48 TABOO AND GENETICS 



exactly the same. One lives in 4 to 8% salt 

 water, the other in 25% or over. If, however, 

 the fresh-water variety is put in the saltier 

 water with the salt-water variety, all develop 

 exactly alike, into the salt-water kind. Like- 

 wise, if the salt-water variety is developed in 

 fresh water, it assumes all the characteristics 

 of the fresh-water kind. Thus the addition or 

 subtraction of a single chemical agent — common 

 salt — makes all the difference. 



If this basis for sex is single, it is represented 

 by the male plumage in domestic birds, the 

 secretions from the sex-glands acting as modi- 

 fiers. But a great deal of evidence has been 

 produced to show that the genetic basis, in man 

 and some other forms at least, is double. That 

 is, we must think of two genetic bases existing 

 in each individual — each representing one of 

 the two types of secondary sex characters. The 

 primary sex (i.e., the sex glands) would then 

 determine which is to express itself. In the 

 domestic birds described above, the male type 

 of body appears in the absence of the ovarian 

 secretion, and the female tj^pe in its presence. 

 In man and the more highly organized mam- 

 mals, we must use " secretions " in the plural, 

 since a number of them, from different glands, 

 act together in a " complex." Goodale, experi- 

 menting with birds, was unable to definitely 

 decide whether the basis for sex was single 



