The evolution of self-control

Abstract

Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.

Keywords: behavior; comparative methods; executive function; inhibitory control; psychology.

Fig. 1.

A phylogeny of the species included in this study. Branch lengths are proportional to time except where long branches have been truncated by parallel diagonal lines (split between mammals and birds ∼292 Mya).

Fig. 2.

Cognitive scores as a function of log endocranial volume (ECV) and residual brain volume (ECV residuals). In both tasks and in the composite measure, ECV was a significant predictor of self-control. Relative brain volume universally explained less variance. Plots show statistically transformed data (see Methods for details). The gray dashed line shows an alternate model excluding the elephant from analysis. NW, New World; OW, Old World.

Fig. 3.

Cognitive scores for primates as a function of (A) absolute and residual endocranial volume (ECV), (B) foraging and population social group size, and (C) frugivory and dietary breadth. Absolute ECV, residual ECV, and dietary breadth covaried positively with measures of self-control. Plots show statistically transformed data (see Methods and Table 2 for details).

Fig. 4.

Ancestral state reconstruction of cognitive skills for self-control. We generated the maximum likelihood estimates for ancestral states along the primate phylogeny using data from the composite measure (average score across tasks for species that participated in both tasks). The red circles along the tips of the phylogeny are proportional to the extant species’ composite scores (larger circles represent higher scores). The blue circles at the internal nodes of the phylogeny represent the estimated ancestral states for the composite score, with the estimated value indicated within circles at each node.