The main point here is that an additional factor influencing axon elimination may be operative in men. Only in men is callosal size, and particularly isthmal area, related to hand preference, a measure of functional asymmetry. Similarly, only in men does posterior Sylvian fissure morphology vary with hand preference. Such sex differences suggest that some sex-related biological factor may influence the regressive mechanisms hypothesized to play a role in determining brain structure related to lateralization. The morphology of the human corpus callosum appears to be different between the sexes.
Hand preference is a rough index of the pattern of brain organization.