Animals and Us

The psychology of human-animal interactions.

Why Are Rape Victims More—Not Less—Likely To Become Pregnant?

Unlike chickens, human females do not have a defense against rapists' sperm

Representative Todd Akin of Missouri made two mistakes when he said recently about pregnancy resulting from rape....“From what I understand from doctors, it’s really rare. If it’s a legitimate rape, the female body has ways to try to shut the whole thing down.”

His first mistake was linguistic. The term “legitimate rape” is an oxymoron. “Legitimate rape” does not exist. End of story.

His second mistake was believing the “doctors” who gave him the idea that the female body can “shut the whole thing down.” (According to the L. A. Times, the “doctors” was one Jack C. Wilke, a prominent anti-abortionist physician and past president of the National Right To Life Committee.)

But is there evidence to support this claim? After all, in some species, females do have the ability to rid their body of unwanted semen. Chickens, for example. Researchers at the University of Sheffield studied this phenomenon in flocks of free ranging chickens (here). The scientists found most sexual interactions between roosters and hens are coerced. (I was not surprised; I used to raise chickens.) I was surprised, however, to learn that hens had the ability to eject sperm from their reproductive tracts. Further, hens are choosy about it. The researchers found that hens were much more likely to eject the semen of low ranking “forced copulators” than the rapists at the top of the social hierarchy who presumably have better genes. In spiders, this is called “sperm dumping.”

So a biological anti-pregnancy mechanism exists in chickens and spiders that kicks in during forced copulations. Is there any evidence that a similar mechanism exists in human females? Are Representative Akin and Dr. Wilke right?

No. In fact, there is evidence that human females are more likely to get pregnant when raped than when they have consensual sex!

Rape Often Leads to Conception: The Evidence

The evidence that women are more likely to get pregnant by rape is described in this article in the journal Human Nature by Jonathan and Tiffani Gottschall. Between November,1995 and May, 1996, the National Institute of Justice, the National Center for Injury Prevention and Control and the Centers for Disease Control jointly conducted a telephone survey of 8,000 randomly selected American women. Some of the questions dealt with rape and subsequent pregnancy. Four hundred and five of the women indicated they had been raped exactly one time. The Gottschall’s used this data to compare the chances of getting pregnant via a rape versus consensual sex.

The Results

Twenty-six of the women who had been raped became pregnant—a pregnancy rate of 6.42%, which increased to 8% when adjusted for contraceptive use.

If you think that this is a low pregnancy rate, you are wrong. Contrary to what most people think, humans are among the most infertile of species. The most widely cited research article on this topic was a study of the relationship between pregnancy and the timing of intercourse among women who were trying to conceive and were not using any birth control. Naturally, the researchers found that the odds of their getting pregnant changed with the stage of their menstrual cycles. Among the “regular cyclers,” a woman’s chances of conceiving ranged from a high of 9% if they had sex on day 13 of their cycle to 0% when they were having their period. Over the entire cycle, however, a woman’s chances getting pregnant from one act of intercourse was only 3.1%. This finding is consistent with other studies of human fertility.

In short, women are at least twice as likely to conceive as a result of rape than by consensual sex.

Why Should Pregnancy Be More Common During Rape?

Why does rape result in increased risk of pregnancy? This remains an open question. The Gottschalls reject some possibilities. These include the idea that rape induces ovulation, (copulation does stimulate the release of an egg in some species), that rapists have more virile sperm, and that rapists have a special capacity to detect women who are ovulating. They do make a couple of conjectures they consider reasonable. The first is that rapists target women who are particularly fertile based on factors such as beauty and age. The second is that women unconsciously “broadcast cues about their ovulatory status that men are capable of registering and interpreting.” These hypothetical unconscious cues could be physiological (e.g. body odor, subtle changes in skin tone) or behavioral. To their credit, however, the authors admit that there is little evidence or no evidence to support their conjectures.

So, sorry Rep. Akin…there is no evidence that human females have a biological mechanism that prevents pregnancy during rape. If anything, it appears that women who are sexually assaulted are MORE rather than less likely to conceive.

Maybe you should start seeing a different doctor.

                                 *     *     *     *     *     *    

Hal Herzog is professor of psychology at Western Carolina University where he teaches a course on human sexuality. He is the author of Some We Love, Some We Hate, Some We Eat: Why It's So Hard To Think Straight About Animals.

Follow on Twitter

Hal Herzog, Ph.D. is the author of Some We Love, Some We Hate, Some We Eat: Why It's So Hard To Think Straight About Animals. more...

Subscribe to Animals and Us

Current Issue

Just Say It

When and how should we open up to loved ones?