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If you care about human evolution, keep an eye out for reports on what happened in South Africa a few years ago. A massive cache of bones was discovered. I’ve been privy to a few preliminary findings, and the implications are explosive, revolutionary, all the hyperbolic language that I tend to avoid. This is a big deal, not just because of the results, but also because of the possibility that this will be an inflection point in how paleoanthropology is done. That is, rather than hoarding fossils the “sharing economy” of science will make itself felt within the individualistic and proprietary domain of the fossil hunters.

If I did the timing right the announcement should drop in a little over a day from when I post this. Keep track of Lee Berger and John Hawks’ Twitter.

 
• Category: Science • Tags: Paleoanthropology 
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First Peoples: Europe came and went. I watched it. In case you didn’t see it there was a big reveal: archaeologists in France have uncovered a site where modern humans were producing arrowheads 50,000 years ago. This is strange for two reasons. First, what were modern humans doing with bows and arrows 50,000 years ago? They emerged in the Paleolithic transition to the Mesolithic, spreading from the Old World to the New. That is, they become common over the last 10,000 years. I don’t recall the narrator addressing this issue at all. But let’s set that to the side: if these finds are associated with modern humans then that pushes their arrival to Western Europe 10,000 years further back. Despite all the arguments about dating the presence and disappearance of Neanderthals from Europe, no one presumes that they went extinct 50,000 years ago. That implies that groups of moderns interposed themselves into Neanderthal dominated Europe in some fashion for thousands of years, until finally the Aurignacian culture arrived and replaced Neanderthals in toto.

At the site in question specifically the researchers have uncovered evidence that moderns and Neanderthals used the same location only a few months apart. But we need to remember modern humans weren’t modern yet, they were just one of the many hominin lineages which have flourished over the past 2 million years. With hindsight we can see that these initial forays were to prefigure what was to come, but at the time the two groups were not quite that different in technology and guaranteed destiny. Modern humans did not have any great advantage, so they may have come and gone depending on the circumstances.

51It8A+EKrL._SY344_BO1,204,203,200_ Perhaps the 50,000 year old moderns in France may be likened to the Norse in Newfoundland. And in fact the analogy to the European settlement of North America, and the replacement of Neanderthals by moderns, is made in First Peoples. But the devil is in the details, as the documentary is somewhat schizophrenic about the specific dynamic until the very end. The two extreme stylized models are “make war” vs. “make love.” With the very clear evidence that modern humans admixed with Neanderthals, the narrative arc of the documentary flips from one where moderns are depicted attacking a Neanderthal camp, to one where a modern human lothario engages in “inappropriate touching” with a Neanderthal female. Though I suppose this was 40,000 years before “affirmative consent” norms, so perhaps we should cut them some slack?

In any case, going back to the analogy with the New World I think we can acknowledge that there were complex scenarios left on the cutting room floor of a one hour documentary. The mestizo population of the New World arose through a variety of means, ranging from love all the way to rape. If modern humans 40,000 years ago were anything like modern humans today, then it seems likely that their interactions would run the gamut from trade and amicable relations, to extermination, with many permutations and positions between these two. We need pick one model as the story.

At the end of it all First Peoples: Europe tells the viewer that Neanderthals were demographically swamped out, rather than killed en masse (there weren’t enough for them to be a mass anyway!). This is an idea that’s been around for a while. With very small populations the idea is that a crest of demographic expansion out of Africa just swallowed up the Eurasian hominins. We literally mated them out of existence. John Hawks elaborates this model at length when he has screen time, which makes sense as he’s been suggesting that large effective population sizes within Africa over the Pleistocene might naturally result in the “out of Africa” pulses we see in the genetic record.

Finally, this episode does now make it crystal clear to me why the original admixture event of Neanderthals with modern humans in the Middle East left its imprint on modern Europeans, and later ones did not. Modern Europeans, whether their ancestry is “hunter-gatherer” or “farmer” descend from a Pleistocene Middle Eastern/Central Asian population in totality, and so only experienced that singular admixture event with Neanderthal Middle Easterners. More concretely, the Mesolithic populations which were overwhelmed and assimilated by farmers during the Neolithic in Europe were themselves descended from peoples who had issued out of the Middle East or Central Asia to replace the first modern Europeans. The Aurignacians (or if later, Solutreans) replaced probably had somewhat higher fractions of Neanderthal ancestry, being further out on the “wave of advance.” But since they left no descendants, to a first approximation there’s no signal of a Neanderthal cline.

The past 50,000 years have been characterized by two phenomena: extinction and admixture. The rest is commentary.

 
• Category: Science • Tags: Paleoanthropology 
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Citation: Racimo, Fernando, et al. "Evidence for archaic adaptive introgression in humans." Nature Reviews Genetics 16.6 (2015): 359-371.

Citation: Racimo, Fernando, et al. “Evidence for archaic adaptive introgression in humans.” Nature Reviews Genetics 16.6 (2015): 359-371.

41ePHetk1dL._SY344_BO1,204,203,200_Nature published a paper recently, New species from Ethiopia further expands Middle Pliocene hominin diversity, which seems to complicate the deep history of the hominin lineage. More precisely, it gets curiouser and curiouser, as the number of human(ish) groups proliferates. Honestly I don’t know well this will hold up, a lot of science seems to fade out. Remember the article in Science, A New Kind of Ancestor: Ardipithecus Unveiled? I’m not totally clear on whether the controversy about this find has resolved. At least we’re at the stage where most people seem to accept that Homo floresiensis was a true hominin lineage, rather than a pathology. (by the way, Carl Zimmer has a good write up on the most recent addition to the human family tree)

Genes are something that is more concrete to me. Nature Reviews Genetics has two pieces of interest in this domain. First, Evidence for archaic adaptive introgression in humans. A close reader of this weblog will find little of surprise; the authors do an excellent job of reducing down the key results of the past five years or so that have issued from the discovery that the ancient whole genome of the Neandertal bears all the hallmarks of having been carried over into some lineages of modern humans. In particular, the authors focus on adaptive alleles and regions through a statistical genomic lens. Second, Svante Paabo has a comment in the same edition, The diverse origins of the human gene pool (ungated), which leans heavily on the previous piece.

51r8Ph-vcaL._SY344_BO1,204,203,200_ Paabo to me seems to finally put to bed some old conflicts which have been roiling the field of paleoanthropogy for decades. I think we’re going to finally see the abating of the rhetorical war between those who promote “Out of Africa” vs. “Multi-regionalism.” The fact is in some ways both viewpoints are worth taking into account. As Paabo, and others, have noted, the former model turns out to likely be correct about the provenance of most recent human ancestry. It is mostly derived from an African or near-to-African (e.g., in the Middle East) population on the time scale of ~100,000 years. But, the latter model’s emphasis on regional evolution and adaptation and gene flow across a meta-population system is also a critical insight in understanding the dynamics of how modern humans came to be.

I do like the fact that Paabo also seems to moving past the idea that genomics will yield the one allele or set of alleles that define what made modern humans so biologically special. I don’t have an opposition to biology as being determinative in our cultural flexibility. But, if anything has been clear in what genomics is telling us about recent human evolutionary history, it’s that it is rather more complicated than we might have imagined. I doubt the uniqueness of the surviving lineage of hominins is going to be any more, or less, subtle in the difficulties of resolution.

I do have one bone to pick with Paabo. He states that:

Adaptation through the acquisition of new mutations is generally a slow process: it is rare for favourable alleles to appear, and these are often lost by chance when they first occur in a single individual or in very few individuals. By contrast, if favourable alleles have emerged in one group, they can spread to other groups relatively rapidly by gene flow. This process, called ‘adaptive introgression’, is well documented in bacteria and plants, and described in some cases in animals but it has not previously been considered an important factor in human adaptation.

The idea of “adaptive introgession” has been something I’ve been thinking about, and talking about, in relation to human evolution since 2006 (Google it). That’s because of the focus that Greg Cochran, Henry Harpending, and John Hawks, put on the topic (all these years later I am also professionally interested in this topic, but that’s for a later post!). Now, it is true that Svante Paabo does not seem to have thought of the issue in much detail. His book Neanderthal Man has no references to “adaptive introgression” according to Google Books. In contrast, 10,000 Year Explosion has 9 mentions of the term.

introgress I will note that the authors of the review paper that Paabo leans on heavily for his comment don’t make this omission where credit is due. They cite both Greg Cochran and John Hawks, with a special laudatory note.

Finally, I want to suggest that to a great extent, Multi-regionalists excepted, the previous consensus in human evolutionary studies tended to overestimate the extinction rate of “archaic” lineages. But, it also underestimated the extinction rate of modern lineages. That is, archaic lineages rooted outside of Africa before ~100,000 years ago may play more of a role in the evolution of our modern lineage than we may have guessed when it comes to both genotype and phenotype. Paabo quotes the standard figures of a few percent for Neandertal ancestry, and ~5 percent of Denisovan among Oceanians. From all I have heard and know this seems about right, but I do wonder if this is actually just a floor. Without ancient genomes I suspect we’d still be debating the possibility of archaic admixture from inferences which only statistical genomicists would have a good grasp of. In 2006 Jeff Wall and Michael Hammer stated that “Neanderthals and an as yet unidentified archaic African population contributed to at least 5% of the modern European and West African gene pools.” They were basically dead right. Second, the ancient DNA is also yielding the conclusion that many local populations which flourished during the Pleistocene outside of Africa seem not have to left much genetic legacy today in the same regions. We’ll get more clarity on the topology of the human phylogeny in the near future, but it strikes me that it’ll exhibit features which are somewhat at variance with what we’d have expected 10 years ago.

 
• Category: Science • Tags: Paleoanthropology 
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Phylogenetic tree of mtDNA lineages, with 40 K B.P Aurignacian "Fumane 2"

Phylogenetic tree of mtDNA lineages, with 40 K B.P Aurignacian “Fumane 2″


220px-Cro-Magnon A new paper in Science, The makers of the Protoaurignacian and implications for Neandertal extinction, seems to establish definitively that the Aurignacian culture, often identified as the first modern human society within Europe, was in fact of modern humans. The part that is of interest to me is the DNA evidence from this paper. In particular, they got a good quality mtDNA sequence, and put it on a phylogenetic tree with other humans. As you can see, it is clearly within the clade of modern humans, and in particular non-African modern humans. More precisely, this individual is a basal branch of haplogroup R, which is common across western Eurasia, and ancestral to many common lineages. The fact that it’s basal isn’t too surprising, this individual is ~40,000 years in the past. Because of the rapid turnover of mtDNA lineages it isn’t surprising if past lineages have gone extinct in a given region, even if total genome content is passed down.

But, I do want to enter into the record that in concert with rumors I’ve been hearing as well as the broad picture of what ancient DNA is telling us about genetic turnover that I doubt that modern Europeans in any way descend from the Cro-Magnon populations of the first settlement of the continent by moderns. Rather, I’d bet that the “hunter-gatherer” ancestry of the Europeans of today goes no further back than the post-Gravettian cultures, and perhaps later. The genetic makeup of ancient populations seems to have been more complex than we’d have imagined, and there were meta-population dynamics which we’re only getting a good grasp of. With low population densities and a fragmented Pleistocene landscape it strikes me as plausible that Palearctic mammals in particular may be characterized by repeated resettlement of the frontier of the range from core source populations after local extinctions and retrenchments.

 
• Category: Science • Tags: Paleoanthropology 
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The_Clan_of_the_Cave_Bear_cover By now you have heard of the recent ancient DNA finding dating from ~40,000 years ago in Southeastern Europe. The individual is a representative of one of the first anatomically modern groups to arrive in Europe…sort of. It exhibits robust characteristics, and may have had some admixture from Neandertals. Now, thanks to ancient DNA, that’s confirmed:

Qiaomei Fu, a palaeogenomicist at Harvard Medical School in Boston, Massachusetts, told the meeting how she and her colleagues had sequenced DNA from a 40,000-year-old jawbone that represents some of the earliest modern-human remains in Europe. They estimate that 5–11% of the bone’s genome is Neanderthal, including large chunks of several chromosomes. (The genetic analysis also shows that the individual was a man). By analysing how lengths of DNA inherited from any one ancestor shorten with each generation, the team estimated that the man had a Neanderthal ancestor in the previous 4–6 generations. (The researchers declined to comment on the work because it has not yet been published in a journal).

Two major points. First, the admixture fraction is way higher than any modern population. This isn’t a fluke. Second, they must be seeing ancestry tract lengths to make this inference. Basically the Neandertal ancestry blocks have been chopped up, but only a finite number of times. This really one-ups talk of “Cherokee great-grandmothers”, that’s for sure.

So what about the earlier results that most of the admixture must have happened in the Middle East? There have been revisions to this model, with many researchers now suggesting that a second pulse might have occurred in eastern Eurasia. But, another possibility is that very little of the ancestry of the first modern Europeans remains in modern Europeans. That is, the later Paleolithic populations of Europe may have replaced the first settlers, just as they in their turn were replaced or assimilated. The landscape of Mesolithic/Neolithic Europe seems demographically complex, so I see no reason not to suspect that the same was the case for the period before the Last Glacial Maximum. There may have been several admixture events with Neandertals, but the “outriders” may have been left no traces in the modern human lineages. It may be that the human “phylogenetic bush” has been extremely pruned many times over, so that most “fossil ancestors” are simply dead ends.

Addendum: As usual, great piece in Nature too.

 
• Category: Science • Tags: Paleoanthropology 
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Credit: Luke Jostins

Credit: Luke Jostins

Human lineages as a whole have been tending toward increased cranial capacity over the past 2 million years, including the one that led to modern people. That is the finding of Luke Jostins several years back when he crunched the paleoanthropological data. This is one major knock at our specialness as humans, since it seems our cousins were progressing through the same stages of development as our own ancestors, before they were swept away by and large. A new paper in Nature reports that H. erectus engaged in more cleverness than we had expected, Homo erectus at Trinil in Java used shells for tool production and engraving. John Hawks has already commented on it so I won’t offer my two cents, as they aren’t worth much. But, it does suggest that we’ve underestimated “early humans.” John points out that many ancient finds might be reinterpreted with a different set of expectations.

On a related note, a new paper attempted to find evidence for classic selective sweeps in our lineage comparison to the Neandertal and Denisovan populations, something feasible because of the existence of high quality ancient genomes. Let me quote from the abstract:

… We tested sites at which humans are fixed for the derived (i.e., nonchimpanzee allele) whereas the Neanderthal and Denisovan genomes are homozygous for the ancestral allele. We observe only weak differences in statistics indicative of selection between functional categories. When we compare patterns of scaled diversity or use our ABC approach, we fail to find a significant difference in signals of classic selective sweeps between regions surrounding nonsynonymous and synonymous changes, but we detect a slight enrichment for reduced scaled diversity around splice site changes. We also present a list of candidate sites that show high probability of having undergone a classic sweep in the modern human lineage since the split from Neanderthals and Denisovans.

As the heirs of the snottily termed “anatomically modern” humans it is hard for us to not think that we came and conquered due to some glittering genetic mutation. The lack of pervasive classic sweeps since the divergence of “us from them” confirms that evolution didn’t go into magical overdrive in our lineage. We are not “more derived” on the Great Chain of Being with chimpanzees as a reference, but simply different. The laundry list of candidate sites will be interesting, but must always be interpreted cautiously. These sorts of results dovetail nicely with the reality that the behavioral chasm between “archaic” and anatomically modern humans until about ~50,000 years ago wasn’t that large at all. Though changes in the fossil and archaeological record can seem punctuated and is discontinuous, I wouldn’t bet against the possibility that genomics points to a dynamic where change between the lineages was driven by gradual evolution via selection on standing variation.

Finally, there’s a recent paper on the nasal anatomy of Neandertals which made some media headlines recently. The most sensational conclusion drawn from nasal architecture is that Neandertals were a separate species from us. As I don’t know much about anatomy, and I don’t care much about species status, this isn’t something I’ll explore beyond just reporting that. But, another aspect is the fact that it seems the morphology of Neandertals has often been compared to modern humans, and judged by modern human standards. It seems entirely likely that Neandertals had different adaptations and an alternative morphological trajectory from our own lineage. Though I don’t think they were as different as some scholars would like to think, we need to be cautious about turning them into a version of ourselves, or at least our Out of Africa selves. The hominin lineage contains multitudes, and we are but one.

 
• Category: Science • Tags: Paleoanthropology 
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Lascaux2One elegant model of the origin of modern humans as we understand them is that we exploded upon the hominin scene, and swept all before us with our suite of cultural creativity. This is the “Great Leap Forward” thesis, supported by the sudden appearance of symbolic expression in European ~40 thousand years ago. In this telling our “archaic” cousins were pre-humans at best, evolutionary dead ends. The archaeology in this case dovetailed with an extreme interpretation of the “Out of Africa” thesis, whereby H. sapiens sapiens issues fully formed in all its glory, and unleashes a demographic supernova on its cousins. Richard Klein’s The Dawn of Human Culture encapsulates this view in totality.

This model had many upsides. One of them was simplicity. Another is that our mental image of ourselves as sui generis, made in the imagine of the gods themselves, is suitably flattered. Unfortunately it seems entirely the case now that this model is wrong. The New York Times reports on the discovery of haunting symbolic expression on the island of Sulawesi, Cave Paintings in Indonesia May Be Among the Oldest Known:

A team of researchers reported in the journal Nature on Wednesday that paintings of hands and animals in seven limestone caves on the Indonesian island of Sulawesi may be as old as the earliest European cave art.

09cave-master1050 The paper in Nature is Pleistocene cave art from Sulawesi, Indonesia. Note that these findings are in Wallacea. Modern humans were certainly there around this time, though it is likely that there were also other lineages, such as H. floresiensis around. What all this is telling us is that we don’t know as much about the past as we think we did, and, that it was complex and multi-faceted.

 
• Category: Science • Tags: Great Leap Forward, Paleoanthropology 
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330px-Homo_sapiens_neanderthalensis Sometimes context is important when processing new information. Something huge is afoot in paleoanthropology, traditionally the study of ancient humanity predicated on analyzing morphological remains. Fossils. Though a fascinating discipline, unfortunately there’s always been an issue of supply and demand. There isn’t much supply of fossils, and there’s a lot of demand to analyze them. This means that monopoly power comes into play, as who has the fossils matters a great deal, not necessarily who has the great ideas. Some researchers have been known to sit on remains for decades. Access to particular field sites is also a precious commodity, and doled out to favorites and allies. Contrast this with the situation in modern genomics, as the swell of data is overwhelming the ability of researchers to analyze it (at least analyze it well!). Of course all of science is a human endeavor, and as such is subject to the whims of political and personal machination. But when the potential fame and glory is enormous, but resources few and far between, as is the case in paleoanthropology, the behind the scenes trench warfare can become quite brutal.

This is why what Lee Berger is doing is such a big deal. Last fall he quickly assembled a team funded by National Geographic to retrieve samples from an exceedingly rich site he happened to stumble upon. Dubbed the Rising Star Expedition the dig yielded ~1,200 remains, many of very high quality. Let that sink in. In a field where a few partial remains can reshape our whole understanding of the past, Berger is sitting on a sample size of over 1,000, many of quite high quality. But he’s not hoarding his find. Rather, he’s aiming to change the terms of how the game is played, and inviting researchers from all over the world to join him in a workshop to collaboratively analyze the results. Here’s the details of what’s going down from National Geographic:

The University of the Witwatersrand, through the Centre of Excellence in PalaeoSciences and the Evolutionary Studies Institute will be holding a unique workshop to study and describe recently discovered fossil early hominin material for a series of high impact publications. It is intended that the Workshop will be held in South Africa from early May until the first week of June 2014.

Output will include authorship on at least one high impact paper as well as continued collaboration and authorship on future research to which he/she contributes. Interested applicants should submit their CV’s, a brief summary of their skills or data sets that would be applicable to such a project (not to exceed 1500 words), and provide three letters of support from established scientists in the field.

Applications should be sent directly to Professor Lee R. Berger at risingstarworkshop@gmail.com and copied to his assistant Wilma.Lawrence@wits.ac.za. Please make the subject line “Rising Star Workshop 2014”.

So far it looks as if the information coming out is focusing on the raw numbers of fossils. This alone going to revolutionize the field. Berger is already an eminent paleoanthropologist, but by this act he has induced a professional inflection point. Things will never be the same. But it is also the case that the scientific yield is going to change the way in which we view the origin and evolution of hominins. I guarantee that. Some of the facts to come are going to blow your mind (and no, I don’t have an inspirational video to go along with that assertion).

 
• Category: Science • Tags: Paleoanthropology 
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250px-Caveman_1 By now you may have heard that mitochondrial DNA, passed down the female lineage, has been extracted from a ~400,000 year old human fossil from Spain. If you haven’t heard, I recommend Ewen Callaway and Carl Zimmer’s takes. The paper is at Nature, so gated, A mitochondrial genome sequence of a hominin from Sima de los Huesos. The big surprise is that these proto-Neandertals carry a mtDNA lineage which is closer to that of the Siberian Denisovans than that of later Neandertals. That’s the specific finding, and if you read the reaction it is rather clear that this is confusing researchers who work in this area. But take a step back, imagine what a world without ancient DNA would be like. Yes, the broad conjectures would be supported (e.g., Out of Africa), but many specific details would be off. So praise the data! Sometimes complexity is closer to the truth, and this is one of those cases. These are good problems to have.

Neander In the primary figure of the paper you can see that these humans are closest on the mtDNA phylogenetic tree to the Denisovans. But, it is important to note that they’re also hundreds of thousands of years older than any other ancient human DNA. Because mtDNA is only passed down through females it tends to be more strongly subject to genetic drift, which might turn over lineages rather rapidly. It is not that unlikely that over hundreds of thousands of years some populations would lose ancestral mtDNA lines. This is what occurred with “mitochondrial Eve.” She wasn’t the only female alive in Africa at the time, but all the other direct maternal lineages went extinct. There are ‘ghost branches’ within the tree which terminated. All you see are the lines of descent back up to the single last common ancestor on the mitochondrial lineage. This doesn’t mean that the ancestry of these women who did not contribute mtDNA disappeared. It is just that their lines of descent may have passed through sons at a given point (my maternal grandmother’s specific mtDNA almost went extinct, she had six son and one daughter). And of course there are other explanations for this pattern, highlighted in the articles linked. Gene flow between lineages, or from a different lineage altogether. We have to remember that the mtDNA of the Denisovan human was more diverged from Neandertals than the whole genome was later found to be, perhaps indicating complex admixture scenarios. The mtDNA tree falsifies, but I do not think it allows us to draw any robust conclusions.

These results are going to get updated in the next year or so with autosomal DNA from the rest of the genome. Even if they can’t get the whole genome sequenced, even a few tens of thousands of markers should be sufficient to clarify issues. Though all of these findings need to be interpreted cautiously in light of the fact that this is a very old lineage, perhaps closer to the time period of diversification for many Eurasian ‘archaic’ H. sapiens than we may have thought.

 
• Category: Science • Tags: Denisovan, Neandertal, Paleoanthropology 
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The BBC has a news report up gathering reactions to a new PLoS ONE paper, The Later Stone Age Calvaria from Iwo Eleru, Nigeria: Morphology and Chronology. This paper reports on remains found in Nigeria which date to ~13,000 years B.P. that exhibit a very archaic morphology. In other words, they may not be anatomically modern humans. A few years ago this would have been laughed out of the room, but science moves. Here is Chris Stringer in the BBC piece:

“[The skull] has got a much more primitive appearance, even though it is only 13,000 years old,” said Chris Stringer, from London’s Natural History Museum, who was part of the team of researchers.

“This suggests that human evolution in Africa was more complex… the transition to modern humans was not a straight transition and then a cut off.”

Prof Stringer thinks that ancient humans did not die away once they had given rise to modern humans.

They may have continued to live alongside their descendants in Africa, perhaps exchanging genes with them, until more recently than had been thought.


In the broad outlines most people still seem to hold that within the last ~100,000 years there was a major demographic pulse which swept out of Africa and populated the rest of the world. Something special did happen. Oceania and the New World were settled by the descendants of anatomically modern humans, whom we can trace back to Africa. The key modifications to the old model seem to be two-fold:

1) The possibility of admixture with other lineages on the way out

2) The sublocalization of the “Out of Africa” scenario, and further admixture with lineages within Africa

There have long been debates about an East or South Africa ur-heimat for the first anatomically modern humans. Others are now even positing a North African origin! To a great extent I wonder if a West or Central African origin is forgone in part due to the paucity of fossil remains entailed by the unfavorable conditions for preservation.

However the details shake out the story seems to be getting more, not less, complicated. This makes for less pithy one liners for the media, but also more work for scientists. Figuring out stuff can be fun!

(Republished from Discover/GNXP by permission of author or representative)
 
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ResearchBlogging.orgThe Pith: We are now moving from the human genome project, to the human genome s project. As more and more full genomes of various populations come online new methods will arise to take advantage of the surfeit of data. In this paper the authors crunch through the genomes of half a dozen individuals to make sweeping inferences about the history of the human species over the past few hundred thousand years.

Since the integration of evolution and genetics in the early years of the 20th century there have been several revolutions in our ability to perceive the underlying variation which is the raw material and result of evolutionary genetics. The understanding that DNA was the concrete substrate of Mendelian genetics, and the rise to prominence of molecular genetic techniques in understanding evolution the 1970s and 1980s, was one key transition. No longer were geneticists simply tracking the coat colors of mice or the visible mutations of fruit flies. In the 1990s the uniparental loci, the maternal and paternal lineages as inferred from the mtDNA and Y chromosomes, came into their own. Finally, the 2000s saw the post-genomic era, and researchers routinely began analyzing data sets of hundreds of thousands of single nucelotide polymorphisms (SNPs), genetic variants, in hundreds of individuals.

In this decade some of the promise of the Human Genomic Project will finally ripen, in that whole genomes are going to be used more and more in analyses. This is exciting, but there are some obvious issues. The human genome has ~3 billion base pairs, vs. the 1 million or less you might manipulate per individual in data sets focused on SNPs. There are some things for which a human genome is overkill. You don’t need a full genomic sequence to ascertain your identity as a member of a particular geographic race. Not only can visual inspection usually suffice to reassure you as to your background, but depending on the scale of granularity you want a random SNP set on the order of ~10,000 should suffice, or as few as 25 ancestrally informative markers! But, if you want to ascertain mutation rates within families will precious and confidence, you do need the full genome.


A new paper in Nature illustrates the possibilities of looking at the whole genome, instead of simply a variant subset. In it, the authors show the power of using only a few individuals’ whole genomes to derive insights about broader population histories. That’s because with a whole genome you obviously are maximizing the amount of data you’re getting in terms of raw sequence, and there’s no need for approximations.

Inference of human population history from individual whole-genome sequences:

The history of human population size is important for understanding human evolution. Various studies…have found evidence for a founder event (bottleneck) in East Asian and European populations, associated with the human dispersal out-of-Africa event around 60 thousand years (kyr) ago. However, these studies have had to assume simplified demographic models with few parameters, and they do not provide a precise date for the start and stop times of the bottleneck. Here, with fewer assumptions on population size changes, we present a more detailed history of human population sizes between approximately ten thousand and a million years ago, using the pairwise sequentially Markovian coalescent model applied to the complete diploid genome sequences of a Chinese male (YH)…a Korean male (SJK)…three European individuals…and two Yoruba male...We infer that European and Chinese populations had very similar population-size histories before 10–20 kyr ago. Both populations experienced a severe bottleneck 10–60 kyr ago, whereas African populations experienced a milder bottleneck from which they recovered earlier. All three populations have an elevated effective population size between 60 and 250 kyr ago, possibly due to population substructure…We also infer that the differentiation of genetically modern humans may have started as early as 100–120 kyr ago…but considerable genetic exchanges may still have occurred until 20–40 kyr ago.

The results of the paper itself are not earth-shattering. It’s really just a test-run of a series of methods which will probably become widespread if they turn out to be more useful than the alternatives. We’ve long seen a pattern in the genetic data of a relatively larger long term African population, and a bottleneck with non-Africans.

In terms of method, first they seem to have focused on patterns of genetic variation on the intra-locus dimension. By this, I mean that they had diploid whole genomes, as every gene necessarily comes in two copies except on the sex chromosomes, and they analyzed the patterns of variation of heterozygosity (two different variants of the gene) or homozygosity (same variant of the gene). These patterns would be distributed across the genome, on the inter-locus dimension, differentiated by recombination events which chop apart the patterns across the genome by mixing and matching chromosomal segments. Recombination events occur steadily across time, so the nature of the patterns can allow one to infer recombination events, the magnitude of which can then lead one to to the time of the last common ancestor of two segments.

As I note, qualitatively they replicated what has long been known, but the authors claim that their model allows for more precise quantitative inferences with fewer parameters. The parameters free to vary in their model were the mutation rate, the recombination rate, and ancestral population sizes. With their assumptions in hand they generated the following figure panel which shows the effective population size inferred from genomes as a function of time:

Moving to the left you come closer to the present, while to the right you move further into the past. Because of the reliance on recombination rates the authors admit that their method lacks power <20,000 years before the present, and > 3 million years before the present. In the former case there are too few recombination events, and in the latter case I assume that the events saturate the genome (they also note that deep balancing selection could generate artifacts). The authors validated their method by simulating genomes, but the results are obviously correct to a first approximation from what we know in other disciplines. You have a major Eurasian bottleneck, and a less severe bottleneck for Africans. Then the bounce back after the Last Glacial Maximum.

The second chart is more complicated, but the take away is that it is from this that the authors inferred that there must have been admixture between the ancestors of West Africans and Eurasians ~20-40, thousand years ago. More intelligibly the authors noted that the X chromosomes of the Korean and African individuals did not diverge nearly as much as they should, in that regions with last common ancestry in the ~20-40,000 year interval were far more numerous in their data than simulated results would imply using a model of total separation 60,000 years ago.

Let’s jump straight to the discussion:

The time frame proposed above for continued genetic exchange between Africans and non-Africans is more recent than the archaeologically documented time of the out-of-Africa dispersal, because there are modern human fossils in both Europe and Australasia that date to >40 kyr ago…Further analysis of additional non-African genomes indicates that this genetic exchange occurred primarily before the separation of Europeans and East Asians…An important caveat to this conclusion is the uncertainty of the per-year mutation rate of 1.0 × 10−9 (2.5 × 10−8/25). Although this mutation rate agrees well with the rates estimated between primates averaged over millions of years…generation intervals as high as 29 years per generation over the last few thousand years23, and present mutation rates lower than 2.5 × 10−8 per generation…are possible in principle. These factors could make our recent date estimates too recent, although it seems unlikely that such inaccuracies would be consistent with a date of final genetic exchange as far back as 60 kyr ago….

If I was a journalist I would probably put this into the “developing….” bin, as there may be revisions to the human mutation rate, as they acknowledge above. In fact I have to wonder if a reviewer prodded them to add that caveat to the paper, though I am also rather sure that many of the authors are quite aware of some of the discussions as to the exact value of this parameter.

My own position as to the details of mutation rates and their implications for modern human origins are inchoate. But, let’s assume that we push back the last common ancestry estimates by a factor of 1.5-2. This may explain Eurasian-African admixture easily, if we presume that the ancestral proto-Eurasians were a liminal African population, which was in position to interbreed with both Africans proper and Neandertals because of their geographically equidistant position. Of course one thing that jumps out at me is that many of these arguments would be resolved if we sequenced a full blooded Australian Aborigines. If this population is descended from the humans who arrived 40-50,000 years ago, then we can test whether the African admixture occurred 20-40,000 years before the present. If the Aborigine shows signs of admixture, then we have to be open to moving the time back to a period when the Aborigines were resident on the Eurasian mainland. Another possibility of course is that the Aborigines we deem indigenous today are actually late arrivals, on the order of ~20-40,000 years, replacing the original humans who arrived ~40-50,000 years ago.

I suspect many of these questions will be answered with larger data sets in the near future. The utility of methods such as the one above will increase once we fine tune some of the parameters. Interesting times.

Citation: Heng Li, & Richard Durbin (2011). Inference of human population history from individual whole-genome sequences Nature : 10.1038/nature10231

(Republished from Discover/GNXP by permission of author or representative)
 
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The media is reporting rather breathlessly a new find out of Arabia which seems to push much further back the presence of anatomically modern humans in this region (more accurately, the archaeology was so sparse that assessments of human habitation seem to have been made in a vacuum due to absence of evidence). Here is the major objection:

This idea is at odds with a proposal advanced by Richard Klein, a paleoanthropologist at Stanford University, that the emergence of some social or behavioral advantage — like the perfection of the faculty for language — was required for modern humans to overcome the surrounding human groups. Some kind of barrier had to be surmounted, it seems, or modern humans could have walked out of Africa 200,000 years ago.

Dr. Klein said that the Uerpmann team’s case for an earlier out-of-Africa expansion was “provocative, but in the absence of human remains, it’s not compelling.

The stone tools of this era are all much alike, and it is hard to tell whether early modern humans or Neanderthals made them. At the sites of Skhul and Qafzeh in what is now Israel, early modern humans were present around 100,000 years ago and Neanderthals at 60,000 years, but archaeologists cannot distinguish their stone tools, Dr. Klein said.

A warmer and wetter climate around this time let modern humans get as far as Israel but apparently no farther, and the new findings from Jebel Faya could represent a second limited excursion. But in this case, it is Africa that is expanding, or at least the African ecological zone, and not modern humans, Dr. Klein said. “The key issue is whether this is an early out-of-Africa movement, but if so, it was far more limited than the modern human expansion to Eurasia roughly 45,000 years ago,” he said.


Image credit: Maathias Kabel

In The Dawn of Human Culture Richard Klein argued that modern humans as we understand them today, protean and highly cultural creatures, are a product of a biological change which reordered our cognitive faculties. Klein pinpoints this change to the “Great Leap Forward” ~50,000 years ago. But, there is a large gap in time between anatomically modern humans, who were resident in Africa nearly ~200,000 years ago, and behaviorally modern humans, who engage in the symbolic cultural production which we perceive to be the hallmarks of humanity. As against this particular model there have always been “gradualists,” who argue that there was no discontinuous biological change which resulted in the shift toward hyperactive cultural production. Stephen Oppenheimer makes the case for this in his book The Real Eve. Oppenheimer suggests that there was a gradual and cumulative cultural evolution. He argues that a proper analogy might be the rate of cultural change in the 20th century vs. than in the 17th century. Obviously we know that genetic evolution can not explain most of the difference in rate of change across the two eras, but looking at archaeological remains from the two periods would make clear their stark differences to a third party observer to the point where I can’t help but think a biological rationale would seem plausible without any other information.

ResearchBlogging.org I have no particular brief for either position in this post. I assume that both the biological and cultural models are too extreme now. The long term persistence of the Oldowan culture in much of the world implies to me that there may have been a biological chasm between hominin groups, and that the Oldowan “culture” was somehow biologically encoded. And yet I am not convinced that the gap between our Neandertal and neo-African ancestors was as great as Klein would have us believe. So now to the paper. First, let’s look at the abstract:

The timing of the dispersal of anatomically modern humans (AMH) out of Africa is a fundamental question in human evolutionary studies. Existing data suggest a rapid coastal exodus via the Indian Ocean rim around 60,000 years ago. We present evidence from Jebel Faya, United Arab Emirates, demonstrating human presence in eastern Arabia during the last interglacial. The tool kit found at Jebel Faya has affinities to the late Middle Stone Age in northeast Africa, indicating that technological innovation was not necessary to facilitate migration into Arabia. Instead, we propose that low eustatic sea level and increased rainfall during the transition between marine isotope stages 6 and 5 allowed humans to populate Arabia. This evidence implies that AMH may have been present in South Asia before the Toba eruption

Some dates to peg into your framework:

- Anatomically modern humans emerged in Africa in the interval of 100-200,000 years before the present

- Modern humans came to dominance in Europe 30-40,000 years ago

- Modern humans arrived in Australia and New Guinea 45-60,000 years ago

In the early 2000s both Y and mtDNA suggested the possibility of a “northern” (via the Levant and through Central Asia) and “southern” (a coastal Indian Ocean route to Southeast Asia and Australia) route of modern humans out of Africa and to the rest of the world. I don’t think this model is easily supported by the data any longer. Rather, it seems more plausible that there was one proto-neo-African population which then divided into a “western” and “eastern” branch (the latter being subdivided between the progenitors of East Asians & Amerindians, Oceanians, and a mostly absorbed substrate in South and Southeast Asia, of whom the Andaman Islanders are relics).

Despite the debates about the details of the branching pattern, a relatively late radiation of modern humans out of Africa seems to have been a good consensus position until recently. There were always anomalies, such as the Skhul and Qafzeh hominins in Israel, who seem to predate the neo-African radiation by ~50,000 years. But it was easy to argue that this was a “false start” of anatomically modern humans who went extinct, in part because they lacked the cultural fluidity of the “second wave” which came out of Africa.

Another major milestone in the big picture of recent human evolution was the Toba explosion. This massive catastrophe occurred ~75,000 years ago, and has been posited as a major force behind the genetic bottleneck of modern humans. The postdating of the radiation of H. sapiens sapiens in relation to this event was suggestive to many that this climatic and geological shock was a major precondition for the emergence of behaviorally modern humans.

With all that in mind, the current set of results shakes up an already destabilized orthodoxy. The dates for the current finds in Arabia are 127, 123, and 95 thousand years before the present, with errors on the order of 10,000 years. Unless there’s a major fault in their assumptions here this seems to confirm a second locus of modern humans besides the Skhul and Qafzeh hominids. Here’s the map:

As you can see the coastline shifted a great deal over the Pleistocene due to the fluctuation of the glaciers. I’ll get into the paleoclimate later, but how do they know these were modern humans? The answer is in the tools:

… Technological patterns at FAY-NE1 show greater similarities with East and northeast Africa…than with other sites known in Arabia. On the basis of these affinities and the contemporaneous presence of AMH in East and northeast Africa, we suggest that assemblage C occupation is attributed to AMH expanding out of Africa during early MIS 5….

All things equal the objection of Klein and other paleonathropologists that relying on tools alone is problematic seems a valid objection to me. But, all things are not equal. Which I will get to….

From what I can gather the main hypothesis being presented here is that there are two correlated patterns which blocked the expansion of anatomically modern humans from Africa to the rest of the world: extreme aridity in an already arid region, and higher sea levels. So the key was to 1) move across the water barrier during phases of low sea level, and, 2) persist until more clement regimes allowed for a population expansion. Here’s a reediting of figure 3 to illustrate the synchrony of parameters:

So how plausible is this? I think very plausible. Since I don’t know much about bones and tools I’m relying on the genetic evidence. In my post We were all Africans…before the intermission I outline a model whereby anatomically modern humans exited Africa well before the “Great Leap Forward” 50,000 years ago, but were bottled up in southwest Asia for much of that period. Even today the southern portions of Arabia are part of the Afrotropic ecozone. In other words, their flora and fauna bear greater resembles to that of Africa than Eurasia.

Can we then outline a plausible narrative which integrates these findings with the genetics? Yes. 100-150,000 years ago anatomically modern humans engaged in a range expansion, and pushed their way out of Africa into ecologically suitable zones in southwest Asia. Because of climatic fluctuations, in particular, the extreme aridity of much of the Pleistocene which was even more extreme than today in this region, these populations experienced multiple population crashes and expansions. It may be that there were many localized or regional extinctions. During this long sojourn in the inhospitable margin between Eurasia and Africa the anatomically modern humans, the neo-Africans, exchanged genes with similarly marginal Eurasian hominins, a branch of Neandertals. This zone was not ecologically optimal for either African or Eurasian descendants of H. erectus, and so the low population densities allowed for there to be a great divergence in their genetic character over the eons. The anatomically modern humans of the Levant and Arabia during the later Pleistocene may be equivalent to the Tuareg of today, a Saharan people who exhibit resemblances to peoples north of the Sahara, with some admixture with southerners, but not numerous enough to be major vectors mediating gene flow themselves.

And then ~50,000 years ago something happened. The neo-Africans of southwest Asia, who had a non-trivial element of Eurasian hominin ancestry, entered in a period unprecedented range expansion, and seem to have absorbed or exterminated other non-African populations. Additionally, they pushed the frontiers of human habitation to Siberia, the New World, and Oceania.

Of course that could be all wrong. Who knows?

Citation: Simon J. Armitage, Sabah A. Jasim, Anthony E. Marks, Adrian G. Parker, Vitaly I. Usik, & Hans-Peter Uerpmann (2011). The Southern Route “Out of Africa”: Evidence for an Early Expansion of Modern Humans into Arabia Science : 10.1126/science.1199113

(Republished from Discover/GNXP by permission of author or representative)
 
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Image credit:
Luna04

My post The paradigm is dead, long live the paradigm! expressed to some extent my befuddlement at the current state of human evolutionary genetics and paleoanthropology. After the review of the paper of possible elevated admixture with Neandertals on the dystrophin locus a friend emailed, “Remember when we thought everything would be so simple once we could finally see this stuff?” Indeed I do remember. The fact that things aren’t simple is very exhilarating, but it is also a major quash on theoretical clarity. Science is after all not a collection of facts, but it is in part facts which one can sieve through a analytic framework.

In hindsight with the relative robustness of ancient DNA results we can make some assessments about the role of human bias within particular heuristic frameworks over the past generation. From the mid-1980s up until 2000 it was victory after victory for the Out-of-Africa with total replacement model. The rise of mtDNA and Y chromosomal lineage studies seemed to buttress the idea of common descent from neo-Africans within the last 100-200,000 years for all human populations. There wasn’t much of a perturbation from this march toward paradigm ascendancy in the aughts, except that there were now also now a trickle of papers which claimed to phylogenetic “long branches” in the human genome. The 2006 Evans et al. paper, Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage, was probably the one that made the biggest media splash. But these were inferences. Subsequent analysis of the draft Neandertal genome seems to suggest that in fact the microcephalin allele in question did not introgress.

Case closed? Obviously not. Now we’re in a different era. The Evans et al. paper may have wrong in the specifics, but its general framework seems to likely have been validated: there are genetic lineages in the modern human genome which are not derived from the neo-Africans. But, let us remember that the overwhelming majority of the human genome is neo-African. A reasonable interval for non-Africans is 90-99% neo-African. But, a non-trivial minority has introgressed or admixed from other lineages. Out-of-Africa is mostly correct, but in some ways so is Multiregionalism. But how do we describe this? “Weighted multiregionalism”? “Mostly Out-of-Africa?” The old terms were nice because they were punchy and precise. If you look at Multiregionalism or Out-of-Africa in Wikipedia the newest results are noted, but it doesn’t seem that they’ve been integrated into the analytic narrative. Yet.

(Republished from Discover/GNXP by permission of author or representative)
 
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Neanderthal, La Chapelle-aux-Saints

Fossils matter. Fossils are evidence. That was Milford Wolpoff’s refrain in the 1987 NOVA documentary which heralded the long cresting of mitochondrial Eve and Out of Africa. Fossils remain highly relevant and important when it comes to deeper time phylogenetic relationships, but it does seem that they have only served to supplement the genetic data when it comes to recent human origins (e.g., calibrate and fine-tune molecular clocks). The paleoanthropologist Tim White, whose own position on human origins is at some contradiction from Milford Wolpoff’s, nevertheless felt the need to reiterate the relevance of fossils at a conference several years ago where most of the participants were geneticists (we received a preview of Ardi). Chris Stringer, who advocated for an Out of Africa model before Allan Wilson and his students roiled the academic waters often seems to have been relegated to nothing more than an adjunct to the molecular biologists in the public mind despite his priority. I think we are a turning point, and must acknowledge that recent human origins can no longer remain a one horse buggy. Genetics itself in the form of ancient DNA research, as well as more powerful analytic techniques utilizing larger autosomal data sets, have overturned and challenged the old conventional wisdom gleaned from trusting inferences derived from the patterns of variation of extant populations.


Consider two books from the early 2000s, The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry, and The Real Eve: Modern Man’s Journey Out of Africa. Both were ambitious works drawing bold lines between the patterns of history and genes, disproportionately maternally transmitted mtDNA (ergo, the references to Eve). Even at the time they were works of hubris, mtDNA is one locus, tracing one long uninterrupted line of foremothers. But it misses the total genome variance, and may be subject to various biases. A decade on though we now have grounds to suspect that much of the story told in both works is false. Europeans may have a more complicated history than we could have imagined. Some of the assumptions behind the second book, that most of today’s genetic variation crystallized during the Last Glacial Maximum ~20,000 years ago, also seems likely to be false.

The genetic data no longer cohere together in a plausible integrated whole. And that is of course the beauty of science, that it is subject to revision and revolution, that it eats away at its own foundations on occasion when those foundations are wanting. The very tools of modern genetics have undercut the confidence in genetics as a whole to answer broad expansive historical questions on its own. This is not a flaw in genetic science, it is the strength of science generally. Unlike some systems of thought science does not rest upon timeless creeds and formulas.

So where now? We need to do more than give lip service to a multidisciplinary perspective. We need to embrace it. This means a new relevance and importance to those who know and can interpret the fossil record. It also means more attention to anthropological and historical patterns, which may indicate the probable sample space of genetic outcomes. It will be harder and more uncertain work than what has come before, but the results will hopefully exhibit closer fidelity to the reality that was. False certainty is worse than an admission of ignorance

Image Credit: Wikimedia Commons

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Anthropology, Human Evolution, Paleoanthropology 
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There is a new paper in PNAS on remains from China which re-order and muddle our understanding of the emergence of anatomical and behavioral modernity in Eurasia. Human remains from Zhirendong, South China, and modern human emergence in East Asia:

The 2007 discovery of fragmentary human remains (two molars and an anterior mandible) at Zhirendong (Zhiren Cave) in South China provides insight in the processes involved in the establishment of modern humans in eastern Eurasia. The human remains are securely dated by U-series on overlying flowstones and a rich associated faunal sample to the initial Late Pleistocene, >100 kya. As such, they are the oldest modern human fossils in East Asia and predate by >60,000 y the oldest previously known modern human remains in the region. The Zhiren 3 mandible in particular presents derived modern human anterior symphyseal morphology, with a projecting tuber symphyseos, distinct mental fossae, modest lateral tubercles, and a vertical symphysis; it is separate from any known late archaic human mandible. However, it also exhibits a lingual symphyseal morphology and corpus robustness that place it close to later Pleistocene archaic humans. The age and morphology of the Zhiren Cave human remains support a modern human emergence scenario for East Asia involving dispersal with assimilation or populational continuity with gene flow. It also places the Late Pleistocene Asian emergence of modern humans in a pre-Upper Paleolithic context and raises issues concerning the long-term Late Pleistocene coexistence of late archaic and early modern humans across Eurasia.

I read the paper, and I really didn’t understand anything between the introduction and discussion. Mostly because it was a detailed exploration of anatomical details, and I’ve never taken an anatomy class. I basically rely on people like John Hawks to tell me what’s going on in that domain. He hasn’t blogged the paper (well, as of this writing), but he did give an assessment to National Geographic:

Still, the jaw and three molars were the only human remains retrieved from the Chinese cave, and the jaw is “within the range” of Neanderthal chins as well as those of modern humans, added paleoanthropologist John Hawks of the University of Wisconsin, Madison.

“If this holds up, we have to reevaluate” the human migration time line, he said.

“Basically, I think they’re right, [but] I want to see more evidence,” Hawks added. “I really, really hope that there can be some sort of genetic extraction from this [fossil].”

The issue of why this is relevant is covered well in the early portion of the paper:

…In eastern Eurasia, the dearth of diagnostic and well-dated fossil remains…has inhibited more than general statements for that region. Fully modern human morphology was established close to the Pacific rim by ∼40 kya, as is indicated by the fossils from Niah Cave in Sarawak…and especially Tianyuan Cave in northern China…The actual time of the transition has remained elusive, because the age of the latest known archaic humans in the region is substantially earlier…The eastern Eurasian age of the transition has been generally assumed to approximate that of western Eurasia (∼50–40 kya), although there have been claims supporting earlier dates for modern human presence in East Asia….

This scenario implies a long term (>100,000 y) restriction of early modern humans to portions of Africa with a brief ∼90 kya expansion into extreme southwestern Asia, followed by a relatively rapid expansion throughout Eurasia after ∼50 kya…The scenario also implies some form of adaptive threshold, roughly contemporaneous with the emergence of the Upper Paleolithic (sensu lato), and a marked behavioral difference between those expanding modern human populations and regional populations of late archaic humans (14).

It is in this context that three fragmentary human remains were discovered in 2007 at Zhirendong, South China…Because it is only well-dated diagnostic human remains that can document the timing and nature of human evolution and dispersal patterns (as opposed to archeological proxies for human biology or imprecise inferences from extant genetic diversity), the Zhirendong remains have the potential to shed light on these ongoing paleoanthropological issues.

jawOK, so the stylized orthodox model would be that anatomically modern humans arose in Africa ~200,000 years ago, and expanded out of Africa ~100-50,000 years ago. Full behavioral modernity emerged a bit later. In the broad outlines I think we can still go with this, but we have reached a level of fine-grained understanding of the evolutionary history of the human past that we need to consider adding detail to the margins of the story. The Denisova hominin, and perhaps H. floresiensis, are a good clue that the human family tree really was bushy, and that the past was filled with players unknown to us. The likelihood of Neandertal admixture also suggest that the other branches of the bush can’t be ignored and considered as without consequence for modern humans. There may be traces of other lineages in other human populations as well; there have long been claims based on inferences from some genetic data of modern populations, but the ability to compare to the Neandertal sequence gave those results from last spring particular credibility. But if the Neandertal admixture results become part of the consensus we should recalculate our probabilities of the other inferences.

linearSo how does it change things? One of the authors of the PNAS paper, Erik Trinkaus, has long made claims of hybridization from the fossil record, and this work falls in line with that tradition. The key here is the fossils seem to exhibit derived features, not ancestral ones. Derived features imply common ancestry of the populations which share the derived traits. If so, Trinkaus and company seem to be pointing to Alan Templeton’s “Out of Africa again and again.” On the other hand, I can’t but help think of Luke Jostins‘ plot of hominin cranial capacities as a function of time: separate lineages all seemed to be going on the same general path in terms of direction. I don’t make the claim here that H. sapiens sapiens was inevitable, but perhaps a common suite of traits which we associate with advanced hominin lineages, in particular the branch of which we are the terminus, were being selected for across the whole clade. In other words, perhaps anatomical modernity exhibits some element of convergent evolution, while behavioral modernity is the true hallmark of H. sapiens sapiens. It sounds crazy, and I don’t really believe it necessarily, but we live in crazy times. We had a neat and tidy story for 20 years between 1985 and 2005, but all good things have to end.

(Republished from Discover/GNXP by permission of author or representative)
 
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cavebread

Food is a fraught topic. In How Pleasure Works Paul Bloom alludes to the thesis that while conservatives fixate on sexual purity, liberals fixate on culinary purity. For example, is it organic? What is the sourcing? Is it “authentic”? Obviously one can take issue with this characterization, especially its general class inflection (large swaths of the population buy what they can afford). Additionally, I doubt Hindus, Muslims and Jews who take a deep interest in the provenance, preparation, and substance of their food are liberals. What Bloom is noticing is actually a general human preoccupation which somehow has taken on a strange political valence in the United States. Somehow being conservative in this country has become aligned with a satisfaction with the mass-produced goods of the agricultural-industrial complex.* Some conservatives such as Rod Dreher have pushed back against this connotation, lengthily in his book Crunchy Cons.

Stepping away from politics, we are a diet obsessed culture broadly. Apparently Christina Hendricks is going on a diet, her aim being to lose 30 pounds. Diet fads come and go. The Atkins approach has faded of late, with the Paleolithic diet coming into fashion. A totally separate market segment, that of raw food, remains robustly popular. This was obvious when Richard Wrangham came out with Catching Fire: How Cooking Made Us Human; raw food enthusiasts would call in to talk shows where he was a guest, sometimes irritated that Wrangham was claiming that cooking was central to the emergence of modern humanity. His contention that raw food practitioners were healthy precisely because they don’t process as much of their nutritional intake because of the relatively coarse character of what they were consuming was clearly discomfiting to many of them. This is because it is at variance with some of the rationale for their diet. They are not cooking the food in part because they believe that that removes a great deal of nutritive value.

ResearchBlogging.org I was thinking about this while reading What is Global History? Offhand the author mentions bread-making as early as 20,000 years go in the process of asserting that many of the preconditions for an agricultural mode of production were already in existence before the end of the last Ice Age. I was surprised by this fact, having never encountered it before. Unfortunately there wasn’t a footnote which I could follow up on, so I thought no more of it. Imagine my curiosity when I stumble upon this paper in PNAS, Thirty thousand-year-old evidence of plant food processing:

European Paleolithic subsistence is assumed to have been largely based on animal protein and fat, whereas evidence for plant consumption is rare. We present evidence of starch grains from various wild plants on the surfaces of grinding tools at the sites of Bilancino II (Italy), Kostenki 16–Uglyanka (Russia), and Pavlov VI (Czech Republic). The samples originate from a variety of geographical and environmental contexts, ranging from northeastern Europe to the central Mediterranean, and dated to the Mid-Upper Paleolithic (Gravettian and Gorodtsovian). The three sites suggest that vegetal food processing, and possibly the production of flour, was a common practice, widespread across Europe from at least ~30,000 y ago. It is likely that high energy content plant foods were available and were used as components of the food economy of these mobile hunter–gatherers.

One of the researchers on the team gave a good quote to Reuters:

“It’s like a flatbread, like a pancake with just water and flour,” said Laura Longo, a researcher on the team, from the Italian Institute of Prehistory and Early History.

“You make a kind of pita and cook it on the hot stone,” she said, describing how the team replicated the cooking process. The end product was “crispy like a cracker but not very tasty,” she added.

The contents of the paper are somewhat dry and opaque to me. The crux of the matter is that there are obviously important reasons why plant materials which may have been present in prehistoric camps aren’t preserved, so there has long been a bias in this area. It seems that the authors found a primitive system of pestle grinders, as well as flour grains. Below are the important figures which show their results:

[nggallery id=16]

The Reuters piece takes a shot at the Paleolithic diet:

The researchers said their findings throw humankind’s first known use of flour back some 10,000 years, the previously oldest evidence having been found in Israel on 20,000-year-old grinding stones.

The findings may also upset fans of the so-called Paleolithic diet, which follows earlier research that assumes early humans ate a meat-centered diet.

Ajlun_BreakfastI don’t know how the Paleo enthusiasts will react to this. I’m actually a guarded fan of Gary Taubes 2002 article in The New York Times Magazine What if It’s All Been a Big Fat Lie? I believe that a strong bias toward refined carbohydrates in your diet is bad for you. I generally don’t go as far as the Paleo enthusiasts in my own diet, but I have many friends who believe in the diet, and it works for them. That being said some of the Paleo people have an evangelistic aspect that probably is the source of shots like the ones above in the article. I am 5’8 and in the 140-150 range, usually in the 140-145 range. I’m not fat, and I’m not Paleo. My blood sugar levels are good. It can be done. Just because you were fat or or unfit and a particular diet works for you doesn’t mean everyone else has to follow the exact same prescription to the T. Human variation matters. South Asians have much higher propensities toward type 2 diabetes than other groups. It follows from that that everyone need not follow the nutritional and lifestyle guidelines of South Asians to get the same odds ratio of developing type 2 diabetes. How guilty you should feel about dessert is a function of the biological cards you bring to the table.

The importance of human variation, genetically and culturally, is relevant to this paper. What exactly does the likely presence of flour in three sites in Europe ~30,000 years ago tell us? Granting the validity of these results we can reject a strong form of the model of a Paleolithic diet which excluded processed starches. Does this now mean that Paleolithic humans were toasting pitas constantly around the fire? I don’t necessarily think so. We don’t know how pervasive this practice was. Human societies vary. Just because they were ancient, and “primitive,” does not mean that all Paleolithic populations were all the same. Second, it sees plausible that Paleolithic man was a generalist with a more diversified diet, all things equal, than his peasant successors. It may be that during the Paleolithic era there were no staples in a way we’d understand it today, rather, they subsisted on what was available at any given time. Perhaps these ancient pitas were reserve sources of sustenance which preserved well when other gathering and hunting had little or no yield. The difference between the Paleo-man and the peasant may then be thought of as the latter making what was once an emergency ration which was a good source of calories in a pinch into the staff of life.

A more general moral may be that we need to rethink our model of a Neolithic Revolution. It may have been a Neolithic Evolution. After the last Ice Age there were at least two independent, and likely more than two, domestication events and shifts toward an agricultural lifestyle. In The Long Summer and After the Ice Brian Fagan and Steven Mithen both imply that the emergence of behavioral modernity during the last Ice Age set the stage for the inevitable shift toward agriculture with the climatic change. So was it was (warm weather) + (modern cognitive capacity) → agriculture? Perhaps. But almost certainly humans were developing skills and competencies over time up until the end of the Ice Age, and with the warmer conditions the switch toward more proactive and intensive cultivation of grains may have been a gradual process of escalation. As population densities began to rise it seems a model could be posited whereby a positive feedback loop was being generated; non-agriculture sidelines were less and less effective as larger populations supported by semi-agricultural lifestyles made greater demands on the local ecology. This may have meant that the shift toward obligate agriculture was inevitable once it became the only viable option. Once the ratchet moved forward there was no going back, and humans had entered a new epoch.

20080818jackfruitToday we live in a consumer age of plentitude. Or at least you live in a consumer age of plentitude if you’re reading this weblog on a computer. We have great choice in goods and services, and can have a wide range of experiences. The past was truly a strange and exotic place; as evidenced by the reality that pre-modern folk took high infant mortality for granted as an unfortunate fact of life, while we today see the death of an infant as a tragedy of the highest caliber. But we mustn’t oversimplify the past. In one episode of the 1989 television series Alien Nation the human protagonist is learning about the religious customs of his partner, an alien. Offhand he mentions his growing awareness to another acquaintance who is also an alien. He then asks if she will be celebrating a holiday he has just learned of, and she responds that she does not believe in that religion. The detective expresses great surprise that the aliens have different religions, to which she quips, “Don’t you?” The point is that the aliens are perceived as an amorphous mass, profoundly different from humanity, and their own internal distinctions are elided in the minds of humankind. And so I believe occurs with human societies of modes of production fundamentally different from our own. “Paleolithic humanity” becomes a type, all difference and variation removed from our conception. “Hunter-gatherer” is distilled down to an image of N!xau from The Gods Must Be Crazy. To get a better handle of how the world is and how it was we need to be careful of this cognitive bias.

Citation: Anna Revedin, Biancamaria Aranguren, Roberto Becattini, Laura Longo, Emanuele Marconi, Marta Mariotti Lippi, Natalia Skakun, Andrey Sinitsyn, Elena Spiridonova, & Jiří Svoboda (2010). Thirty thousand-year-old evidence of plant food processing PNAS : 10.1073/pnas.1006993107

* Just to be clear, I am not personally an unalloyed enthusiast for “natural” methods, whether it be organic or small-scale farming. Rather, I am pointing to the fact that agricultural subsidies have distorted and reshaped the nature of food production, distribution, and consumption. I see nothing fundamentally conservative about being sanguine about the power and influence of the agricultural-industrial lobby, and the corporations which exist in symbiosis with government largesse.

Image Credit: Wikimedia Commons, Serious Eats

Note: Since this post mentions diet I may get some crazy unhinged comments because I know that some people take their diets very seriously, and react harshly to deviationists from the Truth Path. If you have commenting privileges and lose control and post something inappropriate, I will delete it.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Anthropology, Paleoanthropology 
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800px-European_Middle_Neolithic

The German magazine Der Spiegel has a rather thick new article out reviewing the latest research which is starting to reintroduce the concept of mass folk wanderings into archaeology. The title is How Middle Eastern Milk Drinkers Conquered Europe. In the story you get a good sense of the recent revision of the null model once dominant within archeology that the motive forces of history manifested through the flow of pots and not people. This viewpoint came to ascendancy after World War II, and succeeded an older method of interpretation which presumed a tight correlation between race and culture. It repudiated the idea that the flow and change of pottery styles and extant patterns of linguistic dialects may have been markers for the waxing and waning of peoples.

Obviously a pots-not-people model had some major exceptions even during its heyday. The demographic explosion of European peoples after 1492, and especially the Anglo peoples after 1700, occurred within the light of history. Even if it hadn’t it would be ludicrous on the face of it to assert that the modern American population were derived from the indigenous populations, and that they had simply adopted the language, religion and folkways of the British conquerors of North America. But outside the presumed aberration of the European imperialist and colonial venture of the modern era the details on the ground were obscure enough that a model could be imposed from without.

No longer. In non-European societies such as China with extensive records it is clear that demographic increase and colonization were driving forces of the expansion of a given cultural domain. A neglect of this reality could only occur via ignorance of the primary documents. Plausible if one did not know Chinese. As in the case of Spanish conquest of the New World the demographic wave was not total; biological and cultural amalgamation with the native substrate south of the Yangtze did occur to produce a new synthesis. But the revision does not occur just through space, but time as well. The methods of genetics, whereby samples from ancient burials may be retrieved and compared to modern populations, have allowed us to reject the post-World War II assumption that the Etruscans were an indigenous Italian culture. Due to the lack of copious records a theoretical presupposition was able to interject itself into the data. When the story about Etruscan genetic relationships to Near Eastern groups broke in early 2007 I actually proceeded to skim the latest archaeological monographs on the archaeology of this group, and most of them had erudite expositions on exactly how the myriad distinctive aspects of Etruscan culture which suggested an exogenous origin were in fact derived from the antecedent Bronze Age societies of Tuscany.

Ancient DNA extraction is now allowing scholars to map the change in frequencies of genetic markers of archaeologically known groups as a function of both space and time more broadly. I think one can safely see that there are more perturbations, fluctuations, and turnovers, than any pots-not-people model could predict. On the specific issue of lactase persistence it is almost certainly a genetic novelty in Eurasia which arose over the last 10,000 years in a co-evolutionary fashion with animal husbandry. The genomes of modern Europeans suggest this, but we have confirmation from ancient DNA extraction as well. A rise in frequency of a particular allele does not entail a replacement of one population with another; lactase persistence today can exhibit a great deal of variance as a function of geography and ecology because its frequency no doubt responds to local selective pressures. But, in concert with other DNA data (mostly maternal lineages) as well as a fresh look at evidence of cultural discontinuity and rapid pulses of colonization in late Paleolithic and early Neolithic Europe, one must be open to the possibility that the spread of animal husbandry, copious raw milk consumption, and an aggressive and fecund population, were all concurrent processes which were tightly interlocked in some causal sense.

An aspect of this story which I am fuzzy and weak on is the archaeology. You likely know nearly as much about the Linear Pottery Culture as I do. It seems though that this cultural-complex brought agriculture deep into the heart of Central Europe ~7,000 years ago, and there are clear signs that its origin was to the southeast, from the Eastern Mediterranean region. L. L. Cavalli-Sforza’s ‘demic diffusion’ model which argued for the expansion of Neolithic farmers from the Middle East into Paleolithic Europe seemed to suggest that it occurred through a ‘wave of advance‘ impelled by endogenous population growth and gradual migration. The model as reported by Der Spiegel seems at some variance with this. Instead of a gradual advance it seems that there may have been periodic pulses and explosions of demographic advance. Using the historical examples we have this should not be particularly surprising. Overlain atop the reality of an inexorable push across the ‘frontier’ in both North America and China by the colonizing peoples I alluded to earlier it is important to remember that there were periodic punctuations of gradualism by bursts of mass colonization, displacement, and relocation. The migration out of overpopulated New England to the Great Lakes and Upper Midwest in the early 19th century, the retreat to the south by the Han Chinese after the collapse of their first dynasty and the conquest of the north by barbarians. Both of these are examples of the explosive process in demographics and migration which can revolutionize the cultural landscape within a generation or two. From the data that the archaeologists have collected this seems to have occurred with the expansion of agricultural society in Central Europe as well, as the Linear Pottery Culture and its descendants proceeded in fits & starts.

Unfortunately as this is the domain of prehistory we won’t ever know in concrete terms exactly what occurred. In the Der Spiegel piece they report that the agriculturalists had a 500 year pause. Why? If demic diffusion was the primary dynamic through which they expanded there should be no pause. But we can think of a host of scenarios. Perhaps the Middle Eastern cultural toolkit had reached its natural outer boundary, and it was here that the tide turned to the indigenous Paleolithic societies of Europe, which maintained an advantage in the north because of the lack of the adaptability of southerners to new conditions. Humans can be stubbornly conservative in their ways. It is famously asserted that the Norse of Greenland did not adapt to a more inclement regime, and so went extinct (or, possibly evacuated to Iceland). The adoption of potatoes and other productive and useful crops among European peasants was retarded by their instinctive conservatism. We need not imagine a scenario where Paleolithic hunters and gathers would naturally wish to take up the hoe. Nor is it plausible that the agriculturalists would wish to refashion their tried & tested traditions so as to push the outer boundary of their limes.

But all things must change. Something happened, and the agriculturalists shifted the modus vivendi, and the hunter-gatherers gave way. There are detailed historical processes which can give us insight as to how such long-held boundaries could rapidly collapse. Europeans had circumnavigated Africa by 1500, and had had factories and trading posts around the continent’s fringe for over 400 years by the late 19th century. But deep into the 1800s the European presence in Africa was marginal. By 1914 the continent was divided into European zones of control. What happened in the space of a few decades? Quinine and machine guns. The biological barrier to Europeans fell away, and the military superiority was amplified by orders of magnitude. What could have occurred in an analogous fashion in Central Europe? The combination of a mutation for lactase persistence and animal husbandry may have resulted in rapid population growth, leading to densities which precipitated the outbreak of an epidemic. A reduction in population may have had much greater impact on the less numerous and resistant hunter-gatherers. Additionally the economic changes wrought by animal husbandry may have allowed for a scaling up of the organization of war. The Mongol Empire exploded onto the scene in mere decades to sweep across most of Eurasia. Why couldn’t something similar plausibly have occurred in Central Europe on a much smaller scale 7,000 years ago?

Ultimately we’ll never know the details. But in constructing our plausible scenarios for prehistory I suspect that we moderns have a bias toward viewing pre-literate societies as usually small-scale, at best simple chiefdoms. I believe this is a false model, and that there was a non-trivial level of scalability possible among pre-literate societies. Going back to the Mongol example, I see no reason why the initial existence of their polity necessitated literacy, though it may have been essential for its administration and perpetuation. Cultural forms likely marched with confederacies and were driven forward by warlords. This would easily explain the punctuated pattern of the spread of agriculture, as the rise and fall of states has a somewhat spasmodic and periodic character.

Finally, I want to emphasize that the Der Spiegel piece verges on a maximalist position which I am not comfortable with. There is much we don’t know, and I am in no hurry to replace one tired and dogmatic orthodoxy with another. Because the article was translated from German into English I can understand that that is responsible for the artlessness of some of the assertions. But phrases such as “There was no interbreeding between the intruders and the original population” from a German magazine really makes me think they’re suggesting that there were Stone Age Nuremberg Laws. Ethnic separation and differentiation was a reality among many ancient peoples, but so was intermarriage and assimilation. I am aware of the starkness of some of the DNA analyses, which suggest disjoint frequencies across the two populations, but the results are far too spotty at this point to make definitive assertions.

Note: The accompanying map is worth perusing.

(referral credit, Steve Sailer)

Image Credit: Wikimedia Commons

(Republished from Discover/GNXP by permission of author or representative)
 
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manchangeWhen I talk about sexual selection I usually make sure to have an accompanying visual of a peacock to go with the post. But really I could have used a dandy as an illustration, or perhaps in our day & age “The Situation”. Unlike the peacock much of what passes for human “plumage” is not a result of native biological processes, but rather refashioning the materials of other organisms or synthetics into a sort of second skin (or skins with all our layers). In other words, clothes. These artificialities are so essential to our own identity as individuals that they often mark out our tribal affiliations, in pre-modern and post-modern contexts. Whole industries exist to cater to both our utilitarian needs and aesthetic sensibilities in regards to how we dress ourselves. The definition of a cyborg usually connotes a synthesis of biological with electronic. Perhaps that is because our artificial extensions in the form of clothes have seamlessly merged with our self-images, to the point where it would be ludicrous to perceive ourselves as merged entities. If you encountered many of your acquaintances or friends naked not only would embarrassment ensue, but I suspect one might initially not recognize them. A naked physique without distinctive aspects of clothing one associates with someone strips away individual identity.

ResearchBlogging.org But clothing has not been the eternal condition of man, recall that Eve met the fig leaf after an unfortunate sequence of events. In all likelihood our common ancestor with bonobos and chimpanzees were predominantly hirsute, as are most mammals. A mammal without fur is like a fish without scales and birds without feathers. Not impossible, but atypical. But at some point we did lose our fur. When? A 2004 paper offered up an intriguing possibility, that ~1.2 million years ago our lineage became hairless. How did they come to this inference? The authors noted that the consensus sequence of the MC1R locus in humans among dark skinned peoples coalesced back to this period (i.e., the last common ancestor of the MC1R genes which exhibit the ancestral type, which confers dark skin). Once our ancestors lost their fur then they would have been exposed to solar radiation, and so the necessity of dark skin. When did this naked dark ape cover his shame? (yes, I censored one of the images above to make this post “work safe” above the fold) A new paper in Molecular Biology & Evolution offers up a precise date using another proxy, Origin of clothing lice indicates early clothing use by anatomically modern humans in Africa:

Clothing use is an important modern behavior that contributed to the successful expansion of humans into higher latitudes and cold climates. Previous research suggests that clothing use originated anywhere between 40,000 and 3 million years ago, though there is little direct archaeological, fossil, or genetic evidence to support more specific estimates. Since clothing lice evolved from head louse ancestors once humans adopted clothing, dating the emergence of clothing lice may provide more specific estimates of the origin of clothing use. Here, we use a Bayesian coalescent modeling approach to estimate that clothing lice diverged from head louse ancestors at least by 83,000 and possibly as early as 170,000 years ago. Our analysis suggests that the use of clothing likely originated with anatomically modern humans in Africa and reinforces a broad trend of modern human developments in Africa during the Middle to Late Pleistocene.

The evolution-by-lice method has some pretty simple logic behind it. Our parasitic lice have followed us across our journeys. In this case there are two forms being spotlighted, one of the head, and another of the clothes. The genesis of the latter can give us a clue as to the period of time when our species began to be obligate clothed. One presumes that the head lice were the ancestral form, and that the clothing lice derived from them (the head lice took refuge there after we lost our fur). Standard phylogenetic methods which are applied across a range of taxa can then be turned to these two lice populations. When the clothing lice diverge from the ancestral line of head lice it stands to reason that humans must have been wearing clothing. A species which emerges to fill a niche, must have a niche to fill. Eventually the authors arrive at a figure of ~170,000 years before present.

To get from here to there, they looked at four loci: three nuclear genes, 18S rRNA, nuclear elongation factor 1-α (EF-1α), and RNA polymerase II (RPII), and the mitochondrial gene cytochrome c oxidase subunit I (COI). In the age of SNP-chips with hundreds of thousands of markers this may seem paltry, but the questions are far coarser in this case. The authors weren’t looking to generate PCA plots showing the relationship of various disparate head lice lineages or anything so fine-grained. Rather, they were focusing on the speciation of the two lineages from a common ancestor, an archaic head lice population. This is a picture which can be painted in broad strokes, concretely, four genetic strokes.

They found that the ancestral lice went through some sort of bottleneck, likely mirroring their hosts. That was followed by a demographic expansion. Again, mirroring the hosts. Surprisingly the gene flow seems to have gone predominantly from the clothing lice to the head lice! Previous studies using a set of different markers, specifically microsatellites, did not find that the two populations evidenced gene flow after their separation. Additionally, as noted the direction of gene flow is somewhat surprising as the clothing lice population clearly derive from the head lice. This peculiarity makes me think of Sewall Wright’s shifting balance model, whereby population structure and historical events are critical in shaping contingent arcs of evolution.

Figure 1 illustrates their model in the context of prior data:
lice1

Using the genetic data, a Bayesian coalescent model with assumptions of migration, population structure and mutation rates, they generated a distribution of the probable time when head and clothing lice went their (generally) separate ways. The gray line follows the arc of the distribution, with ~83,000 years before present as the mode, and ~170,000 years before the present as the median. Such a probability density distribution seems to imply that clothing lice lineages which we have today emerged at least before the expansion of modern humans out of Africa. As anatomically modern humans emerged ~200,000 years ago in Africa there is a strong probability that clothing in Africa dates back to the archaic lineages.

If the paper cited above in regards to MC1R coalescence is valid, these results indicate a period of “naked years” between the loss off fur by H. erectus (I believe H. ergaster in Africa), and the adoption of clothing by modern humans or some archaic group. The authors correctly note that they can not rule out that other human lineages, such as Neandertals, wore clothing and had their own lice lineages. Despite the evidence of Neandertal admixture, it seems that the lice results are in alignment with the mtDNA, and imply total replacement. Just as Gallo-Roman nobles began donning Frankish trousers perhaps the Neandertals assimilated into modern human bands tossed aside their barbaric capes and took up the clothes of civilized folk with vaulted arches.

Despite their claims of more sophisticated methodology we probably should be a touch cautious about these results. Some of the findings are weird (the gene flow from clothing to head lice) and conflict with earlier work (finding gene flow in the first place). The parallels between lice & men in terms of evolutionary history are both striking and suggestive, but lice are lice, and they may have their own wily ways. And let’s not forget the pubic lice, which tell a different set of stories.

Citation: Melissa A. Toups, Andrew Kitchen, Jessica E. Light, & David L. Reed (2010). Origin of clothing lice indicates early clothing use by anatomically modern humans in Africa Mol. Biol. Evol. : doi:10.1093/molbev/msq234

Acknowledgements: Thanks to Dienekes to the paper pointer.

Image Credit: Wikimedia – Australopithecus & Kemal Ataturk, Anthropologyinfo.com – H. erectus

(Republished from Discover/GNXP by permission of author or representative)
 
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One aspect of human demographic expansions seems to be the fact that we often model them as a constant diffusion process, when in reality there were likely pulses (economic historians can conceive of this as the periodic gaps between land and labor factor inputs). I don’t know much about the human movements prior to H. sapiens sapiens, and from what I can gather the fossil remains are too sparse to be too wedded to a specific model, but it seems clear that anatomically modern human expansion occurred through a series of rapid outward sweeps which would periodically reach a “natural barrier.” Modern humans reached the Solomon Islands ~30,000 years ago, after which there was stasis for ~25,000 years. Only with the Austronesian expansion did humanity push past the Solomons. And this was no baby-step, ultimately the Austronesians went as far as the Hawaiian islands and Easter Island.


The New World is similar. The initial migration out of Africa by modern humans resulted in the range expansion of the human lineage into a region which had been untouched by earlier hominins, Australasia. But after that point tens of thousands of years passed before our species pushed into virgin territory, in this case North America. The when and the how of this though is still up for debate. A new paper PLoS One attempts to construct a plausible scenario by taking archaeological data points and inputing them into a diffusion model. Archaeological Support for the Three-Stage Expansion of Modern Humans across Northeastern Eurasia and into the Americas:

We use diffusion models…to quantify these dynamics. Our results show the expansion originated in the Altai region of southern Siberia ~46kBP , and from there expanded across northern Eurasia at an average velocity of 0.16 km per year. However, the movement of the colonizing wave was not continuous but underwent three distinct phases: 1) an initial expansion from 47-32k calBP; 2) a hiatus from ~32-16k calBP, and 3) a second expansion after the LGM ~16k calBP. These results provide archaeological support for the recently proposed three-stage model of the colonization of the Americas….Our results falsify the hypothesis of a pre-LGM terrestrial colonization of the Americas and we discuss the importance of these empirical results in the light of alternative models.

It’s an interesting paper because it seems to have been triggered in part by inferences made from the genetic data. I don’t know how confident archaeologists are about their radiometric dates, but I think some of the molecular clock results from the genetics of Amerindians need to be taken with a grain of salt (I don’t see many people repeating some of the really ancient coalescence dates for Amerindian Y lineages at this point).

These data seem to indicate that modern humans made it no further than previous hominin groups for several tens of thousands of years. But something happened within the last 20,000 years, and our species made the leap across Beringia. The bottleneck here is certainly not the Bering Strait, which was spanned by land much of the time in any case. Rather, our species didn’t have the biological or cultural capacity to survive in extremely frigid environments. I’ve read modern humans pushed the boundaries of their range in northern Europe further than Neandertals ever did, indicating our flexibility and plasticity. Since the human lineage had been resident in Eurasia for at least one million years that suggests to me that it was behavioral modernity that was key. In particular, how quickly our cultures evolve and shift. Though that flexibility itself may be a function of our biological competencies.

(Republished from Discover/GNXP by permission of author or representative)
 
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I just stumbled onto two amusing articles, Ancient legends once walked among early humans?, and The discovery of material evidence of a distinct hominin lineage in Central Asia as recently as 30,000 years ago is no surprise. The second is a letter from a folklorist:

Sir, The discovery of material evidence of a distinct hominin lineage in Central Asia as recently as 30,000 years ago (report, Mar 25) does not come as a surprise to those who have looked at the historical and anecdotal evidence of “wild people” inhabiting the region. The evidence stretches from Herodotus to the present day. The Russian historian Boris Porshnev suggested that they are relict Neanderthals, although the lack of evidence of material culture suggests a type closer to Home erectus.


Needless to say many are skeptical of folk memories persisting for 30,000 years, though a standard assumption in paleontology is that the earliest and last fossil find of any given species is going to underestimate their period of origin and overestimate the period of extinction. In other words the Denisova hominin lineage almost certainly persisted more recently than 41,000 years ago. But recently enough to spawn legends of Enkidu? I’m skeptical. Someone with a better grasp of the mutation rate in oral history can clarify, but it seems that tall tales would be so distorted over a few thousand years that the initial kernel of truth would quickly be obscured.

Here’s my model for why almost all cultures have tales of various semi-human groups: cross-cultural differences are stark enough that it isn’t too hard to dehumanize other populations. More specifically, I think the biggest gap is going to be between groups who practice different modes of production. Many of the “wild people” as perceived by agriculturalists were probably just marginalized hunter-gatherers who hadn’t taken up the ways of “humans.” Consider how many upper middle class white Americans perceive rural people from Appalachia even in our enlightened age. There are even biological differences, as agricultural populations seem smaller and more gracile in comparison to hunter-gatherers (who consume more fibrous food stuffs, and probably have a more balanced nutritional intake). How hard is to conceive of a small and malnourished agriculturalist being cowed by more robust hunter-gatherer group upon first contact?*

Combine real cultural and biological differences with human imagination, and it seems that this is the most likely explanation for the universality of wild people and strange semi-human folk. It is in other words simply an aspect of evoked culture, nothing that needs special triggers in the form of other human lineages. The main exception I can think of would be Flores Hobbits, who may have persisted down to a very recent period.

* The immediate objection to this possibility is that hunter-gatherer groups tend to get sick very quickly with the approach of high density humanity, and already pushed to less productive land by the time they’re confronting the agriculturists on a daily basis. So they are less likely to be robust.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Human Evolution, Paleoanthropology 
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Razib Khan
About Razib Khan

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