[namarie]

> The main mystery is why it started as late as it did, and not 100,000 years earlier.

Well, there were no humans in the americas 100,000 years ago, for a start.

[ncmncm]

But there were people, and tropics, and people in the tropics. Africa, for example, and Sundaland (mountaintops of which are now Indonesia).

We don't know there weren't people in the Americas then. We have good evidence somebody butchered a mastodon near what is now San Diego, what, 130kya? Might have been H. erectus, they really got around. Any way probably not H. sap.