4 ms·

(as a layman) The original Out of Africa hypothesis had the "happy conclusion" that anatomically modern humans (AMH) evolved in a small group within Africa and

by themgt 11y ago

(as a layman) The original Out of Africa hypothesis had the "happy conclusion" that anatomically modern humans (AMH) evolved in a small group within Africa and then migrated out to populate the rest of the world, displacing (and not interbreeding with) older hominids. And everyone on earth is a descendent of that small first group, so we're all one coherent happy family. The evolving picture today appears much more likely that some not-quite AMHs migrated from Africa to Arabia where they lived alongside and interbred with already-present Neanderthal culture, became anatomically modern and developed Upper Paleolithic tools/culture (which were perhaps actually an evolution of Neanderthal culture), spent a while fairly isolated and evolving in Arabia, and eventually as AMHs migrated out to displace/interbreed with the planet's other hominids. So, awkward because it's a much more complex, convoluted story, with a lot more space for different populations of humans to have significant genetic differences. You're also left with Africa potentially having a population of pre-AMH homo sapiens and other hominids, with only quite recent back-migration admixing in "modern human" DNA.

JoeAltmaier 11y ago
Is it fair to say that anatomically modern humans happened after leaving Africa? Sure some more changes happened; change continued in Africa as well. And the Neanderthal 2-6% is probably not that significant. Another interpretation is, moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D) which allowed more ultraviolet damage thus increased mutations (blue eyes, red hair and so on). In this view, Africa retains 'modern human anatomy'; the rest of the world is a sort of Galapagos Bird situation.
- dmm 11y ago
  I don't understand percentages used to describe genetic similarity. I mean I heard that humans share 50% with bananas and 96% with chimpanzees. So if 4% is the difference between humans and chimps then 2-6% can be very significant, right? Or can those numbers even be compared?
  - JoeAltmaier 11y ago
    Yeah. Don't know. Maybe its "of the genes that vary"?
  - dogma1138 11y ago
    The percentage difference is calculated using a very odd system which ignores all the actual differences. For example if Humans and Bananas each have 5000 coding genes in common the difference will be measured only on those genes we actually share (out of 20-25K coding genes in humans, no clue how many coding genes do bananas have), so the difference is actually much greater than the 50%, 4%, 1% or what ever figure you get because the big differences are simply discarded. These days there's a cartoon for everything :) https://www.youtube.com/watch?v=IbY122CSC5w https://www.youtube.com/watch?v=IbY122CSC5w And this is without even going into gene expression and epigentics which play a role which some might even consider to be bigger than what actual genetic data you might happen to carry along with you. Heck chickens still have the genes to grow teeth and feathered scales like the dinosaurs they've evolved from however these genes are not expressed anymore in nature.
- defen 11y ago
  > moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D) The Vitamin D hypothesis is just that, a hypothesis, and probably not true. In the summer you produce enough after 10-15 minutes, and in the winter you produce none at all above a certain latitude. Furthermore, if it were a simple "loss of melanin" mutation, you would expect something similar to the favism mutation (G6PD deficiency) which protects against malaria - there are lots of ways to have a loss of function mutation, and you see a bunch with G6PD deficiency. Compare to SLC24A5 gene mutation, which reduces melanin production and accounts for a substantial fraction of paleness, and exists in 1 form that is fixed in most European populations. So paleness was probably selected for some other reason. FWIW there is also basically 1 blue eye mutation and 1 main blonde hair mutation. > which allowed more ultraviolet damage thus increased mutations (blue eyes, red hair and so on). I think you basically have this backwards. At the equator, in the evolutionary environment, you need dark skin to survive. Otherwise the sun will cook you. So there is very strong selection pressure to maintain that. Further from the equator, that selection pressure is relaxed. But it is not UV rays causing the mutations - rather, these random mutations happen (for whatever reason) and are not immediately culled by UV radiation, so if they provide some other advantage, it's possible they will win out. Note: Everything I posted is also conjecture, I don't think anyone really knows why paleness mutations exist :)
laglad 11y ago
Is there a link between being 'anatomically modern' (as you describe it) and the propensity to develop tools/culture?
- themgt 11y ago
  The link, I believe, seems weaker than once imagined. Here's a handful more papers/discussion adding to the complexity: http://dienekes.blogspot.com/2012/07/can-we-retire-60000-year-old-coastal.html http://dienekes.blogspot.com/2012/07/can-we-retire-60000-yea... Simple answer is I don't think there's any consensus, but a radically novel view is beginning to emerge, being aided hugely by our newfound ability to genetically sequence ancient fossils.
Poyeyo 11y ago
What you describe as awkward I find much more interesting.
emgoldstein 11y ago
Until the 20th century, most people believed that human varieties were like animal and plant varieties, which can reasonably be expected to display heritable, variety-specific physical and psychological traits. This expectation is a prior, or null hypothesis; evidence is required to refute it. For instance, if you claimed that Great Danes are just as good as border collies at herding sheep, you'd have to present evidence to support this claim, which otherwise seems implausible. Military and political events in the 20th century reversed this burden of proof. The null hypothesis is now that all dogs are equal, at least behaviorally. If you want to claim that Great Danes aren't likely to be good sheepdogs, you have to present evidence showing their inferior performance on herding tasks, and your evidence has to rule out all non-genetic factors. For instance, obviously if your border collies grew up in the sheep pen and your Great Danes didn't, that's a valid non-genetic explanation. It's not especially difficult to raise the bar indefinitely on this test. Well, okay, we haven't changed our minds about collies, Great Danes and sheep-herding. But we have changed our minds about Ashkenazi Jews, Australian aboriginals, and chess. The "out of Africa" narrative suggested considerable genetic homogeneity that supported this politically desirable narrative of universal behavioral equality as a null hypothesis. Recent discoveries in the complex history of human DNA have not been favorable to this narrative. One of the most interesting discoveries is haplogroup A00, a Y chromosome with a divergence time which could be almost 600,000 years ago [1]. This precedes our current use of the species name "Homo sapiens." 23andme now reports estimated Neanderthal ancestry, but to my knowledge they're not telling anyone they have "the erectus chromosome." [1] https://en.wikipedia.org/wiki/Haplogroup_A_(Y-DNA)#A00_.28Perry.27s_Y-chromosome.29 https://en.wikipedia.org/wiki/Haplogroup_A_(Y-DNA)#A00_.28Pe...
- themgt 11y ago
  Wowzers. If I'm understanding that correctly, there are some people alive today whose last common male ancestor with the rest of humanity was a pre-homo sapien? Sheeeit. And yes, after the eventual upturning this evidence is going to force to occur, I think reflections will admit that many made a conscious/unconscious decision to politicize science to avoid being seen as abetting or enabling the sort of horrific philosophies that resulted in the slavery and genocide of the last hundreds of years, culminating in the holocaust. And so, we lysenkoized science for good intentions and perhaps with good results, but the evidence is beginning to overflow the dam, and I worry that it is soon going to be the time for ... people of a liberal mindset, to get behind the new evidence and find a way to rebuild/salvage the philosophical foundations of legal/cultural equality without the happy simple story at the bottom of it, because if we don't, the door is going to open to the right-wing to use this for their purposes against the left's increasingly strained denials

by themgt 11y ago

JoeAltmaier 11y ago

Is it fair to say that anatomically modern humans happened after leaving Africa? Sure some more changes happened; change continued in Africa as well. And the Neanderthal 2-6% is probably not that significant. Another interpretation is, moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D) which allowed more ultraviolet damage thus increased mutations (blue eyes, red hair and so on). In this view, Africa retains 'modern human anatomy'; the rest of the world is a sort of Galapagos Bird situation.

dmm 11y ago
I don't understand percentages used to describe genetic similarity. I mean I heard that humans share 50% with bananas and 96% with chimpanzees. So if 4% is the difference between humans and chimps then 2-6% can be very significant, right? Or can those numbers even be compared?
- JoeAltmaier 11y ago
  Yeah. Don't know. Maybe its "of the genes that vary"?
- dogma1138 11y ago
  The percentage difference is calculated using a very odd system which ignores all the actual differences. For example if Humans and Bananas each have 5000 coding genes in common the difference will be measured only on those genes we actually share (out of 20-25K coding genes in humans, no clue how many coding genes do bananas have), so the difference is actually much greater than the 50%, 4%, 1% or what ever figure you get because the big differences are simply discarded. These days there's a cartoon for everything :) https://www.youtube.com/watch?v=IbY122CSC5w https://www.youtube.com/watch?v=IbY122CSC5w And this is without even going into gene expression and epigentics which play a role which some might even consider to be bigger than what actual genetic data you might happen to carry along with you. Heck chickens still have the genes to grow teeth and feathered scales like the dinosaurs they've evolved from however these genes are not expressed anymore in nature.
defen 11y ago
> moving to Northern climates with reduced sunlight resulted in decreased melanin (to ensure sufficient vitamin D) The Vitamin D hypothesis is just that, a hypothesis, and probably not true. In the summer you produce enough after 10-15 minutes, and in the winter you produce none at all above a certain latitude. Furthermore, if it were a simple "loss of melanin" mutation, you would expect something similar to the favism mutation (G6PD deficiency) which protects against malaria - there are lots of ways to have a loss of function mutation, and you see a bunch with G6PD deficiency. Compare to SLC24A5 gene mutation, which reduces melanin production and accounts for a substantial fraction of paleness, and exists in 1 form that is fixed in most European populations. So paleness was probably selected for some other reason. FWIW there is also basically 1 blue eye mutation and 1 main blonde hair mutation. > which allowed more ultraviolet damage thus increased mutations (blue eyes, red hair and so on). I think you basically have this backwards. At the equator, in the evolutionary environment, you need dark skin to survive. Otherwise the sun will cook you. So there is very strong selection pressure to maintain that. Further from the equator, that selection pressure is relaxed. But it is not UV rays causing the mutations - rather, these random mutations happen (for whatever reason) and are not immediately culled by UV radiation, so if they provide some other advantage, it's possible they will win out. Note: Everything I posted is also conjecture, I don't think anyone really knows why paleness mutations exist :)

laglad 11y ago

Is there a link between being 'anatomically modern' (as you describe it) and the propensity to develop tools/culture?

themgt 11y ago
The link, I believe, seems weaker than once imagined. Here's a handful more papers/discussion adding to the complexity: http://dienekes.blogspot.com/2012/07/can-we-retire-60000-year-old-coastal.html http://dienekes.blogspot.com/2012/07/can-we-retire-60000-yea... Simple answer is I don't think there's any consensus, but a radically novel view is beginning to emerge, being aided hugely by our newfound ability to genetically sequence ancient fossils.

Poyeyo 11y ago

What you describe as awkward I find much more interesting.

emgoldstein 11y ago

Until the 20th century, most people believed that human varieties were like animal and plant varieties, which can reasonably be expected to display heritable, variety-specific physical and psychological traits. This expectation is a prior, or null hypothesis; evidence is required to refute it. For instance, if you claimed that Great Danes are just as good as border collies at herding sheep, you'd have to present evidence to support this claim, which otherwise seems implausible. Military and political events in the 20th century reversed this burden of proof. The null hypothesis is now that all dogs are equal, at least behaviorally. If you want to claim that Great Danes aren't likely to be good sheepdogs, you have to present evidence showing their inferior performance on herding tasks, and your evidence has to rule out all non-genetic factors. For instance, obviously if your border collies grew up in the sheep pen and your Great Danes didn't, that's a valid non-genetic explanation. It's not especially difficult to raise the bar indefinitely on this test. Well, okay, we haven't changed our minds about collies, Great Danes and sheep-herding. But we have changed our minds about Ashkenazi Jews, Australian aboriginals, and chess. The "out of Africa" narrative suggested considerable genetic homogeneity that supported this politically desirable narrative of universal behavioral equality as a null hypothesis. Recent discoveries in the complex history of human DNA have not been favorable to this narrative. One of the most interesting discoveries is haplogroup A00, a Y chromosome with a divergence time which could be almost 600,000 years ago [1]. This precedes our current use of the species name "Homo sapiens." 23andme now reports estimated Neanderthal ancestry, but to my knowledge they're not telling anyone they have "the erectus chromosome." [1] https://en.wikipedia.org/wiki/Haplogroup_A_(Y-DNA)#A00_.28Perry.27s_Y-chromosome.29 https://en.wikipedia.org/wiki/Haplogroup_A_(Y-DNA)#A00_.28Pe...

themgt 11y ago
Wowzers. If I'm understanding that correctly, there are some people alive today whose last common male ancestor with the rest of humanity was a pre-homo sapien? Sheeeit. And yes, after the eventual upturning this evidence is going to force to occur, I think reflections will admit that many made a conscious/unconscious decision to politicize science to avoid being seen as abetting or enabling the sort of horrific philosophies that resulted in the slavery and genocide of the last hundreds of years, culminating in the holocaust. And so, we lysenkoized science for good intentions and perhaps with good results, but the evidence is beginning to overflow the dam, and I worry that it is soon going to be the time for ... people of a liberal mindset, to get behind the new evidence and find a way to rebuild/salvage the philosophical foundations of legal/cultural equality without the happy simple story at the bottom of it, because if we don't, the door is going to open to the right-wing to use this for their purposes against the left's increasingly strained denials