Gender equity can cause sex differences to grow bigger

1960 Le Lac des cygnes ballet - Jean-Paul Andreani and Claire Motte performing on stage at Opera de Paris.  Credit: Christjeudi10, Wikimedia commons
1960 Le Lac des cygnes ballet – Jean-Paul Andreani and Claire Motte performing on stage at Opera de Paris. Credit: Christjeudi10, Wikimedia commons

How do sex differences arise? Few questions animate as much disagreement and contention, in everyday society and in academic study. For as long as the question has been asked, the answers have fallen between two extremes: sex differences arise innately, or they come from social experience.

That same polarity defines much of the study of human behaviour and society, and has done since the ancient Greeks asked whether ideas arose innately (Rationalism) or from experience (Empiricism). The modern fault-line runs deepest between rationalist biology and empiricist socialisation.

Impossible as it might seem for any serious thinker, awake and aware and living in the current Century, to dismiss either biology or socialisation, you might be surprised. Dogmatism and ignorance still stifle the study of human behaviour, and the topics of gender and sex differences in particular. And the lay public is equally awash in tightly-held, but often flimsy ideas about how women and men come to differ, on average, in all sorts of traits.

The evidence is in: samples of women and men differ, on average, in a vast number of personality, emotional, behavioural, cognitive and attitudinal measures. Yes, the sexes overlap. And one cannot and should not rush to inferring anything about a person from the average properties of those who share the same genital configuration. But sex differences are present, found in many replicate studies, and often similar in magnitude across societies.

Rationalist biology holds that such differences have evolved. The combination of traits that made our male ancestors successful fathers differ from those that turned our female ancestors into successful mothers. This idea chimes with the repeated presence of so many sex differences across cultures, but the fact that the magnitude of the differences varies considerably among cultures suggests much more than biological determinism.

The Empiricist thinking that has dominated the study of gender in the social sciences for more than half a century holds that sex differences arise from extensive socialisation, and differences in the power that women and men hold and wield. This view brings us the notion that by ceasing to socialise boys and girls into stereotyped sex roles, and breaking down power inequities within societies, sex differences will diminish.

The idea that teaching, socialisation and structural change will progressively erode sex differences and gendered behaviour has a powerful hold. It underpins social interventions from “No Gender December” (a.k.a. the Christmastime war on pink toys) to the current Stop it at the Start campaign against domestic violence.

Stop it at the Start video, part of an Australian Government campaign to combat domestic violence against women.

A testable prediction

A recent book chapter by eminent evolutionary psychologist David P. Schmitt adds an interesting dimension, sure to be controversial, but also with considerable potential to rejuvenate debate. The book, The Evolution of Sexuality (Springer, editors Todd K Shackleford and Ranald D. Hansen), at US $139 will likely prove inaccesible to readers without access to an academic library.

Alice Eagly, Wendy Wood and Mary Johannesen-Schmidt, among the most persuasive advocates for the primacy of socialisation into sex roles, predicted that increasing gender equality would lead to “the demise of many sex differences”. That prediction seems so intuitive, so consistent with contemporary thinking about gender equity, that it hardly needs testing. But Schmitt didn’t think so. He recognised that not only should the idea be put to the test, but that there exists a wealth of data on cross-cultural on variation in personality, behavioural and other traits that could be matched with good measures of gender equity and sex role ideology.

Counter to the prediction of social role theory, in only 2 out of 28 traits examined by Schmitt did sex differences narrow as gender equity increased. In six traits, the sex difference remained stable, and in 20 traits it widened.

For example, women tend to score higher than men on personality tests for extraversion, agreeableness and conscientiousness. Gender equity tends to elevate all three of these traits, but it does so more in women, widening the average sex difference.

Likewise, men score higher than women for the “Dark Triad” traits of Machiavellianism, Narcissism and Psychopathy. Gender equity has the salutary effect of reducing each of these three rather nasty traits, but it does so more for women than for men, resulting in wider sex differences.

The two traits in which gender equity narrowed sex differences are instructive, too. Women are more likely than men to value resources and wealth in a mate. Gender equity reduces this preference, but does so more in women, narrowing the sex difference. And men tend to report a more unrestricted sociosexuality – fantasising about, attitudes toward and engaging in uncommitted sex – than women do. Sexuality grows less restricted with gender equity in both sexes, but more so in women, again narrowing the sex difference.

The narrowing of sex differences in preference for wealthy mates and sociosexuality are to be expected, and very much in line with the politics of sexual and domestic liberation. This is exactly what any observer of contemporary society would have expected, irrespective of the moral valence they give to the issues involved.

Many behavioural traits showed general changes for the better with increasing gender equity. Personalities take on more socially desirable forms. Couples emphasise love within their romantic relationships. Intimate partner violence declines. And rates of depression decrease. And yet the fact that sex differences in so many of those traits increased opens up considerable new space for empirical study, and for us to question dogma and doctine of all kinds about how sex differences arise.

This study is just a start. There remains some way to travel if we are to make stronger inferences about causation. But it is worth wrapping our head around the paradox that moves toward gender equity in opportunity, including the dismantling of patriarchal power structures, might, paradoxically, also widen sex differences.

Bohemian Like You, the Dandy Warhols.

The Conversation

Rob Brooks, Scientia Professor of Evolutionary Ecology; Director, Evolution & Ecology Research Centre, UNSW Australia

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Why the masculine face? Genetic evidence reveals drawbacks of hyper-masculine features

Miranda Kerr’s face typifies the properties of feminine youthfulness, including a short face, small chin, thick lips and small brow. Source: Eva Rinaldi, Wikimedia Commons
Miranda Kerr’s face typifies the properties of feminine youthfulness, including a short face, small chin, thick lips and small brow. Source: Eva Rinaldi, Wikimedia Commons

Studying sex differences seldom gets boring. While the origins of differences in behaviour and cognition remain fiercely – and quite rightly – disputed, we don’t sweat quite as much about why women and men differ in size and strength. The Darwinian process of sexual selection, in which genes that improve an individual’s reproductive success get inherited by the fruits of that reproduction, does a good job explaining sexual dimorphism (male-female differences) in these traits.

For most of our evolutionary past, bigger men fended off rivals for female attention and out-competed other men to secure status and resources that made them useful contributors to a family. These advantages offset the energetic costs and higher disease risk of building a bigger body. But what of other manly features? What use is masculine hairiness? Or those features that tend to distinguish male from female faces.

Like many other traits, from height to interest in the affairs of the sisters Kardashian, facial features differ between women and men, on average, but there is much overlap between the sexes. Using just the distances between ‘landmark’ features, the differences between masculine and feminine faces come down to complex multivariate vectors, but features like brow prominence, chin size and lip thickness play a big part.

Women and men both rate female faces bearing typically feminine features as more attractive than female faces with more masculine combinations of traits. Which might explain why Miranda Kerr’s full-lipped, round-faced, small-chinned visage seems to be everywhere these days.

So it would be reasonable to predict that lantern-jawed, Neanderthal-browed men at the far-masculine end of the facial distribution would be sought-after by women. But reality is far more varied and interesting.

Women don’t usually find masculine faces more attractive than more feminine male faces. For every Javier Bardem or Josh Brolin, there’s an Orlando Bloom or Zac Efron down the girly end of the man-tinuum. More studies report an overall preference for ‘feminine’ male faces than for ‘masculine’ ones.

Javier Bardem’s prominent cheeks, large brows and jaw give his face an exaggerated masculinity. Georges Biard, Wikimedia Commons
Javier Bardem’s prominent cheeks, large brows and jaw give his face an exaggerated masculinity. Georges Biard, Wikimedia Commons

It seems that women vary in how attractive they find masculine faces. Women at the fertile peak of their cycle favour more masculine faces, or at least less-feminine ones, than women not at the fertile peak or on the pill. Women who rate their own partners as highly masculine, or who describe their ideal partners as highly masculine, prefer more masculine faces in experiments. And women contemplating once-off sex or infidelity are keener on masculine-looking men.

The prevailing view in evolutionary psychology is that highly masculine men make great sperm donors but not necessarily awesome partners and fathers. First the downside: highly masculine men are less committed as fathers and partners, less cooperative, more sensation-seeking in outlook and more likely to seek short-term sexual encounters than less-masculine looking men. These downsides of pairing with a masculine man are thought to result from testosterone’s effects on behaviour.

While low-T, less-masculine guys might make better long-term partners, there might be benefits of a fleeting attraction, at peak fertility, to manly men if they are more likely to sire genetically well-endowed kids. It’s an idea bolstered by the findings that women living in countries with lots of disease prefer faces of more masculine-looking men. As do women primed with images of body fluids, skin lesions and other cues of disease. Developing highly masculine features takes plenty of testosterone, an immunosuppressing hormone. Which means only those with the best immune genes can afford to be taxed with high-T levels in puberty. Or so the story goes.

This is one of those ideas with prurient appeal, but patchy evidence. It’s morphing into what my UNSW colleague Angela Moles calls a ‘Zombie Idea’: compelling and considered self-evidently true by many, but not actually that well supported. Every link, from the attractiveness of masculine facial features to the immunosuppressive nature of testosterone to the claim that masculine-looking men have good immunity genes is contested. We don’t know how big the genetic benefits to children might be, much less whether they can offset the costs to a woman of mating with a highly masculine man.

New kinds of evidence

Only with new kinds of evidence can this complex question be more rigorously tested. And such new evidence has emerged, in the form of a paper in Psychological Science by Anthony J. Lee, Brendan Zietsch* and collaborators.

From an exhaustive suite of measures taken from photographs of teenaged identical and non-identical twins and their non-twin siblings, Lee dissected the extent to which variation in facial masculinity-femininity is due to genetic variation. Interestingly, around half the variation in both male and female facial masculinity could be attributed to additive genetic variation. This is the kind of variation on which the idea of “gene shopping” for genetically superior mates depends.

The extensive genetic variation in masculinity makes more plausible the idea that choosing to mate with a masculine man can result in more attractive offspring. But the genes that made a male face more masculine did not make it more attractive. Worse, these same genes made female faces more masculine and thus less attractive. Families that make manly-looking sons tend also to make masculine-looking daughters.

Overall, this paper deals a substantial blow to the idea that masculine men make good genetic sires. Of course, the genes that confer masculinity on both sons and daughters might have other positive effects, including but not limited to improved immunity. That remains to be assessed, hopefully with the same kind of quantitative genetic evidence.

So, why the manly face?

The evidence that masculine faces predict other testosterone-dependent traits typically associated with men suggests the strong action of sexual selection, but the evidence that female mate choice drives that sexual selection is far from settled. Perhaps masculine looks, like size, are more about signalling to other men. It would be better, for the average dude, not to mess with a manly looking man in a tussle or a fight in just the same way he’d avoid a tall, muscular opponent.

Women’s varied and subtle preferences for masculine looks might be a response to the upside of having a mate who is competitive and intimidating toward other men. Some collaborators and I have shown that those countries where disease is rife and women prefer more masculine men are also characterised by high income inequality – a driver of man-on-man competition and violence. Manly, competitive men might have been better providers and defenders throughout a history more violent and competitive that suburban life is today.

Much about the variable preference for manliness and for bad boys remains to be explained. Much, I fear, might be inexplicable. Like the Tumblr “Hot and Busted” of good-looking arrest mugshots. Or the FreeJahar teens who profess to love the alleged Boston Bomber. But none of it is boring.


Disclosure: I have collaborated with Lee and Zietsch on studies of attractiveness unrelated to this new paper.

Bonus: Is this what the Village People were singing about in “Macho Man”?

Macho Man, one of the Village People’s great international nerve-touchers

Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

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