Oct 16, 2021
Humans are unusual in that we depend on shared foods. We also differ from other great apes in our early ages at weaning, late ages at maturity, short birth intervals and survivorship decades past menopause. Emergence of these patterns, probably in tandem, was crucial to early human evolution. Explanations focus on an ancestral shift to sharable but difficult-to-acquire foods not previously taken by hominins. I evaluate two alternatives in light of observations among modern East African hunter-gatherers. The hunting hypothesis focuses on big game meat and marrow that males acquired to provision mates and offspring, reducing female workloads, enhancing their fertilities and favoring the later ages at maturity needed to learn and perfect essential skills. But modern data show that large animal prey would not have provided the reliable energy stream the argument requires. The grandmother hypothesis identifies certain kinds of savanna plant foods that set up the forager interdependence which propelled all aspects of the life history change. But if so, why did big game hunting and scavenging, dangerous practices in the carnivore-rich environments of the day, yet clearly demonstrated in the archaeological record and provocative with respect to the hunting hypothesis, become established when they did, several hundred thousand years after the start of the shift toward modern human life histories? Greater longevity was crucial. As longevities increased, the growing proportions of post-menopausal females and senior but still fertile males shifted the mating sex ratio from female- to male-biased. While that male bias favored mate guarding, success in that strategy depended on others’ deference to their propriety claims. Agonistic encounters with large predators demonstrated by the archaeology showcased exactly the competitive capabilities that earned such deference.