john hawks weblog

paleoanthropology, genetics and evolution

Kenya

  • Oldowan hunting behaviors at Kanjera South

    Mon, 2013-04-29 16:28 -- John Hawks

    Joseph Ferraro and colleagues have done some neat analyses of the faunal remains from Kanjera South, Kenya [1]. Kanjera South is an archaeological assemblage of Oldowan artifacts and associated animal bones from around 2 million years ago. The site was once a plain next to a lake, and gradually built up clay and silt sediments over years and years of flooding and soil formation. Stone tools and bones stand out in the sediments, representing recurrent activities of ancient humans over a few hundreds or thousands of years. As a result, the site has a good statistical representation of fauna that were hunted by early humans, relatively early in the evolution of our genus.

    This is not the earliest site with evidence for meat acquisition by stone toolmakers. We know that people were butchering animals with stone tools around 2.6 million years ago. But the first really good evidence for hunting strategies is much more recent -- around 1.8 million years ago at Olduvai Gorge. There are actually very few Oldowan-era faunal assemblages large enough to study hunting behaviors. Kanjera South shows that the activities documented at Olduvai Gorge were happening a bit earlier, and the site helps to clarify the kind of context in which we might expect to find more evidence of hunting behavior.

    Hunting versus scavenging is the tiredest chestnut in anthropologists' Oldowan arsenal. Were early hunters really competent enough to bring down a duiker on their own? Or did they steal away pieces of half-eaten zebra carcases when the lions took a break?

    In reality, there is no contradiction here. Undefended meat doesn't last a day in the open, whether on the plains or near waterholes. So scavenging meat from other carnivores usually means facing them down -- not a job for an incompetent killer. Meanwhile, present-day peoples who hunt and gather rely quite a lot on "power scavenging", or taking advantage of other carnivores' successes. The present value of a dead carcass is higher than that of a live animal, as long as it may still escape you. Whether the hunter has to predict prey behavior, or the scavenger has to predict competitors' behavior, both strategies require a depth of planning. So, when it comes to Oldowan-era sites, we should expect to see a mixture of hunted and scavenged remains.

    In that context, we can make some inferences about hominin hunting practices by assessing which kinds of animals they hunted, and which they scavenged. Looking at tooth mark and cutmark evidence is not a perfect way of sorting hunting and scavenging -- because both kinds of marks are rare on faunal elements in archaeological contexts. But sometimes those comparisons lead to clear results. For example, here is the chart showing the number of tooth-marked midshaft fragments from long bones at Kanjera South, in comparison to experimental bone assemblages:

    Figure 3 from Ferraro et al 2013

    Figure 3 from Ferraro et al. 2013. Original caption: Tooth-marked mid-shaft fragments: results from experimental assemblages and excavations at KJS. Figure follows a published model [26]. Hominin-first assemblages refer to remains initially defleshed and demarrowed by hominins, then subsequently exposed to large-bodied carnivores (primarily hyenas). Carnivore-first assemblages refer to remains initially defleshed and/or demarrowed by large-bodied carnivores (primarily hyenas and/or lions). Data for body sizes 1–4 [21]. Modern data (with single standard deviations where available) derived from the literature [23]–[26], [56]–[58]. KJS frequencies are from Table 2 and Table S1. Multiple symbols for KJS indicate the results of multiple analysts. X’s indicate minimum and maximum estimates of damage (see Table S1). doi:10.1371/journal.pone.0062174.g003

    These are cool data. Carnivores who get to chew on bones for a while tend to leave the middle of them covered in tooth marks. If humans get access to the carcass early, they will strip off the meat from those midshafts, break them into bits, and otherwise prevent the taphonomic pathway to carnivore tooth marking. And in the graph we see that the Kanjera South faunal assemblage looks like cases where humans were the agents of defleshing and butchering.

    If humans had primary access to the carcasses, then the transport decisions of ancient hunters should have shaped the bone assemblage at Kanjera South. It is very common in analyses of the fauna from African Oldowan-era sites to divide the prey animals into three size classes -- small, medium and large. The majority of prey species were bovids, ranging from small antelopes to water buffalo, although most were in the small and medium size categories at Kanjera South. Ferraro and colleagues show that for medium-sized bovids, the hominins were taking two strategies. These bovids were too big to carry wholesale to a central place for sharing. So the hunters disarticulated the animals and carried back the legs, leaving the axial skeleton for the most part behind.

    Except for the heads:

    But why acquire, transport, and process an abundance of medium-sized heads? In living animals, these remains contain a wealth of fatty, calorie-packed, nutrient-rich tissues: a rare and valuable food resource in a grassland setting where alternate high-value foodstuffs (fruits, nuts, etc.) are often unavailable [2], [3], [29], [49], [52], [63], [76]–[78]. Medium-sized heads are also relatively dense and durable elements, and their internal contents are generally inaccessible to all but hyenas and tool-wielding hominins [63], [79], [80]. As a result, they are often seasonally-available as scavengable resources in East African grasslands [63], [76], [79]–[83]. Additionally, bone surface modification studies at KJS clearly demonstrate that hominins accessed internal head contents: several cranial vault and mandibular fragments bear evidence of percussion striae. Considered in sum, the presumed availability of these isolated remains across the landscape, the relative abundance of these remains in the KJS assemblages, and unambiguous material evidence that hominins exploited their contents on-site is most parsimoniously interpreted as reflecting very early archaeological evidence of a distinct hominin scavenging strategy – one that included a strong focus on acquiring and exploiting fatty, nutrient-rich, energy-dense within-head food resources (e.g., brain matter, mandibular nerve and marrow, etc.) [e.g., 24,63,76,82,84–86].

    This is John Speth's scenario for fat acquisition from lean animals. The brain is the last part of the body to become fat-depleted during times of stress. If hunters are energy-limited, further lean meat is not going to be valuable to them because protein takes energy to digest. What they need most is fat, and the most ready source of fat is the brain. Accumulation of head elements, whether from hunted or scavenged sources, is an effective behavioral strategy in those circumstances. It's one that we think Neandertals pursued at the end of winter in some parts of Europe, and a strategy followed by hunters in ethnographic and historic contexts as well.

    The paper's conclusion is well-framed as a summary of the overall value of evidence from Kanjera South.

    With regard to evolutionary ecology, the relative uniformity of hominin activities documented through the KJS sequence indicates an evolved foraging adaptation well-tuned to local ecological contexts. This point implies that hominin involvement with, and their presumed consumption of, animal remains had substantial fitness implications. In turn, sufficiently strong selective pressures are implicated as having favored the evolution of persistent hominin carnivory no later than 2.0 million years ago. This date is approximately 200,000–500,000 years earlier than previously documented [11], [20], [33], [45], and increases the known time depth of this adaptation within the hominin lineage (range of dates reflects varied interpretations of faunal materials from Olduvai [20]–[42]).

    This one was fun to read, because the data being built up at Kanjera South are really capable of testing hypotheses about hunting behavior in a way that some of the Oldovai Gorge assemblages have done up to now. Putting the faunal exploitation together with the stone tool evidence, we see a really interesting picture. As I reported a few years ago ("Plant processing with early Oldowan tools"), Kanjera South is one of the locations where we have good evidence of plant exploitation of some kind by Oldowan peoples. The site has also provided evidence about stone material transport decisions and the planning depth of stone flaking ("Technological sophistication of the earliest toolmakers". It is a good illustration of how deep knowledge of a single site, with teams returning to excavations over multiple seasons, can yield a richness of statistical information about hominin behavior.

    References

    1. Ferraro JV, Plummer TW, Pobiner BL, Oliver JS, Bishop LC, Braun DR, Ditchfield PW, Seaman JW, Binetti KM, Seaman JW, et al. Earliest Archaeological Evidence of Persistent Hominin Carnivory Petraglia MD. PLoS ONE [Internet]. 2013;8(4):e62174. Available from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0062174
    Tags: 
    Oldowan
    Kanjera
    hunting
    diet
    Kenya
    Africa
    Early Pleistocene
    Lower Paleolithic
    Synopsis: 
    A faunal exploitation study finds clues about brain consumption and prey choices

  • Palming Homo erectus

    Sun, 2013-04-14 17:22 -- John Hawks

    New Scientist reports on Carol Ward's presentation at the AAPA meetings, describing a new metacarpal of Homo erectus from West Turkana: "Stone tools helped shape human hands". It is a third metacarpal, a bone that happens to be pretty different between known australopithecines and recent Homo. But strikingly none have yet been described for Homo before the Neandertals.

    Because the fossil is younger than the first tools, Ward's team believe it is the first evidence of anatomy evolving to suit a new technology. As stone tools became more widespread, those who had the wrist structure to use them would have had an evolutionary advantage over their weaker-wristed kin. "The way we look today has been shaped by our behaviour over millions of years," says Ward.

    The developmental change represented by this anatomy is a separate center of ossification at the base of the metacarpal leading to a pointy projection called the styloid process. That's a pretty interesting shift in development, and so I'm intrigued that it came closely after the appearance of Homo erectus. Ward also reported that the bone is very long, at the top end of the variation in living people and longer than any Neandertals. Another hint of big people in the Early Pleistocene of East Africa.

    Tags: 
    Homo erectus
    fossils
    morphology
    stone tools
    Kenya
    West Turkana

  • African Homo erectus

    Tue, 2011-11-08 00:14 -- John Hawks
    Synopsis: 
    African specimens from the Early Pleistocene are compared

    This station includes several casts of early fossil Homo erectus, from the Early Pleistocene of Africa. These include:

    • OH 9, from Olduvai Gorge, Tanzania, around 1.2 million years old.
    • KNM-ER 3733, from Ileret, Kenya, 1.65 million years old.
    • KNM-ER 3833, from Koobi Fora, Kenya, 1.6 million years old.
    • KNM-WT 15000, from Nariokotome, Kenya, 1.5 million years old.

    In addition to these specimens, the station has a few comparative casts from earlier hominid species and from other parts of the world.

    What to do: First, consider the issue of sexual dimorphism in these specimens. Which are male and which are female? What features lead you to that conclusion?

    Second, why are the differences between these specimens and Homo habilis, for example, KNM-ER 1813, reflective of a species distinction, instead of sex?

    Study terms: 
    Nariokotome
    Koobi Fora
    Ileret
    Lake Turkana
    Olduvai Gorge
    Tags: 
    Anthropology 105
    laboratory
    explainer
    Homo erectus
    Africa
    Kenya
    Tanzania

  • Digging deeper into the earliest Acheulean

    Thu, 2011-09-01 01:00 -- John Hawks

    I've been ranting on Twitter all day about the new paper on the "earliest Acheulean" by Christopher Lepre and colleagues [1], published in Nature today. The first time I read through the paper, I really thought they'd miffed it. I mean, really, they published a paper on the earliest Acheulean artifacts without putting a picture of them in the paper.

    What actually bothered me more was the lack of any discussion at all about why the assemblage is Acheulean as opposed to, say, Developed Oldowan. The word Oldowan appears only in the context of saying that many localities within the same Kokiselei site complex have only Oldowan-typical assemblages. This started bothering me less as I ran through the citations to earlier work on the Kokilelei localities. But that raised another point of irritation: This Acheulean locality was briefly described already, a long time ago. Why is this news? And given that both descriptions are so superficial, where's the fuller account?

    I had to stop and think about why I was finding this all so irritating. I mean, it's a paper about dating an archaeological locality. It's a perfectly good paper about dating an archaeological locality, full of details about the local geology, methods of sampling and analysis. My reactions weren't a criticism of the paper, really -- although if you're going to write a high-profile paper about your site, maybe you should actually feature the archaeology of the site?

    I've been digging through references all afternoon, trying to get straight exactly why this paper doesn't mention the Developed Oldowan at all. I'm not saying I favor the Developed Oldowan -- just that we deserve some kind of thoughtful review of what constitutes an "earliest Acheulean" site. Is it a purely typological definition based on the presence of bifaces made on large flakes, or is there something more here? That's going to take me a bit longer to review, so I'll just report on some of what I found.

    This isn't news. Hélène Roche and colleagues reported on this locality in 2003, in Comptes Rendus [2], including a date range between 1.79 and 1.65 million years ago. They describe it as "without doubt, one of the oldest Acheulean assemblages in Africa." That's right, if you can read French, you're eight years ahead of Nature.

    This paper adds precision to the earlier estimate, and it's really important to do this well. But if you've been reading about the archaeology of Plio-Pleistocene Africa, finding a date of 1.76 million years for this locality with an Acheulean assemblage is totally expected.

    Roche and colleagues [2] provided only a short description of the KS4 assemblage. Even so, it's more than provided in the current paper by Lepre and colleagues [1]. Here is what the current paper includes about the assemblage:

    The KS4 assemblage (Supplementary Fig. 2) is characterized by the presence of pick-like tools with a trihedral or quadrangular section, unifacially or bifacially shaped crude hand-axes, and a few cores and flakes, all derived from the same mudstone bed. A single subsurface, in situ origin for KS4 is ensured by excavations at the main test trench that recovered several spectacular sets of refitted lithic artefacts (Supplementary Fig. 3). To the exception of a few cores made on basalt, the rest of the assemblage has been knapped from large cobbles or tabular clasts of locally available aphiric phonolite.

    The supplementary information does include photos of three bifacial artifacts and two refits. But there is no technical analysis of the artifacts beyond the paragraph above. There's not even a summary of the number of artifacts found at the site.

    Roche and colleagues added more details (my translation of the French):

    Kokiselei 4 is a highly eroded site in which a series of more or less extensive trenches (total 19 m2) were dug. Among these only one (KS4A) yielded in situ artifacts in sufficient numbers to form an archaeological horizon, with a vertical dispersion limited to only fifteen centimeters, and no faunal remains. Some objects, distributed in a more diffuse fashion, were found in two other test pits (KS4B and KS4C); these are lower in elevation than the main horizon. In parallel to the test pits, a systematic surface collection across 104 m2 (metric grid) was performed, which comprises the total sample of lithic material from KS4 (n = 167). It is characterized by robust, rough pieces of varying sizes, often very large, some scrapers and notches made on cobbles or flakes, by very large cores, by proto-bifaces or bifaces, and by picks with a trihedral section. Two thirds of the proto-bifaces or bifaces are manufactured on oblong pebbles, relatively flat, some quite large, whole or broken into two in the middle according to the major axis and very few retouched. Only a few are free of cortex and / or shaped enough to be called bifaces, the proto-bifaces in turn are made more coarsely, as if the concept of an elongated shape and sharp point was well integrated, but the operating scheme was inadequately implemented. All the tools characterizing a very early Acheulian are present, and it is to this cultural period that we attribute KS4.

    Roche and colleagues also described the other localities, all Oldowan, at a similar superficial level of detail. The conclusion that Acheulean and Oldowan were two industries overlapping at the same time in this area was suggested in that paper.

    That, obviously, leads to the real scientific story here. How could there be two different stone tool traditions overlapping across some fairly large area for more than 300,000 years? If we count Developed Oldowan, that makes three. Some people would count two Developed Oldowans A and B!

    I'm inclined to think that the scenario is false. These really aren't distinct cultural traditions. Archaeologists have created definitions of archaeological assemblages, and the definitions have changed over time. Initially the definitions were entirely typological -- you have a handaxe, you've got Acheulean. Over time, the definitions have become less typological and more inclusive of technical elements -- you make bifacial artifacts on very large flakes, you've got Acheulean. But these technical categories are not unique or necessarily difficult to invent, and may have been repeatedly invented in different groups, just in the way that different groups of chimpanzees have invented nutcracking and termite fishing methods. For these early assemblages, we don't have any way of telling who made what -- the only hominin fossils from Kokilelei, for example, are teeth of A. boisei. We don't know how many different kinds of hominins there were. Maybe there was only one.

    Early Homo is a bundle of mysteries, in other words, and the archaeology doesn't help. Can we make any sense of the development of early stone tool technology, from its initial beginnings to the handaxe-dominated assemblages? What does it mean that both Oldowan-like and Acheulean-like industries dispersed widely throughout the Old World? This is a really interesting scientific problem, involving information transfer, emergent sets of behaviors, invention and creativity, and their effects on survival.

    The paper by Lepre and colleagues discusses the problem of Oldowan and Acheulean coexistence briefly, reviewing the idea that Homo erectus may be tied to Acheulean, leaving open the question of whether more than one toolmaking species existed before 1.5 million years ago. The paper is noncommittal, but I would frame the question very differently. It's self-evident that Acheulean cannot have been a culture, because no human or animal culture exhibits its spatial and temporal properties -- appearing episodically across three continents over a span of 1.5 million years. The real question is whether we can make sense of the many different Acheuleans, and whether other Oldowans (possibly Developed Oldowans) might have similar heterogeneity. Asking whether an Oldowan-bearing population in Africa first dispersed to Dmanisi is begging the question.

    Finding these answers is surely a lot more interesting than what the press has done with this article.

    That's probably what irritates the the most about this: how boring the article and reporting seem to make this topic. When I did the Google News search this afternoon, there are no fewer than 165 news articles worldwide. Nature made its cover image this week a photo of one of the bifaces. You can't get much more of a press push than that for an archaeology story. None of the stories go beyond the very simple "oldest Acheulean" story. Now, I'm used to seeing the "oldest X" storyline a lot in paleoanthropology, it's a perennial favorite of journalists who can't think of anything more interesting to write. But in this case, it's the worst angle -- because it's the part that isn't actually news!

    References

    1. Lepre CJ, Roche H, Kent DV, Harmand S, Quinn RL, Brugal J-P, Texier P-J, Lenoble A, Feibel CS. An earlier origin for the Acheulian. Nature. 2011;477(7362):82 - 85.
    2. Roche H, Brugal J-P, Delagnes A, Feibel C, Harmand S, Kibunjia M, Prat S, Texier P-J. Les sites archéologiques plio-pléistocènes de la formation de Nachukui, Ouest-Turkana, Kenya : bilan synthétique 1997–2001. Comptes Rendus Palevol. 2003;2(8):663 - 673.
    Tags: 
    archaeology
    Early Pleistocene
    Lower Paleolithic
    Acheulean
    Oldowan
    Turkana
    West Turkana
    Kokiselei
    Kenya
    Africa
    Synopsis: 
    A paper reports on the earliest evidence of the Acheulean, but misses the key story.

  • "Nutcracker Man" debunked

    Tue, 2011-05-03 00:44 -- John Hawks

    This week, Thure Cerling and colleagues report in PNAS [1] carbon stable isotope data from 24 specimens of Australopithecus boisei. This is a huge sample as fossil hominins go, and they give a very consistent picture about the diet of this most robust of the australopithecines. These 24 individuals got between 61 and 91 percent of their carbon from grasses.

    My 2005 explainer on stable isotope chemistry and early hominin diets fills in the details about carbon-12, carbon-13 and their relationship to 3- and 4-carbon photosynthetic cycles. The salient aspect of the comparisons involving A. boisei here is that C4 plants, mostly grasses, incorporate relatively more carbon-13 than do other plants, and herbivores assimilate this carbon-13 into their bones and teeth.

    The high ratio of grass-derived carbon in A. boisei is fundamentally different from all living and fossil apes, and it is far higher than the values found for other early hominins. The only other primate that comes close is the fossil giant gelada Theropithecus oswaldi, a savanna-living species.

    What were these extinct species really eating? Was grass the food? For living geladas, grass consumption includes seeds -- a fact that led Clifford Jolly to suggest that early hominins might also have specialized on seeds [2]. Of course, humans today also specialize on grass seeds. We call them grains, eat them in bread and drink them in soda. And beer.

    But what about A. boisei? The large, thick-enameled premolars and molars, with their low cusps, seem well suited to grinding small hard objects and resisting the resulting wear. But Cerling and colleagues devote a good chunk of their discussion to the description of molar wear in A. boisei and other early hominins. Their argument is that the teeth of A. boisei show no signs of "hard object" feeding:

    Of perhaps greater moment than its potential specific simila- rities, the microwear of P. boisei molars, which shows remarkable uniformity over time from about 2.3 Ma to about < 1.4 Ma (9, 24), stands in stark contrast to the wear fabrics exhibited by primate hard-object consumers. Indeed, there is no evidence beyond the anecdotal [e.g., the broken left first permanent molar crown in the KNM-ER 729 P. boisei mandible (8) and the observation that a couple of P. boisei molars show antemortem enamel chipping (25)] that these food items were hard.

    These observations are not new, but putting them together with the evidence of grass consumption makes it pretty clear that seed eating was not a predominant source of dietary carbon. The "Nutcracker Man" sobriquet, applied to A. boisei because of its powerful jaw mechanics, must be false. No significant hard object feeding, very low dietary carbon from trees and non-grassy (or sedgy) plants.

    Instead, Cerling and colleagues propose that both A. boisei and other early hominins wore their teeth on the, well, grassy parts of grass.

    P. boisei cheek teeth display notable gradients of gross wear, resulting in large, deeply excavated dentine exposures, and in this regard, they are similar to other australopith species (e.g., A. afarensis and A. africanus) that also possess low tooth cusps with thick enamel. Thus, like other australopiths, P. boisei undoubtedly had a diet that consisted of foods with abrasive qualities—the gross wear is as likely due to repetitive loading of phytolith-rich tough foods as exogenous grit. Thus, either grass or sedge consumption and/or exogenous grit might well have contributed to P. boisei’s notable wear gradient.

    And:

    Recent dental microwear studies suggest that the mechanical properties of A. afarensis (and A. anamensis) diets were nearly identical to those of P. boisei (9, 24, 40–42). If this is so, could it be that the australopith masticatory package represents an adaptation to C4 resources such as grasses or sedges? The similarity in dental microwear fabrics among the eastern African australopiths, all of which lack any evidence for hard-object food consumption (9, 24, 40–42), is consistent with the notion that their craniodental morphology could reflect “repetitive loading” rather than hard-object consumption (7, 8, 43).

    Grit might get in from eating underground parts like rhizomes. Phytoliths are small, hard silicate structures in the green parts of plants, including the stems and leaves of grass.

    Last year I wrote about carbon isotope analysis of two specimens of Australopithecus boisei, the famous OH 5 "Zinj" specimen, and the Peninj mandible. Both specimens show evidence of a high consumption of grass-derived carbon -- estimated at 77% and 81% grass-derived carbon, respectively. Those levels are characteristic of grazing animals. Cerling and colleagues show that these values are right in the middle of the range among specimens of A. boisei that cover a half million years in Kenya and Tanzania.

    In the paper reporting the carbon stable isotopes of OH 5 and Peninj, van der Merwe and colleagues [3] suggested that A. boisei may have relied on papyrus as a staple. The culms and rhizomes of papyrus both have substantial nutritional content but are very fibrous and require much chewing and spitting out fiber at intervals. The hypothesis would imply that A. boisei relied on these foodstuffs for the majority of its calories.

    Cerling and colleagues do not mention papyrus, and take a much more direct approach on grass-eating. But they do report data on oxygen stable isotopes from the specimens that may be relevant to the ecological context of grass (or sedge) consumption. Oxygen isotopes in bone and teeth reflect the pattern of water consumption by an animal. Oxygen-16 evaporates and transpires preferentially from leaves, so an animal living in an arid environment that gets most of its water from plants will be relatively enriched for the heavier oxygen-18. An animal that depends on drinking water from lakes or rivers will tend to have lower oxygen-18. A. boisei is almost as low in oxygen-18 composition as hippopotamus, suggesting they were strongly dependent on water sources.

    A highly water-dependent grass-eating A. boisei is a very different picture of the biology of this robust species. The South African robust species, A robustus, is very different in this regard. These two species are often lumped together, but this is unfair in many ways to their distinctive anatomical patterns. Knowing that their dietary adaptations were very distinct, we should be more inclined to focus on the details where they differ.

    Bottom line: A. boisei represents a highly distinctive dietary pattern, not present in any living ape, that no longer exists. At least the giant gelada, T. oswaldi, may also have exploited similar resources. Some grass resources, including papyrus corms and rhizomes, have high caloric and nutritional value, but require adaptations to deal with the fibrous content.

    References

    1. Cerling TE, Mbua E, Kirera FM, Manthi FK, Grine FE, Leakey MG, Sponheimer M, Uno KT. Diet of Paranthropus boisei in the early Pleistocene of East Africa. Proceedings of the National Academy of Sciences [Internet]. 2011;108:9337–9341. Available from: http://dx.doi.org/10.1073/pnas.1104627108
    2. Jolly CJ. The seed eaters: a new model of hominid differentiation based on a baboon analogy. Man. 1970;5:5–26.
    3. van der Merwe NJ, Masao FT, Bamford MK. Isotopic evidence for contrasting diets of early hominins Homo habilis and Australopithecus boisei of Tanzania. South African Journal of Science [Internet]. 2008;104:153–155. Available from: http://www.scielo.org.za/scielo.php?pid=S0038-23532008000200016&\#38;script=sci\_arttext&\#38;tlng=en
    Tags: 
    Early Pleistocene
    Koobi Fora
    Tanzania
    A. boisei
    diet
    Kenya
    Olduvai Gorge
    A. robustus

  • The shrinking youth

    Fri, 2010-09-17 13:59 -- John Hawks

    Yesterday the Journal of Human Evolution released a new paper by Rhonda Graves and colleagues, titled “Just how strapping was KNM–WT 15000?” [1]. The paper challenges almost 25-year-old estimates for the body size of this important 1.5 million year old skeleton.

    For all this time, the textbooks have reported that early Homo in Africa had the same tall and elongated physique as current East African people like the Maasai. The new paper says that the textbooks are wrong -- the skeleton doesn't represent an individual who would have grown to be 6'1" (185 cm), instead it was near the end of its growth trajectory, for an adult height of around 5'4" (163 cm).

    That's a pretty massive change, and when the authors presented this work at the AAPA meetings last spring, it wasn't without controversy. So naturally we should look closely at the paper, understand its conclusions, and assess what this new estimate means for our understanding of early Homo. As you might guess from reading some of my earlier posts, I've been thinking that the body sizes of the rest of the Pleistocene record add up to a fairly simple picture. One of the few outliers from this picture was KNM-WT 15000. I'm inclined to think that the new estimate fits the bigger picture -- for example, I wrote this spring about "Shrinking erectus".

    Which means, of course, that I should be even more skeptical.

    KNM-WT 15000 was a juvenile at the time of death, and so any estimate of body size involves some assessment of the skeleton's state of development. This has presented a problem for assessing how much the individual had still to grow at the time of its death. The eruption and development of the teeth appear to be consistent with a fairly young age at death, by most estimates younger than 11 years, and by some as young as eight. That's using a human frame of reference. If we turn to a frame of reference drawn from chimpanzees or other apes, the estimated age at death from tooth development is even a bit younger. In contrast, the state of bone development seems to indicate a somewhat higher age at death: older than 11, and by some estimates as old as 15 years.

    KNM-WT 15000 skeleton

    Graves and colleagues, looking at this apparent mismatch between dental and skeletal development in this specimen, suggests that we need to look at a broader range of possible developmental models for early Homo erectus. A modern human developmental model is not a good fit, and neither is an ape developmental model. So their study involves creating a range of possible developmental trajectories for early Homo. These trajectories are based on data from living apes and humans, but altered by accelerating some phases or changing the intensity of the adolescent growth spurt.

    The growth spurt is very important to this issue, because it's one way that humans and most other primates differ greatly. Growth during that phase of development contributes disproportionately to the tall stature of modern humans. If Homo erectus didn't have the same kind of growth spurt as we do, then the stature of this specimen would have been a lot shorter than we would estimate for a human of the same age.

    The section of Graves and colleagues' discussion that covers the adolescent growth spurt is, to my mind, the central issue in the paper. Their review begins with a survey of literature on why a growth spurt exists. Most assume that there is some kind of trade-off between early weaning in humans, brain growth, and a large adult body size–with the optimal solution being slow juvenile somatic growth, fast juvenile brain growth, and they “catch up” of somatic growth during adolescence. Graves and colleagues assert that this pattern was not present in early Homo erectus, and that a more chimpanzee like growth spurt may be a better model.

    The velocity growth curves for human stature and chimpanzee total body length (summed length of crown-rump, femur, and tibia) highlight the difference between modern human and chimpanzee growth and development (Fig. 1). Both species exhibit growth spurts, but these spurts differ in rate, timing, and duration (Leigh, 1996). Pre-pubertal growth spurts in mass have been documented in many primates ([Tanner, 1962], [Laird, 1967], [Timiras and Valcana, 1972], [Leigh, 1996], [Leigh and Shea, 1996] and [Hamada et al., 1996]), but to date only slight increases in crown-rump length and total body length have been observed in chimpanzees (Hamada and Udono, 2002). Male chimpanzees (and possibly macaques) undergo a small growth spurt in length during the period between emergence of the first and third molars ([Watts and Gavan, 1982] and [Tanner et al., 1990]), but peak velocity is not as high and the growth spurt not as extended as in modern human adolescence. The velocity of chimpanzee growth decreases slightly between the ages of four and eight, and then begins to decline rapidly until adult total body length is reached at between 12 and 13 years of age. Chimpanzee growth spurts therefore differ in their onset, offset, and intensity compared to the modern human adolescent growth spurt (see Fig. 1; [Bogin, 1993] and [Bogin, 1996]). The growth spurts in the “ALH 12.3/25%” and “ALH 12.3/50%” curves approximate the juvenile pre-pubertal growth spurt exhibited by chimpanzees, which is of shorter duration and lesser magnitude than the full-blown modern human adolescent growth spurt. We contend that these curves most closely match what is currently known about growth and development in H. erectus but acknowledge that the data currently available limit our ability to choose a single curve. It is also possible that future studies documenting growth in wild chimpanzee length may provide evidence to support a different set of growth curves.

    Their small stature estimate for KNM-WT 15000 doesn't entirely hang on this point, but this assumption about the growth spurt makes more difference than any other single factor.

    We can reasonably ask: is there any other support for this assumption?

    The apparent mismatch between dental and skeletal developmental patterns in the specimen is consistent with the lack of a humanlike growth spurt. But evidence from the skeleton itself is weakened by the fact that KNM-WT 15000 appears to have suffered from some kind of growth pathology, as argued by Latimer and Ohman [2]. The pathology argument has mostly come into play over the issue of vertebral canal size in the specimen, but anything that affected skeletal growth may well have affected the relation between epiphyseal closure and dental eruption. Naturally, if the developmental pathology was a significant influence on growth, then we shouldn't be using WT 15000 as a model for early Homo erectus stature anyway.

    A more relevant argument is that KNM-WT 15000 is really an outlier when we assume that it would have grown to a very tall stature. On first appearance, this seems correct. We have quite a number of femora from Homo erectus, both inside and outside of Africa. Only two of them approach the length that had been estimated for the Nariokotome adult stature estimate. KNM-WT 15000's former adult estimate is the extreme.

    But looking more closely, both those tall individuals come from generally the same time and place as KNM-WT 15000. KNM-ER 1808 and KNM-ER 736 both preserve partial femur shafts with estimated lengths above 480 mm. Both specimens are a bit older than Nariokotome, between 1.6 and 1.7 million years old. KNM-ER 1808 in particular contributed heavily to the argument that early Homo erectus had a very tall stature, because the partial skeleton includes a fragment of pelvis, argued to be female. A tall woman makes for a very tall species.

    Still, these two specimens don't seem as significant in 2010 as they did twenty years ago. The Gona pelvis suggests that we don't really know the sex of KNM–ER 1808. Its pelvic fragment looks female in the context of living human dimorphism, but quite possibly male compared to the Gona individual. Henry McHenry [3] estimated adult statures for the KNM–ER 1808 and KNM–PR 736 femurs, both around 5'10" (180 cm). Those are the tall end of stature estimates for Homo erectus, both taller than average for living humans. But perhaps neither is surprising when taken as the largest and of the distribution that on the whole is relatively small bodied. An estimate of 163 cm for the adult height of KNM-WT 15000, as suggested by Graves and colleagues, would not be an outlier in this population, but neither would an estimate as large as 180 cm.

    So I think the comparative evidence is equivocal. Revisiting the specimen with a smaller estimate is reasonable, but I think our ability to assess the accuracy of any estimate is very limited. In light of the pathology of KNM-WT 15000, it may not be very relevant to understanding body size evolution in early Homo, anyway.

    The main problem facing us with understanding body size in early Homo is deciding which specimens should be included in which taxa. If we exclude everything except the relatively tall ones, like KNM–ER 1808 and KNM–ER 736, then we are going to end up with a tall stature estimate for a population, putatively H. erectus. But if we include some of the smaller specimens, like KNM–ER 993, or KNM–ER 803 – both contemporaries of the Nariokotome skeleton – than the average for this more inclusive population will be a lot lower. In East Africa 1.5 million years ago we can't assign an isolated femur to a species, and we won't have a good answer for this issue until we have many more associated specimens.

    I tend to think that small stature is the null hypothesis now, given our knowledge of the small stature of the Dmanisi hominins, and the moderate body size of middle Pleistocene Homo everywhere else. There are a few specimens that represent individuals as tall as those indicated by KNM-ER 736 and KNM-ER 1808, but none taller, and many much shorter.

    It's a much deeper topic than one skeleton, but the problems assessing stature in that skeleton help to highlight the difficulty of the problem in a global sense.

    UPDATE (2010-09-18): A reader suggests that I give a link to a 2004 paper by Shelley Smith, which compared the dental and skeletal maturation of KNM-WT 15000 to a large growth series of modern Canadians [4]. She found cases in the sample with comparable mismatches of dental and epiphyseal age estimates, and argued that we can't exclude a humanlike growth spurt for early Homo. That's one reason why I think this issue can't be resolved -- the variation in humans is great enough to encompass the known fossil specimens.

    A similar lack of resolution applies to enamel growth increments in KNM-WT 15000 ("Dental growth in early Homo"). The specimen can't be distinguished from Australopithecus, but the range in modern humans is very extensive.

    At the moment, skeletal correlates of growth don't give us the resolution to answer these questions definitively about early Homo. If we had more specimens, we could at least reduce the component of error from sampling, which would help considerably. But we can't expect that anytime soon.

    References

    1. Graves RR, Lupo AC, McCarthy RC, Wescott DJ, Cunningham DL. Just how strapping was KNM-WT 15000?. Journal of Human Evolution. 2010;59(5):542 - 554.
    2. Latimer BM, Ohman JC. Axial Dysplasia in Homo erectus. Journal of Human Evolution. 2001;40:A12.
    3. McHenry HM. Femoral lengths and stature in Plio-Pleistocene hominids. American Journal of Physical Anthropology. 1991;85:149–158.
    4. Smith SL. Skeletal age, dental age, and the maturation of KNM-WT 15000. Am. J. Phys. Anthropol. [Internet]. 2004;125:105–120. Available from: http://dx.doi.org/10.1002/ajpa.10376
    Tags: 
    body size
    Homo erectus
    Nariokotome
    Africa
    Early Pleistocene
    Kenya
    stature
    Synopsis: 
    The Nariokotome skeleton once defined the tall linear body form for early Homo. Now it's 5'4".

  • Fishy story from Koobi Fora

    Sun, 2010-06-13 08:30 -- John Hawks

    I have to credit a reader for that headline, and for forwarding the paper. It's another case of the infamous PNAS release policy. The press that came from the paper's announcement preceded the paper's availability in this case by a week. That approaches the case where a Hollywood studio won't screen a movie for reviewers before it's released. That means no reviews, which in the case of movies can only mean one thing. It's bad.

    Scientific papers fortunately don't suffer from this shortfall -- the quality of the paper seems more or less unrelated to the release policy of the journal. In this case, the press went with a story that is interesting, but not necessarily that important in the scheme of things. And I don't get to write about it until two weeks after the news stories hit the presses.

    David Braun and colleagues report on the fauna at locality FwJj20 of Koobi Fora, Kenya [1]. The archaeological remains here, including stone tools and fauna, date back to 1.95 million years. It's an interesting time because of what may have been going on with hominin anatomical evolution, but does it represent anything new in behavioral evolution?

    The authors point out that there are archaeological sites that are much older, going back to 2.6 million years. Some of those earlier localities -- notably, the earliest, Gona OGS 6 and OGS 7 localities -- have hundreds of stone artifacts combined with fauna and hominin-modified bones. FwJj20 stands out in combining a very large number of stone artifacts (2633) with a high proportion of hominin-modified bones (5.9 percent of 405 faunal specimens). Even in later deposits such as Olduvai Gorge that have a high number of localities with some stone tools, it is rare to find localities with evidence of butchery of many animals. Those are the kinds of archaeological debris that would be expected of a real focus of hominin behavior. So every additional site like this adds substantially to our knowledge of hominin behavior at the dawn of hunting and gathering.

    Here, one interesting aspect of the faunal exploitation is the small amount of surface modification consistent with bone-smashing. The authors suggest that the site had little marrow extraction than expected based on experimental replication of butchery. There is very little evidence for carnivore activity at the site, and both bones and faunal remains are clustered within a small vertical horizon of around 6 inches in thickness. The presence of small flakes and bone fragments helps to substantiate that the site did not accumulate under the influence of high-velocity water flow, and that it represents a primary activity locus for the hominins who left the tools there.

    The faunal assemblage is interesting for the relatively high proportion of aquatic animals preserved, including both turtle and crocodile bone specimens with cut marks, and some fish bones. This is the part of the paper emphasized in the press that described the site, and the paper gives a good summary of the aquatic proportion of the fauna, including the evidence that the animals were actually butchered by the hominins.

    The skeletal representation of fish bones [over-abundance of cranial fragments: 64% of fish NISP (28)] and turtle/tortoise bones [over-abundance of carapace and plastron fragments: 90% of turtle/tortoise NISP (29)] corresponds to ethnographic and archaeological distributions associated with hominin foraging. The number and taxonomic diversity of hominin-modified bones imply that hominins used the FwJj20 locality for the acquisition of meat from several different carcasses of terrestrial and aquatic animals as well as marrow from mammalian bones. This provides strong evidence of a diverse animal component in the diets of hominins before the appearance of H. ergaster/erectus (Braun et al. 2010:10004).

    But....I think that the relevance of the aquatic animals has been exaggerated. According to the MNI (minimum number of individuals) table in the paper, the turtle and crocodile bones may represent one single turtle and one crocodile. The number of fish bones is also very small -- only 15 total, and the authors do not provide an MNI for fish. Compare these small numbers to a minimum of 11 hippopotamus individuals represented by in situ bone elements, and 17 bovids. One turtle. Seventeen bovids.

    MNI is not the best indicator of dietary importance -- for mammals, it is heavily influenced by mandibles and teeth. Humans may drag mandibles back to a central place as part of the head, even if they eat the rest of the animal elsewhere. Being highly diagnostic, we can work out easily when there were lots of individuals from a mandible -- not so for broken turtle carapace pieces. But it's not very meaningful to count every crocodile bone, either. The site really does not provide any evidence that reptiles and fish simply made up a large fraction of the meat consumed there.

    From my perspective, I think that's just fine. 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.

    Croc, turtle and fish remains also document that the Oldowan-makers were actively foraging in and around river or lake margins. That may not be earth-shaking, since we are, after all, talking about a water-dependent primate in a hot climate. But sometimes the importance of an archaeological discovery is that it strikes a "couldn't have done it" from the record.

    Still, this really isn't a case where anybody could credibly maintain that early hominins were excluded from foraging on lake or river margins. Just last year I discussed two archaeological sites that give evidence for human exploitation of aquatic resources in the Early and Middle Pleistocene. At Trinil, Java, it seems clear that people were exploiting molluscs ("The shells of Trinil"), and the somewhat later Gesher Benot Ya'aqov site in Israel has evidence of systematic fish and crab exploitation ("The fishy spaces of the Middle Pleistocene"). The possible exploitation of papyrus by A. boisei also would show a mastery of shoreline habitats by hominins. It's hard to argue that the threat of the water was lower for robust australopithecines than for Homo.

    Finding such repeated evidence of aquatic resource use, extending back near the dawn of stone tool manufacture, ought to prove one thing: The fatty acids in aquatic meat were not the cause of the expansion of brain size in Homo erectus.

    Oh, I know, the news stories all said exactly the opposite, claiming that the fatty acids were essential to brain growth, and that this shows that stone tools were important to getting this essential nutrient. Hey, Braun and colleagues started it -- they wrote it right in the last sentences of the paper:

    In addition, although animal tissues provide nutrient-rich fuel for a growing brain, aquatic resources (e.g., fish, crocodiles, turtles) are especially rich sources of the long-chain polyunsaturated fatty acids and docosahexaenoic acid that are so critical to human brain growth (2). Therefore, the incorporation of diverse animals, especially those in the lacustrine food chain, provided critical nutritional components to the diets of hominins before the appearance of H. ergaster/erectus that could have fueled the evolution of larger brains in late Pliocene hominins (Braun et al. 2010:10005).

    But "fueled" is a metaphor, not a valid evolutionary concept.

    I accept that reptile and fish meat may be nutritionally desirable. The question is whether they caused the increase in brain size associated with Homo. One way to read that hypothesis is as Lamarckism, which is simply wrong (Larry Moran has commented on that topic). I don't think that any paleoanthropologists are seriously Lamarckist, but some need to be more careful how they describe the relationship of fitness and diet.

    Let me construct a version of the hypothesis consistent with evolutionary biology. Suppose that other factors -- social competition, technological requirements -- induced selection for cognitive skills in early Homo. The response of the population to this selection may have been impeded by selection in favor of smaller brains and/or shorter life histories. That is to say, directional selection on cognition may have been impossible because of stabilizing selection on brain growth. Now diet changes might become relevant, by relaxing the stabilizing selection on brain growth. This scenario might predict an increase in the size of the brain when people began to consistently supply themselves or their children with the right nutrition.

    Understand that I don't subscribe to this hypothesis. We have much to learn about what the "right" nutrition might be.

    But the hypothesis is testable. The archaeology now suggests that significant meat consumption preceded the expansion of the brain by a half million years or more, and that fish and reptile meat made up a hunter-gatherer-like part of early hominin meat consumption from the start.

    Now it could be that later increases in diet quality -- for example, by increasing the total amount of meat, or decreasing nutritional unpredictability -- are what actually caused (or allowed directional selection on) the increase in brain size. That change would be a different hypothesis, however -- the hypothesis that selection against larger brains was relaxed by behavioral innovation. Fish fat could be a correlate of behavioral change in this hypothesiss, but it would not be the cause.

    References

    1. Braun DR, Harris JWK, Levin NE, McCoy JT, Herries AIR, Bamford MK, Bishop LC, Richmond BG, Kibunjia M. 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. 2010;107(22):10002-7.
    Tags: 
    Homo
    Koobi Fora
    stone tools
    Africa
    diet
    Kenya
    Pliocene
    archaeology
    Synopsis: 
    The Turkana Basin joins other areas providing evidence of dietary flexibility and aquatic resource use by early Homo.

  • Malapa and the "problem" skull KNM-ER 1813

    Mon, 2010-05-03 23:51 -- John Hawks

    The announcement of the Malapa skeletons has many of us going back to descriptions of early Homo. After the paper by Berger and colleagues came out last month, I wrote up some notes on KNM-ER 1813. This is another skull, often argued to be Homo, that has struck many people as similar to the samples from Sterkfontein and Makapansgat.

    KNM-ER 1813 has some of the smallest postcanine teeth of any maxillary specimen attributed to Homo habilis. The Malapa MH1 specimen is also small compared to the Homo habilis sample, but not KNM-ER 1813 -- MH1 is larger than KNM-ER 1813 in at least one dimension of all its maxillary teeth.

    Over the past 20 years, led by Wood (1991), most commentators have placed KNM-ER 1813 in Homo. But that assignment reversed many of the opinions on the skull's morphology that had been expressed since its discovery. Richard Leakey (1974) emphasized the differences between KNM-ER 1813 and KNM-ER 1470, which he had earlier attributed to Homo habilis. KNM-ER 1813 is quite a lot smaller in its endocranial volume -- only 509 ml, where KNM-ER 1470 is 752 ml (Holloway 1983).

    Wood framed his discussion of the relationships of the specimen by explicitly listing the features in which KNM-ER 1813 differs from Australopithecus africanus. He began by acknowledging that the overall size and shape of the skull aligns it with A. africanus, whether we consider metric or nonmetric traits. Then he discusses several derived similarities that detract from that simple picture:

    However, detailed differences between KNM-ER 1813 and A. africanus suggest that the general phenetic resemblance may be misleading. One of these detailed differences involves the frontal, and two concern the morphology of the occipital. The frontal of KNM-ER 1813, unlike that of A. africanus, shows a modest, but unmistakable post-toral sulcus and it is also braoder thn that of A. africanus. The occipital of KNM-ER 1813 makes a relatively greater contribution to the sagittal profile than in A. africanus, no matter which of the two locations of lambda is used. In addition, it bears an incipient torus, the shape of which has been interpreted by two independent authors as being reminiscent of H. erectus. All three of these detailed differences are such that the condition in KNM-ER 1813 is derived in the direction of H. erectus (Wood 1991: 92-93, citations omitted).

    The extent of the occiput may be a simple correlate of a larger vault, but the other two characters -- supratoral sulcus and occipital torus, are not.

    When the morphological features of the cranial base of KNM-ER 1813 are assessed against this comparative background, the evidence suggests that the cranial base of KNM-ER 1813 differs from that of A. africanus. Without exception, the expressions of these characters in KNM-ER 1813 are more derived in the direction of Homo than are the homologous characters of A. africanus. The angulation of the petrous temporal and the inclination of the foramen magnum are two particularly crucial indicators of the very different arrangement of the cranial base of KNM-ER 1813 and A. africanus. Further evidence of the relative shortness of the base of KNM-ER 1813 comes from the position of the porion with respect to the anteroposterior axis of the cranium, and the evidence of a relatively wide sphenoid (e.g. the location of the foramen ovale and spinosum and the make-up of the entoglenoid) must also be taken into account. This is not to say that all features of the cranial base of KNM-ER 1813 are Homo-like, for Dean (1984) has shown that the relative sizes of the insertions of the nuchal muscles are still remarkably pongid-like (as in deed they are for many early hominids). However, for several features for which we have good comparative evidence, their expression in KNM-ER 1813 must lead us to reject a close association between it and A. africanus. The anatomy of the mandibular fossa region is also derived with respect to the australopithecines, and Picq has claimed to see in KNM-ER 1813 the basis of a temporomandibular joint morphology that can be traced through KNM-ER 3733 to the condition seen in H. erectus from Asia (Wood 1991: 93, citations omitted).

    Wood here went into a lot of detail about the cranial base because of his earlier work on this part of the anatomy (for example, Dean and Wood 1982). But even this description may seem cursory in light of the variability within A. africanus of these cranial base characters. KNM-ER 1813 is not ideally preserved, missing most of the basisphenoid and basiocciput, and without a good join along the midline back cracking across the occiput to the right asterion. The petrous orientation is very different from Sts 5, which also has a more posteriorly placed foramen magnum. But Sts 19 is not nearly so different in these respects from KNM-ER 1813.

    Now, the cranial base of the MH1 skull from Malapa is still embedded in matrix, so we can't do this comparison yet with that skull. Will it look Homo-like in the ways that KNM-ER 1813 apparently does, or will it fit squarely within the range of Sterkfontein sample? If I were going to put money on the question, I would bet that the cranial base is influenced by endocranial volume. If so, then the small brain of MH1 will determine an essentially australopithecine-like cranial base. We'll see when the scans are examined.

    The point of discussing this anatomy is not because the cranial base is itself intrinsically important. It fades next to more familiar traits such as brain size and dental morphology. But brain and teeth can't answer the question alone -- they need corroborating evidence from other characters. Particularly in cases like KNM-ER 1813, and MH1, with a more Homo-like dentition than brain, we want to find a phylogenetic hypothesis that maximizes consistency across the entire skeleton.

    To understand why, consider another fossil: D2700 from Dmanisi. Rightmire, Lordkipanidze and Vekua (2006) explicitly noted the similarity of the subadult D2700 skull with KNM-ER 1813, including the size, the contours of the facial and vault profile, the size, shape and depth of the palate. The picture reflects the broad similarities noted in the text of that paper:

    KNM-ER 1813 and D2700

    KNM-ER 1813 (left) and D2700 (right), from Rightmire et al. 2006.

    Rightmire and colleagues (2006) note that KNM-ER 1813 is more like H. erectus in some respects than is the Dmanisi specimen -- chiefly, D2700 has little if any development of an occipital torus and has a longer clivus and wider interorbital distance than D2700. Rightmire and colleagues (2006) assume that KNM-ER 1813 represents H. habilis for the purposes of this comparison, and they then show that most of the resemblances between this specimen and D2700 are primitive. That amounts to an argument that D2700 is not H. habilis.

    It's funny that this key point in human evolution is best documented by three skeletons that could all represent 11-year-old boys -- D2700, MH1, and KNM-WT 15000. In the case of D2700, the contrast with KNM-WT 15000 is possibly great, but hard to interpret because of the imperfect state of our developmental knowledge. Along those lines, it becomes clear just how much there is yet to learn about MH1.

    References:

    Dean MC, Wood BA. 1982. Basicranial anatomy of Plio-Pleistocene hominids from East and South Africa. Am J Phys Anthropol 59:157-174.

    Rightmire GP, Lordkipanidze D, Vekua A. 2006. Anatomical descriptions, comparative studies and evolutionary significance of the hominin skulls from Dmanisi, Republic of Georgia. J Hum Evol 50:115-141. doi:10.1016/j.jhevol.2005.07.009

    Wood B. 1991. Koobi Fora Research Project. Vol. 4. Hominid Cranial Remains. Clarendon Press, Oxford.

    Tags: 
    Dmanisi
    Malapa
    A. sediba
    Homo habilis
    Kenya
    Koobi Fora
    South Africa
    Synopsis: 
    The discovery of the Malapa juvenile skull with some Homo-like features provokes a re-examination of the crania of early Homo.

  • Red beds

    Wed, 2010-03-31 08:32 -- John Hawks

    I've been browsing the Smithsonian's website supporting their human origins hall. There's a nice feature about the archaeological work at Olorgesailie, Kenya, focusing on the relation between paleoenvironment and human behavior. Here's a snippet:

    One intriguing indicator is a series of reddened beds found in the later part of the sequence, between nearly 800,000 and 500,000 years ago. These brightly colored patches of sediment were produced by burning of buried plant matter. In some instances, the reddened sediment is associated with melted diatomite, which required an enormous amount of heat and a complete absence of water. The reddened beds required, then, the accumulation of an abundance of swamp plants, followed by burial (only an underground fire could have produced sufficiently high temperatures to melt the silica in the diatomite), followed by intense drought. The fires may have started as lightning ignited the buried materials, much like peat fires in places today.

    Tags: 
    Africa
    Lower Pleistocene
    museums
    paleoclimate
    Kenya
    Middle Pleistocene
    Olorgesailie

  • The trouble about Kenyanthropus and Ardi

    Thu, 2009-12-10 15:32 -- John Hawks

    There are three skulls from putative "hominins" that date to 3.5 million years or earlier. Every one of these skulls is known now from extensive reconstruction or correction for distortion in the original.

    By itself, the extensive reconstruction might not be a problem. But as Tim White has repeatedly shown, the specialists on these crania actively and vociferously disagree about the basic anatomy due to problems reconstructing them. White's ongoing dispute about the skull of KNM-WT 40000 is a matter of public record, both in his initial 2003 article on the skull, and in Michael Balter's description of the recent Royal Society meeting*:

    When the talk was thrown open for discussion, White took the microphone and began firing questions at Spoor about the degree of variation of the cheekbone position among specimens of A. afarensis and other hominin species. “We took that into account,” Spoor responded, “and I just showed you a graph” about it. “I didn’t ask you whether you took it into account; I asked you what it was,” White said. Spoor, clearly frustrated, told the audience that he had no vested interest in this debate. At that point, the session chair interrupted and invited everyone to break for coffee, but Spoor and White continued to debate between themselves for the next half-hour.

    If KNM-WT 40000 were the worst case, that would be bad enough. But Ardi's skull has required reconstruction even more extensive than would be required for the Kenyanthropus holotype.

    In their description of the Ardipithecus skull, Suwa and colleagues (2009) mainly present metrics taken from the CT reconstruction. The publication strikes me as remarkable in that it includes few photographs of the original fossil, and only one or two of the photos are in standard anatomical orientation. A substantial part of the CT reconstruction is based on a second individual (ARA-VP 1/500), of which no photographs are provided. For this, readers may refer back to the single rather poor photo in the 1994 description. Anatomical comparisons in the present paper are limited to visualizations of the CT reconstruction.

    As I've written elsewhere, I think that Suwa and colleagues did a remarkable piece of reconstruction. But it is non-replicable. The CT-reconstruction is a composite of two specimens that includes mirror-imaged parts. A tremendous amount of work went into it, but without access to the component parts, it isn't possible to test or verify the assumptions underlying the present model.

    Another striking thing about the Ardipithecus skull description is the lack of anatomical comparisons with relevant samples. I mentioned above that most of the figures involve metric comparisons -- many of them scaled to the cube root of endocranial volume -- which of course can only be taken on a small fraction of early hominin crania. That leaves out the most relevant specimens in the Hadar sample, including all the cranial specimens from AL 333. It leaves out most of the Sterkfontein collection.

    And it brings us back -- again! -- to Kenyanthropus. Reading back through the paper, it's hard for me to believe that reviewers allowed Suwa and colleagues to publish on Ardi's skull without including any comparisons with KNM-WT 40000. It's the earliest complete skull of an undoubted hominin.

    They're entitled to their opinion that the skull is distorted. I agree. But you can still compare most of its nonmetric features and put some reasonable bounds on its metrics. I mean, they included OH 5, for goodness sake -- which has nothing whatever to do with hominin origins. Including the comparisons wouldn't have changed much about the paper, although I'll point out that there's at least one derived feature of later hominins that KNM-WT 40000 and ARA-VP 1/500 both lack, and which isn't noted either by Suwa and colleagues (2009) or in the table presented by White and colleagues (2009).

    So what should we do? We can't see the scans, no independent reconstructions are possible, and the people who can see the scans refuse to present comparisons of these three skulls that together represent the supposed origin of the hominin lineage.

    AAAARRRRGGHHHH!

    We need to set up multiple sets of independent reconstructors having a replicable go at these skulls. These are the three earliest hominin skulls. Every one of them is crushed in some weird way. It would be a credit to the science to document their reconstruction in nauseating monograph-level detail. They're scans, for goodness' sake -- there's absolutely no argument that access should be limited for any reason.

    If I were running this, I would set up a graduate seminar devoted to putting them together, split among four universities, with results to be reported in a session at the meetings and monographically by e-publication. The issue is not whether we can obtain an exact representation of the original anatomy. The issue is whether we can reject hypotheses about that anatomy. Testing hypotheses requires us to survey the range of possible reconstructions and how they relate to the range of anatomical variation in living and extinct analogs. The more reconstructions, the better the testability.

    At the moment, that testability isn't there. I trust the anatomical expertise of the people who made the models, but they're just single models with no assessment of the range of error. I've written about the importance of open access for these reconstructions already ("Open access and fossil reconstruction"). The points here just amplify that theme.

    * As an aside, I wonder if the title of the Royal Society meeting ("The First 4 Million Years of Human Evolution") contemplated the possibility that there may have been only 4 million years of human evolution in total?

    Tags: 
    Africa
    Kenya
    who-has-the-ct
    Ardipithecus
    Ethiopia
    Kenyanthropus
    open access

Pages

Subscribe to Kenya

Neandertals

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

Denisova

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

Acceleration

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

Malapa

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