RELATING TO SECONDARY SEXUAL CHARACTERS. 63 



ences are involved. The result may seem to mean that the secondary 

 sexual characters themselves have been acquired historically by a single 

 evolutionary step, and that in consequence the opportunity for selec- 

 tion to have accomplished such a result has been enormously facilitated. 

 Such an argument rests, however, as we know to-day, on a false inter- 

 pretation of Mendelian heredity. What the evidence really shows is 

 that one or two genes if present cause the testes to produce some 

 substance that prevents the cock-feathering from developing. The 

 genetic complex may require a hundred or a thousand or more special 

 factors that are directly and indirectly concerned with the development 

 of the cock-feathering, but one or two other factors may suffice to block 

 this machinery; or, to change the metaphor, these dominant factors 

 may be no more than so much sand poured into the clock. The clock 

 may have been slowly built up historically by many contributory 

 "factors," but a little sand may spoil its activity. Similarly in the hen 

 something produced by the ovary prevents the fullest possible genetic 

 action from taking place. Here at present we do not know whether a 

 single factor or a hundred " special" factors are necessary to produce 

 such an inhibition, but if, as one would like to suppose, it is the same or 

 partly the same genes involved in the ovary, and in the testes of hen- 

 feathered males, then a relatively few, one or two, factors will suffice 

 to bar cock-feathering from the female. 



In a case like the clover butterfly, where the genetic relations work 

 out on the theory of one pair of factors that produce two types of 

 females and one type of male, it seems more reasonable to infer that 

 such a difference has not been slowly acquired by many smaller muta- 

 tional changes, because the two types are not adapted to live under 

 two different environments for which their differences fit them respec- 

 tively, but to live in the same environment. It has never been claimed, 

 so far as I know, that these two types of females have arisen through 

 some males preferring one, some another kind of female, so that even 

 although it may seem probable that the genetic situation is simple, 

 the simplicity can not be turned to the advantage of the theory of 

 sexual selection. It is unnecessary to discuss further the origin of the 

 factor or factors suppressing the development of one type in the male 

 or the probability of the multiplicity of such factors. In the case of 

 such species as Papilio memnon and P. polytes, with three types of 

 females, the situation is the same as above, with the addition of the 

 theory of mimicry, that " explains" some advantage accruing to each 

 type of female. Since the latter is only a form of natural selection, 

 we are not further concerned with the change here. Punnett's excellent 

 treatment of the problems involved in his recent book on mimicry 

 brings the subject down to date. 



Meager as is the genetic and surgical evidence at present, it is enough 

 to show that only by further work along these lines can we hope to lay 



