Sandberg excels at the forward edge of economics and technology, but her sociology leans back to the Age of Aquarius. She praises to the skies Marlo Thomas's 1972 unisex album "Free to Be You and Me." She wants to bring back consciousness-raising groups, calling them "Lean in Circles." Women are advised to meet together and carry out "Listen, ask, and share" exercises. Sandberg's "Lean In" website provides "exploration kits" for these séances. One instructs group members to go round the room and finish sentences like "What I am most looking forward to in the month ahead..." and "Today I am feeling..." Is this how Mark Zuckerberg got to the top?

Sandberg's goal is to liberate her fellow Americans from the stereotypes of gender. But is that truly liberating? In a 2008 study in the Journal of Personality and Social Psychology, a group of international researchers compared data on gender and personality across 55 nations. Throughout the world, women tend to be more nurturing, risk averse and emotionally expressive, while men are usually more competitive, risk taking, and emotionally flat. But the most fascinating finding is this: Personality differences between men and women are the largest and most robust in the more prosperous, egalitarian, and educated societies. According to the authors, "Higher levels of human development—including long and healthy life, equal access to knowledge and education, and economic wealth—were the main nation-level predictors of sex difference variation across cultures." New York Times science columnist John Tierney summarized the study this way: "It looks as if personality differences between men and women are smaller in traditional cultures like India's or Zimbabwe's than in the Netherlands or the United States. A husband and a stay-at-home wife in a patriarchal Botswanan clan seem to be more alike than a working couple in Denmark or France."

Why should that be? The authors of the study hypothesize that prosperity and equality bring greater opportunities for self-actualization. Wealth, freedom, and education empower men and women to be who they are. It is conspicuously the case that gay liberation is a feature of advanced, prosperous societies: but such societies also afford heterosexuals more opportunities to embrace their gender identities. This cross-cultural research is far from conclusive, but it is intriguing and has great explanatory power. Just think: What if gender difference turns out to be a phenomenon not of oppression, but rather of social well-being?

Consider, in this regard, the gender disparities in engineering. An article on the Wharton School website laments the paucity of women engineers and holds up China and Russia as superior examples of equity. According to the post, "In China, 40 percent of engineers are women, and in the former USSR, women accounted for 58 percent of the engineering workforce." The author blames workplace biases and stereotypes for the fact that women in the United States earn only 20 percent of the doctoral degrees in engineering. But perhaps American women earn fewer degrees in engineering because they don't have to. They have more opportunities to pursue careers that really interest them. American women may be behind men in engineering, but they now earn a majority of all Ph.Ds and outnumber men in humanities, biology, social sciences, and health sciences. Despite 40 years of consciousness-raising and gender-neutral pronouns, most men and women still gravitate to different fields and organize their lives in different ways. Women in countries like Sweden, Norway and Iceland enjoy elaborate supportive legislation, yet their vocational preferences and family priorities are similar to those of American women.