Do big-brained animals play more? Comparative analyses of play and relative brain size in mammals.

It has been hypothesized that play is more likely to be present in larger brained species. We tested this hypothesis in mammals using independent contrasts, a method that controls for phylogenetic relatedness. Comparisons across 15 orders revealed that the prevalence and complexity of play was significantly correlated with brain size, with larger brained orders having more playful species. Three orders, Rodentia, Marsupialia, and Primates, were used for within-order comparisons among species and, where possible, among families. The comparisons were not significant for rodents or primates, and those for marsupials yielded inconsistent results. Therefore, although a strong relationship is present at the highest taxonomic level of comparison, it diminishes or evaporates at lower level comparisons.