A modular mind? A test using individual data from seven primate species

Abstract

It has long been debated whether the mind consists of specialized and independently evolving modules, or whether and to what extent a general factor accounts for the variance in performance across different cognitive domains. In this study, we used a hierarchical Bayesian model to re-analyse individual level data collected on seven primate species (chimpanzees, bonobos, orangutans, gorillas, spider monkeys, brown capuchin monkeys and long-tailed macaques) across 17 tasks within four domains (inhibition, memory, transposition and support). Our modelling approach evidenced the existence of both a domain-specific factor and a species factor, each accounting for the same amount (17%) of the observed variance. In contrast, inter-individual differences played a minimal role. These results support the hypothesis that the mind of primates is (at least partially) modular, with domain-specific cognitive skills undergoing different evolutionary pressures in different species in response to specific ecological and social demands.

Figure 1. The estimated marginal posterior distributions of the combined species and species*domain effects for each species in each domain.

They convey the uncertainty in the combined effects of both domain-general and domain-specific factors. Larger average values of a latent variable increase the likelihood of good performance, and narrower curves reflect greater precision in identifying the combined effects.

Figure 2. For each domain, image plots of the posterior probability (PP) that the listed row species performed better than the listed column species on average (CH = chimpanzees, BO = bonobos, GO = gorilla, OR = orangutans, SM = spider monkeys, CM = capuchin monkeys, LM = long-tailed macaques).

Values close to 0 (pink shade) indicate the row species perform worse than the column species, whereas values close to 1 (green shade) indicate the row species perform better than the column species. The plots more directly reflect the evidence for differences between species in the combined effects.