A systematic relationship between brain size increase and larynx transformation during hominization
pp. 51-65
in: Jan Wind, Brunetto Chiarelli, Bernard Bichakjian, Alberto Nocentini, Abraham Jonker (eds), Language origin, Berlin, Springer, 1992Abstract
In the present work we suggest that the laryngeal descent in the neck during hominization is not per se evidence of an early specific selective pressure on speech production, but can be explained as a morphofunctional consequence of the various splanchno- and neuro-cranial rearrangements caused by an extreme prefrontal cortex size increase during hominization. The physiology of bone deposition and reallocation processes in the cranium during ontogeny are investigated, and using developmental, comparative, paleontological and clinical evidence, we suggest that most of the cranial rearrangements, typical of modem humans, are systemic morphofunctional adjustments to include a large prefrontal cortex in the braincase. A single, but strong, selective pressure on prefrontal cortex size increase could be the primary cause of most cranial rearrangements, including laryngeal descent into the neck. Once the larynx descended, then, as often happens, natural selection acted opportunistically and reinforced its use in what eventually became a component of an efficient speech organ. Humans can speak, not because of the selective pressure for a change in position of the larynx, but because of the selective pressure to have a large prefrontal cortex to store, process and analyze a large quantity of information from the environment. With a large prefrontal cortex and an inefficient larynx we would speak differently, but we would have 'speech" all the same. On the contrary, with a perfect larynx but no selection for brain increase, we would still be a primate with just some parrot-like capabilities.