The Sixth Extinction: An Unnatural History. By Elizabeth Kolbert. Henry Holt; 302 pages; $28. Bloomsbury; £20. Buy from Amazon.com, Amazon.co.uk BLEAK headlines abound about species on the brink. Monarch butterflies in Mexico are struggling. So are starfish in America, vultures in South Asia and coral reefs everywhere. This is depressing stuff. It’s also a glimpse […]