In Man and Woman, Boy and Girl, John Money and Anke Ehrhardt offer a comprehensive account of sexual differentiation using genetics, embryology, endocrinology and neuro-endocrinology, psychology, and anthropology. Their multidisciplinary approach to gender identity avoids the old arguments over nature versus nurture. Money and Ehrhardt focus instead on the interaction of hereditary endowment and environmental influence. Money and Ehrhardt's work will lead many readers to the conclusion that the differences between man and man, or woman and woman, can be as great as between man and woman.