In their early work, Money and colleagues treated gender identity as if it formed without biological influence. By 1972, in their classic book Man and Woman, Boy and Girl, Money and his colleague Anke Ehrhardt were less certain of the idea of total plasticity, but still emphasized the high degree of malleability in gender identity formation in the first two years of life (Money & Ehrhardt, 1972). Regardless of what combination of biological and social forces contributed to gender identity formation, Money and Ehrhardt believed that gender identity became fixed at some point around 2 years of age. Their concept of early identity fixation became the underpinning for the view that “corrective” surgery for children born with ambiguous genitalia needed to be done swiftly. In more recent years, many have criticized the practice of early surgery (Dreger, 1998a, 1998b; Fausto-Sterling, 2000; Kessler, 1998).