You’ve probably heard of the concept of paying it forward: someone does a small act of kindness for you and, instead of repaying that person, you pay their kindness forward by doing an act of kindness for someone else. This may not seem evolutionarily advantageous at first (the smart thing to do would be to simply accept the act of kindness and not expend energy or resources paying it forward), but remember that we are social animals. The prosocial behavior of paying it forward is beneficial to maintaining the close social ties that enable our species to survive.
So it makes sense that we might see other social animals, like non-human primates, pay it forward as well. However, many scientists think that a pay-it-forward mentality requires some higher cognitive abilities that non-human primates just don’t possess. One of these is the ability to feel and understand gratitude, which hasn’t been found in non-human primates. Social and cultural norms likely also play an important role in paying it forward. For example, if someone does something nice for you, and you don’t either do something nice back or pass it on, your reputation might suffer.
On the other hand, some scientists argue that these higher cognitive abilities aren’t required for pay-it-forward behaviors. Rather, animals could simply use generalized reciprocity (“help anyone, if helped by someone”). Generalized reciprocity is simple; it doesn’t require gratitude, or concern for one’s reputation, or taking the perspective of others, or inhibiting the impulse to look out only for oneself. So through the mechanism of generalized reciprocity, social animals without the higher cognitive abilities of adult humans can still exhibit pay-it-forward behaviors. (Why do I say “adult” humans? Because children don’t initially possess these higher cognitive abilities – they must develop them.)
Some researchers investigated whether non-human primates and human children pay it forward. Leimgruber et al. (2014) had capuchins and 4-year-old children play a game where an “actor” could choose between equal rewards for her and a “recipient”, or unequal rewards. In both cases, the reward for the actor was the same (a grape for the capuchins and 4 stickers for the children). In the equal option, the recipient received the same reward as the actor. In the unequal option, the recipient received less (spinach for the capuchins and 1 sticker for the children).
In order to see whether the capuchins and children would pay it forward, each trial of the game consisted of two rounds. In the first round, Capuchin (or Child) A would be the actor and choose the reward for herself and the recipient (Capuchin B). In the second round, Capuchin A would leave, and Capuchin B would become the new actor, who would then choose the reward for himself and the new recipient (Capuchin C).
Leimgruber et al. were interested in the choice of Capuchin B in the second round. Would he be more likely to choose the equal reward for Capuchin C if Capuchin A had chosen the equal reward for him in the previous round? Such a result would show that capuchins could indeed pay it forward.
The researchers found that, when the equal reward had been chosen for them in the first round, capuchins and children chose the equal reward in round two significantly more often than chance (80% and 70% of the time, respectively). Interestingly, the researchers also found that both capuchins and children also “paid forward” unequal rewards. When the unequal reward had been chosen for them in the first round, capuchins and children chose the unequal reward in round two 75% and 72% of the time, respectively.
Together, these results demonstrate that capuchins and children pass on both positive and negative outcomes (i.e. equal and unequal rewards). This suggests that, instead of a “help-if-helped” mechanism, generalized reciprocity may be more like “give-what-you-get”, where the “give” and “get” can be positive OR negative.
Leimgruber et al. suggest that the results could also be due to affective processes. “Affect” refers to basic positive and negative feelings, which have been found in many species. So, in the case of this study, receiving an equal reward could put an individual in a positive affective state, which could in turn make that individual more likely to give an equal reward in the next round. (The emotions we talk about having as humans, such as shame and the aforementioned gratitude, are considered to be secondary emotions that require higher and more complex cognitive abilities that most non-human animals don’t have.)
So does this mean that when a stranger buys my morning coffee and I pay it forward by helping my neighbor shovel his driveway, I’m influenced by “give-as-you-get” or a positive affective state? Probably not, say the researchers. Adult humans do have concern for their social reputations, can feel gratitude, and can take the perspectives of others, and we are likely greatly influenced by these considerations. But the simple “give-as-you-get” mechanism and the effect of affect form the base upon which these considerations build, allowing humans to make complex social decisions and have incredibly rich social relationships.
Leimgruber, Kristin L., et al. “Give What You Get: Capuchin Monkeys (Cebus apella) and 4-Year-Old Children Pay Forward Positive and Negative Outcomes to Conspecifics.” PLOS ONE 9.1 (2014): e87035.
van Doorn, Gerrit Sander, and Michael Taborsky. “The evolution of generalized reciprocity on social interaction networks.” Evolution 66.3 (2012): 651-664.