"The first three minutes of your life are the most dangerous." In different handwriting: "The last three can be pretty dodgy too." This example of campus-toilet wit is not so funny when applied to the human species as a whole. Philosopher John Leslie (Perspective, February 16) suspects, on probability grounds, that humanity may already have had two minutes of its allotted three. For details of an online discussion with Professor Leslie about the so-called Doomsday argument and other threats to humanity, consult www.routledge.com. The discussion runs from June 1-30 and admission is $25 (about Pounds 17).