Psychology is defined as the study of the mind (Psyche), and comparative psychology as the study of animal minds. Comparative psychology began by testing animals individually on tasks presumed to reflect general cognitive abilities, or a general intelligence factor, and taxa were compared by their achievements on these tasks. Ethologists were less interested in capacities and more interested in species-typical behavior.
Having been schooled in both traditions, I was quick to accept Mason's suggestions in 1960 that the study of primates living in groups would yield more insight into their cognitive capacities than would individual testing. Whereas Chance and Mead (1952) and Jolly (1966), theorized that primate intelligence evolved in part because of the selective pressures of group living, it was a quarter of a century later that Cheney and Seyfarth (1985a,b) suggested that primate intelligence is extraordinary only in the social domain. Today, investigators regularly examine social interactions and their functions in a search for evidence of extraordinary cognitive capacities in nonhuman primates.
As early as 1880, Lauder hypothesized the existence of infanticide, reciprocity, and teaching in animals. He argued that animals understand death, express anger, jealousy, rage and revenge, commit suicide, suffer from moral insanity, and recognize and respond to criminal behavior. We may describe such writings as quaint, but similar terms, arguments, and supporting evidence are used in recent accounts of the abilities of nonhuman primates. These are often presented against a background of sophisticated evolutionary theory, but the evidence is often distressingly sparse.