While exchanging favors with others, humans tend to think in terms of tit-for-tat, an assumption easily extended to other animals. As a result, reciprocity is often viewed as a cognitive feat requiring memory, perhaps even calculation. But what if the process is simpler, not only in other animals but in humans as well? Researchers have determined monkeys may gain the advantages of reciprocal exchange of favors without necessarily keeping precise track of past favors.