Trabecular bone in domestic dogs and wolves: Implications for understanding human self-domestication.

The process of domestication is complex and results in significant morphological, cognitive, and physiological changes. In canids, some of the traits indicative of domestication of domestic dogs compared to their wild counterparts the wolves are prosociality toward humans, reduced stress hormone levels, and reduced cranial capacity. Research suggests that selection for prosociality among dogs resulted in morphological changes such as reduction in cranial capacity, juvenilization of the face, and overall gracile morphology. Interestingly, similar features have been described in modern humans compared to extinct species of Homo, for example, Neanderthals. Therefore, the human self-domestication hypothesis has been proposed to partially explain the gracile modern human skeleton. Specifically, that as modern humans settled in communities, there was increased selection for prosociality (intergroup cooperation); and one of the by-products of this selection was the evolution of a gracile skeleton, including a slight reduction in cranial capacity, reduced brow ridge and tooth size, and low trabecular bone fraction (TBF). However, TBF variation has not been tested between domestic dogs and wolves, who underwent self-domestication. Thus, this study tests the hypothesis that dogs have low TBF as a consequence of domestication compared to their wild counterparts, the wolves, by comparing TBF in the hindlimbs-proximal femur and distal tibia- of the two species. Wilcoxon rank sum tests show that dogs have lower TBF values than wolves in both elements. These preliminary results add to the literature documenting changes in self-domesticated species and provide a potential analog to further the understanding of self-domestication.