The Clovis overkill hypothesis is that human hunters arrived in America about 12,000 years ago and promptly killed off all the large mammals.
Two major problems:
1. Evidence is growing all the time that humans have been in the Americas for much longer, as far back as 20,000 or 25,000 BP.
2. A great many other animals went extinct at the same time, including ones unlikely to be hunted by people, implying that there were other causes involved.
I have a very open mind on the subject. Something happened then, and humans moving in may have been a part of it, but they are probably not the whole story.
Agree that the idea of "native Americans" living in harmony with nature is hooey.
Living in harmony? I don't know if I'd call it that, either. Many nations certainly were very knowledgeable about their surroundings and frugal with their supplies. But that probably had as much or more to do with sustaining life (food, clothing, clean water, medicines) and safety (travel light, avoid war or be able to spring an attack), as it did with living in 'harmony' with nature.
The archaeological evidence for overhunting is hard to find other than in New Zealand--and that was more recent. There is the "blitzkreig hypothesis" that holds that the extinctions occured within a few hundred years of the first arrival of humans in any one place. The American large mammals did disappear suddenly.
1. Evidence is growing all the time that humans have been in the Americas for much longer, as far back as 20,000 or 25,000 BP.
The earlier American humans who had much different skulls than the Siberians may have been situationally more like the Africans who coevolved with large mammals. In Africa the extinctions were low (19 percent) compared to the losses in the Americas. As an aside I can't help but wonder if the early Americans made it off the continents or were extinguished by the invaders (as large mammals?).
A great many other animals went extinct at the same time, including ones unlikely to be hunted by people, implying that there were other causes involved.
Astor's fur gatherers used Nobel's dynamite on beaver dams in large areas of the West. With the beavers gone many other species disappeared as well. Restoration of that ecology now that the streams that once held beaver ponds are arid gullies is nigh impossible. The hydrologic drought caused by the demise of those green hills extends for hundreds of miles downwind.