A MASCULINIZING EFFECT ON THE AUDITORY SYSTEMS OF HUMAN FEMALES HAVING MALE CO-TWINS

Spontaneous otoacoustic emissions (SOAEs) are continuous, essentially tonal sounds that are produced by many normal-hearing cochleas. In hum ans, females generally exhibit more SOAEs than males, a sex difference that exists from birth. However, it is shown here that females having male co-twins [opposite-sex dizygotic (OSDZ) females] exhibit about h alf the average number of SOAEs per ear observed in same-sex female tw ins or female non-twins. Indeed, the average in OSDZ females is about the same as that seen in males-twins or non-twins. The explanation off ered here is that prenatal exposure to high levels of androgens has pr oduced a masculinizing effect on the auditory systems of these OSDZ fe males. Prenatal masculinizing effects have long been recognized in cer tain litter-bearing mammals, but their existence in humans is not well -studied.