Cooperation is powerful.There aren't many highly cooperative species—but they nearly cover the planet. Ants alone account for a quarter of all animal matter. Yet the human capacity to work together leaves every other species standing.We organize ourselves into communities of hundreds of millions of individuals, inhabit every continent, and send people into space. Human beings are nature's greatest team players. And the truly astounding thing is, we only started our steep climb to the top of the rankings—overtaking wasps, bees, termites and ants—in the last 10,000 years. Genetic evolution can't explain this anomaly. Something else is going on. How did we become the ultrasocial animal?In his latest book, the evolutionary scientist Peter Turchin (War and Peace and War) solves the puzzle using some astonishing results in the new science of Cultural Evolution. The story of humanity, from the first scattered bands of Homo sapiens right through to the greatest empires in history, turns...