The evolution of gratitude

Photo by Tim Dennel

We humans intuitively know how important it is to express gratitude. “Thank you” is one of the first phrases we teach our children, and it’s a key thing to learn when we visit a foreign country. There is part of us that would just feel really bad if we didn’t express gratitude when someone has done something for us (well, for most of us at least).

Try going a week without saying “thank you” to anyone. Not your spouse, not a work colleague, not the barista at Starbucks. Imagine how uncomfortable you’d feel! Somehow we just know that this would be upsetting to others, and also bad for us too – we’d get a reputation for being rude, and people would be less likely to help us out in the future.

Where did this strong instinct and understanding come from? Is it something we simply learn from a young age, and have drilled into us? Maybe, but some researchers think it’s an evolved trait – we’re simply born with a gratitude instinct.

A paper from 2008 by Michael McCullough, Marcia Kimeldorf, and Adam Cohen called “An Adaptation for Altruism? The Social Causes, Social Effects, and Social Evolution of Gratitude” looked into this idea a bit.

Gratitude: a prosocial emotion

First, they define gratitude – it’s a positive emotion that comes when we feel we have benefited from someone else’s actions. The researchers label gratitude as a prosocial emotion – in other words, the whole reason it’s there is to nudge humans to act in prosocial ways.

There’s a lot of research supporting this idea. One experiment was particularly clever. Researchers created a situation where some of there participants thought that they’d received some money from another participants. Other participants thought they got this money by random chance.

Then, the participants were given some more money, and told that they could either keep it all themselves, or share it with their partner. As expected, the ones who thought they’d been gifted the money earlier were far more likely to share it in the second part of the experiment.

When asked why they wanted to share the money instead of just keep it all for themselves, they simply said they wanted to express their thanks to the other person, and this was their way of doing it.

So as we see, gratitude makes people kinder – at least, towards people who have already helped them in some way. We call this reciprocity – a fancy word meaning you scratch my back, I’ll scratch yours.

Gratitude is everywhere

So let’s get back to the topic of evolution.

If gratitude was an evolved emotion, you’d expect to find it everywhere – and you do. Just as there’s no culture without anger, love, or joy, we haven’t found one without gratitude. But we can go back even further than that – some researchers have even looked for evidence of gratitude in animals.

Now, this is very tricky to do. Is your cat grateful after you feed her? It’s easy to imagine that she’s happy about it, but grateful? Since cats can’t say “Thank you!”, how would you know?

Well, it’s hard to say for sure. But one way is to think about the idea of reciprocity. In another study, researchers set up a food puzzle for chimpanzees, that couldn’t be completed alone – they needed help from another chimp. When watching them work on this puzzle, the researchers observed that chimps were most likely to help another chimp if that chimp had helped them out previously.

Did the chimps do this because a feeling of gratitude compelled them? Who knows. Emotions are a common tool of evolution, used to nudge behaviour – so it’s certainly possible. But it doesn’t have to be. If the helping was nudged by an emotion, it might have come from a feeling of indebtedness, for example.

Why would gratitude evolve?

Another way of thinking though whether a particular trait is an evolved adaptation, is to consider, what’s the purpose of it?

We have to be careful of just making up nice sounding evolution stories here, but with that said why might gratitude evolve? According to the Selfish Gene view of evolution, there would have to be a benefit to the genes that lead us to feel gratitude. MucCullough, Kimeldorf, and Cohen thought this boils back to the concept of reciprocity again.

As a tribal species, we couldn’t survive on our own – we needed help from other people. This can lead to imbalances – what if you’re doing all the helping, but no one’s helping you? That wouldn’t be fun. Maybe you’ve had a job like that. On the other hand, if everyone’s helping you out, but you’re not lifting a finger to help anyone, then that’s fantastic for you (you’d be an arsehole, but it’s still good for you) and bad for everyone else.

So, perhaps we’d evolve a way of balancing the books, so to speak. A way to know who we should be helping, and by how much. The researchers think gratitude might have been one part of the solution to this problem – that is, maybe it evolved to help facilitate fairer exchanges.

If this was true, we’d expect two things. First, we’d expect the strength of the gratitude we experience to be proportional to the benefit we got. Second, we’d expect to feel more gratitude towards strangers than to people we’re related to.

To the first point, this is something we know intuitively, but studies back this up too. One experiment was set up in a similar way to the money sharing one earlier – participants got a gift that they were told was from another person, and later had a chance to pay the giver back. This time, they varied the amount people received in the first place – people receiving larger gifts were more generous when they had a chance to repay the favour than those who received a smaller gift.

To the second point, why would we expect to feel less gratitude towards relatives? It’s because we share genes with our relatives, and so there’s another system already “built in” to make sure we help them (according to a theory known as kin selection). So, gratitude doesn’t need to “switch on” as much to achieve helping between relatives (although it would help our relationships if we expressed it more often anyway).

A study from way back in 1977 suggests there might be something to this, although this was based on hypothetical scenarios (basically just asking people, if a stranger or a relative helped you out, who would you be more grateful towards). So this study at least doesn’t give super-solid support for this point.

So where does that leave us? Darwin had suggested that gratitude was a universal emotion, which other primates experience. We’re not quite at the point where we can say that’s true, but based on behaviour, so far it seems they at least experience something that does the same job.


Bar-Tal, Daniel & bar-zohar, Yaakov & Hermon, & Greenberg, Martin. (1977). Reciprocity Behavior in the Relationship Between Donor and Recipient and Between Harm-Doer and Victim. Sociometry. 40,. 293-298. 10.2307/3033537.

McCullough, M. E., Kimeldorf, M. B., & Cohen, A. D. (2008). An adaptation for altruism: The social causes, social effects, and social evolution of gratitude. Current directions in psychological science17(4), 281-285.

Suchak, M., Eppley, T. M., Campbell, M. W., & de Waal, F. B. (2014). Ape duos and trios: spontaneous cooperation with free partner choice in chimpanzees. PeerJ2, e417.

Tsang, Jo-Ann. (2007). Gratitude for Small and Large Favors: A Behavioral Test. The Journal of Positive Psychology. 2. 157-167. 10.1080/17439760701229019.

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