Written by Ichimoku Sanjin.
Intelligence is one of the most important qualities that women look for in a partner. They are drawn to men who are well-educated, think critically and engage in interesting conversation. The genes for IQ encompass a large portion of the genome, and intelligence positively correlates with almost everything we consider desirable, from civic engagement to athletic ability.
It therefore makes sense that women would directly select for intelligence. In doing so, they would gain not only direct benefits, such as resources and safety, but also a “eugenic premium” in the form of genetically fitter offspring. And yet there are many holes in what I call the “Einstein Selection Theory” (hereafter the EST).
First, there is a sizeable gap between what women say they want and what they actually want. This is a well-studied phenomenon termed social desirability bias. Research participants skew their answers (consciously or unconsciously) to appease the researcher or to follow social norms — and women do it more often than men.
Many of the studies that claim women are attracted to smarter men are based on self-report surveys, a method especially prone to this bias. In these surveys, subjects are asked to list the traits they find appealing in hypothetical short- or long-term partners. Of course, reality rarely matches hypothetical circumstances, particularly when optimistic thinking and reputational concerns come into play.
A study was carried out in which men and women were asked to rate the importance of physical appearance, personality and money before a speed dating experiment. The researchers then observed the actual importance of these factors in the course of the speed dating. Prior to the experiment, women had rated physical appearance as the least important trait. It ended up being their highest priority, with personality and money coming second and third. Of course, these artificial experiments also suffer from a lack of ecological validity. But they do allow us to scrutinise the self-report data on which the EST relies.
The next problem with the EST is the lack of evidence from trait correlations. Facial attractiveness and intelligence are not associated at the phenotypic or genotypic level. This is contrary to expectations from evolutionary theory because sexually selected traits are usually intercorrelated, either due to pleiotropy (hormonal or genetic) or cross-trait assortative mating (intelligent people choosing more facially attractive mates and vice versa).
Indeed, facial symmetry is a large component of attractiveness and is an indicator of genetic “quality”. If intelligence was an attractive quality in a mate, more attractive people would choose the smartest partner, and their offspring would become smarter and more intelligent than average thanks to cross-trait assortative mating. So what do the data on assortative mating show?
One study observed genetic correlations of r = .37 for educational attainment, r = .13 for height and r = .08 for depression. Both men and women tend to choose partners with similar social, psychological and physical traits (height, weight, eye colour). However, this does not mean that women necessarily prefer smarter men. It could simply mean that women prefer men who are similar to themselves — not too much smarter, not too much dumber.
If sexual selection had been a factor in the rise of intelligence during human evolution, we would expect it to have been particularly important over the last century in industrialised societies. Why? Women in those societies have been much less restricted in terms of their freedom to choose a partner.
However, the trend since the mid 20th century has been toward lower genotypic intelligence. What’s interesting is that the same is not true for height. Selection for height appeared in the 20th century, having not been present in the 19th. A recent Dutch study found that taller men had higher fertility than shorter men, which could be a factor in the overall increase in height. And women’s preference for taller men shows up in all study types, including self-report surveys, laboratory experiments and field settings.
If smarter men were more attractive, women would look for intelligence cues in prospective partners, but it doesn’t seem that they do. For example, men and women wearing glasses were considered less attractive, despite glasses being associated with higher perceived intelligence.
Of course, you could point out that the association between intelligence and wearing glasses is something that emerged from culture, rather than being a biological instinct. Yet humans are incredibly social and have the capacity to reconcile societal standards with our biological instincts. Money, for example, is relatively new on an evolutionary timescale and yet it has a strong influence on social behaviour in general and mate choice in particular.
Brain size is an interesting measure. People with larger brains are, on average, more intelligent, and people with larger brains naturally tend to have larger heads. However, women aren’t attracted to men with a large head or what is some termed a “fivehead”. Most women would prefer a small-headed basketball player to a big-headed boffin like Einstein.
The best evidence against the EST comes from a recent study where measured intelligence did not predict increased mate appeal in either speed dating or other experiments. The study even found a small but significant effect in the opposite direction! Although funnier men were deemed more appealing, having a sense of humour was unrelated to the g-factor. Physical attractiveness was the single most influential factor in determining a man’s appeal. Interestingly, the slight negative effect of intelligence was not due to women being unable to assess the men’s intelligence: the more intelligent men were indeed seen as smarter.
It is worth noting that human adults are sexually dimorphic with respect to intelligence, as documented by Richard Lynn. Males gain an approximately 4 IQ point advantage over females during late adolescence.
Now, sexual dimorphism does implicate sexual selection in the past. However, sexual selection can be driven by female choice or by intra-sexual competition. In most dimorphic species, intra-sexual competition involves physical violence, but in humans it typically involves vying for wealth and status within complex social hierarchies. If Lynn is correct, men may have evolved superior cognitive abilities in order to gain access to influential positions and, in turn, more desirable women. So intelligence may not have been selected for directly, but rather indirectly via its associations with wealth and status.
I already mentioned that smarter men are deemed slightly less attractive in experimental settings. But does this translate into a real-world lack of mating success? The answer appears to be yes.
In 2000, a study was published titled ‘Smart teens don’t have sex (or kiss much either)’. It found that the most sexually active males were in the 75–90 IQ range. Controlling for age, physical maturity, mother’s education and race, adolescents with an IQ of 130 were 3–5 times less likely to have had intercourse than those with merely average IQ. Interestingly, a curvilinear relationship was observed, whereby both low- and high-IQ males were more likely to be virgins than those of average IQ. Yet males with a level of IQ that would qualify for intellectual disability were still more likely to have had sex than those with a very high IQ. (The association between IQ and sexual activity was weaker among females.)
This all makes sense when you think about it. Women swoon over athletes, actors and musicians — not Nobel Prize winners or Math Olympiad finalists.
Industrialisation has led to dramatic changes in sexual morality, with women gaining more freedom to choose their partners. (Today, a woman who lives in a city and owns a smartphone has an effectively infinite pool of men to select from.) And there is no reason to suppose that the aggregate of their choices is positive for humanity; it may very well be negative. Studies have shown that women are more attracted to men with “Dark Triad” traits — narcissism, Machiavellianism and psychopathy — which evolved to facilitate men’s short-term mating strategies. This also explains why certain women are drawn to serial killers, gangsters or psychopaths.
Darwin taught us that deviations from the optimum phenotype are weeded out by natural selection, including traits that are attractive to mates but costly for the individual’s survival. In modern populations this evolutionary trade-off has disappeared and sexual selection operates completely unchecked.
A different version of this article was previously published on Aporia.
Ichimoku Sanjin is an evolutionary anthropologist who works on intelligence, creativity and behavioural genetics. He once published poetry but now prefers the language of R.
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Very interesting and well written article.
The only point of contention I could find was in the assertion that there was a mismatch between wanting a man with money and not wanting one wearing spectacles. Wanting a man with money is obviously eugenic but so is not wanting one with glasses as wearing these codes for a prehistoric genetic weakness that results in being unable to hunt and fight with the rest of the men in the tribe.
Great article. I'll surely bring it up next time I have an argument with my wife. Not.