D.— ZOOLOGY 99 



amongst their white neighbours if and when the standards of personal and 

 public hygiene of the two sections of the community differ at all markedly. 

 Usually the standards of the coloured peoples are lower, and for this 

 reason abortion and miscarriage amongst them are more frequent. It is 

 affected by social status for the reason that in general the higher the status 

 the more generous is the environment, the smaller the family and the 

 greater the attention given to the child-bearing mother. The differences 

 between the social classes in respect of the sex ratio are to be related to 

 differences in the incidence of abortion. In a class-less state with a high 

 standard of living, the sex ratio will be uniformly high. The relation 

 between primary and secondary sex ratios is unaffected when infantile 

 mortality generally is high, and is disturbed when this is low for the reason 

 that high infantile mortality indicates the action of death-dealing diseases 

 of such potency as to overwhelm any difference in respect of viability on 

 the part of male and female. Such diseases kill both boys and girls with- 

 out discrimination. Under these circumstances, since both boys and 

 girls are removed, the sex ratio is unaffected. Low infantile mortality, 

 on the other hand, implies relatively mild attacks of disease-provoking 

 agencies which discriminate between male and female, leaving the female 

 untouched in virtue of her greater constitutional strength, but removing 

 the weaker male to yield a low sex ratio. Since, in this respect, the 

 sexes are so different, it follows that in the case of an ailing male child 

 the doctor is called upon to treat not only the pathological condition but 

 also the condition of maleness. 



The disturbance of the secondary sex ratio that is commonly supposed 

 to be associated with protracted war is not so easily explained. If it is 

 indeed the case that there is a real and significant rise in the sex ratio 

 associated with war then the explanation would seem to be that under 

 the conditions that exist the incidence of abortion and miscarriage falls. 

 It has been suggested that the lengthy absences of husbands with a 

 consequent reduction in the frequency of intercourse and therefore of 

 pregnancy mean rest and repair for the wives and the attainment of a 

 greater degree of physiological fitness. This of course would lead to a 

 lowering of the incidence of abortion in those cases in which pregnancy 

 did occur. Furthermore, war is associated with a rise in the marriage 

 rate, and this means relatively more first babies, and the high sex ratio 

 that obtains amongst such. However, this suggestion of a modification 

 of the secondary sex ratio associated with war demands further examina- 

 tion, for it has been shown that if the sex ratio of a population is traced 

 over a long period of time it is usual to find evidences of a definite secular 

 trend, upwards in some countries, downwards in others (Russell, 1936), 

 so that it may be that the sex ratio associated with war can be evaluated 

 only when it is studied in relation to this movement of the sex ratio 

 generally which can be seen only if 100 or more years are reviewed. 



In explanation of the observed inequality in mortality and longevity 

 of the sexes in man a number of suggestions have been offered. To 

 account for the particularly high mortality of male infants around the 

 time of birth emphasis has been placed upon size differences between the 

 sexes. Typically the male is the larger, with the bigger head and with 



