Paper short abstract:

Metaphor is central to linguistic creativity. Neither words nor rules could evolve until our ancestors were willing to accept patent fictions on trust. The necessary levels of public trust, being inconsistent with primate dominance, had to await the establishment of hunter-gatherer egalitarianism.

Paper long abstract:

Language evolved at a time when all humans were hunter-gatherers. Underlying this development was a novel cognitive principle - metaphor. Chimpanzees and bonobos communicate on the basis of a species-specific repertoire of gesture-calls. When reared by humans, they may go beyond this, learning to use gestural signs with their carers and on occasion resorting to metaphor in order to invent a new sign. Despite strong evidence for this cognitive capacity, primatologists have found no evidence that they do this when communicating socially in the wild.

This paper argues that apes avoid metaphor not because of a cognitive deficiency but, on the contrary, because they are too clever. Ape social intelligence is 'Machiavellian', enabling tactical deception - and for that reason compelling receivers to resist being deceived. In a Darwinian social world - one riven with conflicts over dominance and status - apes do best to resist all signals which might prove to be false. In demanding perceptible veracity, they exclude metaphorical usage as a matter of course.

A metaphor is, literally, a false statement. Evolving humans resisted expressions of this kind until they could afford to place trust in signals which were patent falsehoods. Language, therefore, did not even begin to evolve until the human social revolution came to a head, replacing primate dominance with hunter-gatherer reverse dominance, intersubjectivity and egalitarianism.