Friday, April 10, 2015

The Beauty of The Female Back. Today's Evolutionary Psychology Study.

A couple of readers forwarded me summaries of an evolutionary psychology study about what angle of lower back men* view as the most beautiful in women.  Thanks for those summaries.

I wasn't going to write about the study, because it didn't beep loudly enough on my freakometer**. 

But then I Googled it and found something fascinating about who quoted it:  The first ten pages of Google gave me a large harvest of pickup artist sites, a few misogyny sites and, in general, lots of tough-prehistoric-guy sites.  Many of those sites summarized the study as being about large butts, which is incorrect, but then misunderstanding studies is more common than understanding them.  What was more interesting is that this study  seems particularly loved by those who do not particularly love women.

That's one fascinating fact.  The other fascinating fact is a comment in one study summary:

The second study addressed the question of whether men prefer this angle because it reflects larger buttocks, or whether it really can be attributed to the angle in the spine itself.
Approximately 200 men were presented with groups of images of women with differing buttock size and vertebral wedging, but maintaining a 45.5-degree curve. Men consistently preferred women whose spinal curvature was closer to optimum regardless of buttock size.
"This enabled us to conclusively show that men prefer women who exhibit specific angles of spinal curvature over buttock mass," said the study's co-author Eric Russell, a visiting researcher from UT Arlington.
This morphology and men's psychological preference toward it have evolved over thousands of years, and they won't disappear over night.
"This tight fit between evolutionary pressures and modern humans' psychology, including our standards of attractiveness, highlights the usefulness that an evolutionary approach can have for expanding our knowledge not just of the natural sciences, but also the social sciences," Lewis said.

Emphasis is mine.

To see why that comment is very weird, consider the background of this study:  It is about the natural bend in the lower back of both men and women and the sex differences in the wedged lumbar vertebrae.  Men have two of them wedged whereas women have three.  That wedging, in general, may be related to bipedalism, and the sex difference certainly seems to be, because (from 2007):

"The body must change in dramatic ways to accommodate the baby, and these changes affect a woman's stability and posture," said researcher Katherine Whitcome, an anthropologist at Harvard University. "It turns out that enhanced curvature and reinforcement of the lower spine are key to maintaining normal activities during pregnancy."  
They found a similar trend in the vertebrae of early humans called Australopithecus, but not in those of chimpanzees (our crawling relatives). The finding suggests these spine adaptations evolved at least two million years ago when human ancestors first began to walk upright. Our four-legged ape ancestors didn't have to accomodate [sic] for the extra baby weight, because their bellies just hung lower and there was no significant shift in the center of gravity.
"Natural selection favored this adaptation because it reduces extra stress on a pregnant female's spine," said researcher Liza Shapiro, an anthropologist at the University of Texas at Austin. "Without the adaptation, pregnancy would have placed a heavier burden on back muscles, causing considerable pain and fatigue and possibly limiting foraging capacity and the ability to escape from predators."

Emphasis is mine.

I guess you can argue that two million years could equal "thousands of years?"
But why would the morphology disappear?  There's no reason for it to disappear, because it is useful.  To talk about it disappearing and about "thousands of years" seems very odd.  Very odd, indeed, unless one is aware of the way evolutionary psychology is sold to us as the science of Stone Age women in high heels and Stone Age men driving sports cars and so on.

Then to the study itself (behind a paywall, sadly).  It consists of two sub-studies.  In both of them young male students in the US are asked to state which female side view they prefer.  The women are drawn identical except for changes in the curvature of the lower spine in one study (too little, too much and just right) and in both the curvature and the muscles or fat of the buttocks in the other study.*** 

The researchers conclude that the optimal curvature or lordosis is the preferred one in both studies. Thus:

The convergent results from these independent studies reveal a strong fit between observed standards of attractiveness and a priori predictions based on selective pressures operating during hominin evolution. These tests suggest that selection fashioned not only spinal structures in women for solving pregnancy-related challenges, but also attendant psychological adaptations in men for assessing female physical attractiveness on the basis of these structures.

So what do we mean by "optimal" curvature here?  That's where things get a bit hairy, because it turns out to be the average curvature in the female lower spine.

The authors acknowledge that, but  argue that they have found the reason why the average curvature would be preferred by men, and this has to do with mating and such.   I'd like to see the same study done with heterosexual women, to see if women would rank the pictures the same way or not.  If the explanation in this study holds water we shouldn't find that to be the case, right?  But my guess is that women would rank the pictures the same way.  At least I did.

I would also like to know what percentage of women have curvatures other than the optimal or average one.  If that percentage is very small then the study might amount to something very different from its assertions.  For example, spot-the-woman's-body-in-these-pictures or spot-the-healthy-spine.

To conclude, it's possible that men have an "evolved" mating preference for women with healthy spines.  I wouldn't be surprised, though neither would I be surprised to find that heterosexual women have the same "preference" for how women's spines should look.  What's more fascinating than the study itself are those sites (other than science sites) which link to it.  They have a particular axe to grind and it's the idea that evolutionary psychology of a certain kind gives them a blueprint permission to be sexists and so on.

*I assume these are heterosexual men, though I don't think the study mentioned that.  Just the usual stuff about the men being very young and psychology students at an American University.  Soon we will have a whole genre about prehistory where the evidence comes from American undergraduates!  No possibility of cultural confounding there!

**It didn't suggest, for instance, that managing to get oneself raped is a useful evolutionary adaptation.  Yes, Virginia, that study exists inside the weird and wonderful world of evolutionary psychology.

***  Here, for example, is one picture from the second study where all three women exhibit the same "buttock protrusion" but the causes are different:

Is it really the case that the line of the stomach reveals the underlying causes of spinal lordosis?  I don't know the answer, just wondering.