Mammals can "choose" the sex of their babies in order to continue the species and produce more grandchildren, according to Stanford University School of Medicine news release.
Researchers used 90 years of breeding records from the San Diego Zoo to substantiate a fundamental theory of evolutionary biology: "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," Joseph Garner, PhD, associate professor of comparative medicine and senior author of the study, said in a news release.
The findings were published July 10 in PLOS ONE. According to the news release, the results applied to 198 different mammalian species.
In the study, researchers used three-generation pedigrees of more than 2,300 animals and found that grandmothers and grandfathers were able to "strategically choose to give birth to sons." Healthier sons mean more grandchildren, and the process is believed controlled by the females.
"You can think of this as being girl power at work in the animal kingdom," Garner said. "We like to think of reproduction as being all about the males competing for females, with females dutifully picking the winner. But in reality females have much more invested than males, and they are making highly strategic decisions about their reproduction based on the environment, their condition and the quality of their mate. Amazingly, the female is somehow picking the sperm that will produce the sex that will serve her interests the most: The sperm are really just pawns in a game that plays out over generations."
However, the study does not explain how 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" and "female" 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," Stanford said in the news release.
To read more about the study, click here.
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