Humans may be monogamous

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From: Mike Masnick (
Date: Fri Nov 10 2000 - 10:59:10 PPET

Not to restart an earlier thread (or, rather, avalanche) concerning human
nature when it comes to mating... here's some new evidence suggesting that
humans might be monogamous by nature - based on white blood cell counts.

Do we get to go back to 100 message/day arguments on who gets to sleep with
who now?


Most Promiscuous Species Have The Highest WBC Counts

A new study indicates that evolution of the immune system may be directly
linked to the sexual activity of a species. A comparative analysis of 41
primate species demonstrates that the most promiscuous species have
naturally higher white blood cell (WBC) counts -- the first line of defense
against infectious disease -- than more monogamous species.
The findings are reported in today's issue of the journal Science.

"Our findings strongly suggest that the most sexually active species of
primates may have evolved elevated immune systems as a defense mechanism
against disease," says principal investigator Charles L. Nunn, a research
associate in the Department of Biology at the University of Virginia. "We
looked at animal species with a range of mating behaviors and found a
strong relationship between high WBC counts and high promiscuity in healthy
animals. The more monogamous species have lower WBC counts."

The researchers compared 20 years of data on average white blood cell
counts for 41 primate species. The 41 species represent the major primate
evolutionary groups and the full range of mating behaviors.

Some of the species are highly promiscuous, such as the Barbary macaque,
whose females may mate with up to ten males per day while in heat. Other
species have varying levels of monogamy, including some that mate with one
partner for life.

The researchers found a direct correlation between WBC levels and mating
behavior. Data for each species come from zoos and are composed of
veterinary reports of basal, or normal, WBC counts for healthy females.

"The implication of our finding is that the risk of sexually transmitted
disease is likely to be a major factor leading to systematic differences in
the primate immune system," Nunn says. "This puts the evolution of sexual
behavior in close relation to the evolution of the immune system."

The researchers also compared other behavioral and social factors that
might affect the animals' immune systems, including high population
density, which increases the risk of exposure to disease, as well as
exposure levels to soil-borne pathogens, namely fecal contamination.

They found that mating promiscuity affected WBC counts far more than other
disease risk factors.

"We expected to see a correlation between WBC counts and various behavioral
and ecological factors, but were surprised to find that sexual activity
appears to be the key factor in how the immune system develops," says
co-author John L. Gittleman, U.Va. associate professor of biology. "This
opens up many new questions about behavior and the immune system."

The researchers also compared mean WBC counts of humans to the various
primate WBC counts, and found that humans are on par with the more
monogamous primate species.

"Based on this comparison, humans are more similar to the more monogamous
primate species," Nunn says.

The research is funded by the National Science Foundation and the National
Institute of General Medical Sciences, and was conducted by three U.Va.
scientists in the Department of Biology: Nunn, who specializes in primates;
Gittleman, who uses computational methods to study evolution; and Janis
Antonovics, who studies sexually transmitted diseases. - By Fariss Samarrai

[Contact: Charles L. Nunn, Fariss Samarrai]


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