Think being able to choose your child's gender is some crazy scientific advancement that'll happen far, far in the future? Nah. Turns out, animals have been doing it for years.
New research out of Stanford University found that parents—especially mothers—have some influence on the sex of their babies, NBC News reports. The study, published in the journal PLOS ONE, looked at breeding data of more than 2,300 animals and their offspring (from 198 species of mammal) from the San Diego Zoo.
"This is one of the holy grails of modern evolutionary biology—finding the data which definitively show that when females choose the sex of their offspring, they are doing so strategically to produce more grandchildren," says Joseph Garner, Stanford professor and senior author of the study.
In fact, the findings show it’s mostly mamas that are making the strategic decision on gender, all in the name of adapting to evolution. According to the study, when a mother mostly gave birth to boys, those sons had 2.7 times more offspring than males whose moms had a more equal number of boys and girls. By the same token, the daughters of moms who mostly had girls produced 1.2 times as many offspring as daughters whose moms had an equal mix of boys and girls. "We are talking about a transgenerational game of poker, where the grandchildren are chips, and the cards are sperm," Garner says.
But exactly how dominant mamas influence gender is still a mystery. Some researchers suggest it could have something to do with egg development, hormones, or even a substance moms secrete during fertilization to encourage certain sperm, according to the article.
In any case, Garner tells NBC the study results relate to humans as well. He pointed to a survey of 400 U.S. billionaires that found they were more likely to have boys than girls. Other research showed how higher-ranking wives in a polygamous relationship were also more likely to give birth to a son. "Humans are definitely responding to ancient cues and modern cues," Garner says. "Does that mean that humans can to a certain extent, control the sex of their offspring? It seems as if they can, and it seems as if that works to the extent of 60 to 70 percent."
And, here we thought it was all about our diet. Or sex position. Or time of conception. But good ol’ animal instincts? We should have known.
Lesley Kennedy writes for the Online Shopping Report at ShopAtHome.com. Follow ShopAtHome on Twitter @shopathome and Lesley on Google + or email her at LKennedy@ShopAtHome.com.
A version of this story originally appeared on iVillage.