>Can you suggest a URL/book/whatever where I can learn more about this?
I do not have a academic journal reference to the theory of multiple
migrations. But the following newspaper article from August 21, 1997
is relevant:
http://detnews.com/1997/nation/9708/21/08210077.htm
The article discusses a skull which was recently found in the Columbia
river which radio carbon dating suggests is 8,400 years old. The analysis
of the skull and its disposition have caused controversy:
begin excerpt
The remains, uncovered last summer, provide strong evidence that the New
World's earliest arrivals may not have been direct ancestors of modern-day
American Indians.
Instead, many of the latest studies suggest, America's earliest
inhabitants may have arrived in migrations thousands of years earlier from
places much farther away, most probably southern Asia, but perhaps even
northern Europe.
Kennewick was the latest in a series of finds and re-examinations
beginning in 1992 that have shared a startling common denominator: the
oldest of the skeletons appear to have Eurasian features, as opposed to
the northern Asian features, common to modern American Indians, that are
characteristic of later-date remains.
The issue raises questions about the prehistoric foundation of American
Indians in their ancestral lands. More immediately, it lays open the
question of who wins possession of the oldest remains.
In Kennewick Man's case, a group of tribes in the area have demanded a
halt to all studies and immediate reburial -- a move that some
anthropologists claim would be an affront to historical inquiry. "Some
scientists say that if this individual is not studied further, we, as
Indians, will be destroying evidence of our own history," says Armand
Minthorn, a member of the board of trustees with the Confederated Tribes
of the Umatilla. "We already know our history."
end excerpt