Hominin Evolution in the Middle-Late Pleistocene Fossils, Adaptive Scenarios, and Alternatives

Hominins from Europe and Africa shed light on functional adaptations and other aspects of lifeways during the Middle Paleolithic. By the end of that time span, Neanderthals and modern humans clearly differed physically and perhaps behaviorally. Explanations of the anatomical differences have largely focused on adaptation (directional selection) to climate and habitual activity, but it is hard to rule out the alternative of genetic drift. Drift would have accelerated during periods of low population numbers, while selection operates best when populations are large and expanding. Demographic changes almost certainly tracked climatic conditions in both continents. Environmental and genetic data suggest that European hominins were primarily shaped by drift, while both factors operated in Africa.