As women’s social, occupational, and political engagement expanded in Western nations, social scientists anticipated a great psychological and behavioural convergence of men and women. As Alice Eagly and colleagues wrote, “The demise of many sex differences with increasing gender equality is a prediction of social role theory.” Their perspective is that most sex differences result from adherence to socially imposed norms and expectations. These norms and expectations have changed over the past several generations, as women entered educational, occupational, and political spheres that had been historically dominated by men. Today, in most highly developed nations, women are now the majority in higher education and are on track to become the majority in some formerly male-dominated and high-status professions, such as medicine. Even if one might argue that the gains in gender equality are not complete, social-role theory tells us that we should therefore see the sexes acting and thinking more similarly.

But like many almost-utopian academic predictions, social role and related theories have hit the wall of reality. Instead of convergence of the sexes, we have something closer to a great divergence. To the surprise and dismay of social scientists, many psychological and behavioural sex differences are larger in more gender-equal countries—precisely the opposite of their predictions—which has dealt a major blow to the plausibility of sociological theories of the origin of sex differences. As reviewed by David Schmidt and colleagues, then Marco Balducci, and most recently, Agneta Herlitz and colleagues, the divergence is broad and deep, including aspects of personality, emotional expressiveness, mental health, cognition, and occupational choices and preferences, among others. To be sure, there has been convergence in some areas (for example, intimate partner violence) and no change in others, but the trend is clear—women and men are becoming more different in important ways. Many of the expanding differences are small to moderate for individual traits, but the tableau created is of a substantive divergence.

Expanding liberal mores and a greater range of social and occupational niches enable a fuller expression of individual and sex differences in personality and preferences, among other traits. We are therefore better able to see the true magnitude of innate differences between the sexes in thinking, behaving, and choosing. By analogy, in the US in the 1960s, most families seemed to be similarly entranced by the Ed Sullivan show. But this convergence in viewing habits was driven by a lack of alternatives (there were just three television stations to choose from) rather than a lack of differences between households in their underlying interests. We can see these individual differences better today now that there are hundreds of viewing options available through cable television, streaming, and online entertainment.