EVOLUTION 453 



that they do not, but the high correlation which exists 

 between the reproductive and other organs in the indi- 

 vidual, and the influence which change of environment 

 has on the development of certain organs, at least in 

 some types of life, to say nothing further of its influence 

 on fertility (see pp. 448, 488), should, I think, lead us to 

 hesitate before accepting the view that environment only 

 influences the growth of the individual proceeding from 

 the zygote, and not the characters associated with heredity 

 in the gametes from which the zygote proceeds. 



(ii.) Is there any form of sexual selection among the 

 gametes themselves ? As a rule there are an indefinite 

 number of spermatozoa, and possibly a considerable 

 number of available ova, even when only a comparative 

 few zygotes come into being. It is quite possible that 

 pangamy is not the rule, but that a spermatozoon with 

 definite values of its characters has more chance than its 

 fellows absolutely, or relatively to a particular group of 

 ova, i.e. preferential or assortative mating may exist even 

 for such a conjugation. In this way extreme normal or 

 even abnormal variations in the gametes may under new 

 circumstances attain a conjugation, which under the usual 

 environment would not occur at all or only with extreme 

 infrequency. Thus we might expect the more remark- 

 able deviations from type to occur when very diverse 

 groups of gametes are mingled. In this case the zygote 

 may lead to an individual having characters of the two 

 parental races, not closely akin to the individual parental 

 types. Wide divergence from the individual parental 

 type is usually attributed to reversion or atavism, but as 

 often as not the divergence from the individual parental 

 type is noted, but not the agreement with a definite 

 ancestor. Atavism is said to be most common in 

 hybrids ; it is possibly explicable by extreme normal or 

 even abnormal variations in the gametes being the fittest 

 to attain conjugation under the altered circumstances. 



(iii.) Besides the influence of environment on the 

 gametes and of sexual selection on the zygote, is it con- 

 ceivable that anything else can be influential in determin- 



