In his new book, A Billion Years of Sex Differences, evolutionary psychologist Steve Stewart-Williams argues that almost everyone gets sex differences wrong. Traditionalists exaggerate natural differences, while progressives minimize them and overemphasize nurture and socialization. He aims to promote a nuanced, scientifically rigorous public conversation to guide better policymaking.
Key Claims and Evidence
Stewart-Williams asserts that some sex differences are pronounced, such as attraction to men or women, upper body strength, height, likelihood of murder, and occupational interests. Others, like math ability or conscientiousness, are modest. These differences are best visualized as overlapping bell curves. For instance, height shows that while the shortest humans are almost all women and the tallest are men, there is considerable overlap.
The author, a professor at the University of Nottingham Malaysia, writes carefully, anticipating criticism. One of his papers, arguing that women's underrepresentation in STEM is partly due to inherited cognitive differences, sparked controversy and a complaint to his university, which was dismissed.
Biases in the Field
Stewart-Williams identifies biases like the "gamma bias": minimizing differences that favor men while highlighting those that do the opposite. His research shows that people rate studies showing men as better at something as lower quality and more harmful than studies showing women as better. He also notes the "delta bias," an aversion to traditional sex differences and a preference for the reverse.
He emphasizes that innate differences do not imply one sex is superior, nor do they justify enforcing sex roles. He believes that given freedom, men and women gravitate toward different jobs and lifestyles, with men preferring things and status, and women preferring people and relationships. This is supported by studies showing sex differences are more pronounced in gender-equal countries.
Evidence for Nature Over Nurture
Stewart-Williams presents several arguments: sex differences persist historically and cross-culturally, mirror differences in other species, appear early in childhood or intensify during puberty, resist socialization, and are influenced by prenatal hormones. Evolutionary explanations suggest that because humans form pair bonds and men are involved in child-rearing, sex differences are smaller than in other animals. However, different reproductive strategies create different incentives.
The book is filled with interesting findings, but evolutionary psychology is not always the most useful lens. For example, Stewart-Williams argues that domestic violence is best understood as male aggression rather than patriarchy, citing perpetrators with anti-patriarchal beliefs. He suggests self-control interventions are more effective than targeting ideology. However, domestic violence is higher in patriarchal societies where it is tolerated, showing that culture matters greatly.
Implications for Gender Equality
Stewart-Williams believes that innate differences in professional ambition and interests contribute to women's underrepresentation in STEM and leadership. This is a more convenient explanation than examining how institutions were structured when women were excluded. He notes that men's weaker verbal abilities have not hindered them in literature. Understanding nature's role is important, but it is only one part of a complex story.
