Implicit in the discussion of views taken by Wolfe, Geschwind, and Newmark is a claim that no learning theory based solely on "nurture" can account for the fact that language acquisition in childhood is a trait, in adulthood a skill. The child can master the language system completely, regardless of his intellectual capacity or his social environment, whereas an adult is unable to master at least the sound patterns of a language system completely. There are many adults who are more skilled at language learning than others, and many environments seem more conducive to language learning than others. In this sense, proponents of nurture theories are correct. There is, however, a distinction made between the complete ability of all children to acquire language (a trait), and the varying abilities of adults to master a language (a skill). Presented is the possibility that it is "cerebral dominance" or "lateralization" that accounts for the ability of children to learn language fluently. Of special note is the age of onset of dominance, when the brain has become completely lateralized. It "seems reasonable" that the ability to master a language without a foreign accent before the age of about 12 is directly related to the fact that lateralization has not yet become permanent. Implications for foreign language teaching are briefly touched upon. (AMM)