Another could be due to seasonal variations in the availability of food. One explanation may be the evolutionary necessity of keeping the overall sex ratio close to the 50:50 norm. It was thought that nature favours conception of boys from September to November and girls from March to May. In hard times, it should in theory be more advantageous to give birth to males rather than females because females need more energy than males because of the effort of producing eggs and being pregnant.Ī study in Italy has, for instance, found that couples are more likely to conceive a boy in autumn, while those who want a girl should conceive in spring. As a result of this increased risk for males, nature has compensated by skewing the birth rate in favour of boys, or so it was believed.Īnother could come about if food is at risk of being in short supply. One exception is if male embryos and newborn boys are more likely to die prematurely.
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