Tag: Human Evolution

Reevaluating “multiple origins” for modern humans

Posted on by Razib Khan

Following up on the post below, The Deep Origins Of East African Hunter-Gatherers, as well as some discussions on Twitter, I think I want to do some clarification about where I think we are now. My thoughts shouldn’t be a surprise if you have read everything I’ve said, but I may not have put them all together in one place.

Around the turn of the century, nearly twenty years ago, the consensus had definitively turned against a “multiregional” origin of modern humans, toward one where an “out of Africa” migration ~50,000 years ago was paramount. Many people took the “paramount” part and simply asserted that we are all Africans descended from a population that flourished in the east of the continent about 50,000 years ago. There was a lot of circumstantial evidence to support this, at least spottily, from both archaeology and genetics. There were also problems and lacunae in both fields. But the data was spotty enough that the extreme position was defensible.

We now have a lot more information and need to update our model. First, most people agree that indigenous Eurasian hominins, Neanderthals and Denisovans, contributed to the ancestry of people outside of Sub-Saharan Africa. Additionally, it’s been evident for a long time now that the massive population bottleneck that is present in all non-African populations dating to ~50,000 years ago is far less evident in Sub-Saharan African genomes.

Finally, it’s pretty clear that humans with modern morphology were present within Africa for hundreds of thousands of years before the movement out of Africa.

Therefore, a new reevaluation of the old model that is converging is a possibility is that multi-regionalism was operative within Africa for hundreds of thousands of years, followed by a massive expansion on the northeast edge of Africa that resulted in most of the ancestry of other human groups outside of the continent, with some assimilation (e.g., Neanderthal). This is a far more complicated model than the older one, but sometimes the truth is more complicated than simplicity.

But I think we’ll probably need to make further modifications, and that’s because gene flow is not always unidirectional. Specifically, the Y chromosomal work, in particular, is strongly indicative of migration of lineages more typical of Eurasians expanding within Africa within the last 50,000 years. And, as a commenter on this weblog has pointed out, even the “deep lineages” within Africa, Y haplogroups A and B, show signs of massive expansion within the last 50,000 years.

This may mean that a population liminal to Africa and Southwest Asia underwent a very rapid expansion ~50,000 years ago. The replacement of indigenous lineages was far more thorough outside of Africa, with 5% or less assimilation in most places. But, it probably impacted Africa as well. Though a larger fraction of diverged modern ancestry persisted in Africans than Eurasian hominin ancestry in non-Africans. In other words, the high genetic diversity of Africans today, and particular groups like the Khoisan, is due to the mixture between an ancient migration from the same population that was the source of “out of Africa” in Eurasia and Oceania, and disparate deeply structured lineages within Africa, that date back 200-400 thousand years ago.

Additionally, I think some earlier “modern” lineages were assimilated in eastern Asia with the latest migration out of Africa. And, some of the ancestry within Africa probably predates the origin of anatomically modern humans, analogous to the case of Neanderthals and Denisovans.

Note: This is not that different of a model from Dienekes Pontikos’ ideas in the 2000s, More support for the Afrasian/Palaeoafrican hypothesis, at the high level. Basically the more evidence has come in, the less crazy his model has gotten.

The state origins of “modern humans” in 2018 (it’s a flux)

Posted on by Razib Khan

After reading the supplements to the new Siberian paper I have a few general thoughts that I want to layout.

First, the clines vs. clusters considerations seem to be one we need to revisit. Like the expansion of Native American peoples ~15,000 years ago, it seems that the “Out of Africa” migration pulse happened so quickly that a lot of different groups emerged at the same time. In the new paper the earliest proto-“Ancient North Eurasians” can be modeled as most similar to the West Eurasian branch of humanity (sans Basal Eurasian), but with some minor component affinity to East Eurasians. It could be that this is a function of admixture between the distinct lineages. Or, it could be that there was a fair amount of substructure within the post-Basal Eurasian “Out of Africa” meta-population.

The problem with the idea of lots of structure within this population that I see is that it might depend on the plausible effective population sizes. I’d need to know more ethnography than I do, but it seems not impossible for ~10,000 humans to be highly structured in Paleolithic social contexts, even if they were close geographically. But, this would entail a great deal of xenophobia and likely inter-group conflict.

Second, I am convinced that there were earlier “Out of Africa” migrations. Many of them. As John Hawks pointed out at ASHG the Neanderthals and Denisovans seem to be descended from a migration of African hominins that dates to somewhere after 1 million years ago. This means they replaced hominins that were present in Eurasia for ~1 million years already. Geneticists and paleontologists have both also discovered suggestive clues to likely “proto-modern” human populations that were present and admixing before the rapid expansion of Eurasians and Australasians ~40-50,000 years ago. With more ancient DNA and subtle analysis, I think we’ll find that modern human absorbed some layers between that of Denisovans and Neanderthals and the most recent expansion.

Finally, I think multi-regionalism within Africa is between plausible and likely, and that major back-to-Africa migrations that modify/challenge “Out of Africa” are possible. We are learning a lot. But that means simple elegant models are falling by the wayside.

The new African “multi-regionalism” & pan-Neanderthalism

Posted on by Razib Khan

We live in times when our understanding of the origin and diversification of modern humans is undergoing great change. More concretely, our understanding of what it means to be human is transforming. The terms are overused, but perhaps it could be called a “revolution” or “paradigm shift” between the year 2000 and today.

At the end of 2010 ancient DNA made it highly likely that people outside of Sub-Saharan Africa had non-trivial Neanderthal ancestry. That is, enough ancestry that it is detectable genomically. I should also add that I think it is highly probable that the good majority of people within Sub-Saharan Africa have Neanderthal ancestry. Some of this is due to recent attenuated Eurasian back-migration (e.g., many West Africans, Nilotic people, and KhoeSan have Holocene gene-flow signals which derive from the agricultural expansions of the past 10,000 years). But, I think once deep Pleistocene genomes of African humans are sequenced we will see evidence of some Eurasian back-migration at a very ancient date (there is already some suggestive inferential evidence of this).*

Talking with a few friends this week, I realized that the famous “We are all Africans” t-shirts, which have turned into recognizable memes, should be supplemented with “We are all Neanderthals” t-shirts. So yeah, now selling them on DNA Geeks. If the Richard Dawkins Foundation can make quid on it, why not the Razib Khan et al. Foundation?

This has all been on my mind due to a review paper in Trends in Ecology and Evolution, Did Our Species Evolve in Subdivided Populations across Africa, and Why Does It Matter? (OA). If you read this blog closely you’ll see there’s not much new in it. But, it is a signpost, a marker, of the times we live in. Here’s the important bit:

Together with recent archaeological and genetic lines of evidence, these data are consistent with the view that our species originated and diversified within strongly subdivided (i.e., structured) populations, probably living across Africa, that were connected by sporadic gene flow…This concept of ‘African multiregionalism’…may also include hybridization between H. sapiens and more divergent hominins (see Glossary) living in different regions…Crucially, such population subdivisions may have been shaped and sustained by shifts in ecological boundaries…challenging the view that our species was endemic to a single region or habitat, and implying an often underacknowledged complexity to our African origins.

The first person who explicitly used the term “African multi-regionalism” that I recall was Alwyn Scally, though the general framework was shaping up years before. Frankly, I was waiting for someone to use that word. If Richard Klein’s The Dawn of Human Culture, published in 2002, was the apogee of the old model, often inchoate and more crisp in popularization than within the scientific community that we are all descended from a single East African tribe, this review paper heralds the emergence of a more complex and pluralistic framework. The emergence of modern humans within Africa then may have been a polycentric gradual and interactive process; not a singular explosion against the firmament of the antique savanna landscape.

By the late 2000s, even before the 2010 Neanderthal draft genome paper, it was starting to be evident due to genome-wide analyses of contemporary populations, that the extreme bottleneck clear in non-African populations was much more modest within Africa. That opened the possibility for the existence of deep structure within the continent that pre-dated the “Out of Africa” event. A deeper look at African hunter-gatherers indicated to many researchers that these groups diverged from other modern humans in the range of ~200,000 years before the well. Recent paleontological work has confirmed this genetic insight.

Where we are today is that some people are now arguing for the overthrow of the “Out-of-Africa” idea, whether by replacing it with an “Into-Africa” model of some sort, or resurrecting a more polycentric classical multi-regionalism (“some people” as evident in the increased frequency of emails and Twitter messages I get in this vein). I don’t think we’re there yet, not by any measure. But, it is now in the realm of very unlikely, not extremely unlikely (at least the “Into-Africa” model; it is clear that strong overwhelming demographic pulses from somewhere singular dominate the genome of most modern humans).

* I don’t think it is all that implausible that some Neanderthal back-migration into Africa occurred at some point in the last ~500,000.

Beyond “Out of Africa” within Africa

Posted on by Razib Khan

It looks as if the vast majority (95% or more depending on the population) of the ancestry of non-African humans derives from a population expansion which began around ~60,000 years ago. Before this period some researchers argue there was a non-trivial period of isolation. The “long bottleneck” (David Reich alludes to this in Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past). For the vast majority of humans then the last 60,000 years is characterized by a branching process, some reticulation (e.g., South Asians merge West and East Eurasian lineages) between these branches from a common ancestor, as well as introgression from archaic lineages like Neanderthals and Denisovans.

Though I do accept that it seems that modern humans probably migrated out of Africa before 60,000 years ago, mostly due to the results from archaeology, I think the genetic evidence is strong that these groups contributed very little genetically to contemporary populations.

The situation within Africa is very different. Being conservative it seems likely that the Khoisan ancestral lineage diverged from some other Africans ~200,000 years ago. I say conservative because there are researchers who want to push the divergence much further back. Additionally, several different research groups are now converging in a result that West Africans are a mixture between eastern Sub-Saharan Africans (think the population ancestral to Mota in Ethiopia) and a lineage basal to all other humans. That means that the Khoisan are not the most basal, so even assuming the conservative 200,000 year divergence point for Khoisan, modern humans share a common ancestor earlier than 200,000 years ago.

The upshot here is that around 75 percent of the history of modern humans is within (greater)* Africa. The distinctive “Out of Africa” bottleneck and expansion defines most humans only in the last 25 percent of the history of our species. And, within Africa, the dynamics were very different. The biggest difference is that African populations are not defined by a large number of lineages emerging and diverging around the same period, because there wasn’t a massive and singular expansion within Africa analogous to what occurred outside of Africa (at least until the recent past, with the Bantu expansion). That’s why there’s deep structure within Africa today between groups as divergent as the Bantu, Mbuti, Hadza, and Khoisan.

The term “Basal Eurasian” kind of makes sense in the non-African context because of the singular importance of divergence between lineages in the first 10,000 years or so after the “Out of Africa” event. I’m not sure “Basal human” makes as much sense because there wasn’t a singular event within Africa that allowed for the emergence of modern humans. Rather, it was a process, and probably quite resembles something like multiregionalism.

* Some wiggle room here for the likelihood that modern humans were long present in the liminal Near East.

The Ancient Neanderthal Mariner

Posted on by Razib Khan

More recent stuff on Neanderthals of interest, Neandertals, Stone Age people may have voyaged the Mediterranean:

A decade ago, when excavators claimed to have found stone tools on the Greek island of Crete dating back at least 130,000 years, other archaeologists were stunned—and skeptical. But since then, at that site and others, researchers have quietly built up a convincing case for Stone Age seafarers—and for the even more remarkable possibility that they were Neandertals, the extinct cousins of modern humans.

…

But a growing inventory of stone tools and the occasional bone scattered across Eurasia tells a radically different story. (Wooden boats and paddles don’t typically survive the ages.) Early members of the human family such as Homo erectus are now known to have crossed several kilometers of deep water more than a million years ago in Indonesia, to islands such as Flores and Sulawesi. Modern humans braved treacherous waters to reach Australia by 65,000 years ago. But in both cases, some archaeologists say early seafarers might have embarked by accident, perhaps swept out to sea by tsunamis.

The effective population size of Australian people is just too large for me to imagine that it was only a few individuals swept out on driftwood. There was some sort of sea-going craft which mediated migration to Sahul from Sundaland. Just because we have only recent evidence of sea-going craft doesn’t mean that they weren’t around for tens of thousands of years before that.

I’ve been hearing about Neanderthal tools on islands like Crete, which were never connected with the European mainland, for a while now. It seems that people are finally convinced that this is the real deal, as the stratigraphy came together to confirm dates. One thing that seems obvious from this, as well as Neanderthal “art”, is that the differences between modern humans and Neanderthals were more quantitative than qualitative. Differences of degree, not of kind.

It is hard to deny that modern human expansion between 60 and 15 thousand years ago is sui generis. Hominins didn’t make it to the New World or Sahul, what later became Oceania, until our own kind. There’s also a fair amount of evidence that our lineage pushed the northern frontier of human habitation beyond what Neanderthals ever did. But in the process of marking off our distinctiveness, it seems to me that we’ve overemphasized the differences between us and Neanderthals, and dismissed or ignored evidence of “human-like” “advanced” behaviors from them.

I’ll still go with the prediction that we’ll never find a singular gene which marks us off from other human lineages.

What did modern humans look like during the “Out of Africa” event?

Posted on by Razib Khan


Recently I was having an email exchange with a friend (a prominent public intellectual who is not a scientist), and we were thinking about what “ancestral Africans” looked like. More precisely, the populations which were resident around ~100,000 to ~200,000 years before the present. These are the people who are depicted in paleoanthropology documentaries. Here were some of my major contentions:

1) We don’t know what they looked like
2) They probably were more likely to look like modern Africans than non-Africans
3) But modern Africans are diverse in their looks and we could expect that ancient Africans were too

The neighbor-joining tree above is generated with a naive model of successive bifurcation.

1) Khoisan split off 200,000 years ago
2) Mbuti split off 150,000 years ago
3) Mende split off 100,000 years ago
4) Japanese about 50,000 years ago
5) While Pathan and Basque only 15,000 years ago

The model is wrong in the details. Pathan and Basque have some ancestry is which recently diverged, and much that is deeply diverged. The 15,000 year value is just an average. Similarly, the Khoisan have some Eurasian ancestry. But in the broad sketch it illustrates that some African populations diverged a very long time ago from other groups.

Ancient Africans date to ~200,000 years before the present for all the modern populations. Khoisan to Japanese. You could probably use phylogenetic character reconstruction methods to attempt to infer what ancient Africans looked like…but I’m not sure that it would be useful since modern humans have spread over so many ecologies over such a short span of time.

Outside of Sub-Saharan Africa perhaps on the order of 95% of the ancestry derives from an expansion from a small founder group between 60 and 80 thousand years ago. Removing the “Basal Eurasian” component, groups as diverse as Native Americans, Oceanians and East Asians probably derive their ancestry from a common group which flourished between 50 and 60 thousand years ago (this pulse is the majority of the ancestry of Europeans and South and West Asians as well).

The point here is to illustrate that 50,000 years is definitely sufficient for a great deal of diversity to have emerged in human physical variation. And yet the Khoisan are ~200,000 years diverged from their ancestors within Africa. We actually know that indigenous southern Africans have been selected for lighter pigmentation. We also know that loci associated with pigmentation in modern humans exhibits a lot of variation in Africans, and this variation is likely an ancestral feature of our species.

In sum, the number of generations between ancestral Africans and all modern descendent populations is great enough that I’m not uncertain that we can predict what they look like in anything except their skeletal features. Additionally, most of the history of anatomically modern humans was likely highly structured within Africa. That’s another way of saying that ancient Africans themselves were probably physically diverse.

With all that being said, all things equal ancient Africans probably are more likely to look like modern Africans than modern non-Africans. The main reason is simply that modern Africans occupy the same broad ecological landscape as ancient Africans, and many of our features, from our build to our complexion seem dependent upon environmental pressures. There’s lot of evidence that very light skin is probably a derived characteristic of our species (there are consistent signatures of sweeps around pigmentation loci). And, there is also evidence that some of the archaic introgression into non-Africans may have consequences in our morphology and external physical characteristics. For example, Eurasians seem to have very high frequencies of Neanderthal variants of the keratin gene. This is implicated in hair, skin and nail development.

Addendum: Note that even if we have ancient genomes, polygenic characteristics are still hard to predict. Even today common SNPs only explain a minority of the variation in hair color in Europeans.

Arabia as Africa-across-the-sea

Posted on by Razib Khan

In antiquity ostriches and lions roamed the Syrian desert. The cheetah even still clings to a tenuous existence in the fastness of the central Iranian desert. The point being that the new finding of African modern human remains on the southeast fringe of Arabia ~85,000 years ago shouldn’t be too surprising. Old modern(ish) looking humans date to 73,000 years before the present in Southeast Asia. Modern-like ancestry can be found in eastern (Altai) Neanderthals dating to ~100,000 years ago. And the earliest humans may have arrived in Australia 65,000 years ago.

These dates are important because the genetic results indicate that much of the population divergence of modern Eurasian, Amerindian, and Oceanian peoples dates to the period between 50 to 60 thousand years ago. This was the classic epoch for the emergence of “behavioral modernity,” and the older models of “Out of Africa” which posited a rapid explosive demographic growth after a punctuated speciation even in East Africa ~60,000 years ago.

Today with remains such as Ust’-Ishim man, we can peg the admixture of Neanderthal into modern Eurasians 52,000 and 58,000 years ago. About the same period that the preponderance of the ancestry of modern Eurasians and peoples of Australia and the Americas expanded across the world, as noted above.

Most peoples in Western and Southern Eurasia also have substantial ancestry from another group which doesn’t seem to have much Neanderthal ancestry at all, the “Basal Eurasians” (BEu). This population obtained its name from the fact that it was hypothesized to have diverged from the common ancestors of northern Eurasians (the Pleistocene peoples of Europe and Siberia), eastern Eurasians, the ancestors of the Amerindians, and Oceanians, before these groups moved on and then separated (i.e., proto-Melanesians are closer to Pleistocene European hunter-gatherers than they are to BEu). These facts suggest proto-BEu was a distinct population >60,000 years ago.

The maximum range of Neanderthals

 

Because of the distribution of Neanderthal admixture across so many groups relatively evenly it probably came from a single major admixture event. Geography tells us that the most likely area of this admixture would be somewhere in the northern area of West Asia.

This implies that BEu was probably resident in the southern area of West Asia, and possibly into North Africa. We do not have any samples which are “pure BEu.” Ancient agriculturalist samples from the western Near East and the eastern Near East are high in BEu ~10,000+ years ago, but these populations are still substantially mixed with a population with affinities to Mesolithic Western European hunter-gatherers (WHG). Fu et al. 2016 use a Pleistocene transect to infer that this affinity between Near Easterners and Europeans dates to the period after ~15,000 years before the present. I presume that this late Pleistocene period was when BEu was admixed away as a pure population by an expanding hunter-gatherer culture with a nexus in Southeast Europe and into Anatolia and the trans-Caucasian region.

The recent Arabian find makes sense I think in the context of BEu and other such populations, which had diverged from the Africa metapopulation ~100,000 years ago, but had not pushed further north and east, and so mixed with Neanderthals.

But what about the older modern human remains which are showing up in eastern Eurasia? I think it is entirely likely that these populations left only a little bit of an imprint in modern groups. A paper from a few years back reported having detected such an admixture in Oceanians. The first ancient genome we have from eastern Eurasia >60,000 years ago that is from a modern human will probably yield much more satisfying results.

The big dynamic looming over the likely existence of anatomically modern human range on the edge of Africa in Arabia is that for several hundred thousand years modern humans existed within Africa as a metapopulation. The proto-Out-of-Africa population can only be understood as part of this broader metapopulation. ~100,000 years before the present humans, inclusive of Neanderthals, Denisovans, and modern humans, our species was probably defined by a set of distinct metapopulations. We know that there was gene flow between these metapopulations, but the strong evidence of purifying selection of Neanderthal and Denisovan ancestry in modern human genomes tells us that this gene flow was minimal enough that biological incompatibilities were beginning to build up and the groups were on their way to speciation as defined by the biological species concept.

There is no evidence of this between any modern populations, even the most diverged (e.g., the Khoisan, who carry Eurasian and African agriculturalist genetic material). This means that within the modern human metapopulation gene flow was sufficient to prevent incompatibilities from developing due to isolation. That being said, with the oldest (proto-)modern human skull dating to ~300,000 years, and likely discernible population structure between various African lineages going beyond 200,000 years ago, there are lots of distinct modern human groups with very long histories within Africa and on its periphery.

The earliest point that you could probably say non-African humans diverged from any African (Sub-Saharan) populations is ~100,000 years ago (and this is probably a bit too generous). A conservative estimate would suggest that modern human lineages were emerging within Africa 200,000 to 300,000 years ago. So most of modern humanity’s existence has been within Africa.

The non-African populations descend from a group which underwent a period of reduced population size vis-a-vis all the African groups. But one thing I think is important to remember is that this was probably not exceptional. We know now that over the past 5,000 years African population genetic structure has been reshaped by events such as the Bantu expansion. But there were surely small and marginal groups with low effective population sizes within Africa that either went extinct or were absorbed by other populations.

The difference in the non-African population is that it was on the edge of the modern human range, and likely occupied territory that was relatively isolated from other modern humans due to the dry nature of the Sahara during most of the Pleistocene. This prevented its absorption into more numerous groups of modern humans further south and to the west. And the strong cultural and genetic barriers with the Neanderthals probably limited gene flow as well.

But even in the inclement conditions of North Africa and West Asia for most of the past 100,000 years, modern humans may have had a larger effective population size than archaic Eurasian hominins. And with this larger effective population size, one can imagine that greater cultural creativity and genetic robustness to dynamics such as population declines gave the modern humans a long-term advantage. In this context, the existence of modern human remains in a diverse array of places across warmer areas of Eurasia before 60,000 isn’t that surprising. And, the demographic wave that swallowed Neanderthals and Denisovans probably swallowed the earlier modern humans who ventured into eastern Eurasia before 60,000 years ago!

Who We Are and How We Got Here, a book worth reading

Posted on by Razib Khan

Yesterday I talked to a friend who has a review copy of Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. They gave me a preview (their overall assessment was positive).

I haven’t personally asked to get a copy because, to be honest, I thought there wouldn’t be anything new in it. If you “read the supplements” what more could there be in 368 pages? So I was waiting until the end of the month to buy the book and read it in my own sweet time as due diligence.

Well, this morning I asked a publicist to send me a copy. I will be getting it next week. The reason is that I’m told the latter portions of the book are quite challenging and candid as to what genetics may tell us in the 21st century. Who We Are and How We Got Here is a 21st-century revision and update of The History and Geography of Human Genes. But it’s apparently a lot more.

Also, I make a small cameo in the book, as does Eurogenes and Dienekes. I have always appreciated how the David Reich and Nick Patterson and their whole lab has taken people outside of the halls of the academy seriously. They didn’t need to as a matter of professional necessity but often engage as a matter of decency and seriousness.

Out of Africa to Out of Eden (well, perhaps not yet)

Posted on by Razib Khan

The recent African origins hypothesis for modern humans had several things going for it. First, most of the old fossils that look like modern humans were in Africa. Chris Stringer and others were pushing the African origins of our modern lineage before genetics came to the fore. But of course, you also have DNA. The mtDNA, Y, and autosomal DNA, which tends to show a pattern where Africans are more diverse, and non-Africans are nested within phylogenies of Africans.

In the 2000s the “Out of Africa” model got a little out of control. The stylized narrative was that a small tribe of East Africans developed some genetic mutation that allowed them to exterminate all other human lineages (e.g., language). This is best encapsulated in Richard Klein’s The Dawn of Human Culture. The British science fiction author Stephen Baxter used this idea as a frame in his novel Evolution (the innovation in this novel was religion though). In this view modern humanity was an African saltation, a great leap forward.

We’re at a different point now. The idea of admixture and/or introgression from non-African lineages into African modern humans is widely accepted. Additionally, both genomic inference and paleontology are pushing the roots of modern humanity much further than ~50,000-60,000 years before the present.

So it’s not as surprising to see a paper like this, The earliest modern humans outside Africa:

To date, the earliest modern human fossils found outside of Africa are dated to around 90,000 to 120,000 years ago at the Levantine sites of Skhul and Qafzeh. A maxilla and associated dentition recently discovered at Misliya Cave, Israel, was dated to 177,000 to 194,000 years ago, suggesting that members of the Homo sapiens clade left Africa earlier than previously thought. This finding changes our view on modern human dispersal and is consistent with recent genetic studies, which have posited the possibility of an earlier dispersal of Homo sapiens around 220,000 years ago. The Misliya maxilla is associated with full-fledged Levallois technology in the Levant, suggesting that the emergence of this technology is linked to the appearance of Homo sapiens in the region, as has been documented in Africa.

Now, the reality is that Israel is arguably part of “Greater Africa” biogeographically. So it isn’t that surprising. Or it shouldn’t be.

But, this reinforces the reality that anatomically modern humans were geographically already widespread ~200,000 years ago. I would say that this informs and updates our estimation of the plausibility of the Jebel Irhoud modern humans in Morocco, who flourished ~300,000 years ago. It also makes more sense of the reality that most of the ancestors of the Khoisan likely diverged from other modern lineages ~200,000 years ago (or more, depending on who you talk to). Finally, it makes recent archaeological finds of modern humans or their artifacts in East Asia tens of thousands of years before the great expansion of neo-African humanity50,000-60,000 years before the present much more plausible.

There has been some genetic evidence for modern(ish) human expansion before the 50,000 year date. So this isn’t resting only on paleontological evidence.

Where does this leave us? In The Guardian David Reich observes that ‘It’s important to distinguish between the migration out of Africa that’s being discussed here and the “out-of-Africa” migration that is most commonly discussed when referring to genetic data. This [Misliya] lineage contributed little if anything to present-day people.’

Obviously, this is an important point. But we know that the first modern humans to settle Europe did not leave any descendants either.  The modern human settlement of Europe was still nevertheless important. Second, these early wave humans may have given modern populations adaptive variants that are present at high frequencies in modern lineages.

Finally, there’s the issue that this may reorient our understanding about the demographic origins of human populations. Ever so slightly our priors as to an African genesis for our modern lineage are getting weaker. You have two very old modern fossils on the northwest and northeast fringe of the continent. Ten years back the arguments was between those who argued for an East African origin (most), or a minority who favored a Southern Africa one. Now the whole continent, and perhaps even Arabia, are game.

Ultimately, as always, ancient DNA is going to be the final arbiter.

Neanderthal vs us: for wont of a SNP?

Posted on by Razib Khan

Recently at a human evolution conference in England Svante Paabo (or someone in his group) was alluding to discovering how modern humans and Neanderthals differed by looking at the ~30,000 genetic positions (bases) where modern humans and Neanderthals exhibit fixed differences. That is, Neanderthals and modern humans exhibit totally disjoint frequencies.

I’ve been saying this for years, but I’ll say it again: this is probably a fool’s errand. I do think there are major differences at loci which we know about, such as at FOXP2. But, it isn’t clear that even at FOX2 Neanderthals and modern humans exhibited complete lineage sorting. That is, there’s evidence that the Altai Neanderthal had introgression from modern (or modern-related) human populations, and that those variants were sweeping. And there is still variation in modern human populations at FOXP2.

All Homo exhibit encephalization, credit Luke Jostins

It looks like Soft Sweeps Are the Dominant Mode of Adaptation in the Human Genome (also see Detecting polygenic adaptation in admixture graphs). But it may be that soft selections and recurring gene flow are common features of the broader Homo lineage for several million years.

In other words, looking for silver bullet variants which can explain why we are so special may always fail, because there are no silver bullets (for several years at ASHG I note that there were presentations which attempted to determine the locus of humanity by looking at the loci of functional interest where Neanderthals and modern humans differed). Rather, human exceptionalism is no exceptionalism, and human populations explore a wide space of phenotypes defined by a huge range of allelic variance which spans many of our extant lineages.