Abstract: 

Humans differ from the great apes in our earlier ages at weaning, later ages at first reproduction, shorter birth intervals, overlapping dependents and survivorship decades past menopause. Life history theory and fossil evidence indicate that the transition from a great ape-like ancestral pattern to the human one began before 2.0 Ma. One explanation for the shift identifies foraging for hard-to-acquire plant foods, with the productivity of older females subsidizing still-dependent grandchildren. Use of foods central to this hypothesis has not yet been tracked in the early fossil and archaeological records but can be. The favored alternative explanation attributes emergence of the human pattern to big game hunting and aggressive scavenging by ancestral males to provision mates and offspring. Early Pleistocene archaeological evidence of meat eating is held to support this idea but observations among Hadza foragers in a modern analogue environment suggest that big game acquisition was too unreliable to provide the daily provisioning essential to the argument. Fossil hominin data further show that onset of the life history shift predates evidence for significant big game hunting and scavenging by several hundred thousand years. Those practices may instead be products of the transition. As postmenopausal longevity increased, the fraction of older males grew, shifting fertile-age sex ratios from female- to male-biased. With greater competition for paternities, ancestral males earned deference to proprietary claims on fertile females by displaying formidable competitive capabilities in agonistic encounters with non-human carnivores over large-bodied prey.

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