Today's sketchbook:
KNM-ER 1802 mandible, in occlusal view. This mandible is attributed to the genus Homo, often placed in Homo habilis, although those who believe in Homo rudolfensis generally include this mandible. From the Upper Burji Member of the Koobi Fora Formation, it dates to around 1.9 million years ago.
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.
Wil Roebroeks and Paola Villa [1] review the evidence for human control and use of fire in the archaeology of Europe during the Middle Pleistocene (130,000-780,000 years ago) and earlier. They observe that no evidence of human-controlled fire occurs in Europe before 400,000 years ago. This raises a puzzle: How did humans occupy the northern part of Europe without fire?
The argument about the antiquity of fire is not new. There is very early evidence of fire at Swartkrans, Koobi Fora, and Chesowanja, which includes burned bones and heated artifacts, along with clay nodules that show evidence of heating as high as 400 degrees Celsius. The criticism of these early finds (reviewed by James [2]) centers around the difficulty of distinguishing human-made fire from natural bush fires. The association of the fire with artifacts can be readily explained: archaeologists only look for evidence of fire where they already have artifacts. The remaining question is whether artifacts or bones have been heated to temperatures hotter than those possible in bush fires, thereby providing evidence of human involvement. Burned bone from Swartkrans at least did reach such temperatures, seemingly unlikely without human involvement given their presence in the cave. I tend to think that humans did control fire early in some cases.
Roebroeks and Villa do not dispute possible earlier evidence of fire, but claim that it was not habitual. Or to put it another way, some early humans may have used fire, but many or most did not do so. The lack of fire seems particularly surprising in the northern latitudes of Europe, where sites like Happisburgh (and Pakefield) show evidence of human habitation in the late Lower Pleistocene. Their review of the early sites is really worth reading and impressively compact. Nonetheless, I can't quote it in full; it's just too much text to extract. After a discussion of the earliest archaeological occurrences, they turn to the long sequences from Arago and Gran Dolina, where we really should expect to see some evidence of fire if people were using it.
Arago and Gran Dolina contain long sequences and large quantities of lithic and faunal remains, subjected to taphonomic analyses (34–36). Their settings are comparable to the ones that, in later times, have often provided strong evidence of fire, such as Bau de l’Aubesier, Grotte XVI, and Lazaret in France; Bolomor Cave in Spain (Dataset S1); and Middle Paleolithic/Middle Stone age caves in Israel and in South Africa. Traces of fire have been found in the upper part of the sequence at Arago, in layers younger than 350 ka. No charcoal, no burnt bones, nor any other evidence of fire have been reported from any of the assemblages from the lower levels (dated to MIS 10–14). No charred bones or heated artifacts have been reported from the Gran Dolina sequence (TD4– TD10). Rare charcoal particles have been found in thin sections of the TD6 sediments, but these sediments originate from the exterior of the cave, and there is evidence of low-energy transport (37); thus, the charcoal may not be in situ. However, the high density of human, faunal, and lithic remains as well as their state of preservation and refitting studies (38, 39) clearly indicate an occupation in situ with little postdepositional disturbance. The absence of any heated material from the long sequences of Gran Dolina and Arago, both documenting hominin occupations over several hundred thousand years (36, 40), is striking. This is a strong pattern, which can be tested by future work at other hominin habitation sites. We suggest that the European record displays a strong signal, in the sense that, from ~400 to 300 ka ago, many proxies indicate a habitual use of fire, but from the preceding 700 ka of hominin presence in Europe, we have no evidence for fire use.
One thing that really impressed me visiting Roc de Marsal last summer was that the site preserves a long archaeological sequence in which some levels are densely packed with charcoal and the remains of hearths, and at least one well-defined layer, with abundant evidence of tools and debitage, just has hardly any evidence of fire at all. These were Neandertals, not Middle Pleistocene Homo, and they managed to get by without leaving any clear evidence of fire even though many Neandertal populations clearly did control and use fire extensively, including at this very site at other times.
There really were people living in the Pleistocene of Europe who didn't use fire very much, at least as evidenced by relatively long cultural deposits in well-stratified rock shelters and caves. Unfavorable preservation can explain the lack of charcoal or hearths at some sites, but not all of them. If we don't have a single good instance of fire in Europe before 400,000 years ago, people may well have done without it.
The authors' review of fire evidence after 400,000 years ago in Europe is also very useful, and they include supplementary data table with fuller information and references for all the sites they discuss. It is impressive just how much evidence has accumulated over the years, and Roebroeks and Villa have doggedly tracked it down. They conclude that Neandertals had essentially the same degree of control of fire as Upper Paleolithic humans, and consider the use of fire as a processing step in the manufacture of complex tools:
A recent study provides evidence of early modern humans at the site of Pinnacle Point in Southern Africa regular use of heat treatment to increase the quality and efficiency of their stone tool manufacture process 164 ka ago (13). The authors infer that the technology required a novel association between fire, its heat, and a structural change in stone with consequent flaking benefits that demanded “an elevated cognitive ability.” They also suggest that, when these early modern humans moved into Eurasia, their ability to alter and improve available raw material may have been a behavioral advantage in their encounters with the Neandertals. However, this interpretation ignores that Neandertals used fire as an engineering tool to synthesize birch bark pitch tens of thousands of years before some modern humans at Pinnacle Point decided to put their stone raw material in it. In more general terms, a greater control and more extensive use of fire is sometimes (12) seen as one of the behavioral innovations that emerged in Africa among modern humans and favored the spread of modern humans throughout the world. As stressed by Daniau et al. (52), if extensive fire use for ecosystem management were indeed a component of the modern human technical and cognitive package, one would expect to find major disturbances in the natural biomass burning variability associated with and after the colonization of Eurasia by modern humans. In their study of microcharcoal particles from two deep-sea cores off of Iberia and France, spanning the 70- to 10-ka period of biomass burning, the authors did not recover any sign that Upper Paleolithic humans made any difference: either Neandertals and modern humans did not affect the natural fire regime, or they did so in comparable ways.
I do think the silcrete processing is interesting, but so is the pitch processing. For that matter, the possibility of fire-hardening in the Schoeningen spears would be a case of deliberate production of a complex tool using fire (complex, in that the fire-processing adds a step).
Gesher Benot Ya'aqov, in Israel dating to around 800,000 years ago, is a highly compelling site in terms of evidence of fire. There are distinct hearth areas that correlate with archaeological scatter and have burned nut hulls and other foodstuffs. While Roebroeks and Villa express skepticism about the earlier evidence from Africa (specifically pointing to the high likelihood of bush fire as an explanation), they do accept Gesher Benot Ya'aqov as a likely fire location, while discussing the strength of the evidence. It's not such a high threshold to set; it seems like other sites should be able to meet it if fire was common.
Personally, I am quite ready to accept that fire was invented many times by Lower Pleistocene humans and may have occurred in some regions of the world ephemerally. The maintenance of this tradition may have been a challenge that these early humans couldn't meet over long spans of time. This view does imply that the advantages of fire, including cooking, were not a typical part of the repertoire of Early Paleolithic people. But that would be consistent with what we understand of traditions in other species of primates; where one population may be pursuing complex and apparently valuable extractive foraging that another population lacks, despite otherwise being ecologically similar.
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.
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
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 (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.
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.
(this letter refers to my 2007 comments on Tim Bromage's KNM-ER 1470 reconstruction)
Dear Professor Hawks,
You may dispute Dr Bromage's work on skull 1470 which effectively relegates "rudolfensis" to the Australopithecine genus rather than as some intermediate type approaching Homo erectus - and I tend to lend more credence to a computer simulation than a medieval water displacement method - but it doesn't really change anything. It is still a lone specimen and the 700cc cranial vault volume is at the upper range for some gorillas, certainly macrocephaliac ones.
You might also want to look at a paper in Nature by Fred Spoor entitled "Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya"...
http://www.nature.com/nature/journal/v448/n7154/full/nature05986.html
.... which I think we can safely say confirms that habilis too was a species within Australopithecus genus which in turn is not actually a direct ancestor of modern humans according the the findings of an Israeli team that discovered gorilla-like mandibles in A afarensis remains:
http://www.pnas.org/content/104/16/6568.full
And the finds of Dmanisi suggest a pygmy-like sub-race of Homo erectus which still appear very human-like in this reconstruction by National Geographic of the skulls found in a cave in Georgia.
http://ngm.nationalgeographic.com/ngm/0504/feature2/multimedia.html
Anyway, this is just my humble opinion, although I am fairly certian that any direct lineage from ape ancestors to modern man has effectively collapsed as far as the fossil record is concerned.
Thank you for your comments. Taking your last point first, you seem to imply that Homo habilis (and Australopithecus) are apes, and Homo erectus is a human, and there is no "direct lineage" in between. If you find this idea persuasive, I think you should give some more study to the morphology of Australopithecus.
With respect to Bromage's reconstruction, I hope you don't misunderstand my point about water displacement (which you call a "medieval" method). Using a ruler is a medieval method of measuring distance. If the ruler tells me that my foot is a foot long, and the computer tells me it's only 8 inches, I'm going to be very skeptical about the "simulation" on the computer. Likewise for a computer reconstruction that apparently removes a third of the volume of a well-preserved endocast.
In any event, Bromage and colleagues (2008, J. Clin Ped Dent) published a revised estimate of 700 ml. I think this is also an underestimate considering Holloway's methods, but it is very far from the claim of 526 ml that had appeared in 2007.
It is a mainstream position within paleoanthropology to place H. habilis (or H. rudolfensis) into Australopithecus (for example, see articles by Bernard Wood and Mark Collard, or Milford Wolpoff's Paleoanthropology text). The reason for this placement is usually the small body size and relatively large teeth of H. habilis compared to H. erectus, which may indicate an australopithecine-like niche.
Modern humans have extensive variation in brain size, as do other primates. A single specimen with a brain size of 750 ml within a population that averaged around 500 would not be very unusual. So I agree with you that the size of the brain of KNM-ER 1470 by itself cannot determine the position of H. habilis.
But KNM-ER 1470 is far from alone, and the median size of other specimens (OH 7, OH 24, OH 13, OH 16, KNM-ER 1813) is around 600 ml. That is an increase of at least 30 percent on average compared to A. afarensis, A. robustus or A. boisei. Your point is correct that large male gorilla crania may be over 750 ml. Gorillas are three times the body mass of H. habilis, and in any event do not average 600 ml.
A number of other specimens are less complete or equivocal (they could be H. erectus), including KNM-ER 1805, KNM-ER 1590, and KNM-ER 3732. But their brain sizes do not change the mean; including them in H. habilis (or H. rudolfensis) would not reduce the difference of that species from Australopithecus.
The Dmanisi hominids are certainly interesting. My inclination is to see H. erectus as a polytypic species that varies substantially in body size, just as recent humans do. In that context, a stature of 160 cm is normal, while a shorter stature of 140 cm is small-bodied but not more than many recent hunter-gatherers. The brain size of the Dmanisi hominids is very close to those reported for H. habilis, without considering any correction for body size.
(The writer replied:)
A 6 foot tall hominin appears in the fossil record from about 1.9 MYA distinctly different from other specimens: Its brain size is at the lower end of modern human range, its humerus-femur index is 0.7 as with modern humans, its semi-circular canal is not suitable for the kind of balance needed for arboreal life, its shoulders do not indicate it can brachiate, it is an obligate biped whose wrists show it could not knucle-walk. It is human in every sense - maybe not a homo sapiens, but certainly another type of human.
That was certainly my opinion up to around 2002; I wrote a 2000 article that argued that the large-bodied Homo represented a really new kind of hominid. These days I'm not so sure. The Nariokotome skeleton is relatively late, and the only evidence for large body size at 1.9 million years is the KNM-ER 3228 innominate bone, which we would now interpret as a broad pelvis, but (in light of the Gona pelvis) possibly not a very tall stature.
I am skeptical about skull 1470 in general because, like most fossils, it was found in fragments and had to pieced together - it may also have been deformed by natural processes. Unless you can find more specimens like it, I really don't see how you can justify creating a separate taxon for it, and the same goes for the Gawis skull.
Regards
Good to be skeptical, but remember that 1470 is not alone. Bernard Wood's 1991 Koobi Fora monograph is worth reading through; he did a good job with these issues. Not all agree (I don't with all parts) but it's the essential starting point.
The coming attractions bin at Journal of Human Evolution includes a paper by Kaye Reed, reviewing the evidence of paleoenvironment in the Hadar formation:
Habitat reconstructions of 12 submembers of the Hadar and Busidima formations (˜3.8-2.35 Ma) are presented here along with faunal differences in these submembers through time. Habitats with medium density tree and bush cover dominated the landscape through much of the earlier time period in the Hadar Formation. The lowermost Sidi Hakoma Member is the most closed habitat. The Denen Dora Member shows the influence of frequent floodplain edaphic grasslands with high abundances of reducin bovids. There is an influx of ungulates in the Kada Hadar Member (˜3.2-˜2.96 Ma) that indicates a more arid habitat populated by mammals that were recovered from earlier deposits further south in Ethiopia and Kenya. In the younger deposits from the Busidima Formation at Hadar, the landscape was open wooded grassland with some floodplain environments. The fossil assemblages from the Busidima Formation show a substantial species turnover. Although high numbers of A. afarensis specimens are associated with the lower Sidi Hakoma Member, they clearly inhabited a variety of habitats throughout the entire Hadar Formation. Australopithecus afarensis from Laetoli through Hadar times appears to have been a eurytopic species.
This is a nicely detailed paper, focusing on the amount of wooded/bush habitat, the relation of the hominids to those habitats, and the relative lack of early faunal exchanges with areas further to the south.
The discussion focuses on the range of paleoecologies in which fossil A. afarensis has been found -- including not only Hadar but also nearby Maka and Dikika, and more distant Koobi Fora and Laetoli. Altogether, these localities cover a long time (from before 3.5 up to around 2.9 million years ago). From the range of paleoecologies reconstructed in this paper at Hadar, Reed concludes that A. afarensis did not have a "narrow" habitat preference. It is found in relatively closed woodland, open woodland/bush, and wet grassland/marshland.
There are some differences between localities. At Koobi Fora, relatively few specimens of A. afarensis have been found in the Tulu Bor Member, despite the fact that it occupies the same time as the Hadar sequence. Based on the paleoecological data, Reed suggests that Hadar was a wetter, more closed woodland habitat than Koobi Fora at that time -- Koobi Fora would have included more scrubland punctuated with wetlands and floodplains (here she cites her own 1997 paper).
The early end of the A. afarensis sample is represented at Laetoli. Reed gives a brief review of the paleoecology of that site, which has been interpreted differently by different authors but broadly appears to have had a fairly high amount of rainfall and some patches of forest amid closed woodland:
Thus, the earliest known A. afarensis material was found in deposits showing habitats in which trees and or bushes were fairly plentiful. It is also interesting to note that while the deposits of A. afarensis at Laetoli and Hadar share some perissodactyls, giraffids, suids, and proboscideans, the bovid taxa and those primates other than A. afarensis are not very similar.
Reed concludes that A. afarensis was a "eurytopic" species -- one that inhabited a wide range of habitats and moved broadly across space. It contrasts with the more habitat-selective ("stenotopic") species, which include most of the bovids.
White et al. (1993) suggested broad habitat tolerance for A. afarensis, and indeed, the species has thus far been recovered from regions in which the reconstructed habitat ranges from closed woodland through more open, but wet woodland and shrubland. There is no direct evidence that A. afarensis only existed in riverine forests or grassland habitats, or that they preferred one habitat over another. It is tempting to equate the aridification in the Kada Hadar Member with the extinction of A. afarensis. However, sediments at Hadar are sparse or missing altogether from ˜2.90-2.35 Ma thus obscuring details of the species' demise. All that can be said is that they are no longer present at 2.35 Ma and most of the fauna, including hominins, has been replaced.
Reed KE. 2008. Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.08.013
Just noticing, in this John Noble Wilford article:
A new report, to be published Thursday in Nature, will review more skeletal evidence of the transitional aspects of the Dmanisi specimens.
More later...
UPDATE(2007/09/18): Wilford doesn't directly state the article's theme but it clearly has one: Why the heck can't these people agree about these fossils that have been out of the ground for thirty years?
The first answer that everyone has given him is about the "million year gap" between 3 million and 2 million years ago. People can't agree about early Homo because they can't decide what its ancestors looked like. Without any ancestors, they don't know which of the traits of early Homo are derived.
For a good example, we can turn to a feature Wilford doesn't mention: limb proportions. Recently, a lot of ink has been spilled discussing the evolution of arm size in later australopithecines and early Homo. OH 62 (probably Homo habilis) and A. africanus have been argued to have large arms compared to their legs. A. afarensis and Nariokotome (KNM-WT 15000, probably Homo erectus) have relatively small arms compared to their legs. Did H. habilis and H. erectus have different ancestors? Did H. erectus evolve from H. habilis, reverting its limb proportions to earlier A. afarensis? Or are all these comparisons just batty, since only three specimens have arm and leg elements whose length can be compared? There's no clear answer; but one of the most important specimens in the question (with sort-of-intermediate limb proportions) is the Bouri skeleton, BOU-VP 12/1, which at 2.5 million years old is right in the middle of that "gap."
The more you look at the "gap," the less gap-like it looks. For one thing, we have a pretty good idea of what was going on behaviorally during that million year span. The first stone tools are 2.6 million years old. The technology of these toolmakers -- although simple -- included all the basic manufacturing methods used before 1.5 million years ago. The tools were used to butcher animals and break bones for marrow; so we know that the toolmakers were depending on meat.
Second, we actually have quite a lot of fossils from this time period. The entire South African A. africanus fossil record, with the exception of a few early specimens like STW 573, come from this "gap." A fairly extensive record of the appearance and evolution of early robust australopithecines comes from this time period in East Africa.
And, here and there, a few specimens look Homo-like. Wilford's article discusses AL 666-1. To this we can add the Uraha mandible, Omo 75-14, an additional series of teeth from Omo, and possibly the Bouri BOU-VP 35/1 skeleton.
Properly considered, the rarity of early Homo in these contexts is not a problem; it is information. Wilford quotes Philip Rightmire to this effect, and we can easily expand on the basic concept. Early toolmakers did not undergo an immediate geographic expansion upon their origin. They spread across a relatively narrow strip of East Africa and stayed there for more than a half-million years. They were initially rare. That means that their adaptation was not immediately a barnburner of a success -- the early toolmakers took a while to perfect the adaptation of later Homo.
The middle part of the article takes in another reason for disagreement: whether H. habilis and H. erectus were ancestor-descendant:
Several scientists, notably Dr. White of Berkeley, took issue with the interpretation seeming to imply that evidence for the two species overlapping in time and exhibiting variable sizes was new. That, he said, had been recognized for a couple of decades.
Dr. Kimbel, who was not involved in the new research, defended the authors, saying that they had not "meant to imply that habilis could not have been ancestral to erectus, presumably on the basis of their being contemporaneous at Turkana," the site in Kenya where the fossils were found.
Susan C. Anton, an anthropologist at New York University who was a member of the Spoor-Leakey team, said, "My money is still on habilis as the potential ancestor, but there is a lot of room for additional knowledge, given the dearth of fossils."
None of these statements really disagree with each other. If anything, this particular question may have gotten easier to resolve lately, not as a consequence of new fossils, but as a result of new dates for many of the old ones. Susan Anton is later quoted saying that anagenesis "is the only option that is no longer on the table," and it seems to me that this is the clearest statement most likely to invite some hypothesis testing. But it is fairly clear that this problem cannot be resolved in terms of earlier fossils: I don't think there's any compelling evidence of H. erectus before 1.6 million years ago.
There is one significant word that doesn't appear in the article -- an absence that is especially interesting considering the quoted scientists:
Kenyanthropus
Remember, the dominant theme is about complexity and bushiness. And yet, here's that forgotten branch of the family tree; the one that was supposed to clarify everything by providing a different ancestor for KNM-ER 1470 from other H. habilis specimens, the one that showed a distinct line leading to Homo originating in the Early Pliocene.
I think our bush may have been pruned.
Appropriate to yesterday's post about the hypothesis of a Eurasian-African clade distinction in early humans, is today's paper from Fred Spoor, Meave Leakey and others, describing the KNM-ER 42700 calvaria and the (unassociated) KNM-ER 42703 maxilla.
The cover photo from the issue is brilliant -- a juxtaposition of KNM-ER 42700 and OH 9 at the same scale:
Press photo, credit: Nature/National Museums of Kenya, F. Spoor and J. Reader
I wrote about KNM-ER 42700 a couple of years ago, when it was shown at the meetings. A few things have changed since then. Most important, the specimen is now accepted as an adult, so that it is assumed to have reached its full adult brain size. That also means that the supraorbital torus, angular torus, and other features reflecting robusticity were probably near their maximum development.
I have much to say about this and the other fossil, which the paper attributes to Homo habilis. The press accounts have all led with the (very) uninteresting and conventional. Here's the AP's Seth Borenstein:
The new research by famed paleontologist Meave Leakey in Kenya shows our family tree is more like a wayward bush with stubby branches, calling into question the evolution of our ancestors.
The old theory was that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became us, Homo sapiens. But those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years, Leakey and colleagues report in a paper published in Thursday's issue of the journal Nature.
Here's John Noble Wilford:
Two fossils found in Kenya have shaken the human family tree, possibly rearranging major branches thought to be in a straight ancestral line to Homo sapiens.
Scientists who dated and analyzed the specimens - a 1.44 million-year-old Homo habilis and a 1.55 million-year-old Homo erectus - said their findings challenged the conventional view that these species evolved one after the other. Instead, they apparently lived side by side in eastern Africa for almost half a million years.
Here's Robert Mitchum in the Chicago Tribune:
Two small fossils unearthed in Kenya - the top of a skull, and half of a jawbone - fill an important gap in the evolutionary story of how humans came to be, yet have created as many questions as they have answered.
The similar age and location of the fossils suggest that two early humanlike species, Homo habilis and Homo erectus, closely coexisted rather than coming one after the other on the evolutionary road to modern man, according to a paper published Thursday in the journal Nature.
I could go on. They write themselves, don't they?
But this idea of contemporaneity of H. habilis and H. erectus is neither interesting nor new. Recall yesterday's story about the African and Asian clade hypothesis? News stories had the same lede -- "hominid family tree more complex than thought." This is the ultimate paleontological "dog bites man": "Human Evolution A Bush, Not A Ladder." It's just not interesting anymore.
Why is it old news? Well, we could look back at Bernard Wood's 1991 Koobi Fora monograph, which went into long detail about the assignment of fossils to Homo aff. H. erectus -- fossils that in every case were older than the latest occurrence of Homo habilis at Olduvai.
At least, they thought they were older...
You see, there's some really interesting stories to be told about these fossils. Stories that hasn't appeared anywhere in the press.
Here's a question: Why does that small KNM-ER 42700 skull have all those cranial features from much later, larger, Asian Homo erectus skulls?
Here's what Spoor et al. wrote about it:
The presence of supposedly distinctive 'Asian' characters [18], such as cranial vault keeling and a well separated petrous crest and mastoid process in KNM-ER 42700, underscores the difficulty in separating the African and Asian hypodigms of H. erectus [19]. This difficulty is further accentuated by the observation that the more angulated occipitals and the thicker vaults and supraorbital tori seen in Asian H. erectus are allometric consequences of an increase in cranial size, rather than independent characters (Spoor et al. 2007:689).
Of course, the answer is that they aren't really Asian features. That much is evident from the fact that the later African skulls, OH 9, BOU-VP-2/66 (Daka), and Buia, also have many of them.
KNM-ER 42700 demonstrates that the traits were present in African H. erectus almost from its earliest occurrences. If these early Africans shared the same features as early Asian Homo erectus, then the hypothesis (promoted by many) that these early Africans are themselves an entirely different species, called Homo ergaster must be wrong.
At last, sinking one of those new-fangled bushy human species, and for good? Now, that sounds more like "man bites dog!"
But wait, there's more! Last year, Frank Brown's geochronology group redated many of the early Homo specimens from Koobi Fora, with the surprising result that early Homo erectus no longer included any cranial fossils that were demonstrably older than 1.65 million years. Here's what I wrote at the time:
Looking at what is left in the early part of the sequence is certainly interesting, but just as interesting is how all the H. erectus-like specimens are all bunched together between 1.65 and 1.45 Ma. This is the time interval that already held KNM-WT 15000, KNM-ER 3883, and KNM-ER 42700, and is just older than OH 9. Now we can add KNM-ER 3733, KNM-ER 730, KNM-ER 1808, and KNM-ER 1821. Isn't this an interesting sample? Don't you wish we knew about the other postcrania?
It seems to me that the hypothesis that H. erectus-like hominids first appeared in Africa around 1.65 Ma has interesting archaeological consequences. This isn't long before the appearance of the earliest Acheulean, and it plausibly makes the Developed Oldowan-Acheulean sequence a correlate of this evolution.
It is markedly not coincident with the earliest such evidence in Asia. But that raises the Dmanisi question again, doesn't it?
This is an amazing problem, now. The consensus that Homo habilis and Homo erectus overlapped in time was thrown completely open by the redating. This paper by Spoor and colleagues, by presenting both a new H. erectus specimen and a very late H. habilis specimen, was directed toward this problem. If they are right, it re-establishes the status quo: Homo habilis hung on after the evolution of early Homo erectus, the two species being radically different in their body size (and presumably life history) adaptation, but somehow both making tools and surviving on the same foods.
And yet, this "H. habilis" specimen, KNM-ER 42703, is nearly 200,000 years later than any other member of its species. Almost the only things that makes it H. habilis are its third molars. Are they enough? Or is it Homo erectus, too? Is the overlap completely gone, or will this fossil save it?
And what about that little, tiny, H. erectus skull? At 1.6 million years old, KNM-ER 42700 is a part of the earliest African sample. It's 200,000 years younger than Dmanisi. Did they originate in Asia? Did they evolve directly from their immediate predecessors in Africa, the larger habilines?
You see, this is interesting stuff! It's like a Plio-Pleistocene soap opera -- complete with twins separated at birth, old characters being killed in Amazonian plane crashes and mysteriously returning disguised as someone else.
More tomorrow...
It's a hazardous business, making predictions -- all the moreso because New Year's predictions have a deadline. If they don't happen this year, well, that's too bad, because we'll be checking back a year from now to see how well you did.
Last year, I did pretty well. My 2006 predictions are listed below. I ordered them originally "from most certain to most speculative". As you can see, the first five (i.e., the more "certain" ones) all came true; the last five (i.e., the wild-arsed speculations) didn't. So let's check them out:
So that should give some indication of how to read the list for the next year. I'm listing from more certain to more speculative again, and again I'm excluding most of my own work. The main effect of this is just that I'm not including secrets that I know will be coming out this year. Once again, the predictions are Delphic -- if only I were cleverer, I could make them come out right no matter what!
I ended the year with just a shade fewer than 1 million visits since last January 1. The Neandertal women brought me over 10,000 readers in a single day -- the most ever. I know a few of the big stories from the coming year, but there will be many more that nobody can predict. There's no doubt in my mind that 2007 will be a big year!
