Then you might want to read the results of a new study published this morning in Trends in Ecology and Evolution: "Does the Contraceptive Pill Alter Mate Choice In Humans?"

Dr. Alexandra Alvergne and Dr. Virpi Lummaa of the University of Sheffield review "emerging evidence suggesting that contraceptive methods which alter a woman’s natural hormonal cycles" may be messing up straight peoples' sex lives and married lives. It may also raise "evolutionary questions and concerns," write Alvergne and Lummaa. It goes like this: the type of man a woman finds attractive varies pretty widely according to her menstrual cycle. Women who are ovulating prefer men who are more masculine and "more... genetically unrelated," like the guy on the right, above; women who aren't ovulating prefer guys who are more feminine and genetically more similar, like the guy on the left. Since the pill suppresses ovulation, and since many women are on the pill when they're dating and sleeping around—or "selecting a mate," as the docs put it—women may be marrying men they find attractive on the pill but not so much once they've gone off the pill.

Which women tend to do once they're married and want to have children.

Alvergne and Lummaa theorize that all those suppressed ovulations may have dire consequences where sexual compatibility and long-term marital success are concerned. It can't be pleasant, after all, to realize you're not as attracted to your spouse as you thought you were once you stop taking the pill. And couples who are genetically similar—the kind of pairings the pill promotes—are more likely to have infertility issues. Which is, um, also bad. And then there's this: since men have been shown to find ovulating women more attractive, "...the use of oral contraceptives may influence a woman’s ability to attract a mate by reducing attractiveness to men, thereby disrupting her ability to compete with normally cycling women for access to mate." While their study is sure to be cited by religious nuts waging war on the pill, Alvergne and Lummaa cite all the good the pill has done for women:

Any such effects should be weighed against the multiple benefits that the invention of the pill has brought. This revolutionary contraceptive method has given women unprecedented control over their fertility with the possibility to sample different partners before reproduction, to control their number of children, to reach optimal birth spacing given circumstances or to end reproductive career before menopause if desired, which has had a considerable impact on their social life. For instance, a sharp increase in college attendance and graduation rates for women was observed after the pill was legalized.

Giving women control over their fertility, allowing them to sample different partners, more women going to college—you can see why religious conservatives have problem with the pill. You can download a PDF of the study here. I've also sent a some questions to the study's authors—should women switch to the IUD? should an engaged woman go off the pill to make sure she's not marrying a too-genetically-similar swish? and what does all of this mean for gay marriage? and the ballot booth that is their [RSVP] envelopes?—and I'll share their answers with you when I hear back.