My paper with Carlo Perroni has just been accepted in JEBO. There's an ungated version at my website. Here on my blog I can step back and explain it more informally. And I can be more controversial than in the paper itself, since I have no reviewers to please.
The germ for this came during my year at Northwestern, in a chat with my game theory lecturer, Christoph Kuzmics. He mentioned to me that he was working on evolutionary game theory explanations for costly punishment. The idea of costly punishment is that people are prepared to pay costs so as to punish bad behaviour or take revenge. For example, if a guy starts a bar fight because you spilled his beer, or someone lectures you for leaving litter, that might be costly punishment. Christoph scribbled down the game tree and explained the puzzle. A self-interested person would love to have a reputation for starting bar fights and being a tough guy – they would get their way a lot. But they would never want to actually start a bar fight, as they might lose! So, he wondered how these motivations could evolve.
But, I said, why does it matter? Surely in the real world, if I am strong enough, I can blackmail you to do something which harms you and benefits me – like buying me a new drink. He replied: well, it's just an interesting problem! I was naïve back then and thought that there must be some deeper reason for the interest in this idea, which has spawned a large literature with about 4000 google scholar hits.
Since then, I've come to believe that academics quite often go down rabbit holes of faddism and groupthink, and perhaps costly punishment is an example. We don't claim it never exists, but I suspect it has been greatly exaggerated. For some behavioural economists, costly punishment has become a pillar of social order.
In real societies, punishment of bad behaviour is often not costly, but beneficial to the punishers. For example, in Japan, villagers caught taking too much wood from the forest had to pay a fine, often commuted by the village official to a bottle or two of sake. Not so bad for the official!
Or, here's a nice example from Colin Turnbull (we cut this from the paper to save space). This is what happens when Cephu the pygmy is caught by his fellow hunter-gatherers, putting his traps out of place to get more meat than others:
Cephu knew he was defeated and humiliated.... He apologized profusely, reiterating that he really did not know he had set up his nets in front of the others, and that in any case he would hand over all the meat. This settled the matter, and accompanied by most of the group he returned to his little camp and brusquely ordered his wife to hand over the spoils. She had little chance to refuse, as hands were already reaching into her basket and under the leaves of the roof of her hut where she had hidden her liver in anticipation of just such a contingency. Even her cooking pot was emptied. Then each of the other huts was searched and all the meat taken.(Cited in the excellent Guala 2012.) Again, it's nice to get other people's meat. The logic behind this is simple – the rest of the group can do more harm to Cephu than he can do to them, either by physically harming him or simply by leaving him to fend for himself. As a result, they have a credible threat, which Cephu has to avoid by handing out his resources.
We argue this is common. Much social science literature assumes that communities face a terrible problem – coercion is a public good, so it is underprovided, and everyone just does what they want. There ought to be an anarchy of selfish free-riding. The solution is either a state to provide coercion (but how can we tax people to fund the coercive state? An infinite regress looms...) or perhaps some special motivations so that people "just like" punishing bad guys. Other theorists invoke repeated game theory. This has been hugely influential too: many modern theorists, for example, think that the ideal community makes it very hard to leave, and has a lot of gossip so everybody knows each other's business. (Weird. Most people think of gossip as a bad thing.)
But don't communities often have too much coercion, not too little? A lot of societies are extremely repressive and control individual behaviour very tightly – even without a formal state. Go read Thomas Hardy, or The Mill On The Floss.
Our paper examines this situation. What if a group can coordinate to punish a bad guy? And doing so is profitable, not costly, to them – they make him pay a fine or extract some resources from him. But of course, if so, they could do it not just to bad guys but to anyone. Red haired people. Witches. Outsiders.
We look at societies from this perspective – trying to balance the power to punish with the danger of abusive expropriation. So, the paper is subtitled Expropriating Free-riders and Outsiders. We analyse this situation using a simple model. Then we describe the history of the Californian gold rush, which featured a lot of expropriation, often in the name of "rules" that someone had just invented on the spot. Last, we run a lab experiment, to give us some credible examples of what happens when punishment is profitable. Here's one nice graph. It shows what happens when punishment gets easier, i.e. when it can be inflicted by a smaller coalition of players - this is the M on the x axis. Contributions go down, not up. So, too much punishment can be bad for you.