Cognitive appraisal theorists, psychological constructivists, and social constructivists contend that emotions are not natural kinds and are therefore refractory to classification. Evolutionary biologists and affective neuroscientists, however, have amassed theoretical and empirical evidence suggesting basic emotions are natural kinds. We describe continuity between Maclean's fourfold ethogram, Plutchik's four life problems, and Fiske's four sociorelational models. Plutchik advanced a psychoevolutionary theory of emotions and, by splitting his four existential dimensions by valence, was able to correctly identify eight primary emotions. These are the prototypical adaptive reactions to the eight existential situations, which are also seen as natural kinds. We argue that the concept of primary emotions is an important theoretical advance and additionally enables classification of pairs and triples of primary emotions which form secondary and tertiary emotions. We present a complete classification of the 28 secondary emotions and analyze one of the 56 potential tertiary-level emotions, resentment. Affect-spectrum theory proposes causal relations between the eight valenced sociorelational models and Plutchik's inventory of eight primary emotions. We examine two hypotheses of affect-spectrum theory through a content-analytic, lexical-level study of Euro-Australians and Australian Aborigines. The analysis shows that the positive experiences of communal sharing and authority ranking are predictive of joy and anger, respectively, and joy and anger together are predictive of pride. A parallel analysis indicates that negative involvements in communally shared and authority-ranked social relations predict sadness and fear, respectively; these in turn are predictive of shame.