The coevolution of innovation and technical intelligence in primates

Abstract

In birds and primates, the frequency of behavioural innovation has been shown to covary with absolute and relative brain size, leading to the suggestion that large brains allow animals to innovate, and/or that selection for innovativeness, together with social learning, may have driven brain enlargement. We examined the relationship between primate brain size and both technical (i.e. tool using) and non-technical innovation, deploying a combination of phylogenetically informed regression and exploratory causal graph analyses. Regression analyses revealed that absolute and relative brain size correlated positively with technical innovation, and exhibited consistently weaker, but still positive, relationships with non-technical innovation. These findings mirror similar results in birds. Our exploratory causal graph analyses suggested that technical innovation shares strong direct relationships with brain size, body size, social learning rate and social group size, whereas non-technical innovation did not exhibit a direct relationship with brain size. Nonetheless, non-technical innovation was linked to brain size indirectly via diet and life-history variables. Our findings support 'technical intelligence' hypotheses in linking technical innovation to encephalization in the restricted set of primate lineages where technical innovation has been reported. Our findings also provide support for a broad co-evolving complex of brain, behaviour, life-history, social and dietary variables, providing secondary support for social and ecological intelligence hypotheses. The ability to gain access to difficult-to-extract, but potentially nutrient-rich, resources through tool use may have conferred on some primates adaptive advantages, leading to selection for brain circuitry that underlies technical proficiency.

Keywords: brain evolution; innovation; intelligence; primate cognition; social learning; tool use.

Figure 1.

Number of reports of innovation, tool use and extractive foraging in our survey of non-human primates. Out of the 584 reports of innovation (shaded), 264 or 45% were classified as ‘technical innovation’ (i.e. innovative tool use) and 320 or 55% were classified as ‘non-technical innovation’. In a second set of analyses, we used a broader definition of technical innovation that included novel tool use and novel extractive foraging behaviour patterns. With this broader definition, 351 or 60% were classified as ‘technical innovation’ and 223 or 40% were classified as ‘non-technical innovation’.

Figure 2.

Best-supported graphs using phylogenetic exploratory path analyses including either (a) technical innovation rate, (b) non-technical innovation rate or (c) technical innovation rate including extractive foraging (EF), together with social learning rate, brain size, body size, a life history composite measure, social group size and diet breadth. Edges, i.e. lines, between pairs of variables indicate significant correlations between these variables while taking their correlation with the other variables into account. P-values are indicated for those edges. Analyses of total innovation rate (i.e. technical and non-technical innovations combined) give very a similar picture to figure 2b. Dotted boxes indicate tightly covarying suites of variables.