Wednesday, April 30, 2014

Today's Research Topic: Wide Hips and Promiscuity

I've got a backlog of studies I should write about, but in some cases the popularizers didn't dare to touch them (women have an evolutionary adaptation to get sexually abused)  and in a couple of other cases I haven't figured out what's going on with the methods yet (70-page articles take time).

But a recent evolutionary biology/psychology study about how narrow-hipped women are less likely to engage in one-night stands than their wider-hipped sisters is kind of fun to talk about, because all the popularizations are about that finding.  The researchers argue that this is because narrow hips are a health hazard in giving birth and so women with narrow hips would have some hard-wired evolutionary chip turned on to avoid situations where they might end up pregnant without a committed male partner.  Presumably the idea is that if the woman dies then the baby is more likely to survive if its father is around.

Or so it all sounds, superficially.  But if you read the research paper itself, things get a bit murkier, and that is clear (if murky things can be clear) from the very title of the paper:

Evidence to Suggest that Women’s Sexual Behavior is Influenced by Hip Width Rather than Waist-to-Hip Ratio.

So the researchers, Victoria J. Simpson, Gayle Brewer and Colin A. Hendrie, actually wrote about something a bit more complicated.  They wanted to see if the mythical albatross theory still hanging around the necks of evolutionary psychologists, about the presumed universal male preference for a certain waist-to-hips ratio, predicted which women would have more one-night stands.  Here the hypothesis is that the closer a woman's waist-to-hip ratio is to the ideal, the more potential bees would be swarming her flowers, so to speak.

Alas, they found no correlation with the waist-to-hip ratio and the proportion of a woman's sexual history which consisted of one-night stands.  Hence the focus on the hip width and its correlation with that number. Here the approach does a kind of a u-turn.  From the paper:

In this context, where opportunities for sexual encounters exist, it is women who decide, in all but the most extreme of circumstances, whether mating takes place or not (Clark & Hatfield, 1989). Signals of fertility and attractiveness, such as WHR, serve to influence the number/quality of men available to them (e.g., Hendrie, Mannion, & Godfrey, 2009). However, variations in hip width per se have a direct impact on women’s risks of suffering serious birth related traumas and these have the potential to lead to permanent gynecological damage or even death. Therefore, it was predicted that there may be some relationship between women’s hip width per se and their sexual behavior.

It's a bit muddled, I think, and gives short shrift to the mutual negotiations of sexual interactions.

Why aren't the men making choices here?  After all, they either swarm around the ideal waist-to-hip goddess or they don't, and that swarming is a choice, right?  If no bees are humming around a woman, her choice is meaningless.  Then there's the fact that the research this paper discusses didn't find any correlation between the waist-to-hip ratio and the number of one-night stands as a proportion of the woman's total sexual history.

More generally, I find the idea of "sexual history" slightly odd when the study subjects had an average age of first intercourse of sixteen years and when the age distribution in the study was from 18 to 26 years.  What would happen if studies like this were done on women in their eighties, say?

The study also omitted women who had never had intercourse.  That omission is most likely because the original idea was to study the waist-to-hip theory of attractiveness, and virgins don't provide information on that.  But once we move to the hip width theory, virgins would have been an important sub-group to include, because, following the logic of the researchers, they should contain the women with the narrowest hips.

The study measured hip width (based on bones) and it measured hip and waist circumference.  But other than those measurements, variable collection looks really minimal to me.  We know the women's ages, but we don't know anything else about them.  Yet the environment matters for casual sexual encounters, and not controlling for that may affect the findings. 

For instance, students living on campus have more access to one-night stands than women living in the countryside, cultural and religious norms may differ in studying something like casual sex and they should have been somehow controlled for.  And so on.  --  This is a common problem with evolutionary studies which simply ignore social and demographic data, because it's not in their model and they are not really familiar with the alternative models because they belong to different disciplines.

None of this means that the finding might not be a real one, but it suggests that better studies are needed to study it.  Such studies should look at the actual width of the birth canal, not the distance between the extreme ends of the hipbones, and they should collect all the relevant social-and-demographic data.