Mammal Moms Can Choose Baby's Sex
They subconsciously produce boys or girls, based on a slew of factors
By Arden Dier, Newser Staff
Posted Jul 11, 2013 4:35 PM CDT
This photo provided by the San Diego Zoo shows a rhino with baby Shomili, a four-and-a-half-month-old greater one-horned rhino.   (AP Photo/San Diego Zoo Safari Park, Ken Bohn)

(Newser) – Call it "sneaky Machiavellian girl power," as the lead researcher does in the Washington Post. His study in PloS One concludes that female mammals have the innate ability to determine the sex of their offspring. It's not a conscious decision—the expectant moms somehow factor in a host of environmental and societal factors. The upshot is that if they think a male would grow up to play a dominant role in the pack, they'll have a boy and thus lots of offspring. If they're not so sure, they'll go with a girl, who likely will have at least a few babies even if she's not a dominant member of her group.

“Which means females are really the ones controlling the situation,” says Stanford biologist Joseph Garner, whose team analyzed nine decades of breeding records from mammals at the San Diego Zoo. "If I'm producing nothing but daughters, I'm making a safe bet—I'm going to make the average," he explains to Science Daily. Sons, however, are "high risk, high reward" because non-dominant males might get shut out from breeding entirely. High reward, indeed: Females who produced the most males had up to 2.7 times the number of grandchildren as those with even numbers of male and female offspring, LiveScience reports. Though there isn't much evidence on how the theory applies to us, Garner says humans "are definitely doing this, too ... there’s no question."

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Showing 3 of 34 comments
Jul 25, 2013 7:59 PM CDT
Makes sense that in every situation I know where the male was an a-hole, they had all girls. It shows the mom's desire to keep her own husband a-hole from creating another one in the world. Way to go mom!
Jul 13, 2013 12:38 PM CDT
This is illogical. How can female mammals control anything "unconsciously"? If they are unaware, how can there be choice, and how can this be evaluated and tested? The acid/alkaline balance in the female can tip the scale one way or another, but it isn't fool proof.
Jul 13, 2013 6:44 AM CDT
Did the researchers poll the mammals they were studying?