Sarah Blaffer Hrdy, Mothers and Others, 2011

In Chapter 2, I explained that other primates possess neural machinery for imitation and at least a rudimentary capacity to identify with others. The common ancestor of modern humans and chimpanzees presumably also had every incentive to evolve a sophisticated theory of mind and would have benefited from ever-shrewder and more Machiavellian intelligence or from enhanced pedagogical capacities, yet natural selection never favored their acquisition. What happened, then, in the line leading to the genus Homo to favor evolution of these traits ? In this chapter and the next I hypothesize that novel rearing conditions among a line of early hominins meant that youngsters grew up depending on a wide range of caretakers than just their mothers, and this dependence produced selection pressures that favored individuals who were better at decoding the mental states of others, and figuring out who would help and who would hurt.

It is often asserted that early hominins were selected for a better mind-reading capacity because it would prepare youngsters to acquire culture, or because it would make humans better at coordinating complex activities. Sounds good — except that natural selection, lacking foresight, does not work that way. Blindly groping along with no particular end in view, Mother Nature pays no heed to future benefits such as being better able to generate culture or coordinate large-scale activities. Directional selection favoring improved mind reading required immediate payoffs. Individuals a little bit better at interpreting someone else’s mental state and engaging with them emotionally had to have a better chance than groupmates of surviving and reproducing in the here-and-now. What other apes apparently lacked was an environment in which the components of mind reading and sharing could first develop and then be subjected to selective pressures that favored their possessors.

So what sort of environment would provide already clever and manipulative, highly social (but also highly selfish) apes the opportunity, first, to develop intersubjective abilities right from a formative early age and, then, to benefit from them ? In what sort of environment would natural selection actually favor those who were just a little bit more inclined to share ? In this chapter I will summarize evidence for thinking that hominin infants must have been reared differently from any other ape. By possibly as early as 1.8 million years ago, hominin youngsters were being cared for and provisioned by a range of individuals in addition to their mothers, and these rearing conditions set the stage for the emergence of an emotionally more modern ape. Long before our ancestors evolved into big-brained, anatomically modern humans, early hominins were being reared by alloparents as well as parents. Once outed, this long-hidden secret in our family closet requires us to consider exactly what roles these hitherto unacknowledged benefactors played.

It was the end of the twentieth century before evolutionary anthropologists like myself began to consider just how hard it would have been for foragers to rear surviving children, and then to piece together disparate strands of evidence indicating that the help of group members in addition to the genetic parents was absolutely essential for the survival of infants (birth to weaning) and children (weaning to nutritional independence) in the Pleistocene. The need for alloparental succor transformed the selection pressures that shaped our species, and in doing so altered the way infants developed and then the way humans evolved.