Altruists and envious people who meet in contests are symbionts. They do better than a population of narrowly rational individuals. If there are only altruists and envious individuals, a particular mixture of altruists and envious individuals is evolutionarily stable.

We investigate the quality provision behavior and its implications for the occurrence of collusion in competitive health care markets where providers are assumed to be altruistic towards patients. For this, we employ a laboratory experiment with a health care market framing where subjects decide...