Washington Post: Implicit in much, if not all, modern environmental sentiment is the idea that the natural world has been despoiled by humans -- and if we could just leave it alone, things would get better. But new research suggests that in reality, humans have been altering the natural world for millennia, long before the 15th century dawn of the Age of Discovery, when European societies mastered long-distance ocean navigation and began to spread their cultures, animals and diseases to new continents. The result...