51–60 of 63 posts
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i talk about introgression in this post https://razib.substack.com/p/here-be-humans the piece was not exhaustive and meant to be an intro
Dang, you created this account back in 2015 and your first comment is from 1 hour ago.
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It's worth noting that effective population size != actual population size. The former is simply a lower bound on it. If the population is structured enough and in the right ways, the actual size can be orders of magnitude higher. This has been an issue with several supposed bottlenecks within African populations.
the rule of thumb for mammals is Ne is 30% of census size. i think this is probably an overestimate tbh (assumes poisson distribution of offspring).
Either way, my understanding is that all indications point to middle and late Pleistocene populations being highly structured and "unusual" as far as standard assumptions go.
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Dang, you created this account back in 2015 and your first comment is from 1 hour ago.
yeah. no idea why it's even called 'davisYC' aside from the fact i lived in davis then -razib
I thought this was an interesting article. Summarizing from my very-non-expert POV, he's dividing the world into three groups: a small number (less than 1 million) original African inhabitants; a larger number (about a billion) sub-Saharan Africans who broke off about 100,000 years ago; and then the rest-of-the-world (who went though a tight bottleneck less than 100,000 years ago) about the time they left Africa. The…
"Diversity" can mean a lot of things. In this case, he's referring to the variety of individual alleles. Due to population bottlenecks, most of humanity has reduced variation: for example, at a certain spot in the genome everyone has a T, because everyone who survived the bottleneck happened to have a T there; but in the population that didn't go through the bottleneck, some people have a G instead.
On the other hand, for phenotypical diversity it's not just the set of individual alleles that matters, but their distribution and correlation. For example, let's say height is affected by thousands of genes, for each of which there is an allele that makes you slightly taller and one that makes you slightly shorter, and the combined effect of all these genes is approximately additive.
Then you may have a population A which has both variants for each gene, but they're independently distributed, so everyone is of medium height, with some variance. We also have a population B, which has only one variant left for several of these genes (they have lost diversity!). But B is split into two sub-populations, which differ in the distribution of the remaining height genes: B1 has more tall alleles, and B2 has more short alleles.
Now the average height of B1 is higher than that of A, and the average height of B2 is lower than that of A. You will find very tall people in B1 that you would never see in A, and very short people in B2 that you would also never see in A. So B has more diverse height phenotypes, even though B1 and B2 (even put together!) still have lower genetic diversity than A in terms of the available repertoire of alleles.
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Don't even get me started on the Prime Meridian. It's even more problematic than North being 'up' and South being 'down'! /s
People seem really upset at the notion. Even you can't seem to engage with it as anything but a farce. I have to wonder why. I'm just going to start calling it Super-Saharan Africa. When people point out the issue on their map, I'll just flip it 180°. Google Maps conveniently reorients text. The real fun begins when you decide to make longitude the horizontal aspect. Is it Dexterous Africa or Sinister Africa?
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Note that intermixing between those whom we call 'Sub-Saharan' Africans and the "rest of the world" is definitely not new or unique to the 'Western Hemisphere' as OP seems to assume: we know very clearly from Classical written sources and iconography that there were many peoples of 'Sub-Saharan' appearance well north of the Sahara desert, in close contact with Mediterranean and Levantine (thus, clearly "Out of Africa…
> we know very clearly from Classical written sources and iconography that there were many peoples of 'Sub-Saharan' appearance well north of the Sahara desert, in close contact with Mediterranean and Levantine (thus, clearly "Out of Africa") humans. We also know they had negligible genetic impact. > while these folks were clearly a tiny minority and their distinctive appearance was often remarked upon, this did not h…
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> we know very clearly from Classical written sources and iconography that there were many peoples of 'Sub-Saharan' appearance well north of the Sahara desert, in close contact with Mediterranean and Levantine (thus, clearly "Out of Africa") humans. We also know they had negligible genetic impact. > while these folks were clearly a tiny minority and their distinctive appearance was often remarked upon, this did not h…
They did follow the Egyptian religion IIRC and even tangle with Persians
Absolutely not. They were gone a hundred years before the beginning of Persia.
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"Super-Saharan Africa" was a joke, meant to draw attention to the farce of this associative naming convention in general. Hence "Left Africa" and "Right Africa". :) Now, I'll ask you to take it seriously. If it's not a matter of concern for you, but it is for me, it would seem most fair to address my concern (since it's apparenty beneath your care). But if you do care, I'm happy to have that conversation. As stated,…
I'm going to be honest and say that I'm reluctant to get into a debate with you on this. Simply put, I already know we aren't going to change anyone's mind on this subject. I will say this, it is perfectly fine to worry about hierarchical structures and the impacts they have on people. But the mere existence or implication of hierarchy is not a problem in-and-of itself. Especially in this context, where I am certain…
And that's fine. But you're putting a lot of energy into trying to convince me of that.
Do you see the contradiction? You claim that the nomenclature isn't a big deal, but then you go on to defend it - and even in this defense, you make an effort to wash your hands of the entire matter as quickly as possible. It's a weird appeal to the status quo, which I don't understand. Either the terminology matters to you or it doesn't. Does it? Do you prefer to refer to a "Sub-Saharan Africa"? If you do, why? And if not, why can't we just call it something else?
I am really curious. I think this sort of discourse is perfectly reasonable because it unpacks the meanings behind our initial reactions.
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Don't even get me started on the Prime Meridian. It's even more problematic than North being 'up' and South being 'down'! /s
People seem really upset at the notion. Even you can't seem to engage with it as anything but a farce. I have to wonder why. I'm just going to start calling it Super-Saharan Africa. When people point out the issue on their map, I'll just flip it 180°. Google Maps conveniently reorients text. The real fun begins when you decide to make longitude the horizontal aspect. Is it Dexterous Africa or Sinister Africa?
You'll just confuse people and look like a joker when you explain to them that you've decided to change universally accepted geographic nomenclature on your lonesome because you took a whiff of maybe possibly who knows racism.
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Interesting. What I meant though was introgression with closer groups. IE there clearly were surviving populations that didn't go through the major sapien funnels. Their descendants are in the "very diverse" group. Obviously there was, is and will be "introgression" with them. Were there other such groups, in or out of sub-saharan africa... whos genes we carry?
I'm not sure what you mean by the other closer groups. My understanding of the field is that when anatomically modern humans expanded out of Africa for the first time 60Kya, they encountered Neanderthals and eventually Denisovans. What other "closer" group was out there for them to encounter? The other anatomically modern humans were all in Africa, and it looks like there's been no interbreeding with them for at leas…
90% of the DNA for groups 2 & 3 comes from those 1000-10,000 individuals. A small smattering from neanderthals denisovans and ghosts. What's the rest?
There were anatomically modern humans outside of sub-saharan africa at some point. They just don't have descendants. But, my question applies either way. What matters is that they descend from groups outside of the funnel group, not where they lived.