There are plenty of insane old wives tales that claim to determine the sex of your unborn kid: how low it’s sitting in the womb, how a ring on a string swings over the mother’s belly, or what color drano turns when mixed her urine. But the eggheads at Yale have struck on a way better explanation: a virus, which inserted itself into the mammalian genome 1.5 million years ago. Yep, it’s even weirder than drano pee.
Viruses started invading animal genomes (those are complete sets of DNA, not mini-men in the woods with pointy hats) over 10 million years ago and Andrew Xiao, the senior author of the study, estimates that more than 40 percent of the human genome might be made up of these viral duplications. Most of the time, they remain inactive, but Xiao and his team discovered an active one on the X chromosome in mice, which apparently influences the sex of their offspring. This could account for the relatively equal rate in which boys and girls are born, because when the virus is inactive, males are born at double the rate of females. So, if your family is equal parts boys and girls, congratulations: your brood is going viral.
You’re probably wondering if this discovery will allow you to choose the sex of your next kid, and the answer is maybe. Scientists are working on a mechanism to disable the virus, but it’s because doing so would go a long way to helping them turn off related biological functions that result in cancer. So, if you want to start dabbling in dad eugenics, you can try. Or just settle for a cure for cancer and a kid who’s kind of a virus.
[H/T] Yale University