My entire life I knew I would be a mother, and I knew I would have a girl. I don’t know how I knew it, but this was something I was convinced of from the time I was small. Sure enough, when I became a mother, I did in fact have a girl, and here’s why. Because female mammals can choose the sex of their offspring. Scientists say – in a shocking new discovery – that we female mammals choose our mates based on physiologically sensing that their sperm will produce the resulting offspring we desire.
“You can think of this as being girl power at work in the animal kingdom,” says Joseph Garner, associate professor of comparative medicine at the Stanford School of Medicine. Garner is the lead author of the study proving this evolutionary theory. He says, “We like to think of reproduction as being all about the males competing for females, with females dutifully picking the winner. But in reality females have much more invested than males, and they are making highly strategic decisions about their reproduction based on the environment, their condition and the quality of their mate. Amazingly, the female is somehow picking the sperm that will produce the sex that will serve her interests the most: The sperm are really just pawns in a game that plays out over generations.”
To come to this conclusion, researchers analyzed 90 years of breeding records from the San Diego Zoo, and the results applied across 198 different species. The theory goes that women who want more grandchildren produce sons, and women who want fewer grandchildren produce daughters. How, physically, do females control the sex-selection process? Garner says he isn’t exactly sure, “though one theory holds that females can control the “male” and “female” sperm, which have different shapes, as they move through the mucous in the reproductive tract, selectively slowing down or speeding up the sperm they want to select.”
Garner notes there is data to support his findings as holding true in the human population, as well. For instance, he says, “in polygamous societies, the top-ranking wife is much more likely to have a son than the lower-ranking wife (the son holds the economic power in the family). And a study of 400 U.S. billionaires, published in 2013, found that they were more likely to have sons than daughters — presumably, the scientists hypothesized, because sons tend to retain the family’s wealth.”
For more on this fascinating discovery, visit Stanford.edu.
Photo credit: iStock
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