Some of the earliest and most basic ideas about groups in sociology concern group size. Cooley (1922) described how people universally are members of primary groups, which are small in size, face-to-face, highly intimate, cooperative, and enduring. Prototypes include families and groups of friends. Although people also participate in secondary groups, which are typically larger, less personal, more formally organized, and more limited in duration and purpose, primary group participation appears necessary for teaching children the requisites for participating in society, including language, basic social skills, values, and identities. Simmel (1950) described the profound effects on interpersonal relations when the smallest group, the dyad (pair), expands to a triad. The dyad is unique because it can be destroyed by the loss of a single member, and this feature often leads to a degree of intimacy and closeness not found in larger groups. Adding another person, a third party...