Evaluating the relationship between thoracic form and individual rib cross‐sectional shape

Abstract

Within the context of human evolution, differences in rib cross‐sectional shape have been explained as a means of preserving equivalent pulmonary function in differently shaped thoraces during respiratory excursions (Jellema et al., 1993.). Relatively flat ribs should then be associated with a narrower trunk (modern), whereas rounded ribs should accompany a thorax that is transversely broad ("archaic"). This study tests whether the more modest variation in thoracic shape within living humans related to climatic adaptation may also elicit these differences. To test the influence of thoracic form on individual rib cross‐sectional shape, external shape data was collected from the 4th and 8th ribs of males from within two ecogeographically distinct populations: Inuit (n=20) and Zulu (n=20). Overall thoracic shape at each level was characterized using measures modified from Franciscus and Churchill (2002), and external rib shaft molding was used to capture cross‐sectional shape. The 2‐D outline of each cross‐section was acquired using TPS software (Rohlf, 2007). As predicted, the Inuits, with their wider torso, are determined to have statistically significantly rounder ribs, accounted for by greater medio‐lateral dimensions, though not greater cross‐sectional area. Results are presented in the context of climatic adaptation, as well as previous considerations regarding rib shape and resistance to bending.Research funded with generous support from University of Iowa Student Government, UI Graduate Student Senate, Center for Global and Regional Environmental Research, the Stanley ‐UI Foundation Support Organization.Grant Funding SourceUniversity of Iowa Student Government, UI Graduate Student Senate, Center for Global and Regional Environmental Research, the Stanley –UI Foundation Support Organization