THE RaTIONaL OPTIMIST  How Prosperity Evolves  by MaTT RIDLEY  Fourth Estate ?9.99  Global warming is the latest apparently existential threat to every person on earth, born or unborn. Ridley, in glorious contrast, tells us that the human species has overcome all the challenges that have ever confronted us, and will do so in future. His contribution is to combine the insights of adaS m Smith with those of Darwin. He calls this "ideas having sex"; in our modern interconnected world ideas are increasingly having it away with each other ("the telephone had sex with the computer and spawned the internet").  Many important people, including Prince Charles and his landowner chums of the Soil association, say "sustainability" can be achieved only through self-sufficiency and a rejection of agricultural science. The organic movement's claim to be acting altruistically was for years based on the idea that introducing chemicals into the food chain would increase cancers. Remarkably, when agricultural science came up with GM, the movement tried to discredit it, initially by persuading middle-class mums that their kiddies would be killed by "Frankenfoods". Trillions of GM meals later, and not a known casualty, they now argue that nature is at dire risk if we make genes cross the species barrier. Ridley, with heroic restraint, reminds us that "wheat... is an unnatural 'polyploid' merger of three wild plant species" and, with a scientist's deadpan humour, that "a variety of barley especially popular with organic brewers was first created in an atomic reactor in Britain in the 1950s by massive mutation of its genes followed by selection". Cheers. Ridley's deft demolition of the scaremongering of the organic movement is merely part of a book breathtaking in its sweep and scope.  Dominic Lawson