diet

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. 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:

Braun DR, Harris JWK, Levin NE, McCoy JT, Herries AIR, Bamford MK, Bishop LC, Richmond BG, Kibunjia M. 2010. Early hominin diet included diverse terrestrial and aquatic animals 1.95 Ma in East Turkana, Kenya. Proc Nat Acad Sci USA 107:10002-10007. doi:10.1073/pnas.1002181107

I've had on my stack for quite a long time, a short paper by Nicholas van der Merwe and colleagues, assessing the stable carbon isotope ratios in several specimens from Tanzania. These include the Homo habilis specimens OH7, OH62 and OH65, and the A. boisei specimens OH5 and the Peninj mandible.

The ratio of stable carbon-13 and carbon-12 enable an assessment of the amount of C₄ versus C₃ plants in the diet. I discussed the basic ideas in a longer post from 2005.

The results on the Homo specimens are not too surprising. All three specimens overlap with South African A. africanus. OH7 and OH62 in particular have values around 20% C₄, which is right near the mean observed for South African Homo and A. robustus from Swartkrans. OH65 has a higher C₄ percentage than the other two, but within the range observed for Sterkfontein Member 4 A. africanus, which was significantly higher than Makapansgat or the other South African samples. So it would appear that the diet of Homo habilis did not differ from earlier hominins in terms of the ultimate origin of carbon in grasses versus non-grass plants.

What is more surprising is the extremely high amount of C₄-derived carbon in OH5 and Peninj. They score 77% and 81% C₄, respectively. These are the only two specimens of A. boisei for which these stable isotopes are known, and they are very far from the observed range in the South African A. robustus.

The authors suggest an interesting source for this high C₄ proportion -- papyrus. They described a tasting tour of the wild plants of the Okavango:

Bamford and van der Merwe investigated (and ate) the edible plants of the Okavango Delta in Botswana during the dry season (July 2003), assisted by Ezaya Karesaza, a tourist guide who grew up in this extensive wetland. Among the C₃ plants that are traditionally eaten raw in this region are a variety of fruits and seeds, as well as plants of which the leaves and rhizomes are eaten. The latter include Aeschynomene fluitans, a floating legumi- nous plant, of which the leaves taste like lettuce; Typha capensis, which grows in thick stands along the water’s edge, of which the rhizomes have a pleasant taste; and Schoenoplectus corymbosus, a big water sedge, of which the stem is succulent at the bottom end. Among C₄ plants, the rhizomes and culms of three other species of sedges are edible. These include Cyperus denudatus and C. dives, which grow in the grasslands of the floodplains. Unlike the grasses, they are green year-round, although not particularly prolific. The most common C₄ sedge, by far, is Cyperus papyrus, which grows in dense thickets along the water edge. This species has culms as high as 4 m, of which the lowermost 0.5 m is frequently chewed by local people. It has a soft, white rind about 0.5 cm thick; the interior, about 2 to 3 cm in diameter, is more fibrous. It is chewy and pleasant tasting. The thick rhizome of papyrus is more fibrous and starchy than the culm, somewhat astringent, and requires considerable chewing effort. It produces a bolus in the mouth that has to be spat out at intervals.

They then reported the results of a nutritional analysis of the papyrus culm and rhizome, which have roughly the nutritional and caloric value of domestic potatos, although would require a significant gut flora to deal with the cellulosic content.

All in all, it's very curious that A. boisei is so different in these isotopic values compared to other early hominins. The theme was picked up last year in a paper by Richard Wrangham and colleagues, who focused on the idea of "fallback foods" -- the kinds of foods that an animal does not prefer, but eats when other more highly preferred foods are not available. Considering the very high C₄ proportion indicated by the OH5 and Natron isotope values, it doesn't seem likely that this reflects a fallback strategy, but possibly an initial exploitation of such resources as fallbacks facilitated a later, more developed adaptation to them.

Related posts:

"Chemistry and early hominid diets"

"Robust australopithecine diet ablated"

"Average diet versus extreme diet in robust australopithecines"

References:

van der Merwe NJ, Masao FT, Bamford MK. 2008. Isotopic evidence for contrasting diets of early hominins Homo habilis and Australopithecus boisei of Tanzania. S Afr J Sci 104:153-155.

Wrangham R, Cheney D, Seyfarth R, Sarmiento E. 2009. Shallow-water habitats as sources of fallback foods for hominins. Am J Phys Anthropol 140:630-642. doi:10.1002/ajpa.21122

Today we finally get to learn about the exceptional discovery of four partial hominin skeletons from Malapa Cave, South Africa. Two of the fossil skeletons are described by Lee Berger and colleagues in the current issue of Science, descriptions of two more are still forthcoming.

A kind journalist sent me a copy of the research papers a few days ago, so my graduate students and I have had a chance to think about them a little bit and compare them with other material.

Berger and colleagues have named a new species to contain the fossils, Australopithecus sediba. For anybody who follows paleoanthropology, the new species won't be surprising -- if I found a fossil, I'd surely make up a new name for it, even if I thought it was my great-great-grandmother. In this case, the morphological reasons for naming a new species aren't trivial, but I'll begin by approaching them skeptically, especially in comparison with the large samples of South African fossils both earlier and later than Malapa. I'll conclude that a new species within Australopithecus was probably the right call, but not an easy one.

The press is running with a "new fossils provoke debate" storyline -- are they possible ancestors of Homo or not?

The simple answer to that question is that the Malapa skeletons are too late to be ancestors of Homo. After all, we have early Homo nearly a half-million years earlier.

A more complicated answer is that it depends what we mean by Homo. My feeling is that these skeletons don't comport with what most of us mean when we say "Homo". Most of us have in mind an adaptive shift from Australopithecus to Homo that included larger brain size as a significant element, and the MH1 skeleton has a small endocranial volume.

But if we accept that model of Homo, we have to accept its consequences, as the Malapa skeletons now make clear. One important consequence is that, if we assume that MH1 isn't Homo, we can no longer say have any skeletal evidence of Homo from before 1.95 million years ago. Because the Malapa specimens are more like Homo in their dental and mandibular features than are earlier specimens that have usually been called Homo.

And if we throw out all those earlier Homo specimens...well, then suddenly Malapa isn't too old to be an ancestor of Homo after all.

How old are they?

The fossils lay above a flowstone with a U-series and paleomagnetic date consistent with an age just around 2 million years ago. That's a maximum age for the fossils; they must be younger than that.

The hominins are in water-deposited sediments, which are inferred to represent ancient washes of subterranean water flows through the cave system. Two elements above the flowstone contain the hominin specimens, called facies D and E, and both have normal magnetic polarity. The most likely interpretation is that they belong to the Olduvai paleomagnetic subchron, which occurred between 1.95 and 1.78 million years ago. A specimen of the sabertooth cat Megantereon in one of these facies has a last appearance elsewhere in Africa at 1.5 million years ago. So it appears that 1.78 million years is a very likely minimum age for the fossils.

That's about as good as dating gets in South Africa, where we're used to seeing very wide age brackets on hominin-bearing localities. It means that the Malapa hominins lived at around the same time as KNM-ER 1470 in the Turkana basin, or OH 24 at Olduvai Gorge. Until today, I think we could justly claim that the only australopithecines still known to occur in this time interval were the robust species A. boisei and A. robustus -- although the first appearance of A. robustus might (might) be later than Malapa.

Why aren't they A. africanus?

To me, this is the hardest question to answer.

The Sterkfontein Member 4 sample of A. africanus is tremendously variable. The postcrania of both Malapa skeletons are tremendously informative, but fall within the range of variation at Sterkfontein for almost every feature that the authors reported. The few exceptions (such as humeral torsion and femur neck/shaft angle) are right at the edge of the Sterkfontein range.

In other words, it's my impression that the postcrania of the Malapa skeletons fit within A. africanus. The limits of my impression are that there are a whole lot of observations here, and the paper generally does not report metrics for the postcrania. Maybe the sequel will give us some more surprises.

I would have added a comparison with the Swartkrans A. robustus sample, which overlaps nearly totally in body size with Sterkfontein and contains elements that are in some cases more comparable to the Malapa skeletons. In particular, the os coxa of MH1 looks a lot like SK 3155, and the proximal femur looks like SK 82 to me, at least in the tiny picture provided with the paper. On the whole, I don't think that the Malapa hominins are particularly like A. robustus, I just think that if you put together a reasonably large sample of australopithecine postcrania, these two skeletons don't stand out.

I'll take up the discussion of proportions of the different elements below. My feeling is that the proportions aren't exceptional for Australopithecus, either, but we have to temper that against the observation that really only AL 288-1 (Lucy) is comparable, and it's more than a million years older.

What about the teeth? Generally speaking, the teeth of MH1 and MH2 are both at the small end of the A. africanus range. In a couple of cases (the lower canine of MH1, the lower second molar of MH2), the teeth are absolutely smaller than any Sterkfontein individual. The canines are within the range of A. robustus (remember that the robust australopithecines have small anterior teeth), but the premolars are nothing like the large, molarized Swarktrans sample of premolars.

They're a little small but within the range of those known for Homo habilis at Olduvai Gorge. For example, OH 7 -- the type specimen of Homo habilis has molars that are 1.5 mm larger than MH1 in both dimensions.

But then, Homo habilis really doesn't differ much in tooth size from Sterkfontein.

In size, the Malapa teeth are exactly what you would expect for Homo erectus. The first molars are smaller than those of Dmanisi D2700/D2735, for example. But unlike H. erectus dentitions, the molars of the Malapa hominins get bigger toward the back -- M3>M2>M1.

The Malapa mandibles are strikingly gracile. The MH1 mandible has a relatively vertical symphysis with a small cross-section. The long, parallel upper and lower corpus borders really strike me like a mandible of Homo erectus, something like KNM-ER 993 or OH 22 -- but this impression may be exaggerated considering the M₃ of MH1 has yet to erupt. Metrically, the corpus breadth and height are most like OH 13. There are small australopithecine specimens that compare to this, such as AL 277-1, and it is worth remembering that MH1 is a juvenile mandible. I can't compare the ramus heights with those of other samples because the authors don't report those measurements.

An interesting question: If these mandibles had been found in isolation, would we call them Australopithecus? The Olduvai H. habilis mandibles OH 7 and OH 13 have M3>M2>M1, while OH 16 has M2>M3>M1. The Malapa mandibles look much more like later Homo than do early Turkana basin mandibles like KNM-ER 1801, KNM-ER 1802, or KNM-ER 1482, all of which are much more robust and have larger, more molar-shaped premolars than MH1, and all of which have M3>M2>M1 except KNM-ER 1802 which lacks M₃. This is a quick comparison on my part, but I think the Malapa mandibles look more like Homo than does the existing hypodigm of Homo habilis. It's hard to imagine that the mandibles in isolation would have been referred to Australopithecus. More on that below.

Compared to the mandibles, the cranium of MH1 looks more like its counterparts from Sterkfontein. To be sure, it is an 11-13-year-old juvenile and more gracile in some respects than any of the Sterkfontein crania. But take a look at it next to Sts 71:

MH1 (left) next to Sts 71 (right)

They're not identical, naturally. Sts 71 has higher temporal lines, a slightly smaller vault, and more prominent cheeks. It also has more postorbital constriction compared to MH1, though that isn't obvious from this angle. MH1 has a true superorbital torus, Sts 71 has at best a shade of one. But you can see the similarities -- the angle of the zygomatic process of the maxilla, the narrow and concave interorbital region, the tall and narrow orbits. MH1 has no prominent anterior pillars (bony swellings on either side of the nasal aperture), but Sts 71 is not very different in this region. Sts 71 has bigger teeth.

Consider also Sts 52:

MH1 (left) next to Sts 52 (right)

Again, Sts 52 has anterior pillars and bigger teeth, but the shape of the face is very comparable between these two. The nasal bones in particular are similar in this pair, almost "pinched" at the midline, with a lateral expansion both superiorly and inferiorly.

We can do a similar exercise for most of the features of the MH1 cranium. What is exceptional, in the context of the Sterkfontein sample, is the overall gracility of the masticatory apparatus.

One important thing that is not in the least bit exceptional: Its brain. An endocranial volume estimate of 420 ml (from CT reconstruction) puts MH1 at the bottom of the range of variation at Sterkfontein -- the best-known skull from Sterkfontein, Sts 5, has a volume of 485 ml, while STW 505 has a volume larger than 550 ml. Before MH1, the smallest of the South African crania were estimated to have volumes of 428 ml. This one seems to be smaller mainly by being flatter -- a shape that it shares with early Homo, but I wouldn't say it was without parallel in Australopithecus.

But the smallest endocranial volume known for early Homo is KNM-ER 1813, at 510 ml. That specimen is extreme: the next smallest is 585.

The vault fits in A. africanus, most of the facial features have comparable specimens in the Sterkfontein sample, with some exceptions, and the postcranial skeleton is unexceptional. The teeth are mostly within the range at Sterkfontein with some exceptions. But the mandible -- like those few facial characters -- stands out.

Australopithecus sediba -- a new species within Australopithecus -- then seems like a fair diagnosis. The craniodental derived features are of the sort that would usually justify a new species. Heck, in the case of Kenyanthropus, even more minor differences in the face and size of teeth from contemporary A. afarensis caused Leakey and colleagues (2001) to name a new genus.

Is MH1 really a male?

Berger and colleagues (2010) infer that the MH1 skeleton (the one with the skull) is a male. It is large and more robust than the MH2 skeleton: Its teeth are bigger than the MH 2 skeleton, its mandible is more robust with a taller ramus, the articular ends of its limb bones are a bit larger. In addition, the greater sciatic notch on its preserved os coxa is narrower than other australopithecines like Lucy and Sts 14, and the pelvic inlet may (based on the anterior position of the auricular surface) have been smaller.

But the skeleton isn't really very big. Its endocranial volume is small, its long bones are not nearly so robust as some australopithecines. There are large male australopithecine skeletons -- STW 431, for example -- and MH1 doesn't seem so large as these. Again, it's hard to tell without postcranial measurements, but the sex of this specimen isn't a clear call either way.

The sex of the specimen is important to the way we interpret it, because the features that make it stand out from A. africanus concern masticatory gracility. If it's a female, it doesn't seem quite so different from A. africanus as if it's a male.

Are they Homo?

Let's start with the brain size, which at 420 ml seems to be the most obvious thing separating MH1 from our genus. Well, except for Liang Bua 1 -- with its endocranial volume of, um, 420 ml. Is brain size fundamental to Homo? Maybe. Maybe not.

Alan Boyle's report on the fossils ("Fossils shake up our family tree") has an excellent letter from Don Johanson, who makes the argument that the Malapa fossils should be assigned to Homo. Of course, Johanson and Bill Kimbel in 1996 described a 2.33-million-year-old fossil from Hadar as the earliest clear maxilla of Homo. That maxilla, AL 666-1, resembles Homo in having a more vertical subnasal profile, a parabolic dental arcade, molars that are long relative to their breadth, and a "squared-off" jaw that is relatively straight across the anterior dentition. In other words, basically the dental features seen in the MH1 maxilla.

We've got two choices. Maybe these are genuine shared derived features with these specimens and Homo -- in which case, we should probably name them Homo, as Kimbel and colleagues did for AL 666-1.

Or, there were several australopithecines after 2.5 million years ago with these dental and maxillary (and for the Malapa hominins, we can add mandibular) characters. In which case, they're not signs of Homo at all. They may reflect parallel dental reduction in several australopithecine lineages, all of which faced niche differentiation from the emerging robust australopithecines. One of those lineages may have given rise to Homo, but we don't know which. Maybe it was South African, but it need not have been. It could even have been Asian.

The question is just how important we think brain evolution was to the origin of our genus. If the brain was the key adaptation, then Malapa shows that the dental features are irrelevant to the brain -- because these skeletons have more dental reduction than most of the East African Homo habilis sample, but MH1 has a much smaller brain.

What about tool manufacture?

Part of the logic of pre-2-million-year-old Homo is the emergence of stone tool manufacture 2.6 million years ago. It stands to reason that this major shift in behavior and diet might have given rise to a new adaptive plateau for early hominins, and that would have been tied to the evolution of larger brains. The problem is that we don't have larger brains in any fossil remains until after 2 million years ago -- KNM-ER 1470 remains the earliest hominin with a brain larger than 600 ml. Up to now, people have conjectured that large-brained hominins may have existed earlier, even to the point of arguing about the brain size reflected by the otherwise-robust temporal bone from Chemeron. But it's worth pointing out that none of these pretenders to the Homo throne have smaller teeth than A. africanus. The diet shift that should have been made possible by a meat-eating stone tool economy didn't lead to smaller teeth until much later.

And now we know that at least one small-toothed hominin also was a small-brained one.

We don't know whether the Malapa hominins would have been toolmakers. The fact that they weren't found with tools isn't really evidence either way. Dirks and colleagues (2010) suggest that the skeletons were deposited by water washing them from an initial death trap into a secondary location. If true, it would be a miracle beyond belief for stone artifacts to have made the trip with them.

We do know that stone tools are present in Sterkfontein Member 5 and Swartkrans Member 1, and cutmarked fauna are in the latter. Both these may be roughly contemporaneous with the Malapa hominins, depending on their date. So toolmaking hominins were in the immediate area, around the time that the Malapa hominins lived.

SK 847 is from Member 1 of Swartkrans, and could be as old as the Malapa skeletons. Its endocranial volume isn't known, but facially it looks even more like Homo erectus than does MH1. It seems plausible that this skull represents the local toolmaking population, but even so, this skull does resemble MH1 in several respects, and again we don't know its volume. STW 53, probably a bit older than Sterkfontein Member 5, has also often been referred to Homo but it definitely doesn't have a substantially larger endocranial volume than MH1.

So again, we seem to be faced with two choices: Broaden the definition of Homo to include this very australopithecine-like sample, or restrict it to later large-brained hominins. In either case, brain size and tool manufacture do not necessarily go together.

What's the single most obvious thing that the paper doesn't describe?

Which brings me to the fingertip. MH2 has a distal phalanx. The paper doesn't describe it, even though this bone element has taken on such importance in the evolution of Homo compared to Australopithecus. Big fingertips are supposed to be adaptations to force transfer through the fingertip grip used in tool manufacture.

The picture of the thing is so tiny -- I mean, literally we're talking about two pixels of finger -- that I can't make anything out of it. Does it have a large apical tuft, like OH 7? Or is it like the Hadar distal phalanges, with narrow, apelike apical tufts?

If one was wondering about whether the thing was Homo or not, I would think this is one of the first things you would check....

What about those limb proportions?

For fifteen years, a bunch of otherwise sensible paleoanthropologists have been engaged in a debate about the limb proportions of A. africanus and H. habilis. The reason why this particular question may not be sensible is because the debate is about the length of the arm relative to the leg, but there's no specimen of A. africanus that preserves both the length of the arm and the length of the leg.

What there are: OH 62, a skeleton apparently of H. habilis that has a complete humerus and more than half the length of one femur, STW 431, which has an acetabulum and mostly complete humerus, and Sts 14, which has a partial femur, an acetabulum, and a piece of distal radius. On the basis of these fossils, we've seen some intense debate about the reconstruction of the OH 62 femur length, and a lot of discussion about whether the sizes of articular surfaces are relevant to the function of the limbs. Indirectly, it has appeared that A. africanus and H. habilis shared longer arms than were present in AL 288-1 (Lucy).

Well, now we have two fossil skeletons with both hindlimb and forelimb elements. The paper doesn't address the issue directly, nor does it provide raw measuremnets that would lead to a quick answer. But the humerus is short relative to the size of the femur head, compared to earlier hominins, while a bit long relative to Homo by the same comparison. So it looks like the Malapa skeletons may be somewhere in between.

The authors do argue that OH 62 is an odd skeleton in one respect: They consider the "diaphysial strength" of the humerus and femur. This is a cross-sectional measure of the area of cortical bone, and reflects the robusticity of both forelimb and hindlimb elements. In their estimation, OH 62 has a much stronger arm relative to its leg strength than the Malapa skeletons.

It's not obvious how to interpret this observation. Is OH 62 more apelike in its locomotor pattern than Malapa? Or does the strength ratio vary allometrically with body size, and OH 62 is just at the smallest end of the comparison? Hard to tell without the length measurements.

OK, what's the bottom line?

Here's the important thing. From today forward, there are a bevy of features of the face, teeth and jaw that are no longer "derived characters" of Homo.

Some people will want to fix this by broadening the definition to Homo to include the Malapa skeletons. Others will want to narrow the definition of Homo to include only large-brained specimens.

Every specimen attributed to Homo before 2 million years ago is now up for grabs. Maybe they're Homo, or maybe their resemblances to Homo are just masticatory parallelism. We already know that parallelism explains many of the derived locomotor and masticatory resemblances of great apes, and many strongly suspect that parallelism explains the derived masticatory resemblances of robust australopithecines. If the dental reduction that once was a marker of Homo joins this list, it will hardly be surprising.

If we follow the logic that connects tool use to dental reduction, however slowly and indirectly, then I think we have to conclude that A. sediba was likely a toolmaker and meat-eater. This hypothesis is testable, both by bone chemistry and dental morphology and wear.

Malapa suggests the hypothesis that brain evolution followed the appearance of stone tool manufacture by a considerable delay. If so, I wonder what exactly caused the brain to expand. Did the diet shift to higher-quality foods unfold over a long time, allowing brains to expand only after 3/4 million year delay? Or was brain evolution caused mostly by non-dietary factors, such as social dynamics or climate instability?

Or did the evolution of our genus happen somewhere else, far from the places where we currently have fossil samples? The Rift Valley and South African cave systems may have been wonderful for preserving fossils, but who's to say they weren't relative backwaters when it came to the evolution of Homo?

Well, I'm running out of gas for this installment. More later....

References:

Berger LR, de Ruiter DJ, Churchill SE, Schmid P, Carlson KJ, Dirks PHGM, Kibii JM. 2010. Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa. Science 328:195. doi:10.1126/science.1184944

Dirks PHGM, Kibii JM, Kuhn BF, Steininger C, Churchill SE, Kramers JD, Pickering R, Farber DL, Mériaux A-S, Herries AIR, King GCP, Berger LR. 2010. Geological Setting and Age of Australopithecus sediba from Southern Africa. Science 328:205. doi:10.1126/science.1184950

I blame Harold Dibble. Oh, sure, all these "paleo diet" people point the figure at Loren Cordain, but Dibble was the first to give them a cookbook!

So now, it's a "movement" and it's in the New York Times:

Mr. Durant, 26, who works in online advertising, is part of a small New York subculture whose members seek good health through a selective return to the habits of their Paleolithic ancestors.

Or as he and some of his friends describe themselves, they are cavemen.

Oh sweet mercy. Give me a break.

This guy grows a "cheerful Jim Morrison" beard and installs a small chest freezer in his apartment (there's a photo of the "meat locker" that's supposed to "spook a female guest"), and we're supposed to think he's a weirdo survivalist of some kind? Hasn't this reporter, Joseph Goldstein, ever been outside the city? If he'd gone out to flyover country -- say, New Jersey -- he'd discover bigger deep freezes in the homes of most hunters. The only thing strange about this guy is that he doesn't have a basement to put it in.

Well, how's it working out for them?

Most of the cavemen at Mr. Durant’s gatherings are lean and well-muscled, and have glowing skin. A few wear trim beards. Some claim that they no longer get sick. Several identify themselves as libertarians.

OMG, they're LIBERTARIANS! It's like Manhattan has finally fallen to those "rewilding" people! Come on baby, light my fire!

There's a typical kind of "lifestyle" article in the NY Times, where a reporter interviews three or four people who all do some weird thing, as if they were part of a trend sweeping the nation. But it always turns out that these three or four people all know each other, are all twenty-somethings, all live in some fashionably bohemian area of Manhattan, and (often) just happen to be acquaintances of the reporter.

Now this could be because the NY Times only hires reporters plugged into hot new trends, which are all started by twenty-somethings in Chelsea. Or it could be that twenty-something reporters on deadline tend to "run home to mama" when they can't think of any other ideas.

You tell me which this is:

Another caveman trick involves donating blood frequently. The idea is that various hardships might have occasionally left ancient humans a pint short. Asked when he last gave blood, Andrew Sanocki said it had been three months. He and his brother looked at each other. “We’re due,” Andrew said.

The article itself is pretty deep in snark, and with all its talk of fasting and blood donation, it's like a flashback to 1994. Which I admit is kind of entertaining. The article's lead photograph, posing three of the "cavemen" dressed all in black in front of the Cro-Magnon diorama at the American Museum of Natural History, makes them look like the cast of Pleistocene Twilight.

The only reason I'm really incensed is its promotion of a self-proclaimed guru (whom I won't name), whose website (which I won't link) promotes some of this quackery. Some of the resulting advice seems to be dangerous. For example, a current entry encourages people not to carry or drink water during workouts -- I suppose because cavemen didn't have water bottles? It's a good way to get yourself hospitalized or worse.

I'm the last person to promote gatekeeping in science. But a piece of free advice: Don't get your information about human evolution from non-anthropologists who charge you money for subscriptions and seminars!

Meanwhile, on the Upper East Side we hear from a doctor who prescribes his patients Cordain's Paleo Diet. Supposedly that shows the trend is spreading into the mainstream -- although The Paleo Diet is now eight years running.

I don't think there's anything harmful about adopting a hunter-gatherer-like diet. I do doubt whether it's the most healthful diet for some people -- the point of "adaptation" is to increase offspring number, not longevity! Besides, some populations have been adapting to agricultural diets for ten thousand years. The most healthful diet for you might be the diet of your recent ancestors, not your Paleolithic ones.

But to be honest, the best food is the food that brings you nearer the ones you love. And if frozen venison ribs in your living room can make you "a chieftain of sorts among 10 or so other cavemen", well more power to you. Maybe it will bring you a Wilma Flintstone, too.

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

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

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

How intensive? Well, there is a slight problem:

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

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

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

References:

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

In Science this week, Nira Alperson-Afil and colleagues report on recent excavations at Gesher Benot Ya'aqov, Israel. I saw some of this research presented at a conference, and I thought it was quite amazing to see the preservation of organic materials at this site. The Science paper is a good summary of the high points, presented in a very readable way.

About the site:

Gesher Benot Ya’aqov is located on the shores of the paleo–Lake Hula in the northern Jordan Valley in the Dead Sea Rift (7). The Early to Middle Pleistocene sediments document an oscillating freshwater lake and represent some 100,000 years of hominin occupation (Oxygen Isotope Stages 18–20) dating to 790,000 years ago (8, 9). Fourteen archaeological horizons indicate that Acheulian hominins repeatedly occupied the lake margins, where they skillfully produced stone tools, systematically butchered and exploited animals, gathered plant food, and controlled fire (7, 10–15).

The current paper reports on a single occupation level, characterized by a hearth feature and associated plant, animal, and artifactual remains. Some interesting things:

1. The plant remains:

Although most taxa indicate wet habitats (e.g., lakes, lake margins, swamps, and near streams), the abundant fruit remains of woodland species such as olive, oak, and officinal storax (Styrax officinalis) imply human involvement, as their habitat was likely located some distance from the lake shore. Edible plants include oak acorns, prickly water lily (Euryale ferox) seeds, and water chestnut (Trapa natans) fruits; these were probably staple foods because of the nutritive value of their starchy nuts. Through roasting, the inedible shell of the nuts can easily be peeled and the tannin content of the acorns reduced. The fruits of the wild grapevine (Vitis sylvestris) and olive, and the leaves of the white beet (Beta vulgaris) and holy thistle (Silybum marianum), may also have been consumed.

2. Crabs:

The 17 crab specimens [minimum number of individuals (MNI) = 4 (22)], identified as the extant Potamon potamios, include pieces of the two asymmetric chelipeds, each with a distinctive form of the movable (upper) and fixed (lower) pincer....Of the seven pincers of the large cheliped present in Level 2, six occur around the hearth. These are the only crab remains in this area (fig. S4) (23).

What's not to like about people eating crabs?

3. Spatial patterning. There are two distinct areas of the horizon with anthropogenic activities -- the hearth and a second cluster of tools and stone waste flakes, I'm not very excited about the spatial distribution of activities. The story in the news is about how ancient humans knew how to "keep house" -- they're selling it as a major breakthrough in cognitive evolution.

But the reason why we rarely have archaeological evidence about spatial patterning is that an archaeological horizon doesn't have very good temporal resolution. Here's an alternative scenario to account for the spatial pattern of remains in this horizon: One day, some people came, made tools and ate some fish. Three weeks later, some other people were in the same area, and they stayed for a few days, made a fire, did a bunch of other stuff.

That's pretty much the spatial pattern that I would find if I went back home to Kansas and checked out campsites around the shore of the local reservoir. Few campsites are occupied for very long, and different people use them over time, sometimes with a fire, often not. Sure, we're cognitively advanced. I'm just not convinced that the spatial distribution of our campsite trash is very good evidence about it.

Here's what the paper includes about the spatial patterning:

The evidence from Gesher Benot Ya’aqov suggests that early Middle Pleistocene hominins carried out different activities at discrete locations. The designation of different areas for different activities indicates a formalized conceptualization of living space, often considered to reflect sophisticated cognition and thought to be unique to Homo sapiens (3). Modern use of space requires social organization and communication between group members, and is thought to involve kinship, gender, age, status, and skill (2).

I think this is weak on two grounds -- first because the archaeology is poor evidence about the formal conception of living space, and second because it's not obvious that there's anything very unique about it.

Why not unique? Any animal that can make a structure must have some capacity to pattern spatial activities -- if they don't, there's going to be poop everywhere. Conditioned on the fact that a human social group is sharing a single space, and group members are doing more than one activity, I don't see how you would ever expect to find a uniform scatter of evidence of these activities. There will always be some kind of spatial pattern, from the mere fact that two people can't occupy the same space at the same time.

Remember that Gesher Benot Ya'aqov provides the earliest good evidence of human-controlled fire. It's no coincidence that "spatial patterning" should be found with a fire -- anything that people did anywhere other than by the fire is automatically evidence of a pattern.

4. Fish. Now if there is one big reason why the spatial patterning is useful, it's the interpretation of the fish remains. It's not in the least bit surprising that there would be a lot of fish remains on an ancient lakeshore. But the remains are clustered into two distinct parts of the site, which happen to be the very two locations that humans were clearly using.

In other words, once you accept that the archaeology gives you some evidence of where the people were within the site, you can test for association of the fauna and plant remains with the people. The crabs aren't all around the fire because of a failed attempt to stay warm at night; the people brought them there and ate them. The fish remains are clustered around the fire and flintknapping areas because people were eating them.

Here's a good moral of the Gesher Benot Ya'aqov story: It's now past time to stop talking about whether "pre-modern" humans used aquatic resources. They did, sometimes intensively. I never understood why this argument about seafood and modern humans ever got any traction. We've known for twenty years that coastal Neandertals ate shellfish. We also have known from the numbers in caves near the coast that people never seem to have transported them very far inland. So there was a good reason why you didn't see more evidence of seafood; there just weren't that many sites very near the coast.

So why was it news when a bunch of coastal African sites started producing evidence of shellfish consumption? Evidence that we already had for coastal Neandertals? I don't understand. Well, here we have people eating crabs and lots and lots of fish, 800,000 years ago. We can add the paper by Jose Joordens and colleagues earlier this year about Trinil (I reviewed it in "The shells of Trinil"), a million years ago or more.

Another reason why Gesher Benot Ya'aqov is interesting: outside Africa, Middle Pleistocene sites (and Late Pleistocene sites, for that matter) have a fairly extreme bias toward caves and rock shelters. Caves can preserve evidence of within-site spatial patterns, and certainly offer some exceptional opportunities to track human activity over long periods of time. However, humans aren't very likely to have schlepped hundreds of fish from a lakeshore into some remote cave.

UPDATE (2009-12-18) Thanks to a reader who pointed out a hanging omission; I corrected the text.

References:

Alperson-Afil N, Sharon G, Kislev M, Melamed Y, Zohar I, Ashkenazi S, Rabinovich R, Biton R, Werker E, Hartman G, Feibel C, Goren-Inbar N. 2009. Spatial Organization of Hominin Activities at Gesher Benot Ya’aqov, Israel. Science 326:1677-1680. doi:10.1126/science.1180695

Ann Gibbons has a long news article in the current Science reporting on an interdisciplinary conference on recent human diet evolution ("What's for Dinner? Researchers Seek Our Ancestors' Answers"). The article covers a lot of ground, from Michael Richards' work on the isotopic signature of diet in early Upper Paleolithic people, to Bill Leonard's work on diet adaptations in Siberian reindeer herders, to Jonathan Wells' work on maternal nutritional status and epigenetics.

It's a good "why evolution matters to today's nutritional choices" article.

A section of interest to me:

The agricultural revolution favored people lucky enough to have gene variants that helped them digest milk, alcohol, and starch. Those mutations therefore spread among farmers. But other populations remained more carnivorous, such as the Saami of frigid northern Norway, whose ancestors herded reindeer. Among Saami ancestors, genes to digest meat and fat efficiently were apparently favored. One gene variant, for example, makes living Saami less likely to get uric acid kidney stones—common in people who eat high-protein diets—than are people whose ancestors were vegetarian Hindus and lack this gene variant, says geneticist Mark Thomas of University College London (UCL).

I'll have more on a similar topic later -- recent shifts in genes due to agricultural subsistence has become a favorite subject of local interest. One would think I might get some funding from the Wisconsin dairy industry for this, but nothing so far...

There is an unresolved tension in the article: Is there a better diet for everyone? Clearly some populations have undergone large recent diet changes with bad consequences; the same bad outcomes occur in some people despite possibly adapting to new diets for thousands of years. And yet, every metabolic or diet-related syndrome is variable, and we know that some genes related to digestion and metabolism have rapidly changed. "Westernization" is not as simple as it seems, nor is agriculture (or, for that matter, pastoralism) -- and the responses to each vary for stochastic reasons in different populations.

It's a good interesting complexity, in a field where simple categorical statements can get a lot of attention.

A week or two ago, I was pointed by a press release to some recent research from Bolomor Cave, Spain, where the levels occupied by early/pre-Neandertals have been yielding interesting evidence about diet breadth. The pointer was about "bird consumption", but in this case the birds are all ducks -- genus Aythya, which includes living canvasbacks, for you duck hunters out there. The reference is a newish paper in Journal of Archaeological Science by Ruth Blasco and Josep Fernández Peris.

Something like 155,000 years ago, some hominins brought 8 ducks into the cave, cut them up (leaving cutmarks) and roasted some of them (leaving bone with burned and charred ends where the meat isn't).

Not so terribly surprising, but then we don't have a lot of sites of equivalent age where there's good evidence of repeated bird consumption. The cave also has a lot of rabbit bones, and some tortoises.

Blasco (2008) described the evidence for tortoise consumption from a somewhat later level of the cave (Level IV), dating to before 121,000 years ago. That paper included the gruesome work of identifying human toothmarks that gnawed off the ends of several of the long bones. They also roasted some of the tortoises, apparently before disarticulation.

What I found an interesting element of both papers was the close analysis of the application of fire in the processing of the remains. Naturally from this distance in time it isn't possible to discover everything. But together with experimental archaeology and taphonomy, it may be possible in many cases to test for the presence of ethnographically-attested models of butchering, cooking, and post-consumption processing of the remains.

This means that where the record is good, you can also test for the absence of such behaviors. I was reminded last week that I haven't yet posted my review of Richard Wrangham's book, Catching Fire. In light of several requests, I'm buffing off the rough edges now and I'll post it later this week. When it comes to testing Wrangham's hypothesis -- in brief, that "cooking made us human" -- it is precisely the kind of close archaeological work pursued in these papers that is necessary.

Which makes it interesting that, in these rather recent archaeological levels with clear evidence of cooking, there is good evidence that several of the ducks and tortoises weren't cooked before humans ate them.

References:

Blasco R. 2008. Human consumption of tortoises at Level IV of Bolomor Cave (Valencia, Spain). J Archaeol Sci 2839-2848. doi:10.1016/j.jas.2008.05.013

Blasco R, Fernández Peris J. 2009. Middle Pleistocene bird consumption at Level XI of Bolomor Cave (Valencia, Spain). J Archaeol Sci 36:2213-2223. doi:10.1016/j.jas.2009.06.006

Most people know that hunter-gatherer men hunt meat. Fewer people know the major secondary target for male foraging in many hunter-gatherer societies: honey. The resource is so highly valued that some men spend as much effort foraging for honey as they do hunting.

Chimpanzees also forage for honey. The use of tools to dig for, bash into, and dip honey out of bee nests or hives has long been known from many chimpanzee field sites. For example, Craig Stanford and colleagues (2000) described how chimpanzees in Bwindi-Impenetrable National Park, Uganda, use small sticks to forage for honey from the small nests of stingless bees, while they use much bigger sticks to get honey out of honeybee nests.

Two papers from this year have illustrated a new appreciation for the complexity of chimpanzee toolkits used for honey raiding. Crickette Sanz and David Morgan (2009) describe honey gathering by chimpanzees at the Goualougo, Congo field site, while Christophe Boesch and colleagues (2009) describe the technology used by chimpanzees at Loango, Gabon. Both are relatively new field sites, in which researchers have arrived recently or are still habituating the chimpanzees to their presence. Thus, the variations in chimpanzee behaviors at these sites are still being recognized and just starting to be reported.

Loango National Park is a relatively new field site. As the researchers there continue to habituate the chimpanzees, they have been gathering a series of observations on behaviors that occur differently in Loango compared to other field sites. According to Boesch et al. (2009:2), chimpanzees at the Loango field site do not crack nuts despite a local abundance of them. But far from being simpler in their material culture than other chimpanzees that do crack nuts, the Loango chimps make up for their lack of nutcracking with a complex package of tools for honey extraction:

Gathering honey from underground hives, similar to underground termite fishing in Goualougo, is special in the sense that chimpanzees cannot see where the resource is hidden and use the first tool, the perforator, as an exploratory tool to “feel” where the resource is located underground. In both cases, external indirect signs of food sources are visible (e.g., large termite mounds or small fragile Melipone-made tubes), but the nest itself is not visible and its exact location cannot be inferred. Therefore, chimpanzees have to investigate the soil in order to locate food that can be, in the case of Melipone underground nests, as much as 1 m deep and 70 cm lateral to the visible tube. Locating the underground chamber can take a human between 20 to 40 minutes (Boesch, pers. obs.). The successful locating of honey is apparent from honey sticking to the ends of perforators. To extract honey, a tunnel needs to be dug sideways so as to reach the underground chamber and prevent soil from getting mixed with the honey once the membrane of the chamber is broken (in general, the intact upper membrane of the chamber in the emptied hole can be felt). We think that such tunnels are dug with the help of perforators to loosen the soil. These tunnels are sometimes barely large enough to let a human arm through, and therefore indicate that chimpanzees know exactly where they are aiming. This cannot be done by simply following the bee tube, as it is much too fragile to resist the tool-assisted digging process. Thus, an elaborate understanding of unseen nest structure, combined with a clear appreciation that tools permit the location of unseen resources, and a precise three-dimensional sense of geometry for reaching the honey chamber from the correct angle, is demonstrated by the chimpanzees when extracting underground honey. It has been proposed that an elaborate understanding of causal relationships between external objects is required for flexible tool use to evolve (Boesch and Boesch-Achermann, 2000), and the fact that such exploratory tools are only seen in chimpanzees and humans supports this proposition (Boesch et al. 2009).

I liked the authors' description of how they defined tool types and categorized objects on the basis of signs of use. WIth quite a simple technology, this differentiation appears nevertheless to be of a similar extent to the stone toolkits used by early Homo. What is different is the complexity of manufacture of (some of) the elements of the toolkit.

That topic of basic manufacturing method versus within-toolkit differentiation is addressed by a new study by Thibaud Gruber and colleagues (2009):

Here, we present the results of a field experiment [20] and [21] that compared the performance of chimpanzees (P. t. schweinfurthii) from two Ugandan communities, Kanyawara and Sonso, on an identical task in the physical domain—extracting honey from holes drilled into horizontal logs. Kanyawara chimpanzees, who occasionally use sticks to acquire honey [4], spontaneously manufactured sticks to extract the experimentally provided honey. In contrast, Sonso chimpanzees, who possess a considerable leaf technology but no food-related stick use [4] and [22], relied on their fingers, but some also produced leaf sponges to access the honey. Our results indicate that, when genetic and environmental factors are controlled, wild chimpanzees rely on their cultural knowledge to solve a novel task.

The finer points of tool use lie atop a technological substrate. For one group of chimpanzees, this substrate may be sticks, for another stones (in nutcracking), for another leaves. Social learning may tend to associate some raw materials with manipulatory processes -- a chaïne operatoire, at a very simple level. The complexity of the honey-extraction kits appears to show that, at least for highly valued purposes, chimpanzees can bring together distinct elements into a single technological solution. It's nothing that a three-year-old human can't do, but it's another point in favor of Wynn and McGrew's "Ape's view of the Oldowan" argument.

References:

Boesch C, Head J, Robbins MM. 2009. Complex tool sets for honey extraction among chimpanzees in Loango National Park, Gabon. J Hum Evol 56:560-569. doi:10.1016/j.jhevol.2009.04.001

Gruber T, Muller MN, Strimling P, Wrangham R, Zuberbühler K. 2009. Wild chimpanzees rely on cultural knowledge to solve an experimental honey acquisition task. Curr Biol (in press) doi:10.1016/j.cub.2009.08.060

Sanz CM, Morgan DB. 2009. Flexible and persistent tool-using strategies in honey-gathering by wild chimpanzees. Int J Primatol 30:411-427. doi:10.1007/s10764-009-9350-5

Stanford CB, Gambaneza C, Nkurunungi JB, Goldsmith ML. 2000. Chimpanzees in Bwindi-Impenetrable National Park, Uganda, Use different tools to obtain different types of honey. Primates 41:337-341.

I want to share a paper that might not get a lot of attention but that I think makes an interesting contribution to understanding the ecology of early Homo after its initial dispersal from Africa. The paper is by José Joordens and colleagues, in the early bin at Journal of Human Evolution, titled, "Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia)".

The authors plowed through the old collections of fossil fauna from Trinil, originally from Dubois' excavation, looking to characterize the paleoenvironment in terms of hominin habitat preferences. The fauna are Early Pleistocene in age, possibly as old as 1.5 million years ago, but some uncertainty surrounds that date assessment, which is possibly under a million. What they found was some strong hints that the Trinil humans may have been eating shellfish and using other resources from the swampy lowlands in which the site was formed.

If aquatic resources such as molluscs and fish were available for hominins on Java, what is the probability that they indeed consumed these resources? In coastal areas, terrestrial predators often consume aquatic foods and have a considerable impact on the local aquatic ecosystem (Polis and Hurd, 1996; Roth, 2003). Systematic, often seasonal, predation by non-human terrestrial mammals on freshwater and marine fauna occurs widely. Carlton and Hodder (2003) reviewed occurrence of terrestrial mammals as predators in marine intertidal communities and documented 121 records of intertidal predation among 38 species of terrestrial mammals. For instance, mice, rats, pigs, chacma baboons, brown bears, black bears, striped and spotted hyenas, coyotes, domestic dogs, grey and red wolves, jackals, and foxes in coastal habitats catch and consume crabs, molluscs, fish, and other aquatic fauna (Carlton and Hodder, 2003; Smith and Partridge, 2004).

Terrestrial predators and omnivores eat fish, crabs, crayfish, turtles and shellfish when they get the chance. But the long list here muddies the water, so to speak. We often find hominins in lacustrine and riverine contexts, both because they inhabited those places and because of preservation biases. Those environments often yield evidence of consumption of aquatic organisms, especially shellfish but also fish, crocodiles and aquatic mammals. Somebody ate those animals, and the list above gives a bunch of suspects that aren't hominins.

So maybe we should redirect our null hypothesis -- instead of demanding proof of every instance of Early Pleistocene exploitation of aquatic foods, we should assume they ate the foods available to them. But with 30 or more species noshing on clams, crabs or fish at the shoreline, it's going to be tough to diagnose cases where humans may have been involved.

Well, anyway, what would this reorientation mean for our understanding of the behavioral breadth of early Homo?

The literature cited above shows that systematic aquatic exploitation (either year-round or seasonal) by terrestrial mammals is normal and predictable mammalian behavior when the mammal is 1) omnivorous, 2) living in a coastal marine or freshwater habitat, 3) where nutritious and catchable aquatic prey is available. Considered in the perspective of aquatic exploitation by terrestrial mammals in coastal habitats, the systematic and seasonal aquatic exploitation by Homo sapiens (Marean et al., 2007) and H. neanderthalensis (Stringer et al., 2008) does not differ from that of other mammals. Also, transport of aquatic prey to a base (such as a cave, in the case of H. sapiens and H. neanderthalensis) is not ‘‘modern’’ behavior. For example, Navarrete and Castilla (1993) reported that Norway rat burrows in coastal Chile contain remains of w40 intertidal prey species such as limpets, bivalve molluscs, crabs, and fish. Erlandson and Moss (2001) provide many more examples of terrestrial omnivorous animals transporting aquatic food (remains) to dens, nests, burrows, and caves on land. A label of ‘‘modernity,’’ if applicable at all to aquatic exploitation, should perhaps be reserved for aquatic exploitation with evidence of advanced technology such as fish hooks and boats. The assumption, that early hominins living in a coastal habitat with catchable nutritious aquatic fauna were restricted to eating terrestrial resources, does not agree with published accounts of common mammalian behavior. Therefore, instead of having to provide evidence of aquatic exploitation before it is considered as a realistic option, we propose that the default assumption in hominin evolutionary research should be that omnivorous hominins who lived in coastal habitats with catchable aquatic fauna could have consumed aquatic resources (Joordens et al. 2009).

I like this point a lot: It is a bad sign when archaeologists use a definition of behavioral modernity includes rats but not Neandertals.

Joordens and colleagues suggest that the Trinil faunal collections may already contain evidence of waste heaps (they say, "midden-like" accumulations) of shells:

[T]he presence of a relatively large number of only adult, large-size Pseudodon shells, excavated from a very limited area (Hauptknochenschicht in Trinil), in both the Dubois and Bandung collections, is a discrepancy in the aquatic assemblage that merits further attention for these shells.

But there aren't literally heaps of shells in the records; they have the shells and can only infer their original locations within the excavation at a relatively course grain. So the persuasive parts of the assemblage require us to see through the differnet biases that might have affected the collection. After dismissing a number of possible objections, they continue:

The fact that many of the Pseudodon valves are still paired and well-preserved would suggest that the molluscs were not dead and transported by water before fossilization but were buried in live position. However, the complete absence of small, juvenile shells as well as the mixed occurrence of two different (but equally large-sized) shell forms argues against interpretation of burial of a live population (Van Benthem Jutting, 1937). Instead, the discrepancies suggest that the Pseudodon shells could have been brought together, prior to fossilization, by a size-selective collecting agent who may have used them for consumption of molluscan flesh (Joordens et al. 2009: 13).

They found a similar pattern for another species:

The Elongaria assemblage from Trinil, just like Pseudodon, appears to indicate collection by a selective agent for the purpose of mollusc consumption. The Pseudodon and Elongaria assemblages from Trinil have the characteristics of shell middens (e.g., Waselkov, 1987; Rosendahl et al., 2007): large adult shells only, many complete shells, no signs of damage due to water rolling, signs of damage due to being deliberately opened, presence of human (hominin) bones in the same layer. We conclude that they represent a subtle clue of possible aquatic predation by non-hominins or by hominins (ibid.).

This hypothesis may not be testable further, unless signs of deliberate modification are found on one or more shells. Joordens and colleagues write that such a study is "currently underway". The only other thing to do is apply a higher standard of rigor to possible shellfish features in other Early Pleistocene contexts. Early Pleistocene surface collections dug by vertebrate paleontologists (as opposed to archaeologists) sometimes discard or leave fish bones unidentified, and it is not always clear whether a loose association of shells would be recognized as a possible hominin-accumulated feature.

The paper cites the work of Stewart (1994), who argued for fish consumption at Olduvai Gorge. From that abstract:

Fish remains are associated with many early hominid sites, and five sites at Olduvai Gorge are examined here in detail. The patterns of fish exploitation seen in Late Pleistocene archaeological sites are manifested in three of the Olduvai Gorge sites, making a strong, although not absolute, case for early hominid fish procurement. The implications for early hominid behaviour of fish procurement are several, and include timing of the early hominid seasonal round to exploit spawning or stranded fish, and group size larger than the nuclear family unit, with greater social interaction.

These examples bring to mind the challenge of identifying chimpanzee nutcracking archaeologically. The chimpanzee pattern of behavior is barely systematic enough to pick out from the background. Yet archaeologists have devised some ways to find that slim signal, at least in contexts where they expect chimpanzees to have been active. Late in prehistory, some shell middens were vast and highly-recognizable. Those populations put together the elements of recurrent (or constant) occupation of a site and recurrent transport of shellfish to that site for processing. When we look further into the past, even Neandertals rarely put together those elements in a recognizable way. At the Italian sites where Mary Stiner showed Mousterian shellfish consumption, the presence of shellfish is just at a level where the signal can be picked out due to the lack of other credible transport agents for shellfish remains.

A hitch: Suppose we accept that early humans commonly exploited aquatic resources, even in the absence of specialized archaeological traces of such dietary sources. That does seem to create a problem for the interpretation of stable isotope ratios in fossil humans. I wrote about this issue regarding Neandertal diet ("Neandertals: gone fishin' or not?", see also "Shellfish use by Neandertals" and "Neandertal diet was not dolphin-safe"). It doesn't take much fish to increase the nitrogen-15 composition of bone, making it hard to test hypotheses about the proportion of different terrestrial prey species, and even behavioral interpretations such as weaning age may be thrown off. The problem is too many independent dietary parameters to test with only one estimate. Ignoring the possibility of aquatic resource use helps simplify the interpretation, but that doesn't necessarily make it better.

References:

Joordens JCA, Wesselingh FP, de Vos J, Vonhof HB, Kroon D. 2009. Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia). J Hum Evol (in press) doi:10.1016/j.jhevol.2009.06.003

Stewart KM. 1994. Early hominid utilisation of fish resources and implications for seasonality and behaviour. J Hum Evol 27:229–245.

Last week I made a note about some ongoing work at the Spanish site of El Salt, which suggested taxonomic identifications for burned traces of animal and plant fats.

I was wondering how exactly that kind of identification is done. I don't know any details in the El Salt example, but I was able to find some recent work from Neolithic contexts that makes a similar kind of identification.

For example, Oliver Craig and colleagues (2005) tested potsherds for fatty acid residues, and then subjected those residues to isotopic analysis. The isotopic composition of different weight fatty acids (C18:0 and C16:0) may have different carbon-13 fractions from each other, a relation that varies among different animal taxa. So basically, you fraction out the 18-carbon and 16-carbon fatty acids and measure the ratio of carbon-13 to carbon-12 in the two sample components.

Craig and colleagues were able to show that milk fatty acids have a distinct ratio of carbon-13 fractions compared to body fat (adipose tissue) from the same taxa, basically milk has a lower carbon-13 fraction in the heavier 18-carbon fatty acids. They found most of their sampled potsherds to have a similar ratio, and interpreted that as evidence for the use of milk products in Neolithic central and eastern Europe.

Last year, Evershed and colleagues (2008) came to a similar result, applied to potsherds from early Neolithic sites in the Near East. Evershed published a review article on organic trace analysis in archaeology last year, from which I've drawn this helpful figure:

Figure 2 from Evershed 2008. Original caption: Simple saturated C16:0 and C18:0 fatty acids generated via hydrolysis of triacylglycerols (LHS) during processing and/or burial of fats (and oils), which on their own have limited diagnostic value as biomarkers. However, the plot (RHS) of the δ13C values for these fatty acids shows how the fats of the major Old World domesticated animals can be separated due to differences in the their metabolic and biosynthetic origins. The ellipses are confidence ranges (P = 0.684) and the theoretical mixing ranges. Such plots provide the basis for determining the origins of animal fat residues (adapted from Mukherjee et al. 2005).

The references I've found distinguish fats by mammal taxa only by contrasting pig from ruminant, so I tend to interpret the references to "deer and goat" in the El Salt press report to the fact that they're the resident ruminants. Of course a finer statistical segregation based on more comparative sampling is also possible. Also, Evershed's review goes into some forensic contexts, and shows that human adipose tissue has its own distinctive signature. In theory that would make it possible to find evidence of cannibalism from prehistoric contexts.

References:

Craig OE, Chapman J, Heron C, Willis LH, Bartosiewicz L, Talor G, Whittle A, Collins M. 2005. Did the first farmers of central and eastern Europe produce dairy foods? Antiquity 79:882-894.

Evershed RP. 2008. Organic residue analysis in archaeology: the archaeological biomarker revolution. Archaeometry 50:895-924. doi:10.1111/j.1475-4754.2008.00446.x

Evershed RP and 21 others. 2008. Earliest date for milk use in the Near East and southeastern Europe linked to cattle herding. Nature 455:528-531. doi:10.1038/nature07180

I don't read Spanish well, but I'm going to go ahead and link a news article in a Spanish journal about Neandertal diet and cooking at the Spanish site of El Salt:

Uno de los casos es la aplicación de la química orgánica en el estudio de la estructura de combustión, conocida como el lugar en donde los neandertales hacían las hogueras para calentarse o cocinar. Ahora "estamos empezando a saber que asaban animales como el ciervo y la cabra", señala Galván. Han tenido conocimiento de esta información a través "de las grasas contenidas en las piedras quemadas procedentes del asado de estos animales", dijo la doctora. Asimismo, también han encontrado grasas de origen vegetal y restos de "espinas de peces quemadas". Y es que los neardentales sabían utilizar todas las materias primas que tenían a su alcance.

One example [of a "quantum leap" in excavation techniques] is the application of organic chemistry to the study of hearths, used by the Neandertals for heat or cooking. Now "we are learning that they roasted animals like deer and goats," said [Bertila] Galvan. This information was obtained from "the fat contained in burned rocks from cooking these animals," said the doctor. In the same way, they also found fats of vegetal origin and remains of "burned fish bones." And that shows that the Neandertals knew how to use all the raw materials available to them.

Not much more than that, but I think it's very interesting in light of last week's story about flax fibers. The point is that these microscopic and chemical excavation techniques are able to find some surprising information -- a process in archaeology that is mirroring the application of similar techniques to dinosaurs. Results like these show the great promise of such analysis, or the reanalysis of existing samples. It seems like a very propitious time to be trained in chemical techniques to apply to archaeological sites.

Julien Riel-Salvatore has a little bit of context, Anthropology.net has more, and Martín Cagliani has the most direct discussion, although that does raise the Spanish language problem again!

I'll be waiting for confirmation from other reports from this site, and hope that we can see some replication.