[eddyzh]

Makes a huge claim at the start.

>"The huge gap between those ages could change our understanding about how humans spread across the world. If the ancestors of today’s non-Africans didn’t sweep across other continents until 47,000 years ago, then those older sites must have been occupied by earlier waves of humans who died off without passing down their DNA to the people now living in places like China and Australia."

But at the end gets a bit more balanced

>"He Yu, a paleogeneticist at Peking University in Beijing who was not involved in either study, said that the mystery wouldn’t be solved until scientists find DNA in some of the ancient Asian fossils. “We still need early modern human genomes from Asia to really talk about Asia stories,” Dr. Yu said."

This puzzle is still missing key elements.

[jl6]

It doesn’t seem like an outlandish claim that many waves of humans tried and failed to colonize the world, until one succeeded. I would find it harder to believe that the first to leave Africa got it right first time.

[defrost]

One question raised by a researcher in the article:

    Dr. Skoglund also said it would be strange for non-African ancestors to have arisen about 47,000 years ago while modern humans in Asia and Australia dated back 100,000 years. The sites in question could have been incorrectly dated, he said, or people could have reached Asia and Australia that long ago, only to die out.

Doesn't mesh well with genetic studies from Australia that show a long history of relatively stable regionalism within Australia (with some still unresolved mixing from Denisovan ancestors.

see:

(2016) https://www.abc.net.au/news/science/2016-09-22/world-first-s...

(2017) https://www.nature.com/articles/nature21416

etc.

[jltsiren]

The actual results in papers like these (both the paper in question and the ones you refer to) are typically of the form: "We sequenced these genomes. Then we took the noisy data, made a lot of assumptions, and applied statistical magic to estimate that the populations split approximately X generations ago. We interpret that as Y years ago." Everything beyond that is interpretation, not the result.

Such results are inherently noisy and subject to assumptions. The further back in history you go, the less accurate and reliable the results will be. Ancient DNA comes with its own issues and assumptions, but it helps with the accuracy of the results. Instead of trying to infer something that happened thousands of generations ago, you may now be only hundreds or even tens of generations from the split.

The clearest way forward would be sequencing Aboriginal Australian DNA from tens of thousands of years ago. Then you could get a more accurate estimate for the split between that population and other sequenced ancient populations.

[naijaboiler]

my own theory. Depending on cyclical geography limitations, humans have been forever moving out of Africa sporadically, going way back to Neanderthals and possibly even before. It wasn't just one wave, it was multiple waves from time to time.

The people that ended up in Australia were some of the earliest anatomically modern humans that successfully made the trip out and for some reason or the other were not really able to colonize Europe/Asia and kept venturing south until they ended up in Australia

Other later waves probably made it to the middle east and went back. Some made it a bit into Europe and some of asia. But it wasn't until relatively recent times, that we got waves that finally got a foothold in Europe/Asia and eventually outlasted other homo species that had dominated those areas for a 100,000 years.

I am not an anthropologist. I can't prove anything I wrote. I am just using my own common sense and the evidence that has so far been published.

[defrost]

> and for some reason or the other were not really able to colonize Europe/Asia and kept venturing south until they ended up in Australia

Any people that did settle in Europe to the north during that first pass through further south some 70K years ago very likely were pushed back by the worsening conditions preceding the advance of the Last Glacial Maximum (dry very dusty air, poor vegetation .. and later ice everywhere).

Following the path of best land with least resistance led to following the tropics mostly by land, consistent year round conditions, no winters to store food for, etc.

[withinboredom]

I wonder if this migrate-and-survive is a "great filter" that organisms must do in order to grow. The same thing will likely happen to space colonists, many will go, but only a few will survive.

[robwwilliams]

The dating of the fossils is quite secure. So in this dimension all is good. The DNA sequence is as good given the number of closely related individuals.

Your comments do not apply with any force to this particular study.

[shellfishgene]

I doubt it's correct to assume groups of humans in Africa one day decided to 'colonize' another place and walked thousands of kilometers to settle down elsewhere. It's probably more like a slow expansion (and reduction) of the settled area, no?

[throwup238]

Humans were nomadic before agriculture so they would have been moving all the time anyway. There would have been no settling down.

It’s more likely competitive pressure forced them to expand out further because to a small group, even a small conflict with a neighboring tribe that costs them a few of their fittest members would be particularly traumatic and risky. It’s just easier and safer to migrate.

Archaic humans made it out to South East Asia over a million years ago back when the sea hadn’t even risen to form the major islands like Indonesia. Migration is in our DNA.

[airstrike]

Both processes could coexist, right? I could see myself waking up one day and saying "what's the farthest we can get to? maybe there are amazing things at the end of the journey"

[bee_rider]

I’m not 100% clear on what the two processes are. In particular, early humans already were pretty mobile. So they’d be going from place to place, hunting as they go. Maybe following some migratory animals. If you got wanderlust, I guess you’d only make it a couple days before you ran out of food, so maybe some dozens of miles, and then you are back to doing typical human stuff, right?

[withinboredom]

it can also be stupid politics/religion: "your village is the reason for our famine, your entire village is banned from here. you will walk until you see the mountains and until you no longer see them behind you" ... next thing you know, you're in europe or asia.

[miniwark]

They where all nomadics, so the concept of a village did not exist yet. It was more like family related moving groups, or maybe "clans". That said, at an individual level there was probably a concept of people exchange when meeting another group, or banning of an individual.

[enkid]

I don't think a group of people living somewhere for thousands of years would be "getting it wrong." You're embedding an assumption that evolution has been working toward an end goal of getting humans to spread globally, which isn't how evolution works.

[jandrese]

It doesn't seem all that improbable that humans or close ancestors had colonized other parts of the world for thousands of years only to die off due to climate change/disease/other factors about 40,000 years ago when they had to start all over again. Or maybe the ancestors colonized it and the extinction event was Homo Sapiens out of Africa, although in this case you would expect more DNA mixing. It seems more likely that the ancestors died out for whatever reason and the humans moved into their habitats to refill that ecological niche.

[enkid]

I don't see how you could say that's more likely without evidence, lack significant gaps in archaelogical finds between eras of human presence in a region.

[h0l0cube]

I think the claim is that earlier founders did colonize the world before the final group left and also colonized the world. Land bridges disappeared as the last ice age came to a close, making later attempts more difficult

[tetris11]

I think they just walked to other places as and when the climate changed. Some adapted and stayed, others moved the greener pastures. This slow and climate-driven process can hardly be described as colonization.

[kspacewalk2]

And their failure doesn't mean they're completely absent from our genome.

[mapt]

It doesn't seem like an outlandish possibility.

That's distinct from making a claim, an assertion with supporting evidence.

To make a claim, we would want evidence, and the evidence here would be a genetic isolation (lack of chronological overlap, synonymous with lack of interbreeding) of ancient Asian humans from ancient African humans. This requires sequencing a lot of ancient Asian DNA, which seems not to have happened yet. We barely have a cohesive evidence supported grasp of Neanderthal interactions in Europe, but are gradually updating to support more and more absorption by interbreeding.

[miniwark]

The view of the chinese researcher is in line with the Multiregional origin hypothesis of modern humans, where asian humans may partially come from asia. So his reply is not surprising.

https://en.wikipedia.org/wiki/Multiregional_origin_of_modern...

Instead, the article follow the Out of Africa origin, and therefore did not explain the old chineses and autralian remains. The article try to explain this by saying than it's because this lines where extincts or than the dates are wrong, but this explanations are not very convincing.

[bee_rider]

What’s the most significant difference between the theories? The Wikipedia article says:

> “The primary competing scientific hypothesis is currently recent African origin of modern humans, which proposes that modern humans arose as a new species in Africa around 100-200,000 years ago, moving out of Africa around 50-60,000 years ago to replace existing human species such as Homo erectus and the Neanderthals without interbreeding.[5][6][7][8] This differs from the multiregional hypothesis in that the multiregional model predicts interbreeding with preexisting local human populations in any such migration.”

But it is a somewhat weird quote in the Wikipedia article. They’ve got the whole thing in quotes with multiple citations (so it isn’t clear which citation the quote comes from), it isn’t attributed to anybody in particular, and it doesn’t seem to be a very accurate description of what I though the consensus was, at least. (It is widely believed that humans interbred with other hominids, right?)

[miniwark]

With recent genetics proofs than early human, did have interbreed with at last Neanderthals and Denisovans, this is now indeed more "true" than the "Only from Africa" hypothesis.

Thad said:

- as the time of the emergence of both theories there where no genetics evidences yet in one way or another

- the interbreeding with this two other species is still very small, (less than 5% of the actual genes). There is still no evidences for other important species like Homo erectus (or hedelbergensis, or florensis, etc.)

The truth maybe in between: a major pool of gene from Africa, but with small local parts from all over the ancient world.

The big remaining question is:

- Did sapiens and erectus had babies? And if yes, then, what was the results (Denisova or something else ?).

[PittleyDunkin]

Am I missing something? Surely Europe is the same continent as Asia. Why wouldn't people just walk over? It seems reasonable to assume that if evidence exists on one side of the continent that it'd imply existence on the other side, too. If anything you'd need a theory why they failed to spread to formulate interesting discussion!

[hackinthebochs]

The Steppes are a natural barrier between East and West until the point where technology caught up to make it passable.

[PittleyDunkin]

Well we have human ancestors on both sides of that barrier, so clearly it's not insurmountable in absolute terms, either from taking the souther route or migrating with herds or some other thing I haven't thought about (I'm not sure waterways would get you the whole way, but it'd get you from the urals to either side). The question is why this would pose a barrier to some populations and not others.

EDIT: also, I forgot that a lot of the steppe is forested. Surely that would make it significantly less of a barrier.

[hackinthebochs]

No terrain is insurmountable considering chance and a hundred thousand years. The question is how likely will any given group be able to pass through and flourish on the other side? We have many examples of isolated human populations on islands or across inhospitable barriers that it shouldn't be surprising to find isolated populations on either side of the Eurasian continent. Off the top of my head, Australian aboriginals, the Andamanese and New Guinea islanders are examples of isolated populations with essentially no gene flow between larger populations over 10s of thousands of years. Even the fact that we talk about how many populations ultimately left Africa in prehistory implies there must have been some barrier to overcome.

> also, I forgot that a lot of the steppe is forested. Surely that would make it significantly less of a barrier.

Also consider the ice age and how that affected the degree to which Eurasia was hospitable.

[anonymousDan]

What exactly do you mean by the Steppes? I thought this referred to a grassland region so can't see how it would constitute a barrier.

[hackinthebochs]

Yes, its a continent-spanning grassland. But humans don't eat grass. Sourcing water is also a problem. It's inhospitable to humans without some reliable means of turning grass into nutrition. If we're talking about early humans it would be a significant barrier.