In the summer of 1906, Atlanta, a city previously known for relatively peaceful race relations, saw a spate of newspaper coverage of black attacks on whites, in particular white women. (“Bold Negro Kisses White Girl’s Hand,” screamed one headline.) On September 22nd, four assaults upon white women were reported. Armed with guns, a group of whites went downtown to a black neighbourhood and attacked black men, killing 25. None of the original alleged assaults were later substantiated.
Your first reaction is probably: how appalling. Yes, it is. But also, isn’t it weird?
There’s no evidence that any of the rioters believed they were attacking the alleged sexual criminals. Their targets simply had the same skin colour. That is a strange way to exact justice.
This weird behaviour is replicated all over the world. Ethnic riots typically involve calls for revenge against an entire opposing group, for real or imaginary harms. Or think of the tit-for-tat cycle of violence in Israel and Palestine. If you believe civilized Europe is immune, remember 20th century history. After the First World War, the great economist John Maynard Keynes saw the Treaty of Paris’ devastation of the German economy as an act of revenge. He quoted Thomas Hardy’s play The Dynasts: “Nought remains / But vindictiveness here amid the strong, / And there amid the weak an impotent rage.”
Behavioural economists have long been interested in reciprocity – the idea that one good, or bad, turn deserves another. This seems to be a basic part of human psychology.
Maybe humans reciprocate towards entire groups, not just individuals. If we could demonstrate this in a simple lab experiment, we might learn about a root cause that sustains violent conflict.
My paper with Ro’i Zultan and Itay Ron does that. We put our experimental subjects – Israeli undergraduate students – in teams and had them work together on a simple task. Then they matched with someone from a different group and played a trust game. A trust game is an interaction where you can send me money and I can send some back. Any money you send is tripled, so if I split the difference, we both end up better off. But, if I keep all the money, you lose out: you might feel cheated and angry.
Then, we gave people a chance for revenge. Everybody divided a pie of money between two other players. They knew those players’ team, and their team number. So, if they got the player who cheated them, they could give them less. That is standard, individual-level reciprocity, and indeed we found it.
The crux, though, was when people were matched with other players from the cheater’s team. They knew it wasn’t the same guy. But would they take revenge on his innocent team-mates?
The picture shows the answer. The x axis is how much each subject got back in the trust game. The y axis is how much they gave their partner’s team-mates. There is a positive slope: team-mates of more generous responders in the trust game got paid more.
What about responders? Did they get back at the team-mates of stingy senders who didn’t send much money in the first place? It turns out not. Responders reciprocated towards senders themselves, but not to their team-mates.
So perhaps we have already learnt something about group reciprocity: it seems to require a strong norm violation. Being stingy isn’t strong enough (after all, maybe senders were just scared they wouldn’t get their money back). Running more experiments like this can help us discover how this dangerous, explosive part of human psychology works.
References
Bauerlein, Mark (2001). Negrophobia: A Race Riot in Atlanta, 1906. San Francisco: Encounter Books.
Hugh-Jones, D. Ron, I., and Zultan, R. (2019). Humans reciprocate by discriminating against group peers. Evolution and Human Behavior, 40(1), pp.90-95.
Keynes, J. M. (1919). The Economic Consequences of the Peace.
This blog provides a summary of the paper Humans reciprocate by discriminating against group peers by David Hugh-Jones, Itay Ron and Ro’i Zultan. The paper was published in the Journal of Evolution and Human Behavior in January 2019. You can view the full paper here: http://www.sciencedirect.com/science/article/pii/S1090513817303446