Saturday, May 17, 2014

Fast-moving human evolution

Oldest most complete, genetically intact human skeleton in New World -- ScienceDaily:

Credit, Sklmsta. Creative Commons License
One of the most interesting stories making the rounds this week is the retrieval and analysis of an approximately 12,000-year-old skull in a submerged cave on Mexico's Yucatan peninsula. Two things make this fascinating. One, is that the intact DNA within the skull establishes it as a strong datum point for helping to confirm the origins of modern American Indians. The other is that it's a reminder that human biological evolution moves a lot faster than we used to assume.

Until recently the common assumption was that we hadn't evolved much during the Holocene era. In other words, since the end of the last major glaciation period around 10,000 years ago. However, gene analysis has kicked the legs out from under that hypothesis. While the African pygmies predate the Holocene by around 40,000 years, other forest-dwelling peoples around the world have similarly shrunk in stature since then. Gene variations that support survival at extreme altitudes have become common place in Andean, Ethiopian, and Tibetan populations, and Northern Europeans took on their paleness and fair hair, only very recently.

In the case of the Yucatan skull, the changes are largely cosmetic. The skull has the narrow facial structure associated with Paleo Americans - the oldest known inhabitants of North America. Some of those features are distinct from the features common to modern North American Indians, which has been a data point in the argument that the American Indian peoples are the descendants of a second wave of migration to the continent.

However, the unique lineage of mitochondrial DNA within the Yucatan skull is the same one carried by present day native peoples. Which makes a strong case that the Paleo Americans were both their ancestors and the only migrants to the New World at the dawn of the Holocene.

One skull is not conclusive, of course, but the well-preserved condition of both the genes and the cranium gives it a lot of weight. It also fits well within the current spectrum of archaeological and fossil evidence. It will be interesting to see if additional finds reveal further instances of Paelo bones with American Indian genes.

Public domain, courtesy of Wikipedia

The other recent and fascinating find about the oldest Americans is that Paleos themselves emerged as a group with distinctive features during thousands of years of isolation between North America and Asia, hemmed in by glaciers to the east and west. What we've long thought of as a land bridge between continents was in fact a vast region with its own biota, ecosystem, and pre-history. A homeland for a people, long since lost beneath the sea.

Now, that is a hell of an origin story!

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