Mammals can ‘choose’ sex of offspring, study finds

July 12, 2013

(Credit: Dylan/Wikimedia Commons)

A new study led by a researcher at the Stanford University School of Medicine shows that mammalian species can “choose” the sex of their offspring to beat the odds and produce extra grandchildren.

In analyzing 90 years of breeding records from the San Diego Zoo, the researchers were able to prove for the first time a fundamental theory of evolutionary biology: that mammals rely on some unknown physiologic mechanism to manipulate the sex ratios of their offspring as part of a highly adaptive evolutionary strategy.

“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,” said Joseph Garner, PhD.

Garner is an associate professor of comparative medicine and senior author of the study, published July 10 in PLOS ONE (open access). The results applied across 198 different species.

But how, in fact, do parents manipulate the sex of their offspring? Garner said the mechanism isn’t really known, though one theory holds that females can control the male-generating and female-generating 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.