Beavers ( Castor canadensis ) have been in North America for two million years. Their ponds ease flooding downstream, and support large numbers of bird species, fish, amphibians, and otters. They are a keystone species to an entire eco-system. Humans and beavers have a long history together because they like to live in the same places, but the way we've built our infrastructure has almost guaranteed our two species will be locked in eternal conflict.