August 12, 2008
Sexual Attraction By Odor Changed By Contraceptive Pill

Men who have immune system genes dissimilar to women have odors which are more attractive to women. This is probably an evolutionary consequence of the advantage of giving one's children genetically diverse immune systems. But the hormones in the contraceptive pill alter sense of smell of women so they are more attracted to men who are immunologically more similar.

The contraceptive pill may disrupt women's natural ability to choose a partner genetically dissimilar to themselves, research at the University of Liverpool has found.

The Pill leads a woman's attraction machinery astray.

Disturbing a woman's instinctive attraction to genetically different men could result in difficulties when trying to conceive, an increased risk of miscarriage and long intervals between pregnancies. Passing on a lack of diverse genes to a child could also weaken their immune system.

So the Pill causes a mismatch in mate selection.

Humans choose partners through their body odour and tend to be attracted to those with a dissimilar genetic make-up to themselves, maintaining genetic diversity. Genes in the Major Histocompatibility Complex (MHC), which helps build the proteins involved in the body's immune response, also play a prominent role in odour through interaction with skin bacteria. In this way these genes also help determine which individuals find us attractive.

The research team analysed how the contraceptive pill affects odour preferences. One hundred women were asked to indicate their preferences on six male body odour samples, drawn from 97 volunteer samples, before and after initiating contraceptive pill use.

Craig Roberts, a Lecturer in Evolutionary Psychology who carried out the work in collaboration with the University of Newcastle, said: "The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours.

There's an even bigger problem: If a woman on the Pill meets a guy, finds him pheromonally attractive, gets married, and then stops using the Pill she can suddenly find her husband's smell very much not to her liking.

"Not only could MHC-similarity in couples lead to fertility problems but it could ultimately lead to the breakdown of relationships when women stop using the contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners."

How many marriages and relationships has the Pill brought together which fell apart when the woman stopped taking the Pill?

What could be done about it: Once genetic testing becomes cheap and widely available online dating services could match men and women by comparing Major Histocompatibility Complex (MHC) genes. Avoid dating someone who might seem attractive because you are on the Pill.

But doesn't the MHC attraction mechanism work for men as well? They won't be on the Pill. Are men finding that funny-smelling women who are on the Pill are hitting on them? Someone should do a study on this.

The discovery reported in this post is yet another example of how we are genetically programmed to do and feel as we do.

Share |      Randall Parker, 2008 August 12 09:19 PM  Brain Sexuality

jb said at August 13, 2008 4:00 AM:

Wow, this is fascinating. It might explain a lot of the 'breakdown of marraige'

Nick G said at August 14, 2008 10:19 AM:

"The results showed that the preferences of women who began using the contraceptive pill shifted towards men with genetically similar odours."

No, the results showed that the preferences of women who began using the contraceptive pill shifted towards male body odour samples with genetically similar odours. Have they really shown that "Humans choose partners through their body odour", and further that their research duplicates this behavior? This could be confounded by careful bathing, or other things they haven't thought of. For instance, plenty of promising research shows a micro effect on a body system, but not on larger phenomena or macro phenomena (overall death rates, for instance).

Bob Badour said at August 19, 2008 5:58 PM:

Hmmmm... My ex was on the pill when we met and got married, and off the pill when we got separated and divorced...

Frank Lynch said at December 22, 2008 2:25 PM:

I wonder how closely this is connected to "mid-life crisis" women whose husbands (or they themselves) get their tubes tied and get off the pill. Wouldn't surprise me if there was a strong correlation.

My wife almost left a year and a half ago. Said the "chemistry" just wasn't there for her anymore. She'd just started taking the pill for the first time to treat a euterine fibroid condition. She quit taking them about 3 months ago and she's all snuggly again. Coincidence?

As an ecologist, I also wonder what all hormones from these millions of women being washed into our water ways is doing to critters, and how much of it is making its way back into public water systems. We test for lead and other metals, but we don't treat for chemical hormones (estrogen, etc). How is this affecting human sexuality? Is it contributing to human transgenderism? Nobody will do this research because it's decidedly un-PC, but we should know...

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