Cost and conflict in animal signals and human language
Bergstrom, Carl T.
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The "costly signalling" hypothesis proposes that animal signals are kept honest by appropriate signal costs. We show that to the contrary, signal cost is unnecessary for honest signalling even when interests conflict. We illustrate this by constructing examples of cost-free signalling equilibria for the two paradigmatic signalling games of Grafen (1990) and Godfray (1991). Our findings may explain why some animal signals use cost to ensure honesty while others do not, and suggest that empirical tests of the signalling hypothesis should focus not on equilibrium cost but rather on the cost of deviation from equilibrium. We use these results to apply costly signalling theory to the low-cost signals which make up human language. Recent game-theoretic models have shown that several key features of language could plausibly arise and be maintained by natural selection when individuals have coincident interests. In real societies, however, individuals do not have fully coincident interests. We show that coincident interests are not a prerequisite for linguistic communication, and find that many of the results derived previously can also be expected under more realistic models of society.
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