In this thesis, I use an experimental model to investigate the role of social pressures
in stimulating language divergence.
Research into the evolution of cooperation has emphasised the usefulness of ingroup
markers for swiftly identifying outsiders, who pose a threat to cooperative
networks. Mechanisms for avoiding cheats and freeriders, which tend to rely on
reputation, or on (explicit and implicit) contracts between individuals, are considerably
less effective against short-term visitors. Outsiders, moreover, may behave
according to different social norms, which may adversely affect cooperative interactions
with them. There are many sources of markers by which insiders and outsiders
can be distinguished, but language is a particularly impressive one.
If human beings exploit linguistic variation for this purpose, we might expect
the exploitation to have an influence on the cultural evolution of language, and
to be involved in language divergence, since it introduces a selective pressure, by
which linguistic variants are selected on the basis of their social significance. However,
there is also a neutral, mechanistic model of dialect formation that relies on
unconscious accommodation between interlocutors, coupled with variation in the
frequency of interaction, to account for divergence. In studies of real-world communities,
these factors are difficult to tease apart.
The model described in this thesis put real speakers in the artificial environment
of a computer game. A game consisted of a series of rounds in which players were
paired up with each other in a pseudo-random order. During a round, pairs of
players exchanged typed messages in a highly restricted artificial "alien language".
Each player began the game with a certain number of points, distributed between
various resources, and the purpose of sending messages was to negotiate to exchange
these resources. Any points given away were worth double to the receiver, so, by
exchanging resources, players could accumulate points for their team. However, the
pairings were anonymous: until the end of a round, players were not told who they
had been paired with.
This basic paradigm allowed the investigation of the major factors influencing
language divergence, as well as the small-scale individual strategies that contribute
to it. Two major factors were manipulated: frequency of interaction and competitiveness.
In one condition, all players in a game were working together; in another condition, players were put into teams, such that giving away resources to teammates
was advantageous, but giving them to opponents was not. This put a pressure
on players to use variation in the alien language to mark identity. A combination
of this pressure and a minimum level of interaction between teammates was found
to be sufficient for the alien language to diverge into "dialects". Neither factor was
sufficient on its own.
The results of these experiments suggest that a pressure for the socially based
selection of linguistic variants can lead to divergence in a very short time, given
sufficient levels of interaction between members of a group
