How humans evolved large brains: Comparative evidence

Abstract

The human brain is about three times as large as that of our closest living relatives, the great apes. Overall brain size is a good predictor of cognitive performance in a variety of tests in primates.[1, 2] Therefore, hypotheses explaining the evolution of this remarkable difference have attracted much interest. In this review, we give an overview of the current evidence from comparative studies testing these hypotheses. If cognitive benefits are diverse and ubiquitous, it is possible that most of the variation in relative brain size among extant primates is explained by variation in the ability to avoid the fitness costs of increased brain size (allocation trade-offs and increased minimum energy needs). This is indeed what we find, suggesting that an energetic perspective helps to complement approaches to explain variation in brain size that postulate cognitive benefits. The expensive brain framework also provides a coherent scenario for how these factors may have shaped early hominin brain expansion.

Evolutionary neuroscience of cumulative culture

“…Whether such "intelligence" is thought to be composed of discrete but tightly coevolving innate modules (8) or a general-purpose capacity only "secondarily" specialized by experience (14), the premise is that bigger brains are generally advantageous but can only evolve under a narrow set of conditions. Lifespans must be long enough (i.e., mortality low enough) to reward early investments in growth and additional energetic costs must be accommodated through increased intake or reallocation (4). For many species, constraints such as small body size, unstable environments, and unavoidable mortality from predation and disease may simply make large brains impractical.…”

“…An alternative is to consider cumulative culture, not as a unitary capacity that is either present or absent, but as a complex trait with a correspondingly complex history of gradual or piecemeal emergence. Although any event that altered the evolutionary cost/benefit analysis of either brain expansion generally (4,8) or high-fidelity social learning specifically (2, 16) could theoretically have initiated runaway biocultural coevolution in our lineage, there is no reason to assume this feedback would be indefinitely self-sustaining once initiated, nor that that it would necessarily produce constant increase as opposed to more complex dynamics. In fact, both comparative biological evidence (4) and cultural evolutionary models (19) indicate the potential for just such interactions and dynamics and this is entirely consistent with the emerging paleoanthropological picture of multilineal, intermittent, asynchronous change over human evolution (20,21).…”

“…This indication suggests a more contingent evolutionary history, likely involving multiple inflection points in response to perturbations both intrinsic (19) and extrinsic (20) to hominin behavior systems. If this is the case, understanding coevolutionary feedback dynamics (4,8) and CE processes (2,19) will be necessary but not sufficient to explain the actual path of human evolution, which will additionally require the application of these general principles to explain particular historical contingencies (17).…”

It Takes Two to Evolve Too. The Hypothesis on Three Primary Communication Transitions in Evolution

“…Paternal care was likely a requirement for lengthened gestation and especially infancy -critical factors, which made human encephalization physically possible. For instance, based on the expensive brain hypothesis, advocated by K. Isler and C. Schaik [54][55][56], costs of larger brain in early hominids must be met by increased energy provision to female and offspring, possibly by paternal care. Likewise Kaplan [57,58] studying evolutionary roots of human social organization pointed out the essential role of males in energetics of human reproduction, in contrast to most higher primates.…”

From Sexuality to Eroticism: The Making of the Human Mind

“…The energetic perspective is of great importance for understanding cognition, but it can also be used to understand emotional complexity (Isler & van Schaik, 2014). Through mediation by the medial prefrontal cortex, the intense sexual excitement radiates into the brain framework as a whole and thus spurs the flow of information about the state of affairs.…”