best and most 

 prized characteristics. 



2. Prepotency and Inhreeding.' — More than thirty years 

 ago Darwin recognised that " the subject of prepotency 

 is extremely intricate." It must be admitted this intri- 

 cacy continues^ and is likely to continue until the laws of 

 heredity are better understood. Amongst the other dif- 

 ficulties we have to contend with, there is the impossi- 

 bility of determining the amount of prepotency in any 

 given race or individual, and the fact that prepotency 

 may altogether escape detection, or exist through gross 

 inbreeding where it is least expected. The leader of any 

 given wild herd may be decidedly prepotent, but unless 

 he is mated with the members of some other herd pre- 

 senting different characters the prepotency may escape 

 notice; and again, the members of any given section of a 

 species may, through inbreeding, be highly prepotent, 

 while the members of the other sections (owing to abun- 

 dant facilities for intercrossing) may be non-prepotent. 

 What is true of individuals may be true of races and 

 varieties. The Jews, as a race, are more prepotent than 

 the English — are better or purer bred ; but the prepo- 



d 



