Bicycle racers—even those on different teams—often cooperate to allow the entire group to go faster. (credit: Flickr user Hans905) Human cooperation is thought to have evolved because it benefits everyone involved. But we also know that cooperation doesn’t always make sense when subjected to a cost-benefit analysis. For example, people will often do favors for others when there is no expectation of a personal reward—or without even bothering to think about whether there might be a reward. A recent study published in PNAS presents evidence that humans may engage in these types of uncalculating cooperative activities because it helps their reputation.