It's A Girl! An Ancient Virus May Determine The Sex Of Your Baby

New research finds that the sex of humans and other mammalian babies may be determined by an ancient virus.

Avoiding orgasm, eating more fruits and vegetables, and taking a bath prior to sex are some of the many questionable tips and suggestions out there for conceiving a girl, but new research published in the journal Nature suggests the sex of your baby may have little to do with your diet and pre-sex rituals and more to do with an ancient virus.

A Yale University-led animal study found that the sex of baby mice, and perhaps the sex of human babies, may be determined by a modification of a virus that inserted itself into the X chromosomes of mammalian genes some 1.5 million years ago. Researchers discovered that the way the early embryo deactivates this ancient viral gene could influence the sex of the organism. United Press International reported that the epigenetic marker of the the viral gene is a methyl bond added to adenine, one of the building blocks that form DNA base pairs, which can silence genes.

Researchers found that if the level of this marker is normal, X chromosomes remain active, and females and males will have an equal ratio of being born. If this marker is overrepresented, X chromosomes will be silenced, and males will be born twice as often as females.

It is unknown why this ancient viral gene determines sex ratios, but researchers said in a press release that the virus that influences sex ratios “is relatively recent — in evolutionary terms — and is enriched on the X chromosome.”


“Basically, these viruses appear to allow the mammalian genome to continuously evolve, but they can also bring instability,” said Andrew Xiao, senior author of the study. “Aside from the embryo, the only other places people have found this virus active is in tumors and neurons.”

Remnants of ancient viruses make up more than 40 percent of the human genome, researchers said. In most cases, these remains are inactive, but sometimes they "can interfere with development or health," Xiao told Live Science.

What’s more, Xiao believes that, aside from helping to determine the sex of offspring, this mechanism could be used to suppress cancer since the ancient viral gene could be helping tumors grow.

Interestingly, researchers said that in other organisms, such as the nematode C. elegans and the fruit flyDrosophila, this mechanism plays an entirely opposite role and activates genes rather than suppresses them. "Evolution often uses the same piece but for different purposes," Xiao said, "and that appears to be the case here."

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