Fossil ribcages of Homo sapiens provide new insights into modern human evolution

Abstract

Recent research on the Nariokotome Boy’s ribcage suggests the slender thorax of modern H. sapiens is a derived condition. However, since digital ribcage reconstructions of fossil H. sapiens are not available yet, it is unknown whether these individuals would have had a primitive or derived thorax. To address this issue, we first reconstructed the ribcages of Nazlet Khater 2, Ohalo II H2, Dolní Věstonice 13, and Ötzi. We used geometric morphometrics to compare them to 59 recent H. sapiens and three other Homo fossils (Nariokotome Boy, Kebara 2, Shanidar 3). Fossil H. sapiens ribcages exhibit the typical globular proportions of recent humans. Additionally, size and shape seem to be climate-dependent: smaller, cylindrical ribcages in warmer and more temperate climates (Nazlet Khater 2, Ohalo II H2) contrasted with larger, broader ribcages in colder climates (Dolní Věstonice 13). The ribcage of Ötzi presented mixed features, something that could have been beneficial for seasonal alpine transhumance. This suggests H. sapiens ribcage morphology encompasses both slender and stockier forms, highlighting that human anatomical variation might be more complex and context-dependent than previously thought.