Note: this topic is from 8/28/2014. Thanks afraidfortherepublic, sorry I'd missed this on the first go-round.
“refraining from any mixture with Native Americans to the south or with the ancestors of the modern Inuit.”
Well, that lack of genetic diversity certainly solves the mystery how that group/tribe went extinct in a few centuries...
There were some tribes/groups that were breeding snobs-they went extinct, like the Mohicans, and apparently, these Paleo Indians-a lot of other tribes declined in numbers until they woke up, smelled the coffee, and made some marriage alliances. Marrying relatives really screws up fertility after awhile.