Monday, 28 March 2011

Debunking Mozabites

Mozabites in an unsupervised ADMIXTURE analysis are generally modal for their own component, which then dominates fellow North Africans, and is present in small amounts in some East Mediterranean populations with no likely contact with Northwest Africa (its presence in Iberians has likely other reasons explored later). Under a theory of Neolithic Replacement, this doesn't make sense, since North Africans are agricultural peoples since ancient times...
Thus I decided to try to break them up into Neolithic source components using the supervised mode in ADMIXTURE.

Three likely sources of Neolithic techs and genes are present in the region:

1. Northern Fertile Crescent: In order to distinguish a first wave from secondary waves from other regions in the Fertile Crescent area, I decided to use Basques as a pole. In retrospect maybe Basques absorbed some small but not insignificant secondary wave component too, but since it was likely much less important than in North Africa and the Middle East, the choice is still valid (may have to use populations from further North as a first wave pole next time though).

2. Northeast Africa: Egypt is obviously a major candidate for a secondary "Southern Fertile Crescent" wave. Their fast appearing shining civilization indicates extra surplus food production allowing exceptionally large elites. Surplus food techs would likely expand along with the people using them, since they would allow for higher densities of agriculturalists versus less advanced "first wave"-tech using peoples. However it's expected that secondary wave people (but not techs or seeds) will travel much less far than first wave ones, since already agricultural peoples will effectively resist and learn since they share a similar mindset already.
A complication to use Egypt as a pole is that Egypt very likely received high genetic flow from the Northern Fertile Crescent as it was perhaps a more peripheral but integral part of the West Eurasian Neolithic Core Area from the start of the Revolution. Thing is, Egyptians also have very significant non-Western Asian components they share with other East-Africans, namely Ethiopians and Maasai. Since Ethiopians also seem to have received major influence from the Arabian Peninsula in ancient times, a more southern pole must be sought to make things clearer with less overlapping. If North African populations have East African components, we can use Egyptians directly later, but in this analysis I chose the Maasai.

3. Western Africa: Western Africa's Neolithic Revolution seems to have happened later than the Fertile Crescent one (which failed to expand into the region due to seed-package maladaptation to tropical conditions). Still, there was likely much gene flow between both regions so I included them as the third pole (Yoruba+Mandenka).

Here are the results:

A possible interpretation: Mozabites may be a compound of an earlier Southeastern-subset Fertile Crescent Egyptian wave superimposed by a dominant more advanced Northern-subset Fertile Crescent one. As seeds, cultural practices and genes mixed in the Nile, a second (or third for North Africa) Fertile Crescent wave would expand and Egyptian Civilization would arise in the Nile itselfit.
It's interesting that populations from more arid areas have more "West African" (Mozabites themselves, Libyans, South Moroccans). It may seem more likely that the West-African minor component is derived from later expansion of West Africans and the caravan trade. However little is known, as far as I'm aware of local Forager genetics since no forager populations remain in North Africa today. Foragers likely remained in regions not congenial to agriculture until development of desert Pastoralist (camels, goats) lifestyles in Arabia much later. One tantalizing possibility is that it was more West African-like from the very beginning. The Saharan pump theory may offer some clues, since the Sahara during the Ice Age was much more congenial to (forager) gene flow from the south than today...

The model predicts this "Egyptian wave" would spread to Europe and the more distant Near East using the obvious expansion routes already travelled by first waves. It would however petter out relatively quickly as Egyptian colonists failed to completely overwhelm numerically already neolithic first wave peoples and would become more "first-wave-like" genetically the further one travels from Egypt. I will analyse European populations for evidence of Egyptian/East African admixture next.


  1. The pastoral Nilo-Saharan Maasai are believed to have origins in the Lake Chad Basin, rather than being deeply ancestral to East Africa.

    Trans-Saharan slave trade in the last 1500 years or so is fairly well documented and quite sufficient to account for the West African component in North African populations there.

    The case that there was considerable continuity betweeen epipaleolithic populations and contemporary indigenous populations in Northwest Africa is supported by ancient DNA evidence and physical anthropology.

    A better East African stalking horse might be the non-Ethio-Semitic population of Ethiopia or the Southern Sudanese. But, there is a lot to be said for saying the Egypt, particularly Upper Egypt (which is less influenced by outside admixture) is its own beast from very ancient times.

  2. Ancient Canarians (Guanches) weren't part of the Slave trade...
    They were largely insulated from people from the Continent since several thousand years BP, when they were likely colonized in the Neolithic wave from the Continent. They had limited cultivation of Fertile Crescent crops. Their language was likely in the Berber family.

    Sub-Saharan African admixture in Berber apparently predates the Slave trade. It is thus likely native, and I venture it might be the pre-Fertile Crescenter forager substrate.

  3. Another point. Many people are preconditioned by the American situation. American history is a Neolithic colonization situation and thus can't be extrapolated to very different societies.
    Agriculturalist slaves in a continent inhabited mostly by foragers, semi-foragers, dying of introduced disease, have a major advantage: agriculture and immunity from disease.
    In an agricultural North Africa and Middle East with peasants living at the Malthusian limit there is no such advantage. I very much doubt you could reach 10% of the gene pool, when slaves brought over the Sahara desert in caravans, have severe social and economic handicaps and were mostly used for mine and city work, since peasants were plenty had hard lifes and could be exploited easily. There are no records whatsoever of the number of slaves brought over. All estimates are very wild guesses. I would assume it was at any given time a trickle.

    You can only explain satisfactorily in two ways Subsaharan genes in the region. If they possessed major tech/cultural/genetic advantages over these populations (which may be true for possibly Egyptian derived "East African"). Or if they were already there to start with.

  4. European Jews are among the groups that show up with a Mozabite component in ADMIXTURE studies. Sephardim average a little under 5% and Ashkenazim a little under 2%.