COMPARISON OF MALE AND FEMALE SEXES. 965 



803. Of Sex. The conditions on which the differentiation of sex immedi- 

 ately depend are as yet extremely obscure. M. Marc Thury, 1 who has paid 

 great attention to this subject in cattle, has arrived at the conclusion (which, 

 however, demands much confirmatory evidence for its establishment) that 

 the sex of the progeny of a particular act of sexual intercourse is dependent 

 upon the period of menstruation (in women), or of rut (in animals), at 

 which the impregnation of the ovum takes place. If this occur at the 

 commencement of the period, the offspring will invariably be a female ; if 

 towards the close, male : the cause of the difference being the more ad- 

 vanced stage of maturation of the ovum in the latter case, owing to its 

 having been for a longer period exposed to the warmth of the body of the 

 mother. Ploss 2 attributes the sex of the child to the quantity and 

 quality of the nutriment received by the mother during pregnancy, since 

 from a review of various countries, and a comparison of the relative num- 

 bers of males and females born, he finds that when the food is abundant 

 and plentiful, the proportion of females rises; whilst, under opposite condi- 

 tions, males are most frequent. In mountainous countries the number of 

 males also increases relatively. Treussen (loc. cit.), however, on the other 

 hand, considers that better and more abundant food is required by the 

 mother for the protection of males. There is strong statistical evidence that 

 the relative numbers of Males and Females are in some way influenced by 

 the relative ages of the parents. The following table expresses the average 

 results collected by M. Hofacker 3 in Germany, and by Mr. Sadler 4 in 

 Britain ; between which it will be seen that there is a very striking general 

 correspondence, although both were drawn from a too limited series of ob- 

 servations. The numbers indicate the proportion of Male births to 100 

 Females, under the several conditions mentioned in the first column : 



Hofacker. Sadler. 



Father younger than Mother, . 90.6 Father younger than Mother, . 86.5 

 Father and Mother of equal age, 900 Father and Mother of equal age, 94.8 



Father older by 1 to 6 years, . 103.4 



" " 6 to 9 " . 1-24.7 



" " 9 to 18 " . 143.7 



" " 18 and more, . 20U.O 



Father older by 1 to 6 years, . 103 7 



' 6 to 11 " . 126.7 



11 to 16 " . 147.7 



16 and more, . 163.2 



From this it appears, that the more advanced age of the Male parent has 

 a very decided influence in occasioning a preponderance in the number of 

 Male infants; and this tallies with the fact, that taking the average of the 

 whole of Europe, over which (as a general rule) the state and customs of 

 society bring about a decided preponderance of age, among married couples, 

 on the side of the husband, the proportion is about 106 males to 100 females. 

 This does not hold good, however, in regard to illegitimate offspring, the 

 parents of which may generally be presumed to be more nearly on an 

 equality in this respect ; and it is curious that the proportion of these has 

 averaged 102.5 males to 100 females, in places where the proportion of legit- 

 imate births was 105| males to 100 females. We are not likely to obtain 

 data equally satisfactory in regard to the influence of more advanced age on 

 the part of the Female parent, as a difference of 10 or 15 years on that side 

 is not so common. If it exist to the same extent, it is probable that the same 

 law would be found to prevail in regard to Female children born under 

 such circumstances, as will be stated ( 804) with respect to the Male, 

 namely, that the mortality is greater during embryonic life and early 



1 Notice on the Law of Production of Sexes, etc., Pamphlet, 1863. 



2 Henle and Meissner, 1860, p. 210. 



3 Annales d'Hygiene, October, 1829. 4 Law of Population, vol. ii, p. 343. 



