Infidelity is easy to explain in males. By sleeping around, a guy can potentially impregnate more females and sire more offspring than if he just had one mate. But females cheat, too, even though a woman will only be able to have roughly one baby per year no matter how many male sex partners she has had.
One leading evolutionary hypothesis suggests that a female who mates with multiple males ensures the genetic diversity and quality of her offspring; having higher-quality offspring could theoretically give her more grandchildren later. A 17-year study, published in the June issue of The American Naturalist, challenges this hypothesis.
"This is one of the most careful and most robust studies to explore whether polyandry is adaptive in females," says Tommaso Pizzari, a University of Oxford biologist who was not involved in the research. "The answer is: not really."