my favorite primate

I got Sexual Selection and the Origins of Human Mating Systems by Alan Dixson (author of the incomparable Primate Sexuality) from interlibrary loan yesterday.

Oh. Oh my. I mean, I am just having nergasm after nerdgasm with this book.

Do I love it because Dixson spends so many paragraphs explaining the shortcomings of Baker and Bellis (see especially pp. 74-76), as I have not had sufficient motivation to be bothered to do (though I have scorned them)?

Or is it because he brushes aside the “wishful thinking” (p. 36) theorizing of the same male evolutionary psychologists that I have been exhausted and frustrated by?

Do I love it because Dixson is so careful to remember that western, educated, industrialized, rich, democratic (WEIRD) culture is radically and profoundly different from the environment of evolutionary adaptedness?

Or do I love it because I learned from it, after 15 years as a sex educator, that in fact there IS a male homologue to the uterus (see p. 77)?

Answer: Yes.

This book discusses everything important known to date about the evolutionary antecedents of human sexual systems, without any of the condescending, unscholarly dickweedery that turns evolutionary psychology into a punchline.

If you read nothing else in the book, go to page 185 and read the 10 “highly questionable findings and views which have been reported and cited during the last two decades.” (Three of them – that’s 30% of the most egregious bullshit in the field of the evolution of human sexuality – are Baker and Bellis’s work.)

But perhaps the best part of the book is the handful of paragraphs on pp. 120-122, in which Dixson dismantles, clearly and cleverly, the bunkum about women have a “dual mating strategy.” This particular load of claptrap has been a bugbear of mine for years and years, but I’ve never before seen such a precise and tidy explanation of the shortcomings of both the theory and the reasoning behind it.

The theory itself goes rather like this: because women have different preferences, different “attractiveness ratings,” for different male characteristics depending on their menstrual phase (masculine faces and different MHCs at ovulation, less masculine faces and similar MHC near menstruation), women have evolved a dual strategy to get a genetic father and also a separate parenting father. Someone to provide genes and someone else to provide… well… everything else. A short-term strategy and a long-term strategy.

Dixson, in his understated way, says

I suggest instead that there has been a regrettable tendency for some workers in this field to over-interpret the results of studies where women are asked to express preferences for masculine traits in relations to hypothetical long-term versus short-term mating strategies.

He offers three “drawbacks” to this dual mating hypothesis, which I’ll summarize briefly here, but do go read it in full if you’re interested in this kind of thing!

(1) There isn’t any compelling evidence that the “preferences” that change with the menstrual cycle have any impact on behavior. Changes in women’s sexuality across the menstrual cycle are “situation dependent and subtle by comparison with effects of the ovarian cycle upon sexual behavior in most mammals.” Just because something can be measured in an experiment doesn’t mean it has any impact on real life behavior and decision-making.

(2) Universally, people fall in love; and almost as universally they form dyads – partnerships with a single other person that last over multiple years. These partnerships are known significantly to improve the survival rate of offspring. Given, additionally, the role of jealousy in love, and the concomitant mate-guarding behaviors, a woman takes a greater risk in threatening the dyad so crucial to her offsprings’ survival than in having offspring fathered by a man good enough to be her long-term partner.

(3) The risk of pre-eclampsia “decreases with the duration of a woman’s sexual relationship with her partner.” If she has sex with someone else, the risk of pre-eclampsia “is greatly increased should she conceive as a result.”

Dixson’s alternative hypothesis is simply that the preference for masculine traits is “part of selective mechanisms for primary (i.e., long-term) mate choices.”

I find the first and third argument particularly compelling – the second would seem to be a good target for theoretical evolutionary biology to tackle from a mathematical perspective. They’re all open to empirical investigation. I agree with Dixson that we’re likely to find no significant difference in “cuckolding” behavior around ovulation among naturally cycling women, in any culture. I don’t know if we’ll find a difference in pre-eclampsia among women whose pregnancies are fathered not by their long-term partner.

If you’re interested in the evolution of human sexuality, THIS is the book to read. I’ve already incorporated it into the readings for my fall semester class.