A Billion Years of Sex Differences: The Story So Far
...plus a new review in Quillette and my appearance on the Michael Sartain Podcast
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.
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, 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.
Follow me on Twitter/X for more psychology, evolution, and science.
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Related Reading from the Archive
12 Things Everyone Should Know About Evolutionary Psychology
This is the latest post in my “12 Things Everyone Should Know” series. You can access the full collection here.
A Billion Years of Sex Differences
I recently gave a professorial lecture at my university, focused on some of my theoretical work on the evolution of human sex differences. The following is a lightly edited transcript of the lecture.
Sex Differences in Personality
The graph below shows sex differences in the Big 5 personality traits across the adult lifespan. The first five panels show the differences in each of the Big 5 traits in turn; the final panel shows the trajectory of all five traits across adulthood, averaging across the sexes.