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Old 09-24-2012, 08:42 PM
Blake Blake is offline
Join Date: Mar 2001
Posts: 11,049
Originally Posted by jbaker View Post
I tend to be sceptical of arguments for a relatively recent MRCA. These arguments disregard the existence of "fat tails," statistical outliers that are more extreme than analyses would suggest - the same reason why once-a-millennium events happen in the financial markets every few years.
The problem with that argument is that it makes the alternative even more likely. If "fat tails" make a recent ancestor unlikely, it makes the presence of individuals with no common ancestors even more likely, simply because there are 6 billion ways to find a common ancestor, and only one way to avoid doing so.

They also disregard the existence of radically isolated populations, such as the Sentinelese and some of the peoples of New Guinea..
No people of New Guinea are isolated, radically or otherwise. Some of the agriculturalists were isolated from other agriculturalists, but they all maintained contact and interbred with adjacent HGs.

The Sentinelese have also never been truly isolated. They are just too close geographically to other people. We know that Sentinelese words occur in other Andamanese langauges and we know from British records in the 19th century that there were Sentinelese actually living amongst the other Andamanese peoples. So long as one such event occurred every couple of generations, the Sentinelese are going to have the same ancestor as everyone else.

Given the tiny population of the Sentinels, if even one outsider found their way into the bloodline any time prior to 500 years ago, then the entire group will be descended from them. This is further exacerbated by the effect of disease and the evolutionary advantage of outside genetics providing immunity.

.. and the likelihood that at least some Native Americans have no European or African ancestry (e.g., in some of the uncontacted or minimally contacted tribes of South America).
That would be astonishingly unlikely. The uncontacted tribes of South America are all village farmers and all are in contact with their neighbours, or were until 50 years ago. More importantly, they all seem to be descendants of the great agricultural kingdoms that were decimated from European disease. They aren't people who have always lived like that, they are people whose ancestors just 500 years ago lived in cities under hereditary kings. There seems to be no way that they could be isolated.

Consider also that there are still purebred Hawaiians..
Do you have a reference for this claim? It would be interesting to see how anyone would establish such a fact, given that the Hawaiians had no written language. If an Hawaiian had a Tahitian ancestor born in 1066, how would they ever know? No English commoner could prove that they had no single French ancestor from 1066, and that is a literate culture with some of the world's best written records. I can't see how an Hawaiian could ever be certain that they had no Tahitian ancestry from the same date.

...and while the pre-James Cook Hawaiians were not radically isolated, they were still pretty isolated.
And that is the reason why Hawaiians can't be described as being in any way isolated. We know they weren't radically isolated, to the extent that Hawaiian is mutually intelligible with other Polynesian languages. From both linguistic and archaeological evidence we can be sure that Hawaiians were in constant cohabitation, not just occasional contact, with the outside world until just 800 years ago. It seems likely that the last common ancestor of Hawaiians and other Polynesians is less than 1, 500 years back. That would makes the Hawaiians less isolated than Europeans.