Cooperation, where people pay costs to benefit others, is central to successful human societies. But why are people willing to incur the individual costs involved in cooperating? One set of explanations involves long-term self-interest: if I cooperate with you today, that may make you (or others who find out about my cooperation) more likely to cooperate with me in the future. But people also cooperate even such future consequences are not enough to make cooperation pay off. I explore such "pure" cooperation from using the dual-process perspective from cognitive psychology and behavioral economics, which contrasts cognitive processes that are fast and automatic but inflexible (“intuitive” processes) with those that are effortful and controlled but flexible (“deliberative” processes). I propose the "Social Heuristics Hypothesis" whereby people internalize typically successful behaviors as intuitive heuristics for social interaction. Because most of our important interactions (e.g. those with our co-workers, friends, and family) are long-term rather than anonymous and one-shot, I argue that we intuitively apply a ‘future consequences’ heuristic: our intuitions support strategies which are payoff-maximizing in the presence of future consequences. Deliberation, on the other hand, shifts us towards behavior that is payoff-maximizing in the specific situation at hand. I will present behavioral data from economic game experiments that supports this account: meta-analysis of thousands of participants shows that inducing subjects to carefully deliberate undermines cooperation in 1-shot games (where non-cooperation is payoff-maximizing), but has no effect in games where it can be payoff-maximizing to cooperate.