A Billion Years of Sex Differences: Evolutionary Psychology's Take on Gender

The Evolutionary Perspective on Gender Differences

According to evolutionary psychologist Steve Stewart-Williams, almost everyone gets sex wrong. Traditionalists tend to exaggerate natural differences between men and women, while progressives tend to minimize them and assume that nurture and socialization play a decisive role. In his book "A Billion Years of Sex Differences," Stewart-Williams promotes a more nuanced, scientifically rigorous public conversation about why and how men and women differ to guide better policymaking.

Understanding the Spectrum of Sex Differences

Stewart-Williams identifies varying degrees of sex differences. Some are relatively pronounced, such as attraction patterns, upper body strength, height, likelihood of committing violence, and occupational interests. Others, like ability in mathematics or conscientiousness, are much more modest. These differences are best visualized as two overlapping bell curves. For example, while the average man is taller than the average woman, there is considerable common ground—knowing someone is 5ft 8in doesn't enable confident gender identification.

Research Evidence and Scientific Biases

As a professor of psychology at the University of Nottingham Malaysia, Stewart-Williams examines various physical, psychological, and cognitive sex differences through an evolutionary lens. He identifies common biases in his field, including "gamma bias" (minimizing differences that paint men in a better light while highlighting those that do the opposite) and "delta bias" (an aversion to traditional sex differences and a preference for the reverse).

His research found that when presented with fictitious studies showing men drawing better, lying less, or being more intelligent, people rated them as lower in quality, more harmful, and more worthy of censorship than studies showing women possessed these positive traits.

Implications for Gender Equality and Policy

Stewart-Williams argues that innate differences don't imply one sex is better than the other, nor do they suggest a moral imperative to enforce sex differences. However, he believes that when given freedom of choice, men and women tend to gravitate toward different directions—men toward working with things and status, women toward working with people and relationships.

Interestingly, various studies find that many sex differences—from occupational preference to personality traits—are more pronounced in more gender-equal countries, suggesting that when social constraints are removed, natural tendencies become more evident.

The Future of Gender Research

While Stewart-Williams presents compelling evolutionary explanations for sex differences, the reviewer notes that evolutionary psychology isn't always the most useful lens. For example, understanding domestic violence as primarily a manifestation of male aggression rather than patriarchy may overlook how socialization and culture shape behavior in different societies.

The book contributes valuable insights to the nature versus nurture debate, but ultimately represents only one part of a complex story about human development and gender relations. Future research will likely need to integrate biological, psychological, and sociological perspectives to fully understand the intricate interplay of factors that shape who we are.