28 July 2010

Primates on The Pill find it hard to pull

by Kate Melville

Hormonal contraceptives change the ways in which captive ring-tailed lemurs relate to one another sexually, leading Duke University researchers to speculate that The Pill could also be influencing human mate choice. The Duke study, appearing in Proceedings of the Royal Society B, combined analyses of hormones, genes, scent chemicals and behavior.

The researchers note that contraception alters the chemical cues these scent-reliant animals use to determine genetic fitness, relatedness and individuality. And, as a sort of double whammy to birth-control efforts, male lemurs were shown to be less interested in females that were treated with contraceptives.

"Hormonal contraception is known to alter the attractiveness of scent cues in humans and the presence of fertility cues in other primates," said Duke's Christine Drea. "We wanted to understand all the ways in which contraception changes scent cues and the subsequent way these animals might interact with each other."

The study used the contraceptive Medroxyprogesterone acetate, or MPA (marketed as Depo-Provera). Drea's chemical analysis found that the animals receiving the contraceptive expressed different scent molecules than "intact" females, significantly altering the signals females send about themselves to social contacts and prospective partners. "They smell funny," Drea said.

The findings are part of a series of studies that Drea's group has done using chromatography to tease apart the chemical components of the rich stew of scents produced by lemurs. A female lemur's scent normally conveys not only her fertility status, but also information about identity, her relatedness to others and her genetic homozygosity (an indicator of in-breeding).

If all of that information is scrambled by hormonal contraception, it may in part explain changed patterns of aggression that other studies have noted when captive primates are treated with contraceptives. "There's something very different about these gals," Drea said, adding that males showed clear preferences for the scents of intact females, spending less time investigating odor samples from contracepted females.

Are these findings relevant for our own species? "Humans are known to send and receive olfactory cues about hormonal status and possible compatibility. One has to wonder if human mate choice might be affected in some of the same ways it has been in these primates," Drea concluded.

Unnatural selection: Courtesy of The Pill
Contraceptive Pill Threatening Genetic Diversity?
Cougar sex drive an evolutionary adaptation
Male testosterone levels surge with ovulation

Source: Duke University