A fascinating video by George Monbiot detailing how the re-introduction of wolves to Yellowstone National Park restored a badly degraded ecosystem, even changing the rivers.
What Monbiot left out was how those wolves came to be eliminated in Yellowstone initially. That was us. We got rid of the wolves and almost ruined this great park in the process. Over the intervening 20 years ranchers and others repeatedly sought to again eradicate the wolves but they failed.
And, yes, most of us know that those wolves were brought in from Canada.