Chapter 9 - social groups and social stratification. Social group: a cluster of people beyond the domestic unit who are usually related on grounds other than kinship. Denser populations have greater social groups as a way to organize society. Mode of production influences number and types of social groups. Friendship close ties between at least two people that are informal, voluntary, and involve personal, face- to-face interaction; it is a primary group; tend to be between people of equal social status. Clubs and fraternities social groups that define membership on some sense of shared identity and objectives. Countercultural groups groups that seek to resist conforming to dominant culture patterns. Youth gangs: group of young people found mainly in urban areas, who are often considered a social problem by adults and law-enforcement officials. Defiant individualist: five traits are intense competitiveness, mistrust or wariness, self-reliance, social isolation, and a strong survival instinct.