Jared Diamond North-South axis thesis

Wikipedia at least has the Monte Verde site dated back to 14,500 BP, not 12,000 BP. Moreover you can't just dismiss how long it took for humans to reach as far south as Chile by saying  'It seems more plausible that it was quite fast'. There's just as much reason to suppose it was quite slow - in fact more, because of the disparity in environments  all the way down.

 

Also cf http://www.unl.edu/rhames/monte_verde/monte_verde1.htm for a possible 33,000 year old layer at Monte Verde.

On the other hand, it is known that species like the american lion and the fox spread all the way from North America to Patagonia. If those animals could do why humans couldn't do as well, and very fast. We know early humans were hunters and fishermen, and that lifestyle didn't force them to stay where they were born during a lifetime.

There is a strong case that cultures spread along seacoasts and along rivers, because of the similarity of environments. Indeed the fastest spread Diamond records is the spread through the Indonesian islands to New Guiinea, and the Polynesians spread quickly too.

 

But even moving along sea coast slows up when the temperature and diurnal/annual rhythms change. Evem fisherment have to know when and where to fish.  There's no great reason why the Kwakiutl should have moved down from the salmon-rich north-west down through California.

 

It's probably worth pointing out that such mogrations tend to occur in spurts rather than sreadily, but I agree with fantasus this is better taken out of the History of the Americas since Diamond's theses are not just relevant to America specially.