External Nose Projection
Humans, unlike other apes, possess a projecting, external nose whose overall structure is reflected in a series of derived skeletal features including: nasal bone convexity, an internasal angle, lateral nasal aperture eversion, prominence and anterior positioning of a true anterior nasal spine rather than a nasal tubercle, an acutely angled subnasal alveolar clivus, and an expansion of the breadth of the nasal bones relative to that of the piriform aperture. This constellation of features first appears with the emergence of Homo erectus in early Pleistocene Africa. Although nasal projection undoubtedly evolved in the context of craniofacial and dental reduction during hominin evolution, it also likely represented an adaptive response to the need for respiratory moisture conservation in an arid environment. More specifically, it indicates a shift to increasingly prolonged bouts of activity in such dry and open environments. While the adaptive basis for nose form is questioned by some, substantial evidence from clinical studies, mathematical airflow, temperature/humidity modeling, and quantitative studies showing departure from neutral evolutionary expectations support its adaptive basis. Nonetheless, the precise role of the external nose independent of the internal nasal cavity in terms of conditioning respiratory air and ameliorating moisture loss is incompletely understood.
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