Adaptive Shifts Accompanying the Origin of Homo
Many aspects of the origin of the genus Homo are murky and cannot be resolved with the available data. There is no clear way to define the genus let alone its species, and the evolutionary relationships among the relevant taxa are open to question. Although few experts question the notion that Homo differs significantly from Australopithecus, there is little agreement on what adaptive strategies facilitated change within the Homo clade. Proposed behavioral differences include trekking, endurance running, tool-making, tool-using, hunting, cooking, throwing, language, slower life histories, pro-social cooperation, division of labor, and more. All of these are debated.
Here I will make the argument and review the evidence that, fundamentally, the genus Homo differs from other early hominins through an integrated suite of behaviors, collectively termed hunting and gathering, that emerged sometime between 3 and 2 million years ago. Importantly, the hunting and gathering system (especially hunting) was made possible by selection for a combination of anatomical and physiological adaptations such as the ability to walk and run long distances efficiently, to dump heat effectively, to make and use tools, to process food, and to throw with speed and accuracy. The hunting and gathering system also requires a suite of cognitive and social skills such as the ability to cooperate with non-kin, and to use hypothetico-deductive logic. Although hunting and gathering did not arise instantaneously, and many of the adaptations that made it possible probably predate the genus Homo, its emergent properties made possible increased access to energy. More energy, in turn, drove positive feedback leading to further selection on costly characteristics typically associated with Homo such as increased brain size, larger body size, and slower life histories.