Rape Results In More Pregnancies Than Consensual Sex, Not Fewer

Fact-checking Todd Akin

By Jennifer Abbasi Posted 08.21.2012 at 11:29 am 91 Comments

Todd Akin United States Congress

As you've probably heard by now, in an interview Sunday, Missouri Representative and Republican Senate nominee Todd Akin said he believed that rape-related pregnancy was "really rare." He continued by saying that, "If it's a legitimate rape, the female body has ways to try to shut that whole thing down."

So, now for the facts. Pregnancy resulting from rape is not rare. In fact, a woman is more than twice as likely to get pregnant during a rape than during consensual sex. That said, there may actually be something to the idea that the human female body has evolved an ability to resist rape-related pregnancies, although the potential mechanism is pregnancy termination, not prevention, so it's almost certainly not what Akin was talking about.

Akin now admits he "misspoke" in the interview, although it's not entirely clear which part he's referring to.

Akin's intentions aside, he's just plain wrong when he says rape-related pregnancies are rare (a fact that's even more frightening considering that he is a member of the House Committee on Science, Space, and Technology). Melisa Holmes, an ob-gyn in South Carolina, led a study on pregnancies from rape through the National Crime Victims Center. Holmes's study, which was published in 1996, found that 5 percent of rapes in females of reproductive age resulted in pregnancy, amounting to an estimated 32,101 rape-related pregnancies per year in the U.S. Even that astounding number was a "significant underestimation," she says, because so many rapes go unreported.

More recently, in 2003, husband-and-wife team Jonathan and Tiffani Gottschall, then at St. Lawrence University, identified even higher rape-related pregnancy rates. Analyzing survey results from 8,000 women around the country, they determined that 6.4 percent of rapes in women of childbearing age resulted in pregnancy. In cases where no birth control was used, the rate increased to 8 percent.

Meanwhile, a CDC report released last November concluded that 1 in 5 women have been raped, with 1.3 million women age 18 and up raped in 2010 alone. Doing the math, allowing for the use of birth control, and only including adults, the most recent data suggests that more than 83,000 women became pregnant by a man who raped them in 2010.

Jonathan Gottschall recognizes that there's some "squishiness" in all of these numbers because they're based on self-reported data. Still, he says, "the available data give us no reason to think that conception from rape is rare, or even that it is less rare than conception from consensual intercourse. If anything, the data suggest that things go the other way around." Indeed, a 2001 study out of Princeton and the National Institute of Environmental Health Sciences found the rate of pregnancy from consensual, unprotected sex to be just 3.1 percent.

Rapists subsconsciously target victims based on their likelihood of conception.No one is sure why forced sex is statistically a more successful reproductive strategy than consensual sex. "We think it might be because rapists tend to target young women at peak fertility," Gottschall says. Holmes confirms that most rapes occur in women under 25, and pre-pubescent girls, post-menopausal women and visibly pregnant women are statistically underrepresented among female rape victims, according to Gordon Gallup, an evolutionary psychologist at SUNY-Albany who wrote about rape-related pregnancy in The Oxford Handbook of Sexual Conflict in Humans.

"Rapists don't pick victims at random," Gallup says. "Unbeknownst to them, rapists clearly target victims based on their likelihood of conception. They tend to preferentially target young, post-pubescent females that are in their reproductive prime."

Age alone doesn't it explain it, though, because per-incident rape-pregnancy rates are higher than consensual pregnancy rates even among young women. Seeking out youth and attractiveness -- a fertility cue, according to a growing body of evidence -- gives rapists the reproductive edge, the Gottschalls proposed in their paper. They cited evidence from the 2000 book A Natural History of Rape by University of New Mexico biologist Randy Thornhill and University of Missouri anthropologist Craig Palmer, indicating that rapists seek out young, attractive women.

The Gottschalls wrote: "We propose...that all men -- rapists and non-rapists -- have the capacity to 'read' fecundity cues and pursue the most attractive/fecund women that they can. However, since rapists circumvent the problem of female choice, while non-rapists must confront it, it is plausible that the average instance of rape occurs with a more attractive/fecund woman than the average instance of consensual intercourse. Thus we propose that rapists target victims not only on the basis of age but based on a whole complement of physical and behavioral signals indicating the victim's capacity to become pregnant and successfully carry a child to term."

I called Gordon Gallup for his perspective on rape-related pregnancy. Last year, during a conversation about the antidepressant effects of semen, he mentioned a theory that the nature of a rapist's ejaculate has something to do with his reproductive success. When I asked him to elaborate on that, he told me that semen contains follicle stimulating hormone (FSH) and luteinizing hormone (LH), which trigger ovulation during the female menstrual cycle. FSH is needed for sperm production, but the presence of LH in high levels is more mysterious because it's not important for male fertility. It's possible, Gallup says, that seminal fluid released during forced sex contains higher-than-normal levels of these hormones -- LH in particular -- which may trigger ovulation in the victim.

There's no direct evidence yet of sex-induced ovulation in humans, although there's some very new research hinting at the possibility. The LH in semen has been shown to trigger ovulation in camels, alpacas and llamas. Semen also makes female koalas ovulate, although LH hasn't been identified as the active ingredient in that species' semen yet. A 1973 study found that 70 percent of conceptions from rape occurred outside a woman's most fertile time. And a 1949 study cited seven women who reported becoming pregnant due to rape, despite having not had a period for up to two years leading up to the assault.

The idea that semen produced during rape is especially primed to promote pregnancy seems less far-fetched considering the well-established evidence that what a man is doing when he ejaculates affects the chemical makeup of his semen. Studies on artificial insemination show that semen collected from a man who used his imagination to become aroused and ejaculate is much less likely to result in conception than a sample collected from a man watching porn, Gallup says. Even more potent is semen collected after coitus interupptus, i.e. pulling out during actual sex. The conditions under which a man becomes aroused and ejaculates has been shown to affect factors like sperm count, shape and mobility.

If semen changes based on context, it's plausible, Gallup asserts, that participating in a rape can affect its chemical makeup. Ovulation-inducing semen would be especially useful during rape, which is usually a one-time encounter. As sinister as it is, the ability to unconsciously adjust semen to make it more potent during rape could be one reproductive strategy that evolved in men to increase their reproductive success.

In addition to the devastating physical and emotional consequences of rape for the victim, things are also grim from the evolutionary perspective. "The problem with rape if conception occurs, is that it precludes making an informed mate choice, which is the principal means by which females maximize their fitness," Gallup says. "And it means that the female is not going to be subject to protection and provisioning by the child's father. Women are left holding the bag, so to speak."

Women appear to have evolved mechanisms to counteract these tactics and control their fertility. I've written about these kinds of dueling reproductive forces, known as antagonist coevolution, before. Some quick examples in human females: Research shows that women engage in less sexually risky behavior around ovulation, when they're likely to get pregnant, and their hand-grip strength, a measure of physical resistance, is enhanced during ovulation if they read a sexual-assault scenario, a mechanism that may have evolved to enable the female to more effectively resist rape when they're fertile.

In saying that women "shut down" pregnancy after rape, Rep. Akin unwittingly stumbled upon the concept that women's bodies reject unfamiliar sperm. In 2006, Gallup and his co-author Jennifer Davis published their theory that preeclampsia, a common pregnancy complication that can result in spontaneous abortion, evolved as an adaptive response to unfamiliar semen. (I say unwittingly because Akin was more likely referring to a theory that the fear and trauma of rape causes a woman's fallopian tubes to tighten, thus preventing pregnancy. This idea, proposed by John C. Willke, a physician and a former president of the National Right to Life Committee, has been lambasted by other doctors.)

Psychologist and writer Jesse Bering explained the preeclampsia idea in his excellent post, which I highly recommend you read in its entirety: "By the early 1980s, scientists had started to notice that preeclampsia was more likely to occur in pregnancies resulting from 'one-night stands,' artificial insemination and rape than in pregnancies that were the product of long-term sexual cohabitation. That it was the woman's prior exposure to the male's semen that was responsible for this pattern was evident by the fact that couples who'd been using barrier contraceptives (such as condoms), or who practiced coitus interruptus (in which the man withdraws prior to ejaculation) before they began trying to conceive also had higher rates of preeclampsia than those who'd been engaging in unprotected sex for some time."

Bering continued, "It may be useful to think about preeclampsia not simply as a medical anomaly," reason the authors, "but as an adaptation that may have evolved to terminate pregnancies where future paternal investment was questionable or unlikely."

Now, none of this means that rape-related pregnancies are rare, or that biology should be trusted to ward off these pregnancies. The sheer numbers of pregnancies from rape tell us that it's happening -- a lot. And, obviously, preeclampsia is not the solution. Having the right to choose what to do about it is.

Jennifer Abbasi is a science and health writer and editor living in Portland, OR. Follow Jen on Twitter (@jenabbasi) and email her at popsci.thesexfiles@gmail.com.

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