New research conducted at the Yale Psychology Department suggests young children and even monkeys have a more nuanced understanding of generosity than previously thought.

The researchers found that much like adults, both four-year-old children and capuchin monkeys would repeat the same behavior performed to them to someone else, a phenomenon called paying forward. Finding the behavior in such young children as well as monkeys suggests that paying forward outcomes may be influenced by rudimentary behavioral strategies present early in cognitive development, rather than social or reputational factors, said Kristin Leimgruber, a co-lead author of the study and graduate student in psychology at Yale.

“Our findings that monkeys and children pay forward positive outcomes suggests a need to reconsider the morally and psychologically complex explanations often given for these tendencies in human adults,” Leimgruber. “Although factors like gratitude and social norms likely play a role in this behavior in adult humans, our results indicate that they aren’t required for generosity to be paid forward within a population.”

While past studies have found that humans pay forward positive outcomes, few have attempted to explain the causes of such behavior.

During the study, a group of capuchin monkeys from the Yale Comparative Cognition Laboratory and a group of four-year-old children from preschools in New England participated in donation games where the participants received a positive or negative outcome from another participant in the group, and decided whether to distribute a positive or negative outcome to a different participant in the group. The researchers found that the majority of children and monkeys paid forward the same type of outcome that was received.

Pay-it-forward behavior is not necessarily driven by self-serving and socially influenced motivations, as people thought in the past, said Adrian Ward, a study co-author and a postdoctoral research associate at the University of Colorado. The research suggests the existence of a general, basic reaction that motivates this behavior, and gives a clue as to how cooperation and altruism may have evolved in human beings. Future studies will investigate the conditions for adults to pay forward positive and negative outcomes, Ward said.

“I love the evidence that four-year-old children and capuchin monkeys pay good deeds forward as well as back,” said Adam Grant, a professor at the University of Pennsylvania Wharton School who was not involved in the study. “It suggests that generosity is both more common and more sustainable than most people expect.”

Grant said that future studies should explore how pay-it-forward phenomena manifest in markets.

The study was published in the journal PLOS ONE on Jan. 29.