"I want to illustrate the relevance of metaphysics to ethics by reference to what is the greatest moral problem that has ever faced the human race: the question of nuclear war...the threat of nuclear war makes us envisage macro effects (effects on all people and the whole earth): the end of the human race, perhaps also of mammalian life itself, and the end of the prospect of humans evolving into yet higher and more wonderful forms of life...Those who comfort themselves with the thought that mutual deterrence has kept the peace for thirty years forget the importance of low probabilities in the macro context. Indeed what does it matter, from the perspective of possible millions of years of future evolution, that the final catastrophe should merely be postponed for (say) a couple of hundred years? Postponing is only of great value if it is used as a breathing space in which ways are found to avert the final disaster. And even a small probability that we shall not have this breathing space will yield negative expected utility of macro dimensions."