john hawks weblog

paleoanthropology, genetics and evolution

Middle Pleistocene

  • Low-velocity spatter from the Neandertal palette

    Sat, 2012-01-28 16:43 -- John Hawks

    Paleolithic archaeology is the home of some of the best forensic work anywhere. I've often written about impressive analyses of stable isotopes, microscopic starch grains, phytoliths, and wear traces on artifacts. Among these, some of the most detailed studies involve the use of pigments by ancient people. Out of these, last week's paper by Wil Roebroeks and colleagues [1] really stands out by wringing every drop of information out of an ancient archaeological horizon.

    I wrote last fall about the pigment "workshop" at Blombos, South Africa, which is around 100,000 years old ("Blombos pigment workshop"). And some time ago I wrote extensively about pigment use among Mousterian-era Neandertals ("Pigment use and symbolic behavior in the Neandertals"). These kinds of studies face many challenges. If a mineral pigment has been used by ancient people, it will often exist in a site only in tiny pieces. At best, some accumulation of the mineral pigment might give an indication of intentional use by ancient people. In this case, the material was scattered in a dozen or so tiny droplets over a diameter of 15 meters.

    Mineral pigments have uses other than decoration. Sometimes they were used as part of a formula to make glue, which we can find still adhering to the back end of stone points. Ochre may also have been used in the process of softening animal hides. These uses were reviewed by Lyn Wadley [2], who has done more than anyone to uncover the ways MSA people processed ochre in South Africa. Pigments were used by humans as early as 200,000 years ago in Africa, and earlier than 100,000 years ago in West Asia (Skhul and Qafzeh [3]) and Europe.

    The new study by Roebroeks and colleagues extends the time of pigment use in Europe to earlier than 200-250,000 years ago, which is newsworthy. It is notable that this time is early enough to suggest that the common ancestral population of European and African archaic humans may have also used pigment (or have been capable of learning to use it given the right cultural or ecological conditions). But to me, much more interesting is the way the red ochre was discovered in the archaeological site, and the experimental replication of the process by which it was deposited.

    In the course of the archeological excavations, one of the sites, site C (excavated between 1981 and 1983), yielded 15 small concentrates of red material, with maximum size of 0.2–0.9 cm and 0.1–0.3 cm thick, with sharp boundaries to the sedimentary matrix (Figs. 1 and 2). The contrast in color between the bright- red concentrates and the yellowish-brown (Munsell soil color 2.5Y5/3) to grayish-olive (5Y5/3) sediment was striking (Fig. 2), facilitating recovery of these small, friable pieces at this site, excavated over an area of 264 m2 (Fig. 3). Although the red material has been interpreted as hematite (15, 23), these finds did not play a role in the history of ochre use, even though Maastricht-Belvédère became one of the flagship sites of Middle Paleolithic archeology, reviewed extensively in numerous textbooks (24).

    These hematite features are pictured in several ways in the article and supplement. They are tiny: here is one of them, on a piece of sediment that was removed in total from the site:

    Red ochre droplet from Roebroeks et al 2012 supplement

    Detail of Figure S4 from Roebroeks et al. 2012 supplement, showing red hematite concentration upon sediment fragment removed from site.

    It is simply remarkable to me that this excavation in the early 1980s uncovered an ancient sediment horizon using such great care that these tiny patches of red ochre were found. All were only a few millimeters in size. They were highly visible against the surrounding sediment, which helps to confirm that they don't belong there. Other aspects of the archaeology were likewise carried out meticulously. For example, the paper presents two refits of flakes and cores taken from the site, demonstrating that primary reduction of stone artifacts happened there with some products taken away from the site.

    The paper notes the lack of hematite in local contexts where people might have found it, arguing that it must have been imported from a distance of at least 40 km from a natural source. The archaeological presence of contemporary tools taken in the opposite direction toward that hematite source helps support this argument. Forty kilometers isn't terribly far for hunter-gatherers, but it is interesting.

    The experimental aspect of the paper is only sketched out in the text, and is described much more fully and illustrated in the supplement. Roebroeks and colleagues, looking at the small patches scattered across a diameter of 15 meters, guessed that they were a low-velocity spatter dropped from some kind of liquid. So they set out to reproduce it:

    We hypothesize that the best explanation is that the fine hematite material was originally concentrated in a liquid solution, and that blobs of this ochre-rich substance became embedded in the sediments during use of the liquid,spilled on the soil surface. To test this interpretation, we performed an experiment to observe the impact of drops of a hematite-rich liquid on the site C sediment (SI Text). Despite the limitations of this experiment, the similarity of the experimentally produced concentrates to the archeological concentrates at both macroscopic and microscopic levels is remarkable (SI Text) and lend support to our interpretation of how the material entered the sediment.

    The experiments are illustrated very nicely in the supplementary information for the paper. Here's one of the photos:

    Red ochre droplet experiment, figure S10, B from Roebroeks et al 2012

    Figure S10b from the supplement of Roebroeks et al. 2012. Original caption: "(A and B) Experimental hematite dots created on a 'smoothed' dry surface (50-cm height, 0.3-cm drops). The concentrates are within small craters produced during impact of the drops on the dry sediment."

    Their "hematite liquid" consisted of ground mineral combined with rainwater, "launched" from a height of a half meter. Sounds like something that should be for sale in a natural cosmetics store.

    What were these ancient people doing with liquid ochre? Good question. Given the unique care of excavation, the local context in which the mineral is highly visible in the fine sediment, I wonder how many other instances of similar deposits may have been lost over the years. It is sometimes excruciating to wait for results from an archaeological discovery, but the extremely slow and careful excavation methods do obtain results that could not be gotten any other way.

    I was privileged to see some details from another excavation this week, where even greater care is being taken. It's totally remarkable some of the things that are out there waiting to be found.

    References

    1. Roebroeks W, Sier MJ, Nielsen TK, De Loecker D, Parés JM, Arps CES, and Mücher HJ. 2012. Use of red ochre by early Neandertals. Proceedings of the National Academy of Sciences [Internet]. Available from: http://www.pnas.org/content/early/2012/01/17/1112261109.abstract
    2. Wadley L. 2005. Putting ochre to the test: replication studies of adhesives that may have been used for hafting tools in the Middle Stone Age. [Internet] 49:587 - 601. Available from: http://www.sciencedirect.com/science/article/pii/S004724840500117X
    3. D'Errico F, Salomon H, Vignaud C, and Stringer C. 2010. Pigments from the Middle Palaeolithic levels of Es-Skhul (Mount Carmel, Israel). Journal of Archaeological Science [Internet] 37:3099–3110. Available from: http://dx.doi.org/10.1016/j.jas.2010.07.011
    Tags: 
    pigment
    Neandertals
    experimental archaeology
    Middle Pleistocene
    Lower Paleolithic
    Synopsis: 
    A discovery of red ochre use by ancient Europeans before 250,000 years ago

  • When anthropological and geological facts collide

    Mon, 2011-11-28 01:56 -- John Hawks

    This passage is the first paragraph of the introduction to Franz Weidenreich's monograph, The Skull of Sinanthropus pekinensis [1].

    In my earlier contributions to the study of Early Man I pointed out repeatedly the danger of confusing anthropological facts with geological facts. In determining the character of a given fossil form and its special place in the line of human evolution, only its morphological features should be made the basis of decision; neither the location of the site where it was recovered nor the geological nature of the layer in which it was imbedded [sic] are important. Discrepancies cannot be smoothed out by bringing morphological facts and opposing geological data into closer harmony with artful interpretations or by touching-up reconstructions. It is a generally accepted conception that Man has developed in the course of time by gradual transformation from an ape-like type to the type he presents today. Viewed from this fundamental standpoint, it is logical to assume that the more a form resembles the supposed ancestor the more ancient it will be, or that the more ancient it is the more "primitive" it should be.

    I am concerned with this passage today because of a re-emerging mismatch of evidence from the morphology of Middle Pleistocene humans and the genetics of Neandertals. Some paleoanthropologists have asserted that Europeans of the Middle Pleistocene were the exclusive ancestors of Neandertals. I have in the past written that Middle Pleistocene Europeans were among the ancestors of Neandertals, with sustained gene flow from other populations including Africa [2]. The Sima de los Huesos people, maybe 600,000 years old, resembled the (much) later Neandertals in several aspects of their anatomy, as did other Middle Pleistocene Europeans.

    The genetic differences between living people and the ancient Neandertal genomes appear consistent with the emergence of distinct African and Neandertal populations only within the last 400,000 years or less [3], [4].

    Such a recent date seems a poor match for the morphological evidence of Neandertal ancestry in Europe. I can think of several ways to make these morphological and genetic comparisons concordant with each other, all of which balance some shift in one body of inference against the other. As long as we can't pin down the human mutation rate within a factor of two ("What is the human mutation rate?"), there's a lot of room to make different population models consistent with the genetic data.

    This is, in today's language, Weidenreich's point. Morphological data must be interpreted in accordance with evolutionary principles, and if it doesn't fit a temporal scheme, it doesn't fit. Likewise, genetic similarities must be explained in their own evolutionary framework. These two sources of evidence must in the end be consistent with a single history. We will find that consistency not by shoehorning the evidence together, but by interpreting each with the strongest possible skepticism concerning assumptions and models.

    Weidenreich's introduction illustrates two cases. The simpler, from our point of view today, was Piltdown. Many establishment anthropologists, particularly in Britain, had maintained that Piltdown was a morphologically advanced ancestor of modern humans, which had lived early in the geological record of human evolution. Weidenreich had been an early and prominent critic of this idea, because he was convinced that the specimen simply did not fit together with its supposed geological context.

    I cannot believe, even making very liberal allowances for these uncertainties, that such incongruity between morphology and chronology as is found in the case of Piltdown can be completely brought into accord. The only hope of solution in this case would lie in assuming that the human bones were not contemporaneous with the layer in whih they were found but were deposited there later. Otherwise, modern man must be much more ancient than we ever imagined, or else Western European man did not pass through evolutionary stages as did the hymans of other regions of the earth.

    We now know, of course, that Weidenreich was entirely correct. The apparent geological facts were false, and the "advanced" characters of the specimen were simple reflections of the fact that the skull is a modern human skull.

    The other problem Weidenreich discussed in some detail was the phylogenetic position of the Steinheim skull. Like Piltdown, this specimen had been placed in a Presapiens context by other workers. Steinheim lacks most of the derived characteristics of later Neandertal specimens. Weidenreich, along with many of his contemporaries, accepted its lack of Neandertal features as evidence for affinity with modern humans. In Weidenreich's view, this similarity with modern humans was "anachronistic". Even so, the case did not challenge an evolutionary interpretation, only the assumption that features could evolve from "primitive" to "modern" along a single line. If we admit that Neandertal features were not in all cases "primitive", even if they may resemble superficially the characteristics of some apes, we can accommodate specimens like Steinheim within a population model where both moderns and Neandertals may have derived (and in some cases, secondarily derived) characters that appeared afterward.

    This scenario requires us to straighten out the analysis of the characters themselves, a process for which larger fossil samples are essential. It was to that end that Weidenreich supposed the Sinanthropus sample to be of such great utility. The subtext of the introduction was to illuminate the kinds of evolutionary problems that could be further illuminated by a full description of fossil variation. Finding variation in fossil humans did not repudiate the concept that modern humans had evolved in stages from primitive ancestors, but helps to clarify cases where the evolution has not been a simple linear progression. In many cases, features that are superficially "primitive" may actually have been secondarily derived in recent humans compared to earlier hominins.

    Along similar lines, I ran across this old post: "Dobzhansky on Weidenreich's species concept", in which Dobzhansky predicts:

    Some modern populations may carry genes that were present in the Neanderthaloids, and other moderns may not carry such genes.

    References

    1. Weidenreich F. 1943. The Skull of Sinanthropus pekinensis: A Comparative Study on a Primitive Hominid Skull. Pehpei.
    2. Hawks J, and Wolpoff MH. 2001. The Accretion Model of {Neandertal} Evolution. Evolution 55:1474–1485.
    3. Green RE, Krause J, Briggs AW, Maricic T, Stenzel U, Kircher M, Patterson N, Li H, Zhai W, Fritz MH, et al. 2010. A Draft Sequence of the Neandertal Genome. Science [Internet] 328:710–722. Available from: http://dx.doi.org/10.1126/science.1188021
    4. Reich D, Green RE, Kircher M, Krause J, Patterson N, Durand EY, Viola B, Briggs AW, Stenzel U, Johnson PLF, et al. 2010. Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature [Internet] 468:1053–1060. Available from: http://dx.doi.org/10.1038/nature09710
    Tags: 
    Franz Weidenreich
    history of anthropology
    Neandertal DNA
    Neandertals
    Zhoukoudian
    Middle Pleistocene
    Steinheim
    Piltdown
    morphology
    phylogenetics
    Synopsis: 
    Weidenreich's introduction to the Sinanthropus cranial monograph illuminates some issues I'm facing with ancient genomes.

  • Meet Homo heidelbergensis

    Tue, 2011-11-15 08:28 -- John Hawks
    Synopsis: 
    The Mauer mandible is the type specimen of Homo heidelbergensis

    The Mauer mandible comes from just southeast of Heidelberg, Germany, and was found in ancient sands deposited just more than 600,000 years ago. Upon its description, the mandible was attributed to a new species, Homo heidelbergensis.

    Through the years, anthropologists considered H. heidelbergensis to be a more primitive species than Neandertals, very different from recent humans. Many anthropologists attribute other remains from the European Middle Pleistocene to this species. Probably the most important sample would be the Sima de los Huesos remains from Spain, but other crania and skeletal elements from sites across Europe have been put into the species. A few anthropologists would also include specimens from other parts of the world.

    Other anthropologists disagree. They believe that Mauer is an early member of the same population that includes Neandertals. Others would go further, noting the evidence that Neandertals are part of the ancestry of modern humans, and put Mauer into our species, Homo sapiens.

    This station has several mandibles for you to compare with Mauer, including some Neandertals, modern humans, and Homo erectus individuals.

    What to do: Compare the morphology of the Neandertal and Mauer mandibles to the modern humans. What features differ?

    Consider what you know about earlier hominid mandibles (or compare one at the station). Do you think Mauer is a possible ancestor of Neandertals? What about an ancestor of modern humans? Does it have mostly primitive dental features, or does it share derived features with one or the other?

    Study terms: 
    Mauer
    Homo heidelbergensis
    Neandertal
    Sima de los Huesos
    Tags: 
    Anthropology 105
    laboratory
    explainer
    Germany
    Mauer
    Europe
    Middle Pleistocene

  • Mailbag: Where did Neanderancestors live?

    Sat, 2011-07-16 08:54 -- John Hawks

    Re: European Middle Plesitocene (via Twitter):

    Maybe a dumb question....how do you know Neandergenes derive from Africa vs. f.e. recent Africa and Neandergenes both derive from Atapuerca?

    Not a dumb question at all. I discussed this exact issue with David Reich last week. There is no strong fossil argument for an African ancestor at that time, Europe and West Asia are anatomically and archaeologically just as plausible. My inclination is to suspect Africa because of the deep genetic variation still retained in that population, but that variation could have been retained in other ways -- particularly since every scenario of human origins now must involve population mixture.

    Tags: 
    Neandertals
    Neandertal DNA
    Middle Pleistocene
    Denisovans

  • Population structure within Africa: has "modern human origins" become a non sequitur?

    Tue, 2011-03-15 16:33 -- John Hawks

    When I wrote about the Denisova genome late last year, I claimed that "A large-scale reorganization of the science of human origins is upon us."

    I'm glad I had the sense to write that. A lot of people have pointed back to that quote over the last few months. Still, I know that the full implications of the Denisova and Neandertal genomes haven't really sunk in. "Large-scale reorganization" takes time.

    A new paper by Brenna Henn and colleagues in PNAS [1] shows how the shifting landscape has caught many geneticists off their footing. Submitted before the Denisova genome, but long after the Neandertal, the paper is titled, "Hunter-gatherer genomic diversity suggests a southern African origin for modern humans". In today's landscape, with only one instance of the word "Neanderthal" in the paper, the conclusions are obviously incomplete.

    The "southern African origins" conclusion of the paper comes out of a simple analysis that assumes that the best-fit maximum for genetic diversity (as assessed by linkage) is the most likely point of origin of the population. That would be true if the African population emerged by a series of founder effects from a single small ancestral population -- the "serial founder effect" model that I have criticized here before. But of course in 2011, we know that model is false, because it is predicated on a lack of ancient mixture with Neandertals or other populations. If the serial founder model can't work outside Africa, it certainly can't work inside Africa, where populations were larger and regionally diversified during by the beginning of the Late Pleistocene. Without that false assumption, the "southern African origin" evaporates. The primary observation, a cline of linkage disequilibrium within sub-Saharan Africa, can be explained with reference to mixture of populations without assuming an origin and expansion from one geographic location.

    I don't want to criticize overmuch. Many ongoing research projects are casualties of our new knowledge of ancient genomics, and we'll see more papers like this before the fallout has settled. Simplistic founder models, acceptable only a year ago when these projects were conceived, are now unquestionably false. Ancient population mixture is the order of the day, and we don't have any simple, plug-in-the-data models to apply to data like these.

    Instead, I want to consider the power of the data in this article to answer some fundamental questions about African population history. Henn and colleagues report on SNP genotyping of several Bushman groups from southern Africa and Sandawe and Hadza people from eastern Africa. These data are on the 550k SNP platform that was used by 23andMe before the recent increase to 1M SNPs. That means the data are comparable to many other studies. They are not entirely comparable with other samples of African genetic variation, and the authors cut the total number of SNPs down to the 55,000 that overlap among all the genotyping platforms used in their analysis. For this reason, the paper presents a genome-wide set of 55,000 SNPs across many African populations.

    It's far from the perfect sample. I expect we'll be able to do much more with the full 550k dataset from the hunter-gatherer populations. The data have been made publicly available for download, and here we're already starting to investigate them.

    Within the current paper there is a very useful analysis of the broader dataset using the ADMIXTURE software. ADMIXTURE assumes that the current samples represent a mixture of ancient populations that were more distinct than today's. I went through this algorithm with my students in class Wednesday and Friday, which I'm sure was an intimidating process to most of them. The math is not too conceptually daunting; it's just hard to conceptualize how all the possible interactions relate to gene frequencies when you are assuming more than a few putative ancestral populations. Razib Khan gives an impressive step-by-step guide to performing an ADMIXTURE analysis, including some of these samples.

    I'm not in love with this analytical method -- there's no reality check on its assumptions. But its output can be informative about many aspects of population structure. Here are some first approximations:

    1. The genetic diversification of African populations was once much greater than today. Razib Khan points out the homogenizing effect that agricultural populations have had on the African continent, particularly during and after the Bantu expansion. I think the current data suggest that earlier processes involving LSA hunter-gatherers also tended to homogenize populations.

    For example, when eight initial clusters are assumed, the ADMIXTURE analysis constructs them in a way that most of the ancestors of today's Bushmen were in a population with a high degree of genetic divergence from the other seven ancestral populations. The FST between the Bushman ancestral population and others ranges from 0.1 (for forest pygmies) to a high of 0.25 (from Europeans). That estimate is nearly double the equivalent statistic in today's populations.

    Again, we don't have to believe the assumptions underlying the ADMIXTURE algorithm, but it does highlight the basic partitioning of diversity in the African population. Today there is high diversity within African population samples, and some of that diversity can be traced back to populations of 100,000 years ago or more. Some of the diversity that once existed among these populations has now been spread within them instead. The populations got genetically closer over time.

    A model of successive population expansions, bringing ancient populations genetically closer and closer together, is also what we may see in other places. As we have learned more about the mtDNA of ancient Europeans, it has become clear that successive expansions and migrations of people into Europe have radically reshaped the gene pool.

    2. Click languages have no genealogical unity. Over the years, many linguists and anthropologists have proposed that Hadza, Sandawe, and Bushmen are closely related to each other, despite their geographic distance, because they all speak languages that use click sounds. No historical linguist has ever successfully demonstrated a system of sound changes or detailed correspondences among these languages, but people promoting the hypothesis seem immune to these kinds of facts.

    The genetics show a very clear and ancient differentiation of these hunter-gatherer peoples. In the ADMIXTURE analysis, some of the largest genetic distances are among these peoples. By itself, that may not be surprising; these are the populations that have most evaded the homogenization that followed the spread of farming. The Hadza themselves are strikingly distinctive, and their genetics may reflect a history of small population size during the last several hundred years. The potential for genetic drift in this population was very high. Still, the genetic relations are just the opposite that would be expected if speakers of these click languages had shared a common origin.

    Seems to me that this could have been the lede of the paper, if it had been written differently. A bit more exploration of the hunter-gatherer data (probably incorporating some haplotype-level analysis to give a better estimate of the ages of events) would demonstrate this point very well.

    3. By the time we find "modern" humans in West Asia, the African population had long since diversified into regional populations. This is not news; the mtDNA evidence has suggested for several years that southern Africa and the remainder of sub-Saharan Africa were already regionally differentiated before 120,000 years ago. There have also been hints of this diversification from whole-genome evidence (including the supplement of the Neandertal genome paper last year). Here we have a clear indication that the regionality extends to every African hunter-gatherer population.

    4. Hunter-gatherers have relatively little evidence for recent positive selection. The supplementary data of the current paper includes a short discussion of selection and a list of candidate loci in the hunter-gatherer samples. There is relatively little overlap in candidate regions for selection among these samples. Different genes have been selected in different populations, and not all that many of them. This is not surprising if the selection is relatively new -- the last 20,000 years or maybe more, given the distances and amount of historical population structure estimated for the data. It's also consistent with the demography of these populations. It will be interesting to check, but I would speculate that the signature of selection will on average appear older in these samples than in populations that have historically been agriculturalists.

    5. Where's the Aterian? North Africa is relatively depauperate in variation in the large combined dataset. That may stem mostly from Holocene events, including the spread of West Asian populations across North Africa. But the low variation there doesn't readily fit the idea that an out-of-Africa dispersal of genes came from a North African source. I don't think the observations in the paper (centered around linkage disequilibrium with a very low SNP count) are enough to settle anything about this question, but I'd be nervous if I were busy trying to make the Aterian seem important to the modern human origins issue.

    Bottom line

    As interesting as these assertions look, I don't think that a lot of African prehistory is about to be rewritten. Obviously, geneticists need to get serious about reading some African archaeology. We already know that African regional populations were large and diverse during the Middle Stone Age, and that's a very good fit to the kind of genetic diversity we are seeing in these samples.

    The barrier is Holocene population history. Agricultural populations grew, spread, mixed with and absorbed hunter-gatherers, and what we left are the shattered remnants of ancient African population structure. Linkage may be the most powerful way we have to consider historical hypotheses using these SNP data, but if we're going to rely on it we have to control for recent demography and selection.

    And of course, it will be interesting to see a model that can integrate both Neandertal-African and within-African population histories. I don't really have a bang-up finish for this post, because there is immediately more work to be done with these data.

    References

    1. Henn BM, Gignoux CR, Jobin M, Granka JM, Macpherson JM, Kidd JM, Rodr\'ıguez-Botigué L, Ramachandran S, Hon L, Brisbin A, et al. 2011. Hunter-gatherer genomic diversity suggests a southern African origin for modern humans. Proceedings of the National Academy of Sciences [Internet] 108:5154–5162. Available from: http://dx.doi.org/10.1073/pnas.1017511108
    Tags: 
    population structure
    Bantu
    Hadza
    Middle Pleistocene
    Neandertal DNA
    Africa
    Bushmen
    hunter-gatherers
    Middle Stone Age
    admixture

  • Did humans colonize the northern latitudes without fire?

    Mon, 2011-03-14 20:47 -- John Hawks

    Wil Roebroeks and Paola Villa [1] review the evidence for human control and use of fire in the archaeology of Europe during the Middle Pleistocene (130,000-780,000 years ago) and earlier. They observe that no evidence of human-controlled fire occurs in Europe before 400,000 years ago. This raises a puzzle: How did humans occupy the northern part of Europe without fire?

    The argument about the antiquity of fire is not new. There is very early evidence of fire at Swartkrans, Koobi Fora, and Chesowanja, which includes burned bones and heated artifacts, along with clay nodules that show evidence of heating as high as 400 degrees Celsius. The criticism of these early finds (reviewed by James [2]) centers around the difficulty of distinguishing human-made fire from natural bush fires. The association of the fire with artifacts can be readily explained: archaeologists only look for evidence of fire where they already have artifacts. The remaining question is whether artifacts or bones have been heated to temperatures hotter than those possible in bush fires, thereby providing evidence of human involvement. Burned bone from Swartkrans at least did reach such temperatures, seemingly unlikely without human involvement given their presence in the cave. I tend to think that humans did control fire early in some cases.

    Roebroeks and Villa do not dispute possible earlier evidence of fire, but claim that it was not habitual. Or to put it another way, some early humans may have used fire, but many or most did not do so. The lack of fire seems particularly surprising in the northern latitudes of Europe, where sites like Happisburgh (and Pakefield) show evidence of human habitation in the late Lower Pleistocene. Their review of the early sites is really worth reading and impressively compact. Nonetheless, I can't quote it in full; it's just too much text to extract. After a discussion of the earliest archaeological occurrences, they turn to the long sequences from Arago and Gran Dolina, where we really should expect to see some evidence of fire if people were using it.

    Arago and Gran Dolina contain long sequences and large quantities of lithic and faunal remains, subjected to taphonomic analyses (34–36). Their settings are comparable to the ones that, in later times, have often provided strong evidence of fire, such as Bau de l’Aubesier, Grotte XVI, and Lazaret in France; Bolomor Cave in Spain (Dataset S1); and Middle Paleolithic/Middle Stone age caves in Israel and in South Africa. Traces of fire have been found in the upper part of the sequence at Arago, in layers younger than 350 ka. No charcoal, no burnt bones, nor any other evidence of fire have been reported from any of the assemblages from the lower levels (dated to MIS 10–14). No charred bones or heated artifacts have been reported from the Gran Dolina sequence (TD4– TD10). Rare charcoal particles have been found in thin sections of the TD6 sediments, but these sediments originate from the exterior of the cave, and there is evidence of low-energy transport (37); thus, the charcoal may not be in situ. However, the high density of human, faunal, and lithic remains as well as their state of preservation and refitting studies (38, 39) clearly indicate an occupation in situ with little postdepositional disturbance. The absence of any heated material from the long sequences of Gran Dolina and Arago, both documenting hominin occupations over several hundred thousand years (36, 40), is striking. This is a strong pattern, which can be tested by future work at other hominin habitation sites. We suggest that the European record displays a strong signal, in the sense that, from ~400 to 300 ka ago, many proxies indicate a habitual use of fire, but from the preceding 700 ka of hominin presence in Europe, we have no evidence for fire use.

    One thing that really impressed me visiting Roc de Marsal last summer was that the site preserves a long archaeological sequence in which some levels are densely packed with charcoal and the remains of hearths, and at least one well-defined layer, with abundant evidence of tools and debitage, just has hardly any evidence of fire at all. These were Neandertals, not Middle Pleistocene Homo, and they managed to get by without leaving any clear evidence of fire even though many Neandertal populations clearly did control and use fire extensively, including at this very site at other times.

    There really were people living in the Pleistocene of Europe who didn't use fire very much, at least as evidenced by relatively long cultural deposits in well-stratified rock shelters and caves. Unfavorable preservation can explain the lack of charcoal or hearths at some sites, but not all of them. If we don't have a single good instance of fire in Europe before 400,000 years ago, people may well have done without it.

    The authors' review of fire evidence after 400,000 years ago in Europe is also very useful, and they include supplementary data table with fuller information and references for all the sites they discuss. It is impressive just how much evidence has accumulated over the years, and Roebroeks and Villa have doggedly tracked it down. They conclude that Neandertals had essentially the same degree of control of fire as Upper Paleolithic humans, and consider the use of fire as a processing step in the manufacture of complex tools:

    A recent study provides evidence of early modern humans at the site of Pinnacle Point in Southern Africa regular use of heat treatment to increase the quality and efficiency of their stone tool manufacture process 164 ka ago (13). The authors infer that the technology required a novel association between fire, its heat, and a structural change in stone with consequent flaking benefits that demanded “an elevated cognitive ability.” They also suggest that, when these early modern humans moved into Eurasia, their ability to alter and improve available raw material may have been a behavioral advantage in their encounters with the Neandertals. However, this interpretation ignores that Neandertals used fire as an engineering tool to synthesize birch bark pitch tens of thousands of years before some modern humans at Pinnacle Point decided to put their stone raw material in it. In more general terms, a greater control and more extensive use of fire is sometimes (12) seen as one of the behavioral innovations that emerged in Africa among modern humans and favored the spread of modern humans throughout the world. As stressed by Daniau et al. (52), if extensive fire use for ecosystem management were indeed a component of the modern human technical and cognitive package, one would expect to find major disturbances in the natural biomass burning variability associated with and after the colonization of Eurasia by modern humans. In their study of microcharcoal particles from two deep-sea cores off of Iberia and France, spanning the 70- to 10-ka period of biomass burning, the authors did not recover any sign that Upper Paleolithic humans made any difference: either Neandertals and modern humans did not affect the natural fire regime, or they did so in comparable ways.

    I do think the silcrete processing is interesting, but so is the pitch processing. For that matter, the possibility of fire-hardening in the Schoeningen spears would be a case of deliberate production of a complex tool using fire (complex, in that the fire-processing adds a step).

    Gesher Benot Ya'aqov, in Israel dating to around 800,000 years ago, is a highly compelling site in terms of evidence of fire. There are distinct hearth areas that correlate with archaeological scatter and have burned nut hulls and other foodstuffs. While Roebroeks and Villa express skepticism about the earlier evidence from Africa (specifically pointing to the high likelihood of bush fire as an explanation), they do accept Gesher Benot Ya'aqov as a likely fire location, while discussing the strength of the evidence. It's not such a high threshold to set; it seems like other sites should be able to meet it if fire was common.

    Personally, I am quite ready to accept that fire was invented many times by Lower Pleistocene humans and may have occurred in some regions of the world ephemerally. The maintenance of this tradition may have been a challenge that these early humans couldn't meet over long spans of time. This view does imply that the advantages of fire, including cooking, were not a typical part of the repertoire of Early Paleolithic people. But that would be consistent with what we understand of traditions in other species of primates; where one population may be pursuing complex and apparently valuable extractive foraging that another population lacks, despite otherwise being ecologically similar.

    References

    1. Roebroeks W, and Villa P. 2011. On the earliest evidence for habitual use of fire in Europe. Proceedings of the National Academy of Sciences [Internet] 108:5209–5214. Available from: http://dx.doi.org/10.1073/pnas.1018116108
    2. James SR. 1989. Hominid use of fire in the {Lower} and {Middle Pleistocene}: a review of the evidence. Current Anthropology 30:1–26.
    Tags: 
    Early Pleistocene
    Koobi Fora
    Swartkrans
    technology
    Europe
    fire
    Gesher Benot Ya'aqov
    Neandertals
    Middle Pleistocene
    Synopsis: 
    Wil Roebroeks and Paola Villa claim the archaeological record doesn't provide evidence for systematic fire use in Europe before 400,000 years ago.

  • Mailbag: Chinese subspecies and Denisovans

    Tue, 2010-12-28 23:42 -- John Hawks

    Re: Denisova:

    Thank you for the very rapid FAQ on this fascinating new article! As you say,
    the findings should not be unexpected. Even the contribution from archaics to
    present-day Melanesians was foretold by the New Mexico group. Maybe this will
    put some sanity into those recurring "Modern humans are from China not Africa"
    stories. Pleistocene Homo sapiens in Asia just gets no respect! This seems to
    show a population of “Chinese Neanderthals” replacing H. erectus and later being
    replaced by OOA, but neither is quite 100%.

    Just thinking… If present-day populations, Neanderthals, and “Denisovans” make a
    near-trichotomy of SUBSPECIES, perhaps Homo sapiens mapaensis Kurth 1965 or Homo
    sapiens daliensis Wu Xinzhi 1981 will be found to have priority…

    Yes, I suspect those names may be available, depending on the timing of these population divergences. The Chinese record has several shoes left to drop.

    Tags: 
    Middle Pleistocene
    paleogenomics
    taxonomy
    China
    Denisova

  • Neandertal stories on parade

    Sat, 2010-12-04 23:21 -- John Hawks

    Long-time science journalist Robin McKie has a long article in The Observer about the Neandertals this weekend: "Neanderthals: how needles and skins gave us the edge on our kissing cousins".

    The article puts together several aspects of recent inquiry into Neandertal biology -- the genome sequencing, the dating questions over Châtelperronian artifacts from Grotte du Renne, and some of Steve Churchill's work on projectile versus thrusting weapons. There's a real interesting mix of stuff here, some that I agree with and basically find uncontroversial, and other stuff that I find to be outlandish or unsupported by any evidence.

    For example, McKie talked to Brian Fagan, who has a new book out (Cro-Magnon) that tries to describe the human "edge" over Neandertals. A good topic, but this paragraph is completely misleading:

    But which specific traits gave us such an advantage that we were propelled to global glory at the expense of the Neanderthals? In the suite of behaviours that we evolved in Africa 150,000 years ago, what were the characteristics that really made a difference and can therefore be considered as defining human attributes? There are many candidates – complex language and superior memory, for example. However, among many scientists there appears to be consensus that imagination and opportunism were critical attributes.

    There is no "suite of behaviours that we evolved in Africa 150,000 years ago." There just aren't any. There's no good evidence of symbolic expression, no projectile points, no subsistence innovations, no evidence of long-distance raw material procurement or trade. That's the big problem we have substantiating a modern human advantage -- the "modern" humans didn't seem to get many behavioral innovations in Africa that the Neandertals didn't get, and the Neandertals got them almost as early.

    It is an undeniable problem; there's no sense glossing over it. Churchill's (and John Shea's) ideas about projectile weapons are right now among the most reasonable suggestions, because there do seem to be relatively early (ca. 85,000-90,000 year old) projectile points in Africa.

    It would be convenient if there were better evidence that projectiles were a singular innovation. But as John Shea [1] wrote in 2006, the idea of projectile weapons seems to have gotten around widely, possibly including Neandertals:

    The evidence currently available instead favors an indigenous origin for projectile point technology in the Levant ca. 40–50 Ka. Similarly, the earliest European Upper Paleolithic stone artifacts that fit the TCSA criteria for projectile points, Chatelperronian points, Font Robert points (as well as Aurignacian split-based bone/antler points) do not have clear chronological antecedants in the Levant (though it is possible that other as-yet-unidentified projectile point types do). While it is possible that over-production of atmospheric radiocarbon between 30 and 50 Ka [39] obscures rapid geographical diffusion of projectile point technology the typological variability of the earliest likely stone and bone projectile points in Africa, the Levant, and Europe do not currently support a diffusion/migration hypothesis. It is vastly more likely that projectile point technology was developed convergently among African, Levantine and European hominin populations.

    I probably wouldn't stretch so far as to say that the Châtelperronian Neandertals were using projectile weapons, even if the points are consistent with that hypothesis. But considering that a big element of McKie's story is the dispute over the Châtelperronian evidence of ornamentation (at Grotte du Renne), I think it's fair to remind people that those late Neandertals had a lot of things going on. All the skeletal associations with the industry are Neandertal, and there are multiple sites representing the interesting material culture elements.

    I've actually been stunned lately by the number of people who have asked me about the Grotte du Renne paper and it's "demolishment" of the case for Neandertal ornamentation. I say stunned, because people seem completely unaware of the substantial Mousterian record of pigment processing and use.

    My candidate for the most subtly controversial element of McKie's story: the opening passage about the Swanscombe skull:

    Many treasures [at the Natural History Museum] compete for attention, but there is one sample, kept in a small plywood box, that deserves especial interest: the Swanscombe skull. Found near Gravesend last century, it is made up of three pieces of the brain case of a 400,000-year-old female and is one of only half-a-dozen bits of skeleton that can be traced to men and women who lived in Britain before the end of the last ice age. Human remains do not get more precious than this.

    However, the Swanscombe find is important for another, crucial reason: the skull is that of a Neanderthal

    I say that's controversial because it asserts that this 400,000-year-old skull is a Neandertal. The case for Swanscombe as a member of the Neandertal lineage has been mostly chronological, not because it has any pattern of derived Neandertal morphology. There were people in Europe before the Neandertals, they had a subset of Neandertal features, and so they were plausibly early members of a Neandertal lineage. But the genetic work this year, discussed later in the article, argued that humans and Neandertals shared a common ancestral population only 250,000-400,000 years ago. If that's true, the chronology is all wrong for Swanscombe to be a Neandertal itself. Indeed, this chronology would not permit Swanscombe to be a member of a population exclusively ancestral to Neandertals.

    But what, then, is it?

    I think the chronology is wrong, and I doubt whether the evidence will soon let us distinguish gene flow from isolation at this time depth. There's not much sense talking about the "human-Neandertal ancestral population" when some Neandertals were ancestors of some humans.

    Still, the Middle Pleistocene European population focuses the problem. If Neandertals themselves had derived much of their gene pool from Africa in the Middle Pleistocene, as the genetic work has suggested, what does that mean for specimens like Swanscombe? And if we substantially lengthen the chronology of human diversification, what does that mean for Middle Pleistocene Africans?

    References

    1. Shea JJ. 2006. The origins of lithic projectile point technology: evidence from Africa, the Levant, and Europe. Journal of Archaeological Science [Internet] 33:823–846. Available from: http://dx.doi.org/10.1016/j.jas.2005.10.015
    Tags: 
    hunting
    MSA
    Neandertals
    art
    Upper Paleolithic
    Europe
    Middle Pleistocene
    Neandertal DNA
    Swanscombe
    Chatelperronian

  • The paleolakes of Egypt

    Fri, 2010-12-03 13:08 -- John Hawks

    A paper in the December issue of Geology, by Ted Maxwell and colleagues [1], describes evidence for a "Lake Erie-sized" paleolake in southwestern Egypt. The existence of a large ancient lake has been suspected for many years based on the presence of fish fossils in Middle Pleistocene contexts far from any current body of water. The new paper uses range-sensing imagery to assess the likely extent of the paleolake from elevation data, one known occurrence of fish fossils, and landscape features that appear to substantiate an ancient lake terrace:

    We believe that the middle and late Pleistocene drainage was influenced by repeated Nile flooding, following on the working hypothesis of Haynes (1985), who suggested a large Pleistocene lake that drained into the Nile from what he termed the Kiseiba-Dungul depression. Using the elevation of the fossil (Middle Paleolithic) Nilotic fish found at Bir Tarfawi (Van Neer, 1993) as a base level, the SRTM data indicate that a paleolake at that level (247 m) would have flooded the entire Kiseiba-Tushka depression (Fig. 3), and is the same elevation at which the Selima paleochannels and other channel remnants to the west blend into the terrain (Fig. 2). We interpret the combination of topographic coincidence and ages of Middle Paleolithic occupations at Selima and Tarfawi as evidence of at least one lake level at that elevation, forming a local base level, reducing the competence of inflowing streams, and inhibiting channel incision below ∼247 m. Such a lake would have covered an area of 68,200 km2, and would have extended from the Sudan border (22°N) north to the Kharga and Dakhla Oases, until dammed by the limestone plateau at 26°N.

    They believe that the lake would have been filled by Nile outflow. The paper does not commit to any chronology, except to point out that a few late Acheulean sites are present in the basin near a presumed lower lake level of 190 m, which may represent a relatively stable size, flooded once or multiple times to the higher level of 247 m. Wired has a nice short description of the paper, which includes some dates that are not actually discussed in the paper.

    A better understanding of the Nile corridor is of course very important to the issue of human movement into and out of Africa during the Late Pleistocene. More recent Late Pleistocene and Holocene paleolakes are known up and down the Nile valley, from the Fayum to Darfur.

    I wonder if a Nile corridor that was ostensibly more habitable may have actually excluded gene flow back into Africa. A denser and more stable human population in this area would have been a relative population source much of the time, sending migrants out into adjacent regions. These regions would have been much less habitable at some times, but displacement of the large Nile valley population may have been impossible. Furthermore, a larger Nile corridor population would have been a reservoir for endemic parasites and diseases that would have posed challenges for migrants into the region.

    The problem on an evolutionary timescale is not getting people out of Africa, but explaining the level of population structure between regions that constantly shared an overland and shoreline connection.

    References

    1. Maxwell TA, Issawi B, and Haynes VC. 2010. Evidence for Pleistocene lakes in the Tushka region, south Egypt. Geology [Internet] 38:1135–1138. Available from: http://dx.doi.org/10.1130/G31320.1
    Tags: 
    Africa
    Middle Pleistocene
    paleoclimate
    Egypt
    geology
    Synopsis: 
    Acheulean-era people may have lived along an Erie-sized lake in the Nile corridor.

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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

Denisova

From a finger bone of an ancient human came the record of a completely unexpected population. My lab is working on the science of the Denisova genome.

Acceleration

The advent of agriculture caused natural selection to speed up greatly in humans. We're uncovering some of the ways that populations have rapidly changed during the last 10,000 years.

Malapa

Just outside Johannesburg, the Malapa site is producing some of the most exciting finds in human evolution. This site is the headquarters of the Malapa Soft Tissue Project.