Saturday, 23 April 2011

The Fertile Crescent variation: a model

Up to this point, I've been concentrating on "macroscopic" ADMIXTURE runs defining the affinity of populations in the Fertile Crescent zone, from Scandinavia to North Africa to West Asia.
I've presented runs proposing a two core Neolithic Replacement model, with a Northern "Mesopotamian" Core best preserved today in North Europeans; and a Northeast African Southern "Nile" Core today inexistent as the predominant component in any population, but important in North Africa, also in the Near East and to a lesser extent, in Southern Europe. These runs, as a bonus, also revealed a "Siberian"-like small component in peripheral and mountain populations, very suggestive of aboriginal DNA absorption.
I still think this model is a very coherent first approach to intra-Fertile Crescent variation. However as always, the picture becomes more complex as one digs further, in a more "microscopic" way.

So I'm restating my model in a more detailed manner. My confidence is not extremely high, but I think this is the simpler model to explain patterns.
1) The first Neolithic people in the World are born in the Mesopotamia/Levant/Anatolia around 10.000BC
2) Europe like all of Northern Eurasia (and the Americas) is inhabited by Siberian/Amerindian-akin foragers
3) Most of Africa is inhabited by San/Pygmy-akin foragers
4) Climate change leads to the Green Sahara, a savanna-like environment with very large lakes and river valleys, inhabited by peoples existing in a gradient of DNA variation, much as Siberians/Amerindians. To the west, these people are more West-African-like, to the East more East-African-like. In the Northeast and Nile valley a related people, similar but distinct to both modern West and East Africans, develops incipient Neolithic capabilities.
5) Mesopotamians reach a critical point in their Neolithic evolution. They then expand in all directions namely: Western Anatolia and Europe; Caucasus and Steppe river valleys; Iran plateau and India; and also Southwest Asia and into the Nile itself. Due to prolonged genetic and environmental contact with neighbouring peoples, replacement is incomplete, especially in the more developed Nile valley. Replacement is largely complete in Europe and the Northwest of the Subcontinent though.
6) Thus a western subset of the Mesopotamian/Anatolian/Levantine core expands into the Med and Atlantic regions; and up the Balkans into the fertile Central European river valleys. A Northeastern subset into the Caucasus and Steppe. And a related Eastern subset into Iran and India.
7) The Nile populations are absorbed by invading Southwestern subset Mesopotamian populations. This new hybrid population reaches a balance around 6000BC and then expands into the Green Sahara absorbing West and East-African-like foragers and semi-foragers in the process. Berber languages are born in the area.
8)The Sahara dries up and refugees with variable Neolithic capabilities flee to North Africa, the Sahel region, East Africa and back to the Nile valley.
9) All the environmental stress and ensuing selection of organizational and food producing strategies leads to the evolution of a more advanced Neolithic lifestyle in Egypt. Food surpluses become more abundant. A new more efficient critical point is reached and a new Neolithic wave is born, carrying Afro-Asiatic tongues. It expands from Egypt in all directions. Egyptian Civilization is born.
10) Afro-Asiatic speakers migrate into Mesopotamia itself, as well as Anatolia and all over the Mediterranean following the routes of earlier Anatolian migrations. Sumerian becomes extinct and is replaced by Akkadian.
10) At some point (first or second Nile wave) North Africans spill into Iberia, blending with majority Anatolian elements mostly into fertile coastal regions in the West and South of the peninsula.
12) The West and East Anatolian (Mesopotamian) waves clash in the Northern European plains. The resulting melting pot of seeds, ideas and genes is archaelogically known as the Corded Ware culture. A new Neolithic lifestyle adapted to cold and sandy soils is born, depending on Rye monoculture and other innovations. This people then expand into Scandinavia, British Isles, and to a smaller degree into Western France and Iberia, blending with Wheat-planting West Wave Basque-like peoples but bypassing the modern Basque country. Militarized elites bring the horse from the steppe simultaneously or following later. In the opposite direction, movements into Siberia, and directly from the Steppe into India begin.

Dienekes has new unsupervised results. Bear in mind that unsupervised mode fails to detect components corresponding to ancient but currently inexistent populations (such as ancient Northeast and Northwest Africans) and that it tends to represent admixed clines containing the majority component and such unrecognized minority components as a series of closely related spuriously independent components.
My above model is quite in accordance with his results. I will be exploring FC structure further with supervised runs.

1 comment:

  1. An interesting scenario again Diogenes. I am quite interested to see the variations within Europeans of the different ''Fertile Crescent'' components in project participants. Also I am still very interested in the small ''Forager'' or Siberian/Amerindian like components that also show up in many Europeans.