  People tend to align their use of language to the linguistic behaviour of
their own ingroup and to simultaneously diverge from the language use of
outgroups. This paper proposes to model this phenomenon of sociolinguistic
identity maintenance as an evolutionary game in which individuals play the
field and the dynamics are supplied by a multi-population extension of the
replicator-mutator equation. Using linearization, the stabilities of all
dynamic equilibria of the game in its fully symmetric two-population special
case are found. The model is then applied to an empirical test case from
adolescent sociolinguistic behaviour. It is found that the empirically attested
population state corresponds to one of a number of stable equilibria of the
game under an independently plausible value of a parameter controlling the rate
of linguistic mutations. An asymmetric three-population extension of the game,
explored with numerical solution methods, furthermore predicts to which
specific equilibrium the system converges.
