From a recent letter in Nature by Rand, Greene and Nowak:
We find that across a range of experimental designs, subjects who reach their decisions more quickly are more cooperative. Furthermore, forcing subjects to decide quickly increases contributions, whereas instructing them to reflect and forcing them to decide slowly decreases contributions. Finally, an induction that primes subjects to trust their intuitions increases contributions compared with an induction that promotes greater reflection.
The interesting part of the article is the mechanism that the authors propose as being behind the intuitive cooperative response:
[P]eople develop their intuitions in the context of daily life, where cooperation is typically advantageous because many important interactions are repeated, reputation is often at stake, and sanctions for good or bad behaviour might exist. Thus, our subjects develop cooperative intuitions for social interactions and bring these cooperative intuitions with them into the laboratory.
They tested this mechanism by checking whether cooperation was favoured where people were from a cooperative environment:
Even in the presence of repetition, reputation and sanctions, cooperation will only be favoured if enough other people are similarly cooperative. We tested this prediction on AMT with a replication of our baseline correlational study. As predicted, it is only among subjects that report having mainly cooperative daily-life interaction partners that faster decisions are associated with higher contributions.
Thus, there are some people for whom the intuitive response is more cooperative and the reflective response is less cooperative; and there are other people for whom both the intuitive and reflective responses lead to relatively little cooperation. But we find no cases in which the intuitive response is reliably less cooperative than the reflective response. As a result, on average, intuition promotes cooperation relative to reflection in our experiments.
In many of the debates about cooperation and why it occurs, we forget that there is often a direct benefit to being cooperative. In most of life today, cooperative behaviour is the path to success.
The effect of the external environments highlights an important point on trust, a core part of the cooperative behaviour in the experiments. Trustworthiness is important generating trust. As Garett Jones recently wrote:
When people are trustworthy, when cultures and laws make honorable behavior common, when people so fully take it for granted that promises are kept that they use the passive voice--because it just doesn't matter who made the promise--that's when trust blossoms.