Some questions could still be answered to make a stronger case that nonhuman primates do feel gratitude or some evolutionary building block of gratitude.
First, huge evidence in humans suggests that gratitude is important for creating new relationships, but not so much for upholding existing ones. If the opportunity arose to study a newly formed group of primates over the long term, we would expect to see exchange diminish over time.
Along the same lines, we should also expect to see more exchange among non-kin than kin. Since helping your family also increases your genetic contribution to the next generation, reciprocity isn’t necessary for motivating that kind of helping behavior.
Finally, all of the research uses reimbursement of favors as the claimed way to acknowledge a past favor done. While this is likely the best, most noticeable measure we possess, it’s quite unlike from a verbal thank you given from one human to another.
There may be an understated expression, gesture, or some other communication that other species use to admit kind acts.The challenge for us will develop a deep understanding of other species’ communication systems to discover it.
We’ve come a long way since Darwin first projected that gratitude may be a universally experienced emotion. Although we aren’t yet at the point where we can speak well enough to understand their expressions of gratitude, the behavior of our closest relatives certainly suggests that we humans aren’t alone in the importance we place on gratitude.
The research suggests that, in all probability, our propensity for gratitude does have deep evolutionary roots, and it’ll be up to us to find out how deep they go.
We often blame our worst propensities, like aggression and competition, on our evolutionary history. It’s important to remember that some of our most positive qualities like empathy and gratitude are also a part of this history. When we discover these personalities in our closest relatives, it’s a powerful reminder that the good in human nature is deeply rooted, as well.
