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Language in humans has evolved culturally rather than genetically, according to a study by UCL (University College London) and US researchers. By modelling the ways in which genes for language might have evolved alongside language itself, the study showed that genetic adaptation to language would be highly unlikely, as cultural conventions change much more rapidly than genes. Thus, the biological machinery upon which human language is built appears to predate the emergence of language. According to a phenomenon known as the Baldwin effect, characteristics that are learned or developed over a lifespan may become gradually encoded in the genome over many generations, because organisms with a stronger predisposition to acquire a trait have a selective advantage. Over generations, the amount of environmental exposure required to develop the trait decreases, and eventually no environmental exposure may be needed - the trait is genetically encoded. An example of the Baldwin effect is the development of calluses on the keels and sterna of ostriches. The calluses may initially have developed in response to abrasion where the keel and sterna touch the ground during sitting. Natural selection then favored individuals that could develop calluses more rapidly, until callus development became triggered within the embryo and could occur without environmental stimulation. The PNAS paper explored circumstances under which a similar evolutionary mechanism could genetically assimilate properties of language - a theory that has been widely favoured by those arguing for the existence of 'language genes'. The study modelled ways in which genes encoding language-specific properties could have coevolved with language itself. The key finding was that genes for language could have coevolved only in a highly stable linguistic environment; a rapidly changing linguistic environment would not provide a stable target for natural selection. Thus, a biological endowment could not coevolve with p