Abstract

The study of cognition and social complexity is dominated by the social brain hypothesis. We suggest that the assessment of the association and causation between social complexity and cognition needs to go beyond the association between brain size and social, genetics, ecological or developmental explanations. The social brain/social intelligence hypothesis has received much support, but there are important criticisms and key results, which do not support the hypothesis, that researchers should not overlook. Correlation is not the same as causation, and there is little empirical evidence to support causation, yet researchers often discuss the results as though they were causation. Several hypotheses were proposed to explain variation in brain size, and the hypotheses are not mutually exclusive, even though researchers tested as though they were or only test 1 hypothesis. There is little reason to believe that each of the proposed hypotheses do not explain some of the variation in brain size, and an assessment of the relative importance of the non-mutually exclusive hypotheses based on how much of the variance each hypothesis explains is still missing. There is much potential to the study of the cognitive underpinnings of social complexity, which have received little attention in favour of readily available data sets on brain size. The intra-specific variation in social complexity and cognition abilities within and among populations has received little attention. Researchers in the 1980s proposed that experimental designs in neuroscience were needed, and some progress has been made in this direction. Researchers should conduct experimental designs in neuroscience and multidisciplinary research to validate that a specific, single function or multi-functional brain regions are indeed involved in the expression of a specific behaviour. Comparative studies across different taxa continue to be useful, and they should include ecological, developmental, genetic, cognitive abilities, brain size and relational and structural variables rather 1-2 measures of one of these variables. Cognition varies across taxa, and comparative analyses of cognitive abilities may not be meaningful at different taxonomic hierarchies. As such, we propose that researchers should perform comparative analyses of cognitive abilities within genus, family, order and class, when such analyses are meaningful. We also suggest conducting multiple two or more species comparisons between species with similar ecology. Some traits within and among species are under selection, are fixed, and/or are constrained, whereas as others are not, and researchers should consider this when conducting comparative studies. Yet researchers are still debating whether group size is a good proxy of social complexity, rather than validating it, and whether it associates with brain size.