In an old Russian parable, two frogs are dropped into milk churns. One, realising it cant jump or climb to safety, gives up and drowns. But the other refuses to accept defeat. As it continues to thrash around in its churn, the milk slowly turns to butter, allowing the frog to leap to safety. The world is divided into optimists and pessimists, but Sumit Paul-Choudhury, astro-physicist turned journalist and a former editor of the New Scientist, believes that optimism gives us an evolutionary advantage. It can even make the difference between life and death, he claims in his new book, The Bright Side. Among others, he cites the case of Ernest Shackleton, who somehow survived after his boat, Endurance, sank in the Antarctic in 1915. Despite being stranded on the ice for months, Shackleton led all 27 crew to safety. The quality I look for most is optimism, he said of his men. Ironically, Paul-Choudhury became an optimist after the death of his wife from cancer. We cant make a perfect world, he says. But we owe it to ourselves, to those around us, to those we have lost and those who have yet to come, to make the best of it that we can.