ON THE HERITABILITY OF SPONTANEOUS OTOACOUSTIC EMISSIONS - A TWINS STUDY

Spontaneous otoacoustic emissions (SOAEs) were measured in human monoz ygrotic (MZ) and dizygotic (DZ) twins and in a sample of non-twins. Th e number of SOAEs exhibited was more highly correlated in MZ co-twins than in same-sex DZ co-twins. Model-fitting to the correlations sugges ted that about three-quarters of the individual variation in the expre ssion of SOAEs is attributable to genes. There was no convincing evide nce far the heritability of specific SOAE frequencies. In accord with past surveys, SOAEs were more numerous in right than left ears, and in female than male subjects. Also investigated were the numbers of SOAE s exhibited by dark- versus light-eyed people and by MZ versus DZ twin s. Those differences in our data were small and not statistically sign ificant, but they were in a direction consistent with other studies: m ore SOAEs in dark-eyed individuals and in MZ twins. The view presented here is that SOAEs themselves are unlikely objects for natural select ion, and probably are epiphenomena resulting from selection for those cochlear mechanisms that contribute to good hearing sensitivity-which is related to SOAE expression. It is argued that, in addition to genet ics, other factors have the potential to affect the specific numbers o f SOAEs that are expressed. For example, same aspects of the complex p renatal process of producing a male fetus are presumed to be responsib le for the smaller number of SOAEs seen in males than females.