Between XX and XY: Intersexuality and the Myth of Two Sexes

What makes someone a boy or a girl? Is it external genitalia, chromosomes, DNA, environment, or some combination of these factors? Not even doctors or scientists are entirely clear. What is clear is that sex is not girl/boy or XX/XY, switching between two poles like an on/off switch on a radio.

Rather, sex is like the bass and treble knobs on that radio. In this eye-opening exploration of the science of sex, Gerald N. Callahan, PhD, challenges our notion of two opposite sexes. Human sex…