http://www.sciencemag.org/news/2018/11/frequent-inbreeding-may-have-caused-skeletal-abnormalities-early-humans

These bowed femurs were found (top to bottom) in China’s Tianyuan cave, Russia’s Sunghir burial site, and the Czech Republic’s Dolní Vĕstonice site.

Early humans faced countless challenges as they fanned out of Africa: icy conditions, saber-tooth cats, and, according to a new study of ancient skeletons, an unusually high number of birth defects, both debilitating and relatively inconsequential. It’s unclear why such abnormalities seem to be so common, but scientists say one strong possibility is rampant inbreeding among small hunter-gatherer groups.