Elevated Sinistrality in Transsexuals

On the basis of both Geschwind andBehan's (1984) theory—that at least part of the genesis of left-handedness can be ascribed to overexposure to testosterone during fetal development—andDorner's (1980;Dorneretal., 1991) theory—that transsexuality emerges from prenatal overor underexposure to androgens infemale-to-male (FTM) andmale-to-female (MTF) transsexuals, respectively—it was predicted that thefrequency of left-handedness in FTM transsexuals would be higher than in the general population. In MTF transsexuals, by contrast, thefrequency of left-handedness was expected to be lower or the same as in the general population. Results showed that the prevalence of lefthandedness in both FTM and MTF transsexuals is nearly two times higher than in the general population. The generally higher prevalence of left-handedness among transsexuals, combined with the absence of the predicted sex difference, indicates that either Dorner's theory on the etiology of transsexuality or Geschwind's model of the genesis of left-handedness, or both, need to be revised.