DECEPTION, TELLS, AND THE EVOLUTION OF COMBINATORIAL COMMUNICATION
Human language is characterized by an arbitrary association between signal and meaning and by the combinatorial assembly of larger units of meaning from smaller referential units (Lachmann, Számadó, & Bergstrom, 2001). The stabilization of honest signaling in such systems on evolutionary time scales remains an important theoretical challenge. Lachmann et al. (2001) propose that arbitrariness can be preserved by social enforcement of honest signaling, while combinatoriality requires that the punishment of deception be associated with whole messages rather than their components. Scott-Phillips (2008) suggests that social exclusion, fueled by gossip, provides a cheap mechanism for punishing deceptive signalers. But gossip about reputation can be deceptive, as all teenagers know, and hence it seems unlikely in the absence of modeling evidence that language can guarantee its own reliability and ensure honest signaling.
We propose that the reliability of signals in human language can be preserved by a group of largely involuntary, non-linguistic signals, which we call tells; as in poker, a tell is (often) a sign of deception. The sensitivity of humans to kinesic and paralinguistic channels and the use of these channels in mediating mammalian social relationships is well-known (Bateson, 2000). More recent work demonstrates that by measuring these largely involuntary channels one can predict the outcome of many social interactions in modern humans (Pentland, 2008). The effect of such involuntary channels on the evolution and stability of honest signaling in another channel has not been studied; we take a first step by analyzing the effect of tells on three game theoretic models of signaling, two standard and one combinatorial.
In the first game, two players decide whether to escalate a conflict (Gintis, 2009); the tell reveals whether the first player has signaled its relative strength honestly. The first player is under evolutionary pressure to minimize the proba-bility p of giving a tell, and the second to become sensitive to smaller tells. The second game begins in an honest signaling equilibrium: the signaler provides information about the world via an arbitrary signal. We then change the payoffs to incentivize signaler deception. The tell alone cannot change the outcome; punishment following tells, however, preserves the signaling equilibrium for values of p > pmin, depending on the incentive and punishment for deception.
The third game is a model of combinatorial signaling. Lachmann and Bergstrom (2004) show that combinatorial signaling has a unique vulnerability to deception: individual signals can have a negative value of information (the receiver is worse off for having received that signal). This results from the fixed mechanism for combining signal components into signal meanings. Lachmann and Bergstrom (2004) suggest that this vulnerability explains why combinatorial communication has evolved so rarely. We find that honest combinatorial signaling can be stabilized when the probability of the signaler giving a tell exceeds a threshold set by the receiver's response strategy.
These games suggest that the combination of multiple signaling channels has rich strategic implications, worthy of further investigation; tells, in particular, provide a mechanism for stabilizing combinatorial communication against deception, and probably do so in concert with social enforcement. As primates, human ancestors possessed highly developed mechanisms for extracting information about social relationships from non-vocal and perhaps largely involuntary behaviors. The ability to read these behaviors could be recruited to stabilize combinatorial signaling in the primary channel, freeing our ancestors to gossip with confidence – and to talk about much more.
Note from Publisher: This article contains the abstract and references.
