Dmanisi

After my Q and A with paleoanthropologist Mica Glantz, I got a lot of great response -- people really liked reading about work in the field from somebody other than me!

So, I'm going to make these interviews a regular feature. When I was in Michigan last week, I got a chance to talk with Adam Van Arsdale, who graciously agreed to answer some questions about his work.

UPDATE(11/29/2007): After posting, I heard from a reader who reminded me that I omitted Adam's affiliation and info! Adam is a lecturer in anthropology at the University of Michigan. You can find out more about his interests on his webpage.

Hawks: You were lucky enough to work at one of today's most exciting paleoanthropological sites, Dmanisi. What can you tell us about your experience there?

Van Arsdale: Dmanisi is a wonderful place and I can't say enough positive things about the site and all the people I have worked with through the project. To begin, the site itself is just a nirvana for anyone with an interest in history or prehistory. The primary excavation area is in the middle of a ruined medieval citadel complex which rose to prominence as a trading town along the silk road; down from the promontory are the tombs of Mongols who sacked the city in the 12th century; further down are early Christian burials, and along the river are the remains of bath houses for travelers along the Silk Road. It is a literally a place where time seeps out of the ground.

Leaving the setting aside, the people associated with the project have been wonderful to work with. The size of the excavation team would vary but there would be times when, at the end of a long excavation day, I would find myself sitting at a long dinner table surrounded by 40 people speaking more than half a dozen languages. In the years I worked there as a graduate student I think we had students and researchers from 15 different countries (and I'm probably missing a few). Everyone who works at the site, including the local residents of Patara Dmanisi, adds their own character to the project. As a graduate student, my summers at Dmanisi served as something of a Paleoanthropology bootcamp, with regular discussions and debates between all of us with very different training and different theoretical perspectives on the issues of human evolution.

And then on top of all of this there are, of course, a remarkable set of fossils and archaeological materials.

Hawks: Do you want to give a shout-out to anybody in Georgia?

Van Arsdale: There are too many to name, but certainly David Lordkipanidze, who first invited me to Dmanisi in 2001, deserves recognition. I'll also add Gocha Kiladze, Teona Shelia and Dato Zhvania, who began working at Dmanisi in 1991 as students and who continue to play a significant role in the operation of the site today. One of the great things about the site is that it has served as a tremendous springboard for Georgian students interested in paleoanthropology. I think it is a safe bet we will be hearing a lot from our Georgian colleagues in the years ahead.

Hawks: Your dissertation work focused on the Dmanisi mandibles. I know that you still have publications coming out on these, so feel free to keep quiet about anything you're saving for print. What can you tell us about the sample?

Van Arsdale: The Dmanisi mandibles are a remarkable sample. They show a huge amount of morphological variation in a set of fossils derived from a temporally and geographically constrained set of deposits. One of the mandibles is in many characters the largest mandible assigned to the genus Homo. Two of the others are quite small, with variably large and small teeth. And the fourth specimen is one of the earliest edentulous mandibles in the hominid record. Given the current season, it is perhaps appropriate to describe the sample as a real cornucopia of variation. And the location and date of the site itself is surprising. Dated to 1.8 million years and about 2000 miles from the outlet of the rift valley in northeast Africa, the site is a long way from the contemporaneous and well-known deposits from the Turkana Basin in Kenya and Olduvai Gorge in Tanzania.

So how do we account for all this variation? That was basically the question of my dissertation. I sought to answer this question by testing a series of hypotheses focused first on sources of intraspecific variation, particularly age and sexual dimorphism, then secondarily on hypotheses of interspecific differentiation (i.e. multiple species). I then evaluated the results of these quantitative tests in the context of the comparative anatomy of the Dmanisi sample. Sparing you all the details, I think there are strong reasons to consider the Dmanisi hominid sample as that of a single species, but one displaying considerable amount of variation associated with age and possibly elevated levels of sexual dimorphism relative to what we observe in contemporary and recent human populations.

Hawks: Of course, your work required a lot of comparisons with other samples, and mandibles are among the most common skeletal elements represented in the fossil record. How did you handle your comparative work?

Van Arsdale: Paleoanthropology is at its root a comparative discipline. It is difficult to interpret any set of fossils outside of some comparative model. My work is no different. In asking questions about variation associated with age and sex, my dissertation is really asking how strange (or not strange) does the variation in the Dmanisi sample look if we treat it like a mixed age and sex sample of humans? Of chimpanzees? Of gorillas? Each of these species possess somewhat differing patterns of variation so that our final understanding of the Dmanisi specimens is based on a combination of similarities and differences with these different comparative models.

You can also try to understand the sample from the perspective of other fossils. These comparisons are more challenging because we have less certainty regarding the things we think we know about fossils. For example, in my dissertation I also make a series of comparisons between the Dmanisi mandibles and a sample of Australopithecus boisei mandibles from East Africa. It is much more difficult to say for certain whether any given fossil specimen is male or female, and in the absence of well preserved teeth, young or old. That uncertainty limits the power of the hypothesis tests we can bring to the question by limiting the amount of information we have to work with.

One of the exciting aspects of Paleoanthropology's comparative perspective is that new fossils give us new ways of looking at old fossils. Possibly the most exciting aspect of the Dmanisi fossils is that they provide us a tremendous platform from which to look back at these large samples from East and Southern Africa that we have known about for a long time and reexamine questions which had either previously been unanswerable or whose accepted answers no longer seem so clear.

Hawks: Any stories you can share about your travels?

Van Arsdale: One of the more unique experiences from my travels occurred while I was tagging along with a graduate student from Yale on her project involving 4.5 million year old fossil exposures in the Tugen Hills of the Central Rift Valley, Kenya. I was off on my own one day, walking along one of the exposures when I came across what appeared to be part of a fossilized crocodile skull just barely sticking out of the ground. I sat down and began very carefully exposing its boundaries so that it could be properly prepared and taken out. After about 20 minutes of this, a young Tugen boy came out of the bushes and sat down next me and began watching me work. I tried to say a few words of greeting in my very rudimentary Kiswahili, but either my pronunciation was too terrible to be understand (quite likely) or he was too young to have yet learned Kiswahili (he looked like he was between 8 and 10). After a few more minutes the boy, who had been carrying a small bow and set of arrows, took out one of his arrows and began using its steel tip as a mini-trowel. I would have discouraged him out of fear he might damage the fossil or go on trying to dig up other fossils in the area, but as I watched him he was exceedingly careful and seemed completely enraptured by the work. It was just one of those moments where, while the event was going on, I recognized how amazingly unique it was. Here we were, a graduate student from the University of Michigan with twenty plus years of formal education and a young Tugen boy with at most a few years of schooling, sitting side by side on a hillside in the middle of Kenya carefully exposing a 4.5 million year old fossil. The only common language between us was the action of my Marshalltown trowel and his handmade arrow point and a basic curiosity in this fossil.

Hawks: It's a story you hear from students a lot: teeth and mandibles are "bor-ing". But of course, they're the best representatives of variation we have through much of human evolution -- if you want to study evolution, you'll be studying jaws and teeth. What keeps these questions exciting for you?

Van Arsdale: One of the reasons I enjoy looking at mandibles and teeth are that they can potentially provide a window into numerous aspects of human evolution. As you point out, they are the most abundant element in the fossil record and therefore provide a large set of data with which to address questions of evolutionary relationships and evolutionary change. They can also tell you something about the ecology and diet of the individual specimen. Finally, they tell us something about how an organism develops throughout life and ages.

This also means that questions regarding variation in jaws and teeth can be difficult to answer because many different processes might account for the observed variations. When testing hypotheses about mandibular variation it is important to keep this in mind. It is always striking to me how many hominid type specimens are or have served at some time as type specimens for a new species. This is in part a reflection of their relative abundance, but I think it also reflects how difficult it is to adequately address all the potential sources of variation in mandibles. If you accept the conclusions of my research, the Dmanisi mandibles serve as a cautionary tale in this regard.

Hawks: Some readers may know that you and I share the same graduate advisor, Milford Wolpoff, who has certainly been a strong influence on the way I approach evolutionary questions. But I also find myself going back to other people who influenced my training. Who/what really got you interested in the field, or shaped the way you think about evolution?

Van Arsdale: I initially entered anthropology by happy circumstance. Entering college (Emory University) I was interested in majoring in both English Literature and Evolutionary Biology. My first year two things happened; I realized Emory's biology department was primarily focused on microbiology and full of pre-med students (something I was not interested in) and I took my first Anthropology course to fulfill a distribution requirement. I was immediately hooked. Here I could have the best of both worlds... an integrative approach towards understanding what it means to be human and a careful examination of the evolutionary processes which have shaped the pattern of human evolution. I owe a huge part of my perspective to Milford and the other faculty and students I worked with as a graduate student, but I don't think I fully realized the influence my undergraduate teachers had on my perspective till the AAA meetings last year when I was able to attend a session honoring the graduate advisor (Jack Kelso) of my undergraduate advisor (George Armelagos). I listened to talks by people I had never met, but with whom I share some of my academic phylogeny, and what I heard were familiar themes on the interaction of human biological and cultural processes. This bio-cultural perspective is something I carry with me from Emory and is evident in the approach I take towards questions of Pleistocene human evolution, where changes in human skeletal form cannot be understood outside of the context of our ever-expanding brains and the increasingly complex ways in which we interact with the people and environments around us. Now that I am teaching, it is something I am aware of when I am in front of the undergraduates in my own classes.

Hawks:Some of your current research involves a lot of genetic modeling. How did you get into this area? Can you tell us about some of your thoughts?

Van Arsdale: My interest in genetic modeling first began as an undergraduate. In part it reflects my status as an admitted math nerd. I like numbers, I like using computationally intense models and simulations to address specific hypotheses, and I like understanding how evolutionary and cultural processes interact in dynamic ways. But when I was an undergrad my interest in genetic models stemmed out of my interest in modern human origins and the belief that any really good model should be able to simultaneously explain the pattern of fossil, archaeological, and genetic evidence. At the time there was quite a bit of discussion not just about how the increasing amount of genetic data related to previously held understandings of the fossil and archaeological record, but also how compatible data from different genetic systems were with each other. In particular, data from non-recombinant genetic systems (mtDNA and parts of the Y-chromosome) seemed to provide a different picture of human evolution than data from recombinant genetic systems. My attempt to understand these differences is what really drew me into aspects of genetic modeling.

Since that time my interest genetic modeling has really developed out of what I consider an anthropological approach towards understanding genetic systems. I like to quote one of the take-away messages from the dissertation defense of another Michigan graduate, Keith Hunley, who modeled genetic aspects of South American population structure in his dissertation. As Keith said in his defense, what people do matters. Most genetic models are dependent on a variety of demographic parameters (population size, structure, etc.), all those things that people do. And yet most geneticists do not, or simply cannot directly address these demographic parameters with the data available to them. As a paleoanthropologist, one role my research serves is to provide better understandings of what people did and the ways in which they interacted in the past so as to better inform such genetic models.

On a more theoretical level I am very much interested in exploring how the unique ways in which humans shape and interact with our evolutionary landscape serves to structure genetic variation and the evolutionary forces which shape it.

Hawks: What's the next step for you? Where do you go from here with your research?

Van Arsdale: Most of the questions I am working on now reflect my current thinking that the basic pattern which characterizes Pleistocene human evolution; the complex interaction between increasing cultural complexity, expanding ecological niches, and basic anatomical changes (encephalization, dental reduction); establishes itself early in the Pleistocene if not prior than that. Essentially, that sometime around 2-2.5 million years ago a group of hominids stopped acting like bipedal apes (the Australopithecines) and started acting human. This basic human pattern then continued to develop and characterize Pleistocene hominids until about 10-20,000 years ago when we stopped acting like humans and started acting like domesticated humans.

By understanding how this pattern manifests itself early in the Pleistocene, for example, by considering how, why and with what changes human populations expanded into places like Southern Georgia as early as 1.8 million years ago, you can develop broader understandings of the Pleistocene as a whole. I am just finishing up two projects related to this broad topic, one examining the Habiline-Erectine transition in the Lower Pleistocene and another attempting to characterize broad demographic changes within the Pleistocene.

I also want to continue my involvement in paleoanthropological field work and would like to continue examining Plio-Pleistocene deposits in Western and Central Asia. Dmanisi is an incredible site and has provided a great amount of detailed evidence to address questions of human evolution from this time period. But the detailed picture it provides encompasses only a narrow range of time and space...the more we can expand that window the better we can understand the broad patterns of change which characterize humans in the Plio-Pleistocene.

I've seen the "palms facing forward" quote in a few news reports about last week's Dmanisi postcrania paper. It's pretty nonsensical when you see it devoid of context. Consider Bruce Bower's Science News article:

However, the arms of Dmanisi hominids appear more like those of australopithecines, an earlier line of hominids. For instance, unlike people, the new specimens have upper arms that are straight rather than slightly curved, their shoulders are relatively narrow, and their palms are oriented forward rather than inward.

This is quite a vision, isn't it? How exactly is that humerus curved, again? And they stand with their palms forward? What?

OK, so it's tough to give a description of humeral torsion while making it sound important. Your humerus has two ends. The proximal end, called the head, attaches to your shoulder; the distal end is part of your elbow joint. When you are born, the head of your humerus faces toward the back (posteriorly). As you grow up, the humerus twists, so that the head faces inward toward your body (medially). The amount of twist is called the torsion; it is measured relative to the cross-section of the distal end of the humerus.

Nobody really knows what purpose is served by this twisting growth pattern. Presumably, the twisting adjusts for a change in the orientation of the shoulder joint, although that growth pattern has yet to be documented. But humans are more twisted than apes, and low humeral torsion is the key link that people are pointing out between Dmanisi and Homo floresiensis. So the articles are forced to describe it somehow. As a paleoanthropologist, I'm used to describing skeletal changes in punchy ways. Humeral torsion is a challenge -- without a really clear explanation of its function, it is hard to describe it in concrete, memorable terms.

Where does the "palms-forward" interpretation come from? We can trace it to Daniel Lieberman's commentary:

In modern humans, the elbow joint is typically rotated relative to the shoulder joint, so that the forearm naturally hangs with the palms facing inwards; but the new Dmanisi humeri lack torsion, so their palms would have been oriented more forwards. Lack of humeral torsion, a highly plastic and variable feature, suggests something different about the shoulder in these specimens.

Now, I'm sure that most of my readers will be scratching their heads over this one. People carry their hands palm-inward not because the humerus is twisted, but because the radius is habitually rotated across the ulna. That's the same reason why my hands are currently palm-downward on the computer keyboard. The humeral torsion is entirely irrelevant to the palm position when the arms are "naturally hanging" -- I can assure you, all of my children walk with their palms facing inward, despite the fact that their adult humeral torsion hasn't developed.

And of course, if humeral torsion is really about the orientation of the shoulder joint, as Lieberman suggests, then it really has no importance to the function of the elbow at all -- different torsion values would maintain the same lower arm mechanics with different shoulder orientations.

Still, neither the function nor adaptive value of humeral torsion are obvious. As Lieberman mentions, the trait is variable -- Larson and colleagues (2007) reported ranges in recent human populations extending from less than 110° to more than 170°. The value for the adult Dmanisi D4507 humerus is 110°, at the very lowest end of the modern human range; the value for the subadult D2680 is 104°. Humeral torsion continues to increase until age 16 in living people, although most change occurs before age 8 (Edelson 2000).

Larson et al. (2007) suggest that low humeral torsion is related to a short clavicle -- the idea being that the shoulder joint (glenoid fossa) was anteriorly (forward) placed, and the head of the humerus therefore had to face more posteriorly. I'm not sure that explains the low torsion at Dmanisi, since the Dmanisi clavicles aren't especially short -- like the long bones, they are right in the middle of the modern human range. But they might have had an anteriorly-facing glenoid fossa even if their clavicles weren't short, and given the low humeral torsion I suppose they probably did.

None of this means that the Dmanisi people or any other early hominids stood with their palms forward. Paleoanthropologists usually do a really good job of describing anatomy in down-to-earth terms, but humeral torsion seems to be a challenge!

References:

Edelson G. 2000. The development of humeral head retroversion. J Shoulder Elbow Surg 9:316-318. doi:10.1067/mse.2000.106085

Lieberman DE. 2007. Homing in on early Homo. Nature 449:291-292. doi:10.1038/449291a

Larson SG, Jungers WL, Morwood MJ, Sutikna T, Saptomo EW, Duw RA, Djubiantono T. 2007. Homo floresiensis and the evolution of the hominin shoulder. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.06.003

By now, the news of the Dmanisi hominids' small size has been out for years. There was a National Geographic feature on the story more than four years ago -- before my twins were born. If you think about early Homo, you've been incorporating the small body sizes represented by the Dmanisi postcrania into your thinking for some time now. The resulting conclusion has been repeated in lots of stories: "Early humans didn't need long legs to leave Africa."

So it came as no surprise when this week's report by Lordkipanidze and colleagues confirmed the short stature of the Dmanisi hominids:

Stature and body mass of the Dmanisi individuals calculated from various independent long bone measurements yield estimates between 145-166 cm and 40-50 kg, respectively (Table 1 and Supplementary Information 8). Their small stature might be interpreted in two different, but non-exclusive, ways. On the one hand, it might represent a plesiomorphic character shared with earliest Homo (cf. H. habilis) (125-157 cm and 32-52 kg), whereas the KNM-WT 15000 specimen appears to be derived in this respect (150.5-169.1 cm and 45.5-70.6 kg). On the other hand, differences in stature between the Dmanisi and KNM-WT 15000 hominins might reflect adaptation to different palaeoecological contexts (Lordkipanidze et al. 2007:308).

Except for one thing: They're not short.

Like too many papers these days, the details are hidden away in the supplements. Nobody's ever very interested in them, I guess. The supplements to this paper give most of the details about how the authors estimated mass and stature for the three individuals: the subadult represented by the D2680 humerus and D3160 femoral shaft fragment, the "large adult" reresented by the D4507 humerus, D4167 femur, and D3901 tibia, and the "small adult" represented by the D3442 first metatarsal.

Body mass estimates were calculated using the equations for femur, humerus, tibia, and metatarsal I [ref. 72, this is McHenry and Berger 1998]. The inferred body mass of the large adult individual is between 47.6 kg and 50.0 kg. The body mass of the small adult individual, calculated from the first metatarsal (D2671) is 40.2 kg. Based on humeral and femoral dimensions, the body mass of the subadult is between 40.0 kg and 42.5 kg.

Stature estimates for the subadult Dmanisi individual were obtained with prediction equations for juvenile samples; estimates based on humeral length (D2680) yield a value between 144.9 cm and 161.4 cm. Stature estimates for the large adult individual were obtained from humeral, femoral, and tibial dimensions, yielding a range of 146.6 cm - 166.2 cm. Stature estimates based on the length of the first metatarsal (D3442) yield a value of 143.0 cm (Lordkipanidze et al. 2007:S14).

Americans are handicapped to various extents because they lack an intuitive grasp of how long a meter is. The stature range for the subadult individual, 145 to 161 cm, is equivalent to a range from 4'9" to 5'3". For the "small adult", the single stature estimate of 143 cm is equivalent to 4'8" -- remembering that this is for a single foot bone. The "large adult" range of 147 to 166 cm is equivalent to a range from 4'10" to 5'5".

We can take a number of perspectives on these stature estimates. The Dmanisi adults were a bit shorter than the average American. According to the CDC, the average stature of American men aged 20 years is 176 cm (5'9"), with only 10 percent of men shorter than 167 cm at this age. Women aged 20 years have an average stature of 163 cm (5'4"), with 10 percent of women shorter than 155 cm at that age.

The Dmanisi subadult is a different story. American girls aged 12 years have an average stature of 151 cm (4'11"), and 95% of girls are taller than 139 cm. There's nothing very unusual about a 12-year-old who is 4'9" tall (145 cm), and the upper 95 percent confidence limit of 5'3" (161 cm) would have made this 12-year-old several inches taller than my wife Gretchen at that age. Twelve-year-old boys are not taller than girls -- they average around an inch shorter. The Dmanisi subadult skeleton is not short for a living human -- in fact, if the individual was a boy, he may have been a bit tall.

But living Americans are hardly the right comparative sample. Estimates of body size in early Homo have been framed around the question of whether the hunter-gatherer adaptation requires large bodies. For this question, we shouldn't compare the Dmanisi body sizes to fat Americans with their Flintstones childrens' vitamins, but instead to prehistoric hunter-gatherers.

Fortunately, there have been many analyses of stature in recent and prehistoric hunter-gatherer populations. Some of the comparisons in the current paper fit this criterion -- the North African Epipaleolithic sites of Afalou and Taforalt are in their comparative samples, which also include the bones of some early agriculturalists from Turkey. So to get an indication of the way the Dmanisi statures compared with these populations, we can look directly at Figure 3 of the paper. Here's the first panel, Figure 3a, which shows the Dmanisi tibia as a six-pointed star, and human tibiae as the letter "Z":

There, you can see the D3901 tibia is considerably shorter than the entire human sample. Except, oops! The figure is wrong. Table 1 reports a range of human tibia lengths from 290 mm to 374 mm; this figure shows a range from around 320 to over 440.

The correct range of tibia lengths is shown in Figure 3c, plotted as the y axis with femur length as the x axis:

There you can see the star for the D2901/D4167 individual, right in the middle of the recent human comparative sample. It's not short at all -- it's in the middle of the distribution.

The same thing goes for the D4507 humerus, illustrated along with the D4167 femur in Figure 3b:

A few comparisons with other hunter-gatherer samples confirm that the Dmanisi statures are typical of recent populations. Pretty and colleagues (1998) studied an archaeological sample of Aboriginal Australians from the Murray River region. Using stature estimation methods for the tibia, femur and humerus, they found that males in their sample (n=55) had an average stature of 166 cm and females (n=40) an average of around 153 cm. Wells (1952) reported a mean for !Khu (Northern Bushmen) males of 158 cm and females of 148 cm, both with standard deviations around 5 cm. Ruff (2000) puts the average stature of males at Pecos Pueblo at 161.2 cm with a range from 155 to 168 cm. In the KNM-WT 15000 monograph, Ruff and Walker (1993) report the average stature of African population samples, excluding Pygmies, as 162.3 cm. And although it is common knowledge that the Early Upper Paleolithic people of Europe were tall, the average male stature in the Late Upper Paleolithic was around 166 cm, and the average female stature around 153 cm (Formicola and Giannecchini 1999) -- virtually the same as Australians.

At their expected values, the statures of the Dmanisi adults were approximately the same as !Khu and Pecos Pueblo, and around four inches shorter than the averages (but taller than more than 10 percent) of these other groups. Compared to living people, they just weren't short.

That is all assuming that the "large adult" specimen is actually a male. Lordkipanidze et al. (2007) support this assignment based on the proximity of the remains to the D2600 mandible, which is clearly a large male. I don't have any reason to doubt the assignment, although the stratigraphic details in the paper don't clearly show the association -- the "large male" remains including D2600 appear clustered, but the specimens aren't labeled and don't all seem to be represented. If the skeleton turned out to be female, it would be an inch or two taller than average for the larger groups above.

I have focused on stature rather than mass, mainly because it is more reliably estimated from bone lengths than mass is from articular breadths, but also because it is more heritable. Still, the same basic observations apply: hunter-gatherer populations are not heavy people, and a mass estimate of 50 kg would not be exceptional for a male.

So why is everybody saying that these individuals are small? The real contrast is not between Dmanisi and living people, but between Dmanisi and the large East African "H. erectus" specimens, like KNM-WT 15000, KNM-ER 1808, KNM-ER 736, KNM-ER 739, and OH 28. And yet, these large specimens are hardly typical in East Africa: they are the upper end of a range of variation in postcrania extending down to Lucy's size, barely more than a meter tall. We have often assumed that these larger specimens belong to H. erectus, and I have argued for such an assignment in print (Hawks et al. 2000). But I think that the lower end of this range of variation is completely up for grabs -- especially considering the small size of the KNM-ER 42700 cranium.

There is one good argument for associating East African "Homo erectus" exclusively with the large-bodied specimens: KNM-ER 1808 and OH 28 are both apparently female (based on their pelves), but both have tall statures, based on their femora. McHenry (1991) puts KNM-ER 1808 at 180 cm and OH 28 at 171 cm. It is the large size of these female specimens that argues for a reduction in sexual dimorphism and average large body size in Homo erectus. It is that association -- low sexual dimorphism and large body size -- that argued for a significant increase in home range size and dispersal potential in this species. I'll call it the "long-legged colonists" hypothesis: the idea that hunter-gatherer ecology, large body size, and low sexual dimorphism were linked to each other, all enabling long-distance dispersal and the initial colonization of Eurasia. The Dmanisi body sizes refute this hypothesis.

But looking back, the "long legged colonists" hypothesis was half incorrect chronology and half wishful thinking. Why would early humans have needed statures near the extreme of modern human populations, if recent hunter-gatherers have relatively small bodies? Recent hunter-gatherers have maintained large home ranges, sexual division of labor, and large mammal hunting with statures no larger -- and often smaller -- than the current global average. The largest stature estimates for early Homo fossils are well above the average statures for any but the very tallest human populations.

Even the tallest modern human populations average substantially shorter than the tall East African fossil stature estimates. Ruff and Walker (1993:259) report the mean for living Africans "of tall stature" as 166.6 cm. That's a midsex average of 5'6" for tall populations. The tallest population in the world now is the Dutch, where 21-year-old males average 184 cm. That's virtually the same height as estimated for KNM-WT 15000 as an adult, but remember that the Dutch stature is an average; as it stands, KNM-WT 15000 is an extreme. Early East African Homo was not as tall as late-twentieth century Dutch; they must have averaged substantially less.

And as for chronology: all of the tall-stature early Homo specimens are now substantially later in time than Dmanisi. Only KNM-ER 1808 might approach Dmanisi in age. The rest of these tall stature specimens are at least 200,000 years younger.

We are left with a remaining question about variability: Were these early humans (Homo erectus) unusually variable in size? I don't think so. If anything, they appear to have exhibited less variation in stature than human populations today. No ancient population was as tall as the Dutch. It is not even clear that early Pleistocene East Africans were as tall as recent East Africans, although they may have been so. No fossils yet assigned to Homo erectus were as short as Pygmies; although some Homo habilis-associated postcrania were even shorter. If the species boundaries are drawn right, there may be no problem of variability in the postcrania.

That may be a big "if". The limited degree of variation is fairly remarkable considering that the fossils in question span over a half-million years of time, in East Africa and Eurasia. Maybe there ought to be more variation than anyone is now assigning to H. erectus, and the species boundaries are wrong after all...

References:

Formicola V, Giannecchini M. 1999. Evolutionary trends of stature in Upper Paleolithic and Mesolithic Europe. J Hum Evol 36:319-333.

Fredriks AM, Van Buuren S, Burgmeijer RJF, Meulmeester JF, Beuker RJ, Brugman E, Roede MJ, Verloove-Vanhorick SP, Wit, J-M. 2000. Continuing positive secular growth change in the Netherlands 1955-1997. Pediatric Res 47:317-323.

Lordkipanidze D and 17 others. 2007. Postcranial evidence from early Homo from Dmanisi, Georgia. Nature 449:305-310. doi:10.1038/nature06134

Lieberman DE. 2007. Homing in on early Homo. Nature 449:291-292. doi:10.1038/449291a

Pretty GL, Henneberg M, Lambert KM, Prokopec M. 1998. Trends in stature in the South Australian Aboriginal Murraylands. Am J Phys Anthropol 106:505-514. doi:10.1002/(SICI)1096-8644(199808)106:4<505::AID-AJPA5>3.0.CO;2-H

McHenry HM. 1991. Femoral lengths and stature in Plio-Pleistocene hominids Am J Phys Anthropol 85:149-158.

Ruff CB, Walker A. 1993. Body size and body shape. Pp. 234-265 in The Nariokotome Homo erectus skeleton, Walker A, Leakey R, eds. Harvard University Press, Cambridge MA.

Ruff CB. 2000. Body size, body shape and long bone strength in modern humans. J Hum Evol 38:269-290. doi:10.1006/jhev.1999.0322

Wells LH. 1952. Physical measurements of northern Bushmen. Man 52:53-56.

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.

I'm mining the data supplements from the Dmanisi postcrania paper for interesting stuff. There is a section (Supplement 4) on the paleoecology, which evaluates the site in terms of the faunal list:

The combination of topographic and vertebrate palaeontological information allows to infer a differentiated landscape pattern. Over a distance of a few kilometres, the landscape character changed from a flat and fairly wet river valley with gallery forests (indicated especially by the frequently recorded Eucladoceros and the elaphine deer Cervus abesalomi) to flanking slopes with shrub vegetation of varying densities, turning into dry meadows in the southerly exposed areas with more intense insolation. Extended tree savannah to open grasslands characterised the higher ground out of the valley. In addition to savannahs, semidesert-like rocky terrains existed on the lava outcrops in the vicinity of the site. Testudo graeca and Hystrix refossa indicate temperate climatic parameters.

Supplement 3 concerns the faunal resemblances with other geographic regions: they conclude that the greatest similarity is with Europe, and faunal similarities with Africa are

mainly due to the co-occurrence of common carnivore genera (e.g. Homotherium, Megantereon, Panthera) or, among herbivores, widespread genera like Equus.

Homotherium and Megantereon are the sabretooths.

References:

Lordkipanidze D and 17 others. 2007. Postcranial evidence from early Homo from Dmanisi, Georgia. Nature 449:305-310. doi:10.1038/nature06134

Elizabeth Culotta's article on the Liang Bua conference appears in this week's Science. It's a real treat: around 2500 words worth of description of the proceedings, and quite balanced.

Here's the passage relevant to Laron syndrome:

At the meeting, Dean Falk of Florida State University in Tallahassee, who has concluded from computed tomography (CT) scans of the skulls of LB1 and microcephalics that the hobbit is a new species, tackled the Laron's hypothesis head-on. Hershkovitz and colleagues note that many Laron's patients also lack the sinuses of a normal human head. And although in most people the texture of the mastoid process--the bony bump behind the ear--is spongy and air-filled, in Laron's patients this bone is dense. CT scans of LB1's skull show that it has normal sinuses and a porous mastoid process, Falk said. "We don't think LB1 comes close to looking like their description of Laron's," she said firmly. Hershkovitz responds that some Laron's patients do have normal sinuses, and so their presence does not disprove the hypothesis.

Obviously, I'm not going to quote the whole thing; the paragraph just before that one did a good job laying out the many, many similarities between LB 1 and Laron patients, which I wrote about earlier this summer.

There is some discussion of paedomorphosis, with Christoph Zollikofer weighing in that the anatomy may represent the retention of juvenile traits in a derived, dwarf Homo erectus. I have to say, I don't buy that idea. The proposed juvenile features are the lack of humeral torsion (this develops during early childhood), the "flat face" and the short legs. But it's not clear that the legs are relatively short, and if "flat face" means a lack of facial projection, that is easily explained either by allometry or the fact that its teeth are smaller than H. erectus. The humeral torsion in particular has turned out to be a red herring, since Jungers and Larson have presented that LB 1 is within the range of recent Australians. And, of course, paedomorphosis can't explain the tiny brain -- which is only two-thirds the size of the 1-year-old Mojokerto endocast!

The problem with invoking paedomorphosis is that, of course, you still have to account for why different features are juvenilized at different levels or rates. Since many have attributed the anatomy of living people to a paedomorphosis of Homo erectus characters, presumably LB 1 is a product of a different and distinct version of paedomorphosis. Which is as much as to say the idea is a non sequitur.

Morwood is now arguing for descent from early pre-erectine Homo or Australopithecus, while there is some discussion about whether Dmanisi is a plausible ancestor. These are all attempts to minimize the amount of evolutionary change on Flores; I think that is misguided. If the island really generated a highly derived lineage, then let it be highly derived! On the other hand, the article notes that many are now looking (or seeking funding to look) for similar fossils on lots of other islands, from Sulawesi to the Philippines.

There is some new information on the archaeology, notably the use-wear analysis of some of the artifacts:

Because the tools were found near animal bones, especially baby pygmy elephants called Stegodon, researchers had inferred that the little people used the tools to process meat. But to [Carol] Lentfer's surprise, most of the tools she examined were used for working with woody and fibrous plants, perhaps to craft spear shafts of wood or bamboo or items like traps. "It looks like a tool kit for making other tools," she said in her talk.

This is accompanied by some discussion of the archaeology including comments by James Phillips.

Anyway, read the article. I doubt that we will hear anything new on this score for quite some time.

References:

Culotta E. 2007. The fellowship of the hobbit. Science 317:740-742. doi:10.1126/science.317.5839.740

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...

I keep seeing this story about Tim Bromage's "computer-simulated" reconstruction of KNM-ER 1470.

Bromage said his team's reconstruction includes biological principles not known at the time of the skull's discovery, which state that a mammal's eyes, ears and mouth must be in precise relationships relative to one another.

"It doesn't matter if you're a rat, a kangaroo, an elephant, a human or a dog -- their [facial features] are all organized to a very specific architectural plan," Bromage said.

Well, let's see. Here's the lateral view of the old and new reconstructions in the article:

The photo accompanying the article

Wow, that new reconstruction sure has a sloping face doesn't it? Oh wait! It's rotated at a different angle from the old reconstruction! Let's use Photoshop to fix that right up:

Same picture, with the reconstruction rotated to the Frankfort horizontal, like the old reconstruction.

Well, now, that's better. Now the vaults are at the same orientation. And the reconstruction does have a bit more sloping face. By about 5 degrees.

Now, a good cast of ER 1470 comes with the face and vault in separate pieces. There is only one join between them, at the nose, and it's not a very good one. Every graduate student in the world has probably taken these two pieces and rotated them back and forth to decide on the best angle. No doubt, there is five degrees of variation between them all. I'm perfectly willing to believe that the skull should have five more degrees of inclination to its face.

I wish that new reconstruction had the nasal bones pictured, though -- a greater slope makes the join there worse, which is probably why the original reconstruction was made with the more vertical orientation. Oh wait! It looks like the nasal bones have been crammed back under the frontal bone! That seems odd...considering the fronto-nasal suture is there underneath the small browridge. Hmm...

I think this particular issue is one for which more detail will be necessary. That seems like an unreasonable placement of the nasal bones, but we only have the one view to work with.

There is a lot of talk about the brain size of the specimen. I don't have any details of the presentation, and it is possible that Bromage was incorrectly quoted. Here is what the article says:

The new reconstruction suggests H. rudolfensis' jaw jutted out much farther than previously thought. The researchers say the cranial capacity of a hominid can be estimated based on the angle of the jaw's slope and they have downsized KNM-ER 1470's cranial capacity from 752 cubic centimeters to about 526 cc. (Humans have an average cranial capacity of about 1,300 cc.)

That, of course, is utter nonsense. Ralph Holloway produced an endocast, the joins between the fragments are good, and the volume of 752 cc was measured by water displacement. Why in the world would you estimate brain size from the face when you have a perfectly good vault? It has to be a misquote.

The article quotes Bob Martin as a skeptic:

"What they're claiming is you stick the face out, and because the face sticks out more the brain capacity has to be less. I don't follow that at all," said Martin, who is an expert on hominid skulls and who was not involved in the study.

"They haven't changed the skull at all; they've simply rotated the face outwards," Martin added.

He mentions that the 752 cc estimate is not a problem in comparison to other contemporary hominids. We can also mention the Dmanisi crania, the largest of which (D2280) has a brain size essentially the same as KNM-ER 1470, at 1.75 million years. KNM-ER 1470 is one of the most solid endocranial volume estimates in the fossil record. It's the face that's crummy!

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

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

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

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

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

You dirty louse

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

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

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

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

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

Here's a short one:

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

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

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

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

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

My what small teeth you have

This part is a little confused:

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

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

Splitting straws on habiline brains

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

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

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

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

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

Out of Africa

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

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

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

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

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

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

References:

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

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:

• 10. We will see a name for the Flores pathology. OK, we got several names, and the issue is far from settled, but this was the year that the Homo floresiensis doubters struck with their papers on the remains.
• 9. There will be two Neandertal genome-related announcements. I undercalled this, since there were three -- the initial announcement in June of the Neandertal Genome project, the announcement and publication in November of the initial sequence results, and the announcement about possible introgression of microcephalin.
• 8. No Ardipithecus. Sometimes, predictions write themselves.
• 7. "Population cluster" will become the new "race". This one is debatable, but enough papers on multi-ethnic SNPs have used the term this year, that I think it is emerging as the replacement for the race concept for a certain class of geneticists. I expect it will continue -- "cluster" has such a neutral computer-program-centric connotation, that people like to use it.
• 6. There will be another paper (yes, besides the one last month) using genetics to estimate the time of the human-chimpanzee divergence. The date will be 5 million to 7 million years ago. Oh, my. There have been bigger messes than the Patterson et al. 2006 paper, but not many. Yes, it was yet another paper with a 5-million to 7-million-year-old divergence, but it had so much more!
• 5. Evidence of recent selection will be found for several Y chromosome genes. Wishful thinking or prediction for the next year? You decide!
• 4. Sahelanthropus postcrania will be published. This one didn't happen this year, but I'm carrying it over onto the 2007 list.
• 3. There will be an ancient DNA announcement from China. Someday it will happen, but not this year or next.
• 2. StW 573 will be proposed as a new species ancestral to all later hominids. Well, we got the opposite -- with a new younger date, StW 573 was proposed as the ancestor of...nobody! Which was by far the smaller of the redating stories this year.
• 1. A Hawks weblog post will be cited in a peer-reviewed research paper. We can only hope this happens in the coming year, but carrying it over just seems desperate...
• BONUS: A new Georgian hominid will be a robust australopithecine. I still think somebody will find an australopithecine outside Africa in the next decade, but it's not to be from Dmanisi -- the hominids are too localized in a single feature.

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!

• 10. Sahelanthropus postcrania will be published.
• 9. Two words: Holocene evolution.
• 8. Despite (or because of) the success of the Neandertal genome project, there will be no genetics of any kind published on early modern skeletal material.
• 7. The mitochondrial history of human dispersals will become more and more detailed, but no paper will test against other loci.
• 6. Another (yes, another) paper about the chimpanzee-human divergence will peg it between 5 and 7 million years ago.
• 5. Three papers with new Ethiopian fossils.
• 4. Another early Upper Paleolithic specimen will emerge from a museum collection.
• 3. A big year for Miocene apes, which will look increasingly important in the story of human brain evolution.
• 2. Maturation rate in early Homo becomes a dead issue, because of the variation in dental and skeletal maturation in living people.
• 1. The year will end without a single new hominid species having been named.
• BONUS: A dramatic development in the problem of pre-2.0-million-year-old Homo.

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!

In case you haven't been paying attention, the chronology of early African Homo has been completely turned upside-down this year. Well, "upside-down" isn't precisely right; "displaced younger by a quarter-million years" is better.

The redating has come from Frank Brown's group, which in a series of papers has defined and dated stratigraphic units between the major tuffs of the Koobi Fora formation, between the KBS Tuff at 1.87 Ma and the Chari tuff at around 1.38 Ma. Gathogo and Brown (2006) outline the consequences of this redating for fossils of early Homo. Their paper focuses on the fossils from area 123 at Koobi Fora, but discusses the likely consequences of redating on other localities.

Fossils of Homo now estimated to be 1.65 +/- 0.15 myr in age in the Koobi Fora region are currently assigned to at least two taxa on the basis of both crania and mandibles. Homo habilis is represented by specimens KNM-ER 1501, 1502, 1805, and 1813, and H. ergaster is represented by specimens KNM-ER 730, 1812, and 3733 (for attributions, see Wood, 1991, 1992; Wood and Richmond, 2000). The ages of specimens KNM-ER 1501, 1502, 1812, and 1813 have been discussed above, and although not the main focus of this paper, a few notes are offered below on the others.

Specimen KNM-ER 730 derives from a level 5 m below the Koobi Fora Tuff Complex in Area 103 (Feibel et al., 1989), and is thus ca. 1.6 myr old. Feibel et al. (1989) gave an age of 1.85 myr for KNM-ER 1805, but this specimen lies "just below the base of the Okote Tuff" in Area 130 (Leakey et al., 1978), and is more likely closer in age to that of the base of the Okote Tuff Complex (ca. 1.6 myr) than it is to that of the KBS Tuff (1.87 myr). On the basis of mollusc-packed sandstones and algal horizons correlated from Area 102 to Area 104, Feibel et al. (1989) estimated that KNM-ER 3733 was 1.78 myr in age. Although the age of KNM-ER 3733 cannot be confirmed without additional fieldwork, the White Tuff, with an estimated age of 1.63 myr (Brown et al., 2006), is the nearest unequivocally identified unit in the local section in Area 104. This tuff is exposed <300 m from the location of KNM-ER 3733, and Tindall (1985) records only 8 m of section below the White Tuff nearby. Therefore KNM-ER 3733 should be approximately the same age as KNM-ER 1813. Indeed, all specimens from Koobi Fora assigned to H. aff. H. erectus by Wood (1991), many of which are now referred to H. ergaster (Wood and Richmond, 2000), are now estimated to be 1.45 to 1.65 myr old with the exception of KNM-ER 2598. The latter specimen, which is a partial occipital bone from Area 15, was placed 4 m below the KBS Tuff by Feibel et al. (1989) and estimated to be about 1.9 myr old. This age estimate is reasonable because strata do not extend more than 7 m above or below the KBS Tuff at the recorded location of KNM-ER 2598 (Gathogo and Brown 2006:7-8, emphasis added).

This raises a question: Just how much evidence is left for large-bodied H. erectus-like hominids earlier than 1.65 Ma?

Wood (1991) didn't diagnose postcrania, and Gathogo and Brown (2006) don't comment on them. At least KNM-ER 1808 would seem to fall under this umbrella, since Wood (1991) did diagnose that. But more important in bracketing the evolution of large body size is KNM-ER 3228, a hip bone previously dated to 1.95 Ma. It's pretty big for a human, let alone an australopithecine. On the other hand, McHenry and Coffing (2000) suggested that KNM-ER 3228 might belong to H. rudolfensis. To my eyes, this would make it a pretty big specimen compared with femora like KNM-ER 1472 and KNM-ER 1481, but who knows?

Another uncomforable fit in an H. rudolfensis would be KNM-ER 2598. It sure looks like a large-brained, thick-boned specimen. It doesn't look much like KNM-ER 1470. But then, maybe 1470 is the unusual specimen...

Gathogo and Brown (2006) take on directly the issue of KNM-ER 1470 and KNM-ER 1813. The two were formerly considered contemporaries at around 1.89 Ma, but now KNM-ER 1813 is only 1.65 Ma.

KNM-ER 1813, lateral view

The real offshoot of this is that there are no longer any early small-skulled habilines. The question of whether KNM-ER 1470 and KNM-ER 1813 were too different to belong to a single species has drawn a lot of ink, but it was always a non sequitur, because the two weren't the only crania to consider. The more interesting observation had been that Olduvai Gorge preserved only small-skulled habilines, while Koobi Fora had both small and large ones. This was not only a geographic problem but also a temporal one, since the Olduvai habilines were all relatively late (less than around 1.8 Ma) and the Turkana habilines were mostly earlier.

Now the situation has changed. The small Turkana habiline, KNM-ER 1813, is now contemporary with the Olduvai sample. There are no longer any small-skulled early Turkana habilines. KNM-ER 1805 makes sense as a male of the later, small-skulled sample because it is relatively small-brained but robustly built (e.g., with a sagittal crest). That leaves KNM-ER 1470, KNM-ER 1590, KNM-ER 3732, and KNM-ER 3735 as plausible habilines before 1.85 Ma.

This seems like a nice sample as a possible ancestor for both later large-bodied Homo and later habilines. Heck, Wood (1991) even wrote this in his description of KNM-ER 3735:

Some features (e.g. vault thickness) ally it with a Homo erectus-like hominid, but in other areas (e.g. the frontal) it is more like crania such as KNM-ER 1813, a conclusion endorsed by Walker (1987) and by Leakey et al. (1989). Tobias (1989) includes KNM-ER 3735 within H. habilis (Wood 1991:134-135).

What more could you ask of a common ancestor? But then if some of this ancestral population would be expected to resemble later H. erectus-like specimens, then why not KNM-ER 2598?

And what, exactly, would make such a population -- with its mixture of H. erectus-like and habiline-like features -- different from Dmanisi? The answer, of course, is KNM-ER 1470. It's still the odd one in this lineup. But then, it does have the largest brain in this set, which might help to explain the rounded occiput.

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?

References:

Brown FH, Haileab B, McDougall I. 2006. Sequence of tuffs between the KBS Tuff and the Chari Tuff in the Turkana Basin, Kenya and Ethiopia. J Geol Soc 163:185-204.

Gathogo PN, Brown FH. 2006. Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estiamtes of its fossil mammals, including hominins. J Hum Evol (in press) DOI link

McDougall I, Brown FH. 2006. Precise ⁴⁰Ar/³⁹Ar geochronology for the upper Koobi Fora Formation, northern Kenya. J Geol Soc 163:205-220.

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

Science is carrying an exchange of technical comments about microcephaly and the endocast of LB1. Bob Martin and colleagues weigh in with an argument for why LB1 was a microcephalic. Dean Falk and colleagues respond that the microcephaly explanation can't account for the endocast's features.

So what's the real story?

In Nature a couple of weeks ago, Robin Dennell and Wil Roebroeks had a provocative paper exploring the possibility that early humans (i.e. Homo erectus) originated in Asia rather than Africa.

The paper is all speculation of course; there is no evidence of any earlier hominid in Asia.

But it is the good kind of speculation. Although maybe not quite this big:

Most probably, we are on the threshold of a profound transformation of our understanding of early hominin evolution that might prove as far-reaching as the demise of the notion of Man the Hunter in the early 1960s (Dennell and Roebroeks 2005:1103).

Here's the abstract:

The past decade has seen the Pliocene and Pleistocene fossil hominin record enriched by the addition of at least ten new taxa, including the Early Pleistocene, small-brained hominins from Dmanisi, Georgia, and the diminutive Late Pleistocene Homo floresiensis from Flores, Indonesia. At the same time, Asia's earliest hominin presence has been extended up to 1.8 Myr ago, hundreds of thousands of years earlier than previously envisaged. Nevertheless, the preferred explanation for the first appearance of hominins outside Africa has remained virtually unchanged. We show here that it is time to develop alternatives to one of palaeoanthropology's most basic paradigms: 'Out of Africa 1' (Dennell and Roebroeks 2005:1099).

It is worth reviewing exactly what "Out of Africa 1" is supposed to be. The paradigm is that emergence of hominids from Africa required increases in brain size and/or body size, coincident with the emergence of hominids like KNM-ER 3733, KNM-WT 15000, and others. The motivation for this hypothesis is simple: australopithecines have not been found outside of Africa. Nor has anything like Homo habilis, which is australopithecine-sized but has larger brains.

Of course, it is questionable just how basic this paradigm is. Consider what I (and my colleagues) were able to write only seven years ago:

The problem is that significant range expansion out of Africa occurred a half million years or more later than the first H. sapiens [corresponding to others' H. erectus or H. ergaster]. Population size before then may have remained small, and this is not an inconsequential time span, being one quarter of the time H. sapiens has existed. An important date in behavioral evolution is 1.5 MYA because it is marked by the earliest appearance of the Acheulean, the ubiquitous hand-axe industry of the Early and Middle Pleistocene.... Before this time, humanity was limited to Africa and immediately adjacent sections of Asia such as the Levant (Hawks et al. 2000:7).

Evidence for large body size in Late Pliocene humans (notably KNM-WT 15000 but also many others) made it very plausible that larger bodies were necessary for dispersal from Africa. But without good evidence for such dispersal before around 1.4 million years ago (and arguably not before 1 million years), larger bodies could not be assumed to be a sufficient condition for dispersal. Writing about the origin of humans, we had to consider all these alternatives -- at a time when the Dmanisi sample consisted of a single uncertainly dated mandible and the Mojokerto date stood alone with very questionable provenience.

Now we know that hominids did leave Africa by at least 1.8 million years ago. Dmanisi has almost singlehandedly changed the perspective.

And in doing so, it made much more convenient the hypothesis that large body size was both necessary and sufficient for dispersal from Africa. If the date of dispersal and the date of human origins are the same, then it is natural to propose that the coincidence is more than chance.

I would say this is more of a convenient hypothesis (and an easy story to tell) than it is a basic paradigm. The idea that large body size caused dispersal from Africa may have been a local minimum in terms of parsimony (at least as long as the body size of the Dmanisi fossils was not known), but it was only one alternative among many still in play.

And it remains a plausible hypothesis -- after all, the Dmanisi remains are a bit larger than australopithecines, and they might well have shrunk from a larger early-human-like size after reaching Asia instead of before.

But Dennell and Roebroeks give motivations for examining some alternatives.

The only reason why the earliest tool assemblages in Asia are attributed to H. erectus s.l. is that palaeoanthropologists have already decided that, in effect, it was the only hominin capable of migration out of Africa, and with sufficient Wanderlust to do so (Dennella and Roebroeks 2005:1099).

Homo erectus sensu lato (s.l.) means Homo erectus "in the loose sense", which would include not only the "strict sense" (sensu stricto) H. erectus. from Java and China, but also hominids like OH 9 and KNM-ER 3733 from Africa, and presumably the Dmanisi hominids.

A long passage reviews the total faunal evidence from Asia during the Late Pliocene. The thrust of the passage is that there are very few sites with extensive fauna, and of these most preserve mainly large-bodied herbivores. There are a few hints that a hominid-friendly fauna may have existed, including the presence of baboons. But there are no hominids of any kind at the vast majority of Asian localities -- Dmanisi is a real exception in the Plio-Pleistocene record.

This is the key taphonomic argument: if we have only found Early Pleistocene humans from continental Asia within the past ten years, then how can we preclude there having been australopithecines there? Dennell and Roebroeks argue that if there were australopithecines, we shouldn't necessarily expect to have found them yet -- we just haven't looked extensively enough.

A close read of the section raises a caution, though. One of the main arguments for the incompleteness of the Asian record is that sites don't preserve each others' fauna.

It is also likely that the full range of taxa is incomplete for the Indian subcontinent, because Megantereon and Pachycrocuta are not recorded in India but are present in Pakistan; in Pakistan, there is no evidence of Camelus and small primates, and in neither country is Homotherium recorded, although this is present to the west at Dmanisi, to the north at Kuruksay, central Asia and to the east at Longuppo, south China (Dennell and Roebroeks 2005:1100).

Of course, all of these species are recorded in Asia taking all the sites in aggregate; this is hardly an argument for the overall weakness of the record -- just an argument that no individual site is an adequate record of the continent's fauna.

To me, the important question is not whether australopithecines as currently known from Africa were in Asia. A more troubling possibility is that the australopithecines that we now know from Africa were not the only (or main) manifestations of early hominids in Africa. Large parts of Africa that we might expect to be congenial to hominids, like the Zambesi basin, have few or no fossils at all. The recovery of the Bahr el Ghazal mandible (Brunet et al. 1994) certainly makes clear that hominids were living across a much larger area than we have adequately sampled. But that mandible is, although not identical, certainly very similar to known contemporary hominids in its adaptation.

The question is whether hominids had adapted to other ecologies that are much less satisfactorily sampled than the East African rift. They probably weren't living where chimpanzee and gorilla ancestors did, but where else might they have been? Some such ecologies -- like the coasts -- would make early dispersal very plausible.

(In this regard, early humans are not the only hominids who lack a satisfactory ancestor. Who was the ancestor of A. aethiopicus? In what ecology did the first robust hominid arise?)

So what is the broader set of hypotheses that we should consider? Dennell and Roebroeks suggest:

If the above taphonomic review suggests that we cannot show the absence of hominins from areas in Asia at a time before the little evidence we have indicates their presence, we need to consider alternatives to the current Out of Africa [that is, their "Out of Africa 1"] model. There are three issues here. The first is when hominin(s) first left Africa -- might they, for example, have left shortly after they acquired the ability to make stone tools, the earliest of which are currently 2.6 Myr old? Or could they have left even earlier, about 3.0Ð3.5 Myr ago, when some australopithecines were already living in the African grasslands? The second issue is whether we yet know the full range of hominins that inhabited both Africa and Asia in the Late Pliocene and Early Pleistocene. Even in east Africa, several new taxa have been claimed in the past decade (for example, A. anamensis, A. garhi, Ardipithecus ramidus and Kenyanthropus platyops) and doubtless more will be found. (An indication of how little we know about Pleistocene east Africa is that only recently has the first fossil evidence for chimpanzee been found.) In Asia, the recent discoveries of H. georgicus and H. floresiensis should make us very wary of assuming that H. erectus s.l. was the only player on the Asian stage in the Early Pleistocene. Third, Asia might not have been the passive recipient of whatever migrated out of Africa but might have been a major donor to speciation events, as well as dispersals back into Africa. Such two-way traffic is well documented for other mammals in the Pliocene and Early Pleistocene, such as Equus and bovids, with more taxa migrating into than out of Africa. There is no reason why hominin migrations were always from Africa into Asia, and movements in the opposite direction might also have occurred, as has been suggested for the Olduvai OH9 (refs 13, 58) and Daka specimens. We should even allow for the possibility that H. ergaster originated in Asia and perhaps explain its lack of an obvious east African ancestry as the result of immigration rather than a short (and undocumented) process of anagenetic (in situ) evolution (Dennell and Roebroeks 2005:1100-1101).

Of course, most of the evidence indicating the presence of hominids is not fossil but archaeological. On this topic, Dennell and Roebroeks have much to say:

Any stone tool assemblage in Asia dated as older than 1.9 Myr ago (the earliest date that Homo is supposed to have left Africa) is either dismissed or (more usually) ignored; undated Oldowan tools are assumed to date from after 1.9 Myr ago and not from 2.6 Myr ago (the date of their first appearance in east Africa); and stone tool assemblages in Asia dated to the Olduvai Event (1.77Ð1.95 Myr ago) and not associated with hominin remains are automatically attributed to Homo erectus s.l. However, there is no reason why Oldowan assemblages in Arabia cannot be older than 1.9 Myr old, or why the tools from Ain Hanech (Algeria) or Erq el Ahmar (Israel) were made by H. erectus s.l. [instead of other hominids] (ibid:1102, references omitted).

There is a section about what exactly absence of evidence can tell, a short critique of using continents as proxies for biogeographic units:

As noted earlier, Pliocene grasslands extended all the way from west Africa to north China, and 'Savannahstan' might prove a more useful spatial unit for modelling early hominin adaptations and dispersals within them than simply an undifferentiated 'Africa' or 'Asia'. For example, the African hominins 1.9Ð1.7 Myr ago at Koobi Fora (Kenya) and Ain Hanech (Algeria), and their slightly later counterparts in Asia at 'Ubeidiya (Israel), and Majuangou (north China) were all living in broadly comparable grassland environments, and it makes sense to place them within the same frame of reference.

I think there is much of value to consider here; but it is less a revolution and more a statement of the field in transition. There are also alternatives that are not considered in this paper but that may be equally plausible -- most notably, the idea that early humans themselves may have been substantially polymorphic (witness KNM-ER 42700), or that brain size rather than body size may have been a prerequisite to dispersal (since habilines, Dmanisi, and H. erectus s.l. are all allometrically similar in brain size).

National Geographic News also has an article about the paper.

References:

Dennell R, Roebroeks W. 2005. An Asian perspective on early human dispersal from Africa. Nature 438:1099-1104. Full text (subscription)

Hawks J, Hunley K, Lee S-H, Wolpoff M. 2000. Population bottlenecks and Pleistocene human evolution. Mol Biol Evol 17:2-22.

This week's Nature is carrying a paper by Morwood, Brown, and colleagues (2005) presenting additional skeletal material from Liang Bua as well as a commentary by Daniel Lieberman. Thanks to a reader, I found the permission slip from Nature lifting the embargo, so I can let fly without bogarting the kind journalist who forwarded me the paper.

What is noteworthy about the new bones?

The paper discusses three important specimens. The first is the adult mandible LB6/1. In its overall size and morphology it is similar to the mandible of LB1, reported last year. Like LB1 it lacks a chin and Morwood et al. (2005:1013) compare its symphyseal morphology to Dmanisi D211. Overall, the mandible is slightly smaller in tooth size and corpus size compared to LB1, and its ramus is quite a bit shorter.

LB6/1 is part of a partial skeleton. The other elements are not described in the paper, but they are listed: a portion of proximal ulna, a partial right scapula, a foot bone, one each of finger and toe bones, and a complete radius 157mm long. That's a short radius -- barely more than 6 inches. It was broken during life and healed.

Wait a minute. Did you say a 6-inch long radius?

Funny how nobody else seems to have picked up on this yet.

The authors estimate a brachial index (radius to humerus) for LB1 of 78 percent, estimating likely radius length from the ulna. This would put LB1 within the range of "tropical" human populations. If the LB6 individual had the same "tropical" brachial index, its humerus would be around 200mm long. That's 43mm shorter than LB1.

This admits a couple of explanations:

1. LB6 was simply a smaller individual than LB1. The mandible is more or less consistent with this hypothesis, which may therefore be the most likely.
2. LB6 did not have the unusually long arms of LB1. Where LB1 is australopithecine-like, perhaps LB6 was more humanlike. This seems less likely, but it would be consistent with the idea that the proportions of LB1 represent some kind of pathology.

Wait a minute. Did you say australopithecine-like proportions?

Yes, the LB1 humerus and ulna are relatively long compared to the femur:

For example, the humerofemoral index of 85.4 is outside the range of variation for H. sapiens, but is the same as AL 288-1 A. afarensis, and midway between the indices for apes and humans. The more complete left ilium [pelvic bone] also indicates that the pelvis is flared antero-laterally, consistent with an australopithecine-shaped thoracic region. Body proportions of LB1 are the same as AL 288-1 A. afarensis, but differ from all other hominins for which they are reliable data, including H. erectus (Morwood et al. 2005:1016).

"Outside the range of H. sapiens" is also outside the range of any Pleistocene human, by the way.

Didn't you say this was an australopithecine when it came out a year ago?

Well, yes. My first post on the subject was titled, "Liang Bua: an australopithecine from Flores?" And I did present a rationale for believing that the skeleton was australopithecine rather than Homo. My point initially was that the combination of small body size and relatively small brain size was very simple to imagine as a descendant of an australopithecine, but very difficult to imagine in a descendant of Pleistocene Homo.

Some other features of the skeleton resemble Australopithecus. None of them individually is sufficient to label the skeleton as australopithecine, but together they are suggestive. For example, the pelvis is broad, with a very prominent anterior superior iliac spine. It's very similar to australopithecines like AL 288-1 (Lucy) or Sts 14.

But we don't know to what extent the breadth and morphology of australopithecine pelves are consequences of their phylogeny as opposed to allometric consequences of their small body sizes. In other words, LB1 might look australopithecine-like because it is small, instead of actually being an australopithecine.

The postcanine teeth are relatively large for a human, but they are far from australopithecine-like in size. Aside from their size, the first molars are the largest; just the opposite of the australopithecine condition. The roots of the premolars are completely uninformative, since both australopithecines and early Homo have the bifurcated roots found in both Liang Bua mandibles. So if this was an australopithecine-derived population, it had evolved considerably smaller teeth. Happily, this evolution of smaller teeth might also account for the gracile, Homo-like facial morphology.

OK, so it's an australopithecine, right?

Maybe. It would not only have to be an australopithecine; it might have to be a DWARF AUSTRALOPITHECINE.

Consider that the femur length of LB1 is just a millimeter shorter than Lucy and its body proportions are basically the same. Lucy (AL 288-1) is not only the most complete known australopithecine skeleton (barring STW 573, which is yet to be described), it has the smallest limbs. There are some individual bone fragments with smaller dimensions than Lucy's, but not very much smaller. At the same time, there are many larger specimens. Some of these, like the Sibilot radius KNM-ER 20419, are a whole lot larger.

Now at Liang Bua, LB1 is nearly the biggest specimen. Brown et al. (2004) do report another radius from an older part of the deposit with an estimated length of 210mm. Again assuming the same brachial index, this would correspond to a humerus of 269mm, around an inch longer than LB1.

But the other two adult long bones reported are the LB6 radius (157mm) and the LB8 tibia. At an estimated 216mm, this tibia is substantially shorter than the 235mm LB1 tibia. There is no comparably complete australopithecine femur, but if Lucy (missing around a third of the shaft) was around the same length as LB1, then LB8 would be shorter than any australopithecine.