We test whether humans are intuitively inclined to cooperate with or punish strangers using a natural field experiment. We exogenously vary the time available to help a stranger in an everyday situation. Our findings suggest that subjects intuitively tend to help but behave more selfishly as thinking time increases. We also present suggestive evidence that time pressure can increase rates of punishment. We discuss our results with respect to findings in the lab on cognitive models of dual-processing and the origins of human cooperation.