On October 10, 1970, the day she was born, she was named Dorothy Maree Alaniz — a baby girl. Curiously, though, no one filled out a birth certificate that day. When the certificate was finally filed on November 5, the name on it was Rudolph Andrew Alaniz. Within less than one month after her birth, this girl became a boy. Every year in the United States, more than two thousand children are born with an intersex condition or disorder of sex development.

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 an either-or proposition: not girl/boy, 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. Between XX and XY provides a fascinating look at the science of sex and what makes people male or female. There are people born XXY, XXXY, or XXXXY, or with any number of variations in X or Y chromosomes, but those who do not fit into society's preconceived notions about sex often face a difficult path in life. Dr. Callahan explores why humans are so attached to the idea of two sexes, and examines our obsession with sex and sexual intercourse through the ages.

"Combining passion with current scientific information, Callahan, an immunologist/pathologist at Colorado State University, explains why our conception of two sexes is more a social than a biological construct. He argues that there are no simple, foolproof ways to determine sex. For example chromosomal structure, XX for females and XY for males, is not fully predictive because of various genetic disorders that can play a larger role. Similarly, genitalia can be quite varied and represent a continuum of difference rather than two discrete points. Callahan does a good job of exploring intersex individuals, who are neither male nor female, and argues that they need to be accepted for what they are and not viewed as defective. Further, he provides provocative evidence that surgical gender reconstruction is often unsuccessful. Although Callahan attempts to make the case that some non-Western societies have a less bipolar view of gender, his abbreviated presentation is not very convincing. He is, however, persuasive that better understanding of and respect for sex and gender variability would be far healthier for the 65,000-plus intersex people born each year and society in general. (July)" Publishers Weekly (Copyright Reed Business Information, Inc.)

Providing a fascinating look at the science of sex and what makes people male or female, this book explains dozens of intersex conditions — such as hermaphroditism, Klinefelter syndrome, and androgen insensitivity syndrome — and includes personal interviews with people living with these conditions telling their surprising and often heart-wrenching stories.

Even doctors and scientists are not entirely sure if external genitalia, internal sex organs, chromosomes, DNA, environment, or some combination define a person's sex, but this examination shows that sex is not an either-or proposition: not girl/boy, XX/XY — there are babies born XYY, XXX, or with any dozen or more known variations in the X or Y chromosomes. The history and the current treatment for intersex conditions as well as the options that are available today for the ambiguous child are covered in this captivating account that truly shows what it means to be human.

Gerald N. Callahan, Ph.D., is an author and an immunologist/pathologist with more than 30 years of experience in biomedical research. He is the author of Infection: The Uninvited Universe and Faith, Madness, and Spontaneous Combustion. He is currently an associate professor at Colorado State University. He lives in Fort Collins, Colorado.