What situations breed ingroup favouritism?

When we meet strangers, we are often nicer towards those that look like they belong to our own group – a behaviour often termed ingroup favouritism. Examples of what constitutes a group may have to do with sharing interests (such as cheering for the same football team or having similar clothing style) or having common origin (such as being born in the same country or even the same part of the village). However, numerous psychological experiments have shown that groups can even be defined arbitrarily, say by the outcome of a coin flip – I will still be nicer to the group of heads than that of tails if I was randomly selected to be in the former. Why is this? Can we say something about the type of situations that would breed ingroup favouritism?

Since ingroup favouritism is a preference that probably evolved (biologically or culturally) over a long period of time, it is hard to carry out a psychological experiment to see when it evolves or not. However, by using mathematical models, we can look at different situations, and derive logically when ingroup favouritism can and when it cannot evolve.

Different types of situations as defined by their strategic structure, often called a game. The left panel shows the different kinds of games as defined by the game matrix, in the middle. The right panel shows how common ingroup favouritism is in the respective games. Prisoners’ dilemmas versus harmony games are situations where, whatever you do, it is always best for me to defect versus co-operate, respectively. Anti-co-ordination games are those where I prefer to do what you are not doing, while in co-ordination games, I want to do the same as you. We can see that ingroup favouritism evolves in the latter two, and in particular in a type of co-ordination games called stag hunts, where optimal co-ordination is risky and easier to achieve between trusting individuals.

So far, most mathematical models presented by researchers on ingroup favouritism have dealt with so called prisoners’ dilemmas – situations where you can choose to be nice, but where it is always in your self-interest not to. Ingroup favouritism then means that you go against your self-interest specifically towards people from your own group. But even if ingroup favouritism evolves in these models, it mainly does so between relatives or people that meet regularly – but not between strangers.

Maybe, then, it is not in situations resembling a prisoners’ dilemma that ingroup favouritism evolved. Of course, there are also other types of situations – situations that may even have been more common in our everyday lives.

Apart from prisoners’ dilemmas, there are situations where our selfish interests are aligned with our commons interests, but where it may still be difficult to arrive at the best solution. One such situation has to do with co-ordination, where I prefer to do the same as you: Which side of the road should I drive on? Can I talk to strangers on the bus or is that inappropriate? Another has to do with anti-co-ordination, where I prefer to do the opposite of you: Who brings the appetiser and who brings dessert to a potluck? Who gets the last piece of the cake?

Could ingroup favouritism towards strangers evolve in these types of situations? The finding in the mathematical model suggested here is that, indeed, ingroup favouritism does not evolve in prisoners’ dilemmas, but it does in these other two types of situations.

In co-ordination situations, if we show signs of being from the same group, then we expect the other person to, say, drive on the right-hand side of the road, and wanting to chat on the bus, while if you are from a different group, I still do not know what to expect (and typically I would refrain from chatting on the bus – even if that is what we would both prefer).

And in anti-co-ordination situations, groups specialise in doing different things. As soon as these things are not equally advantageous, one group is better off than the other. For example, people in group X get used to getting the last piece of the cake, since Y prefers to avoid the fight. In a party of only Xs, however, this specialisation is not possible, so they still have to offer the piece to someone else once in a while. In the end, the cake is offered more often to ingroup than to outgroup members.

The theoretical result from the mathematical model is that, on average, people behave nicer towards their own group, even if they are strangers, not in matters of unselfish co-operation, but in matters of co-ordination and anti-co-ordination.

Fredrik Jansson
Institute for Analytical Sociology, Linköping University, Norrköping, Sweden
Centre for the Study of Cultural Evolution, Stockholm University, Stockholm, Sweden



What games support the evolution of an ingroup bias?
Jansson F
J Theor Biol. 2015 May 21


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