[HN Gopher] Out of Africa's midlife crisis
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Out of Africa's midlife crisis
Author : nkurz
Score : 94 points
Date : 2021-07-08 13:37 UTC (9 hours ago)
(HTM) web link (razib.substack.com)
(TXT) w3m dump (razib.substack.com)
| rayiner wrote:
| I subscribe to Razib's substack. His writing style is a little
| weird and scattered, but he writes a lot about how this area of
| science is rapidly changing, and has good coverage of new hominid
| fossil discoveries.
| PaulHoule wrote:
| Yep, my take was that the content of this article is brilliant
| but there is something annoying about the writing at the
| paragraph level that needs work.
| valarauko wrote:
| I've been reading Razib for close to 20 years, and he's never
| been a great, or even a very good writer. He more than makes up
| for it with how prolific he is, and I appreciate how frank he
| is with his theories.
| imbnwa wrote:
| Related https://www.discovermagazine.com/planet-earth/how-africa-
| bec...
| nkurz wrote:
| 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 surprising part is that measured genetic diversity within the
| small group of original Africans is greater than that of rest-of-
| the-world. Counter to intuition that skin tone is a strong
| indicator of relatedness, a Swede and an Andaman Islander
| probably have more common genetics than two members of different
| tribes who both live in the Kalahari desert in Namibia.
|
| I'm confused though by his comments about "our species' one-time
| amazing levels of genetic diversity." Overall, he seems to be
| espousing the idea that "diversity" is something we once had lots
| of, but have lost over time. Is this true? Did the the different
| tribes of African Bushmen start out as genetically distinct as
| they are today, or did they start from a common population and
| diverge over the last 200,000 years? Were those who left Africa
| always distinct from those who stayed, or did they change through
| selection (and interbreeding with Neanderthals and Denisovans)
| over time?
| valarauko wrote:
| > Did the the different tribes of African Bushmen start out as
| genetically distinct as they are today, or did they start from
| a common population and diverge over the last 200,000 years?
|
| While groups like the San have a great deal of diversity within
| the group, they are also distinct from other Hunter Gatherer
| groups as well. The San are separated from the Hadza by about
| 110K years, IIRC.
|
| > Were those who left Africa always distinct from those who
| stayed, or did they change through selection (and interbreeding
| with Neanderthals and Denisovans) over time?
|
| Yes, those who left Africa were the remnants of a distinct
| population, separated from the ancestors of sub-Saharan
| Africans by 40K years when they left Africa 60Kya.
| Camillo wrote:
| > I'm confused though by his comments about "our species' one-
| time amazing levels of genetic diversity." Overall, he seems to
| be espousing the idea that "diversity" is something we once had
| lots of, but have lost over time. Is this true?
|
| "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.
| AlotOfReading wrote:
| As a general rule, species start out with fairly high levels of
| diversity from natural processes of evolution. What happened
| with the out-of-Africa population is what's known as the
| founder effect. A small population leaves and becomes
| reproductively isolated. Whatever diversity can be found in
| their descendents is largely limited to the diversity that was
| present in the founding population.
|
| One thing that should be made very clear is that ancient
| population structures generally don't map neatly to modern
| cultures or languages. It's best to treat modern terms as
| labels of convenience.
| dorfsmay wrote:
| Do we have any idea about the size of the original
| population, the size of the group which left for Europe, the
| size of the group's who migrated to central/west Africa?
|
| I had heard that there were several waves of migration
| towards Europe, do we have a better estimate about this?
| Wouldn't multiple waves over time provide more diversity?
| davisYC wrote:
| you can infer sizes from genetic diversity ('effective
| pop')
|
| for the out of africa group i've seen sizes from 100 to
| 10,000. i used 1,000 to 10,000 as a likely moderate number,
| and the range also points to the census size being larger
|
| we can assume that conditional on the size of OoA the other
| groups were way larger (10x or more). otoh, the main thing
| i did not explore is that i am now believing that africans
| themselves especially agriculturalists are 'compounds' of
| various bottlenecked groups (why west africans are closer
| to eurasians than they are to khoisan)
| AlotOfReading wrote:
| 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.
| davisYC wrote:
| 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).
| AlotOfReading wrote:
| I'm not sure that's super applicable to humans. Doesn't
| it also assume panmixia and non-overlapping generations?
|
| 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.
| wskinner wrote:
| Yes. This information is in the article.
| zozbot234 wrote:
| 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") humans. Even more than this, we know of such 'Sub-
| Saharan' folks who were very deeply integrated in ancient
| Mediterranean and Levantine societies, and while these folks
| were clearly a tiny minority and their distinctive appearance
| was often remarked upon, this did not hurt their social
| standing in any sense; there was even a well-known Egyptian
| dynasty of "Black" pharaohs.
| thaumasiotes wrote:
| > 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
| hurt their social standing in any sense; there was even a
| well-known Egyptian dynasty of "Black" pharaohs.
|
| You say that like social standing determines who gets to be
| king. The Nubian pharaohs got their position in the standard
| way, by conquering Egypt. They weren't native, they took very
| little interest in their new territory, and they didn't last
| very long.
|
| There was a well-known Chinese dynasty of Mongol emperors.
| What do you think the social standing of Mongols in China was
| before and after that happened?
| dalbasal wrote:
| For me, it's easier to understand these ideas by adopting a
| "lumper" mentality to human history. IE, Neanderthals,
| Denisovans, late Erectus & other archaics were just populations
| of humans. Sections on a large map of human diversity. On another
| section were, for example, that small subpopulation accounting
| for most modern human genetics. Near that little section were
| other subpopulations that even a "splitter" would call Sapiens.
| Just because they're Sapiens and we're Sapiens doesn't mean that
| they left more genetic legacy than Neanderthal subpopulations.
|
| I do have some questions though...
|
| _" If you don't have Sub-Saharan African ancestry, all of your
| ancestry (aside from your differential rates of
| Neanderthal/Denisovan ancestry) goes back to the same
| 1,000-10,000 humans that split off from other Africans."_
|
| No introgression with other Sapien populations? We know that
| Sapiens existed outside of Sub-Saharan Africa long before that
| bottleneck. Are all additions to that genetic stock from other
| species?
|
| Also, what's the relationship between genetically isolated and
| genetically diverse? Most of our ancestors went through single a
| bottleneck 60kya-120kya, with non africans going through at least
| one more. Theirs did not go through that bottleneck _or_ a
| seperate one. Coincidence, or is it part of the story somehow?
| valarauko wrote:
| > No introgression with other Sapien populations?
|
| Perhaps indirectly. As he addresses later in the text, it's
| possible that Denisovans in South East Asia encountered _Homo
| erectus_ and interbred with them. The Denisovans appear to have
| more population structure as compared to Neanderthals, and
| introgression from _H. erectus_ might explain some of it.
| Considering that South East Asia and Papua New Guinea has the
| highest Denisovan introgression in modern humans, it 's
| possible that some of that _H. erectus_ ancestry ended up in
| those of us from East of the Indus.
|
| For what it's worth, I have seen other studies pop up from time
| to time that claim to have found introgression from some
| unknown ghost sapien population, but these outliers usually go
| away by tweaking the parameters.
| dalbasal wrote:
| 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?
| valarauko wrote:
| 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 least 100K years. There has been a small
| introgression _back_ into Africa by non-Africans within the
| last few thousand years, but that 's a separate issue.
| davisYC wrote:
| 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
| throwaway894345 wrote:
| Dang, you created this account back in 2015 and your first
| comment is from 1 hour ago.
| davisYC wrote:
| yeah. no idea why it's even called 'davisYC' aside from the
| fact i lived in davis then -razib
| throwaway894345 wrote:
| I followed you on Twitter for several years and also
| heard your interview on the New Liberals podcast. Would
| love to see you around here more often as well.
| dalbasal wrote:
| Cheers. These blogs are a treat.
| TimonKnigge wrote:
| I'm curious if this genetic diversity is just something that
| shows up as a number on a computer, or does it translate into
| something phenotypically* visible?
|
| Also, how much of, say, our medical/biological knowledge actually
| only applies to the descendants of the bottleneck mentioned in
| the post? I understand the "very diverse" in the article have
| better things to do than be subjected to researchers, but reading
| the article I can't help but be curious what this genetic
| diversity means in practice?
|
| *) not necessarily visually
| bsanr2 wrote:
| On an extremely tangential note: I wish we would stop using the
| term, "Sub-Saharan." The semantic quandaries should be obvious,
| but it also subscribes to a curious linguistic glitch of putting
| the North and South into a hierarchy that only exists if you are
| rather incurious about the ambiguity of geographic perspective
| (see: the infamous "upside down" Gall-Peters projection for some
| mind-blowey fun). I would personally prefer something like "SOS
| (South-of-Sahara) Africa," or perhaps even something as
| provocative as "Africa Major" (riffing on Asia Minor and
| referring to the fact that that part of the continent is, in
| fact, a majority of its landmass).
| throwaway894345 wrote:
| Putting aside the absurd nitpick on the "Sub-" prefix (everyone
| understands that this refers to "South" and not some position
| on a hierarchy).
|
| > (riffing on Asia Minor and referring to the fact that that
| part of the continent is, in fact, a majority of its landmass).
|
| Isn't Asia Minor a bit more than half of Turkey? It's certainly
| not a majority of all of Asia...
| bsanr2 wrote:
| >Putting aside the absurd nitpick on the "Sub-" prefix
| (everyone understands that this refers to "South" and not
| some position on a hierarchy).
|
| Is it absurd? Do they understand? Can you show me how you
| know this?
|
| >Isn't Asia Minor a bit more than half of Turkey? It's
| certainly not a majority of all of Asia...
|
| Sorry, I can see where I was unclear. I was referring to
| Africa.
| throwaway894345 wrote:
| > Is it absurd? Do they understand? Can you show me how you
| know this?
|
| It is absurd, they do understand, and I know it because I'm
| a native English speaker and I've never been in a
| conversation where anyone was confused by the term nor even
| in which someone bothered to clarify that they didn't mean
| to imply a hierarchy. I'm sure you're going to understand
| that this is satisfactory evidence and not resort to some
| sort of "BuT Do YoU kNoW eVeRy SiNgLe PeRsOn On ThE
| PlAnEt?!" nonsense.
|
| > Sorry, I can see where I was unclear. I was referring to
| Africa.
|
| Ah, thanks for clarifying. That makes sense.
| bsanr2 wrote:
| >It is absurd.
|
| Again, how so? The two connotations are not mutually
| exclusive.
|
| If the goal is to avoid implying a hierarchy, why not
| change to a term that has no connection to hierarchy?
| throwaway894345 wrote:
| Because there's no indication that it causes confusion
| for anyone except, perhaps, you. There is a lot more
| ambiguity in English than this and we don't put aside all
| of our other problems to deal with this. Anyway, these
| kind of semantic debates are the most boring, dull,
| tedious things I can think of (see also the people who
| think we need to replace "latinos" with "latinxs") so I'm
| going to entertain myself with anything else besides this
| thread.
| bsanr2 wrote:
| I never held that it causes confusion. The duplicity of
| meaning is probably, in fact, a bonus for some. I don't
| like that duplicity. I would rather the terminology be
| unambiguous and direct, if it is possible (and, in this
| case, it is).
| QuesnayJr wrote:
| They meant "Africa Major" would be a majority of Africa.
| fallingknife wrote:
| Nobody in their right mind actually thinks placement towards
| the top of a map actually denotes some kind of hierarchy.
| bsanr2 wrote:
| Orienting with terms like "top" and "bottom" inherently
| denotes hierarchy. Whether you ascribe _meaning_ to that
| hierarchy (and I think people do) is another matter.
|
| Explicitly stating direction rather than something that only
| refers to it with the aid of outside knowledge (the common
| orientation of maps) would be better. Otherwise, why don't we
| spin the map 180 degrees? Now the "correct" term would be
| "Super-Saharan Africa." Which is just as silly.
| BitwiseFool wrote:
| Don't even get me started on the Prime Meridian. It's even
| more problematic than North being 'up' and South being
| 'down'! /s
| bsanr2 wrote:
| 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 180deg. 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?
| [deleted]
| BitwiseFool wrote:
| >"Even you can't seem to engage with it as anything but a
| farce. I have to wonder why."
|
| No need to wonder, it's because I see it as a farce. The
| idea that the top / bottom aspect is something that
| _needs_ to be re-evaluated because it implies hierarchy
| is something so inconsequential that I just can 't bring
| myself to take it seriously. And, if you really wanted to
| flip the hierarchy then you've got the same 'problem'
| just in reverse.
|
| I know you really want to change the way people think but
| adopting the term "Super-Saharan Africa" is just going to
| make you look strange. I guarantee you no one will think
| "oh, this person means the southern part of Africa, but
| from the reference point of the equator to the South
| Pole." They're going to think "Wait what? A bigger
| Sahara? Desertification? What?"
| bsanr2 wrote:
| "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 would like
| to remove hierarchy (or the connotation of hierarchy)
| from the terminology altogether, and more explicitly
| refer to directionality. If you disagree with this
| course, please say why (beyond, "It shouldn't matter,"
| because at this point we'd have agreed that it does).
| BitwiseFool wrote:
| 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 the impact of North
| being considered 'up' and South being considered 'down'
| has not materially harmed anyone living down under. I
| also see no evidence that this paradigm/convention is
| actually harmful. Only speculation that it could be, in
| an indirect way, and for reasons I don't find compelling.
|
| I'm also concerned that we're going to slip into one of
| the least productive kinds of argument, trying to define,
| redefine, and shift the meaning of words. So I'd like to
| avoid all of this and let bygones be bygones.
| fallingknife wrote:
| > and I think people do
|
| Yes there do seem to be a lot of Eskimo supremacists
| around.
| bsanr2 wrote:
| I'm not sure what this is supposed to mean.
| api wrote:
| There is no top of the map since there is no objective frame
| of reference in space. The axis on which the Earth spins
| relative to its orbit is a point of orientation but which
| side is the "top" is arbitrary.
| BitwiseFool wrote:
| >"top" is arbitrary"
|
| Sure, but at the end of the day you've got to pick a frame
| of reference and people have settled on North being the
| 'top'. You can draw a map that ignores this convention and
| still have it be valid but you're going to confuse a lot of
| people.
|
| For what it's worth there's more landmass and population in
| the Northern Hemisphere so make of that what you will.
| fallingknife wrote:
| Yes, everybody knows that, and if someone asks me where
| Greenland is on a map, I will say "at the top" like a
| normal person.
| api wrote:
| You don't reference the galactic orientation by reference
| to the nearest superclusters? Pleb.
| nerfbatplz wrote:
| The enemy's gate is down
| cto_of_antifa wrote:
| Niceee
| selimthegrim wrote:
| I've never heard anyone from the Indian subcontinent complain
| about this.
| rayiner wrote:
| That's because they don't know it's a dog whistle for "sub-
| human continent." /s
| bsanr2 wrote:
| There are more than a billion souls there; I would take that
| bet.
| allemagne wrote:
| I don't think this is an extremely important thing to worry
| about, but I do think you have a point and I like the term
| "Africa Major."
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