In his recent book, a Colorado State University expert has pooh-poohed the common myth that there are only two sexes.
Gerald Callahan, an associate professor of immunology and the public understanding of science at Colorado State University, writes in 'Between XX and XY: Intersexuality and the myth of two sexes' that the stereotypical view of two sexes - me Tarzan, you Jane - limits people's understanding and appreciation of their own biology.
He argues that there is a range of sexual characteristics that stretches from the testosterone-inflated Tarzan to the womanly "perfection" of a stereotypical Jane, and all the variations that lie in between.
The standard model of human development is built on 46 chromosomes, including two that determine sex: XX for female, XY for male.
Callahan, however, insists that not everyone ends up 46XX or 46XY.
According to him, variations in sperm or egg, in the mixing of cells from mother and father and in the cell division that follows can all stir the genetic soup into alternative outcomes.
"(The possibilities) are as grand and as varietal as the fragrances of flowers: 45X; 47XXX; 48XXXX; 49XXXXX; 47XYY; 47XXY; 48XXXY; 49XXXXY; and 49XXXYY," he writes.
While geneticists are familiar with such variations, says Callahan, the general public is still stuck in a black and white, XX/XY world.
Callahan's book is spent exploring the understanding of intersexuality, from the physicians of ancient Greece to today's neuroendocrinologists.
He also weaves in the stories of people who live in the stretch between the classic male and female endpoints.