Books

A Billion Years of Sex Differences

Steve Stewart-Williams

According to an old joke, everyone knows that men and women are different… except social scientists. In A Billion Years of Sex Differences, evolutionary psychologist Steve Stewart-Williams tackles some of science’s most controversial questions: How do men and women differ? Where do the differences come from? And how do they shape modern life?

The result is the most up-to-date, balanced, and engaging account of human sex differences yet written, covering everything from dating and mating to aggression and parenting, from children’s toy preferences and workplace gender gaps to mental health and the politics of equality. Drawing on a century of research – and a billion years of evolution – Stewart-Williams explains why many sex differences appear despite socialization, not because of it; why in our mating and parenting patterns, humans are more like the average bird than the average mammal; and why sex differences are sometimes a sign of societal health rather than injustice.

With more than two decades of research in evolutionary psychology and an international reputation in the field, Steve Stewart-Williams is uniquely positioned to challenge prevailing views in this fraught debate. Avoiding the extremes of either overstating or denying the differences, he argues that, rather than trying to make men and women identical, we should strive for a world where bias and barriers are eliminated, and where people are free to be themselves whether they conform to gender norms or defy them.

Hardback

ISBN: 9781800756472

Published: June 4, 2026

Ebook

ISBN: 9781800756489

Published: June 4, 2026

Category:
Non-fiction

Reviews for A Billion Years of Sex Differences

Praise for The Ape That Understood the Universe:

‘An eloquent and elegant exploration of human nature in the light of evolution, illuminating many modern social and political dilemmas’ – Matt Ridley, author of The Red Queen and Nature via Nurture

‘The best update of the gene’s-eye view I have seen for a long time. This book will turn your view of human nature inside out and upside down’ – Susan Blackmore, author of The Meme Machine and Consciousness: An Introduction

‘Takes the reader from first principles to a deep understanding of the evolutionary and cultural underpinnings of human behaviour. Not only has Stewart-Williams produced a work of deep understanding, he has also produced one which is a real page turner. A twenty-first century successor to The Selfish Gene‘ – Lance Workman, co-author of Evolutionary Psychology: An Introduction

‘A great introduction to human nature … Stewart-Williams shows how genes and memes entwine to explain our deepest concerns and our highest aspirations. This fun, easy-going, science-savvy book will make you smarter about your emotions, your relationships, and your society’ – Geoffrey Miller, author of The Mating Mind, Spent and Mate

‘A captivating, page-turning, voyage of discovery. Stewart-Williams is not only an experienced evolutionary psychologist but also a talented and insightful writer with a memorable turn of phrase’ – The Psychologist

‘A sharp, fun, contemporary, succinct overview that best represents evolutionary psychology and also covers the basics of cultural evolutionary theory’ – Human Nature

‘A thrilling review of our best explanations of human behaviour at a time when such theories are under attack … a wonderful entry point into learning how the scientific method works – it doesn’t care what you believe, nor what you wish were true’ – Aero

Author

Steve Stewart-Williams

Steve Stewart-Williams is a New Zealander who moved to Canada, and then to Wales, and then to Malaysia, where he’s a professor of psychology at the University of Nottingham Malaysia. His first book, Darwin, God, and the Meaning of Life, was published in 2010. His second book, The Ape That Understood the Universe, was published in 2018.