28 THE EVOLUTION OF SEX. 



Differentiated Unisexuality; and regards them as parallel to the stages 

 of historic evolution. Even for the first stage, however, when the 

 elements are still very primitive, he would not allow the accuracy 

 of the terms neutrality or indifference. The elements in both sexes 

 are almost similar, but yet their future fate has been decided. 



Sutton has also emphasized his conviction that in the individual 

 development a state of embryonic hermaphroditism obtains, and 

 maintains that one set of elements predominates over the other in 

 the establishment of the normal unisexual state. Ploss and others 

 take up a similar position in regard to an early hermaphrodite state. 

 It can only be concluded that the higher the organism is in the 

 series the earlier is its sexual fate sealed; and that it is only in 

 lower vertebrates, and among backbonelesss animals, that we can 

 speak of prolonged neutrality of sex, or embryonic hermaphroditism. 



II. Answers to the Question — What Determines Sex? — 

 To the question what settles whether an organism shall develop into 

 a male or into a female, many and varied answers have been given. 

 At the beginning of the last century, the theories of sex were esti- 

 mated at so many as five hundred, and they have gone on increas- 

 ing. It is evident that even an enumeration of these is not pos- 

 sible, nor is it indeed desirable. As in so many other cases, our ideas 

 respecting the determination of sex have been looked at in three 

 different ways. For the theologian, it was enough to say that " God 

 made male and female." In the period of academic metaphysics, 

 still so far from ended, it was natural to refer to " inherent proper- 

 ties of maleness and femaleness' ' ; and it is still a popular ' ' explana- 

 tion " to invoke undefined "natural tendencies'" to account for the 

 production of males or females. This mode of treatment, it need not 

 be said, is being abandoned by biologists. It is recognized that the 

 problem is one for scientific analysis; thus the constitution, age, nutri- 

 tion, and environment of the parents must be especially considered. 

 These investigations, which are mainly restricted to observation and 

 statistics, will be first noticed; the more experimental researches, and 

 the general conclusions, will be discussed in the next chapter. That 

 the final physiological explanation is, and must be, in terms of pro- 

 toplasmic metabolism, we must again, however, remind the reader 

 (see p. 22, note). 



III. The theory that there are two kinds of ova, respectively 

 destined to develop into males or females, is more than a mere beg- 

 ging of the question. The constitution of the ovum is undoubtedly 

 a fact of primal importance, but we must also recognize that what is 

 virtually decided at this early stage may be counteracted by later 

 influences of an opposite character. The hypothesis of two kinds of 



