We've all heard about the dangers of unsafe sex. Some primate species may handle the risks of a promiscuous lifestyle by adapting better immune systems, a group of researchers at the University of Virginia report in this week's edition of Science. Because the immune system is designed to protect against harmful infections, it makes sense that species with a higher risk of acquiring a disease would have evolved a tougher immune system to compensate. Several factors could potentially raise the risk of infection among primates, such as a larger population size or density.
Primates vary widely in their social behavior, including sexual habits.
Some species like the gibbon are monogamous, while female barbary macaques can have up to ten male partners a day. The group compared levels of white blood cells across primate species as a measure of immune preparedness. Although there are many components to the immune response, the level of circulating white blood cells represents a first line of defense against a foreign invader. In general, the more promiscuous the females were, the higher their levels of white blood cells. Humans, by the way, have a relatively low white blood cell count that is consistent with being mostly monogamous.