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Human language and social cognition are closely linked: advanced social cognition is necessary for children to acquire language, and language allows forms of social understanding (and, more broadly, culture) that would otherwise be impossible. Both "language" and "social cognition" are complex constructs, involving many independent cognitive mechanisms, and the comparative approach provides a powerful route to understanding the evolution of such mechanisms. We provide a broad comparative review of mechanisms underlying social intelligence in vertebrates, with the goal of determining which human mechanisms are broadly shared, which have evolved in parallel in other clades, and which, potentially, are uniquely developed in our species. We emphasize the importance of convergent evolution for testing hypotheses about neural mechanisms and their evolution.

The quality of a social relationship represents the history of past social interactions between two individuals, from which the nature and outcome of future interactions can be predicted. Current theory predicts that relationship quality comprises three separate components, its value, compatibility and security. This study is the first to investigate the components of relationship quality in a large-brained bird. Following methods recently used to obtain quantitative measures of each relationship quality component in chimpanzees, , we entered data on seven behavioural variables from a group of 11 ravens,, into a principal components analysis. The characteristics of the extracted components matched those predicted for value, compatibility and security, and were labelled as such. When the effects of kinship and sex combination on each relationship quality component were analysed, we found that kin had more valuable relationships, whereas females had less secure and compatible relationships, although the effect of sex combination on compatibility only applied to nonkin. These patterns are consistent with what little knowledge we have of raven relationships from aviary studies and show that the components of relationship quality in ravens may indeed be analogous to those in chimpanzees.