Dr Obel used a set of data collected between 1989 and 1992. Duringthat period 8,719 expectant mothers were asked to fill in questionnaires thatinquired, among other things, about their level of stress. Dr Obel found thatthe more stressed a mother had been, the less chance she had of having givenbirth to a boy. Only 47% of children born to women in the top quartile ofstress were males. That compared with 52% for women in the bottom quartile. DrObel suspects the immediate cause is that male pregnancies are more likely tomiscarry in response to stress than female pregnancies are, especially duringthe first three months. However, that is difficult to prove. More intriguing,though, is the ultimate cause, for he thinks it might be adaptive, rather thanpathological.
That is because the chances are that a daughter who reachesadulthood will find a mate and thus produce grandchildren. A son is a differentmatter. Healthy, strapping sons are likely to produce lots of grandchildren, byseveral women-or would have done in the hunter-gatherer societies in which mosthuman evolution took place. Weak ones would be marginalised and maybe evenkilled in the cut and thrust of male competition. If a mothers stressadversely affects the development of her fetus then selectively aborting boys,rather than wasting time and resources on bringing them to term, would makeevolutionary sense.
That, in turn, would explain why women in rich countries, who areless likely to suffer from hunger and disease, are more likely to give birth tosons. That this likelihood is, nevertheless, falling suggests that rich womens lives maybe more stressful than they used to be.
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