The Relationship of the Lower Ribcage with Liver and Gut Size: Implications for Paleoanthropology

Abstract

Organ–skeleton relationships are understudied in biological anthropology. The torso skeleton is often used to infer the organ size and evolution in hominins; ribcage “types”, in particular, are used to infer the abdominal organ size in hominins. This study is a quantitative examination of the relationship between the lower ribcage and two organs: the liver and the intestines (“gut”) in humans. Specifically, we test whether the ribcage breadth, shape, and “flare”, at the level of rib 10, covaries with the liver volume and gut volume in Homo sapiens. Liver size, gut size, and ribcage measurements are taken from CT scans (N = 61). The results show sex differences in the gut–ribcage relationship. The gut volume is associated with ribcage breadth and flare in both sexes. The liver volume is not associated with any ribcage measurements. We conclude that sex differences in the organ–skeleton relationship complicate the previous simplistic view that the size of the liver or the gut could be inferred through a fossil’s ribcage type. Biological anthropologists should continue to explore sex differences in organ–skeleton relationships, when attempting to understand the evolution of visceral organs and the torso.