By Matthew Warren

Imagine that you live in a village which is threatened with rising sea levels. If you don’t do anything, your home is going to be flooded. You could pool your resources together with other villagers and build a large dam around the entire village to ensure that everyone’s property is safe. Or, if you have enough resources yourself, you could build a smaller dam around your own house, protecting your property — and leaving everyone else to either do the same or try and co-operate without you.

Human societies constantly face similar choices between public and private solutions to pressing issues: think about the provision of healthcare or education, for instance. But only some people can afford to build a dam around their own house, or send their child to a private school. Now a new study in Nature Communicationssuggests that when group members are…