UC Irvine

In this dissertation, I argue that a significant but previously overlooked factor in the evolution of human prosociality is the coevolution of commitment and cooperation. Commitments can serve to secure mutually beneficial interaction in the face of short-term incentives to cheat. They do so by simultaneously incentivising an agent to act in line with her signalled intent and acting as a marker through which trustworthy partners can be identified. I show how different methods of undertaking commitments in our evolutionary history have enabled more sophisticated forms of cooperation over time which, in turn, create the selective environment for the evolution of increasingly effective commitments.

I argue that pre-linguistic commitments secured the stability of cooperation in early hominin group hunting as early as two million years ago and that hunting laid the foundations for larger-scale cooperation. In particular, I argue that signalling participation in group hunting opens up opportunities for beneficial interaction by way of creating a social bond. This potential for future beneficial interaction increases the cost of defection from acting against one’s signalled intent since defection may entail exclusion from these benefits. This incentivises cooperation, acting as a commitment. Though I use hunting as the illustrative example, there are likely many other cooperative activities in our ancestral environment that possess the same formal features of commitment, for example, participation in joint gathering or collection of resources. This small-scale collaboration via commitment then enabled the formation of our proto-language and the expansion of the group into a multi-level society. This created a selective environment for the emergence of more sophisticated communication among members of the wider group, culminating in language.

Language enabled us to undertake commitments via explicit and implicit promising. Explicit promises take the form of direct assertions of one’s intentions to cooperate. Implicit promises often take the form of gossip about a third party. To illustrate, signalling one’s disapproval of a normatively-laden behaviour can lead another to believe that the disapproving agent will not act in like manner, and if she does, she may be subject to exclusion from the benefits of current or future interaction. Analogously for signalling one’s approval. I suggest these two forms of linguistic commitment allowed for more effective communication in cooperative ventures and expanded the range of cooperative activity that could be undertaken. Language allows us to commit with more specificity, to commit to spatially and temporally remote events and to make conditional commitments, among other benefits. Language and reputation sharing also increases opportunities for detection and punishment of false commitments.

A further development in our evolutionary history – the capacity to view some norms as universally applicable or externalised – adds even more power and scope to our commitment practices. To directly assert one’s attitudes toward an externalised, usually moral, norm or gossip about another’s violation of an externalised norm is to suggest one’s own commitment to that norm. This is because such norms are considered applicable to all, including oneself. Implicit commitments which take the form of gossip concerning cultural norm-violation only apply where the interlocutor has reason to believe that the gossiper is part of the same cultural group and occupies the same social role as the person about whom they are gossiping. However, commitments based on externalised norms require fewer inferences on the part of the interlocutor. She need only believe that the agent takes the norm to be universally applicable. Furthermore, in expressing attitudes towards externalised norms, the agent not only advertises her future behaviour but simultaneously reveals to her interlocutor that she is willing to exclude others who do not behave similarly, since she takes this norm to be applicable to all. This secures better correlated interaction.

Finally, the cooperation enabled by earlier forms of commitment permitted the development of institutionalised third-party punishment, which offered a new enforcement mechanism for commitments. That is, we see the development of commitments backed by physical or financial consequences. This enforcement is carried out by third parties and it is typically conducted in an organised manner with the backing of common resources. Modern examples include legal contracts or oaths. Yet again, these commitments allow for safer cooperation among an even wider network of individuals. Third-party enforcement strengthens the credibility of commitments and can, as a result, lower the cognitive demands of trust. It also provides new partner detection and control mechanisms. So, I argue that as the range of our cooperative enterprises extend so, too, do our means of safely engaging in cooperation through the use of more effective forms of commitment.

Alongside highlighting an important feature in the evolution of human prosociality – the coevolution of commitment and cooperation – this dissertation explains why we commit in the various ways that we do. That is, this dissertation sheds light on how we commit without language, why we believe linguistic promises, why we take other people’s gossip statements to be commitments and why we have codified commitments in our institutions. Each of these is a response to a changing cooperative environment in which it is increasingly important to find effective ways to ensure that we make choices that serve our long-run interests and which signal our trustworthiness to others.