I’m not a biologist, so I welcome comment from real biologists in what follows here. It’s my understanding, however, that evolutionary biology really tries hard to avoid the “just-so” stories of many popular accounts. Example: you may read that giraffes evolved their long necks because they helped the animals reach leaves other browsers couldn’t. But that’s a post-hoc explanation: we know giraffes use their necks that way, but we can’t know what the original evolutionary “reason” was, or whether the browsing is a side effect from some other advantage, like mate selection. I imagine it’s a strong temptation to tell explanatory stories (and I’m sure I’ve done it myself), but it’s not really scientific to do so. As with anecdotal evidence, “just-so” stories may be true or false, but there’s no way to evaluate their correctness without additional information.
Which leads me to this article in Slate, citing a study that claims women walk in a less sexy manner and have greater hand strength during ovulation to help prevent rape. Several people have already done comprehensive take-downs of this article and the study it’s based on (by Jerry Coyne, PZ Myers, Amanda Marcotte, and I’m sure many others), so I’ll just summarize what they’ve already said:
- The study is based on a small sample without much in the way of controls, so it’s a little untrustworthy from the outset. There’s also some question about whether the results are consistent with other studies.
- Even if the immediate result (women walk in a less sexy manner and have greater hand strength during ovulation) is true and universal, extrapolating it to an evolutionary rape-prevention strategy is questionable, since it’s no better than a “just-so” story.
- A logical consequence of the study would then be that women are OK with assault when they aren’t ovulating, which doesn’t make any sense.
- Finally, many other studies have shown definitively that rape in humans is not about sex or reproduction, but about the power the rapist exerts over the victim.
So much for the Slate article and the study it summarizes. It does highlight in its extremity many of the problems with evolutionary psychology, the field that tries to understand the human psyche (language, social behaviors, etc.) using the tools of evolutionary biology. By itself, this is a honorable undertaking, but it’s fraught with danger: so many human behaviors are culturally weighted, so it’s difficult to disentangle what is innate from what is contextual. As the late great Stephen Jay Gould was fond of pointing out, natural evolution is Darwinian—characteristics acquired by adults aren’t transmitted to offspring, while cultural evolution is Lamarckian—we teach our children, and knowledge is cumulative over time. So little girls’ preference for the color pink in the US is culturally-defined (and hasn’t always been true!), not innate, but occasionally evolutionary psychologists will present studies attempting to show the opposite.
The problems of evolutionary psychology in the end will be corrected by scientific methodology. If they can be tested by experiment or other kinds of hard evidence, as opposed to “just-so” stories, specific claims of evolutionary psychology will be vindicated or invalidated as with any other scientific endeavor. However, as long as so many evolutionary psychology studies seem to be focused on finding evolutionary explanations for some of humankind’s worst behaviors (rape, genocide, racism, etc.) and failing to back them up with good evidence, it’s irresponsible for the media to report stories that are actually pseudoscience. Doing so damages legitimate evolutionary psychologists’ reputations, and harms the reputation of science itself in the eyes of the public.
(Slight edit: I misspelled PZ Myers’ name in the original post.)