Friday, December 19, 2008

mate economics

Lately, I've been reading a lot about women's mate preferences. Professional reasons, I assure you. One of the more intriguing methodologies I've come across has used economic principles, like minimum standards and diminishing marginal returns, to examine people's priorities in mate characteristics. The central issue at hand is sex-differences.

Briefly, evolutionary psychologists have proposed that (heterosexual) men and women tend to value different things in romantic partners because of their reproductive value. These differences emerge based on the asymmetric costs of sex. In our species, like most mammalian, females get pregnant. Therefore, women have to be particularly careful about mating situations since there's the possibility of internal fertilization. Remind yourself that we're talking evolutionary history here, and how our ancestral environment shaped the design of our respective male and female brains. Thus, any reference to reliable contraception (such as the pill) is irrelevant. Robert Triver's parental investment theory predicts, specifically,that the sex making the largest investment in lactation, nurturing and protecting offspring (women, in our case) will be more discriminating in mating - and the sex that invests less in offspring (men) will compete for access to the higher investing sex.

Sex differences in mating strategies and preferences are particularly visible in species like the elephant seal, where there is a vast sex disparity in parental investment. Males compete (vigorously) for access to reproductive females, and females choose to mate only with the most dominant males. Females, in effect, are "choosing" nothing more than the genetic quality of their mate, since he'll have absolutely nothing to do with parental care.

Humans, admittedly, are a different story. We're defined by intense bi-parental care of our offspring, due in large part to our extended childhood and period of vulnerability - which in turn exists because our massive brain needs time to develop and acquire boatloads of information. Thus, we might expect sex-differences in mating strategies and preferences to be less extreme in our species - and they are. But don't doubt that they still exists. Men cheat more than women, crave a wider variety of sexual partners, and tend to be less discriminating. For example, if you ask men and women what's the likelihood that they'd have sex with someone they've known for 1 year... or 1 month... or 1 week... or 1 hour... you get data like these:

(cool data presented in a shitty graph)

A positive number on the y-axis indicates a positive inclination to have sex, so it's interesting to look at where the lines cross the x-axis for both men and women. For women, it's around 6 months. For men, it's around 1 week. Now, admittedly, these data were collected approximately 20 years ago and some might argue that "things have changed, man! Women hook up ALL the time, now." Bullshit. If anything, recent evidence suggests that college women are having less sex nowadays than they did 10 years ago, even if they are engaging in more non-commital make-out sessions with boys in the back of the bar/party/van/etc.

When it comes to specific mate preferences, or what we look for in members of the opposite sex, we're all pretty choosy. Neither men nor women (some fools notwithstanding) mate indiscriminately. But there's still the question of what we prioritize. What traits do we particularly value in our partners? And here we will find some interesting sex differences that again can readily be explained by evolutionary theory.

Briefly, men tend to place greater importance on physical attractiveness than women do. This largely has to due with cues of youth and reproductive fertility. Women, in contrast, tend to place greater importance on resources than men. "Resources" in this context can mean many things - it could mean actual wealth, for example, or traits that help one acquire wealth (such as industriousness, intelligence, social status, etc.). This largely has to do with finding a mate that can help support the family and offspring survival outside of immediate investments, like breastfeeding. Our ancestors survived, and successfully passed on their genes, because of this reciprocal cooperation and division of labor.

If you ask men and women to rank a list of traits that they value in marriage partners, you'll get something like this (from Buss & Barnes, 1986):

(click for larger image)

Men and women agree that "kindness and understanding" are vital. There is no sex difference there, or with an appreciation for intelligence, creativity, and health. However, three items stand out on this list: 1) physical attractiveness, 2) college graduate, and 3) good earning capacity. Each of these shows a strong sex difference in how men and women ranked their importance. Can you guess who ranked each one higher?

This is all well and good, but isn't how mate-choice works in the real world. We deal with people who are amalgamations of many traits, a combination of physically stunning but none-too-bright, or brilliant and rich but cruel. What do we do in these situations? Well, we prioritize. We weigh costs and benefits, and depending on what we're looking for at that moment in our life, we make (imperfect) decisions. Herein lies the brilliance of the economic mate-choice model, introduced by Normal Li and Doug Kenrick.

You have 20 "mate-dollars" to spend on a potential sexual partner. This is only going to be a one-night stand and you'll never see this person again. You can distribute this money across a number of traits, including physical attractiveness, kindness, intelligence, and so on. Where do you put your money? What do you value most highly?

Perhaps not surprisingly, when phrased like this - with a relatively small budget and a casual sex scenario - both men and women put a lot of money into looks (66% of budget for men, 54% for women).

But now, let's say, you're shopping for a marriage partner... a soul mate. What will you invest in? Will you really put that $15 into attractiveness, when you're sacrificing intelligence, amicability, and empathy? Well, if you're a man, you're more likely to (actually, men put about 1/3 of their budget into looks, even for a long-term partner - compared to 25% for women).

(from Li & Kenrick, 2006)

A clever model. Social psychology can sometimes leave a bad taste in my mouth, because it's based so heavily on self-report data and is often atheoretical. But I admit to liking evolutionary-minded analyses like these, which demonstrate (in many ways) what we've long suspected: men and women are different. But the valuable lesson here is that they're different for a reason, and that reason isn't as simple or dull as "culture taught them to be so."

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