▫ Owing to disparate, piecemeal anthropological discoveries, the story of human descent is a fragmented tale.
▫ 14–8 MYA in Africa, hominids and apes parted ways from a common primate ancestor. Dramatic climate change was a strong external driver in the radiation of hominids, reflected in traits that afforded generality: dietary diversity, greater mobility, and the savvy to deal with shifting environments.
2 MYA there were at least 8 contemporaneous hominids, all in Africa, all with populations as low as 10,000 or less. The number of hominin species was whittled down to 4 by 100,000 years ago; thinly spread in Africa, Europe, and Asia. Glaciation took a terrible toll.
▫ Both environmental and social demands drove hominin evolution. One of the most important traits developed was an increasing capacity for complex language. Though an incremental advance compared to other animals, the significance of language in human descent cannot be overstated.
▫ Monogamy as the dominant mating system facilitated the growth of tribes through marriage bonds. Culture extended inclusive social bonding, creating the multilevel, nested structures of alliances that characterize human societies. The productive advantage in large-scale sociality is cooperation.
▫ Hominins underwent evolutionary changes from the Pleistocene to the Holocene: more gracile, with less sexual dimorphism. Those adaptations arose from multiple influences, but a warming climate was doubtlessly instrumental.
▫ Humans arose by 315,000 years ago, somewhere in Africa. Like many hominids before them, they migrated outwards in waves, speciating along the way.
▫ Despite remarkable diversity, where any biologist would otherwise find multiplicity, modern humans are considered a single species. Distinctive human phenotypes and cultures used to be called races; a term now generally deprecated as divisive rather than descriptive.