Homo erectus

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.

In last week's Nature, Russell Ciochon has a remarkable essay:

For many years, I used Longgupo to promote this pre-erectus origin for H. erectus finds in Asia. But now, in light of new evidence from across southeast Asia and after a decade of my own field research in Java, I have changed my mind. Not everyone may agree; such classifications are always open to interpretation. But I am now convinced that the Longgupo fossil and others like it do not represent a pre-erectus human, but rather one or more mystery apes indigenous to southeast Asia's Pleistocene primal forest. In contrast, H. erectus arrived in Asia about 1.6 million years ago, but steered clear of the forest in pursuit of grassland game. There was no pre-erectus species in southeast Asia after all.

I think it's interesting how much speculation Nature is willing to publish about hominid evolution in Asia. The 2005 review article by Robin Dennell and Wil Roebroeks, "An Asian perspective on early human dispersal from Africa," speculated that the origin and early evolution of Homo may have been in Asia, not Africa. And of course, several papers on the hobbits have included speculations about the pattern of early Homo in Asia, in pursuit of ways to derive Homo floresiensis from early hominids not yet found in Asia.

Ciochon's essay is part of this new tradition, but it bucks the trend. Instead of arguing that Asia was the home to an undiscovered diversity of hominids, he instead argues that the hominids have been overestimated (in part by himself) and that some fossils represent an undiscovered diversity of apes.

Ancient orangutans (Pongo) and Gigantopithecus are already known from China. Ciochon proposes a third lineage of great ape, one that would be similar to the earlier Lufengpithecus from China and Thailand:

Later, we had to field a serious proposal that Longgupo belonged to Lufengpithecus (4, 5). Although the age disparity remained troubling, the dental similarities could not be denied. I began to imagine a mystery ape as a possible solution to the problem.

The "age disparity" Ciochon refers to is that Lufengpithecus is known from the Late Miocene and very earliest Pliocene, but not the Late Pliocene. Still, if the teeth look like Lufengpithecus, it seems probable that the "mystery ape" actually is a late-surviving Lufengpithecus, or at least a close relative. Reference 5 is a paper by Dennis Etler, Tracy Crummett and Milford Wolpoff, which is available (PDF) from Etler's excellent website. Wolpoff refers to this in his 1999 book, Paleoanthropology:

The Longgupo mandible is actually a fossil ape that is related to Lufengpithecus, the missing P₃ was sectorial in shape.  However the prestigious British Journal Nature hastily published it as a hominid, with a picture of the specimen on its cover, and subsequently refused to accept papers establishing its identity.  The misidentifications actually started decades ago, when G.H.R. von Koenigswald identified an ancient australopithecine-like hominid from South China based on worn, isolated teeth, which he named “Hemianthropus.” These turned out to be worn postcanine teeth of a medium-sized Pongo species. The resemblances of the other materials to Australopithecus species were real enough, but they were not unique resemblances. A. Kramer and Zhang Yinyun have each shown there are no synapomorphies that support the hypothesis of Asian australopithecines.

So it's not a new idea that Longgupo represents an ape, or that the ape was different in size and morphology from Pongo or Gigantopithecus. It is probably natural that early paleontologists might associate these ape teeth with the hominids -- until 40 years ago, most paleontologists thought that hominids went back far into the Miocene. They were wrong, but a mistake like "Hemianthropus" was a natural one. The opposite mistake -- "Meganthropus" as an australopithecine-like hominid -- was also a natural consequence of the assumption that an unrecognized hominid diversity existed in Asia. That assumption has outlived Meganthropus, as we've seen.

Ciochon adds the idea that the ape may also be represented at other contemporary or later sites, and is apparently unwilling to attribute them to Lufengpithecus, at least not yet. He does not mention the isolated upper incisor from Longgupo, but he does appear to accept the claim that the two stone artifacts from the site are intrusive elements that are not contemporary with the jaw. The same is probably true of the incisor, which Etler and colleagues found morphologically most like living East Asians.

Ciochon suggests that some of the Hemianthropus collection may be his mystery ape:

Von Koenigswald viewed Hemanthropus as a distant relative of African Australopithecus. Later research revealed that these were worn or atypical orangutan teeth and Hemanthropus was quickly abandoned. But, had von Koenigswald actually discovered evidence of the mystery ape? In October 2005, I examined the original Hemanthropus collection. Among the many worn orangutan teeth I found several small ape teeth that very closely resembled the mystery ape teeth from Mohui. Perhaps von Koenigswald was the first to lay hands on the mystery ape.

It's not an easy task to sort through large samples of teeth trying to sort them into sets. Particularly not with these teeth -- sure, Gigantopithecus falls right out, but worn orangutan teeth aren't very easy to tell from hominids, much less "mystery apes." Ciochon ends his essay with a plan to revisit the existing samples of teeth, trying to document the variation in the mystery lineage. Sounds like a good topic for a TV show. There's a historical angle, lots of museums, a personal hook, reversal of fortune, the whole "mystery ape" thing....

Meanwhile, the introductory paragraph at the top of the post raised two issues, not one. The first is the focus of the rest of the essay: Longgupo represents a third ape in Pleistocene China; smaller than both Gigantopithecus and Pongo. The second idea is covered briefly near the end of the essay, but I think it deserves more consideration. Is it true that humans reached China 1.6 million years ago, and then "steered clear of the forest"?

Here's what Ciochon writes:

Homo erectus, it seems from this perspective, hunted grazing mammals on open grasslands, and did not or could not penetrate the dense subtropical forest. In fact, there is no record of early hominins living in tropical or subtropical forested environments in Africa or Asia.

In resolving the mystery, two other Asian sites come to mind: Jianshi (Hubei province, China) and Tham Khuyen (Lang Son province, Vietnam). At both sites, teeth labelled variously as Australopithecus, H. erectus and Meganthropus are most likely to be the mystery ape instead. Others have come to similar conclusions; a 2009 paper identifies a tooth from Sanhe Cave (Chongzuo, Guangxi province, China) as belonging to an unidentified ape.

The map accompanying the article is mysteriously depauperate of actual early hominid sites in China. Considering their locations relative to the proposed distribution of subtropical forest in Pleistocene China, I don't see an immediate objection to the hypothesis. The earliest Chinese archaeological sites, from the Nihewan basin near Beijing (Majuangou and Xiaochangliang) and also from around the Yellow River (Gongwangling and Xihoudu), are north of the Stegodon--Ailuropoda fauna. Yuanmou may have been forested at this time, but the hominid teeth there appear to be later (Hyodo et al. 2002), when the Ciochon's forest-plains biogeographic proposal may no longer hold. Josette Sarel and colleagues (2009) report on stone tools from Baerya Cave, which does preserve the Stegodon--Ailuropoda fauna, but these are so far undated and the stratigraphy has not been worked out. For all we know, the association is no clearer than at Longgupo, but that may change.

The other early Chinese sites with hominid teeth, Ciochon suggests are not hominids -- Mohui and Sanhe. Since he has examined the Mohui teeth (Wang et al. 2007), this isn't an idle speculation, and it would be odd for humans to drop their teeth around these sites without dropping a single stone tool. If he's right, that would make the earliest clear evidence of human occupation of South China into the Middle Pleistocene in age.

So, it's an interesting generalization. It remains to be seen how true it may be -- was early Homo really limited to a biogeographic strip of plains and savanna as it left Africa, or were the early humans more broadly adapted -- or adaptable?

References:

Ciochon RL. 2009. The mystery ape of Pleistocene Asia. Nature 459:910:911. doi:10.1038/459910a

Ciochon R, Long VT, Larick R, González L, Grün R, de Vos J, Yonge C, Taylor L, Yoshida H, Reagan M. 1996. Dated co-occurrence of Homo erectus and Gigantopithecus from Tham Khuyen Cave, Vietnam. Proc Nat Acad Sci 93:3016-3020.

Etler DA, Crummett TL, Wolpoff MH. 2001. Longgupo: Early Homo colonizer or Late Pliocene Lufengpithecus survivor in South China? Hum Evol 16:1-12.

Hyodo M, Nakaya H, Urabe A, Sagua H, Xue S, Yin J, Ji X. 2002. Paleomagnetic dates of hominid remains from Yuanmou, China, and other Asian sites. J Hum Evol 43:27-41. doi:10.1006/jhev.2002.0555

Sarel J, Zhang P, Weng Z. 2009. Recent discoveries in Baerya Cave (Bijie District, Northern Province of Guizhou, China). Antiquity 83 (online).

Wang W, Potts R, Yuan B, Huang W, Cheng H, Edwards RL, Ditchfield P. 2007. Sequence of mammalian fossils, including hominoid teeth, from the Bubing Basin caves, South China. J Hum Evol 52: 370-379. doi:10.1016/j.jhevol.2006.10.003

Zhu RX, Potts R, Xie F, Hoffman KA, Deng CL, Shi CD, Pan YX, Wang HQ, Shi RP, Wang YC, Shi GH, Wu NQ. (2004). New evidence of the earliest human presence at high northern latitudes in Northeast Asia. Nature 431:559-562.

I don't have a lot to say about the new footprints from Ileret, described by Matthew Bennett and colleagues. Seems like a nicely done study, particularly given the length constraints in Science.

With respect to the comparison with Laetoli, I think that the perspective article by Robin Crompton and Todd Pataky sort of hits the important questions:

Were the Ileret footprint makers' feet the first to function just like ours? Do the Laetoli prints represent more "apelike" foot function? Do all regions of a footprint record local maxima in foot pressure, or do some record how pressure changes over time, as braking forces change to propulsive ones? None of these questions can be answered at present. It is not even clear whether a nondivergent big toe is important for the extended push-off typical of human walking or just a by-product of other anatomical changes (1, 2, 4, 8). The effect of substrate recoil or of later abrasion on the reliability of footprint measurements must also be established (6-8). But the findings of Bennett et al. herald an exciting time for studies of the evolution of human gait.

Merely quantifying significant differences in the prints doesn't really tell us much about australopithecine gait or foot function. My impression of footprints (har!) is that it's tough to analyze them.

There's much about adduction of the big toes in the press and the abstract of the paper. The text description doesn't quite support the interpretation that Ileret is identical to recent human footprints, though:

The angle of hallux abduction, relative to the long axis of the foot, is typically 14° compared to, and statistically distinct from (table S4), 8° for the modern reference prints and 27° for the Laetoli prints (Fig. 4A).

They're closer to Holocene people than to Laetoli, since the range of living prints overlaps with these. The statistics are trickier than they might look, since these are multiple trails, but each consisting of the prints of a single individual. So I'm skeptical that they really are statistically different from humans in their big toes.

But anyway, they're in-between Laetoli and humans, so that makes a good evolutionary sequence!

I'm a bit skeptical of the body size estimation in the paper. Not the regression -- that's pretty straightforward. More the interpretation that the foot size is necessarily "Homo erectus/ergaster", or that they're a "perfect fit" for the Nariokotome skeleton.

The average foot length recorded for the FwJj14E trail is 258 mm. Two hundred fifty eight millimeters is not a very big foot -- it's a shade bigger than a U.S. men's size 8. You can have a tall person with a size eight shoe, to be sure. But their height estimate of 1.75 m is not all that tall -- it's 5 foot 8 inches, which is around the 25th percentile for height for American men (and around the 90th percentile for American women).

Now, the question here is whether that's sufficient to make them "Homo erectus/ergaster" prints, or whether they might be A. boisei. That depends on whether Australopithecus had big feet. It doesn't seem to unlikely that a male A. boisei might be 1.4--1.5 m in height, and if they had relatively big feet, well then Katy bar the door!

I don't have any strong feelings -- at 1.5 million years old, these prints might be too recent to be A. boisei anyway. But it seems to me there is this question about body size estimation, when you don't have any evidence about the body proportions.

References:

Bennett MR, Harris JWK, Richmond BG, Braun DR, Mbua E, Kiura P, Olago D, Kibunjia M, Omuombo C, Behrensmeyer AK, Huddart D, Gonzalez S. 2009. Early hominin foot morphology based on 1.5-million-year-old footprints from Ileret, Kenya. Science 323:1197-1201. doi:10.1126/science.1168132

Crompton RH, Pataky TC. 2009. Stepping out. Science 323:1174-1175. doi:10.1126/science.1170916

Scott Simpson and colleagues describe their find of a 1.5-million-year old, relatively complete pelvis of early Homo from Gona Ethiopia. The paper is in Science this week.

[UPDATE (2008-11-15): I've added Figure S4 from the data supplement, which is a nice comparison of the new pelvis reconstruction, BSN49/P27, on the top row, with the reconstructed pelvis of AL 288-1, "Lucy".]

The first thing I want to say about this paper is the complete stupidity of the journal in placing almost every graph, measurement, and piece of analysis in the online supplement. There is a decently detailed paper here, with some good illustrations, but it's broken up into fragments by the publication style.

In fact, when I read through the paper the first time, my thought was, "Gee, that's a pretty superficial report -- there must be two or three more papers to write here somewhere." In the online supplement, there are extensive comparisons, but none of them appear in the printed article.

That's no discredit to the authors, since after all it's good to have your paper printed in Science. But wow, if this is the way that the science has to go, it's ridiculous. The lack of comparisons in the printed article has to be glaring, even to readers from outside the field.

The anatomy

The pelvis is pretty much within the size range known for other early Homo specimens. Its bi-iliac breadth (roughly, the width of the body across the hips) is just under a foot, at 288 mm. That's not nearly the largest known for fossil hominids -- the Sima de los Huesos male pelvis (Pelvis 1, Arsuaga et al. 1999) has a bi-iliac breadth of 340 mm; the Jinniushan female os coxa may correspond to a pelvis of nearly that size or even a bit larger. The BSN49/P27 pelvis is only 3 cm broader than Lucy's, but that is enough to make it larger than average for recent human females. Fossil Homo had broad pelves with widely flaring ilia, a consistent observation across all Pleistocene specimens.

The most interesting thing is that the pelvis has itty-bitty acetabula. The acetabulum is the socket for the head of the femur; it's part of the hip joint. So naturally, the size of the acetabulum reflects the size of the femur head, and both of these reflect (imperfectly) the magnitude of forces passing through the joint. The most stable components of these forces come from the weight of the body and the muscles that stabilize the hip, and the largest forces come from dynamic loading as the person runs or jumps. For this reason, a small acetabulum probably means small body size.

Simpson and colleagues estimate that their acetabula, with a supero-inferior diameter of 41 mm, would correspond to a femur head diameter of around 35 mm (33.4 to 36.8, estimated by regression). In the context of the fossil record, that is an exceptionally small femur head diameter.

1. A number of fossil femora attributed to early Homo are quite long -- following the long-limbed KNM-WT 15000 model. These femora, including KNM-WT 15000 itself, as well as Likewise, other acetabula of early Homo have much larger diameters, including KNM-ER 3228 and OH 28. The acetabular diameter of BSN49/P27 is much smaller than these large specimens.

2. There are other femora attributed to early Homo that are shorter than those of KNM-WT 15000, with smaller head diameters. For example, the Dmanisi D4167 femoral head has a diameter of 40.0 mm, KNM-ER 1472 is 40.0 mm, and KNM-ER 1481 is 43.4 mm. The estimated femur head diameter for BSN49/P27, at most 37 mm, is smaller than any of these.

3. However, in the context of living small-bodied humans, the acetabular diameter of BSN49/P27 is not unusual. McHenry (1992) reports femur head diameters for a small number of recent Khoisan (36 mm) and Pygmy (33 mm) individuals, and Berger et al. (2008) report the mean femur head diameter of a sample of Andamanese as 37.3 mm. Each of these mean sizes for contemporary populations would be consistent with the acetabular diameter of BSN49/P27.

4. On the other hand, it isn't obvious that the bi-iliac breadth of BSN49/P27 would fit within these small-bodied populations. For example, Ruff (1994) reports bi-iliac breadths for a number of Pygmy individuals, all of which are at least 30 mm smaller than the 288 mm value estimated for BSN49/P27.

The third point is enough for me -- what the specimen really says (along with many others) is that the variation in body size among Early Pleistocene Homo was extensive, like that of living people. Still, the fourth point does seem to indicate a difference in pelvic (and femoral) proportions compared to humans. Let's assume for a moment that the specimen really represents an apparently small, broad female individual. What does that mean?

For one thing, it really does have to cast doubt on the "standing tall" theory for the evolution of early Homo. Many articles were written in the 1990's and early 2000's to explain why early Homo was tall and thin, and Australopithecus was short and thick. These papers followed the discovery of KNM-WT 15000, which really influenced people's thinking about early Homo. The explanations included thermoregulation, water conservation, climbing effectiveness, home range size, gut/brain energetics, predator confrontation, infant body mass, and life history constraints.

Strangely (perhaps), nobody ever actually tried to test which of these differences were more important than others. They were often content to draw up predictions about the consequences of a KNM-WT 15000-like body shape, compared to Lucy's (AL 288-1) body shape. In some ways, the situation was similar to explanations for the origin of bipedality -- there are many possible explanations, but few attempts to test them in a quantitative way.

Could one pelvis really throw all these arguments into disarray? Well, honestly, they're already in disarray -- the Dmanisi hominids were enough to tip things over the edge. The fact is that early Homo erectus simply didn't look uniformly like KNM-WT 15000. There are many body sizes represented in early Homo, even within Africa, considering the other new small-bodied African Homo erectus specimens, like KNM-ER 42700.

Plus, the arguments never grappled with another obvious blind spot: We have no reason to think that male australopithecines had size/shape proportions exactly like Lucy's, or Sts 14's, or even the small Homo habilis skeleton OH 62. I'm not talking about limb proportions, here, but stature/bi-iliac breadth and other gross proportions of the body shape. It is doubtful that large australopithecine individuals would have had the same proportions as the smallest specimens known, and yet that is the model many have used.

This provokes an obvious question: Is the new pelvis, BSN49/P27, an australopithecine? To be sure, it's a lot bigger than the relatively complete female australopithecine pelves, like AL 288-1 (Lucy) and Sts 14. But its acetabular diameter does fit easily within the size range of australopithecines. Mayer and van Gerven (1978) provided an estimate for the vertical acetabular diameter of SK 50 (which was malformed by a probable dislocation) of 41 mm, the same as the new pelvis. SK 50 even has a large ilium, although probably not large enough to make a 288 mm bi-iliac breadth.

But no, it's not an australopithecine. BSN49/P27 is compellingly female, based on its large and round pelvic inlet, large pelvic outlet with wide greater sciatic notches, and large subpubic angle. Plus, it has a more prominent, thicker iliac pillar than known australopithecine os coxae. This is not as robust as the early Homo specimens KNM-ER 3228 or OH 28, but together with the rounded pelvic inlet it suggests affinity with Homo rather than Australopithecus. So, small, broad-hipped human it seems to be -- based on acetabular diameter, we would infer this to be a smaller individual than those represented at Dmanisi, or those represented by KNM-ER 1472 and KNM-ER 1481. Again, all those arguments about the "tall, thin" body shape of early Homo erectus are out the window.

Now, I've gone through this whole write-up without discussing the "infant head size" estimates featured in the paper. I don't have anything to add to that issue, other than to point out that this pelvis could have birthed a good fraction of modern human infants -- not all, certainly, but many. That's one way to look at developmental variability: Ancient Homo would not have been uniform in brain growth rates; nor are living humans.

References:

Berger LR, Churchill SE, De Klerk B, Quinn RL. 2008. Small-bodied humans from Palau, Micronesia. PLoS ONE 3:e1780. doi:10.1371/journal.pone.0001780

McHenry HM. 1992. Body size and proportions in early hominids. Am J Phys Anthropol 87:407-431.

Ruff CB. 1994. Morphological adaptation to climate in modern and fossil hominids. Yrbk Phys Anthropol 37:65-107.

Simpson SW, Quade J, Levin NE, Butler R, Dupont-Nivet G, Everett M, Semaw S. 2008. A female Homo erectus pelvis from Gona, Ethiopia. Science 322:1089-1092. doi:10.1126/science.1163592