Book excerpt: Now updated with groundbreaking research, this award-winning classic examines the construction of sexual identity in biology, society, and history. Why do some people prefer heterosexual love while others fancy the same sex? Is sexual identity biologically determined or a product of convention? In this brilliant and provocative book, the acclaimed author of Myths of Gender argues that even the most fundamental knowledge about sex is shaped by the culture in which scientific knowledge is produced. Drawing on astonishing real-life cases and a probing analysis of centuries of scientific research, Fausto-Sterling demonstrates how scientists have historically politicized the body. In lively and impassioned prose, she breaks down three key dualisms -- sex/gender, nature/nurture, and real/constructed -- and asserts that individuals born as mixtures of male and female exist as one of five natural human variants and, as such, should not be forced to compromise their differences to fit a flawed societal definition of normality.