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paleoanthropology, genetics and evolution

Swartkrans

  • 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: Fire starters

    Mon, 2010-05-17 13:51 -- John Hawks

    Regarding the use of fire, I’ve always been intrigued by how early Homo was able to continue its trek northward (ex. Dmanisi) without it. It would seem that a traveling hominid would frequently find itself out in the open (at night!!) without access to secure shelter while, at the same time, it was also experiencing more dramatic seasonal changes.

    I understand that the two-stone method of making fire isn’t particularly easy for an amateur. It would seem, however, that bashing rocks together to make tools on a dry savannah for a few thousand generations would have produced a clue as to how this worked. In fact, I would be surprised if they weren’t accidentally burning the neighbor-hood down on a regular basis. Maybe the initial production and control problem was learning how to put all these blazes out, not how to start them.

    There is evidence for fire in Swartkrans Member 3, which may be as old as 1.5 million years. The really good evidence from Gesher Benot Ya'aqov is sufficient to demonstrate control and habitual use of fires by 800,000 years ago. So it is not a safe assumption that the early occupation of temperate latitudes preceded fire use. If a 1.8-million-year-old site had evidence of fire, I think few of us would be surprised.

    The fire drill was repeatedly independently invented in different populations during the Late Pleistocene and Holocene -- it's one of the classic examples of diffusion and independent invention in cultural anthropology. So friction methods for fire making seem intuitive enough that humans come up with them again and again. To my mind these is easier and more consistent than the rock striking method, but who can say for sure?

    It does leave the question of why the systematic use of fire for landscape control is so late.

    Tags: 
    South Africa
    Dmanisi
    Europe
    Gesher Benot Ya'aqov
    Swartkrans
    Asia
    Early Pleistocene
    fire

  • Shrinking erectus

    Tue, 2010-04-27 10:02 -- John Hawks

    Ann Gibbons reports on the AAPA meetings with a story about all the Homo erectus pelvis and stature papers ("Human ancestor caught in the midst of a makeover," subscription required). Research on the proportions of early Homo was the main event of the meetings, and Gibbons really caught the highlights of the story.

    I wrote about body size in Homo erectus a few months ago, and much of the story follows from the basics I outlined there ("The changing height of Homo erectus"). But there I emphasized that the estimated adult height of KNM-WT 15000 was an outlier in a relatively small body size distribution.

    What I didn't anticipate is that some interesting work might come along to question the tall adult stature estimate for that skeleton. Gibbons describes the work of Ronda Graves and colleagues, presented at the meetings:

    Using intermediate growth rates, graduate student Ronda Graves of Stony Brook University in New York state calculated that Nariokotome Boy would have had less time than originally predicted to reach his adult height when he died. She estimated at the meeting that he would have reached 163 cm in height and 56 kg in weight as an adult—"shorter and wider" than previously thought.

    This seems very short, at least when I first saw it. On reflection, Ohman and colleagues (2002) had provided a stature estimate at death of KNM-WT 15000, as only 147 cm, and they suggested it might have been as short as 141 cm. That's an awful lot shorter than had previously been estimated on the basis of regressions.

    If Graves and colleagues are right about the lack of a human-like growth spurt, an additional 20 cm (8 inches) wouldn't be unusually small for an adult stature. Those stature estimates would put KNM-WT 15000 between the 50th and 90th percentiles for American 10-year-old boys, or between the 25th and 75th percentiles for 11-year-olds. By contrast, an adult stature of 163 would be around the 3rd percentile for adult American men. The assumptions about growth totally determine the outcome for adult height.

    The credibility of the growth assumptions can only be tested by looking at other adult and juvenile remains. There is much more to say on this topic, but I'll point out one relevant comparison: The estimated stature of the adult skeleton from Dmanisi, including the complete D4167 femur and D3901 tibia, is between 145 and 166 cm. Graves' KNM-WT 15000 stature estimate is right within this range.

    Meanwhile, there was a lot of disagreement about hips.

    [Scott] Simpson and Linda Spurlock of the Cleveland Museum of Natural History realigned the pieces of Nariokotome Boy's pelvis, guided by a female H. erectus pelvis from Gona, Ethiopia, that Simpson reported 2 years ago (Science, 14 November 2008, p. 1089). They found that the widest measure from side to side on the boy's pelvis is 255 to 260 millimeters rather than 225 to 230 mm. This would give the boy an adult hip breadth of 295 to 301 mm rather than the 266 mm originally proposed, and would match those of the short, wide-hipped female from Gona, whose pelvic breadth was 288 mm. "H. erectus was not simply a small-brained modern human," says Simpson.

    Simpson's reconstruction seemed reasonable, and it's actually not that big a difference -- roughly an inch and a half (3 cm) in bi-iliac breadth. The main differences were in the overall shape of the pelvis, being shorter with a more flaring iliac blade.

    Gibbons describes the disputation that happened after Chris Ruff's presentation. Ruff has suggested that the Gona pelvis may not represent Homo -- that its broad proportions and small acetabula (hip sockets) suggest it may have belonged to an australopithecine (presumably, A. boisei).

    Much of the disagreement comes down to the estimation of femur head diameter from acetabulum breadth -- Ruff (2010) gave an estimate of 32.6 mm, Simpson and colleagues estimated between 35 and 36 mm, based on a different method. What you would want is enough acetabula of both genera to be able to examine their variation directly. We don't have such a sample; what we have are a few acetabula and several femur heads. We have the additional problem that living people seem to have a different relation of femur head and acetabulum diameters than in other anthropoids, and it's not obvious which should be applied to early hominins.

    I guess (in the relative absence of data) that this acetabulum diameter of the Gona pelvis was in the zone of overlap between Homo and Australopithecus. There's no question that later Homo -- say after 1 million years ago -- is substantially larger in acetabulum diameter, from every specimen so far described. But there are occasional small specimens of Homo even in the Middle Pleistocene. At 1.15 million years old, the Gona specimen is more than 300,000 years later than the last known occurrence of Australopithecus. The femur head that would fit the Gona acetabulum would be smaller than KNM-ER 1472 or D4167 from Dmanisi, both around 40 mm. At least one australopithecine femur head (AL 333-3) is that large, so the femur head diameter distributions do overlap. The STW 431 acetabulum diameter is a sliver larger than that of the Gona pelvis (Ruff 2010 makes it 3 mm bigger, but other workers have given a smaller estimate). SK 3155 may well be Homo and has a smaller acetabulum.

    Of course, if we go as far as SK 3155, we have to consider the topic of the Malapa innominate. Can we tell small-bodied Homo from Australopithecus on the basis of pelvic morphology? Several people writing about the Gona pelvis have made it sound like a bigger version of Lucy's. But that's not really true. The australopithecine-like appearance comes from its breadth and consequent features, including the long pubes and flaring anterior ilia. The rest? Maybe there's something here for a clever anatomist.

    UPDATE (2010-04-27): I have some e-mail about the last occurrence of A. boisei, which I wrote above was more than 300,000 years older than the Gona pelvis.

    The most potent counterargument is Swartkrans Member 1, which has uranium-lead dates around 830,000 years ago, and has been placed by many workers around a million years ago. I actually hadn't been thinking of South Africa. But it is relevant, as the East African record between 1.4 and a million years ago may not be strong enough to argue that the last occurrence of A. boisei is really very close to the extinction time.

    Meanwhile, there is OH 36, an ulna from Olduvai Gorge that may represent A. boisei. Since it's (obviously) not cranial, and is quite large and robust compared to postcranial remains that are associated with A. boisei, I've always been very skeptical of that assessment. If there's one feature of the ulna that actually has some phylogenetic importance in the Early Pleistocene, I figure it's size.

    But given the current question about body size, that reason for skepticism may have receded in importance. On the other hand, OH 36 seems to represent a substantially bigger individual than the Gona pelvis, so maybe introducing robust australopithecines into the mix doesn't help anything.

    Several things puzzle me. Even into Member 1 times, Swartkrans is dominated by A. robustus, with very little Homo. In East Africa, A. boisei is never quite so predominant in the hominin assemblage as the case in South Africa, but was nevertheless very common up to 1.5 million years ago. Did it persist much later? Was it cryptic from the point of view of the fossil record? Are the Swartkrans dates older than we think?

    References:

    Gibbons A. 2010. Human ancestor caught in the midst of a makeover. Science 328:413. doi:10.1126/science.328.5977.413

    Ohman JC, Wood C, Wood B, Crompton RH, Günther MM, Yu L, Savage R, Wang W. 2002. Stature-at-death of KNM-WT 15000. Hum Evol 17:129-141. doi:10.1007/BF02436366

    Ruff C. 2010. Body size and body shape in early hominins -- implications of the Gona pelvis. J Hum Evol (in press) doi:10.1016/j.jhevol.20 09.10.0 03

    Tags: 
    body size
    stature
    East Africa
    Homo erectus
    Malapa
    A. robustus
    pelvis
    Early Pleistocene
    Swartkrans
    Gona
    KNM-WT 15000
    A. boisei
    meetings
    Synopsis: 
    The 2010 AAPA meetings featured a fight about the Nariokotome and Gona pelves.

  • (Best) forgotten tales of paleoanthropology, 1

    Tue, 2007-03-13 21:58 -- John Hawks

    The New York Times has given over free access to its e-archives, normally behind the "Times Select" paywall. It is a great opportunity to institute a new series, "(Best) forgotten tales of paleoanthropology," where I link to great (or not-so-great) moments in the field.

    For my first installment, here's an osteodontokeratic flashback from 1948:

    Baboon Killers' Method 1,000,000 Years Ago Traced in Recent Tactics of African Tribe

    By PHIL RAY

    JOHANNESBURG, South Africa, Dec. 24 -- For those who like their mystery stories steeped in the ages, we present a plot that may be 1,000,000 years old: "Who bashed the baboons of ancient Africa, and how?"

    ...

    Baboon skulls have been found in abundance in the rocks and fill of South Africa's ancient caves, and the great majority of these skulls are found to be fractured as if by a blow on the top of the head. The fracture is usually neat and distinct, indicating that whoever gave the blow did so expertly and with an instrument suited to killing baboons with speed and efficiency.

    Prof. Charles L. Camp and Dr. Frank Peabody of the University of California expedition now working in South Africa have uncovered a large number of baboon skulls at Taungs, finding six fine specimens in a single chunk of rock less than two feet across its largest dimension. All showed the same evidence of a sudden and violent end -- and a neat fracture about an inch and a half in diameter. Many others have been unearthed by Dr. Robert Broom at Sterkfontein and still others have been found at Makapoans [sic], generally showing the same neat fracture.

    At this point the story discusses Dart's well-known view that australopithecines had killed the baboons with clubs. And then:

    New evidence was uncovered by Professor Camp during his recent trip to South-West Africa. He discovered that the Klip Kaffir tribesmen, or Bergdaramas, who live in the Waterberg region, once hunted baboons with clubs. According to his aged native informant, a "knob-kerrie," or light stick about half as long as a walking stick and with a knob head was used.

    As far as I can tell, the "neat fracture" argument never returned in print.

    For a recent discussion of the accumulating agents for the South African caves (focused on Swartkrans), I suggest my colleague Travis Pickering's paper, "Beyond leopards: tooth marks and the contribution of multiple carnivore taxa to the accumulation of the Swartkrans Member 3 fossil assemblage". Berger and Clarke (1995) discuss the hypothesis that eagles were involved in the accumulation of the Taung fauna, including those baboons.

    References:

    Pickering TR, Domínguez-Rodrigo M, Egeland CP, Brain CK. 2004. Beyond leopards: tooth marks and the contribution of multiple carnivore taxa to the accumulation of the Swartkrans Member 3 fossil assemblage. J Humn Evol 46:595-604. doi:10.1016/j.jhevol.2004.03.002

    Berger LR, Clarke RJ. 1995. Eagle involvement in the accumulation of the Taung child fauna. J Hum Evol 29:275-299.

    Tags: 
    Sterkfontein
    forgotten
    Swartkrans

  • Snapshots of the science

    Sun, 2007-03-11 22:07 -- John Hawks

    The new Human Origins hall at the American Museum is the occasion for a big Newsweek story, with the tagline, "The New Science of Human Evolution". Author Sharon Begley isn't stingy with the prose:

    Whether or not you believe the hand of God was guiding these changes, the discoveries are overturning longstanding ideas about how we became human.

    Not that fossils are passé. New discoveries are pruning and reshaping humankind's family tree as radically as bonsai. The neat traditional model in which one species gave rise to another like Biblical "begats" has been replaced by a profusion of branches, representing species that lived at the same time as our direct ancestors but whose lines died out. It's like discovering that your great-great-grandfather was not an only child as you'd thought, but had a number of siblings who, for unknown reasons, left no descendants. New research also shows that "progress" and "human evolution" are only occasional partners. More than once in human prehistory, evolution created a modern trait such as a face without jutting, apelike brows and jaws, only to let it go extinct, before trying again a few million years later. Our species' travels through time proceeded in fits and starts, with long periods when "nothing much happened," punctuated by bursts of dizzying change, says paleontologist Ian Tattersall, co-curator of the American Museum's new hall.

    It's a little sad to see the article organized around a 15-year-old storyline. No More Unilineal Evolution! Hey, if it's a "new science", why do we keep hearing from the same old people?

    Still, there are some brain evolution subplots, and a few genes mentioned. Aside from the flowery analogies, Begley is a good writer and can capture the essence of most of these stories in a few lines. As an exercise, let's try to take those few lines and change one crucial word to find the weakness of each hypothesis. For each quote, I'll strike out a word in the article and add the correct word in brackets.

    You dirty louse

    For example, let's start where the article does, with the "body lice = no fur" story:

    That fork in the louse's family tree, [Mark Stoneking] and colleagues at Germany's Max Planck Institute for Evolutionary Anthropology concluded, occurred no more than 114,000 years ago. Since new kinds of creatures tend to appear when [correct word: after] a new habitat does, that's when human ancestors must have lost their body hair for good - and made up for it with clothing that, besides keeping them warm, provided a home for the newly evolved louse.

    You see how easy that is? Yes, new species adapt to new niches, but there is no reason to think this happens immediately. For that matter, there is no reason to think that hominids lost their fur instantaneously.

    And hey, if the theme of the article is that human evolution has lots of extinct branches, then why doesn't that apply to louse evolution? We just saw last week how complex the louse phylogeny has been in hominoids. Who says that the current body louse was the first to fill that niche?

    Oh, savanna, don't you cry for me!

    Here's a short one:

    The apes that stayed in the forests hardly changed; they are the ancestors of today's chimps. Those that ventured into the newly formed habitat of dry grasslands [correct phrase: open woodlands] had taken the first steps toward becoming human.

    None of the earliest hominid sites are open savanna. All of them come from sites that preserve other woodland creatures.

    By the way, my favorite quote in the whole thing comes here:

    Instead, evolution played Mr. Potato Head, putting different combinations of features on ancient hominids then letting them vanish until a later species evolved them.

    I just love that analogy! Forget "mosaic evolution". I'm calling it "Mr. Potato Head evolution" from now on.

    My what small teeth you have

    This part is a little confused:

    And it helps explain why Lucy's kind were the way they were. Afarensis women and men stood three to five feet tall and weighed 60 to 100 pounds. They had small [correct: big] teeth good for fruits and nuts, but not meat. (The available prey was [correct: competing predators were] enough to make one a confirmed vegetarian: hyenas the size of bears, saber-toothed cats and other mega-reptiles and raptors.) That suggests that early humans were more often prey than predators, says anthropologist Robert Sussman of Washington University, coauthor of the 2005 book "Man the Hunted." The evidence is as stark as the many [correct: two] fossil skulls containing holes made by big cats and [correct: one containing] talon marks from raptors.

    Well, that's taphonomy for you. There is plenty of evidence for predation on ancient hominid bones, and a National Geographic News article from 2002 details work showing the contribution of felids. But only two skulls have holes that may have come from ancient cats (those would be SK 54 from Swartkrans and D2280 from Dmanisi). Only Taung has evidence of raptor damage.

    Splitting straws on habiline brains

    Dmanisi has left people pretty confused about what explains hominid dispersal from Africa. Some are groping for other hypotheses. Just check out this paragraph:

    Erectus shows that brain size is too crude a measure of a species' talents. At Dmanisi, the brains range from 600 to 770 cubic centimeters, comparable to the more primitive habilis. But while erectus did not distinguish themselves in brain size, brain structure is more telling [correct: nor does its brain structure provide any clues]. They were [correct: They were not] the first of our ancestors to have an asymmetric brain, as modern humans do; Australopithecus species do not [correct: did]. Asymmetry is a mark of increasing specialization and therefore complex cognitive ability [correct: of questionable value, since apes and australopithecines have asymmetries to varying extents]. Erectus used it to, among other things, discover and tame fire [add: apparently much later]. What they did not use it for is technology. Tools found with the Dmanisi fossils include cutting flakes, rock "cores" from which flakes were made and a chopper, all primitive even for their time [correct: like those made in Africa]. "The old idea that you needed a master's degree in stone tools to leave Africa is crazy," says Bernard Wood.

    Wow, how confusing. The Dmanisi crania had H. habilis-sized brains. They're like KNM-ER 1470. So brain size isn't the key characteristic that allowed hominids to disperse from Africa. Nor is body size, since the Dmanisi hominids were relatively small. That's a genuinely interesting problem.

    But asymmetry doesn't solve it. KNM-ER 1470, either Homo habilis or Homo rudolfensis depending on your taste in hominids, has a well-defined Broca's area on the left hemisphere, which I would say is the main informative aspect of asymmetry in fossil endocasts. Chimpanzee brains are asymmetrical in some respects, so "asymmetry" itself is an irrelevant criterion without some specific anatomical feature in mind. The thing that people used to think might be important was petalial asymmetry -- one hemisphere of the cortex shifted forward compared to the other. Early Homo endocranial surfaces show fairly strong petalial asymmetries, including KNM-ER 2598 and KNM-WT 15000. But some Australopithecus endocasts share a similar pattern of asymmetry with later hominids (Holloway and De La Costelareymondie 1982). We don't know how to interpret petalial asymmetry in functional terms, by the way. There appears to be some correlation with handedness, but it's not clear that hand preferences and petalial asymmetries evolved at the same time or for the same reason.

    Somebody could write a really interesting story just out of the material in this one paragraph. Just not this story!

    Out of Africa

    The bottleneck scenario always seems like a hard one for journalists to get right. This article is no better than usual:

    Peter Underhill, a molecular anthropologist at Stanford University, tracked 160 such changes in the Y's of 1,062 men from 21 populations across the world. Applying the molecular-clock technique, he concludes that the most recent common ancestor of all men [correct: all Y chromosomes] alive today lived 89,000 years ago in Africa. The first modern humans-and therefore, unlike the earlier wave of Homo erectus into Asia a million years ago, the ancestors of everyone today-departed Africa about 66,000 years ago.

    These pilgrims were strikingly few. From the amount of variation in Y chromosomes today, population geneticists infer how many individuals were in this "founder" population. The best estimate: 2,000 men. Assuming an equal number of women, only 4,000 brave souls ventured forth from Africa [correct: were isolated from other humans for thousands of years inside Africa]. We are their descendants.

    Hard to get straight: genetic drift takes a long time to fix a gene. We don't necessarily know the number of founders of the out-of-Africa population; what we do know is how many individuals the ancient African population must have had under the hypothesis of genetic drift.

    Other genes might well have more recent common ancestors, who would also have been more recent common ancestors of all men. This is especially true if any genes were under selection.

    People who see my meetings talk will appreciate the irony of that last sentence...

    References:

    Holloway RL, De La Costelareymondie MC. 1982. Brain endocast asymmetry in pongids and hominids: some preliminary findings on the paleontology of cerebral dominance. Am J Phys Anthropol 58:101-110. doi:10.1002/ajpa.1330580111

    Tags: 
    Homo erectus
    Dmanisi
    Swartkrans
    Homo rudolfensis
    Homo habilis
    out-of-Africa
    A. afarensis
    paleonews

  • Robust australopithecine diet ablated

    Sat, 2006-11-11 10:27 -- John Hawks

    Sponheimer and colleagues (2006, link) zapped some Swartkrans teeth with lasers to measure their 13C content. I wrote quite a bit here last year about australopithecine diets, including a long review of isotopic evidence for australopithecine diets.

    With respect to dietary differences between A. africanus and A. robustus (the two species with any substantial isotopic sampling), there are four essential observations:

    1. The apparent C4 dietary content of the two species is basically the same, and fairly high.
    2. High C4 foods are not so easy to come by, they include some grasses and sedges and the animals who eat them.
    3. The Sr/Ca ratios of the two species are fairly different.
    4. The postcanine teeth of A. robustus seem to be adapted to crushing and grinding, moreso than A. africanus.

    One hypothesis for the difference in Sr/Ca ratios is exploitation of underground tubers (warthogs and mole rats have elevated Sr/Ca similar to A. africanus). A mix of C4 foods has been proposed to solve the grass-eating problem, including seeds, rhizomes, insects, lizards, and herbivore meat. But these don't really solve the postcanine tooth conundrum, and while they may both be true; neither is really testable.

    OK, so does the new laser ablation study solve any problems? First, let's read a bit about what exactly it is, and why it might be useful. Ann Gibbons has written a ScienceNOW article:

    [A] team of American and British researchers studied the teeth of four individuals of Paranthropus robustus (also known as Australopithecus robustus) from the Swartkrans Cave in South Africa. The team scanned the teeth with a sensitive laser, which did not destroy the teeth but etched them lightly enough to free carbon gases long trapped in the enamel. Because different plants absorb atmospheric carbon dioxide differently, the researchers were able to see what types of vegetation the hominids ate based on the ratio of carbon isotopes in their teeth.

    An accompanying perspective by Stanley Ambrose explains:

    In contrast to conventional methods, the laser ablation technique used by Sponheimer et al. barely penetrates the enamel surface of an area of less than 0.5 mm2 and is thus nearly nondestructive (2). Laser ablation also avoids the problem of time averaging in large drilled grooves. Moreover, perikymata can be counted, providing a good estimate of the minimum time interval sampled and of the duration of tooth formation.

    The Paranthropus teeth studied by Sponheimer et al. show interesting patterns of seasonal variation in diet and climate. All have the isotopic composition of mixed feeders, and two show at least ca. 40% variation in the proportions of C3- and C4-based resources over 1 year. One individual had a predominantly C3-based diet and foraged in a cooler, more humid environment; it may have formed its tooth in a very wet year. The others ate more C4-based foods in a warmer, drier environment. Their average carbon-isotope ratios are similar to those of adaptively versatile savanna baboons (2). Analyses of seasonal variation in teeth of modern and fossil baboons and of other hominin species are necessary to evaluate dietary specialization in Paranthropus and niche overlap with other hominin species.

    Back to me. There are two possibilities. First, the differences between 13C values for different samples might be sampling the actual dietary variability of single A. robustus individuals over the course of their tooth development (in this paper, sampled over a course of a couple hundred days).

    Or second, they may just be sampling noise.

    The paper presents comparative data to suggest that this is actual variability in diet and not isotopic noise. They sampled some steenbok teeth from Swartkrans with the same technique. Steenbok are consistent C3 browsers; their diet doesn't vary much in its 13C proportion over time. And the samples from the steenbok teeth didn't show very much variation across different sampling zones from the same tooth. Hence, it looks like the samples from different perikymata actually may give a consistent picture of dietary 13C composition over time.

    Compared to the steenbok, the A. robustus samples show great heterogeneity in 13C content. This heterogeneity is manifested when looking at multiple samples from the same tooth, and it is also manifested when looking at different individuals. So far, that would seem to indicate dietary heterogeneity -- the A. robustus individuals ate a different mix of foods over time, and different individuals ate different foods.

    On the basis of the magnitude of difference (particularly within the single specimen SKX 5939), Sponheimer et al. propose that some individuals must have gone from a diet predominantly composed of C3 foods to one predominantly C4 within the span of two years (estimated 644 days).

    Here's how their paper concludes:

    A dental microwear study of the earlier (3.0 to 3.7 Ma) hominin Australopithecus afarensis found no evidence that its diet changed over time or in different habitats (20). In contrast, stable carbon isotope (3, 4) and dental microwear texture analyses (1) of the slightly younger (3.0 to 2.4 Ma) hominin A. africanus demonstrated that its diet was far more variable. This suggests the possibility that a major increase in hominin dietary breadth was broadly coincident with the onset of increasing African continental aridity and seasonality after 3 Ma (21, 22) and only shortly antedated the first probable members of the genera Homo and Paranthropus (23-25) and the earliest stone tools (26). The undoubted toolmaker Homo is thought to have been a dietary generalist that consumed novel foods such as large ungulate meat and tubers that are abundant in savanna environments (27-30). Paranthropus, in contrast, with its extremely large and flat cheek teeth, thick enamel, robust mandible, and heavily buttressed facial architecture, is often portrayed as a dietary specialist (27-29). Further, it has been argued that this specialization contributed to its extinction when confronted with increasingly dry and seasonal environments later in the Pleistocene, whereas Homo's generalist adaptation was crucial for its success (28, 29). Our results suggest that Paranthropus had an extremely flexible diet, which may indicate that its derived masticatory morphology signals an increase, rather than a decrease, in its potential foods. Thus, other biological, social, or cultural differences may be needed to explain the different fates of Homo and Paranthropus (31).

    We have lots of other reasons to believe that robust australopithecines were not dietary specialists, as pointed out by Wood and Strait (2004). Robust australopithecines had broad geographic ranges, were able to disperse over long distances, and persisted despite substantial climatic and environmental changes. The evidence for dietary differences across the lifespan is certainly consistent with this.

    It does, however, make for an interesting conundrum: if australopithecines were selected on the basis of their ability to find different foods over the course of years, that suggests a strong role for social learning of more food types and broader geographic ranges. But if this was the path taken by robust australopithecines, what was the path taken by Homo?

    References:

    Ambrose SH. 2006. A tool for all seasons. Science 314:930-931. DOI link

    Gibbons A. 2006. Not just nuts and berries for these hominids. ScienceNOW 9 Nov. Full text

    Sponheimer M, Passey BH, de Ruiter DJ, Guatelli-Steinberg D, Cerling TE, Lee-Thorp JA. 2006. Isotopic evidence for dietary variability in the early hominin Paranthropus robustus. Science 314:980-982. DOI link

    Wood B, Strait D. 2004. Patterns of resource use in early Homo and Paranthropus. J Hum Evol 46:119-162. DOI link

    Tags: 
    A. afarensis
    Swartkrans
    A. robustus
    A. africanus
    diet
    Synopsis: 
    A study by Matt Sponheimer et al. demonstrates how diet changed during the growth of a single A. robustus individual.

  • Mata Menge stone tools

    Thu, 2006-06-01 00:25 -- John Hawks

    Adam Brumm and colleagues (2006) describe the stone artifacts from the Mata Menge archaeological site on Flores. This site is one of several described by Morwood et al. (1998, 1999) dating to the Lower-Middle Pleistocene boundary. This paper places the date for the artifacts between 880,000 and 800,000 years ago.

    Mata Menge and other contemporary sites (there are three with stone artifacts dating to before 700,000 years ago) do not preserve any hominid bones, and there is no evidence that H. floresiensis was there making these tools. But the paper is being interpreted in the context of H. floresiensis -- because one scenario has these hominids evolving in situ from earlier Homo erectus, which presumably made these early tools.

    Reuters article

    "Small-brained or not, Homo floresiensis was capable of making stone tools, and therefore the standard story of the relationship between brain size and behavioral complexity in human evolution may be less straightforward than currently assumed," said the team's leader, Adam Brumm of the Australian National University in Canberra.

    Until now it was thought that the larger the brain, the smarter the hominid. Brumm said his findings suggest that may not be the case.

    "The causal relationship between brain size and the complexity of tool behavior in humans is assumed, not demonstrated," Brumm said. "Until now stone tools have only been found in association with large and relatively large-brained hominids, but Homo floresiensis changes that, forcing us to rethink the way we associate big brain with sophisticated behavior."

    A Nature News article by Michael Hopkin also reviews the find and the recent Flores flap.

    The paper itself is relatively short and most consists of description of the 500-some-odd artifact assemblage from Mata Menge. The comparison with the tools from Liang Bua take up relatively little space. That's too bad, because a long description of the Liang Bua artifacts would be very welcome. But that apparently must wait. In the meantime, here is the concluding paragraph from the paper:

    The stone artefact assemblages from Mata Menge and the Pleistocene levels of Liang Bua are remarkably similar. We still do not know the species identity of the Mata Menge knappers, as no associated hominin remains have been recovered so far, but the age of the site clearly precludes modern humans. At Liang Bua, however, the skeletal remains of at least nine individuals are represented in finds from the Pleistocene levels, and all diagnostic elements are of H. floresiensis. The most parsimonious explanation for this is that the stone artefacts from Mata Menge and Liang Bua represent a continuous technology made by the same hominin lineage. Pronouncements that H. floresiensis lacked the brain size necessary to make stone artefacts are therefore based on preconceptions rather than actual evidence.

    I think that logic bears repeating:

    1. Modern humans could not have made the ca. 800,000-year-old Mata Menge tools.
    2. The Mata Menge tools look similar to the Liang Bua tools.
    3. H. floresiensis is at Liang Bua.
    4. Therefore, H. floresiensis or its ancestors must have made both the Mata Menge tools and the Liang Bua tools.

    Item 1 is certainly true. Item 3 is circular -- since it is the existence of H. floresiensis that the tools are supposed to demonstrate, or at least support.

    In any event, the mere presence of H. floresiensis (assuming it is real) cannot demonstrate that the species made the tools. We can compare Liang Bua to Swartkrans, which preserved many specimens of Australopithecus robustus and only a small number attributable to Homo. Despite the lopsided proportions of the fossils, there has been no resolution to the question of who made the Swartkrans tools -- far from it, actually. Most of us assume that most of the tools were made by Homo, although it is not possible to exclude the possibility that A. robustus made some of them. But really, this is only a preconception about the abilities of Homo and A. robustus. And, hey, it is only a preconception that prevents us from saying that the tools were made by baboons, which were very abundant in the cave as well.

    So the presence of H. floresiensis is relevant only if modern humans were not possible makers of the Liang Bua tools. A bit more on that below.

    The key question beneath the conclusion of the paper is whether item 2 is accurate -- are the Mata Menge tools really similar to the Liang Bua tools? This is where the paper seems weakest to me. It is really a stretch to claim that these assemblages were linked by any kind of tradition.

    Of course, it would be a stretch in any one place to claim a single tradition spanning 700,000 years or more -- that is a transfer of information across some 35,000 generations. Sure, the Acheulean was maintained for this amount of time or more, but it's not obvious that the Acheulean comprises a single tradition, or that there was much information transfer at all. If the Liang Bua and Mata Menge tools were no more similar than two Acheulean sites of the same age separation, then I would say there was no evidence of a tradition linking them. So even if the tools looked fairly similar, there still might not be a compelling case for descent or isolation based on the artifactual similarities.

    But all that presupposes that the tools are similar. Here, I just don't see it. There are two pieces of evidence that supposedly show similarity between the Mata Menge and Liang Bua tools. The first is a similar type of "perforator" -- in other words, a pointy tool that is flaked bifacially to accentuate the point. If you get Nature, you can look at the figure comparing these "perforators" from Liang Bua with the earlier "perforators" from Mata Menge. Go ahead, look. Other than the fact that they both are pointy, I don't see the similarity. The Liang Bua examples are extensively shaped by bifacial flaking; only one of the Mata Menge examples even looks like there was any attempt to shape the "point" unifacially.

    Now, consider that these "similar" tools were taken from a sample of over 500 for Mata Menge and a sample of over 3000 from Liang Bua.

    The other proposed similarity is this:

    For instance, both assemblages show an emphasis on the use of volcanic/metavolcanic fluvial cobbles as raw materials, along with the transportation of flake blanks for use as cores. Core reduction strategies at Mata Menge and Liang Bua are also very similar, with special emphasis on freehand reduction of cores both bifacially and radially. In fact, small, invasively reduced radial cores from the two sites are virtually indistinguishable. In addition, single platform cores, multiplatform cores, cores with 'burination' scars from the production of elongated flakes, 'truncated' flakes and cores indicating anvil-supported percussion and 'perforators' occur in both assemblages (Fig. 4). The maximum dimensions of flake scars on Mata Menge and Liang Bua cores are also very similar (Fig. 5; see also Supplementary Information). This is notable given that Liang Bua cores were more often on flakes, whereas Mata Menge cores were predominantly cobbles and hence tend to be bigger.

    "Occur in both assemblages" could link any stone tool assemblages in the world.

    Morwood et al. (2004) picture some of the more "advanced" tools from Liang Bua, including blades and microblades (which they suggest were hafted). If these occurred in both assemblages, they might be on to something. But really there are no special similarities between Mata Menge and Liang Bua.

    What about those modern humans? They were in Australia by 50,000 years ago. They have to have been passing by Flores by that time, or earlier. The early Liang Bua tools are supposed to be as old as 95,000 years. Maybe modern humans weren't there then, but it's not yet clear from the dates so far presented that any of the artifacts are that old, either. Dates in excess of 70,000 years for modern humans would be credible, and might well explain the site. Whatever is the case, it seems very unlikely that the earliest date for modern humans on Flores could be as recent as this:

    In contrast, the first skeletal evidence currently available for modern humans on the island, at Liang Bua around 10.5 kyr bp, is associated with various changes and additions to the stone artefact record, including an increased emphasis on the use of chert and the appearance of new stone artefact types (for example, edge-glossed flakes, grinding stones), as well as the first evidence for symbolic behaviour, such as personal ornaments (for example, beads), pigments and formal disposal of the dead.

    So an increased use of chert and deaccentuation of the local volcanic stone is characteristic of the non-floresiensis tools, according to this paper.

    But the "perforators" from Liang Bua pictured in the paper are on chert!

    Some observations: A cultural transition within modern humans in the region around 10,000 years ago would not be surprising. Cultural transitions also occurred in Australia shortly after that time, possibly related to an influx of new people from Indonesia. That this transition might be associated with greater symbolic behavior also is sensible within the Australasian context, where a Holocene transition to greater symbolic behavior occurred.

    References:

    Brumm A, Aziz F, van den Burgh GD, Morwood MJ, Moore MW, Kurniawan I, Hobbs DR, Fullagar R. 2006. Early stone technology on Flores and its implications for Homo floresiensis. Nature 441:624-628. DOI link

    Hopkin M. 2006. Old tools shed light on hobbit origins. Nature 441:559. DOI link

    Morwood MJ, O'Sullivan PB, Aziz F, Raza A. 1998. Fission-track ages of stone tools and fossils on the east Indonesian island of Flores. Nature 392:173-176.

    Morwood MJ, Aziz F, Nasruddin, Hobbs DR, O'Sullivan PB, Raza A. 1999. Archaeological and palaeontological research in central Flores, east Indonesia: results of fieldwork, 1997-1998. Antiquity 73:273-286.

    Morwood MJ, Soejono RP, Roberts RG, Sutikna T, Turney CSM, Westaway KE, Rink WJ, Zhou J-X, van den Burgh GD, Due RA, Hobbs DR, Moore MW, Bird MI, Fifield LK. 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431:1087-1091.

    Tags: 
    Middle Pleistocene
    Swartkrans
    A. robustus
    Homo erectus
    Flores

  • More microwear from South African australopithecines

    Thu, 2005-08-04 23:34 -- John Hawks

    Scott and colleagues (2005) examined dental microwear in some Swartkrans (A. robustus) and Sterkfontein (A. africanus) specimens. The interesting part of the study is the use of fractal analysis to quantify the complexity of scanned surfaces. They scanned a very tiny area of each tooth, around 200 micrometers on a side. Then they fed the scans through an algorithm to calculate texture.

    The basic link to diet is the same as before: hard, brittle foods leave scars and pits, tough pliable foods leave directional marks like scratches.

    Some results:

    Fossil hominin results indicate that P. robustus (Asfc 4.29 2.150) has microwear textures more complex (chi-squared = 8.17, P A. africanus (Asfc 1.686 +/- 0.52) (Fig. 2c, d). These results are consistent with the hypothesis that P. robustus incorporated more hard and brittle foods in its diet. However, some overlap in Asfc for the hominins (Fig. 3b) suggests that P. robustus was unlikely to have been a specialized hard-object feeder. It is more likely that hard, brittle foods were an occasional but important part of the diet. Previous studies have emphasized average differences between species rather than overlap, because low repeatability associated with observer error made assessments of within-species variability difficult.

    In contrast, the microwear textures of Australopithecus africanus (epLsar1.8 0.0045 +/- 0.00163) show greater anisotropy (chi-squared = 3.84, P = 0.05; Kruskal-Wallis test) and epLsar variability (F = 7.38, P P. robustus (epLsar1.8 0.0028 0.00060) (Fig. 2c, d). These data suggest a tougher diet on average for A. africanus compared with P. robustus, but one that is also more variable in its toughness (Scott et al. 2005:694).

    The interesting thing is the overlap between the two samples. The authors also compared cebus and howler monkeys, finding extensive variation in both taxa, with minimal overlap in distributions (howlers are leaf-eaters, cebus eat a wider range of foods including some hard items). The two hominids overlap almost completely in "surface complexity" (i.e. whether they are pitted and scarred), with the main difference between the samples being an average greater complexity in A. robustus and an average greater anisotropy (i.e. grooving and scratching) in A. africanus. A third or so of each sample lie in the region of overlap in both variables.

    From these measures, the diet variation within each species appears to be more extensive than the differences between them. The authors suggest this pattern of differences may represent a basically uniform diet with different fallback foods:

    The greater variation in complexity for P. robustus and in anisotropy for A. africanus suggests that these species altered different components of their diet, but that there was probably substantial overlap in the fracture properties of their preferred foods. Thus, the clear differences between A. africanus and P. robustus microwear may relate, in part, to differences in critical dietary resources consumed only periodically during the year (Scott et al. 2005:695).

    That would certainly be concordant with the stable isotope data. I guess it's a good thing for them that these two species weren't contemporaries.

    References:

    Scott RS, Ungar PS, Bergstrom TS, Brown CA, Grine FE, Teaford MF, Walker A. 2005. Dental microwear texture analysis shows within-species diet variability in fossil hominins. Nature 436:693-695. Full text (subscription required)

    Tags: 
    A. africanus
    A. robustus
    Sterkfontein
    diet
    Swartkrans

  • The Ultimate Survivor!

    Sun, 2005-03-20 22:06 -- John Hawks

    OK, I was drawn in by the first few minutes, so I'm liveblogging the National Geographic show, "The Ultimate Survivor."

    8:02 -- Lee Berger has fossil evidence of a giant race of ancient humans?

    8:05 -- The basic theme is the bush vs. ladder theme. To illustrate the ladder, they have an australopithecine pick up a steel baton and pass it on to later hominids. Forty years of Hollywood technology since "2001" and we've got a bunch of plasticine freaks passing a steel baton. I want the monolith back!

    8:10 -- The idea of a family tree is very easily illustrated--use a tree. So we have a tree with hominid pictures on it. But did you notice that this particular tree looks remarkably like Ernst Haeckel's primate phylogeny tree?

    8:13 -- Establishing the bush theme: Kenyanthropus as a new species apart from A. afarensis. Louise Leakey is featured.

    8:16 -- Obviously Kenyanthropus was a different genus. It has brown fur and Lucy has black fur!

    8:22 -- The Homo erectus model is a little distracting. He looks like an airbrushed white guy. Are these the same actors the BBC used?

    8:23 -- On to Dmanisi. Reid Ferring says there are many piles of round river stones that were probably collected for throwing. They show a couple of hominids throwing rocks at a sabertooth. OK, the skull suddenly fleshing to life in Lordkipanidze's hand is frightening. There's a Hollywood touch.

    8:35 -- Gretchen is complaining about their made-up common names, "Nutcracker" for A. boisei, "Handyman" for Homo habilis. Is there any point to dumbing it down this way? Who do they think is watching?

    8:38 -- Swartkrans burned bones. "If these burned bones aren't the result of a natural fire, then they are the first evidence of a controlled fire by humans." Well, yes, since those are the only two choices.

    8:39 -- RICHARD WRANGHAM ALERT! He's talking about fire IN FRONT OF A SMOKING WEBER GRILL! NOW HE"S CHEWING RAW MEAT! Whoa, man, that grill is smoking up a storm....NOW HE'S BEATING MEAT ON A TREE!

    8:42 -- This is a very clever illustration of the small gut, small tooth, small jaw muscle changes, with body parts computer morphing.

    8:48 -- Lucinda Backwell is talking about A. robustus diet and termites. There is really too much narration here. I would much rather hear the scientists telling us about this stuff. It's not that complicated that it needs to be dumbed down.

    8:55 -- "Lee Berger is on erectus's trail." He's excavating a fossil hyena den. He has a leg bone from an ancient human that he estimates was six feet tall. The amazing thing "is that we think it's a child or female." Berger and Steve Churchill build a reconstruction of the Kabwe specimen. OK, this is nothing new -- it was published in 1923, people! I guess this is just going along with the theme of giving everything a nonsensical name: "Goliath" is the name for Homo rhodesiensis. Nothing against Lee and Steve; I'm sure they think it is as hokey as I do. On the other hand, they did pose in front of a computer at a library workstation to have a mockup of a hominid computer-inserted in the film later....

    9:06 -- Steve Chuchill is measuring the volume and surface area of his H. rhodesiensis mold. He ends up dangling a macabre skin with face painted on. Too cool!

    9:07 -- The voiceover still hasn't called it anything but Goliath, but the hint that it may have went to Europe means that we may be talking about Homo heidelbergensis instead. Hey, I have a suggestion: if the taxonomic names are too complicated, maybe we could call them all Homo sapiens and just talk about the site names?

    9:10 -- Another Flores snippet. The film is really jumping around a lot, but it is clear that the only new thing is Flores, and the rest is just a summary of results from paleoanthropology over the last five years.

    9:15 -- The hobbit skeleton laid out includes a humerus and ulna. The computer-generated hobbits are walking around the Liang Bua excavation like Kevin Pollack and his buddy in "Willow."

    9:20 -- "Goliath!" The reconstruction of Kabwe is 6 foot 4 inches. I especially like the veins popping out on the arms -- he's a pro wrestler! -- and that goes with the theme of him being hot all the time. He didn't have the surface area to get rid of heat in a hot, moist climate, so he had to stay where it was dry. Not sure what the problem is here, exactly; are there no large people living in Africa now?

    9:26 -- Henshilwood at Blombos. Nice shots of the ocean, and reconstruction of the cave during occupation. Good emphasis on the incised ochre chunks. This is a nice part.

    9:30 -- "Equipped with greater brain power, some of us headed to Europe." A suddenly Caucasian modern human comes face-to-face with a Neandertal! BZZZAP -- they're gone!

    9:32 -- Back to Flores: "For thousands of years, modern human migrants likely shared this island with another species: hobbits." Hmmm...could it be that these modern humans made all those tools at Liang Bua? Nope, can't ask that question.

    9:36 -- Commercial break. How is it that they can make "Hogzilla" seem intrinsically more interesting than human evolution?

    9:37 -- Spencer Wells "has made a startling discovery about our struggle to survive: we almost didn't make it." Wells is selling us Toba! Voiceover:"There is no way to know how many of us died...only how many lived." Wells:"It may have taken a global catastrophe to actually kick-start the mind into high gear." OK, the concept du jour is "survivor genes," that were spread around Africa before Toba erupted (they haven't named the volcano for us yet) and allowed some people scattered around Africa (but nowhere else? except for Neandertals and hobbits?) to survive. I guess this is supposed to explain why our genes show geographic diversity dating to the Lower Pleistocene?

    9:42 -- "You don't wear jewelry unless you care about what others think about you, and that is a uniquely modern human trait." Well, and Neandertals....

    9:45 -- Lice genetics. "Body lice live under clothes, not just the rough animal hides worn by earlier humans." What?

    9:51 -- FoxP2: it allowed us to ululate, and that sets us apart from other animals, "more than any other human talent, it is the ultimate power tool."

    9:52 -- RICHARD WRANGHAM ALERT: The grill is still smoking. "Chimpanzees have bouts of violent aggression with each other about 100 to 1000 times more often within their communities." "We have a coalition of the timid." "That kind of killing [of violent people within groups] led to selection against the genes that cause aggression within groups." That, and BEATING MEAT AGAINST A TREE! OK, that's overkill. In any event, this is one of the most sensible parts of the show, and it's only two minutes long. This could be expanded into a half-hour section--how did cooperation arise in ancient humans?

    9:55 -- "Consider the tuber." Lee Berger is mincing, grating, ricing, and macerating potatoes with 18 different kitchen tools. And yet, he isn't in Wrangham's backyard. Hmmm...better to stay out of the SMOKY MEAT WARFARE ZONE.

    9:58 -- Steve Churchill gets the last word: "Wherever we encountered them, we outcompeted them. We made this come to pass."

    Tags: 
    A. boisei
    Swartkrans
    Neandertals
    tv
    A. robustus
    Dmanisi
    Homo habilis
    Flores
    Kenyanthropus
    A. afarensis
    Homo erectus

  • Age of hominids from Sterkfontein

    Fri, 2005-03-04 22:53 -- John Hawks

    A recent spate of articles has carried on a debate about the age of the Sterkfontein hominids. Sterkfontein is a complicated site, including several distinct caverns and deposition layers, called members. The dating of these layers is a serious problem because of their complex stratigraphy and the lack of volcanics that could be subjected to radiometric dating. Until recently the only insights into the age of the fossils came from uranium-series dating and paleomagnetic analysis of calcite deposits in the caves.

    The Sterkfontein deposits are divided into six members, and hominid have been recovered from Member 5, Member 4, and Member 2. Most of the hominid remains assigned to Australopithecus africanus come from Member 4, which was long thought to date to between 2.8 million and 2.6 million years. Before Member 5 was deposited, there was erosion on the top of Member 4, and the two are separated by an unknown period of time. This deposit is generally thought to be less than 2 million years in age, perhaps extending as recently as 1.4 million years (Kuman and Clarke 2000). In recent years, excavations lower in the deposit, including the Jacovec cavern and the Silberberg grotto, have produced hominid fossils attributable to Member 2. These were initially believed to be around 3.5 million years old.

    The most important fossils from Member 2 belong to the specimen StW 573. The foot bones of this skeleton were initially found in a dump of breccia outside the cave (Clarke and Tobias 1995). The origin of the bones was traced to Member 2, and they were matched to the broken end of a tibia still in situ in the Silberberg grotto. The skeleton is now known to be largely complete, including a skull and mandible, forelimb and hindlimb elements, and much else. It appears to be considerably more complete than the "Lucy" skeleton from Hadar, AL 288-1, or any other australopithecine, but it is not yet fully excavated from the overlying breccia and flowstone. The idea that this skeleton might date to 3.5 million years was potentially very important. At this date, it would be a contemporary of A. afarensis from Laetoli and Maka (it would be earlier than the Hadar deposits). It is not clear yet whether StW 573 anatomically resembles A. afarensis or is more similar to later South African hominids, but this would certainly be an important question to answer from the respect of early hominid phylogeny.

    Making Sterkfontein later

    McKee (1996) suggested that Member 2 was likely immediately earlier than Member 4. His argument was that the fauna of Member 2 were all found in Member 4, but several species were absent from Makapansgat Member 3 and 4, which date to between 3.2 and 2.9 million years. He proposed that this could be explained by the chance lack of these species at Makapansgat, but viewed that possibility as less likely than the hypothesis that the species appeared after Makapansgat Member 4, to be found in the later Sterkfontein deposits.

    Clarke and Tobias (1996) responded to this argument by noting the long stratigraphy of Member 3 between the Member 2 and 4 sequences, with several flowstones that must have taken a long time to deposit. They note that although Makapansgat does not preserve all the Member 2 fauna, the species that are absent are known from other African sites prior to 3.5 million years, and therefore are not of use in dating the deposits. The exception is one baboon species, Papio izodi, which is known only from Member 4 and Taung, and may therefore be rare enough to be absent from other sites.

    Berger and colleagues (2002) argued that the entire Sterkfontein sequence is substantially later than had previously been thought. They base their argument on biostratigraphic and paleomagnetic considerations. They have a number of reasons for this:

    1. The presence of Equus in the deposit, which is not radiometrically dated in Africa earlier than 2.36 million years ago.
    2. In addition to Equus, several other taxa are found in Member 4 that do not have secure radiometric dates above 2.5 million years anywhere in Africa.
    3. A later date for Member 4 would suggest that the sequence of magnetic samples from the site should be displaced earlier by a reversal cycle. This would place the top of Member 2 within the Olduvai subchron, and the StW 573 hominid would then date to between 2.15 and 3.04 million years ago. If this is displaced by another cycle more recently, StW 573 would date to as recently as 1.07 to 1.95 million years.

    As far as Equus, Kuman and Clarke (2000) are at pains to show that it actually may not occur in Member 4. According to them, only one equine tooth has been excavated from Member 4 in situ, with the remaining bones taken from fill that may derive from Member 5. They argue that the one tooth is insufficient evidence of the presence of the genus, considering the possibility of erosion from later deposits.

    Making Sterkfontein earlier

    Partridge and colleagues (2003) dated the Sterkfontein Member 2 deposits by using the radioactive decay of cosmogenic isotopes. These are created when cosmic rays from outer space interact with the elements in quartz grains near the earth's surface. In particular, aluminum-26 and beryllium-10 accumulate in quartz grains at a predictable ratio. These two isotopes have different half-lifes (26Al = 1.02 million years, 10Be = 1.93 million years), which means that once the quartz grain is buried and no longer exposed to cosmic rays, the ratio of the two isotopes changes.

    Sediments near the StW 573 specimen gave a date estimate of 4.17 million years, while the orange breccia in the Jacovec Cavern gave an estimate of around 4.02 million years. These date estimates are substantially earlier than were previously estimated for these localities at the site.

    It was not possible to date Member 4 in this way, because it is shallow enough that cosmic rays can still affect the quartz grains used for dating.

    Partridge et al. (2003) do not present a response to Berger et al. (2002), except to note that their earlier dating "is unsustainable on stratigraphic and faunal as well as on paleomagnetic grounds" (612, note 12). In any event, there seems to be no strong biostratigraphic reason to place Member 2 at either an earlier or later date; the preserved fauna is not specific as to age.

    Member 5 stratigraphy

    Kuman and Clarke (2000) review the stratigraphy of Member 5. The most important hominid specimen that has been attributed to Member 5 is StW 53, a nearly complete skull that has been variably attributed to A. africanus or Homo habilis. Kuman and Clarke (2000) show that the skull derives from an area that likely is intermediate in age between Members 4 and 5 proper. They call this area the "StW 53 Infill." No artifacts derive from this area. The authors argue that the infill is likely more recent than Member 4 because of the presence in the deposit of Theropithecus oswaldi, a species found in the later Swartkrans Members 1--3, and associated with drier open grassland habitats. On this basis, they place the StW 53 Infill between 2 million years ago and 2.4 million years, which marks the earliest appearance of T. oswaldi in East Africa.

    According to Kuman and Clarke (2000), Member 5 can be divided by the presence of two distinct tool industries. The Oldowan Infill dates to between around 2 million and 1.7 million years ago, and preserves 3245 excavated artifacts (Field 1999). The paleoenvironment seems to indicate a grassland. The later phase is referred to the Acheulean because of the presence of bifaces, and is placed between 1.7 and 1.4 million years ago. Like the earlier Oldowan infill, the Acheulean infill represents a predominantly grassland fauna, similar to Swartkrans.

    Kuman and Clarke (2000) provide a list of hominid fossils with their probable associations in the stratigraphy. They also discuss the taxonomy of the fossils and their resemblances with elements of the earlier Member 4 and Swartkrans remains.

    More on Sterkfontein

    More on Makapansgat

    References:

    Berger LR, Lacruz R, de Ruiter DJ. 2002. Brief communication: Revised age estimates of Australopithecus-bearing deposits at Sterkfontein, South Africa. Am J Phys Anthropol 119:192-197.

    Clarke RJ, Tobias PV. 1995. Sterkfontein Member 2 foot bones of the oldest South African hominid. Science 269:521-524.

    Clarke RJ, Tobias PV. 1996. Faunal evidence and Sterkfontein Member 2 foot bones of early hominid. Science 271:1301-1302.

    Field AS. 1999. An analytic and comparative study of the Earlier Stone Age archaeology of the Sterkfontein Valley. MasterÕs thesis, University of the Witswatersrand.

    Kuman K, Clarke RJ. 2000. Stratigraphy, artefact industries and hominid associations for Sterkfontein Member 5. J Hum Evol 38:827-847.

    McKee JK. 1996. Faunal evidence and Sterkfontein Member 2 foot bones of early hominid. Science 271:1301.

    Partridge TC, Granger DE, Caffee MW, Clarke RJ. 2003. Lower Pliocene hominid remains from Sterkfontein. Science 300:607-612.

    Tags: 
    Olduvai Gorge
    Sterkfontein
    A. afarensis
    Homo habilis
    Hadar
    Swartkrans
    A. africanus
    Pliocene

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