The boarding school where I was a pupil in the 1990s provided the perfect microcosm for anyone interested in how “survival of the fittest” plays out among humans. In a boarding house of 50-plus rambunctious boys, all of us employed various strategies to avoid becoming isolated and bullied, from forming coalitions to gaining popularity by selling cheap batteries (my own deterrent-based approach involved cultivating a reputation as a karate fanatic).
Then there was the minority of larger-than-average boys whose sheer size meant they had little to worry about. These chaps had an understandable swagger and confidence about them – their outgoing, assertive personalities seemed to reflect their physicality.
Was that correspondence between their body and character traits a chance correlation, or had their personalities developed in response to their physiques? One theory holds that it could be the latter. Known as “facultative personality calibration”, this is the idea that our personalities develop in a way that best suits the other genetic cards we’ve been dealt, including our size, strength, and attractiveness.
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Evidence supporting facultative personality calibration is growing – not only in terms of how one’s looks influence our personality traits, but even our approaches to finding romantic partners and our political beliefs. (It’s worth noting that the theory remains tentative thanks to a dependence so far on mostly correlational and inconsistent data, and because there are alternative explanations for the findings, such as that our personality traits can shape our bodies).
Consider trait extroversion, which involves not only being more sociable, but also more adventurous and willing to take risks. In evolution, it would make strategic sense if stronger, more physically capable people exploited their bodily advantages by being more extroverted.
That’s exactly what some research has found. One study out of Germany’s University of Göttingen recently reported that of more than 200 men, those who were physically stronger and who had more “macho” bodies – including larger chests and biceps – also tended to be more extroverted, especially in the sense of being more assertive and physically active. The same strength-extroversion association was not found among the women in the study.
Other research has found that physically more formidable men also tend to be more prone to aggression and less neurotic (as in, less fearful and worrisome). Again, this makes sense if you see personality as an adaptive strategy. If you are physically weak, then being cautious and wary of danger is likely to lengthen your lifespan. But if you are physically formidable, you can afford to be more of a risk-taker.
There are intriguing parallels to these ideas among behavioural ecology scholars studying animals. These researchers have noticed how, in many species, the animal’s “personality” (their tendency toward boldness or timidity) varies adaptively in response to their bodily state – for instance, one study showed that larger jumping spiders were bolder in the face of a potential predator than their smaller counterparts.
It’s noticeable that a lot of the human research on the association between physical strength and extroversion and aggressiveness has focused on men. This is because, according to evolutionary theory, physical strength and fighting ability is more of an asset to men who must compete with each other for mates. One study out of the University of California, Santa Barbara looked at both men and women and found the usual association between physical strength and trait extraversion, but the link was noticeably more robust among men.
The same study measured participants’ attractiveness, another physical attribute that could, in theory, make it advantageous to develop an extroverted personality style. Results showed that for women as much as for men, greater attractiveness tended to go hand in hand with being more extroverted – thus suggesting that some of these body–personality trait dynamics can play out for women too.
“The present findings demonstrate that a surprisingly large fraction of the between-person variance in extraversion can be predicted from physical strength and physical attractiveness,” the researchers wrote.
What’s more, their findings could not be explained entirely by differences in a key gene related to androgen function (likely to influence strength, attractiveness and aspects of personality). That bolstered the idea that physical attributes increase extroversion, rather than the body-personality associations merely reflecting shared genetic effects.
It’s not just people’s extroversion and neuroticism that are associated with their physical attributes. Other research has suggested that your approach to hooking up with relationship partners may also be a strategic adaptation influenced by your bodily and facial features, especially if you are male. For instance, in their research involving hundreds of undergrads, Aaron Lukaszewsk at Loyola Marymount University and colleagues, including Christina Larson and Kelly Gildersleeve at the University of California, found that the men (but not the women) who were stronger – based on a weight-training test – and more attractive were more likely to say that sex without love is okay, and that they could happily have sex with someone without being close to them.
This pattern of findings is consistent with the idea that among our male ancestors, those in better physical shape had more reproductive success by engaging in lots of casual sex and that such a sexual strategy has since evolved as a response to being physically capable. “The current findings support the hypothesis that stronger and more attractive men have more sex partners in part because these men are calibrated toward the pursuit of uncommitted mating opportunities,” the researchers wrote.
Just how far-reaching are the ties between how you look and who you are? For men, even political views could be implicated. In a study published this year, a pair of political scientists reported evidence from 12 countries, including the US, Denmark and Venezuela, suggesting that stronger, more muscular men were more likely to be against political egalitarianism. The rationale is that in our ancestral past, such men were more likely to thrive in a society where it was everyone for themselves. The findings for women were mixed, with some studies finding strength correlated with a greater endorsement of egalitarianism and others showing the opposite pattern.
“Just as physical strength shapes the conflict behavior of other animals in the domains that are important to them (e.g., mating and territorial contests), physical strength appears to shape the behavior of the political animal in this key conflict domain,” the researchers wrote.
We often think of our personalities and beliefs as reflecting the essence of who we are – whether shy or outgoing, commitment-phobic flirt or devoted partner, left-wing or right-wing. And we like to think that these traits derive from cerebral, moral or even spiritual sources.
The idea that these aspects of ourselves might instead, at least in part, reflect a strategic adaptation to our physical size and appearance remains for now a controversial theory. But it’s one that, like a boarding house full of boisterous children, provides a humbling reminder of our animalistic roots.
Dr Christian Jarrett edits the British Psychological Society's Research Digest blog. His next book, Personology, will be published in 2019.
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