What can trabecular bone tell us about activity levels and self‐domestication?

Abstract

Various studies have compared trabecular bone fraction (i.e., TBF both volumetric and areal) among modern humans, great apes and fossil hominins and found that modern humans have gracile skeletons in having low TBF. This has been observed even among populations engaging in greater levels of activity such as foraging compared to farming. These findings raise questions about when and why the gracile human skeleton emerged. Although, sedentism has been proposed to explain this phenomenon, another hypothesis that may explain the unusually gracile modern human skeleton is the human self‐domestication (HSD) hypothesis. This hypothesis proposes that selection for prosociality among mammals with increased cognition resulted in changes in morphological features e.g., having a slight reduction in cranial capacity, a globular cranium, and thin cranial bones. In fact, other mammals thought to have undergone self‐domestication such as bonobos vs. chimpanzees, domestic dogs vs. wolves exhibit this trend in prosociality, and display differences in morphological traits such as feminization of the skull, and a reduction in cranial capacity among others. Thus, these observations provide an opportunity to test the HSD hypothesis. The present study tests this hypothesis first, by examining whether domestic dogs have low TBF (gracile skeletons) compared to their wild relatives: the wolves, foxes, and coyotes based on the understanding that domestic dogs are prosocial relative to their wild counterparts and therefore, would exhibit low TBF as a by‐product of selection for prosociality. Secondly, by estimating TBF in the human fossil record comparing hominins from the Pleistocene (early Homo and upper Paleolithic Homo), and recent modern humans from the Holocene. MicroCT and pQCT scanning were used to image proximal femora and humeri, which were then analyzed using Quant3D to quantify TBF. One‐way ANOVA with Tukey post‐hoc correction was used to identify differences among species. Results show that, indeed the domestic dogs across breeds studied exhibit low TBF compared to wolves and other canids. Secondly, that recent modern humans have low TBF compared to Pleistocene hominins. These results suggest that it is plausible that apart from sedentism, selection for prosociality may have had an effect on gracility, however, more work on other prosocial species that underwent self‐domestication needs to be done to further test this hypothesis and better understand the mechanisms responsible for it. These findings indicate that the highly gracile skeletons of modern humans and the increased risks of bone fracture associated with a decline in bone mass have evolutionary underpinnings‐ albeit relatively recent‐ than has been considered before.Support or Funding InformationNASA WV Space ConsortiumThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.