A social group exhibits some degree of social cohesion and is more than a simple collection or aggregate of individuals, such as people waiting at a bus stop, or people waiting in a line. Characteristics shared by members of a group may include interests, values, representations, ethnic or social background, and kinship ties. Kinship ties being a social bond based on common ancestry, marriage, or adoption. In a similar vein, some researchers consider the defining characteristic of a group as social interaction. According to Dunbar's number, on average, people cannot maintain stable social relationships with more than 150 individuals.