For her new book, Pink Brain, Blue Brain: How Small Differences Grow Into Troublesome Gaps—And What We Can Do About It, Eliot immersed herself in hundreds of scientific papers (her bibliography runs 46 pages). Marching through the claims like Sherman through Georgia, she explains that assertions of innate sex differences in the brain are either “blatantly false,” “cherry-picked from single studies,” or “extrapolated from rodent research” without being confirmed in people. For instance, the idea that the band of fibers connecting the right and left brain is larger in women, supposedly supporting their more “holistic” thinking, is based on a single 1982 study of only 14 brains. Fifty other studies, taken together, found no such sex difference—not in adults, not in newborns. Other baseless claims: that women are hard-wired to read faces and tone of voice, to defuse conflict, and to form deep friendships; and that “girls’ brains are wired for communication and boys’ for aggression.” Eliot’s inescapable conclusion: there is “little solid evidence of sex differences in children’s brains.”
Yet there are differences in adults’ brains, and here Eliot is at her most original and persuasive: explaining how they arise from tiny sex differences in infancy. For instance, baby boys are more irritable than girls. That makes parents likely to interact less with their “nonsocial” sons, which could cause the sexes’ developmental pathways to diverge. By 4 months of age, boys and girls differ in how much eye contact they make, and differences in sociability, emotional expressivity, and verbal ability—all of which depend on interactions with parents—grow throughout childhood. The message that sons are wired to be nonverbal and emotionally distant thus becomes a self-fulfilling prophecy. The sexes “start out a little bit different” in fussiness, says Eliot, and parents “react differently to them,” producing the differences seen in adults.