What Do Sex, Twins, Spotted Hyenas, ADHD, and Sexual Orientation Have in Common?

The otoacoustic emissions (OAEs) measured in a collection of special populations of humans and certain nonhuman species suggest that OAEs may provide a window into some processes of human prenatal development and sexual differentiation. For reasons that are unclear, OAEs appear to be highly sensitive to events occurring during prenatal development that seem to be related to the degree of exposure to androgens a fetus receives. The (largely circumstantial) evidence for a relationship between androgen exposure and OAE strength comes from a series of studies of twins, children with attention-deficit/hyperactivity disorder, people of differing sexual orientations, and spotted hyenas, among others. Some conclusions are bolstered by parallel studies using auditory evoked potentials (AEPs). OAEs and AEPs are simple, objective, noninvasive measures that appear to have potential as tools of value to researchers working on a wide variety of basic and applied topics beyond audition.