Even though we continue to find evidence of very early Homo occupation across different parts of Eurasia (including in this case Wallacea), the tendency in archaeology and population genetics is still to not take the evidence very seriously and just assume our Homo Sapiens specific evolution was always fundamentally African. So these 1.4 million Sulawesi people (and other early Eurasian Homo) were side-shows, and not relevant to our own direct lineage. All Eurasian Homo simply died out over the last million years, and only the African branch made it down to the present.
You see this even in archaeogenetics, when the relationship between Denisovans, Neanderthals, and humans is discussed. I think the generally reported tmrca of all three lineages is something like 750k- 1 mil ybp, but it's usually assumed that the Neanderthal and Denisovan lineages were themselves out-migrations from an African source, and that the homo sapiens lineage just stayed in Africa. The split we know now wasn't so clean at least between humans and Neanderthals since it seems there was some admixture between the two at some point in the Middle Paleolithic.
The human/Neanderthal complexity aside, it's clear that Denisovans are essentially the outgroup in our trio. What precludes the possibility that a million years ago East Eurasia was the main well-spring of the Homo lineage, and the branching and west-ward migration went Denisovan > Neanderthal > homo sapiens? If Denisovans represent the outgroup within Homo, why would we assume East Eurasia was always a sink and not a source for primary Homo evolution?
I think Sundaland is a perfect region for very early development of sea travel. Constantly changing coastline, emerging and disappearing little islands, mangrove beachfronts which are difficult to pass on land provide an excellent incentive. Lots of available greenery, including bamboo and other easily floatable material provide means.
It might have started not even a transport vehicle, but a simple floating vessel to help collect floating coconuts or shellfish and such, and later increase in size to carry a human.
What I am very skeptical of is early crossing of the Red Sea around Bab el-Mandeb or elsewhere. It is totally different - mostly barren. There is nothing to construct anything floating from, even during the periods when it was wetter than today, it was very sparse. There is hardly an incentive also - when the other shore is visible, it is just as barren. I think it was first crossed much later - maybe closer to Holocene.
I agree the Bab el-Mandeb has been overemphasized as being the principal locus of out of Africa dispersals, but I think there's a chance it could have served as an important corridor going the other way.
New archaeological research over the past 10-15 years has shown the Arabian peninsula has been repeatedly occupied during past humid periods by humans and other large mammals (elephants, hippos, rhinos, etc). During dry phases in the peninsula, populations would have either gone extinct or been driven into local refugiums which maintained more consistent access to water. The Yemeni highlands seem like a good example of a possible refugium, as even today it's one of the wetter corners of the peninsula and seems to have had above-average moister conditions in the past too.
I think it's an interesting possibility to consider that the "Yemeni refugium" may have been overloaded with incoming human groups during the onset of dry spells, or else always had a limited ceiling of population it could sustain (it's not a super large region) which forced surplus populations to boil off and expand outward when they reached the local carrying capacity. Given the immediate environment in the rest of the peninsula would have been very arid and unsuitable during drier periods, they would have been funneled across the Bab el-Mandeb into Africa for lack of any other local alternative.
There's nothing preventing movement from the Horn into Arabia, but I think it's less likely because any human populations in the vicinity of the Bab-el Mandeb in the Ethiopian highlands would have had a greater range of territory they could migrate too - they could move further south into Ethiopia or west into south Sudan, relatively humid regions themselves etc. Or, given the Ethiopian highlands are pretty big, they could have just stayed put and been rather insulated from dramatic climate shifts effecting the rest of the region. Either way, they had a wider range of contiguous territory they could expand and diffuse into, as opposed to any potential "Yemenis" who had only one option once they'd reached the local carrying capacity.
I actually agree with you about "Yemeni refugium" and that Bab el-Mandeb might have seen more migrations into Africa rather than out of it. Yemeni highlands, for example, have today some population with a rare mtDNA L6 haplogroup, which is also present scattered in Ethiopia. The usual story with that is that is must be a trace of migration from African horn to SW Arabia, but I think more likely it was in the other direction, since L6 is concentrated in this refugium but in Ethiopia it is scattered.
The greater concentration of L6 in SW Arabia could be due to founder effect, especially if the branch diversity there is low and the tmrca of those lineages in the region is relatively recent.
On the paternal side, there are a lot of basal branches of not just y-E, but A, B and even ultra rare D0 in Arabia. Like you noted, any common African/Arabian lineage sharing is usually assumed to reflect recent Africa > Arabia flow, but l share your skepticism that it was always so unidirectional. I really don't think we'll ever be able to truly resolve a lot of these questions without more ancient DNA from Southwest Asia and Northeast Africa across the last 50-100k years.
I don't think founder effect can be seen a lot. Populations moved much more intensely than what science considered some 20 years ago. We know in Europe there was a complete genetic turnover several times during the UP and more in neolithics. In other places less well known yet, but why would it be different?
Majority of ancient and rare genetic lines today exist far from places they emerged in, most often they are concentrated in refugia, where they survived. I think there is hardly any genetic line that emerged before Holocene still reside near its original source.
That's an interesting perspective regarding Bab el-Mandeb. It was much narrower during periods with the lowest sea level. I think that a relevant factor is shoreline complexity; a highly complex shoreline with structures that are more easily accessed from the water may provide greater incentive for development of small floating platforms and simple watercraft.
Even though we continue to find evidence of very early Homo occupation across different parts of Eurasia (including in this case Wallacea), the tendency in archaeology and population genetics is still to not take the evidence very seriously and just assume our Homo Sapiens specific evolution was always fundamentally African. So these 1.4 million Sulawesi people (and other early Eurasian Homo) were side-shows, and not relevant to our own direct lineage. All Eurasian Homo simply died out over the last million years, and only the African branch made it down to the present.
You see this even in archaeogenetics, when the relationship between Denisovans, Neanderthals, and humans is discussed. I think the generally reported tmrca of all three lineages is something like 750k- 1 mil ybp, but it's usually assumed that the Neanderthal and Denisovan lineages were themselves out-migrations from an African source, and that the homo sapiens lineage just stayed in Africa. The split we know now wasn't so clean at least between humans and Neanderthals since it seems there was some admixture between the two at some point in the Middle Paleolithic.
The human/Neanderthal complexity aside, it's clear that Denisovans are essentially the outgroup in our trio. What precludes the possibility that a million years ago East Eurasia was the main well-spring of the Homo lineage, and the branching and west-ward migration went Denisovan > Neanderthal > homo sapiens? If Denisovans represent the outgroup within Homo, why would we assume East Eurasia was always a sink and not a source for primary Homo evolution?
Thanks for pursuing this angle, thanks in part to your comment I'll be following up on this element this week.
I think Sundaland is a perfect region for very early development of sea travel. Constantly changing coastline, emerging and disappearing little islands, mangrove beachfronts which are difficult to pass on land provide an excellent incentive. Lots of available greenery, including bamboo and other easily floatable material provide means.
It might have started not even a transport vehicle, but a simple floating vessel to help collect floating coconuts or shellfish and such, and later increase in size to carry a human.
What I am very skeptical of is early crossing of the Red Sea around Bab el-Mandeb or elsewhere. It is totally different - mostly barren. There is nothing to construct anything floating from, even during the periods when it was wetter than today, it was very sparse. There is hardly an incentive also - when the other shore is visible, it is just as barren. I think it was first crossed much later - maybe closer to Holocene.
I agree the Bab el-Mandeb has been overemphasized as being the principal locus of out of Africa dispersals, but I think there's a chance it could have served as an important corridor going the other way.
New archaeological research over the past 10-15 years has shown the Arabian peninsula has been repeatedly occupied during past humid periods by humans and other large mammals (elephants, hippos, rhinos, etc). During dry phases in the peninsula, populations would have either gone extinct or been driven into local refugiums which maintained more consistent access to water. The Yemeni highlands seem like a good example of a possible refugium, as even today it's one of the wetter corners of the peninsula and seems to have had above-average moister conditions in the past too.
https://www.researchgate.net/figure/When-Arabian-Middle-Palaeolithic-archaeological-sites-are-plotted-on-the-CCSM3-climate_fig9_272832960
I think it's an interesting possibility to consider that the "Yemeni refugium" may have been overloaded with incoming human groups during the onset of dry spells, or else always had a limited ceiling of population it could sustain (it's not a super large region) which forced surplus populations to boil off and expand outward when they reached the local carrying capacity. Given the immediate environment in the rest of the peninsula would have been very arid and unsuitable during drier periods, they would have been funneled across the Bab el-Mandeb into Africa for lack of any other local alternative.
There's nothing preventing movement from the Horn into Arabia, but I think it's less likely because any human populations in the vicinity of the Bab-el Mandeb in the Ethiopian highlands would have had a greater range of territory they could migrate too - they could move further south into Ethiopia or west into south Sudan, relatively humid regions themselves etc. Or, given the Ethiopian highlands are pretty big, they could have just stayed put and been rather insulated from dramatic climate shifts effecting the rest of the region. Either way, they had a wider range of contiguous territory they could expand and diffuse into, as opposed to any potential "Yemenis" who had only one option once they'd reached the local carrying capacity.
Has anyone connected this research with early Homo artifacts on Socotra island ?
This is a great question. I'm waiting to hear more from Socotra.
Thank you! I'll check the link.
I actually agree with you about "Yemeni refugium" and that Bab el-Mandeb might have seen more migrations into Africa rather than out of it. Yemeni highlands, for example, have today some population with a rare mtDNA L6 haplogroup, which is also present scattered in Ethiopia. The usual story with that is that is must be a trace of migration from African horn to SW Arabia, but I think more likely it was in the other direction, since L6 is concentrated in this refugium but in Ethiopia it is scattered.
The greater concentration of L6 in SW Arabia could be due to founder effect, especially if the branch diversity there is low and the tmrca of those lineages in the region is relatively recent.
On the paternal side, there are a lot of basal branches of not just y-E, but A, B and even ultra rare D0 in Arabia. Like you noted, any common African/Arabian lineage sharing is usually assumed to reflect recent Africa > Arabia flow, but l share your skepticism that it was always so unidirectional. I really don't think we'll ever be able to truly resolve a lot of these questions without more ancient DNA from Southwest Asia and Northeast Africa across the last 50-100k years.
I don't think founder effect can be seen a lot. Populations moved much more intensely than what science considered some 20 years ago. We know in Europe there was a complete genetic turnover several times during the UP and more in neolithics. In other places less well known yet, but why would it be different?
Majority of ancient and rare genetic lines today exist far from places they emerged in, most often they are concentrated in refugia, where they survived. I think there is hardly any genetic line that emerged before Holocene still reside near its original source.
That's an interesting perspective regarding Bab el-Mandeb. It was much narrower during periods with the lowest sea level. I think that a relevant factor is shoreline complexity; a highly complex shoreline with structures that are more easily accessed from the water may provide greater incentive for development of small floating platforms and simple watercraft.