Boy or Girl? The Answer May Depend on Moms Eating Habits
Ok, I will file this story under "Teaching", since I do talk about the determination of sex in my Child Development course. But the idea that food intake determines the child’s sex has always been part of the culture belief of Chinese. It’s interesting to read the 200 comments after the article.
Boy or Girl? The Answer May Depend on Moms Eating Habits - New York Times Blog
The data is based on a study of 740 first-time pregnant mothers in Britain who didn’t know the sex of their fetus. They provided records of their eating habits before and during the early stages of pregnancy, and researchers analyzed the data based on estimated calorie intake at the time of conception. Among women who ate the most, 56 percent had sons, compared with 45 percent among women who ate the least. As well as consuming more calories, women who had sons were more likely to have eaten a higher quantity and wider range of nutrients, including potassium, calcium and vitamins C, E and B12. There was also a strong correlation between women eating breakfast cereals and producing sons.
Among the comments, there is Dr. Zuk:
As an evolutionary biologist (and guest blogger here a while back, thanks for the opportunity, TPP!), I wanted to explain why biologists think it might be adaptive for females – human or animal – to have male offspring under some circumstances and females under others. In many, though not all, species, males compete for access to females; some males triumph and monopolize the available mates, and a lot of males never have an opportunity to mate at all. Females, on the other hand, can generally find a male and become pregnant.
This means that a mother producing a daughter is assured, evolutionarily, that her genes will be passed on at least in a modest number of descendants. A mother producing a son, however, may either have a large number of descendants, if that son is successful at competition, or none at all, if that son is a loser. Mothers in good condition (from eating a good diet, presumably) would therefore do well to produce a son. Mothers in poor condition risk producing a weedy male that cannot compete with rivals. But if that mother has a daughter in less-than-tiptop condition, she will still probably find a mate, so selection is expected to favor this kind of bet hedging over evolutionary time.
This hypothesis was developed back in the 1970s by biologists Bob Trivers and Dan Willard, and it has received some support in studies of animals like red deer and wild sheep. The mechanism isn’t clear; as some readers have noted, it must work via differential retention of male vs. female embryos at an early stage, since it’s the father’s sperm that determines sex. Does the hypothesis apply to humans? Hard to say. Our ancestors were probably not monogamous, so the opportunity for this kind of selection was there. But we don’t have the kind of all-or-nothing mating system shown by the deer, in which males provide no parental care and can be completely shut out of mating in a particular season. Nonetheless, it’s an interesting study, and for me provided yet another example of how close we are to our mammalian relatives.
Not everybody was a biologist, of course. Knightlaw said:
Personally, I was not eating any food “during the time of conception” of my two children. I think my husband might have thought that was kinda distracting, you know?
To which the blogger replied:
FROM TPP — Conception doesn’t occur at the exact moment of intercourse. I believe it can occur up to 72 hours or so after sex.