Extraordinary intelligence and the care of infants

Abstract

We present evidence that pressures for early childcare may have been one of the driving factors of human evolution. We show through an evolutionary model that runaway selection for high intelligence may occur when (i) altricial neonates require intelligent parents, (ii) intelligent parents must have large brains, and (iii) large brains necessitate having even more altricial offspring. We test a prediction of this account by showing across primate genera that the helplessness of infants is a particularly strong predictor of the adults' intelligence. We discuss related implications, including this account's ability to explain why human-level intelligence evolved specifically in mammals. This theory complements prior hypotheses that link human intelligence to social reasoning and reproductive pressures and explains how human intelligence may have become so distinctive compared with our closest evolutionary relatives.cognitive science | evolutionary dynamics | developmental modeling T he breadth and power of human cognition is qualitatively unlike that of even our closest evolutionary relatives. Although our mental abilities clearly aid survival and reproduction, our cognitive capacity also appears to go far beyond what is minimally required to live and reproduce, permitting us to engage in a remarkable breadth of cognitive and technical endeavors. The question of why human intelligence and brain size exhibits a drastic change over recent evolutionary history has not yet been resolved. Numerous authors have theorized about possible factors that may have given rise to humans' powerful cognitive systems. These theorized factors include social learning and interaction (1-10), diet (11-13), relational/analogical abilities (14), language (15, 16), the rise of female food gathering (17), hunting (18, 19), a constellation of traits leading to improved causal reasoning (20), and general elaboration of abilities found in primates (21,22). Although these theories often make testable predictions about the relationship between brain size and other factors, theyhave not yet explained why human intelligence so far exceeds that of other primates. They also do not explain why intelligence took so long to evolve in the history of life, nor do they provide mechanistic accounts of how proposed factors could concretely lead to the enormous increase in brain size and intelligence seen through hominid evolution (23, 24).Here we show that extreme intelligence could have arisen through a positive evolutionary feedback loop: Humans must be born unusually early to accommodate larger brains, but this gives rise to particularly helpless neonates. Caring for these children, in turn, requires more intelligence-thus even larger brains. In this situation, brain size may be linked between parents and children in an unusual way. Increased brain size may help adults care for altricial neonates, yet also make such neonates less likely to survive childbirth due to physical constraints. We develop a formal model of this situation and show that it may re...

Bridging Evolutionary Biology and Developmental Psychology: Toward An Enduring Theoretical Infrastructure

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Thank your intelligent mother for your big brain

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