Promiscuity linked to stronger immune system

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Promoting Intimacy and Other-Centered Sexuality

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Promiscuity linked to stronger immune system

By LEE BOWMAN Scripps Howard News Service
November 09, 2000

- The more promiscuous a species is, the more powerful its immune system, a new study suggests.

White blood cell counts were significantly higher in primate species where females have more mating partners, indicating that their immune systems are attuned by the greater risk of sexually transmitted diseases, reports a team led by Charles Nunn, a research associate in biology at the University of Virginia.

"There's a very strong relationship between high white blood cell counts and high promiscuity in healthy animals. The more monogamous species have lower white blood cell counts," said Nunn. And despite the impression that soap operas might give about our propensity to monkey around, humans have white blood cell counts that are consistent with being monogamous, the researchers found in a separate comparison.

The study, published Friday in the journal Science, involved comparing 20 years of data on average white blood cell counts for 41 primate species from a range of evolutionary groups and an array of mating behaviors. They included the Barbary macaque, whose females may mate with as many as 10 males in one day, to some species that mate for life. "Our findings strongly suggest that the most sexually active species may have evolved elevated immune systems as a defense mechanism against disease,'' Nunn said. 'This puts the evolution of sexual behavior in close relation to the evolution of immune system."

The researchers also compared other behavioral and social factors that might affect animals' immune systems, including high population density, which raises the risk of exposure to disease, as well as to pathogens from their environment. But they found that promiscuity affected the white cell counts far more than any other risk factors.

"We expected to see a correlation between white cell counts and various behavioral and ecological factors, but we were surprised to find that sexual activity appears to be the key factor in how the immune system develops,'' said John Gittleman, an associate professor of biology at the University of Virginia who studies evolution.

The research was funded by the National Science Foundation and the National Institute of General Medical Sciences.

On the Net: http://www.sciencemag.org.
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