Tropical rain forests, bizarrely, are the products of prisoner’s dilemmas. The trees that grow in them spend the great majority of their energy growing upwards towards the sky, rather than reproducing. If they could come to a pact with their competitors to outlaw all tree trunks and respect a maximum tree height of ten feet, every tree would be better off. But they cannot.
Matt Ridley, in The Origins of Virtue
John Perry, introduction to Identity, Personal Identity, and the Self