Monkey Sex Promiscuous primates have healthier immune systems, study says

Humans, you may be interested to know, are on the prudish end of the sexual spectrum.

We're far from the chimpanzee, whose females have sex an average of 580 times, with nine males, to produce one offspring. We're much closer in sexual habits to gibbons, which mate for life.

We know promiscuity is not a good strategy for individuals — be they monkeys or humans — for boosting the immune system. The increased exposure to sexually transmitted diseases may kill or render sterile those who sleep around.

But a recent study indicates that, over the span of millions of years, promiscuous primates actually develop a stronger immune system.

"We're not talking about things that would change in an individual, but rather over evolutionary time," said Charles Nunn of the University of Virginia, lead author of the study that appears in this week's issue of the journal Science.

The study found human levels of the white blood cells that fight off disease are much lower than, say, the Barbary macaque, whose females regularly mate with 10 different partners a day, changing every 20 minutes.

In the case of the sluttish simians, only a tiny percentage were lucky enough to have a surplus of white blood cells, which they survived to pass on to their offspring.

Over millennia, these primates evolve stronger immune systems as protection against STDs, says Nunn. Common STDs among primates include herpes, papilloma virus, which causes genital warts, and Simian Immunodeficency Virus — the primate version of HIV.

"Promiscuous primates have higher white blood cell counts because they're the first line of defense against disease," Nunn said.

His team looked at 20 years of data on 41 primate species. It turns out the most promiscuous — like chimps and macaques — have high levels of basal white blood cells, and monogamous species, like the white-handed gibbon or Titi monkey, have lower levels.