As many commentators about sex research are fond of pointing out, in the fourth century B.C.E., the philosopher Plato offered a fanciful account that attributed the origins of erotic desire to divine punishment. Zeus punished the first human beings for impious and willful misbehavior by splitting them in half. 1 Erotic love, the desire to reunite lost halves, is the legacy of that punishment. Plato's mythology described not only the erotic entanglements of men and women but of men and men as well as women and women. Since then, the debate about the origins and meaning of eroticism, and especially same-sex eroticism, has only grown more contentious. Some twenty-five hundred years and a great deal of failed research later, questions about the origins of erotic interests still enjoy considerable prominence, though lately it has not been philosophers but scientists who have taken up the inquiry, and they study not eros but sexual orientation. Genetic loading, fetal hormone exposure, and cerebral lateralization have supplanted gods, divine wrath, and mortal longings as the categories used to investigate and explain erotic desire.
Since scientific efforts to account for sexual orientation commenced in earnest in the nineteenth century, researchers have reported differences between gay and straight people in their fat distribution, metabolism, hair quality, height, lisping, lipid levels, the angles at which they carry their arms, susceptibility to paranoia, and an almost indefinite number of biophysical and psychodevelopmental traits. 2 From these alleged anatomical and behavioral differences between gay and straight people various competing conclusions have been drawn about the origins of erotic desires: that they result from events in psychosexual development and are therefore primarily psychological in origin