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, 366 (1567), 1017-27

The Evolution of Primate General and Cultural Intelligence


The Evolution of Primate General and Cultural Intelligence

Simon M Reader et al. Philos Trans R Soc Lond B Biol Sci.


There are consistent individual differences in human intelligence, attributable to a single 'general intelligence' factor, g. The evolutionary basis of g and its links to social learning and culture remain controversial. Conflicting hypotheses regard primate cognition as divided into specialized, independently evolving modules versus a single general process. To assess how processes underlying culture relate to one another and other cognitive capacities, we compiled ecologically relevant cognitive measures from multiple domains, namely reported incidences of behavioural innovation, social learning, tool use, extractive foraging and tactical deception, in 62 primate species. All exhibited strong positive associations in principal component and factor analyses, after statistically controlling for multiple potential confounds. This highly correlated composite of cognitive traits suggests social, technical and ecological abilities have coevolved in primates, indicative of an across-species general intelligence that includes elements of cultural intelligence. Our composite species-level measure of general intelligence, 'primate g(S)', covaried with both brain volume and captive learning performance measures. Our findings question the independence of cognitive traits and do not support 'massive modularity' in primate cognition, nor an exclusively social model of primate intelligence. High general intelligence has independently evolved at least four times, with convergent evolution in capuchins, baboons, macaques and great apes.


Figure 1.
Figure 1.
Phylogenetic distribution of general intelligence. (a) Mean and standard error primate gS1 scores for apes, Old World monkeys, New World monkeys and prosimians. Apes (formula image = 1.55 ± 0.65) score more highly than other primate taxa, but no significant mean differences were found between Cercopithecoidea (formula image = −0.02 ± 0.15), Ceboidea (formula image = −0.26 ± 0.18) and Prosimii (formula image = −0.48 ± 0.17) (ANOVA F3,56 = 8.17, p < 0.0001;Fisher's PLSD, critical differences: ape versus prosimians = 0.93, versus New World = 0.81, versus Old World = 0.77, p ≤ 0.0001). (b) Primate intelligence scores, as measured by primate gS1, showing phylogenetic relatedness based on a composite tree [45]. Multiple convergent evolutionary events favoured high intelligence across primate lineages with independent responses to selection in Hominoidea, Macaca, Cebus and Papio. (c) Photographs illustrating examples of behavioural flexibility in the four high gS lineages, covering foraging, technical and social domains (from left to right: Cebus nut-cracking (Copyright © L. Candisani/Minden Pictures), Macaca food washing, Papio fishing (Copyright © Bursch), Pan handclasp grooming (a putative cultural tradition) (Copyright © M. Nakamura).
Figure 2.
Figure 2.
Primate gS1 covaries with performance of primate species in laboratory tests of comparative intelligence. gS1 score correlates strongly with three measures of performance, (a) Deaner et al.'s [28] measure compiled across multiple heterogeneous cognitive tasks (n = 18, r2 = 0.36, p = 0.009; similar results are obtained using independent contrast analysis: n = 17, r2 = 0.23, p = 0.047), (b) the combined performance across all learning tasks in the Riddell & Corl [50] dataset (‘combined Riddell rank’; ρ = 0.95, p = 0.012), and (c) ‘learning sets’, the single task (from [50]) that provides the largest dataset (ρ = 0.89, p = 0.048). Deaner et al. [28] examined the sources contained within the Riddell & Corl [50] dataset, and thus these datasets are not fully independent. However, we include both since they represent different criteria and methodologies for data compilation. Regression lines are included for illustration. Red, apes; blue, Old World monkeys; green, New World monkeys; orange, prosimians.

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