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This essay attempts to address the perennial question ‘Why Paranasal Sinuses?’. In doing so it highlights the flaws in many much-favoured but ill-founded theories concerning the role of these sinuses in humans. It is concluded that the question can only be fully answered through a greater understanding of differential growth changes within the craniofacial massif.

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There is considerable speculation about the role and significance of the para-nasal sinuses in the Hominoidea, and this study aims to present new data about an old problem from cephalograms of dried crania. Measurements of frontal sinus volumes were determined for Gorilla gorilla gorilla; G. gorilla beringei and Pan troglodytes. By adopting an allometric approach it was determined that (1) the frontal sinus volume of Gorilla is relatively smaller than that of Pan, and that the frontal sinus of G. g. gorilla is relatively smaller than that of G. g. beringei. (2) Frontal sinus volume scales in a positive allometric fashion relative to skull length. Since the slope is steeper for Pan, frontal sinus volume is increasing at a faster rate than in Gorilla. Sexual dimorphism in frontal sinus volume is present. Thirty crania of Pongo were investigated for evidence of pneumatization of the frontal bone. In no case was secondary invasion of the frontal bone by the maxillary antrum observed. (3) In Gorilla, the nasal cavity volume scales isometrically with skull length. The scaling relationships discussed do not support any ‘functional’ role of the frontal sinus associated with nasal function but suggest a ‘structural’ role associated with craniofacial architecture.