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.
Highlights
The extraordinary ecological and demographic success of humanity is commonly linked to our capacity for innovation
In a second set of analyses, we examine a broader definition of technical innovation, including both innovative tool use and innovative extractive foraging, reflecting arguments that extractive foraging played a role in primate cognitive evolution [42,43]
Our analyses examine the relationship between technical innovation, non-technical innovation, and both absolute and relative brain size, as well as several factors that have been shown to covary with brain size and/or innovation rate, including body size, life-history variables, social group size, rstb.royalsocietypublishing.org Phil
Summary
The extraordinary ecological and demographic success of humanity is commonly linked to our capacity for innovation. We humans would appear to possess an unprecedented capability to devise novel solutions to life’s challenges, to express these solutions in our behaviour, tools and technology, and to propagate innovation through social learning. Genetic studies suggest that this capability is longstanding, with hundreds, possibly thousands of human genes subject to positive selection over the past 100 kyr, with a primary hypothesis for why many of these alleles spread being adaptive responses to human learning and cultural activities [1,2,3]. The domestication of plants and animals and associated consumption of novel foods seemingly selected for alleles expressed in human digestion, as well as in resistance to animal-borne diseases [1 –3]. While humans may be exceptional innovators, we are far from the only species that devises novel behaviour patterns. Recent research reveals that many animals will invent new behaviours or modify existing behaviours (e.g. devise more efficient foraging techniques), that such innovation is taxonomically widespread and that there is considerable inter- and intraspecific variation in innovation rates [4]
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