The evolution of outsider exclusion

The rate of migration between different parts of a population can be important in determining evolutionary outcomes. This paper presents a mathematical model in which some individuals act to exclude immigrants from their group. It is shown that outsider exclusion can be favoured by evolution, even when outsider excluders incur a large cost. In addition, it is shown that the evolutionary mechanism which causes increases in the frequency of outsider excluders is a form of kin selection or group selection. A second model shows that a similar mechanisms can act to favour the evolution of reluctance to mate with immigrants.