Sexually despotic men rewrite history

Alfred L. Kroeber (left) with Ishi, the last member of California’s Yahi people, in 1911. Wikimedia Commons
Alfred L. Kroeber (left) with Ishi, the last member of California’s Yahi people, in 1911. Wikimedia Commons

“Heredity”, opined the pioneering cultural anthropologist Alfred L. Kroeber in 1915, “cannot be allowed to have acted any part in history”. I have yet to encounter a crisper expression of the view that biological explanations have no place in the study of society and history. Kroeber’s words have resonated through the social sciences for a century, divorcing nurture from nature, social from biological, at considerable harm to our understanding of society and what it means to be human.


Fortunately, many 21st Century anthropologists, economists, neuroscientists, geneticists, sociologists and thinkers so busily inter-disciplinary that they defy dusty departmental labels, are consigning the hoary distinction between nature and nurture to the past. Likewise the distinction between heredity and history is steadily dissolving as the where intimate links between evolutionary fitness and major historic transitions come into view.

Last week’s European Journal of Human Genetics, for example, carried a fascinating article led by evolutionary geneticist Patricia Balaresque exploring the signature of historic population expansions in the distribution of Y-chromosome genotypes of men alive today.

The Y of who, what and when

The the human Y chromosome represents a tiny portion of the genome, including the genes that trigger a foetus to develop into a male, rather than following the default female pathway. Every now and then a small change occurs in one of the less important parts of a Y-chromosome’s DNA. Such a change is passed to a man’s sons, those sons’ sons, and so on. That means there’s quite a bit of variation in these Y-chromosome sequences in any human population.

Marco Polo at the Kublai Khan. Miniature from the Travels of Marco Polo c 1298.
Marco Polo at the Kublai Khan. Miniature from the Travels of Marco Polo c 1298.

So if a man happens to have many sons, who each go on to have many sons and so on, one might detect a sudden surge in the frequency of the Y-chromosome sequence borne by that line of men (patriline). In 2003, a large team from Oxford University detected evidence of just such an event. Across much of Asia, one particular Y-chromosome sequence was carried by 8 percent of all men. In a paper pithily titled “The Genetic Legacy of the Mongols”, they famously fingered Genghis Khan as the chief suspect.

The pattern of variation within the lineage suggested that it originated in Mongolia approximately 1,000 years ago. Such a rapid spread cannot have occurred by chance; it must have been a result of selection. The lineage is carried by likely male-line descendants of Genghis Khan, and we therefore propose that it has spread by a novel form of social selection resulting from their behavior.

Where by ‘behaviour’ they mean more than the Great Khan’s triumph in unifying the Mongols and establishing the largest continuous empire history has ever known. For Khan was as much about the establishment of a genetic dynasty as a political one. According to one disputed quote, he once said:

The greatest joy for a man is to defeat his enemies, to drive them before him, to take from them all they possess, to see those they love in tears, to ride their horses, and to hold their wives and daughters in his arms.

Or words to that effect.

Such a genetic legacy is far more than the work of a single man. It is likely that Khan’s uncles, brothers and cousins, played a substantial role, too. And his direct male descendants spread both his empire and his genetic legacy. Ghenghis’ grandson, Kublai Khan, married four main Empresses, but, according to Marco Polo’s Travels was attended to by hundreds of beautiful young women, working five at a time in three-day shifts. And a much greater number of women, recruited to the palace but, after a second round of screening, not deemed perfect enough for the Khan himself, were bestowed on Kublai’s nobles, many of whom would have been relatives sharing his patriline and Y-chromosome.

Khan not the only one

The Mongol expansion is far from the only such event to leave a genetic signature. A 2005 paper identified a particularly successful lineage that expanded about 500 years ago in Northeastern China, possibly through the lineage who established the Quing Dynasty.

Last week’s findings report on a survey of 5321 men from 127 Asian populations, testing for evidence of similar population expansions. Belaresque and her collaborators identified eleven such events, including the ones tied to the expansions of the Mongols and the Qing dynasty. And some of those events date back as far as 2100 BCE.

The earliest expansions, between 2100 and 300 BCE, are associated with the flourishing of agriculture in the Fertile Crescent, East India, and South East Asia. As agriculture took hold, elites accumulated wealth and influence beyond anything our hunter-gatherer ancestors could have conceived. These represent perfect conditions for sexual despots: male rulers who take many wives, keep numerous concubines or mistresses, and have many offspring. They also establish successions that favour their male descendants, handing them the wealth and power to become sexual despots themselves.

Another expansion began around 1100 CE in the Near East and expanded to the South East Indian coast. This might be a signature of the “rapid expansion of Muslim power … after the establishment of a unified polity in the Arabian peninsula by Muhammad in the 7th Century and under the subsequent Caliphates”.

The Mongol and Qing expansions, and another from Northeast China beginning no earlier than 850 CE, were not associated with the establishment and spread of agriculture, but rather with nomadic, pastoral lifestyles made possible by the domestication of horses. Pastoral nomads ruled the steppes for thousands of years, thanks to their horse-powered mobility and fighting ability.

They established several empires, giving rise to hierarchies, elites and patrilineal reproductive despots like the Khans and the Qing. And their Silk Road trade corridor facilitated westward expansion of their genetic dynasties.

Heredity and History

Even in the rather well-studied case of Genghis Khan we are well beyond certain idenfification of the individual progenitors whose success sparked each expansion. Innovative analyses and lucky ancient DNA finds may yet do so for some cases. But the ability to detect great tides of patrilineal descent in societies of various types offers far more interesting possibilities than compelling personal narrative.

The evidence shows that with great power and wealth can come great evolutionary fitness. The tools are now falling into place to assess how much the psychological adaptations that shape reproductive success have given history its shape.

This is one tale where History certainly represents HIS Story. The fact that new Y chromosome sequences can spread so fast and so wide when history’s tide turns suggests that a very small number of sexually despotic men can leave massive numbers of descendants. But each man who traces his descent back to Genghis Khan or another such super-ancestor through an unbroken male line has sisters who do so too, save for the very last branch in their family tree. If 2% of people in Asia descend on a male-only lineage from the same male ancestor as Khan, then how many times do they descend from him through at least one female ancesor?

Each of us descends many times over from a great many sexual despots. It would be Kroeber-like wilful ignorance to be think we don’t also inherit many of the genes that biased their behaviour toward the accumulation of power, the vanquishing of rivals and reproductive despotism.

And when I say “we”, I don’t only mean men. Every man has a mother. Every descendant of Ghenghis Khan is also a descendant of his mother Hoelun.

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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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Fear, conservatism and out-group attitudes: a genetic link?

Australia’s eight-month election campaign is apparently underway. It’s a prospect that excites only those shady consultants, pollsters and party power-brokers whose livelihoods depend on running focus groups, devising strategies and pulling political strings.

Instead of ignoring the whole show, I have been reading up on insights that biology can provide into an election campaign. Perhaps some political consultants will want to gratuitously overpay me to talk about this stuff at some posh lunch or dinner?

For more than 60 years, psychologists have probed the underpinnings of variation in political opinion and, especially, left-right differences. Ten years ago, a meta-analysis of 88 studies across 12 countries and over 22,000 cases showed that political conservatism is strongly predicted by local instability of conditions, as well as an individual’s anxiety about death, inability to tolerate ambiguity and uncertainty, needs for order and structure, fear of threat and loss.

Conservatives are also less open than other people to new experiences and have somewhat lower self esteem, on average.

New developments in personality psychology, evolution and neuroscience have added to what we know about the left-right divide. Last year’s interminable American election campaign unleashed a slew of studies and books concerning the ways in which biology shapes politics, campaigning, and election outcomes. A lot of the research documents differences between Republicans and Democrats. Some of the insights are peculiar to the US. Others provide general perspectives on the reflexes and intuitions underpinning conservative or progressive political identities.

Last year, in this column, I touched several times on the biological underpinnings of political opinion:



Cooperation with members of one’s own group, and mistrust of strangers who are not part of one’s own group, provides a central tension in all human social living. This tension constitutes the origin of xenophobia as well as its mirror-twin: zealous nationalism or patriotism.

Some new research adds considerably to our understanding of the relationships between fear, feelings toward out-group members and left-right political attitudes, as well as to why not everybody responds to fear in the same way.

Peter K. Hatemi and colleagues report in the American Journal of Political Science that people more disposed to social fears tend also to be less tolerant of immigrants and people of other races, and they identify more often as politically conservative. That’s old news. What sets this paper apart is that it comes from a study of nearly 30,000 people in over 8,636 families. And this allowed the authors to explore how genetic relatedness and shared environment shape the associations between fear, out-group attitudes and political conservatism.

Some 62% of the association between fear and conservatism was due to shared genetic origins, and 75% of the association between fear and negative attitudes toward outgroups came from a shared genetic basis. This makes the associations much more powerful than mere correlations: it suggests that the genes that dispose individuals to fear also tend to dispose them toward conservative attitudes, especially a mistrust of out-groups.

How these associations develop with experience, and why these traits share so much of their genetic basis remain to be tested. Just because two traits share considerable genetic variation does not mean political attitudes are fixed by some nightmarish determinist destiny. The associations between fear and attitudes grew weaker, in this study, in more educated individuals.

People’s political identities and attitudes are built from a bewildering number of environmental and genetic sources. I predict than in time the interactions between environment and genotype will be exposed as complex and shifting.

One thing I noticed from the first figure in the AJPS paper (see below) is that low fear levels don’t reveal much about a person’s politics. Low-fear people can be found across the political spectrum. But high-fear people tended to be universally conservative.


As Rose McDermott, the study’s second author put it:

It’s not that conservative people are more fearful, it’s that fearful people are more conservative.

Stay vigilant

Politicians have always known that they could channel the fears of voters for short-term electoral gain. I recall from my teenage years in South Africa how, whenever P.W. Botha’s apartheid government seemed vulnerable, they, and the state broadcaster, would revert – entirely without subtlety – to emphasising “swart gevaar” (Afrikaans for “black danger”).

In Australia, as in many other parts of the world, immigration and the issue of refugees stokes out-group fear. And one can be certain that politicians will provide a rich supply of oxygen to those fears over the coming campaign.

Conservative thought has plenty to offer, and there are usually many good reasons to consider conservative ideas. But politicians who cynically prod the fear reflexes of their constituents to tap into their ancient prejudices are sacrificing the public good for their personal gain. And they should be challenged and ridiculed when they do it.

Hopefully, an emerging understanding of exactly how the well-worn links between fear and voter conservatism work can be used to blunt the effectiveness of scaremongering politicians. And perhaps an understanding of how promoting and valuing rational thought can be used to elevate the quality of our politics?

Not for the first time, I think Noel Turnbull’s recommendations from an article he published at last year bear quoting in full:

One way to encourage the slower, more rational thoughts, which also encourage our better angels is very much in the hands of politicians. For instance, if it was left to a vote capital punishment would never have been abolished in many Western countries but politicians took the leap on moral grounds helped by extensive public campaigns.

When politicians reverted to pro-capital punishment atavism, such as former Victorian Liberal opposition leader Alan Brown, their leadership came under threat. In contrast one of his successors, Jeff Kennett, was extraordinarily principled on questions such as race and just refused opportunities to add to the fires and the atavistic comments while publicly demonstrating a strong commitment to multiculturalism.

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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New ideas on the genetics and evolution of homosexuality

When I give talks about the relevance of evolution to modern life, I can count on one regular question interrupting an orderly transition from lecture theatre to bar. Sometimes it comes with a “bet-you-didn’t-think-of-that-one” sneer. Far more often it is asked earnestly and with palpable empathy. The Question?

How do you explain homosexuality?

The very real fact that a large proportion of people across the world are sexually attracted to members of the same biological sex provides a giant obstacle to a Darwinian view of life.

And I am always happy to field this question because it allows me to explore, with the audience, some of the layered complexity of evolution. But a simple, definitive answer remains, for now, beyond reach. That may start to change, however, with a paper published today in The Quarterly Review of Biology.

Born this way

Evolutionary biology can be a bit of a blunt instrument. Especially when it seeks to explain big, categorical differences – like sex differences. Focusing at a broad scale means a lot of nuance and individuality gets ignored or trampled. Which is why so many authors – quite unfairly – write off all biology as determinism.

Fortunately, biological ideas about homosexuality tend to be more welcome than biological ideas about, say, gender. That may be because so many gay people strongly feel they were “born this way”. And because ideas about homosexuality being a choice or a curable condition proliferate in all but the most enlightened places.

But being “born this way” isn’t necessarily the same thing as the traits involved being genetically determined. Genetic claims require genetic evidence. In support of a genetic basis, sexual orientation has a moderate to high heritability. Heritability being the statistic that describes how much of the variation in a trait is due to genetic differences among individuals.

But despite the statistical vapour-trail indicating a substantial genetic basis, the search for major genes involved in homosexuality has been far less fruitful. And then there remains the problem so beloved of seminar questioners. How could any such genes have persisted through millenia of selection if they lead to sexual preferences that do not produce offspring?

The idea that “gay people don’t have children” is simplistic and, historically, wrong. Being gay does not necessarily mean not having a family, and throughout history many – perhaps most – homosexuals spent time in heterosexual unions, having children. And yet even if a small proportion did not, this could have exerted strong evolutionary selection against any genes involved.

But perhaps those genes provided some other kind of evolutionary advantage that outweighed the direct cost of having fewer kids. Here, theories lie thick upon the ground. First, there is the idea that homosexual relatives provide exceptional help to their heterosexual relatives who are raising families. Any genes that raise the chances of homosexuality, then, are passed on through relatives. And the extra help means more nieces and nephews carrying those genes.

The second group of ideas hinges on the idea is that genes that make reproductively successful females can impose costs when they find themselves expressed in males. And the opposite can happen for genes that enhance male fitness. Some support for this idea exists as well, including evidence that families in which females tend to be highly fertile also have a higher proportion of gay men than one might expect by chance.

And Brendan Zietsch has written here about his own work showing that psychologically feminine men and psychologically masculine women who are heterosexual also tend to be more sexually attractive. He argues that genes that raise the chances of an individual being same-sex attracted also massively raise the mating success of heterosexual bearers being reproductively successful.

Each of these ideas has some empirical support, but not such strong support that the case can be closed. It remains likely that there is no single explanation and that several biological influences together shape sexual orientation.

The new idea

But today’s big story is an entirely new idea that hinges not on traditional genetics but instead on epigenetics. The fact that gene expression is modified by molecules that attach to particular genes, but can later be removed, is revolutionising almost every biological field, including evolution.

Genetics defies metaphors, but I’ll try to mangle one for folks who prefer J.K. Rowling over modern molecular genetics. If we think of a person’s DNA as a recipe book – say Advanced Potion Making by Libatius Borage – then the epigenetic marks (or epi-marks) are the annotations and corrections made in pencil by the owner. Epi-marks have many functions, many of them tailoring the DNA instructions to suit the circumstances in which an individual finds him- or herself.

Most epi-marks get erased before the recipe is copied and handed down to an individual’s offspring. But that isn’t always the case. Sometimes there are good adaptive reasons why offspring inherit epi-marks from a parent. And sometimes, like Harry Potter inheriting the Half-Blood Prince’s potions book, they receive annotated instructions that were not intended for them.

Bill Rice, Urban Friberg and Sergey Gavrilets recognised that epi-marks are an essential component of sex differentiation. Males and females share an entire genome and so development is fraught with instructions intended for embryos of one sex but not the other. One class of epi-marks protects female foetuses from the masculinizing effects of fetal testosterone. Another protects male foetuses from being feminized when oestrogen signals would otherwise trigger female development.

Different genes are involved in the development of genitals, reproductive organs, body shape, sexual orientation and every other trait where genes shape sexual differentiation. And so epi-marks to these different genes will have different influences on those traits.

Mostly, these kinds of epi-marks should not be passed from parent to offspring. But occasionally some are. And when the epi-marks on genes that effect sexual orientation get passed from father to daughter then some traits that would normally develop in female-specific ways end up more masculinized. Likewise mother-son transmission of epi-marks can result in the feminization of some traits that would normally develop in a more masculinized fashion.

I should stresss that the new paper is a mathematical model showing that this scenario can work. The authors marshal plenty of circumstantial evidence that it probably does work. But the idea needs to be directly tested.

Apart from the fact that this is one of those rare ideas that completely changes how we look at the evidence, I am most exited by the way this idea reframes how we look at sexual development. I suspect that this idea will, in time, also shake up the science of sex-differences and our understanding of how gender arises.

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