individuals who violate group norms; and doing all this across time frames that stretch from the distant past to multiple possible futures (9). Consistent with this hypothesis, measures of sociality in troops of baboons have been found to be highly correlated with infant survival, and cross-species comparisons have shown that the evolution of large and metabolically expensive brains is more closely associated with social than ecological complexity (9).
Our survival depends on our connection with others. Born to the most prolonged period of utter dependency of any animal, human infants must instantly engage their parents in protective behavior, and the parents must care enough about their offspring to nurture and protect them. If infants do not elicit nurturance and protection from caregivers, or if caregivers are not motivated to provide such care over an extended period of time, then the infants will perish along with the genetic legacy of the parents (J0). Our developmental dependency mirrors our evolutionary heritage. Hunter/gatherers did not have the benefit of natural weaponry, armor, strength, flight, stealth, or speed relative to many other species. Human survival depended on collective abilities, not on individual might.
Selfish Genes, Social Brains
It is the gene that is obligatorily selfish, not the human brain. Genes that promote behaviors that increase the odds of the genes surviving are perpetuated. One implication of this simple insight is that evolution can be viewed as the competition between genes using individuals and social structures as their temporary vehicles. The genetic constitution of Homo Sapiens in the long
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run derives not solely from the reproductive success of individuals, but also from the success of their children to reproduce. Hunter/gatherers who did not form social connections and who did not feel a compulsion to return to share their food or defense with their offspring may have been more likely to survive to procreate again, but given the long period of dependency of human infants their offspring may have been less likely to survive to procreate. The result is selection that strongly favors the ability to process information that could contribute to the formation and maintenance of social capacities and connections — that is, a social brain. These social capacities evolved hand in hand with genetic, neural, and hormonal mechanisms to support them because the resulting social behaviors helped humans survive, reproduce, and care for offspring sufficiently long that they too survived to reproduce (//-1/3). Relative to other animals, the striking development of and increased connectivity within the human cerebral cortex, especially the frontal and temporal regions, are among the key evolutionary developments in this regard. The cerebral cortex is a mantle of between 2.6 to 16 billion neurons with each neuron receiving 10,000 to 100,000 synapses in their dendritic trees (e.g., 14). The expansion of the frontal regions in the human brain contributes to the human capacities for reasoning, planning, performing mental simulations, theory of mind, and thinking about self and others. The temporal regions of the brain, in turn, are involved with aspects of social perception, memory, and communication. The means for guiding behavior through the environment emerged prior to neocortical expansion.
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