Following relatively recent revelations that there were substantial civilizations in both North and Central America before the arrival of Europeans, comes news about South America. The Amazon basin has long been believed to be dense rain forest with a few isolated tribes. Modern researchers have now demonstrated that humans flourished between about 1,500 years ago and 400 years ago. They lived in urban societies that, even if they did not resemble traditional cities, matched them in population and social organization. -- The Economist reports.