Wednesday, November 3, 2010

Fertile Crescent: Still With Us?

Who were the people of the Fertile Crescent who first domesticated wheat and sheep?   Are their descendants still with us today?  With recent advances in genetic population analysis, it may be possible to infer who these people were.As you may know, it is possible to collect genetic data from people and analyze it to roughly determine ancestry.  With new population analysis tools such as ADMIXTURE, it is now possible to run autosomal DNA population ancestry simulations on large groups of people.  These are more precise than the mt-DNA and y-DNA population analyses that have been popular for the last several years.

One such large population autosomal analysis has recently been run on Eurasian populations.  Please see K=10 results in Dienekes' Anthropology Blog. 

What can be inferred from Dienekes' simulation?  Let's look at populations of the Fertile Crescent.

If you look closely at the stacked bar chart results, you will see a consistent three component pattern across Fertile Crescent populations.  If you remove the other components and renormalize the results, today's people of the Fertile Crescent are represented by a three component cocktail (thanks Gioiello):

Yes, the components do vary in their proportions, but in a predictable way.  Cypriots have more of a Southern European emphasis, Armenians and Turks have more of a West Asian emphasis and Syrians, Jordanians and Egyptians lean increasingly toward Southwest Asia.  Based on geography, it's a predictable mix.

So what?

First of all, with the exception of Cypriots, the Southern European component is consistent from Armenia to Egypt.  That 20-26% Southern European proportion, bounded by West Asia on the north and Southwest Asia on the south is a telltale signature of the ancient Fertile Crescent.  It's everywhere and is rather evenly distributed, indicating that it is a very ancient Southern European and Fertile Crescent component.

Why else does the Fertile Crescent cocktail look ancient?  The Fertile Crescent three component signature is mixed with other components:  Mozabite and Ethiopian components in Southwest Asia.  Armenia and Turkey show other admixture events from geographically adjacent Lezgins and from Northeast Asia.  Island dwelling Cypriots show influence from Southern Europeans.  However, those three admixture events appear to be independent, indicating that the Fertile Crescent signature predates them.

If that is true, then it would be possible to suggest an ordering of these admixture events.  We can't put a date on them, but we do know that the Fertile Crescent cocktail predates other admixture events in the region.  It appears to be widespread, covering the triangular region bounded by Armenia, Egypt and Cypress.  It also appears to be relatively stable, particularly in the 20-26% Southern European component. 

If the Fertile Crescent signature is ancient, then it's important that there isn't much "gain" or "loss" in the autosomal DNA population components.  Examination of other ADMIXTURE results indicate that it is a general principle, not confined to the Fertile Crescent, that population admixture proportion is somewhat stable over timespans that predate written history.

If that is true, then it may be possible to operate linearly on autosomal population data to infer ancient admixture events.  In the next few days, I'll be posting some other results on inferred ancient Eurasian admixture events.

I welcome your comments. 

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