The relationships between otoacoustic emissions and relative lengths of fingers and toes in humans.

Both otoacoustic emissions (OAEs) and the relative length of the index and ring fingers (the 2D:4D ratio) exhibit large sex differences, and both exhibit masculinization effects in female homosexuals and bisexuals. Because these sex differences exist in young children, the implication is that both types of measure are affected by prenatal androgen exposure, but it has been unknown to what degree these two types of measure are related. Accordingly, OAEs and the relative lengths of the fingers and the toes were measured in 59 heterosexual females, 55 heterosexual males, 29 homosexual females, and 33 homosexual males. The correlations between the two types of measure were unexpectedly quite low in both the heterosexual and nonheterosexual groups. For example, the correlation between number of spontaneous OAEs per ear and 2D:4D was less than 0.25, for both sexes and both sexual orientations. One interpretation of these results is that the prenatal hormonal mechanisms producing the sex differences in OAEs differ in quality, degree, or timing from those producing the sex differences in relative finger length. That is, OAEs and 2D:4D may be windows onto slightly different prenatal processes or times during prenatal development. Measures of mental-rotation ability also were obtained on these participants, and those correlations with relative finger length also were small.