john hawks weblog

paleoanthropology, genetics and evolution

MSA

  • Blombos pigment workshop

    Fri, 2011-10-14 02:23 -- John Hawks

    I know that some readers are starting to wonder if I've forgotten about paleoanthropology lately. Let's just say that the Neandertal and Denisova genomes have me very busy, and I don't think you'd want it any other way.

    But on the paleoanthropological front, Science has released a paper by Chris Henshilwood and colleagues [1] describing two toolkits used by ancient MSA people more than 100,000 years ago to grind pigment and mix it with animal fat, presumably for painting.

    I want to share a picture from the article (credit G. Moéll Pedersen), which shows one of the two toolkits in situ. I want to make a point about it that would be difficult without seeing the photo:

    That photo shows Tk1, the first toolkit. Now, here's the description of what Henshilwood and colleagues were able to interpret from the artifacts in the photo:

    We infer that manufacturing proceeded as follows: Pieces of ochre (FS1 and FS2) were rubbed on quartzite slabs to produce a fine red powder, and some were knapped with large lithic flakes. The ochre chips resulting from the latter were crushed with quartz, quartzite, and silcrete hammerstones/grinders. Quartzite grinders were used to crush goethite or hematite-rich lutite. Medium-sized mammal bone was crushed, probably with a stone hammer. The red or reddish brown color and cracked, flaky texture of some of the trabecular bone suggest that it was heated before crushing, probably to enhance the extraction of the marrow fat. The hematite powder, charcoal, crushed trabecular bone, stone chips, and quartz grains and a liquid were then introduced into the Haliotis shells and gently stirred (figs. S5, S25, and S26). Charcoal is rare in the layer-CP matrix, suggesting that it was a deliberate addition to the mix. The quartz and quartzite chips, produced during the action of crushing the ochre, and the quartz grains may have been incidentally incorporated.

    You can see how the complex interpretation was made possible by finding these things in association as part of one feature. If one or two of these pieces had been found separately, many archaeologists would be skeptical of such a story. Indeed, even the interpretation of this toolkit might appear incredible were it not for the second toolkit also found at the site. Archaeologists are conservative that way, they don't like to overinterpret the evidence. Even this series of events -- grinding, heating, mixing, and so on -- isn't very complicated compared to many activities that humans do every day. It's an example where Henshilwood and colleagues have advanced what archaeologically can show beyond a shadow of doubt about ancient people, but still leaves a gap in our understanding of the ancient cultural system.

    A complex behavioral pattern that is actually found cannot have been an isolated instance. Complexity implies a tradition of which these toolkits are only miniscule remnants.

    In this light, I should point out that the Blombos evidence is by far earlier than other evidence of pigment grinding and heating, but not unique in the South African MSA. Last year I linked to a Jennifer Viegas story about red ochre production at Sibudu Cave, South Africa. This is Lyn Wadley's work [2], and the research paper has since been published in the Journal of Archaeological Science. Also in that journal last year was a paper by Francesco d'Errico and colleagues [3], which described pigment nodules found in the Middle Paleolithic in Mt. Carmel site of Skhul, Israel. We have quite a lot of circumstantial evidence about pigment use in these early contexts both inside and outside Africa, and more is building all the time.

    The archaeological record is bad in many ways. The wooden artifacts preserved at Abric Romani, Spain, are another example of an exceptional archaeological find. I've been meaning to write about them since Julien Riel-Salvatore mentioned them last month. Archaeologists have been working the Middle Paleolithic for nearly 150 years, yet we know next to nothing about wooden artifacts. Abric Romani is not entirely alone, but is enough to show the existence of a broader tradition occupying this blind spot, because the extensive shaping of artifacts and labor used to create them implies a cultural knowledge and utility.

    References

    1. Henshilwood CS, d'Errico F, van Niekerk KL, Coquinot Y, Jacobs Z, Lauritzen S-E, Menu M, and Garcia-Moreno R. 2011. A 100,000-Year-Old Ochre-Processing Workshop at Blombos Cave, South Africa. Science 334:219 - 222.
    2. Wadley L. 2010. Cemented ash as a receptacle or work surface for ochre powder production at Sibudu, South Africa, 58,000 years ago. Journal of Archaeological Science [Internet] 37:2397–2406. Available from: http://dx.doi.org/10.1016/j.jas.2010.04.012
    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: 
    wood
    art
    art in science
    Blombos
    South Africa
    Abric Romani
    Spain
    Europe
    MSA
    Synopsis: 
    Complex toolkits from Blombos, South Africa, show pigment processing before 100,000 years ago.

  • Shellfish gathering, paleoanthropological strawman

    Sun, 2011-09-18 15:26 -- John Hawks

    We have known for many years that Lower Paleolithic people were using shellfish, fish, and littoral resources at sites across the Old World, from Trinil [1], Koobi Fora [2], Gesher Benot Ya'aqov [3], and elsewhere. I've discussed the evidence several times (maybe most usefully in "The shells of Trinil"). As I wrote last year ("Fishy story at Koobi Fora"):

    Aquatic animals aren't important because of their sheer numbers, but because they tell us about the flexibility of foraging behavior. Living hunter-gatherers eat turtles and reptiles when they can, and because they are usually small food packages, they often eat them where they find them instead of returning to a base camp first. Hunter-gatherers are flexible in what they eat and where they eat it. FwJj20 is showing at least a substantial taxonomic flexibility in the meat-eating of early Oldowan hunters.

    So why do we keep seeing stories that make shellfish consumption look like news when it's done by Neandertals, MSA Africans, or anybody else?

    I'm writing about this today because of a new paper in PLoS ONE by Miguel Cortés-Sánchez and colleagues, reporting on the shellfish remains in Bajondillo Cave, Spain [4].

    Shellfish collecting has been well characterized in some Mousterian contexts. Mary Stiner treated it systematically in her 1993 monograph, Honor Among Thieves, which is part of the graduate education of most young Paleolithic archaeologists. Stiner spent a lot of text quantifying shellfish use and gave a good discussion of the biases that make archaeologists find less evidence of shellfish consumption than there probably was.

    Most important, when you can walk along a shoreline and nosh shells, you're not very likely to haul many of them back to a cave several kilometers from the shore. In the Holocene, we find lots of archaeological localities where people were systematically collecting many shells and cooking them for large groups. For this purpose, the people carried baskets or sacks of shellfish for a good distance, and after they were consumed, the shells sometimes built up into large trash piles, or middens. We don't see shell middens in Mousterian or MSA contexts, but then we see very little of that kind of behavior with any kind of resources in MSA or Mousterian times. Here's what I wrote in 2008 ("Neandertal diet was not dolphin safe"):

    [I]t was hard to understand the excitement that accompanied last year's paper by Curtis Marean and colleagues (2007), who found evidence for shellfish exploitation at Pinnacle Point, South Africa. The press reported the result as if there were a shell midden, with abundant evidence for consumption. But actually the number of shells is fairly small -- all the shells from all the layers reported weigh less than a kilogram. That looks similar to the pattern of exploitation that Stiner had reported for the Neandertals at Moscarini, and more or less like the pattern at Vanguard and Gorham's Caves.

    The African MSA-era site with the most direct evidence of shellfish exploitation is at Abdur, Eritrea, where the stone tools are found in an ancient shore terrace, presumably at the very place where shellfish exploitation was happening [5]. That paper hinted at even earlier sites with similar evidence from Acheulean contexts along the Red Sea rift, where subsidence of the rift floor has left some ancient coral reefs exposed, Acheulean tools embedded within them. I should also point out indirect evidence on the basis of species abundance for human exploitation of giant clams in the Red Sea ("The ancient struggle for existence between humans and giant clams").

    In other words, archaeologists have found quite a lot of evidence of coastal resource use by early people, despite the steep biases against it. In the case of aquatic animal exploitation, they've got it as early as the Oldowan, 1.95 million years ago [2].

    Cortés-Sánchez and colleagues [4] add detail to this record but don't really broaden the picture. Mousterian shellfish acquisition around 150,000 years ago, well before the last interglacial, is earlier than many well-known instances of MSA shellfish utilization. But we know that much earlier humans were using these coastal resources, so it's hardly news. As at other sites, the mollusc remains are not very dense: a minimum of 16 shells in one layer, 66 shells in another, 80 in a third. If I were going to make a story out of it, I would direct more attention to the pearl, first I've ever heard of in a Neandertal site.

    More important is the paper's demonstration that humans actually processed the shells. Cortés-Sánchez and colleagues contrast the condition of continental and marine molluscs in the same levels, to show the systematic breakage and burning of the marine species:

    [A]lmost all of the marine mollusks exhibit intensive mechanical fracturing, with sharp edges on their shells suggestive of an absence of post-depositional transport, and very few appear complete (i.e., barely 7% at Bj19). Such fracturing, coupled with the absence of shells eroded by water, indicates that the marine mollusks from Bajondillo Cave, and in particular those from Bj19 do not represent “background fauna” from the nearby beach, a phenomenon that has recurrently caused problems in the association of early Middle Paleolithic shellfish deposits from the Mediterranean with paleo-human activities. In addition, a substantial percentage of the mussels exhibit burning marks (Figure 4: 1–6). These are recorded on 48% of the adult specimens from Bj19, the young mussels never exhibiting such traces. Thermo-alterations suggest consumption rather than passive burning, given that in most cases only the outer portions of the shells appear carbonized and/or flaked. An indirect line of evidence supporting this same hypothesis is provided by five of the epibiont barnacle remains that fire not only detached from the mussel shells but that in that process were thoroughly carbonized, as is the case of the four specimens from Bj18 (Figure 4: 8,11) or else calcined, as happens with the specimen from Bj19 (Figure 4: 12).

    I appreciate the paper's list of 24 previously-published Neandertal sites that present mollusc remains. It would be useful to compile a broader list including MSA sites. Personally, I hope to never read again a headline about how surprising or significant was shellfish use by early humans.

    References

    1. Joordens JCA, Wesselingh FP, de Vos J, Vonhof HB, and Kroon D. 2009. Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia). Journal of Human Evolution 57:656-71.
    2. Braun DR, Harris JWK, Levin NE, McCoy JT, Herries AIR, Bamford MK, Bishop LC, Richmond BG, and Kibunjia M. 2010. Early hominin diet included diverse terrestrial and aquatic animals 1.95 Ma in East Turkana, Kenya. Proceedings of the National Academy of Sciences of the United States of America 107:10002-7.
    3. Alperson-Afil N, Sharon G, Kislev M, Melamed Y, Zohar I, Ashkenazi S, Rabinovich R, Biton R, Werker E, Hartman G, et al. 2009. Spatial Organization of Hominin Activities at Gesher Benot Ya'aqov, Israel. Science [Internet] 326:1677–1680. Available from: http://dx.doi.org/10.1126/science.1180695
    4. Cortés-Sánchez M, Muñiz A, Simón-Vallejo ía D, Lozano-Francisco ía C, Vera-Peláez JL, Finlayson C, Rodríguez-Vidal J, Delgado-Huertas A, Jiménez-Espejo FJ, Martínez-Ruiz F, et al. 2011. Earliest Known Use of Marine Resources by Neanderthals. PLoS ONE 6:e24026.
    5. Walter RC, Buffler RT, Bruggemann JH, Guillaume MM, Berhe SM, Negassi B, Libsekal Y, Cheng H, Edwards RL, von Cosel R, et al. 2000. Early human occupation of the Red Sea coast of Eritrea during the last interglacial. Nature 405:65-9.
    Tags: 
    shellfish
    diet
    Neandertals
    Middle Paleolithic
    Mousterian
    MSA
    modern
    behavior
    foraging
    aquatic resources
    Synopsis: 
    Why do archaeologists always make shellfish gathering sound like news, when we know it's not surprising?

  • Views from Rhino Cave, Tsodilo Hills, Botswana

    Tue, 2011-05-31 03:55 -- John Hawks

    Sheila Coulson, Sigrid Staurset and Nick Walker [1] (doi isn't working yet, so here's a PDF link, 12 MB) have published a long summary of findings from Rhino Cave, in the Tsodilo Hills of northern Botswana. These hills are huge isolated rock formations, or inselbergs, that jut out of relatively flat surrounding countryside. That makes them highly visible in the folklore and traditions of local people, and some caves in them have been used by people for tens of thousands of years.

    Coulson and colleagues describe the setting of Rhino Cave, named for a rock painting within it.

    It is...easy to understand how the site evaded detection, as it is perched high on the northernmost ridge of Female Hill and can only be approached by scrambling over, or squeezing between, massive boulders. Gaining entry to the cave is only slightly less arduous. On the western side of the ridge there is a raised, narrow, crawl space that ends with a considerable drop into the site. Alternatively, the wider eastern entrance offers two options: a two-meter jump or a slide down a steep boulder face, followed by a scramble over a rock-strewn opening near the present day floor.

    I love these kinds of sites where you know that every lithic was brought in by people. That can tell you a lot about how people used the site, and the authors use that to advantage. But Coulson and colleagues do not yet have new dates for the deposits. The old dates appear too recent and are problematic because of their mismatch with other local MSA sites such as White Paintings Shelter and ≠Gi, both between 66,000 and 95,000 years old. The Rhino Cave assemblage may be comparable to these in age. The paper reports that substantial amounts of exotic stone materials including silcrete and chalcedony must come from more than 50 or 100 km away, respectively.

    MSA exotic flakes from Rhino Cave, figure 5 from Coulson et al. 2011

    Some of the flakes made from exotic raw materials, Figure 5 from the paper. All photos in the article copyrighted and used courtesy of Sheila Coulson.

    There is a lot to the lithic collection besides the points, but I think these are interesting and certainly visually striking.

    MSA points from Rhino Cave, figure 4 from Coulson et al. 2011

    Coulson and colleagues noticed that many of the points were burned, and this was not easily explained by the incidental presence of fires in the cave, nor did it particularly appear to be explained in terms of the "heat-treating" that people used to make silcrete more suitable for artifact production at some other MSA sites.

    In summary, there is a very distinctive pattern of burning at this site. A group of 26 MSA points and their associated debitage are heat damaged to the point of destruction. However, they have not been exposed to long-term burning of the type that is commonly found when an artifact is discarded into a hearth -- a common feature on any number of Stone Age sites. It is suggested that these MSA points and their associated manufacturing debitage were selectively and intentionally burnt in short-term restricted fires that caused their coloring to change to various reddish hues.

    This is part of what Coulson and colleagues tentatively call evidence of symbolic or ritual behavior at the site. People climbed up to this out-of-the-way place with colorful stone from far away. The manufacturing debris shows that they made stone points in the cave. And they then left many of those points in the cave, some of them burned and destroyed or abandoned. At a minimum, it's curious. Adding everything together (including the cupules discussed below), it seems clear that the site was not used for purely utilitarian purposes. What that means about ancient social or cognitive systems is not obvious.

    The article is open access, and full of amazing full-size color photos. I don't know why everyone doesn't publish their sites this way. For example, here's a photo of the site and night, where Coulson and colleagues experimented with flickering light against the carved wall:

    Rhino Cave, night-time flicker light, figure 17 from Coulson et al. 2011

    This stone face, which has been pecked at and scooped out for many thousands of years, is the most distinctive aspect of the site. Coulson and colleagues believe that some of the existing marks reflect very great antiquity, and they have natural spalls of the rock face that broke off in MSA times and integrated themselves into MSA layers. Some (maybe most) of the cupules are recent, and the pictorial art inside the cave is also late. But at least some of the surface carving appears to have been MSA in age.

    Rhino Cave, cupules in rock wall, figure 12 from Coulson et al. 2001

    Cupules in rock face, detail.

    The paper discusses some evidence for pigment grinding at the site, including smooth-edged pieces of specularite and several small striated sandstone slabs (say that fast five times) presumably used as grindstones. Color goes together with the burning (to enhance color?), but this combination is not found elsewhere. Rhino Cave is in that way unique.

    They indicate that the rock face is exposed to flickering daylight through a shaft at certain times, which they attempted to simulate with the flickering light photograph. Really I can't think of any better way to give readers an impression of what it would be like to visit the site.

    References

    1. Coulson S, Staurset S, and Walker N. 2011. Ritualized Behavior in the Middle Stone Age: Evidence from Rhino Cave, Tsodilo Hills, Botswana. PaleoAnthropology [Internet] 2011:18–61. Available from: http://dx.doi.org/10.4207/PA.2011.ART42
    Tags: 
    MSA
    Africa
    Botswana
    sites
    art
    Synopsis: 
    Summary of Sheila Coulson and colleagues' richly illustrated work on this MSA-era site

  • 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

  • MSA ochre "factory"

    Thu, 2010-06-03 11:49 -- John Hawks

    Jennifer Viegas covers the recent discoveries at Sibudu Cave, South Africa: "Stone Age color, glue 'factory' found".

    A once-thriving 58,000-year-old ochre powder production site has just been discovered in South Africa. The discovery offers a glimpse of what early humans valued and used in their everyday lives.

    The finding, which will be described in the Journal of Archaeological Science, also marks the first time that any Stone Age site has yielded evidence for ochre powder processing on cemented hearths -- an innovation for the period. A clever caveman must have figured out that white ash from hearths can cement and become rock hard, providing a sturdy work surface.

    This appears to have been a site of intensive processing, with thousands of pieces of ochre nearby. I wonder whether the intensification implies a trade network for exchange of the product.

    Tags: 
    Sibudu
    art
    South Africa
    MSA

  • Misinformation about brain evolution

    Mon, 2010-03-29 10:58 -- John Hawks

    Due to Jerry Coyne, I encountered an interview in the Guardian with Colin Blakemore: "Colin Blakemore: How the human brain got bigger by accident and not through evolution."

    The headline is a misnomer, as Blakemore is not denying evolution, he is denying selection. But Blakemore's argument is based completely on a false presentation of the facts. Consider:

    The question is: why is it so big compared to the brains of our predecessors, such as Homo erectus? Until 200,000 years ago, there had been a gradual increase in brain size among hominins, starting three million years ago. Then, abruptly, there was a remarkable increase of about 30% or so.

    That's Blakemore. Now, here's a chart of endocranial volumes of Pleistocene human fossils:

    Endocranial volumes of Pleistocene human fossils

    Endocranial volume against time for fossil Homo.

    Time is in thousands of years before present, running left to right.

    As you can see, there's no sudden jump 200,000 years ago, or at any other time. The data, such as they are, are consistent with a single pattern of increase over time, as pointed out by Sang-Hee Lee and Milford Wolpoff (2003).

    Heck, it's the lack of a sudden jump that has gotten all the attention. Because if "modern" humans suddenly showed up in Africa 200,000 years ago, and all of a sudden had vastly larger brains than any other hominins, wouldn't that be a simple and tidy story? Don't you think we'd all be talking about the sudden origin of modern humans as reflected by their larger brains?

    It just didn't happen.

    Well, it's one thing to be empirically wrong. That's a simple error that's easily corrected. But Blakemore, relying on the erroneous assumption of a single shift in brain size, asserts that neutral macromutations must be an important mode of human brain evolution:

    Genetic studies suggest every living human can be traced back to a single woman called "Mitochondrial Eve" who lived about 200,000 years ago. My suggestion is that the sudden expansion of the brain 200,000 years ago was a dramatic spontaneous mutation in the brain of Mitochondrial Eve or a relative which then spread through the species. A change in a single gene would have been enough.

    I hope that the empirical pattern is enough to convince you that this hypothesis is false. The "sudden increase" simply did not happen.

    But in case you need more persuasion: Blakemore here assumes that the increase in brain size had no negative consequences. Otherwise it couldn't proceed neutrally. Here is his argument:

    The environment of early humans was so clement and rich in resources that this greedy new brain, which would have absorbed even more of the body's energy, could be sustained without danger. Later, when times got hard, during droughts or climate changes, it helped us deal with these crises, which could otherwise have killed us off, by dreaming up novel ideas to problems.

    You see the outline: Life was easy, and humans could grow fat-brained, like so many sheep. Fortunately, our fat brains were then useful when times were tough. Blakemore describes this as somehow different from the idea that brains were adaptive -- it's in fact just another adaptive story for larger brains.

    But it falls apart, when we consider that assumption -- life was easy. I put it to my students this way: Suppose you lay a lot of sugar beets out on your land. What will happen to the deer population?

    The answer is not that the deer will grow fat-brained and later evolve to conquer humanity. The answer is that there will be a lot more deer.

    Population growth is much faster than adaptation, and it's hundreds of times faster than a neutral gene can transit through the population. Humans in the past were not a static population, living in peace with an abundant environment. They were repeated faced with Malthusian crises -- on submillennial timescales. That's why a close understanding of climate variability is so relevant to our evolution. The fact that tools and behaviors change so slowly in the Middle Pleistocene is informative -- it shows that humans weren't coming up with dramatically new ways to track shifting ecologies.

    And that means that the selection pressures of the energetic and life history constraints on the brain were repeatedly imposed on human populations. A substantial increase in brain size should have immediately been disadvantageous -- if it had no compensatory benefits to fitness.

    What remains is testing the hypotheses about those benefits to fitness. Blakemore actually is presenting one such hypothesis -- that a larger brain mostly was adaptive because of its ability to transmit traditions. That's testable, and is consistent with the greater transfer of information apparent in recent archaeological traditions compared to Middle Pleistocene ones. But there are other hypotheses as well, and it is quite difficult to compare them with the available record.

    That's why it's so important to state the empirical record accurately.

    UPDATE (2010-03-29): A reader points out that Malthusian crises, in terms of resource or food availability, may have been avoided by warfare or predation -- people kill each other instead of starving. I see that point, particularly where we consider the way that epidemic disease can relax competition for food until population growth resumes. Performing well under predation or competition would be one way that brain size might have had compensatory benefits to fitness beyond its energetic and life history costs.

    References:

    Lee S-H, Wolpoff MH. 2003. The pattern of evolution in Pleistocene human brain size. Paleobiology 29:186-196.

    Tags: 
    paleoclimate
    demography
    MSA
    population growth
    brain
    Middle Pleistocene

  • Return of the "amazing" Boskops

    Mon, 2010-01-04 09:19 -- John Hawks

    Oh, good grief!

    [post UPDATED]

    I have had an unusual number of hits the past few days, so I went through my logs looking for the source. Turns out people are reading my 2008 review of the "Boskops race"("The 'amazing' Boskops").

    Over 10,000 people have read that post since the New Year began. That post has always gotten a recurring readership, because of a 2008 book by Gary Lynch and Richard Granger, Big Brain: The Origins and Future of Human Intelligence.

    Evidently the book is about to come out in paperback. And Discover magazine, which gave the book a fairly positive review on its release, has now reprinted an excerpt detailing the wondrous features of the Boskops race ("What Happened to the Hominids Who Were Smarter Than Us?"). Someone copied the whole thing to Richard Dawkins' website. And people reading the excerpt are trying to find out more about this fantastic story, and finding my blog.

    Well, to all those seeking the light of paleoanthropology, welcome!

    To those who have linked the post: I want to let you all know that your links have directed more than 10,000 people to find some actual true information about the "Boskop race". Good work out there!

    What can I do to update people, now that this story is spreading once again? My original post gives a short history, but was not based on a real review of the book. I was just trying to get some accurate information out there.

    Now I have read the excerpt, and much (but not all) of the Boskop-related text in the book (courtesy of Amazon).

    It's worse than I feared. The excerpt actually presents 1920's-era anthropology as if it were the state of our knowledge about Boskop and the "Boskop race" today. I have not found any passages in the book or chapter notes that contradict the excerpt's portrayal. I cannot find references or citations of post-1940 research on skeletal remains or archaeology from southern Africa. There's no hint of what happened after archaeologists began to use radiocarbon dating, nor do we hear even the identity of any specimens, except for the original (and fragmented) Boskop skull itself.

    How can this be? From the book's notes, it appears that the authors didn't find any information on these topics:

    One of the oddities in the Boskop story is the disconnect between the rich trove of references from the early twentieth century, and the paucity of references after that time (Lynch and Granger 2008: 218).

    I find that very sad, because there is a much richer trove of references after 1958. Archaeologists have developed a deep understanding of the chronology and material culture of LSA and later hunter-gatherers around the Cape and northward. Skeletal biologists have studied the health status, demography, and morphology of Holocene and earlier peoples. Some have even examined the endocranial volumes of southern African skeletal samples, and have tested the hypothesis of trends in brain size over time.

    All this work shows a very different picture than that sketched by Lynch and Granger.

    I'm going to be very measured, because while I am often snarky, I rarely come straight out and write that something is bunk. The portrayal of "Boskops" in the Discover excerpt is so out of line with anthropology of the last forty years, that I am amazed the magazine printed it. I am unaware of any credible biological anthropologist or archaeologist who would confirm their description of the "Boskopoids," except as an obsolete category from the history of anthropology.

    [UPDATE (2010-01-04): I have heard from Amos Zeeberg, the Web editor at Discover. He writes that the excerpt was intended to run identified as a "controversial idea, but that context didn't come across as intended." The web page has been changed to make that context clear, and to link to my discussion here. I think it's great that he responded so quickly, although I think that this case is not controversial, it's non-science. ]

    Besides that, the authors make several questionable statements about the relative sizes of parts of the brain and their relation to cognition and behavior in ancient hunter-gatherers.

    IQ of fossils

    We have no credible way of estimating the IQ of a fossil skull. The excerpt claims:

    Even if brain size accounts for just 10 to 20 percent of an IQ test score, it is possible to conjecture what kind of average scores would be made by a group of people with 30 percent larger brains. We can readily calculate that a population with a mean brain size of 1,750 cc would be expected to have an average IQ of 149.

    First of all, there never was any human population with a 1750 cc average brain size.

    Now, taking the counterfactual: A regression equation within a population can predict an expected value for an individual within that population. But in population genetics, the average IQ that we would predict for a population with a 1750 cc average, depends on how the brain got to be that size. Natural selection on intelligence or brain size would have altered the relation that holds within humans. Nor do we know whether the present-day correlation would have characterized any ancient population -- or indeed most living human populations. The current value in Europeans may be an artifact of Holocene genetic changes.

    The authors do not list the specific regression that they use, or its source. The correlation relates to the proportion of variance explained by the relation of brain size and intelligence is irrelevant to this prediction. What we want to know is the slope of the regression. The prediction here would require a slope of 0.14, assuming it had been derived from a population with a mean male volume of 1400 cc and an average IQ of 100. That's a higher slope than I've seen reported in any analysis of the brain size - IQ relationship.

    The "inconceivable" prefrontal cortex

    We know little about the relative sizes of cortical areas in fossil hominins. The excerpt claims that the prefrontal area of a Boskop must have been "inconceivably large"

    Going from human to Boskop, these association zones are even more disproportionately expanded. Boskop’s brain size is about 30 percent larger than our own—that is, a 1,750-cc brain to our average of 1,350 cc. And that leads to an increase in the prefrontal cortex of a staggering 53 percent. If these principled relations among brain parts hold true, then Boskops would have had not only an impressively large brain but an inconceivably large prefrontal cortex.

    First of all, there was never any human population with an 1750 cc average brain size.

    Again, the example is a misapplication of regression, in this case an among-species regression. The excerpt appears to assume that the evolution of relative prefrontal area among human populations must have followed the same disproportionate pattern of increase as that between humans and chimpanzees. Prefrontal cortex volume is larger, relative to brain size, in humans compared to other primates. But this relation is not very much larger in humans -- recent estimates range from less than 10 to 30 percent compared to chimpanzees (Holloway 2002, Schoenemann et al. 2005). Even if some ancient humans had a second burst of expansion, again as great as that on the hominin lineage leading from apes to us, their prefrontal volume would hardly be "inconceivably large".

    And there's no reason at all to assert such a second, bonus expansion of prefrontal area in ancient humans. The prefrontal area ought to scale close to the total brain size, as it does within living people.

    Science fiction

    The authors actually cite and discuss Loren Eiseley's Immense Journey, which I discussed in my earlier post. Eiseley was a naturalist/anthropologist/science writer, and a very popular essayist -- he's the kind of person we could use more of today. But his reflections on the "Boskop people" were a fictional trope -- and were already, in 1958. He was a great writer, but relying on Eiseley for up-to-date information on anthropology is like relying on Truman Capote as an authority on crime.

    Suppose that we take the "Boskops" story just as a science fiction fairy tale -- a story showing that evolution is not synonymous with progress, as the authors imply. I still conclude that much of the other information about brain size in the excerpt is questionable or false.

    The authors speculate:

    Our big brains give us such powers of extrapolation that we may extrapolate straight out of reality, into worlds that are possible but that never actually happened.

    That's Boskop, all right. Extrapolated straight from worlds that never happened!

    References:

    Broom R. 1918. The evidence afforded by the Boskop skull of a new species of primitive man (Homo capensis). Anthropol Pap Am Mus Nat Hist 23 (2):63-79.

    Brothwell DR. 1963. Evidence of early population change in central and southern Africa: Doubts and problems. Man 63:101-104.

    Dart R. 1923. Boskop remains from the south-east African coast. Nature 112:623-625.

    Dubow S. 1996. Human origins, race typology and the other Raymond Dart. African Studies 55:1-30.

    Henneberg M, Steyn M. 1993. Trends in cranial capacity and cranial index in Subsaharan Africa during the Holocene. Am J Hum Biol 5:473-479.

    Holloway RL. 2002. How much larger is the relative volume of area 10 of the prefrontal cortex in humans? Am J Phys Anthropol 118:399-401. doi:10.1002/ajpa.10090

    Pycraft WP. 1925. On the calvaria found at Boskop, Transvaal, in 1913, and its relationship to Cromagnard and Negroid skulls. J Roy Anthropol Inst 55:179-198.

    Schauder DE. 1963. The anthropological work of F. W. FitzSimons in the Eastern Cape. S Afr Archaeol Bull 18:52-59.

    Semendeferi K, Armstrong E, Schleicher A, Zilles K, Van Hoesen GW. 2001. Prefrontal cortex in humans and apes: a comparative study of Area 10. Am J Phys Anthropol 114:224-241.

    Singer R. The Boskop "race" problem. Man 58:173-178.

    Singer R. 1962. Presidential Address 1962: The South African Archaeological Society: The future of physical anthropology in South Africa. S Afr Archaeol Bull 17:205-211.

    Stynder DD, Ackermann RR, Sealy JC. 2007. Craniofacial variation and population continuity in the South African Holocene. Am J Phys Anthropol 134:489-500. doi:10.1002/ajpa.20696

    Tags: 
    MSA
    pseudoscience
    South Africa
    Boskop
    paleoneurology
    race

  • Seeds of MSA diet breadth

    Sat, 2009-12-19 20:56 -- John Hawks

    Julio Mercader reports in a short Science paper that the MSA stone artifacts from Ngalue cave, Mozambique, preserve thousands of grains of sorghum starch, along with a few other grasses and palm pith.

    The role of starchy plants in early hominin diets and when the culinary processing of starches began have been difficult to track archaeologically. Seed collecting is conventionally perceived to have been an irrelevant activity among the Pleistocene foragers of southern Africa, on the grounds of both technological difficulty in the processing of grains and the belief that roots, fruits, and nuts, not cereals, were the basis for subsistence for the past 100,000 years and further back in time. A large assemblage of starch granules has been retrieved from the surfaces of Middle Stone Age stone tools from Mozambique, showing that early Homo sapiens relied on grass seeds starting at least 105,000 years ago, including those of sorghum grasses.

    This is another of those very interesting technical developments in archaeology. The use of grass seeds may not be surprising in itself. Some think that australopithecines were eating grass seeds for a substantial amount of their diet; some (notably Clifford Jolly and Jonathan Kingdon) have suggested that grass seeds were one of the resources that prompted the evolution of bipedality. The dental reduction in early humans doesn't argue strongly against seed consumption; they are an important part of the diet for many recent hunter-gatherers including Australians. But it's nice to see a direct confirmation that humans were gathering seeds relatively intensively.

    How intensive? Well, there is a slight problem:

    It is not clear why the tools should be mostly coated with grass starches and not so much with other types of starch. It is possible that high-starch–bearing grass refuse built up considerably in the cave’s main chamber at times of human occupation, thus coating both tools that were used in the processing of grass seeds and others that were not.

    Hmmm. On the one hand, that means pretty intensive grass collection. On the other, if such a substantial fraction of the actual sedimentary debris in the cave was composed of anthropogenic plant waste, it's probably not possible to get an accurate picture of the importance of the seeds as a fraction of the diet. It's a data point: these people, living around this cave, used a lot of Sorghum grasses and processed seeds in some way with stone tools.

    It makes me wonder about what non-stone implements they may have used. Winnowing baskets?

    References:

    Mercader J. 2009. Mozambican grass seed consumption during the Middle Stone Age. Science 326:1680-1683. doi:10.1126/science.1173966

    Tags: 
    plants
    Africa
    MSA
    Mozambique
    Late Pleistocene
    diet

  • Middle Stone Age bed and breakfast

    Thu, 2009-10-15 00:39 -- John Hawks

    On occasion, I point out interesting findings from archaeological chemistry and microscopic study of site formation processes. Last month, I pointed to the ability to distinguish animal and plant fat residues on ancient artifacts. Before that, there was the discovery of flax fibers from the Upper Paleolithic of Dzudzuana Cave, Georgia.

    In July, a paper by Paul Goldberg and colleagues described the "micromorphology" of the sediments from Middle Stone Age levels of Sibudu Cave, South Africa. The excavations at Sibudu have been able to distinguish many distinct stratigraphic units with distinctive spatial locations and compositions. Micromorphology involves looking at these sediments in microscopic detail, picking out small grains of crushed bone, charcoal, plant fibers, phytoliths, and other materials.

    Goldberg and his colleagues were able to make some very cool observations. For one thing, they have charred drips of broiled grease:

    Two types of amorphous organic combustion remains were identified in samples from Sibudu: a type with a typically vesicular texture and a type with a cracked texture. The first type was found as isolated bodies, subrounded with a diameter of 10 µm to 1 mm, and they exhibited no evidence of cell structure. Bubbles or vesicles give the bodies a highly porous nature, and they are often thin walled. The microstructure of these homogenous or finely heterogeneous isotropic particles and their droplet-shaped occurrence suggest that these bodies were originally fluid and that they underwent a degassing process but have since hardened. These bodies resemble char and are probably derived from the burning of flesh or animal fat (104-105).

    Mmmmm...MSA barbecue. The other type of "amorphous organic combustion remains" are charred resins, from trees or seeds. Mmmm...MSA smokehouse.

    Second, they have beds.

    Because of its long fibrous nature, it seems that this material consists of herbaceous plants, possibly some type of sedge, reed, or grass. There is no evidence to suggest that this plant would have grown naturally in the rock shelter, and the presence of clay aggregates derived from the river valley found in association with the laminated plant fibers implies that the grass or reed was transported to the cave from the nearby Tongati River by the shelter’s inhabitants.

    The compact and laminated structure of the organic fibers in this microfacies also suggests that, once brought to the cave, the grass or reed was subjected to compaction, most likely through trampling. Further evidence supporting the interpretation of trampling is seen in the stringers of charcoal, clay aggregates, and burnt bone that define horizontal and subhorizontal surfaces on top of and within the laminated organic fibrous material. Pieces of éboulis and lithic fragments also define surfaces wi thin the microfacies. The fact that this grass or reed was transported to the cave by humans and that once there it was influenced by human trampling suggests that this microfacies represents a type of constructed bedding. If this is the case, then Sibudu contains the oldest evidence for constructed bedding, significantly older than that reported at the open-air site of Ohalo in Israel (Nadel et al. 2004).

    The bedding material was in some instances burned, in some instances swept or trampled in such a way that the regular alignment of the phytoliths was jumbled and disrupted. They interpret this as efforts to "maintain" the site -- in other words, housekeeping:

    What seems a likely and reasonable scenario is that the original organic matter of this laminated layer of sedges, grass, or reeds was completely combusted, resulting in total ashing of the organic material. The calcitic ash in this microfacies was transformed through phosphatization, as evidenced by the presence of a few remnant pockets of phosphate in this microfacies. The fact that large crystals of gypsum often form directly below these phytolith layers provides suggestive evidence for the downward leaching of CO3- or P-rich solutions.

    Just an aside -- that is such interesting chemistry, like the organic materials and ash are melting down into the underlying deposits.

    The association between microfacies 2 and 4 suggests that the sedges, grass, or reeds that were brought into the cave for bedding were usually burned and probably by humans when they no longer used the bedding. This observation explains the sequence seen in samples SS-6 and SS-5 of laminated nonburnt fibrous organic material grading into laminated burnt fibrous organic material with phytoliths (microfacies laminated type 2B); the sequence is finally capped by a layer of laminated phytoliths.

    Why did they burn the stuff? The authors guess that they were trying to cut down on parasites:

    Together, this evidence shows that not only were the occupants of Sibudu bringing grass or reeds into the cave—likely for the construction of bedding—but they were periodically burning them, possibly as a means to remove pests or insects that had colonized the beds. (Smoldering goat dung and organic matter can be observed in many parts of the Middle East, including Hayonim, where tick removal is one of the important objectives; P. Goldberg 1992, personal observation.)

    The MSA at Sibudu dates to between 45,000 and 65,000 years ago, with the best evidence for bedding in the units that OSL puts around 50,000 years ago. The implications of the "site maintenance" and spatial characteristics of the site are mentioned in the paper's conclusion:

    Organization of living space, and particularly a deliberate use of space, has been suggested by Wadley (2001) and also Binford (1996) as an important trait of culturally modern behavior, reflecting a more complex social organization. While the evidence from the laminated units at Sibudu may reflect such organization, the lack of evidence for such spatial organization, such as is the case for the lower homogeneous layers at Sibudu, should not automatically suggest that occupation in these units was any less complex.

    If spatial organization of living space is a "modern" behavioral feature, it is one shared by Neandertals (I noted that briefly in a 2006 post). But then, it's shared by any number of invertebrates, also. I think the interpretation of this kind of behavior will have to wait until we have more sites investigated with comparable methods. As the introduction to the current paper points out, a lot of spatial information could be brought out of these micro-scale studies, if they were conducted routinely.

    References:

    Goldberg P, Miller CE, Schiegl S, Ligouis B, Berna F, Conard NJ, Wadley L. 2009. Bedding, hearths, and site maintenance in the Middle Stone Age of Sibudu Cave, KwaZulu-Natal, South Africa. Archaeol Anthropol Sci 1:95-122. doi:10.1007/s12520-009-0008-1

    Tags: 
    archaeology
    early modern
    South Africa
    plants
    Africa
    MSA
    Synopsis: 
    Archaeological chemistry at Sibudu turns up evidence of grease drippings and bedding.

  • Paleoclimate in southern Africa

    Sat, 2009-04-18 21:45 -- John Hawks

    The Tswaing Crater is around 40 km from Pretoria, South Africa. It was created by an asteroid impact some 200,000 years ago, which released roughly the energy of the Tunguska explosion of 1908. The crater's floor has a salt pan, where people have gone to gather salt since MSA times. The floor has been cored, with analyses of sediment salinity and pollen, giving a record of climate over the last 200,000 years. For example, a 2007 paper by Kristen and colleagues:

    Sediments from Lake Tswaing (25°24'30'' S, 28°04'59'' E) document hydrological changes in southern Africa over the last 200 Ka. Using high-resolution XRF- scanning, basic geochemistry (TIC, TOC, TN), organic petrology and rock-eval pyrolysis, we identify intervals of decreased carbonate precipitation, increased detrital input, decreased salinity and decreased autochthonous (algal and bacterial) organic matter content that represent periods of less stable water column stratification and increased rainfall. Between 200 and 80 Ka BP, these intervals appear to be contemporaneous with local summer insolation maxima, indicating a strong influence of precessional variability (~23 Ka) on African subtropical climate. This influence weakens during the last glacial period (~80 to 10 Ka BP), when humid intervals at 73 to 68 Ka, 54 to 50 Ka, 37 to 35 Ka and 15 to 10 Ka BP are largely out of phase with insolation changes, and presumably reflect southward displacement of the ITCZ (Inter Tropical Convergence Zone) and/or changes in ocean circulation.

    I'm pointing to this study because it is one that documents wetter periods during the span between the Howieson's Poort (roughly 60,000 years ago) and the Last Glacial Maximum (around 18,000 years ago). There are some who have claimed that this was a long span of aridity in southern Africa -- but more recent evidence makes it clear that the climate was not unimodal but fluctuated as in earlier and later time frames. Also, the climate was simply not arid, compared to "megadrought" periods documented in East Africa before 70,000 years ago.

    Thanks to a reader, I've been reading an excellent 2008 paper by Peter Mitchell, which documents archaeological sites and paleoclimate data leading to the conclusion that habitation in southern Africa was not significantly interrupted during late MSA times. I'll refer to it more extensively later, but in the meantime I'm noting some recent work that Mitchell may not have had available when he was writing his article.

    In a similar vein, I can point to an article by Louis Scott and colleagues (2008), which examined pollen records from Tswaing Crater as well as the Wonderkrater spring, and speleothem isotope evidence from Lobatse Cave, Botswana. Correlating the records from different sites in the same general area -- in this case, all from the savanna biome of southern Africa -- is very important. Distant climate records, such as the Greenland or Vostok ice cores, give some indication of global climate fluctuations, but it is not usually obvious how these fluctuations will affect specific regions of the world. One lake sediment core from southern Africa helps to show the local climatic fluctuations, but some may be highly localized, while others may reflect regional water and temperature variations. Hence, the correlations among many sites in a single region allow us to talk about climate fluctuations on a scale relevant to human populations.

    Again, the region-wide picture in southern Africa between 60,000 and 20,000 years ago does not yield a picture of static, arid or cool conditions. The time period covers almost two full precessional cycles of insolation in southern Africa, and thus covers a wide range of local climate variation. To sum up, I'll cite Mitchell (2008:54), who relied on some earlier work from the Tswaing Crater record:

    Peak annual precipitation may have reached 650–720 mm, with the late MIS 3 peak at the low end of this range. The minimum precipitation experienced was about 535 mm; today’s figure for comparison is 630 mm. Thus, although there were certainly periods when rainfall was reduced compared to the present , such reductions still exceeded by some margin the levels experienced by much of Limpopo Province or the highveld today, and for about a third of the time rainfall was actually higher than at present. Moreover, a generally cooler climate should have reduced evapotranspiration, and thus enhanced effective precipitation, more than these raw estimates suggest.

    These sources are relevant for the savanna of the northern and eastern parts of South Africa. The region is ecologically diverse, and Mitchell considers different parts of the region in turn.

    References:

    Kristen I, Fuhrmann A, Thorpe J, Röhl U, Wilkes H, Oberhänsli H. 2007. Hydrological changes in southern Africa over the last 200 Ka as recorded in lake sediments from the Tswaing impact crater. S Afr J Geol 110:311-326. doi:10.2113/gssajg.110.2-3.311

    Mitchell P. 2008. Developing the archaeology of marine isotope stage 3. S Afr Archaeol Soc Goodwin Ser 10:52-65.

    Scott L, Holmgren K, Partridge TC. 2008. Reconciliation of vegetation and climatic interpretations of pollen profiles and other regional records from the last 60 thousand years in the Savanna Biome of Southern Africa. Palaeogeography, Palaeoclimatology, Palaeoecology 257:198-206. doi:10.1016/j.palaeo.2007.10.018

    Tags: 
    Africa
    paleoclimate
    MSA
    South Africa

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Neandertals

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Malapa

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