Why blue eyes?

[rat_avatar]

@you_with_the_face

Just read this article and it brought to mind your post.

Ancient, unknown strain of plague found in 5,000-year-old tomb in Sweden

Perhaps we will find a plague from when blue eyes spread, but this was way after they were common in Europe.

While all blue-eyed people share a common ancestor, Cheddar Man shows that the previous estimates of it arising in the past 10,000 years was wrong. Not too long ago it was thought the trait originated 10,000 years ago near the black sea, but the date is much earlier than that. It was probably some place after those people turned left after leaving Africa unlike skin color which is a unique combination of multiple genes, that did become in Europe later but most of the mutations probably traveled with those people from Africa.

When you have multiple genes in play plus a mutation tracing it becomes harder.

[Grim_Render]

@rat_avatar

There is a lot of information here, but we are talking about lighter skin, which was after the LGM.

Feel free to replace:

As Siberia was only populated

With

As Siberia was only **re-**populated

You know, I am pretty sure current knowledge is that Siberia was inhabited through the LGM.

@rat_avatar

Unfortunately the speculative nature of this isn’t captured in pop-science stories. Trying to describe functions of selection and drift it would require an entire set of volumes to cover all bits of data and so I do have to simplify, especially as today speculative claims are the best we have and are considered more concrete than they would be under normal scientific rigor.

What we don’t have is evidence of Paleolithic samples with light skin in Europe yet, and we think it wasn’t common or a majority until probably the iron age. The challenges and grow when someone wants to claim it was a selected for trait because the archeological evidence doesn’t really support that with any firm stance so one has to layer on top of challenging DNA data.

I do wish you’d read my last cite.

[rat_avatar]

@Grim_Render

You know, I am pretty sure current knowledge is that Siberia was inhabited through the LGM.
I do wish you’d read my last cite.

That connects people from what is now around borders of Russia, China, Mongolia and Kazakhstan with European migrants?

We can extend the discussion to the migration of people across the world, but unless you are claiming that the specific populations that resulted in these traits were from the Enets, Nenets, or the Huns it is immaterial. There were migrations but not until much later.

Note I did read your cite, and while the origin of the a few of the light-pigmentation alleles would require revision after my cite above,

After investigating the presence of light-pigmentation alleles and haplo types in different hunter gatherers and early farmers across Europe and Anatolia,* it seems as if eye and light skin pigmentation alleles entered Europe several times during different migration events*. In particular, the light skin pigmentation variant arrived to Scandinavia already in the Mesolithic with migrants from the northeast, whereas the blue-eye variants probably arrived in Scandinavia with migrants from the south.

Siberian and East Asian populations shared 38% of their ancestry with a 45,000-yr-old Ust’-Ishim. If you go that far back North Eurasians (ANE) are the ancestors of Western Siberians, Europeans, and indigenous Americans, so to claim it directly for the mutations that arose in later Europeans becomes problematic.

But note the opening paragraph of your above cite:

The late-glacial and post-glacial dispersal of humans to Scandinavia has been the focus of extensive archaeological debate.

(emphasis mine)

And also note:

However, around 14,000 cal BP the evidence of human presence becomes scarce (10, 11), only to be followed by a new advance of apparently episodic pioneer settlements from around 12,800 cal BP (15–18).

Note that 14,000 BP number is in Hamburg, and note Figure S.1.1. Nothing in this paper conflicts with my claims.

We were able to calculate phenotype prediction scores for two out of seven investigated ancient SHG individuals. Note that results obtained for Hum2 should be treated with caution due to low coverage at a number of polymorphic sites

The authors are quite clear about the speculative nature of some of their claims. But they are also speculating it was selected for and not drift from the start.

Interestingly, the eye and light skin pigmentation phenotypes observed in all SHGs could potentially be explained by admixture between WHG and EHG groups. The high relative frequency of the blue-eye color allele in SHGs, resembles WHG, while the intermediate frequencies of the skin color determining SNPs in SHGs seem more likely to have come from EHG, since both light-pigmented alleles are virtually absent from WHG. However, for all three well-characterized skin and eye-color associated SNPs, the SHGs display a frequency that is greater for the light-skin variants and the blue-eye variant than can be expected from a mixture of WHGs and EHGs. This observation indicates that the frequencies may have increased due to continued adaptation to a low light conditions.

Note the “may have” portion showing that this is a speculative claim. They are working off the presumed “selected for” theory, but can you explain why you think this is hard proof of that?

Your cite actually calls out my claims that both hair and eye color could have been due to drift.

Hair and eye-color pigmentation on the other hand could have been affected by drift and sexual selection as less mutations need to be involved (274).

The researchers seem completely aware of and in fact go to great lengths to point out the speculative nature of their claims.

[Grim_Render]

@rat_avatar

That connects people from what is now around borders of Russia, China, Mongolia and Kazakhstan with European migrants?

We can extend the discussion to the migration of people across the world, but unless you are claiming that the specific populations that resulted in these traits were from the Enets, Nenets, or the Huns it is immaterial. There were migrations but not until much later.

So you are not saying that Siberia was only populated about 10 000 years ago, and you are not saying that Siberia was re-populated after people were pushed out by the last glacial maximum?

Ok, I think we may have been talking past each other. Now, I am not quite sure where the relevance of Ust’-Ishim is. To one of the hunter-gatherers of 13 000 BC, Ust’-Ishim was twice as far in the past as that hunter gather is to us. Ust’-Ishim was from about 45 000 years ago, as opposed to 14-15 000 years ago for this particular lot. You of course know that Siberia is big. I mean, utterly huge. Its more than twice the size of Europe, excluding Russia. Given an area that size and a time span that long, we would expect a lot of variety.

@rat_avatar

The authors are quite clear about the speculative nature of some of their claims. But they are also speculating it was selected for and not drift from the start.

Note the “may have” portion showing that this is a speculative claim. They are working off the presumed “selected for” theory, but can you explain why you think this is hard proof of that?

There was a selection in a population that arose from a mixture of dark and light skin genes. The Western hunter-gatherers were dark skinned. The light-skinned variants are pretty old, and did not come with the WHG lot. Scandinavian Hunter-gatherers are generally modeled as a mix of Eastern and Western hunter-gatherers. And these genes did not come from the Western lot.

It is quite true though that the selection appears to have continued and the SHGs and later demonstrate higher allele frequencies than the EHGs.

I suppose you could hypothesize that the genes were present at very low frequencies and only experienced selection once in Scandinavia. This does not seem like a likely explanation though, given that they seem to have appeared with the migration of a people from the east and down through the norther coast of Scandinavia which presumably had experienced the same latitude and environmental pressures for a significant period beforehand. Presumably far longer than the amount of time the Scandinavian selection took.

We could also look at my first cite which has a section titled : “Phenotypically informative markers in hunter-gatherer populations (pages 50-54)” where they report in the “Pigmentation” section that EHG had, from what I cant see from the figures, SLC24A5 completly fixed in the EHG population, and SLC45A2 at ~75 %. Only slightly less than todays northern europeans.

Interestingly, they report the blue eyes allele at 50 % in the EHG samples, which I hadn’t noticed before.

Admittedly, I am not sure which samples or what coverage they are basing this on, since the paper is the genomic history of southeastern Europe they don’t seem to reference the sources for the EHG and SHG that I can see.

When looking, I did find another interesting tidbit though: The blue eyes allele has shown a extreme and persistent north - south gradient in allele frequency that has been persistent through the last 8 000 years, leading to speculations that it may be advantageous in the north and disadvantageous in the south.