For ring-tailed lemurs, it's love at first sniff. But for ring-tailed lemurs on birth control, it might be a different reaction.
Duke researchers found that hormonal contraceptives change the scent female lemurs give off, altering how their male counterparts relate to them as both relatives and romantic partners.
Not only did the contraceptives jumble chemical signals of kinship, but guy lemurs were dramatically less attracted to the gals on the Pill.
The findings, published last month in the journal Proceedings of the Royal Society B, suggest that birth control can "muck up" important primate communication signals, says co-author Christine Drea, a professor of evolutionary anthropology at Duke.
The next question is whether the results apply to humans.
"Lemurs don't breed while on contraception - but humans do," said Jeremy Chase Crawford, lead author of the study while a research associate at Duke. "So if humans are affected in the same way as lemurs, contraception could potentially mess up mate choice."
Lemurs made a good study subject because they are known to rely heavily on smell for communication, airing their odors as a kind of advertisement for fertility, genetic makeup and kinship. Also, hormonal birth control has historically been tested in them and similar primates.
In the study, 12 female lemurs were administered the contraceptive medroxyprogesterone acetate (MPA), otherwise known by its brand name Provera or Depo-Provera.
When the female lemurs' genital secretions - containing about 300 different molecules - were analyzed, the researchers found that birth control caused major changes in chemical composition.
As a result, the 13 unrelated male primates in the study reacted much differently to females on the Pill. They spent significantly less time sniffing out the odors from those on birth control, a sign of waning sexual interest.
The findings could help explain aggression among kin in primate groups where contraception is used for population management, Drea said.
"If Betty doesn't smell like Betty anymore, there are behavioral consequences," she said.
While the study didn't look at humans, it's long been known that many animals - including our own species - gauge potential mates by getting a good whiff. Previous studies have uncovered evidence that the Pill can muddle interactions in both directions: how a woman perceives potential mates, and how much they're attracted to her.
In sweaty T-shirt experiments conducted by Swiss scientists in 1995, women were asked to sniff the sweat-soaked shirts of guys and decide which ones they preferred. Women who were not taking birth control overwhelmingly favored the odors of guys with immune systems most different from their own. Meanwhile, women on the Pill showed the exact opposite trend, picking the most molecularly matched mates.
Since being on the Pill mimics pregnancy - hormonally, at least - the researchers explained the results by suggesting these women are subconsciously avoiding stirring the genetic pool, as men that resemble kin would supposedly be more likely to stick around.
Then in 2007, researchers at the University of New Mexico found that while lap dancers not on the Pill made on average $20 more during their fertile phase of the month, the tips of women on contraceptives were unchanged.
The combination of findings suggests that the Pill could alter mate preferences - even if not consciously realized by either party.
Still, there's a difference between a preference for a mate and actual selection of that mate.
While the lemur studies support what has been found in humans, they "do not tell us yet whether the effect of hormonal contraceptives on male preferences is strong enough to affect mate choice and offspring," said Dr. AlexandraAlvergne, an evolutionary anthropologist at the University of Sheffield in the United Kingdom.
Only that can shed light on whether birth control can tinker with evolution, Alvergne said.
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