Suicide poses a mystery to science. How do people manage to get up the nerve to shoot themselves, hang themselves or take a lethal dose of a drug, when doing so violates the strongest instinct that’s been bred into us over millions of years of evolution? This is not morbid curiosity. The answer could be key to addressing a persistent public health problem: suicide kills about 800,000 people every year, according to the World Health Organisation. In the US, the rate has been climbing over the past two decades. In his textbook on evolutionary psychology, David Buss of the University of Texas quotes survey results showing suicidal thoughts are correlated with feeling burdensome to others and, especially for men, few prospects to reproduce. For people over 70, suicidal thoughts were correlated with poor health and financial trouble. But there has to be more behind the few who actually attempt suicide, because many people have such problems and feelings and do not try to kill themselves...