68 The Science of Life. 



to the practical importance of the question in connection 

 with man and domesticated animals. The number of 

 speculations on this matter and on the general nature 

 of sex has been well-nigh doubled since Drelincourt, in 

 the last century, brought together two hundred and 

 sixty-two "groundless hypotheses ", and since Blumen- 

 bach quaintly remarked that nothing was more certain 

 than that Drelincourt's own theory formed the two 

 hundred and sixty-third. Subsequent investigators 

 have, of course, long ago added Blumenbach's to the 

 list, which is still mounting up. 



It must not be supposed that all the many theories 

 as to the determination of sex have been merely arm- 

 chair musings, for numerous experiments and observa- 

 tions have been made by breeders and physicians. 

 What vitiates almost all, however, is the fatal defect, 

 that, while attending to one factor, e.g. the relative age 

 of the parents, the relative vigour of the parents, the 

 nutrition of the embryo, no sufficient care has been 

 taken, and in most cases no attempt has been made, to 

 eliminate other probably operative factors, either ex- 

 perimentally or by statistical devices. There is at least 

 a strong probability, that every ovum of an organism 

 with separate sexes has from the first a predisposition 

 towards becoming a male or towards becoming a 

 female, but that this predisposition may be altered by 

 the nutrition of the ovum, by changes in the period 

 before fertilization, by fertilization itself, and by en- 

 vironmental influences (of nutrition, temperature, &c.) 

 during embryonic or even larval life, until the period 

 is reached when the sex of the offspring is fixed. We 

 cannot, and need not, discuss the problem here (see 

 revised edition of The Evolution of Sex, 1899); we wish 

 simply to point out the probability that many factors 

 determine the result, and that insistence upon one 

 alone (e.g. Prof. Schenk's insistence upon the diet of 

 the mother) is almost certain to be fallacious. 



