Tuesday, December 29, 2009

267. The Baseline Scenarios -- 43: The Migration

Now that we have a picture, however provisional and incomplete, of what HMP and HMC might have been like, we can turn our attention to the migration itself. And the first thing we need to ask is whether they walked, or whether they had some sort of boats, rafts or possibly even sailing vessels. It's difficult to imagine how they could have undertaken such a journey without some sort of oceangoing vessel, first to carry them across the Red Sea and then to enable them to cross the various rivers they would have encountered, especially the extremely wide and swampy Indus delta. The best way to get around such an obstacle would be to avoid it by taking to the sea. In the case of the Indus, this could have been the only way. If they had seagoing vessels, as indeed seems likely (for this and other reasons I'll be getting to shortly), they could have traveled very quickly. If not, it would have been a very long and difficult slog.

The next question that comes to mind is: how did they obtain water? A migration along a river coast almost guarantees a plentiful supply of fresh water, but traveling along an ocean coast is a completely different matter. The mystery is compounded by the especially difficult conditions afforded by the Indian Ocean coast, where precipitation is controlled by the monsoon cycle: very little rain most of the year; much too much during the summer monsoon season.

If proceeding on land by foot, they would have been completely at the mercy of the law of large numbers, i.e., their slow progress would have meant submission to the overall statistical trend, which would have left them completely without water for months on end during at least some parts of their journey. If proceeding by sea, they would have been moving more quickly and could have gotten lucky, i.e., they could have taken advantage of an anomalous period during which rainfall might have been more plentiful than usual during months when rainfall would ordinarily have been extremely sparse or nonexistent.

The means of transportation is related to other issues as well. If, for example, it took a thousand years to get from the Bab El Mendab to the Indus Delta, where would the tremendous population generated in all that time have expanded to? According to Stephen Oppenheimer, the land mass to their north would have been uninhabitable "until after 50,000 years ago, when a moist, warm phase greened the Arabian Desert sufficiently to open the Fertile Crescent" (The Real Eve, pp. 129-30).

All indications, therefore, are that they would have had to move very quickly across the coast, most probably by means of some sort of oceangoing vessels, which could have carried them long distances within
very short periods of time. The entire crossing from the Horn to the Sahul could, conceivably, have taken only a few hundred years and, if conducted at top speed, less than a hundred. Which leaves open the possibility that only a few or possibly no colonies might have been established over long stretches of their passage.

The Indus Delta would certainly have been a major waystation. First, it would have offered a plentiful supply of fresh water, which may well have been badly needed. Second, it would have presented an interesting option: continue along the Indian Ocean coast, or veer north along the coast of the Indus. If this were the voyage of a practical people, the northern route, with its plentiful water supply would have been the only option, especially given the almost inevitabe hardships that would already have been caused by unreliable and irregular precipitation. I have a feeling there must have been a split at that point, with at least some of them following the river northward, most likely along the western coast, and the rest continuing eastward, as before. My reasons will become clear as we proceed.

As I see it, due to the considerable hardships entailed by their decision to forge ahead, those continuing eastward would have been motivated largely by a desire to explore.

(to be continued . . . )


Maju said...

"Oceangoing vessels" are major words. I think it's plainly impossible and unrealistic, and that includes sails or at least serious types of them, as they need pulleys to be managed and, in general, a kind of sophisticated naval and carpentry craft that is pretty much unthinkable for the age and the small populations that hunter-gatherer lifestyle can mantain.

Simple boats much as hollowed logs, rafts or skin canoes were, I agree a feature, as they are needed not just to cross straits and exploit properly coastal resources but also to cross rivers, swamps and lakes, even in the context of Africa.

I don't really understand your issue with water. Coasts are where rivers and creeks always lead to and anyhow at the time of the migration there was for sure a different type of climate and I would dare say that it is highly likely that the migrant population made their feat in one of the pluvial periods of the Paleolithic, either the Mousterian pluvial, c. 50,000 BP or the Abbassian pluvial c. 100,000 BP (this is another reason why I'm not happy with the usual dates for OoA c. 70,000 BP and I'd rather favor an older date).

People in any case were not able and in fact did not adventure deeply in the Saharan-Arabian desert before the domestication of the camel. However they were surely able to live at their edges.

As you can see in this image, coastal South Arabia is even today not part of the desert, even if it's somewhat arid. And does support some stable population even in today's arid conditions. Once arrived to South Asia, water should have been widely available.

DocG said...

Maju, by "oceangoing vessel" I mean just that and no more. I don't know enough about sailing or the capabilities of "hunter-gatherer" to argue that they would have had sailing vessels. But whatever they had, it would have to have been capable of operating in the ocean, no?

As for my "issue with water," I really don't know what conditions would have been like as far as water is concerned, but this is certainly another issue worth exploring, I would think. As you indicate, it could possibly help us arrive at an estimate for the time of exodus.

The availability of water would have to have been a major factor in their survival and the question is: was rainfall plentiful at that time, and if not did they just get lucky?

And I don't see any rivers in the map of the Arabian desert. I wonder if there were any at all on their path until they reached the Indus.

Maju said...

But whatever they had, it would have to have been capable of operating in the ocean, no? -

Sounds like you mean open ocean, like Austronesians or Vikings. To that I say quite clearly no.

Abel to operate in calm coastal waters? I'd say yes.

Crossing into Sahul in the relatively favorable conditions of the Ice Age's low sea levels is already considered quite challenging for that time. They made it: but that was their extreme limit.

And I don't see any rivers in the map of the Arabian desert.

Only very large rivers are apparent. It's not a proper map but a satellite image with a yellow line drawn on top to indicate the limits of the Arabian Desert according to the WWF.

Anyhow, just check for the corresponding regions in Wikipedia to get a basic idea on how is this area today (not necesarily in the past).

Hadhramaut says: "It consists of a narrow, arid coastal plain bounded by the steep escarpment of a broad plateau (al-Jol, averaging 1,370 m [4,500 feet]), with a very sparse network of deeply sunk wadis (seasonal watercourses). The undefined northern edge of Hadhramaut slopes down to the desert Empty Quarter. (...) The Hadhramis live in densely built towns centered on traditional watering stations along the wadis. Hadhramis harvest crops of wheat and millet, tend date palm and coconut groves, and grow some coffee".

Dhofar reads: "Dhofar and a small portion of the northern tip of Yemen are directly exposed to the South East monsoon from mid-August to late September or early October; this is known as the Khareef. As a result, it has a lush green climate during the monsoon season and for sometime after until the vegetation loses its moisture. Dhofar's temporarily wet climate contrasts sharply with the neighboring barren Empty Quarter Desert. The Salalah plain was once a well cultivated area with a sophisticated irrigation system. During World War I it was fertile enough to produce food and grain to supply a large proportion of the requirement of the British Army fighting in Mesopotamia".

So, while arid, these regions can support life and be inhabited by humans. These two regions constitute the most arid strip of coastland that the migrants would have needed to cross, if they followed the southern coastal route and did not go via the fertile crescent (or both).

Another maybe even more arid barrier would be the SE Iranian desert, that decimated Alexander's army at its return from the expedition to India. Overall I do have the impression that the region between core Yemen and the Indus was a difficult one but not impossible, not more difficult than the harsh conditions that Bushmen face today for example. Enough to delay the expansion somewhat and guarantee that the migrant population was small until arrival to South Asia but not enough to impede it.

German Dziebel said...

An interesting paper addressing many of the questions discussed on this blog, including a gap in India, is Evaluating the mitochondrial timescale of human evolution, by
Phillip Endicott, Simon Y.W. Ho, Mait Metspalu and Chris Stringer. Trends in Ecology and Evolution Vol.24 No.9, 2009. Basically, neither the dates, nor the route of an out of African migration are clear and supported by evidence. The authors note that genes in India are no older than elsewhere in Eurasia.

Maju said...

An interesting paper, German. Thanks.

Here there is a direct link (PDF).

However I don't see why you claim what you claim based on this paper. All it says is that there are HUGE uncertainties re. the molecular clock age estimation methods, something that I already knew and have been arguing for a long time.

It does say (again a well known fact) that the oldest known fossil of our species in South Asia is younger than in most other places. But it does not say "genes in India are no older than elsewhere in Eurasia". In fact they say the opposite:

The lacuna in South Asia appears to be even greater because there is sound genetic evidence that population expansion in modern humans commenced here substantially before other regions outside of Africa [35].

What shows again how you tend to read genetic papers systematically wrongly, in a wishful thinking sense.

German Dziebel said...

I must have misread it, as I was in hurry. Apologies. I trust you that this is what the paper says.

"What shows again how you tend to read genetic papers systematically wrongly, in a wishful thinking sense."

I don't have any wishful thinking. Out of America is built on evidence that doesn't depend on the ebb and flow of genetic dates. Regardless of the dates some genetic labs assign to South Asian genes, from my perspective, until they find African-specific lineages outside of Africa (say, Y-DNA A and B, mtDNA L0, L1, L2), the out of Africa hypothesis is not confirmed. We do have M1 and U6 in Africa, though.

Maju said...

The phylogeny is not dependent on age estimates, German. It is only dependent on community of mutations or lack of it: sets and subsets. What age have the nodes of the tree is, of course, slippery science, just like your kinship studies.

M1 and U6 are known to be part of the backmigration into some areas of Africa that happened as extension of the colonization of West Eurasia. U6 in fact is restricted to North Africa, in all aspects a part of West Eurasia.

You also have Y-DNA R1b and J1 in Africa... but like the aforementioned mtDNA clades they have a West Asian origin.

And of course, yes: you do have loads of wishful thinking. Remember that the one who is easiest to fool is almost always oneself.

Maju said...

By the way, Victor may want to read that reference #35, which is not other than Atkinson, Q.D. et al. (2008) mtDNA variation predicts population size in humans and reveals a major Southern Asian chapter in human prehistory. Molecular Biology and Evolution 25, 468–474 and appears to demonstrate a much greater expansion in Southern Asia (incl. Indochina) than elsewhere.

Maju said...

But (sorry again for posting fragmentarily) that the supplemental material excludes that Indochina would be the core of that South Asian demic hyper-growth.

DocG said...

Maju: "appears to demonstrate a much greater expansion in Southern Asia (incl. Indochina) than elsewhere."

I've read that paper. The problem is that it lumps SE Asia with the South Asian peninsula, so the results are ambiguous for our purposes. However, a dramatic expansion in population size is not inconsistent with a major bottleneck (or bottlenecks), and this is how Oppenheimer sees it as I recall. I'll be posting more on this soon.

German Dziebel said...

"It is only dependent on community of mutations or lack of it: sets and subsets. What age have the nodes of the tree is, of course, slippery science, just like your kinship studies."

Luis, you're again trying to engage me into a useless debate. I know how phylogenies are constructed, and the current ones are likely wrong. In the same ways as the dates deduced from those phylogenies are baloney. It's very simple: group mutations shared across wide geographic areas together (the stability angle) and keep geographically restricted ones separate (the diversity angle). So, you should always give priority, when determining common descent, to geographically more common mutations, the other random commonalities are homoplastic. African lineages have tons of "private polymorphisms" not found anywhere else. I've even seen the actual PCR images. But it's not because they are old but because they went through bottlenecks and then re-expansions as foraging demes were budding off and streaming into Africa. Some of them are shared within Africa but it's probably due to homoplasy.

Kinship studies and linguistics have 200 years behind them, this means solid experience dealing with data and with phylogenies. Only species-internal structures drive phylogenetic inferences, no Human-Chimp divergence induced illusions. Sampling involves population wide systematic data and not randomly picked individuals. (Now they keep discovering new and new lineages in America because they can never sample as many tribal groups as linguists and ethnologists have info on.) Pop genetics is a young science both in terms of dating and phylogenies. It got ahead of itself and confused everybody. Now people can only worship it because there's no rational way to relate to it.

You are the person driven by wishful thinking, too: you want to belong to a large group of enlightened thinkers, you want to imbibe the sweet juice of consensus and you want to believe that you understand "science." So your subjective motivation for picking out-of-Africa and "defending" it is clear. But why would someone, with my education and experience, pit himself against the consensus, if it weren't for the desire to establish the truth? What am I wishing for? The truth. Only in this sense my thinking is wishful.

German Dziebel said...

The Atkinson paper is another bizarre example of genetic isolationism. Read this: "Plots of population size through time show slow growth in sub-Saharan Africa beginning 143–193 kya, followed by a rapid expansion into Eurasia after the emergence of the first non-African mtDNA lineages 50–70 kya."

Archaeology says the opposite: there's no population growth in Africa until 45-50K (see Klein's recent papers in Evolutionary Anthropology and PNAS); there's no evidence for an expansion out of Africa at 50 or 70 K years. And what happened with our ancestors between 193K and 70K? Have Bushmen been separated from the rest of humanity for 200K years? They would have been a new species by the time other humans left Africa and they would have probably been replaced like all other pre-human species with no interbreeding...

German Dziebel said...

"M1 and U6 are known to be part of the backmigration into some areas of Africa that happened as extension of the colonization of West Eurasia."

Exactly. So, now we only need similar evidence for a "front migration" out of Africa. We need a branch of L0 or L1 in modern India, Southeast Asia or Australia. Or a branch of L2 or L5 in ancient Kostenki remains from 30-40K. Too bad, we don't have anything of this sort. The presence of L6 in West Asia (and its absence in Africa) suggests that L lineages began forming outside of Africa. This may have happened around the time M1 and U6 entered Africa or earlier. M1 and U6 just stayed in the North and Northeast, while L lineages continued into Sub-Saharan Africa. As they conquered new territories, they fragmented, went through bottlenecks and then re-expanded. What we see in Africa is exactly the pattern of a colonized continent.

Maju said...

Did you read my last post, German? It is kinda annoying not knowing if what I posted just after what I can read now was read or not due to your "moderation" system.

The supplementary material overcomes your objection in any case.

Maju said...

Luis, you're again trying to engage me into a useless debate.

Sorry. Let's leave it here then.