Nuclear war, holes in the ozone layer, disease, genetic engineering, asteroids and supernovas - any of these may bring human history to an end. But are we in imminent danger of extinction? John Leslie assesses the risks facing the human race and concludes: yes, we probably are. Leslie pays particular attention to the 'doomsday argument'. This argument, arising from the undeniable fact that we are a very young species, substantially increases the likelihood of our extinction.