Buller on mating preferences

Chapter 5 of David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature is mostly about the critique of studies that purport to demonstrate human mate preferences, covering males and females in turn. Buller's critique here is not that the theoretical basis for differences in male and female preferences is weak, or that there is no theoretical reason to suppose the mate preferences asserted by evolutionary psychology (males prefer young fertile females, females prefer high-status males). He does argue against both theoretical points later in the book, however, and here he reiterates his doubt that such preferences might be adaptations and part of a universal developmental program.

But the focus here is to refute the specific evidence that is supposed to demonstrate human mate preferences. Most of the chapter therefore takes the form of a batting practice, as Buller takes pitches from many different studies and clubs them down one by one. It's therefore not the most interesting piece of writing, but it does carry a sort of emotional satisfaction -- sort of like a long game of Whack-a-mole.

Now, if the evidence for the claim that females prefer high-status males is as weak as I've made out, why is the claim so widely accepted? I think the reason is that we are captivated by a particular picture of the relation between sex and status among our primate relatives, and this picture affects our perception of human mating. It is widely accepted that among non-human primates high-status males have greater mating success than males lower in the status hierarchy. This belief is due partly to the popularity of the engaging work of the primatologist Frans de Waal, who has been one of the main purveyors of this idea. Once we're convinced of the strength of the correlation between status and mating success among our primate relatives, the standards of evidence that are required to convince us of a correlation in humans get lowered considerably. As de Waal says: "In monkeys and apes there is a clear link between power and sex. High-ranking males enjoy sexual privileges, and are more attractive to the opposite sex. We need only look at recent events in the White House (and at a television spectacular like 'Who Wants to Marry a Multimillionaire') to see how much the link exists in us too." (Buller 2005:250, citing de Waal's 2000 New York Times book review of Thornhill and Palmer's Natural History of Rape)

Buller lists two problems with this viewpoint. First, of course anecdotal evidence is not enough to demonstrate mating preferences in humans generally. Beyond anecdote, there is precious little evidence that female humans actually do prefer high-status mates.

This may sound surprising to anyone cognizant of the literature on mating preferences in humans. As Buller describes, a major confounding factor is that people tend to mate assortitively with others of like backgrounds, interests, and prospects. These include financial prospects. They also include attractiveness, which is correlated with financial prospects in industrialized societies. This means that saying anything generally about female mate preferences must both make sure that the samples are representative (i.e. that they don't include one socioeconomic class to the exclusion of others) and that the confounding factors must be controlled (i.e. that an apparent preference for high status is not actually explained equally well by the preference for attractiveness).

As it turns out, the majority of work attempting to determine female mate preferences in humans has been done by surveying female undergraduate students at universities. Some of this work has been done by surveying women at their sororities! Now, of course female undergraduates including sorority members have mating preferences, and these preferences carry information about the mating preferences of females in society. But the sample of females who attend universities (especially private ones) and who belong to sororities (especially at private universities) is not characteristic of the population at large -- it is a sample biased toward women who expect to achieve high education status, who may have expectations of high income levels, and who disproportionately come from upper middle class backgrounds. That these women may prefer high-status men might be explained by a general preference for high-status men. Or it may be explained by a preference for men with similar interests, education, and prospects to their own.

Buller reviews studies that don't follow this bias and concludes that the evidence for a female mating preference for high-status men is weak or nonexistent. Indeed, reading this section is a bit like reading a slasher-movie as the hypothesis raises up again and again with each new study, and Buller strikes it down once more.

For me reading the book, the message is that data on human psychological preferences (at least for long-term life choices) really are not available in studies of human self-reported preferences or real-world behavior. There are just too many ways that preferences can vary (where studies generally ignore variation in preferences and focus on the averages only) and too many compromises that people must make in their behavior (when they can't get what they might prefer). This is the case in spades when Buller considers male mating preferences -- and the question of whether males prefer young women with waist-to-hip ratios of 0.70. He finds, again, that there is strikingly little evidence in favor of this preference, and that most of the evidence is flawed.

A sophisticated reader might point out that Buller hasn't really refuted the EP interpretations; he has merely provided alternatives that explain the observed data equally well. Buller is able to make these arguments effectively because of the large possible set of confounding factors, and because of the evolutionary psychology focus on averages instead of variation. When more information is available, Buller shows that it fails to support the EP interpretation. When more information is not available, Buller argues that the missing information is necessary to test the EP interpretation. In both cases, he is convincing that the evidence is weak or nonexistent. But Buller actually does note that some studies actively refute the EP expectations -- for example, the study of Kinsey's sexual behavior data that shows greater sexual activity by lower status males.

The other objection to the analogy from primates is that primate studies don't actually show a strong female preference for high-status males. Certainly some studies (on some species) do show this, but others show either no apparent female preference, a slight preference for low-status males, or multiple strategies where some females prefer low-status males at least some of the time. And many of the studies that show a correlation of high-status with male mating success are not demonstrating anything about female preference, but instead about male control of mating access. The idea that primate females generally prefer high-status males is a non-question: some species may show such preferences, others do not, and within species there may be substantial variation in mate preferences among females.

Buller leaves the chapter with one final point: selection might not be able to make a mate preference adaptation like the one proposed by EP anyway. Consider the way such a preference should work: people prefer as good a mate as possible, but since these are in high demand, they may have to settle for less than the prefer. Buller puts people on a scale from 1 to 10 -- the preference hypothesis supposes that everyone wants a 10, but they will tend to be able to mate with 10's themselves, which leaves 9's mating with 9's and 6's mating with 6's. But. says Buller, there's no reason to suppose that 6's have less offspring or lower long-term reproductive success than 10's. In genetic terms, if there is no reproductive benefit to a 6 in mating with a 10, then a 10 preference does not have a selective advantage over a 6-preference, at least as far as 6's are concerned. We might even think that 6's would be better off assessing their mating prospects early on and choosing 6's deliberately, instead of wasting a lot of time trying to attract a 10.

Noting that there may be a limit beyond which settling for a lower-quality mate may negatively impact reproduction, Buller notes:

The real question, then, is whether male status and female youth are characteristics that females and males respectively can "trade down" while still achieving comparable reproductive success. My skeptical argument presupposes that, within limits, they are. Evolutionary Psychology's view of human mate preferences presupposes, in contrast, that male status and female youth are characteristics that couldn't have been traded down by our ancestors without a corresponding decline in reproductive success (Buller 2005:256).

Buller points out that the most EP has to support this hypothesis is hypothetical arguments about the EEA. Indeed, the sort of thing one would have to know is the long-term success over many generations of different mate preferences, the heritability of such preferences within a hypothetical ancient population where they were polymorphic, and the differences between the modern environment where these features were observed and the hypothetical ancient environment where humans evolved. It's all exceedingly tenuous.

More on Adapting Minds

References:

Buller DJ. 2005. Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. Bradford Books, New York. Amazon