Gratitude. I wrote about it a few weeks ago from my human primate perspective, but let’s look at it through a non-human primate perspective as the second part of the gratitude perspective.
According to the Merriam-Webster’s dictionary, it’s defined as “the state of being grateful: thankfulness.” Although it may be considered anthropomorphic to suggest primates experience gratitude, there is an alternative for this idea in primatology. In evolutionary theory, there is a similar idea given by Trivers (1971) as reciprocal altruism, sometimes referred to as reciprocity; a performed behavior that benefits the recipient at the cost of the actor wherein the transaction is later repeated with the original recipient repeating the behavior at its own cost for the benefit of the original actor.
There are multiple instances that come to mind when reciprocity is concerned in primatology. There are alarm calls, an act that draws the attention on the actor after it spots the item of which merits alarm. Additionally, there are instances of resource sharing (giving food at the expense of one’s self when a potential threat is not being able to find food later), defensive strategies, and grooming as a form of social maintenance.
Among some of these examples, one in particular that I think illustrates the idea well is a food resource experiment performed with captive tufted capuchin monkeys (Cebus apella) as displayed here from YouTube up until the 2:05 mark (with narration from Sir David Attenborough):
From what I was able to see, there were originally 5 hazelnuts in the jar. Vulcan is the capuchin which had the flint rock and on the other side, Virgil was the one with the hazelnuts. After Vulcan gave the flint to Virgil to cut the top open, he then handed Vulcan 3 of the 5 hazelnuts from the jar.
To me, the point worth noting here is that the researchers gave the capuchins an odd number of nuts—forcing one individual to take more than the other did. Moreover, I think it’s also impressive that Virgil gave more to Vulcan, who performed less work, at the expense of losing out on a potential food resource.
Because this is a short clip from a documentary, it’s difficult to know whether or not these behaviors were reciprocated in the actual study if Vulcan was given the jar of hazelnuts and Virgil was given the stone or if this behavior is commonplace in captive versus wild tufted capuchins, but it does beg the question:
In this circumstance, was Virgil perhaps acting out a type of behavior similar to gratitude for the stone by offering the lion’s share of hazelnuts?
Trivers, R.L. (1971). The evolution of reciprocal altruism. Quart. Rev. Biol. 46: 35-57.