Christopher Ryan Ph.D.

Sex at Dawn

How The Pill Could Ruin Your Life

Liberator of millions, The Pill presents unexpected problems.

Posted May 11, 2010

To honor both Mother's Day and the 50th anniversarry of the birth-control pill, a few words on some potentially disastrous unforseen effects of using The Pill:

Every woman knows her menstrual cycle can have profound effects on her eroticism. Spanish researchers confirmed that women experience greater feelings of attractiveness and desire around ovulation, while others have reported that women find classically masculine faces more attractive around ovulation, opting for less chiseled-looking guys when not fertile. Since the birth control pill affects the menstrual cycle, it's not surprising that it may affect a woman's patterns of attraction as well. Scottish researcher Tony Little found women's assessment of men as potential husband material shifted if they were on the pill. Little thinks the social consequences of his finding may be immense: "Where a woman chooses her partner while she is on the Pill, and then comes off it to have a child, her hormone-driven preferences have changed and she may find she is married to the wrong kind of man."

Little's concern is not misplaced. In 1995, Swiss biological researcher Claus Wedekind published the results of what is now known as the "Sweaty T-shirt Experiment." He asked women to sniff T-shirts men had been wearing for a few days, with no perfumes, soaps, or showers. Wedekind found, and subsequent research has confirmed, that most of the women were attracted to the scent of men whose major histocompatibility complex (MHC) differed from her own. This preference makes genetic sense in that the MHC indicates the range of immunity to various pathogens. Children born of parents with different immunities are likely to benefit from a broader, more robust immune response themselves.

The problem is that women taking birth control pills don't seem to show the same responsiveness to these male scent cues. Women who were using birth control pills chose men's T-shirts randomly or, even worse, showed a preference for men with similar immunity to their own.

Consider the implications. Many couples meet when the woman is on the pill. They go out for a while, like each other a lot, and then decide to get together and have a family. She goes off the pill, gets pregnant, and has a baby. But her response to him changes. There's something about him she finds irritating-something she hadn't noticed before. Maybe she finds him sexually unattractive, and the distance between them grows. But her libido is fine. She gets flushed every time she gets close enough to smell her tennis coach. Her body, no longer silenced by the effects of the pill, may now be telling her that her husband (still the great guy she married) isn't a good genetic match for her. But it's too late. They blame it on the work pressure, the stress of parenthood, each other. . . .

Because this couple inadvertently short-circuited an important test of biological compatibility, their children may face significant health risks ranging from reduced birth weight to impaired immune function. How many couples in this situation blame themselves for having "failed" somehow? How many families are fractured by this common, tragic, undetected sequence of events?

Some of this material appears in Sex at Dawn: The Prehistoric Origins of Modern Sexuality.

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