Fascinating. Strong Mothers Bear More Sons:
In an Ethiopian community facing hard physical work and regular food shortages, British researchers have found that strong mothers appear more likely to bear sons than daughters.The discovery suggests that during tough times, mothers’ bodies somehow manipulate the sex of their children to maximize the chance of successful reproduction, anthropologists Dr. Ruth Mace and Mhairi Gibson write in the Proceedings of the Royal Society of London.
This is because bringing a boy to term is more physiologically demanding on the mother, as boys grow faster in the womb and tend to be bigger, Mace said. And in biological terms, undernourished males might have more trouble finding a partner.
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The link between muscle mass and male children was particularly marked, they say. Among women whose arm muscle was less than 33 centimeters, three boys were born for every five girls. In those with the biggest muscles — over 38.9 centimeters — eight boys were born for every five girls.Although this phenomenon has been seen in wild animals, this is the first time it has been reported in humans, Mace said.
For metric-impaired Americans, 33 cm is 13 inches, and 38.9 cm is over 15 inches — which is huge for a woman.