The human tendency toward homogeneity is a cornerstone of social psychology. Classic studies going back to at least Asch (1955, 1956) and Sherif (1936) suggest that, when interacting with others, variance in human thought and action disappears as people conform to other group members and group norms. Convergence is considered to be a primary consequence of social interaction and group life. In fact, group life often becomes synonymous with uniformity and conformity among members. So, it is not surprising that research on emotion as a group-level construct focuses on homogeneity and on the mechanisms that propel group members to share emotional reactions (see Anderson & Keltner, this volume; Barsade & Gibson, 1998; Bartel & Saavedra, 2000; Hatfield, Cacioppo, & Rapson, 1994; Hatfield & Rapson, this volume).

Although group dynamics researchers have documented powerful pressures that drive out variance, variance within groups has also been a persistent, if less frequent, theme as well (Cartwright & Zander, 1960; Schein, 1965). Groups do not transform members into clones: Variance persists in even the most homogenous groups, and such variation can have important consequences. Some modern research on group cognition does imply the value of examining variation in groups. The widely studied notion of transactive memory, for example, is predicated on the heterogeneity of information held by group members – that group members know and remember different things (e.g., Liang, Moreland, & Argote, 1995; Moreland, 1999; Wegner, 1986).

In agreement with Sartre (1948), many theorists have argued that emotion is a way in which people imbue the world with meaning (see Abu-Lughod & Lutz, 1990; Harré, 1986; Osgood, 1971). Although this perspective emphasizes the individual as making the social world meaningful through emotion, it also suggests that individual emotion is necessarily about people's experience of the world. Thus, many contemporary thinkers argue that understanding emotion is essential to understanding social experience and behavior. For example, in the past fifteen years, the sociology of emotion has grown into a vibrant subfield (for reviews, see Kemper, 1990; Thoits, 1989) with examinations of emotion in the context of social relationships (e.g., Scheff, 1994), social status (e.g., Kemper, 2001), and social movements (e.g., Goodwin, Jasper, & Polletta, 2001). The anthropology of emotion has also grown in this same period and offers a challenge to individualistic and universalistic approaches to emotion (for reviews, see Lutz & Abu-Lughod, 1990; Lutz & White, 1986). Political scientists have also become fascinated with the way in which emotions influence political behaviors, including voting, policy support, and party support (e.g., Goodwin et al., 2001; Iyengar et al., 1984; Kinder & Sanders, 1996).