Skepticism and Rape Adaptations

It isn't terribly difficult to find well-written, skeptical pieces on evolutionary psychology. In fact, several have come out quite recently. They examine current evo psych theorizing in the light of scientific requirements for proof of any such theory.

Kate Clancy wrote a post on the variety of human behavior that evo psych studies attempt to represent by using mostly college undergraduate research subjects. In addition to her concern over undergraduates' WEIRD (Western, Educated, Industrialized, Rich, and Democratic) demographics, she notes other ways in which these research participants aren't representative of the whole of humanity they're being used to study:

Another problem is that most work on relationships in EP tends to be heteronormative, meaning that they think nothing of assuming that either everyone is straight, or the universally best behavioral strategy is to be straight. They also tend to assume that the best strategy is to be monogamous, with occasional sneaky infidelity permitted if one can get better genes or more offspring that way (keep in mind that there is a difference between what might be biologically advantageous in a certain context, and what is culturally appropriate – the argument here is not against the culture of monogamy).

But heterosexual monogamy is only one reproductive strategy of many that humans employ. Depending on how you measure it, monogamy and polygyny (single male, multi female marriage) vie for the most frequent strategy – in fact, polygyny occurs in about 80% of modern human societies (Murdock and White 1969). There are even a few rare populations that practice polyandry, which is the marriage of a single female and multiple males. And, even in those populations where monogamy is practiced, serial monogamy is far more frequent than lifetime monogamy: this means that individuals have a series of monogamous relationships rather than find one mate for life (so no, divorce is not a modern human invention).

And that's not even getting into the nonhuman primates with whom we share a fair amount of evolutionary history. In short, Clancy makes the case that if we wish to describe a behavior as evolutionarily adaptive in humans as a whole, we need to consider more than a subset of the behavior in a single culture.

Also looking at the challenges that evo psych must meet in order to scientifically determine the adaptive value of a behavior is Jeremy Yoder. In a multipart series examining the evidence that homophobia is an evolved trait, he breaks down the multiple lines of evidence required:

When evolutionary biologists say a trait or behavior is "adaptive," we mean that the trait or behavior is the way we see it now because natural selection has made it that way. That is, the trait or behavior is heritable, or passed down from parent to child more-or-less intact; and having it confers fitness benefits, or some probability of producing more offspring than folks who lack the trait. Lots of people, including some evolutionary biologists, speculate about the adaptive value of all sorts of traits—but in the absence of solid evidence for heritability or fitness benefits, such speculation tends to get derided as "adaptive storytelling."

A few particularly interesting points were brought up in these posts. One, which should be obvious but often seems not to be, is that evo psych is talking about biological mechanisms for behavior, which means that a demonstration that the behavior is widespread is not enough to support claims that a behavior is evolved.

To recap: Gallup proposed that homophobia could be adaptive if it prevented gay and lesbian adults from contacting a homophobic parent's children and—either through actual sexual abuse or some nebulous "influence," making those children homosexual. In support of this, he published some survey results [$a] showing that straight people were uncomfortable with adult homosexuals having contact with children.

I pointed out that all Gallup did was document the existence of a common stereotype about homosexuals—he presents no evidence that believing this stereotype can actually increase fitness via the mechanism he proposes, or that it is heritable.

The next item of interest didn't come from Yoder, but from Jesse Bering, who wrote the article to which Yoder was responding. Bering described his affection for research that is done "without curtseying to the court of public opinion." Yoder points out that a study providing a rationale for homophobia didn't exactly run counter to public opinion in 1983, when it was done.

Later, in a response to Yoder's first post, plus those of others, Gallup himself suggests that his critics "tip-toe around the fact that my approach is based on a testable hypothesis" and "go out of their way to side-step the fact that the data we’ve collected are consistent with the predictions" because the hypothesis is "politically incorrect or contrary to prevailing social dogma." Given that Yoder specifically discussed the relevance of his data to his theory, it's difficult to award Gallup the mantle of abused maverick he and Bering both claim for him.

Earlier this year, Jerry Coyne wrote (in response to another Bering article), a caution about building strong evo psych edifices on slim foundations. In this case, he examined the idea of the "rape module"--a genetic, inherited predisposition among human men to commit rape--and of specific, genetically programmed, inheritable behaviors in women designed to avoid this "rape module."

Well, one can debate whether reading a story about rape is the same thing as being sexually assaulted, or whether a marginal increase in handgrip strength would have been sufficient in our ancestors to fight off a rapist. But the important part of these studies is that they were apparently one-offs—they have not, as far as I know, been replicated by other researchers. Do we accept single results, based on surveys of American undergraduates at a single university, as characterizing all modern women?

As we know, many studies in science, when repeated, fail to replicate the initial results. Think of all the reports of single genes for homosexuality, depression, and other behavioral traits that fell apart when researchers tested those results on other groups of people! And if an author did an initial study (not a replication) of handgrip strength that didn’t show the relationship with ovulation, would that even be publishable? I think not.

I suggest, then, that the results of evolutionary psychology often reflect ascertainment bias. If you find a result that comports with the idea that a trait is “adaptive,” it gets published. If you don’t, it doesn’t. That leads to the literature being filled with positive results, and gives the public a false idea of the strength of scientific data supporting the evolutionary roots of human behavior.

In addition to critiquing the studies themselves, Coyne also notes that this is not the first time the "rape module" idea has been criticized.

Thornhill and Palmer’s book was controversial, with many critics claiming that the authors were trying to excuse or justify rape. Bering takes after these critics, properly noting that “‘adaptive’”does not mean ‘justifiable’,” but rather only mechanistically viable.” But what he doesn’t mention is that there were strong scientific critiques of the “rape module” idea as well. I produced two of them myself, a long one in The New Republic and a short one with Andrew Berry in Nature, pointing out not only scientific weaknesses in the evolutionary scenario but Thornhill and Palmer’s unsavory fiddling with statistics, distorting what the primary data on sexual assault really said. Bering doesn’t mention the scientific controversy, noting only that “it’s debatable that a rape module lurks in the male brain.”

The New Republic article is itself a strong skeptical look at the science used to bolster the concept of the "rape module." I recommend reading it in its entirety. Coyne discusses the various versions of the idea that rape is a product of evolution (one trivially vague enough to be meaningless--but intuitively acceptable--and one stronger and requiring proportionally more evidence) and how they are played against each other in such a way that they could describe any evidence. He also applies a broader understanding of crime to provide alternate explanations that don't require a biological predisposition to explain patterns of victimization, and he explains how the evidence in three studies used depend on statistical manipulation. He also examines claims that rape can only be prevented properly using an evo psych framework for understanding it.

Given the availability of people like these, with the tools and inclination to turn a skeptical eye on the topic of evolutionary psychology, it is perhaps no surprise that Center for Inquiry Michigan is promoting a speaker tomorrow night on the topic of evo psych and rape. What is surprising, however, is the identity of the chosen speaker. Dr. Todd Shackelford is the director of the Evolutionary Psychology Lab at Oakland University.

Dr. Shackleford will present a talk on the competing theories of rape as a specialized rape adaptation or as a by-product of other psychological adaptations. Although increasing number of sexual partners is a proposed benefit of rape according to the "rape as an adaptation" and the "rape as a by-product" hypotheses, neither hypothesis addresses directly why some men rape their long-term partners, to whom they already have sexual access. He will present the findings of two studies that examined these hypotheses, discuss the limitations of this research and highlight future directions for research on sexual coercion in intimate relationships.

Now, the problem is not that Dr. Shackelford is an evo psych researcher. There are people doing good work in evo psych. The problem is that Dr. Shackelford isn't doing good work on this topic. In particular, the work he is presenting, relating female infidelity to rape of female partners by male partners, doesn't tell us anything that the already robust scientific literature on rape hasn't already told us.

In the 2006 paper that Shackelford will be presenting tomorrow, "Sexual Coercion and Forced In-Pair Copulation as Sperm Competition Tactics in Humans," (pdf available) Goetz and Shackelford demonstrate a correlation in heterosexual couples between the likelihood of female infidelity (past or present, rated by the male or female partner) and the likelihood of male sexual coercion, up to and including rape via physical assault. This isn't news. We already know that men who endorse rape myths and the acceptability of sexual violence against women under certain circumstances are more likely to rape. One of the common attitudes that predicts rape is that "sluts" lose the right to say, "No." ("Nice girls don't get raped.") Non-monogamy is used to excuse rape, and not merely rape by prior sexual partners.

Non-monogamy also isn't alone among excuses for rape (Scully and Marolla, 2005, pdf available). The idea that women secretly want the sex is common. Rapists claim that the circumstances of the rape were beyond their control due to drugs, alcohol, or emotional problems. People see demands for sex as more reasonable in circumstances where financial contributions to a date or relationship are uneven. None of these, however, are examined whether they similarly contribute to rape within an existing relationship. Without that, the 2006 paper tells us nothing about whether potential female infidelity triggers "sperm competition tactics."

Nor is this Shackelford's only study that ignores our broader knowledge of crime in a way that selectively supports evo psych explanations for violence against women. In the 2002 paper, "Understanding Domestic Violence Against Women: Using Evolutionary Psychology to Extend the Feminist Functional Analysis," (pdf available) Peters, Shackelford, and Buss note the trend toward fewer domestic assaults of post-menopausal women as support that domestic assault is evolutionarily selected as a means of controlling fertile women. They do this using New York City police incident reports for assaults against women only.

They don't use data from the National Crime Victimization Survey, despite the fact that they cite the survey in the paper. Nor do the results for female victims don't look substantially different than those they do use. From the NCVS:


Then there is the NCVS data for males:


There are fewer assaults overall, but the pattern isn't much different. In fact, the pattern isn't much different if you look at other types of crimes, either.


Given this information (the report on the age of crime victims dates to 1997), the challenge isn't to explain why the rates of domestic assault fall off near menopause, but to explain what is common to all crime experienced by females in the U.S. that produces that age curve, whether the crime is sexually motivated or not. This study, by again ignoring the data on the broader topic, fails to tell us anything about what it purports to be studying.

In order to actually present a skeptical view of a topic, it is not enough to assert, as some evo psych advocates do, that yours is the minority viewpoint or not widely accepted. That is simple contrarianism. Skepticism and honest inquiry require that one deal with all the information available on the topic. They also require that we not use the absence of information that would allow us to choose between explanations to argue for only one of these explanations.

The studies produced on this topic by Dr. Shackelton don't meet either criteria. That is what makes it disappointing that CFI Michigan has chosen to uncritically promote his work. [ETA: This topic is discussed at some length in the comments. They're worth reading.]

Citations

Goetz, A., & Shackelford, T. (2006). Sexual coercion and forced in-pair copulation as sperm competition tactics in humans Human Nature, 17 (3), 265-282 DOI: 10.1007/s12110-006-1009-8

Peters J, Shackelford TK, & Buss DM (2002). Understanding domestic violence against women: using evolutionary psychology to extend the feminist functional analysis. Violence and victims, 17 (2), 255-64 PMID: 12033558