The dynamics of the group beneficial trait when bias is strong and the group beneficial trait lowers extinction rates (

*n* = 1,000,

*m* = 0.02,

*s* = 0.2,

*g* = 0,

,

*β* = 1.0). There are 50 groups. The probability of extinction in group

*i* each time period is

*ε*(1 −

*x*_{i}) where

*x*_{i} is the frequency of the group beneficial trait in group

*i* and

*ε* = 0.015, a value that when combined with the distribution of frequencies yields extinction rates roughly consistent with those observed in tribal societies (Soltis et al. ) assuming simulation time periods of 1 year. Empty habitats are recolonized by immigrants from a single surviving group. Initially, there is one group in which the frequency of the group beneficial variant is one and zero in all other groups.

**a** Relatedness quickly reaches an equilibrium value of about 0.8 even though groups are quite large because strong bias maintains the group beneficial norm at either a high or low frequency in every group. Here, relatedness is mainly not the result of common descent.

**b** The group beneficial trait spreads because groups with a high frequency of the group beneficial trait are much less likely to become extinct.

**c** Distribution of frequencies across groups as the group beneficial trait increases. Throughout the process, strong bias maintains groups at strongly different frequencies, and adaptation occurs because groups with a low frequency of the group beneficial variant are more likely to go extinct than groups with a high frequency of the variant

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