Found on Saturday Morning Breakfast Cereal, via The Astronomist, the cleanest illustration I've seen anywhere of the Prisoner's Dilemma:
The comic ends with a (brief) survey of attempts to convince people to act altruistically rather than selfishly. For me, the more interesting question is how to transform the structure of social interactions, so that altruism is the right choice for individuals as well as for the whole group.
Friday Fabulous Flower - dwarf daffodils
20 hours ago in The Phytophactor