Wednesday, February 18, 2015

Basal Eurasian

During the Neolithic farmers from West Asia came to Europe and brought with them agriculture & in time began intermixing with the local hunter-gatherer groups on the continent like what Lazaridis et al. 2013-2014 refers to as "West European Hunter-Gatherers". [1]

These farmers also brought with them one quite divergent theoretical ancestral component which was initially discovered through the studying of their genomes and that would be Basal Eurasian.


Now, something to quickly recall and/or understand before I go on and explain what Basal Eurasian is would be what's strewn out on the diagram above from Lazaridis et al. 2013... 

And what is strew out on it is that virtually all Out-of-Africa populations [note] from modern Eastern Non-Africans & West Eurasians to pre-historic groups such as Ancient North Eurasians and Eastern European Hunter-Gatherers (the non-Basal Eurasian ancestry in modern West Eurasians); predominantly descend from one incredibly ancient & seemingly bottle-necked Homo Sapien Sapien population of ultimately African origins. [note]

These African origins are demonstrable in terms of autosomal DNA such as how the "Non-African" ancestral group of all Out-of-Africa populations fitting as sharing a "root" with African populations such as Mbuti pygmies (like in the diagram above) or even through Haplogroups where all the mtDNA markers outside of Africa descend from the seemingly East African but definitely African Haplogroup L3- :


Theoretical spreading of Haplogroup L3
-or through observing how all Out-of-Africa Y-DNA Haplogroups (including Y-DNA E in Africa) are descended from one ancestor dubbed "Halogroup CT" which in turn is descended from Haplogroup BT which is then descended from Haplogroup A with A & BT being African Haplogroups.

Haplogroup "leaf" that demonstrates Haplogroup A's basal position among all other Y-DNA Haplogroups
The Out-of-Africa model while we still need to study how exactly how it happened like if there were numerous dispersal events out of Africa or just one; is essentially a genetic fact and also an archaeological fact in that the earliest remains of our species and genus exist in Africa and not Eurasia.

This is all relevant because within the story of the Homo Sapien Sapien family tree; Basal Eurasians are, for now ,thought to be a group that apparently cut-off from the original ancestral group to all Out-of-Africa groups and then became supposedly isolated from other "Non-Africans" who seemingly continued to remain as "one group" that in time diverged into supposedly two or many branches.


I'm sharing this diagram again because it really explains Basal Eurasian to perfection. And I'll explain how as you hopefully observe it alongside this text... Once again I'll say that there was one seemingly bottle-necked group that all Out-of-Africa groups descend from and then, supposedly, Basal Eurasians cut off from this group and as does seemingly another group.

Basal Eurasians supposedly remained genetically isolated from this other group and the various divergent groups in Africa while this other group continued to go on and diversify in time into the non-Basal Eurasian Out-of-Africa genetic diversity we see today. 

Regardless of how the branching happened & how many complex mixtures formed various modern populations; eventually the ancestors of East AsiansOceaniansSoutheast Asians & the non-Basal Eurasian ancestors of West Asians, Europeans and South Asians formed from this other group that eventually diversified.

This may sound weird to some... How on Earth did Basal Eurasians not over what could have been a  period of over 60,000 years not also diversify into separate branches like the separation we see between Eastern Non-Africans Vs. Ancient North Eurasians & European Hunter-Gatherers for example?

Well, the thing to understand for now is that Basal Eurasian is really just a sort of statistical concept. A way of explaining why Early European Farmers (and various Out-of-Africa ancestry carrying groups that seem to carry the same kind of "West Asian / Near Eastern" ancestry they carried) don't fit well as fully descending from a common ancestral clade with groups like Eastern Non-Africans, Ancient North Eurasians and European Hunter-Gatherers.

Eastern Non-Africans, Ancient North Eurasians and European Hunter-Gatherers share a lot of genetic drift and ancestry with each other and we discovered as well that Ust-Ishim, a man who died over 40,000 years ago; existed in a genetic state that preceded their divergence even if he diverged from the ancestors of these groups before or around when they were diverging from each other. [2]


As I explain here; Ust-Ishim is "basal" to all Out-of-Africa groups whether modern ones like Eastern Non-Africans such as the Andamanese Onge or the East Asian-related ancestry in the Karitiana Native American population or ancient Out-of-Africa groups such as Ancient North Eurasians & European Hunter-Gatherers.

Ust-Ishim is quite literally physical evidence that these groups descend from a common ancestral clade and continued to share genetic drift with each other until a few tens of thousands of years ago where they for now supposedly diverged into two separate branches, one ancestral to the Eastern Non-Africans & another ancestral to Ancient North Eurasians & European Hunter-Gatherers.

And while this branching may eventually grow a good degree more complex with more and more ancient DNA being studied; the point to get here is that modern Europeans and West Asians (including those West Asians lacking African admixture); do not fit into this model.

They don't fit properly as a "down-stream" development from what Ust-Ishim was in the way an Andamanese islander or a Western European Hunter-Gatherer would. This in the researchers' eyes implies an element in them that preceded Ust-Ishim's genetic state and whom Ust-Ishim is not "basal" to as the diagram shared above from Haak et al. 2015 clearly stipulates. [3]

[2]
We don't have actual ancient DNA data from West Asia or North Africa or anywhere that could truly explain what Basal Eurasian honestly is so we for now have to work with this current statistically based concept. [note]

Because the thing is; Basal Eurasian doesn't look "African" as some including I once might have implied but rather still clearly looks as though the original Out-of-Africa group that Lazaridis et al. 2013-2014 dubs the first "Non-Africans" are indeed ancestral to it, but then it clearly doesn't seem to be a downstream development from Ust-Ishim and lacks the extra shared genetic drift and ancestry between Eastern Non-Africans and groups like Ancient North Eurasians.

So I'll say what I've said quite often; we need more ancient DNA data to truly understand what Basal Eurasian was but what I explained above is essentially the current academic view...

 That view being that it is a highly divergent Out-of-Africa lineage that diverged from the Homo Sapien Sapien ancestors of Eastern Non-Africans and groups such as Ancient North Eurasians and European Hunter-Gatherers before they ever diverged from one another. Making it more distinct from them than they are from each other as well.

As for its "modern spread"... It ultimately looks to be associated with having West Asian/Near Eastern related ancestry like the non-West European Hunter-Gatherer related ancestry in Early European Farmers or the non-East African related ancestry in some Bedouins as I mention here


The Eurogenes K=8 admixture run is one of the best show of how much of such "Near Eastern" ancestry various global populations have


Such ancestry as you can see in the spreadsheet linked to with the above text is found all over the world from East Africa to the Sahel region among Fulanis to North Africa to Europe, Central Asia, South Asia and finally what looks to be its homeland of West Asia or the general Middle East / Near East region.

All these groups carrying such West Asian / Near Eastern-related ancestry through various different migrations and distinct influences throughout Human history ultimately carry Basal Eurasian ancestry as Basal Eurasian seems to be part of the ancestral package this West Asian / Near Eastern-related ancestry carries with it.


Reference List:




Notes:

1. There was indeed and older and more long version of this post on Basal Eurasian at the exact same page you're reading this one but I felt it was over-bloated and perhaps even boasted some inaccuracies here and there so here's a much more short and straight forward post explaining Basal Eurasian.

2. If you saw the "[note]" at the end of the fourth paragraph then here are your links: [-] , [-] , [-]. African populations carrying substantial West Eurasian ancestry like various Horn Africans would indeed carry more Neanderthal ancestry than Yorubas though, evidenced by how in the first study linked to; Maasais are noted to carry notably more Neanderthal ancestry than Yorubas due to their Eurasian ancestry which they ultimately acquired via Cushitic admixture.

3. From what I can tell; Haak et al. didn't include groups like Papuans in its analysis when it made that statement about Ust-Ishim being basal to European Hunter-Gatherers and Eastern Non-Africans so I contacted Iosif Lazaridis who was involved in the study and he essentially confirmed that Ust-Ishim would indeed be basal to Eastern Non-Africans like Papuans or Australian Aborigines as well, though he noted that the Denisovan admixture in these groups can complicate such models.

6 comments:

  1. wouldnt basal eurasian people resemble indigenous arabians today?

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    1. No idea what they'd look like. We'd need fully Basal-Eurasian samples as well craniometric and body-type data on them to know. Arabians are not fully "Basal" at all. They're somewhat less Basal than Natufians, as far as I can tell, so they'd be modeled as below 50% Basal-Eurasian hence their phenotype isn't really a good example of what the theoretical Basal Eurasians looked like.

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  2. Why do you write "Homo Sapien Sapien" instead of Homo sapiens sapiens?

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    Replies
    1. Just have a habit of forgetting the "s", I guess. Strange thing for you to fixate on, though.

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