Abstract

AbstractHuman childhood and adolescence is the period in which adult cognitive competences (including those that create the unique cooperativeness of humans) are acquired. It is also a period when neural development puts a juvenile’s survival at risk due to the high vulnerability of their brain to energy shortage. The brain of a 4 year-old human uses ≈50% of its total energy expenditure (TEE) (cf. adult ≈12%). This brain expensiveness is due to (1) the brain making up ≈6% of a 4 year-old body compared to 2% in an adult, and (2) increased energy metabolism that is ≈100% greater in the gray matter of a child than in an adult (a result of the extra costs of synaptic neuromaturation). The high absolute number of neurons in the human brain requires as part of learning a prolonged neurodevelopment. This refines inter- and intraarea neural networks so they become structured with economical “small world” connectivity attributes (such as hub organization and high cross-brain differentiation/integration). Once acquired, this connectivity enables highly complex adult cognitive capacities. Humans evolved as hunter-gatherers. Contemporary hunter-gatherers (and it is also likely Middle Paleolithic ones) pool high energy foods in an egalitarian manner that reliably supported mothers and juveniles with high energy intake. This type of sharing unique to humans protects against energy shortage happening to the immature brain. This cooperation that protects neuromaturation arises from adults having the capacity to communicate and evaluate social reputation, cognitive skills that exist as a result of extended neuromaturation. Human biology is therefore characterized by a presently overlooked bioenergetic-cognition loop (called here the “HEBE ring”) by which extended neuromaturation creates the cooperative abilities in adults that support juveniles through the potentially vulnerable period of the neurodevelopment needed to become such adults.

Highlights

  • The absolute large size of the adult human brain and its high relative size compared to the human body (Jerison, 1973), are usually considered critical to these aspects of human uniqueness (Sherwood et al, 2008)

  • The nature of the relationships between brain size uniqueness and human cooperative and cognitive abilities are poorly understood. Another concern is the nature of the process by which the unique traits of the human brain and human cognition were selected during the Middle Paleolithic

  • One potentially relevant but presently unreviewed area for exploring these issues is the bioenergetic liability during neuromaturation that affects the human brain while acquiring adult cognitive capabilities

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Summary

Introduction

The atypical and unique aspect of human child and adolescent support raises the possibility that the evolution of juveniles with large brains is critically dependent upon juvenile’s existing in the social cooperative circumstances that provide high quality energy support during their complex and prolonged neuromaturation. This liability exists because the large immature human brain occurs in a small body making it dominate factor upon juvenile energy needs.

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