John Money presents his “twins case” before the American Association for the Advancement of Science in 1972, while Brenda begins her second round of first grade. The case, Money explains, will be published in his book Man & Woman, Boy & Girl. Though dense, the book “was surprisingly straightforward and was reducible to one organizing idea stated again and again in its three hundred pages” (66). That argument is “that the primary factors driving human psychosexual differentiation are learning and environment, not biology” (66).

Still, the book recognizes the influence “of prenatal hormones on adult sexual behavior” (66). Prebirth biology, though, is overridden by “postbirth environmental factors” (66). This is Money’s “nurturist bias” (66). Colapinto explains that it is not hard to see the limits of Money’s conclusions, especially as he explains how difficult experiments are given ethical limitations. Without planned experiments, the Reimer twins are “the ultimate matched pair” for his tests, since their “biology was as close to identical as any two humans could be” (67).

Money’s book refers to Brenda often. It emphasizes contrast between Brenda and her brother. Her dominance seems to shift with time to become a more motherly kind of dominance. In Money’s picture, “the twins embodied an almost miraculous division of taste, temperament, and behavior along gender lines” (69).