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This is the latest post in my “Smarter People” series. Check out the full collection here.

Are smart people naughty or nice? A new study suggests the latter. Analyzing data from 1.2 million Swedes, the researchers found that smarter individuals were more likely to vote, more likely to donate to charity, and more likely to own an eco-friendly car. They also tended to score higher on a self-report measure of altruistic behavior.

Importantly, the intelligence-prosociality link held even when comparing twins within the same family. This suggests that the link isn’t just due to confounding by shared genes or shared upbringing. It therefore strengthens the case that intelligence directly increases prosociality.

How might it do this? Possible explanations include more rapid acquisition of moral norms, better moral reasoning, a better appreciation of others’ perspectives, and a better understanding of the benefits of mutual cooperation. Curiously, having a higher income explained little if any of the intelligence-prosociality link.

The paper is titled “An inquiry into the relationship between intelligence and prosocial behavior: Evidence from Swedish population registers,” by Mikael Elinder and Oscar Erixson. You can access it here for free.

How You Can Support the Newsletter

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Darwin’s theory of sexual selection is one of the most powerful ideas in evolutionary biology. It’s also one of the most controversial. Is it really true, as Darwin proposed, that sexual selection acts more strongly on males than females? Is it really true that males across the animal kingdom are more ornamented and better built for combat, whereas females are more parental? Or are these just evolutionary myths based on Victorian norms and a handful of cherry-picked examples?

A major cross-species analysis put Darwin’s theory to an unusually ambitious test, looking at sexual selection, ornaments, weaponry, and parental care across the animal world. The results provide a clear verdict on Darwin’s thesis - while also highlighting some fascinating exceptions that point to a deeper explanation for evolved sex differences.

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It’s podcast time again, folks! A few weeks ago, I had the great pleasure of returning to ’s Uncomfortable Conversations. Josh and I had a fun, wide-ranging discussion about my book, A Billion Years of Sex Differences, and related topics.

We also discussed the recent “vibe shift,” and how ideas that got me into hot water a few years ago are gradually becoming acceptable topics of conversation again (touch wood). At one point, Josh made the very funny observation that,

When you first came to my attention three years ago, you were this defiant voice standing up to the mob and now, fortunately, you’re just the - no offense - boring academic that you should be by just saying true things accurately.

My immediate response was that I much prefer the latter! I did add, though, that it was kinda cool being a badass just for making a commonsense observation backed by a mountain of research: that men and women are different.

Here’s the blurb for the episode:

Are men innately more violent? Are women innately more people-focused? What explains gay people, campness, transgenderism? How much of the sex differences are cultural, and how much is hardwired by our evolutionary psychology?

The science of the sexes has come a long way. Steve Stewart-Williams is a psychology professor who wrote the groundbreaking book The Ape That Understood the Universe and whose new book is A Billion Years of Sex Differences: How Evolution Shaped the Minds of Men and Women.

Steve joins Josh to explore the science of the sexes, from aggression to promiscuity to parenting, and what recent research reveals about how, and why, men and women behave the way we do.

The episode is available on Apple Podcasts, on Spotify, and wherever else you get your podcasts. It’s also available on the Uncomfortable Conversations YouTube channel.

If you enjoy the conversation and would like to explore these ideas in more depth, you can pick up a copy of A Billion Years of Sex Differences here.

Buy A Billion Years

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• The ability to post comments and engage with me and the N³ Newsletter community

Paid subscriptions also help support my efforts to explore important and controversial topics, and give me the financial freedom to follow the evidence wherever it leads without fear of cancellation.

Thank you!

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Why are men so much more likely than women to die doing something spectacularly unwise? Why are they overrepresented among extreme sports enthusiasts, workers in dangerous occupations, and people whose last thought is, “Yeah, this seems like a good idea”?

Across cultures, throughout history, and in many other species, males are consistently more willing than females to roll the dice. In this excerpt from my book A Billion Years of Sex Differences, I explore what the research says about sex differences in risk-taking and where they come from. Among other things, we’ll discuss:

• How we know that sex differences in risk-taking aren’t just a mirage - and aren’t just a product of culture

• Why men dominate both the Darwin Awards and the Carnegie Hero Awards

• Why natural selection sometimes favors traits that reliably get people killed

• Why sex differences in risk-taking explode after puberty

• What chimpanzees can teach us about human risk-taking

You can find the full collection of excerpts here, or pick up a copy of A Billion Years of Sex Differences here.

Reckless Abandon

The fact that men engage in more aggression than women – and more of a range of antisocial behaviours – stems in part from another important sex difference: the sex difference in the tendency to take risks. As most people are all-too aware, boys and men are bigger risk-takers than girls and women. This sex difference helps explain various stubborn facts. It helps explain why boy toddlers are more likely than girl toddlers to end up in the emergency room; why men are over-represented on the Wikipedia page of inventors killed by their own inventions; and why more men than women participate in extreme sports – that is, sports extremely likely to kill you, such as base jumping, hang-gliding, and motor racing. It helps explain why men do most of the riskiest jobs in the world – including construction worker, fisherman, logger, taxi driver, and truck driver – and why more than 90% of workplace fatalities are men. And it helps explain why men are more likely than women to accept stupid dares, gamble away their life savings, invest in cryptocurrencies, die while taking extreme selfies, and hit send on an email without reading it through first.

It’s quite a résumé . . . and we’re only just getting started! Men are more likely than women to get into car accidents, even when you statistically control for the fact that men drive more. This isn’t because men are less skilled at handling a vehicle; it’s because they more often drive too fast, tailgate, and drive drunk. At the same time, despite their Russian roulette driving habits, men less often wear seatbelts. Not only are men more likely to crash a car, they’re more likely to get hit by a car while crossing the road. This isn’t because motorists try to run men down; it’s because men are more likely to try to cross when it’s unsafe. Yep, scientists have sat by the side of the road tabulating men’s and women’s road-crossing habits, and that’s what they’ve observed. And not only are men more likely to be struck by cars, they’re more likely to be struck by lightning. This isn’t because God hates men; it’s because men are more likely to work outdoors and less likely to think ‘Hmmm, there’s a storm coming; maybe I should go inside.’

Every year, the British Medical Journal publishes a light-hearted Christmas edition. The 2014 offering included an article testing the hypothesis that men engage in more ‘idiotic risk-taking’. To that end, the authors looked at the demographic makeup of Darwin Award recipients. Darwin Awards are bestowed on individuals whose actions ensure ‘the long-term survival of the species, by selectively allowing one less idiot to survive’. Notable recipients include the would-be aviator who strapped helium balloons to a lawn chair then drifted over Los Angeles for 14 hours before being rescued, and the terrorist who put insufficient postage on a letter bomb, then unthinkingly opened it when the parcel was returned to his door. Crunching the numbers, the researchers found that 88% of Darwin Award winners were men, consistent with their ‘male idiot theory’.

To be fair, although men take more idiotic risks, they also take more heroic ones. More than 90% of Carnegie Hero Awards go to men, to give just one example. Still, whether idiotic, heroic, or a mixture of both, the root cause of the sex difference is the same: Men are more tolerant of risks.

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If you’ve taken an introductory psychology course, you’ll have heard about general intelligence, also known as g. g is a general-purpose cognitive ability that’s brought to bear on every cognitive task. It’s what IQ tests aim to measure.

What makes us think that there’s any such “thing” as g? Simple: the fact that people who do well on one kind of cognitive test also tend to do well on others. Good at vocabulary? You’re more likely to be good at math as well. Good at math? You’re more likely to have a good memory - and good spatial abilities and good processing speed. The positive correlation among cognitive tests suggests an underlying factor that contributes to performance on all of them. Whatever exactly that factor is, it’s what psychologists call g.

The evidence for g’s importance is overwhelming. People with higher IQs tend to stay in education longer, enter higher-status occupations, earn more, enjoy better health, and even live longer. These aren’t just cherry-picked, small-sample, yet-to-be-replicated flukes. They’re among the strongest and most consistent findings in psychology.

The Nature-Nurture-Nietzsche Newsletter

12 Things Everyone Should Know About IQ

This is the first post in my “12 Things Everyone Should Know” series. You can access the complete collection here…

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3 years ago · 169 likes · 10 comments · Steve Stewart-Williams

But although people who do well on one cognitive task tend to do well on others, no one does exactly as well on every task. Two people can have exactly the same IQ score but different profiles of strengths and weaknesses. Jojo may have exceptional verbal skills but only somewhat above average math skills. Loretta may process information at lightning speed but fall behind on abstract thinking. Martin may have an intuitive feel for machinery and electronics but lack the gift of gab.

Should we expect these individuals to end up having similar life outcomes simply because their overall IQs are the same?

For many years, the conventional wisdom in psychology was basically “yes.” General intelligence was thought to do almost all the heavy lifting. As one influential paper put it, specific cognitive abilities contribute “not much more than g.”

But recent research by Tobias Edwards and Colin DeYoung, published in the journal Intelligence and Cognitive Abilities, suggests otherwise. Using data from nearly 19,000 Americans across two generations, the researchers showed that your specific abilities shape your occupation, income, and job status, over and above IQ.

Edwards and DeYoung extracted three specific abilities statistically independent of g: technical ability, processing speed, and math-vs-verbal ability - a factor reflecting the extent to which people are better with numbers than words. They then looked at the extent to which IQ and these specific abilities correlated with people’s life outcomes.

The following four graphs summarize their main findings.

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Graph 1: IQ Matters More With Age - But Specific Cognitive Abilities Matter Too

The first figure shows how cognitive abilities predict income and occupational status across the adult years. The key message is that IQ becomes increasingly important with age, while specific abilities have a fairly stable impact.

The effect of cognitive abilities on earnings is worth zooming in on. As you can see, in people’s late teens and early twenties, general intelligence barely predicts earnings at all. Indeed, in one of the two datasets, the relationship is briefly negative. This is presumably because, in their first years out of high school, many cognitively gifted individuals are still in education, trying different jobs, or not yet in positions where their cognitive talents can fully express themselves. It takes until the mid-twenties for IQ to really start making waves - but when it does, it soon becomes the strongest cognitive predictor of income.

Meanwhile, tech ability shows almost the opposite pattern. It has a positive effect on income in the late teens and early twenties - the exact time when general intelligence does nothing - but then crosses the zero line and drifts negative as people age. That’s the earnings fingerprint of the kid who left school to become an electrician or mechanic before their classmates had even decided on a major. It pays off in the short term, but then traditional academic pathways overtake it.

Graph 2: It’s Not Just Family Background

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Taking Stock

It’s been a month since I got back from the book tour for A Billion Years of Sex Differences, and I’ve finally had a chance to catch my breath and take stock of how things have gone. Overall, I’ve been very pleased with the reception the book has received. Among other things:

• It’s been featured in the four major UK newspapers: The Times, The Guardian, The Telegraph, and The Independent.

• Reviews of the book have been overwhelmingly positive, even in outlets where I expected a tougher ride, such as The Guardian and The New Statesman. Highlights include reviews in The Australian, The Bulletin (Sweden), Male Psychology Magazine, The New Zealand Herald, Quillette, The Sunday Telegraph, and ZNews (Vietnam).

• I’ve been on more podcasts in the last two months than I’d been on in my entire career before that. Most notably, Chris Williamson flew me to Austin, Texas, to make a second appearance on his Modern Wisdom podcast: one of the biggest podcasts in the world.

• I’ve done interviews for various outlets, including The Telegraph, Skeptiker, How To Academy, and The Scottish Herald. The Herald interview was for a long-form piece about me and my ideas, which should be out in mid-August.

• Next week, I’ll be making my first TV appearance on BBC Business Today, which has an estimated global audience of 15 million viewers. [Update: The BBC cancelled on me at the last minute because of breaking business news. We’ll see if they reschedule. BBC Radio 4 Today cancelled on me at the last minute a few months ago too but never rescheduled, so I’m not holding my breath. Rather annoying…]

• I published my first op-ed in The Independent: an overview of some of the book’s key ideas.

• My publicist is working on getting an excerpt from the book into The Spectator in the near future.

• A Billion Years made The New Zealand Listener’s list of the best books of 2026 so far. To my surprise, appearing in The Listener meant more to me than earlier mentions in The New York Times and Rolling Stone magazine, because my family always got The Listener when I was growing up. Also, my mum happened to spot my name there unexpectedly, which made it particularly special.

• The book has been nominated for the Baillie Gifford Prize for Non-Fiction.

• Several academics have confirmed that they’ll be using it in their classes.

• Readers from around the world have been posting photos and videos of the book online. This one wins the book-in-the-most-exotic-location award:

• A friend from London texted last week to say she’d spotted a random stranger reading the book on the train. For some reason, out of everything that’s happened, this was one of the highlights.

• I’ve started working with Prometheus Books on the North American edition of A Billion Years, which will hit the bookshelves on January 19. I’m looking forward to another book tour and round of promotional work then.

• Most gratifying of all, though, is the sense that the conversation about sex differences is changing. Ideas that seemed almost unspeakable a few years ago are increasingly being discussed openly and seriously. If A Billion Years of Sex Differences is helping nudge the conversation in that direction - even a little - I’ll consider it a success.

A New Review in Quillette

The latest review of A Billion Years of Sex Differences has just appeared in Quillette. It’s by the evolutionary biologist Jerry Coyne, who described the book as “essential reading.” Here’s an excerpt:

In A Billion Years of Sex Differences, Steve Stewart-Williams argues that it’s time to engage these questions with data. Summarising existing research, he comes down closer to genetic determinism than to blank-slatism. That is, he sees significant sex differences in thinking, behaviour, and preferences as having a substantial genetic basis, but he recognises too a role for sociocultural influences.

Stewart-Williams handles his hot potato gently. He is careful to admit when we lack good evidence for a purported sex difference; when we lack information about the genetic basis of a difference we can document; and when, as with homosexuality, we have that genetic information but remain ignorant about how the difference evolved. (Homosexuality is one such puzzle, since it has a partial genetic basis, but, under simple Darwinian logic, genes that reduce reproduction should be eliminated from populations.)

And he addresses at length—and counters—the view that inherited sex differences will lead to bigotry. Instead, he recommends that both sexes should have equal opportunities, with everyone free to choose their own path. In the end, it’s obvious that the more we understand the basis of sex differences, the better equipped we are to address them. This measured, timely, and informative book is essential reading at a time when many scholars not only insist that male–female differences are culturally generated but go further, denying that there are just two sexes.

My Appearance on the Michael Sartain Podcast

This was a fun one. Michael Sartain is a Las Vegas–based dating coach who also runs bikini beauty pageants and a popular podcast. He’s a longtime fan of evolutionary psychology, and has been a very generous supporter of my last book, The Ape That Understood the Universe. We recently sat down together - Michael in Las Vegas, me in Kuala Lumpur - to discuss A Billion Years of Sex Differences, and evolutionary psychology in general. Here’s the blurb for the episode:

In this episode, I sit down with evolutionary psychologist Steve Stewart-Williams for an in-depth conversation about human nature, biological sex differences, attraction, relationships, personality, and the controversial science behind evolutionary psychology.

Steve is a professor of psychology at the University of Nottingham Malaysia and the author of Darwin, God and the Meaning of Life, The Ape That Understood the Universe, and his latest book, A Billion Years of Sex Differences.

We explore why evolutionary psychology remains one of the most misunderstood and politically controversial areas of psychology. Steve explains why both traditionalists and progressives can misrepresent sex differences, why recognizing biological influences does not mean defending traditional gender roles, and why describing human nature is not the same as deciding how society should operate.

The episode is available on Apple Podcasts, on Spotify, and wherever else you get your podcasts. It’s also available on Michael’s YouTube channel.

You can pick up a copy of A Billion Years of Sex Differences here.

Buy A Billion Years

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This post was free to read for everyone. If you’d like access to all Nature-Nurture-Nietzsche-Newsletter content, please consider a paid subscription. A paid subscription gives you:

• Full access to all new posts and the archive

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Thank you!

Steve

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Our personality traits help determine which story elements we enjoy in movies. People high in openness prefer movies involving exploration, discovery, and intellectual debate; people high in extraversion prefer movies involving romance, friendship, and nurturing children; people high in conscientiousness prefer movies in which characters defend their values or condemn wrongdoing; and people high in agreeableness prefer movies that involve warm, empathetic characters - and that don’t involve rage or revenge. These and other personality-preference links are found in the following graph.

The links are modest, indicating that personality is just one factor among many shaping people’s movie preferences. Still, they’ve been replicated in 22 of 23 countries. That’s a remarkable degree of cross-cultural consistency.

The findings suggest that people’s movie preferences are better understood in terms of fine-grained narrative themes than broad genres. Two films in the same genre can attract very different audiences if they foreground different themes, while the same person may enjoy films from different genres if they share the same themes.

The findings come from a fascinating recent preprint by Edgar Dubourg and colleagues. Here’s the abstract.

Why do people prefer certain fictional stories over others? Personality traits capture stable individual differences in motivational sensitivities: Openness reflects exploration, Neuroticism reflects threat-reactivity, and so on. If so, these traits should systematically predict preferences for narrative features that engage the corresponding motivational systems. We test this hypothesis across three preregistered studies. In Study 1, we directly measured individual preferences for motivationally salient narrative features in a cross-cultural survey of 9,201 participants from 23 countries. Personality traits predicted preferences and the overall pattern replicated in 22 of 23 countries. In Study 2, we confirmed these predictions using ecologically valid data from 574 movies, annotated by large language models for the same narrative features and linked to the Big Five profiles of 3.5 million Facebook users. The predicted associations replicated at the population level. In Study 3, we tested a complementary structural prediction: if story preferences reflect an underlying motivational architecture, then the co-occurrence structure of narrative features in stories should mirror the co-preference structure across individuals. Using Mantel tests, we found strong structural correspondence, replicated across all 23 countries. Together, these findings support a model in which story preferences arise from universal motivational systems whose sensitivities vary across individuals.

If you want to dig deeper into the details, you can read the preprint for free here.

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How You Can Support the Newsletter

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Welcome to the July 2026 edition of the N³ Newsletter Linkfest: a collection of links to papers and articles that grabbed my attention over the last month. On the menu today…

• The classic study showing that experts often predict the future no better than chance

• Why dating apps may be making romance harder, rather than easier

• The female multitasking myth

• Why the gender-equality paradox might not be about gender equality at all

• The downside of belief in free will

• How AI cheating is undermining education

• How spraying mosquitoes may be creating a new breed of super-mosquitoes

On top of that, we’ll ask: Are mRNA vaccines safe? Does paracetamol during pregnancy increase the risk of kids developing autism and ADHD? And why have autism and ADHD diagnoses skyrocketed in recent years?

Around half the items are free to read for everyone; the rest are for paid subscribers.

You can access the complete collection of Linkfests here.

Orangutan Playdates

Even orangutans arrange playdates for their kids. Drawing on fifteen years of data, researchers found that orang mothers make extra trips to the territories of other mothers with similarly aged offspring so their youngsters can play together. Play isn’t just fun and games, you see; it’s crucial for social development. That’s why it evolved - and presumably why orang mums evolved to facilitate it. [Link.]

Chimpanzee Muscles

This chimp with alopecia reveals a truth usually concealed in fur: Chimps. Are. Ripped. [Link.]

Two Classic Findings in Psychology

1. Choice Blindness

   How well do we know our own preferences? Not as well as we might imagine. In a classic demonstration of “choice blindness,” researchers secretly swapped participants’ preferred jams and teas for the options they’d rejected, then asked them to explain their choices. Around two-thirds failed to notice the switch - and happily justified a choice they’d never made. [Link.]

2. The Expert Illusion

   In one of the most sobering studies in all of psychology, Philip Tetlock had hundreds of academics and political pundits make predictions about various economic and geopolitical matters. The experts often did no better than chance in their predictions. Not only that, but they did worse than simple rules like “assume no change” or “extrapolate the current trend.” [Link.]

The Latest from Political Psychology

A 30-year longitudinal study found that adolescents prone to internalizing problems such as depression and anxiety were more likely to lean left politically in midlife, whereas those with externalizing problems such as impulsivity and aggression were more likely to lean right. [Link.]

The recent birth decline in the US is driven largely by people on the left. Conservatives and centrists have maintained roughly replacement-level fertility since World War II, while fertility has slumped among left-leaning individuals. Education is associated with fewer children, religious attendance with more. [Link.]

The Nature-Nurture-Nietzsche Newsletter

12 Things Everyone Should Know About Political Psychology

This is the latest post in my “12 Things Everyone Should Know” series. You can access the full collection here…

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2 years ago · 101 likes · 3 comments · Steve Stewart-Williams

More Dating Apps, Fewer Relationships

Why are rates of pairing up and having children falling, even while dating apps serve up more options than ever? According to a 2020 study, part of the answer is that when we have too many options, we automatically become pickier - and suddenly no one’s good enough for us. This effect is particularly pronounced for women. [Link.]

Are Single Women Happier?

Most single women believe they are: 76% of those aged 18-29, according to one survey. On average, though, married mothers are happier than their unmarried, childfree counterparts. [Link.]

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The latest review of A Billion Years of Sex Differences is out!

It’s by Hannah Barnes in The New Statesman, and I’m happy to report that it’s very positive. I’m particularly excited about this one because The New Statesman leans progressive, so I was bracing myself for a bumpy ride. I’m therefore over the moon that it went down so well. (Admittedly, part of my excitement might be the extra-shot latte I just downed.)

Barnes’s piece is titled “Ignoring sex differences harms us all: The tendency to ignore sex variations harms men and women both – and damages scientific credibility.” Here’s an excerpt:

Men and women are different. But saying so has become taboo, according to the evolutionary psychologist Steve Stewart-Williams. A vocal minority, he states, sees positing the existence of sex differences as “a moral transgression”, to which the typical response is to “cancel, punish and shun”. This is particularly pronounced in academia, where biases distort discussion, he argues. In the Western world, there’s a predisposition towards minimising sex differences. There are other biases. “Studies finding anti-female bias are shouted from the rooftops,” while “those finding no bias or bias against men are reported in a whisper or simply ignored”, Stewart-Williams writes in his new book, A Billion Years of Sex Differences.

This lack of honesty matters. “If we want to make the world a better place, we need good science,” he maintains. That’s not possible “if scientists are afraid to diverge from the pre-specified conclusions of an academic political monoculture”. He argues that not only are there clear differences between the sexes, but the basis for them – in large part – is our “million-year journey of human evolutionary history”. This goes for everything from dating and toy preference to mental and physical health.

“In large part” is key. Stewart-Williams is no gender traditionalist. He rejects those who “exaggerate” differences between men and women. So too, the sex difference-minimisers who argue that if differences exist they’re “a product of discrimination and socialisation” – and that equality requires their abolition. Both views lack balance and fall foul of the science, he says.

Stewart-Williams advocates for a third way: one that acknowledges both nature and nurture, and which neither overstates nor underplays sex differences…

[T]his is an important book. In A Billion Years of Sex Differences, Stewart-Williams is making a profound argument: magnifying or minimising sex differences doesn’t just ignore science, it leads to harm. By failing to treat us as individuals, we end up discriminating against men and women. In medicine, both exaggerating and denying sex differences can be dangerous: doctors overlook gender atypical problems or presentations, for example missing eating disorders in men and heart attacks in women.

Gender-role individualism is Stewart-Williams’s proffered solution. We should “establish a fair and level playing field”, and let people make informed choices. We can work towards eliminating sex differences “created or amplified by unjust bias or barriers”. But we must acknowledge that “the sexes do differ on average, and we can’t just lie about that”, he says. Instead, we should “tell the truth carefully”.

This is the book’s ultimate message. Truth matters. If we deny differences that “everyone can see with their own two eyes”, the public simply won’t trust scientists on “politically charged topics”. Perhaps that ship has already sailed. Trust in “experts” has been in freefall for years. But an environment in which scientists, politicians, academics and others feel able to tell the truth – however uncomfortable – and not to be punished for doing so, is worth fighting for.

You can read Hannah Barnes’s full review here.

And if you’d like to pick up a copy of A Billion Years of Sex Differences, you can order it here.

Follow me on Twitter/X for more psychology, evolution, and science.

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Another highlight of my recent book tour was my trip to the HowTheLightGetsIn Festival in Hay-on-Wye. It was a wonderful festival with a great vibe, amazing food, and stimulating conversations. The organizers really know how to look after their speakers, covering transport to and from the festival, meals, and accommodation in the Welsh countryside - and even providing drivers to ferry us around. I could get used to that kind of treatment…

While I was there, I led a “Champagne, Cake, and Philosophy” event on my book A Billion Years of Sex Differences, caught my first glimpse of the book in the wild (in the festival bookshop), and took part in a debate on the notion of being “spiritual but not religious.” I spotted various famous faces, including Simon Baron-Cohen, Kathleen Stock, and Rowan Williams, and at one point found myself sitting next to Jeremy Corbyn in the green room. And I finally met several people in person who I’d previously known only online, including , , , and .

Meeting Michael, in particular, was long overdue. He wrote the foreword to my second book, The Ape That Understood the Universe, and kindly endorsed A Billion Years of Sex Differences. He also published one of my “12 Things Everyone Should Know” posts in his Skeptic magazine. Despite knowing each other for years, however, we’d never actually met. It turns out we have a lot in common - including remarkably similar stories about how we proposed to our wives.

As well as speaking at the festival, Michael was recording episodes of his podcast, The Michael Shermer Show. He and his Strategy Director, Alexander Reiman, rented a nearby village hall to use as a makeshift studio, and interviewed various festival attendees - including yours truly. Michael and I had a wide-ranging conversation about A Billion Years and various other topics I’ve written about over the years.

Among other things, we discussed:

• The evolutionary origins of sex differences

• Sex-role-reversed species - that is, species where all the usual sex differences are flipped into reverse

• Greater male variability and the Larry Summers controversy

• Why both sexes prefer research that puts women in a better light than men

• Sex differences in STEM

• Whether murder-suicide has an evolutionary basis

• The young male syndrome and sex differences in crime

• Whether IQ is a valid scientific concept or pseudoscientific nonsense

• The replication crisis in psychology

The episode is available on Apple Podcasts, on Spotify, and wherever else you get your podcasts. It’s also available on the Skeptic YouTube channel.

Hope you enjoy it!

• You can order A Billion Years of Sex Differences here.

• You can read the first chapter of The Ape That Understood the Universe for free here.

Follow me on Twitter/X for more psychology, evolution, and science.

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The capacity for violence is one of the oldest and most troubling features of human nature. Why, though, are some people so much more prone to it than others? And why, across cultures and throughout history, have men committed the overwhelming majority of violent acts?

In this extended excerpt from my book, A Billion Years of Sex Differences, I look at what decades of research reveal about one of the largest and most consequential sex differences known to science. Among other things, we’ll see that:

• Men are not only the main perpetrators of violence but also the main victims

• Five lines of evidence point to an innate contribution to sex differences in aggression

• Contrary to popular opinion, the most violent members of society aren’t young men

• Greater male aggression often appears despite culture, not because of it

• Greater male aggression has the same evolutionary underpinnings as the stag’s antlers and male gorilla’s canines

If you enjoy this excerpt, you can explore the full collection of excerpts here, or pick up a copy of A Billion Years of Sex Differences here.

The Strong, Violent Type

Let’s start our tour of the dark side with the antisocial trait that looms above all others: aggression. As mentioned, men are more aggressive than women, at least when it comes to face-to-face or direct aggression. Men shout more, fight more, and kill more. In experiments, they’re more likely to give people electric shocks, and in the real world, they’re less likely to back down from a trivial altercation. Even men tamed by modern civilization – men who’d never throw a punch in real life – watch more violent movies, play more violent video games, and have more fantasies about killing people.

To be fair, when it comes to indirect aggression – spreading rumours about people, excluding them from the group – we find either no sex difference or that women engage in slightly more. For everything else, though, men are in pole position.

As with most sex differences, the sex difference in aggression gets progressively larger for rarer, more extreme acts: a good example of the tail-of-the-distribution effect. Men are somewhat more likely to engage in verbal aggression; much more likely to engage in physical aggression; much, much more likely to engage in violent crime; and much, much, much more likely to kill someone – or, for that matter, to kill themselves.

It’s not that men are vastly more anger-prone than women; the sexes don’t particularly differ in how angry they get or how often. Instead, men tend to be less self-controlled, and less concerned about the negative consequences of overt aggression, from ruptured friendships to injuries and imprisonment.

Few would deny that men are the main perpetrators of violence. Who are its main victims? Many assume that it’s women – and when it comes to sexual violence, they’re right. For every other kind of violence, however, men are more often found in the victim column. This pattern is particularly stark when we look at homicide data. In almost every society on Earth, men are more likely than women to be murdered. Most of the time, the killer is a man as well. Women kill much less often, but when they do, the victim is usually a husband or a boyfriend. Apparently, both sexes prefer to kill men.

Now for the usual disclaimer: The fact that, on average, men are more aggressive than women doesn’t mean that men are the aggressive sex whereas women are the gentle sex. That would be like saying that, because more men than women have a same-sex sexual orientation, men are the gay sex whereas women are the straight sex. Some members of both sexes are highly aggressive, and most members of both are not, at least in the modern world. You know what I’m going to say next, though: Among the minority who are highly aggressive, more are XY than XX.

An Unfortunate Inheritance

Where does the aggression sex difference come from? For some the answer is obvious: culture. A standard cultural explanation would be that, in various ways, society encourages male aggression but discourages aggression in females. Parents, teachers, and peers reward boys for aggressive behaviour, at least in its milder forms. And even when they don’t reward it, they often turn a blind eye to it in boys in a way they never would with girls: Boys will be boys, after all. Meanwhile, movies and other media constantly model male aggression for impressionable young male minds. The subtext is clear: ‘This is the way you should be.’

As always, no one should deny that social factors help shape the sex difference in aggression. But is the difference entirely due to social factors?

Some would say yes. Writing in The New York Times, for instance, psychologist Michael Reichert argued that, although males are more violent than females, this tendency is not innate. However, at least five lines of evidence suggest that Reichert was wrong, and that there’s also an innate contribution.

1. Stubbornness of the Sex Difference in Aggression

One line of evidence for an innate contribution is the fact that the aggression sex difference persists even in the face of countervailing social pressure. Contrary to the idea that we encourage male aggression, parents and teachers spend a lot more time telling boys not to be aggressive than they do girls. This isn’t because they approve more of girls’ aggression; it’s because boys are more often aggressive. But notice the implication: Rather than being created by socialization, the sex difference survives even in the face of socialization in the other direction.

To pre-empt a common misunderstanding, this isn’t to say that socialization has no effect on the sex difference. Clearly, it does; the size of the difference varies considerably from culture to culture and time to time. The point is that socialization couldn’t be the entire explanation, because the difference persists even when socialization pushes harder against male than female aggression. Indeed, socialization may often make the difference smaller than it would otherwise be, not larger.

2. The Developmental Trajectory of Male Aggression

A second line of evidence concerns the unfolding of the aggression sex difference over the lifespan. As psychologist John Archer observed, if socialization alone were pulling the strings, we’d expect to find no difference in aggression in infants, followed by a steady increase in the size of the difference across childhood, as socialization makes its mark on our minds. But that’s not what we find at all.

First, the sex difference in aggression is apparent from the moment kids are mobile enough to make aggression an option: Boys fight more and lash out more, and engage in more rough-and-tumble play. Importantly, these differences appear long before boys and girls start selectively imitating same-sex role models, and long before they even understand that they’re boys or girls.

Second, rather than starting at zero then escalating in boys as the effects of socialization compound, aggression starts out high for both sexes. The most violent category of human being is the toddler, and the only reason we don’t worry more about the epidemic of toddler violence is that toddlers are small and cute, and can’t do much damage with their tiny fists. From this early summit of violence, both sexes become progressively less violent as the years go by. This is a major stumbling block for the theory that children are socialized to be aggressive. To my eye, it suggests instead that they’re socialized not to be. Throughout the process, however, boys are always more aggressive. Is this because anti-aggression socialization is stronger for girls than for boys? No; as we’ve already seen, it’s usually the opposite. But even if it were stronger for girls, the data don’t readily fit with a socialization explanation. Rather than the sex difference getting bigger as children absorb the message that female aggression is less acceptable, the gap remains roughly static throughout childhood.

So far so bad for the socialization hypothesis – and it’s only downhill from here. The next point where the facts come unstuck from the theory is in the decade or so following the onset of puberty. During this biologically critical window, the aggression sex difference suddenly explodes as men ramp up their aggressive antics. The evolutionary psychologists Margo Wilson and Martin Daly dubbed this rapid-onset increase in male misbehaviour the young-male syndrome. The most reliable evidence for the syndrome comes from homicide records. In childhood, neither sex is particularly homicidal. In the years after puberty, however, homicide rates suddenly skyrocket for males. Is this because society starts socializing males to be more aggressive? On the contrary, young male aggression is a serious problem facing every society, and thus most try to restrain rather than inflame it. Nevertheless, it persists.

Finally, as young adulthood gives way to middle age, the sex difference in aggression shrinks, largely because men begin mellowing. The socialization explanation gives us no reason to expect this. As we’ll see soon, though, an evolutionary explanation does.

3. Getting Hormonal

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One of the highlights of my recent book tour was my trip to Austin, Texas, for my second appearance on the Modern Wisdom podcast with .

After flying in from London, I did a one-on-one interview with Chris about my new book, A Billion Years of Sex Differences, followed by a roundtable with Chris, , and Macken Murphy: four hours of podcasting on four hours’ sleep. After that, I took my first ride in a self-driving car. All in all, it was an amazing trip.

Chris and his team released the one-on-one interview last week, and in typical Modern Wisdom fashion, it’s doing the kind of numbers that most podcasters can only dream of. Here’s the blurb for the episode:

Why is it so difficult to talk about the differences between men and women today? It’s important to recognize that men and women deserve equal respect and opportunity, but that does not mean they are exactly the same. There are differences between the sexes that can be meaningful, valuable, and even beautiful. So what are those differences, and why has discussing them become so polarising?

Expect to learn why talking about sex differences is so controversial, what the actual definition of sex is, why there are challenges to the binary idea of sex, the largest sex differences between men and women, how sex differences reveal themselves via personality, the danger of denying and/or not respecting the differences in sex, and much more…

The episode is available on Apple Podcasts, on Spotify, and wherever else you get your podcasts. It’s also available on Chris’s YouTube channel.

If you enjoy the conversation and would like to explore these ideas in greater depth, you can pick up a copy of A Billion Years of Sex Differences here.

Buy A Billion Years

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A fascinating new paper explores the evolutionary psychology of parental care, and comes to two major conclusions.

First, parents differ in how they treat their sons vs. their daughters: Daughters receive more relationship guidance, protection, and emotional support, whereas sons receive more athletic training and encouragement to be competitive. Sons also have fewer restrictions on their sexual behavior.

Second, mothers and fathers differ in the types of parental care they provide. Mothers are more involved in direct care, bonding, social/moral guidance, and discipline. Fathers are more involved in athletics and in teaching mechanical and practical skills.

These findings are summarized in the following graph.

According to study authors Francis (Sid) Dougan, William Costello, and David Buss, these results make good evolutionary sense. Throughout our evolutionary history, daughters and sons faced different adaptive problems, and needed different kinds of parental input. At the same time, evolved differences between men and women meant that fathers were often better equipped to provide certain forms of input, while mothers were better equipped to provide others.

Here’s the abstract of the paper:

Most research on human parental investment has focused on overall parental effort or resource allocation, overlooking the fact that human investment spans a broad suite of material, instructional, and social forms of investment. This array of investment enables examination of how evolutionary processes have elaborated parental care into distinct domains. Where daughters and sons historically faced different recurrent adaptive problems, selection should have favoured biases in parental investment that cultivate in each offspring the competencies relevant to its sex-specific challenges (e.g., navigating greater reproductive costs for daughters; navigating contest competition for sons). Likewise, mothers and fathers should differ in parental investment domains where their own evolutionary and life histories afforded greater sex-specific expertise. To test these hypotheses, we used linear mixed-effect models to analyse 105 adults’ (49.5% female) ratings of parental investment received across 73 behaviours organised into 13 domains. Results were largely consistent with predictions. Daughters received more parental investment in mating and relationship guidance, protection, and material support. Sons received greater parental investment in athletic training, permissiveness regarding sexual behaviour, and competitive encouragement. Mothers invested more than fathers in direct care, bonding, social and moral guidance, and discipline. Fathers invested more in athletics, and mechanical and practical skills. Domains linked to adaptive challenges common to both sexes (e.g., direct care) showed no offspring-sex differences in parental investment. The patterns accord with the evolutionary hypothesis that parental investment maps onto sex-differentiated adaptive problems. Discussion explores hypotheses about the interactions between socialisation practices of parents and sex-linked predispositions in offspring.

• You can access the paper for free here.

• You can read a user-friendly Twitter/X thread about the research by first author Sid Dougan here.

• I discuss the evolution of sex differences in parental care in my new book, A Billion Years of Sex Differences, and in my earlier book, The Ape That Understood the Universe.

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This is the latest post in my “12 Things Everyone Should Know” series. You can access the full collection here.

To mark the publication of my third book, A Billion Years of Sex Differences, I’m releasing a post I’ve had in mind for several years, but that I thought I should save until the book was out: 12 Things Everyone Should Know About Sex Differences.

Few topics in psychology generate more heat than this one, but few are backed by a larger body of scientific evidence. The aim of this post is to highlight some of the best-established differences in the scientific literature, and what the research says about their origins. Are they due solely to culture, or is there also an innate component? If the latter, why did the innate component evolve?

Before getting started, though, a warning: It’s easy to misunderstand claims about sex differences. The image below explains what scientists mean - and what they don’t mean - when they say that, on average, men score higher than women on a given trait (or vice versa).

With that in mind, let’s start our exploration of some of the key findings from the science of sex differences.

1. On average, men are more interested than women in casual sex and sexual variety. Note that this isn’t to say that “Men are promiscuous, women monogamous”; it’s an average difference, not a categorical one. The table below summarizes some of the voluminous evidence that the sexes differ in this domain.

2. On average, men place more weight than women on a long-term mate’s looks - see the first graph below. Women, in contrast, place more weight than men on a mate’s wealth and status - see the second graph below. Both differences are found in all or almost all nations; the graphs just show a representative sample.

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I recently appeared on one of the best-named podcasts in Podcastistan: the Maiden Mother Matriarch podcast with . We discussed various topics related to my new book, A Billion Years of Sex Differences, including:

• The largest psychological sex difference in our species. Can you guess what it is?

• The tail-of-the-distribution effect: the fact that even small sex differences at the mean translate into large differences at the extremes of the distribution

• When sex stereotypes are right and when they’re wrong

• Sex differences in direct vs. indirect aggression

• Whether women perpetrate as much intimate partner violence as men

• Sex differences in occupational choice

• The downsides of affirmative action for women

• The greater male variability hypothesis and why it’s controversial

• The gender-equality paradox: Is it real?

• Why we’re still in denial about sex differences

The episode is available on Apple Podcasts, on Spotify, and wherever else you get your podcasts. It’s also available on Louise’s Maiden Mother Matriarch Substack.

You can pick up a copy of my book, A Billion Years of Sex Differences, here.

Buy A Billion Years

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This post is free to read for all, so please feel free to share it.

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For as long as I can remember, the standard story in the social sciences has been that women and minorities are routinely discriminated against in STEM fields: Their research is judged more harshly, and they’re less likely to be hired or promoted. Evidence is mounting, however, that this story is increasingly out of date. A new preprint reports that, when evaluating identical CVs, STEM professors in the United States rate the research records of women and Black people as superior to those of men and White people, and are more likely to recommend them for promotion or tenure.

The key results of the research are shown in the following table.

This pattern is plausibly the result of efforts to correct for historical anti-female and anti-Black bias. Rather than eliminating that bias, however, we seem to have inadvertently reversed it, at least in some domains.

The research was conducted by Deborah Wu and Nilanjana Dasgupta. Here’s the abstract of their paper:

Gender and race disparities persist among tenure-track faculty in the United States, especially in STEM, where women hold 26% of academic positions and Black and Hispanic faculty together comprise only 7%. We conducted a randomized controlled experiment with 796 tenured biology and chemistry professors employed at 183 U.S. doctoral-granting institutions to investigate their evaluation of pre-tenure faculty’s research readiness for tenure and promotion in research-intensive universities. Faculty received an identical CV with only the candidate’s name varying to signal their gender and race, using a 2 Race (Black vs. White) by 2 Gender (male, female) between-subjects factorial design. Results revealed that STEM faculty evaluated female and Black candidates’ research record significantly more favorably and recommended them for tenure and promotion at higher rates, compared to male and White candidates with identical CVs. Findings remained largely consistent even after controlling for faculty participants’ own gender, race, and rank. We speculate that social norms about diversity, equity, and inclusion prominent in 2020-21 when these data were collected during the COVID-19 pandemic and shortly after George Floyd’s murder may have heightened faculty’s awareness of gender and race bias, increased motivation to be fair in decision-making, and led to compensatory judgments to increase diversity in STEM careers.

Note that, in the Discussion section of the paper, Wu and Dasgupta offer the following caution:

Our studies were conducted during a time in which promoting faculty diversity was widely accepted and encouraged. The current climate in higher education has drastically shifted away from discussing diversity in employment since the federal executive orders of 2025 under the Trump administration, which may alter how academic leaders approach these decisions today. The observed favoring of Black and female candidates over others may not generalize to our current-day context and to other environments in which diversity norms are less prescriptive.

My guess is that the bias would still be found; the government rules have changed, but STEM professors’ attitudes and values probably haven’t. Still, this is an empirical question, and it will be interesting to see how future research pans out.

• You can access Wu and Dasgupta’s paper here for free.

• I discuss bias in favor of women in STEM in Chapter 10 of my book, A Billion Years of Sex Differences.

• HT for pointing me to this paper.

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Many of our most strongly held beliefs about gender, race, and inequality turn out to be mistaken.

In this third installment of my series on popular social-science myths (see also here and here), I look at six more claims that are widely accepted but poorly supported by the evidence. Among other things, we’ll see that voters may be less sexist than people assume, that women’s health is not as neglected as we’re often told, and that some of our most cherished assumptions about war, poverty, and economic inequality don’t stand up to scrutiny.

As always, my aim isn’t to push a political agenda but simply to compare popular narratives with the available data. The results, I think, are both surprising and illuminating.

1. The Myth of Voter Sexism

Americans tend to overestimate voters’ prejudices against women and ethnic minorities. Democrats are particularly prone to this - which ironically makes them less likely to support female or minority candidates due to concerns about electability.

2. The Myth That Women’s Health is Ignored

We’re often told that men’s health gets more funding and attention than women’s. Various datasets suggest, however, that it’s actually the other way round. The graph below, for instance, shows relative investment in women’s vs. men’s health in Australia over the last decade or so. Throughout that time, women’s health received considerably more funding than men’s.

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This is the latest excerpt from my book, A Billion Years of Sex Differences. You can access the full collection here, or pick up a copy of the book here.

In this installment, we’ll see…

• How mate choice shaped the evolution of men’s and women’s minds

• Why women care more about their looks and men about their status and wealth

• How sexual selection explains women’s greater proneness to body-image problems

• The evolutionary roots of eating disorders and “bigorexia”

• Why evolved mate preferences help explain the gender pay gap

Why Mate Choice Matters

Let’s now tiptoe into more controversial territory. Mate preferences not only help shape men’s and women’s bodies, they also help shape their minds. If people want a smart mate, a kind mate, or a funny mate, the species will inevitably evolve to be smarter, kinder, and funnier. Not only that, but we’ll evolve a motivation to hone and display the traits that potential mates desire.

You can probably see where I’m going with this. Because the sexes have somewhat different desires, each may have evolved somewhat different traits – and also somewhat different priorities about which traits to hone and display. How might this have played out in our species?

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Many people think of prejudice as primarily a right-wing phenomenon. Philosopher Mike Huemer argues instead that it’s found right across the political spectrum. In his view, many contemporary progressives display the same psychological tendencies associated with older forms of bigotry, just directed at different targets.

Below is a brief excerpt from an excellent Substack essay he recently published on the topic, titled “Progressive Intellectuals: Image vs. Reality.” If you enjoy it, be sure to check out the full essay - it’s well worth your time.

If you move in even moderately high-status circles in our society, you’re basically never going to run into right-wing bigots. But you’re going to be repeatedly bombarded by left-wing bigotry...

Some manifestations of this prejudice:

1. Collectivist obsession

Progressive intellectuals are obsessed with race, sex, and other “identity groups”, far more so than normal Americans... When two people have a conflict, the progressive “anti-racist” needs to know the races of the two people before he decides which side he is on. The “anti-sexist” feminist needs to know the genders of the two people.

2. Animosity

A classic feature of racism is animosity toward one or more particular races. In traditional, right-wing racism, that would be hatred toward blacks, Jews, Latinos, and perhaps Asians. Traditional sexism involves having lower respect for women (though perhaps not hatred).

In contemporary, left-wing racism, we see hatred toward white people, and perhaps Jews, and perhaps Asians. (The Jews get it from both sides.) In left-wing sexism, we see hatred and contempt for men.

Progressives don’t like to think of themselves as hate-mongers. But if someone talked about any other group the way progressives talk about white men—e.g., talking about the harms of “whiteness”; going on about wrongs committed by white men, emphasizing their race and sex, while passing over wrongs committed by other groups—progressives would take one nanosecond to label that “hate speech”.

3. Scapegoating

Progressives like to blame white people for most of the world’s problems. This is another classic feature of racism. Right-wing racists such as the Nazis tried to blame the Jews for most of society’s problems. It doesn’t cease to be racism just because you pick a different race to scapegoat.

4. Stereotyping

Another classic feature of racism: negative stereotyping. Traditional racists would stereotype Jews as greedy, blacks as criminals, etc. Traditional sexists stereotype women as less capable than men. Left-wing bigots, on the other hand, stereotype white men as abusers and oppressors, and other groups as victims of white males.

That is the first element of progressive self-deception: they style themselves warriors against prejudice, but they are the biggest force stoking prejudice in our society. They think that their prejudice is different because the group they’re attacking is actually bad. They don’t see their stereotypes as stereotypes but just as the truth. That, of course, is what all bigots think.

Follow me on Twitter/X for more psychology, evolution, and science.

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Welcome to the June 2026 edition of the N³ Newsletter Linkfest: a collection of links to papers and articles that grabbed my attention over the last month. On the menu today…

• Why you should be wary of people who want to be seen as highly moral

• How GLP-1s affect dating and employment

• Casual sex and self-esteem in men vs. women

• Homosexuality in rats

• The surprising connections between mental and physical health

Around half the items are free to read for everyone; the rest are for paid subscribers only. I tend to put my spicier content behind a paywall, so if you’ve got a high spice tolerance, consider becoming a paid subscriber.

You can access the complete collection of Linkfests here.

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How Many Senses Do We Have?

Most people would say five - but according to many neuroscientists, we have a lot more than that. Depending on how we slice the cake, we might have ten, or maybe 21, or maybe 33. [Link.]

GLP-1s and the Female Obesity Penalty

A new study suggests that weight loss can have effects far beyond health. Among women starting GLP-1s, single women were more likely to enter relationships, and unemployed women were more likely to find work. Women already in relationships or employment saw little change, suggesting that the “obesity penalty” operates largely through first impressions during the early stages of relationship formation or hiring. [Preprint; Link.]

Evolutionary Mismatch in the Classroom: Boys Are More Mismatched Than Girls

Why do more boys than girls struggle in the classroom? Part of it may be mismatch between the demands of school and boys’ evolved nature. To start with, boys are, on average, more physically active than girls and less suited to prolonged sitting and verbal instruction. As a result, they’re more likely than girls to be flagged as having behavioral difficulties. On top of that, schools often fail to capitalize on boys’ relative cognitive strengths in spatial and mechanical reasoning. [Link.]

Are Free Speech Advocates Secret Racists?

Nope. Across multiple datasets from multiple nations, people who placed more value on free speech were more likely to hold racially tolerant attitudes. This is consistent with the idea that free speech and tolerance spring from the same broader liberal ethos. [Link.]

The Ideological Turing Test

Can you describe your political opponents’ views well enough that they wouldn’t be able to tell whether you agree with them? If so, you’ve passed the “ideological Turing test,” an informal measure of how well you understand your opponents’ positions. According to new research, people who do better on this test - that is, people who understand their opponents’ views better - tend to be less hostile toward their opponents: They see them as less ignorant, less irrational, and less immoral. [Link.]

Do Men Earn More? If So, Which Ones?

Everyone’s heard the claim: Men earn more than women. According to recent data, however, the generalization isn’t quite right. A more accurate formulation would be that married men earn more than women, and also than single men. Single men, in contrast, earn no more than women. Is this because men knuckle down when they marry, or because women are more likely to marry high earning men? It seems to be largely the latter. [Link.]

Women in Academia Do Just as Well - Until They Become Mothers

Before they have children, women do roughly as well as men in academia. Afterwards, however, women fall behind. What explains this pattern? Candidate explanations include that academia discriminates against mothers rather than women in general (seems unlikely); that despite considerable efforts to improve things, the demands of an academic career are still hard to juggle with motherhood (could be part of it); and that women’s priorities change after having children (seems like a plausible contributor). [Link.]

Moral Double Standards

People who want the world to see them as highly moral are more likely to judge others harshly, while turning a blind eye to their own moral failings. [Link.]

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