Abstract
The social intelligence hypothesis suggests that living in large social networks was the primary selective pressure for the evolution of complex cognition in primates. This hypothesis is supported by comparative studies demonstrating a positive relationship between social group size and relative brain size across primates. However, the relationship between brain size and cognition remains equivocal. Moreover, there have been no experimental studies directly testing the association between group size and cognition across primates. We tested the social intelligence hypothesis by comparing 6 primate species (total N = 96) characterized by different group sizes on two cognitive tasks. Here, we show that a species’ typical social group size predicts performance on cognitive measures of social cognition, but not a nonsocial measure of inhibitory control. We also show that a species’ mean brain size (in absolute or relative terms) does not predict performance on either task in these species. These data provide evidence for a relationship between group size and social cognition in primates, and reveal the potential for cognitive evolution without concomitant changes in brain size. Furthermore our results underscore the need for more empirical studies of animal cognition, which have the power to reveal species differences in cognition not detectable by proxy variables, such as brain size.
Highlights
Primates are characterized by large brains relative to their body sizes [1]
The social intelligence hypothesis has been proposed as a major explanatory framework for primate cognitive evolution, and states that group living has favored the evolution of cognitive skills for competing with conspecifics for access to food and mates while maintaining and monitoring social relationships in large, stable, social groups [11,12,13,14,15,16,17,18]
A direct comparison of the 6 species’ overall scores indicated significant species differences (H = 16.88, df = 5, p,.01) and Dunn-Bonferroni post hoc comparisons revealed that Lemur catta scored higher than Varecia variegata, but that no other pairs differed significantly
Summary
Primates are characterized by large brains relative to their body sizes [1]. The social brain hypothesis has provided an explanatory framework for this phenomenon, suggesting that the cognitive demands of large social groups have favored greater degrees of encephalization in primate species, including humans [2,3,4,5,6]. A central prediction of the social intelligence hypothesis is that social group size should correlate positively with cognitive skills across species It is currently unknown whether there is a robust linear relationship between group size and cognitive skills observed in primates, or any other taxa
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