The researchers followed up these correlational studies with a set of experiments in which they directly manipulated both this apparent influence on the tendency to cooperate—processing speed—and the cognitive mechanism thought to be associated with this influence—intuitive, as opposed to reflective, decision-making. In the first of these studies, researchers gathered 891 participants (211 undergraduates and 680 participants from a nationwide sample) and had them play a public goods game with one key twist: these participants were forced to make their decisions either quickly (within 10 seconds) or slowly (after at least 10 seconds had passed). In the second, researchers had 343 participants from a nationwide sample play a public goods game after they had been primed to use either intuitive or reflective reasoning. Both studies showed the same pattern—whether people were forced to use intuition (by acting under time constraints) or simply encouraged to do so (through priming), they gave significantly more money to the common good than did participants who relied on reflection to make their choices. This again suggests that our intuitive impulse is to cooperate with others.
Taken together, these studies—7 total experiments, using a whopping 2,068 participants—suggest that we are not intuitively selfish creatures. But does this mean that we our naturally cooperative? Or could it be that cooperation is our first instinct simply because it is rewarded? After all, we live in a world where it pays to play well with others: cooperating helps us make friends, gain social capital, and find social success in a wide range of domains. As one way of addressing this possibility, the experimenters carried out yet another study. In this study, they asked 341 participants from a nationwide sample about their daily interactions—specifically, whether or not these interactions were mainly cooperative; they found that the relationship between processing speed (that is, intuition) and cooperation only existed for those who reported having primarily cooperative interactions in daily life. This suggests that cooperation is the intuitive response only for those who routinely engage in interactions where this behavior is rewarded—that human “goodness” may result from the acquisition of a regularly rewarded trait.