IxXXvi GENERAL INTRODUCTION. 



venting the confusiou that would result from free inter- 

 breeding. Sterility has doubtless been acquired in some 

 cases slowly, in others abruptly, but how it has been 

 acquired it is impossible in most cases even to guess. 

 Intersterility has not hitherto been acquired by any of 

 our breeds of pigeons, or dogs, or horses, or cattle ; but 

 this may be due to their comparative youth, or to the 

 artificial conditions under which they were produced and 

 live. Romanes believed that the moment any variety 

 became sterile, or nearly sterile, with other varieties and 

 with the parent species, that same moment it mounted 

 the first rung of the ladder leading to specific rank. That 

 sterility between varieties would improve their chances of 

 developing into species is sufiiciently evident ; but that ia 

 the majority of cases sterility, however acquired, is the 

 starting-point — the password — towards specific distinction 

 has not been established. 



Mr. Galton thinks prepotency is a highly heritable 

 sport. Sterility may also be a sport, an aberrant varia- 

 tion, not due to or associated with any demonstrable 

 structural changes. 



It seems to me experiments might show that preferen- 

 tial mating accounts for much. Horses are quite re- 

 markable for their strong likes and dislikes, and the same 

 may be true of many other animals. Preferential mating 

 (apart from sterility) might, through inbreeding, gradu- 

 ally build up distinct more or less intersterile prepotent 

 varieties. 



That intersterility may occur without any apparent 

 change in the reproductive organs is extremely probable. 

 This is suggested by the fact that a large number of wild 

 animals invariably fail to breed— are virtually sterile — 

 in confinement. But intersterility seems to arise without 

 even any appreciable change in the environment, and it 

 is well known that a not inconsiderable number of animals, 

 though perfectly formed, are quite sterile ; or, what is 

 even more suggestive, sterile with some individuals but 

 not with others, or sterile until the system receives some 

 sudden shock, or until changes are gradually produced by 



