Abstract:
In this paper we develop and test a theory of the dynamic behavior of voluntary groups. The theory combines an image of
social network structure with the concept of natural selection to model changes in group composition over time. We consider
the group to be a population of members subject to natural selection in sociodemographic space. According to the theory, the
probability that members will enter or leave the group depends upon the number and strength of social network ties that
connect group members to each other and to nonmembers. We analyze an event history dataset constructed from interviews
using Life History Calendar method and information on ego-centered social networks developed from the General Social
Survey Network Module. We test the hypothesis that network connections inside a group are associated with reduced
membership turnover, while connections outside the group increase turnover. We find that weak ties and network connections
that span greater distances in sociodemographic space are positively correlated with leaving current groups and joining new
ones. We conclude that weak ties are a major source of change in group composition.