Jeff Tollefson, reporting for Nature:
Studies dating back to the 1950s suggested that small indigenous tribes merely scratched out a living in primitive villages before the arrival of Europeans. But more recently, researchers have proposed that the Amazon hosted complex societies that turned swathes of the forest into farms and orchards. Some estimates place the prehistoric population of the Amazon as high as 10 million — a huge number considering that the current population is around 30 million.
It’s not just the Amazon—researchers are finding these sorts of ghosts in Europe, too.