 That different researchers reach such disparate conclusions about the efficacy of group selection is partly because they are using different models with different parameter values. Several assumptions, routinely used in group selection models, were highlighted, that biased the results of these models against the efficacy of group selection (Wade 1978). For example, many group selection models use a specific mechanism of migration; it is assumed that the migrating individuals mix completely, forming a “migrant pool” from which migrants are assigned to populations randomly. All populations are assumed to contribute migrants to a common pool from which colonists are drawn at random. Under this approach, which is used in all models of group selection prior to 1978, small sample size is needed to get a large genetic variance between populations (Wade 1978: 110; see discussion in Okasha 2003, 2006).