Homo erectus

UPDATE (2008/4/15): The presentation was withdrawn from the meetings. I'm told that the information in the abstract is accurate, and that the withdrawal doesn't concern the science...

And no, the room wouldn't have been nearly big enough...

ORIGINAL POST:

Just flipping through the abstracts volume...this looks interesting:

New Homo erectus crania from Ethiopia

Simpson, S. W., Semaw S., Quade, J., Levin, N. E., Butler, R., Rogers, M. J., Holloway, R. L., Renne, P. R., Dupont-Nivet, G., Stout, D., Everett, M.

By the Early Pleistocene, members of the genus Homo were distributed throughout Africa and Asia, spreading into Europe by the Middle Pleistocene. As expected from such a widely distributed and long-lived species, variation in anatomical details is marked. This variation has fueled debate about the number of Early Pleistocene Homo species that existed and their relationship with modern humans. Here we report on two newly discovered hominid adult crania - one female and one male - dated to 1.5-1.7 My from the Busidima Formation, Gona Paleoanthropological Research Project area, Afar State, Ethiopia. An additional H. erectus cranial fragment (˜1.24My) is also reported. These crania are near contemporaries of specimens from Kenya, Tanzania, Republic of Georgia, and Southeast Asia and are attributable to Homo erectus. These fossils document a greater degree of brain size variation than previously known and allow a better accounting of the magnitude and character of cranial sexual dimorphism in size and shape.

New fossils, "greater degree of brain size variation," very cool. I hope they have a big enough room.

Lee Berger, Steve Churchill, Bonita De Klerk, and Rhonda L. Quinn have written a paper in PLoS ONE describing the skeletal remains of small-bodied humans recovered from two caves in the Rock Islands of Palau.

Full disclosure: I was the academic editor for this paper at PLoS.

OK, editor, what did you do for the paper?

The editor's role is to evaluate the manuscript's suitability for publication -- does it conform to the journal guidelines? Is it scientifically valid? Does it cite the existing literature appropriately? Do the observations support the claims made? A few manuscripts may be rejected immediately, because they fail to meet basic criteria of scientific value or readability.

Most manuscripts require the editor to seek out the opinions of additional experts in the process of peer review. PLoS ONE, unlike most journals, is committed to openness in the review and publication process (journal information).

In the case of this manuscript, I think it was a good fit to PLoS ONE because of the potential to report the new finds in an open access forum, where anyone can read the original research. It is not a monograph on the archaeology or skeletal biology of the sites, it is merely a preliminary report. However, unlike the kind of preliminary reports that we often see in journals like Nature or Science, in this case the journal provided more space for description and the potential to provide long lists of specimens. Many of those additional details were added to the manuscript in response to my editorial comments. If you read the reviewer reports for the paper (available at PLoS ONE), you can see that these additional details were essential to the scientific value of the manuscript, and that is why I required them. In addition, I suggested many other changes that would increase the value of the manuscript. The final version reflects the authors' responses to these changes: a preliminary report on the skeletal remains, in context, given the limitations presented by preservation and the need to conserve and prepare additional specimens.

Rex Dalton made the National Geographic Society's involvement with the research into a news story. Do you have any involvement with the media for a story?

Nothing at all. Sadly, most good manuscripts don't get any media attention.

Dalton emphasized the media attention to the find, particularly focusing on the role of the National Geographic Society. NGS produced a documentary about Berger's work on Palau (he is an NGS grantee).

In this case, National Geographic funded the work and apparently produced a documentary about it. Their production wasn't disclosed to the journal, and I view it as irrelevant to the scientific evaluation of the manuscript.

Paleoanthropologist Tim White is quoted in Dalton's story, saying that it appears that the "review process [was] driven by popular media." Since White was not involved in the review process of this paper, he obviously is just speculating.

I tend to give him the benefit of the doubt, since in this story it appears that Dalton was trying to play up any contrary quotes about the findings. Why else would he run otherwise-uninformed comments of the kind in the story?

I would tend instead to ask these questions: Does the Nature Publishing Group (NPG), in publishing Rex Dalton's piece, have a vested interest in the credibility of their own journals, in comparison to open access outlets like PLoS? Do NPG journals regularly receive manuscripts and publish them based on the associated media attention? Do they have an interest in pressuring grant agencies, like the NGS, into encouraging submission of manuscripts to NPG journals instead of alternate outlets? Does NPG have a well-established record of running stories questioning the value of open access publications?

In other words, consider the sources.

But aren't there other, normal-sized people on Palau at the same time?

In Elizabeth Culotta's article about the Palau specimens, she quotes archaeologist Scott Fitzpatrick:

But archaeologist Scott Fitzpatrick of North Carolina State University in Raleigh, who has worked in Palau for a decade, says he doesn't think the bone beds represent a true population. In a site only 4 kilometers from Berger's caves, he has excavated the burials of Palauans of similar age--and normal stature. That would seem to rule out isolation and island dwarfing, he says. "It would be very unusual to have a group of people living in close contact with a normal size population who evolved to be smaller." Instead, "the most parsimonious explanation is that they were Palauans with a genetic anomaly leading to small people who were buried in a clan or family plot."

Fitzpatrick has been excavating on Palau for a long time -- in comparison, Berger is a real Johnny-come-lately, who happened across his sites while on a vacation. So it's fair to say Fitzpatrick knows what he is talking about -- he has documented the earliest radiocarbon-dated cemetery on Palau, dating to approximately 3000 years ago.

The osteology of the skeletal remains from that cemetery, Chelochol ra Orrak, were reported by Fitzpatrick along with Greg Nelson, in 2006. That preliminary report is similar in form to this one, and they report measurements of the specimens. There are fewer specimens in that cemetery than are reported by Berger et al. from their caves, but the reported measurements are very comparable.

For example, Nelson and Fitzpatrick (2006:5) report a single femur complete enough to assess length; it has a maximum length of 392 mm and a maximum head diameter of 38.5 mm. This is smaller than the maximum femur length for the Khoisan sample reported by McHenry (1991), with an average length of 405.1 mm (S.D. 20.86), but longer than his (2) Akka Pygmy specimens (330 mm, S.D. 5.66). Berger and colleagues have no femora sufficiently preserved to estimate length, but their two femoral heads have diameters of 38.8 and 36.1 mm. These compare to Andamanese mean values of 37.3 mm and a San mean of 42.3 mm; McHenry's Khoisan sample has a mean of 37 mm.

Berger et al. report the proximal mediolateral diameter of two tibiae (63.1 and 53.1 mm); Nelson and Fitzpatrick (2006) report one specimen with a epiphyseal breadth of 64.8 mm and an estimated maximum length of 318 mm; the paired tibia has a length of 315 mm. By comparison, Flower (1885) reported a mean tibia length for Andamanese females of 321 mm.

In other words, the comparable remains published by Nelson and Fitzpatrick (2006) and Berger et al. (2008) appear to be consistent in size, and all within the range for small-bodied and pygmy human populations. One caveat is that the crania are as yet not directly comparable: Berger et al. cannot assess the crania from their caves because they remain to be prepared. Nelson and Fitzpatrick (2006) report two adult crania, the more complete of which (presumably male) is not a small skull, averaging larger in all preserved dimensions than Andamanese. Berger et al. (2008) report larger skeletal remains from areas that they believe are later in the chronology.

In any event, we don't need to posit two distinct populations living side-by-side to explain these remains. Working out the actual dynamics of this population over time is going to require a detailed understanding of several complicated stratigraphies, as well as detailed comparison of the skeletal remains. Whether they do in fact represent a single population must be determined by comparing the bones from these different sites with each other in a longer treatment. I hope that the analysts can get together to assess the sample as a whole.

Is this an extreme case of island dwarfing?

There's no question that the bones are small. However, I would not characterize them as extremely small compared to other small-bodied human populations. The paper provides a series of comparisons of linear dimensions of the Palauan remains to other small-bodied skeletal samples, including San, Onge, and Great Andamanese. In most cases, the Palauan remains average slightly smaller than these small-bodied samples, but within one standard deviation of the mean. A few adult specimens are substantially smaller, but it is not obvious that they are outside the range of living pygmy populations.

I should mention that is also true for the Liang Bua skeletal remains from Flores -- they are not obviously outside the range of living pygmy human populations -- despite the fact that none of the publications have reported comparisons with pygmy populations.

So, this would seem to be within the ordinary range of dwarfing in human pygmy populations. That raises the possibility the people may have been derived from such a pygmy population -- for instance, by colonization from the Philippines where small-bodied populations such as the Aeta and Batak are found today. There may be nothing exceptional about a relatively long-distance colonization of Palau by these peoples, who must after all have gotten to the Philippines!

I would say that the initial dispersal of the many small-bodied populations of mainland and island Southeast Asia is shaping up to be a very interesting anthropological topic. This population history has been partly obscured by the subsequent expansions of agriculturalists -- indeed, new colonizations like that of Palau may represent the effects of such interactions. Only traces of the ancient diversity remain, so it is difficult to reconstruct the ancestral population structure. But it is becoming increasingly clear that this was a cosmopolitan population, inhabiting several outlying island groups as well as areas of mainland Southeast Asia and the Sunda shelf.

In that context, small body size must be explained not merely as a consequence of inhabiting small islands, but more generally as an adaptive strategy for hunter-gatherers living in tropical ecologies. That is also true in the African context, so it should come as no surprise.

What do these small-bodied skeletons tell us about Homo floresiensis?

These ancient skeletons from Palau are not anything other than small-bodied modern humans. There is no question about that.

However, the bones share some interesting features with the Flores specimens. Here is what the authors say about the resemblances:

We feel that the most parsimonious, and most reasonable, interpretation of the human fossil assemblage from Palau is that they derive from a small-bodied population of H. sapiens (representing either rapid insular dwarfism or a small-bodied colonizing population), and that the primitive traits they express reflect possible pleiotropic or epigenetic correlates of developmental programs for small body size. In the comparisons drawn below, we note the shared possession of these traits with the Liang Bua fossils not to imply phylogenetic affinity or taxonomic identity, but rather to caution that some of the primitive features argued to reflect an ancestor-descendant relationship between H. erectus and H. floresiensis may also be homoplastically shared with modern humans from Palau, and thus that care must be exercised in interpreting their taxonomic and phylogenetic significance.

Also:

These results also suggest that the simple presence of additional small-bodied specimens with reduced chins (that cannot be shown to share all of the traits considered taxonomically significant in the Holotype Flores LB1) is insufficient to confirm the taxonomic validity of H. floresiensis.

I think that's pretty much the extent of what the Palau skeletal remains can say about the Flores sample. This is a reminder that the best comparative material is relatively local -- they should be compared to regionally similar populations, and populations of similar body size, rather than random people from European museum collections.

I think they also provide a cautionary note to the kind of trait-based typological classification that has been applied to the Flores specimens. Just because a sample lacks so-called "derived" features of "anatomically modern" populations, does not make it a member of a pre-human hominid population. "Anatomically modern" is itself a typological classification. Living people are variable and many express morphological features shared with fossil humans of various ages.

To be sure, the Flores LB1 specimen presents a large number of features that would be unusual in a living person, and the hypothesis that it represents a distinct human species is well-supported on this basis. On the other hand, it also has some features that are derived in recent human populations and others that are relatively common in small-bodied human populations in the region.

Nevertheless, the Palau remains do not provide any positive support to the idea that the Flores LB1 specimen is a microcephalic modern human. In particular, like other small-bodied human populations, none of the Palau skeletal remains indicate anything like the reduced brain size of LB1. There is nothing in this research concerning wrist morphology, humeral torsion, rotated premolars, or any of the rest of the odd features of LB1, nor is there any assessment of the paleopathology of the remains.

References:

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

Nelson GC, Fitzpatrick SM. 2006. Preliminary investigations of the Chelechol ra Orrak Cemetery, Republic of Palau: I, skeletal biology and paleopathology. Anthropol Sci 114:1-12.

Flower WH. 1885. Additional observations on the osteology of the natives of the Andaman Islands. J Roy Anthropol Inst G Br Irel 14:115-120.

I'm just doing some background reading about the body size of pygmies (for both obvious and not-so-obvious reasons) and I thought it worth making a note of this quote, from last year's paper by Andrea Migliano, Lucio Vinicius, and Marta Lahr:

Finally, the data presented here show that pygmy body size evolved through earlier cessation of growth, being therefore the result of changes in late rather than early stages of growth. This explains why brain growth, which is completed years before the onset of adolescence (28), is not affected in human pygmies (29). Therefore, if Homo floresiensis is a dwarfed form of Homo erectus, as proposed in ref. 29, the evolution of small body size on Flores could be understood as the life history consequence of ecological conditions in islands, such as increased extrinsic mortality rate and reduced resource availability (30); however, its small brain size and low encephalisation require the postulation of different adaptive mechanisms affecting earlier stages of development.

That's the concluding paragraph of what is a very nicely-done study of mortality and fertility in pygmy populations. It came out the during the acceleration press flurry in December, so I wasn't able to write it up at the time. It's certainly worth doing so, though.

The paper proposes that pygmy human populations are small because of a life history tradeoff. A "tradeoff" is the idea that a phenotypic change in either direction may have advantages and disadvantages, and selection may arrive at different optima in different populations.

In the case of life history and body size, both growing longer (and larger) and maturing faster (and smaller) have possible payoffs. Growing longer may have a fertility payoff, as larger size facilitates larger infants and shorter birth intervals. But maturing faster has a direct payoff of shortening the generation length -- all other things equal, an individual improves her fitness by reproducing younger.

So either younger or older maturation may enhance fitness, in some circumstances. Which will work in any given population depends on other factors -- in particular, the mortality pattern. If individuals have a high risk of death in early adulthood, delaying reproduction will be a bad strategy. In short, individuals should reproduce at 16 (or earlier) if there is a fair chance they will be dead by 25 or 30.

Naturally, everyone would rather live longer. But assuming that people can't control when they die, the only way to insure their fitness is to reproduce earlier.

This hypothesis, presented by Migliano et al., is about the proximate mechanism of evolution. The authors seem content to rely on traditional hypotheses about locomotion, nutrition, and thermoregulation to explain the ultimate causes of small body size -- "ultimate" in the sense that these may be the environmental causes of high mortality:

If our hypothesis is correct, the causes of the extremely high mortality rates among human pygmies need to be explained. It is here that the traditional hypotheses explaining the small body size of pygmies may prove useful. Although the challenges posed by thermoregulation, locomotion in dense forests, exposure to tropical diseases, and poor nutrition do not account for the characteristics of all pygmy populations, as pointed out by Diamond (5), they may jointly or partially contribute to the similarly high mortality rates in unrelated pygmy populations. We argue that the small body size of African and Asian pygmy populations evolved independently as a case of evolutionary convergence, resulting from a life history tradeoff between the fertility benefits of larger body size and the costs of late growth cessation under the circumstance of significant young and adult mortality.

The demographic data presented in the paper are sobering -- particularly the low survivorship values for pygmy populations across late childhood and early adulthood. However, I wonder how much of the early adult mortality in the pygmy demographic data is attributable to new pathogens. These are certainly important today, but they would not have been during most the time that small body size was being selected in these groups. On the other hand, ancient endemic pathogens and parasites also may contribute to those mortality numbers, and these might well have occurred at higher intensities in forest peoples across their histories.

References:

De Souza R. 2006. Body size and growth: The significance of chronic malnutrition among the Casiguran Agta. Ann Hum Biol 33:604-619. doi:10.1080/03014460601062759

Migliano AB, Vinicius L, Lahr MM. 2007. Life history trade-offs explain the evolution of human pygmies. Proc Nat Acad Sci USA 104:20216-20219. doi:10.1073/pnas.0708024105

It's that time of year again -- the time when those boring ``Year in Review'' magazines are on newsstands, and when pundits make fools of themselves predicting what will happen in the next year.

Well, I'm not too proud to join the fools, as I've shown the last two years. In 2006, I got five predictions right out of ten. Not bad for my first outing, but you'll see that last year's predictions fared even better:

• 10. Sahelanthropus postcrania will be published. I'm frankly shocked that this didn't happen. I don't doubt the rumors, but I'm starting to wonder whether this story is more interesting than it looks....
• 9. Two words: Holocene evolution. OK, this was a little unfair, considering that my work was an important part of making this prediction come true. Still, Discover made ``recent human evolution'' one of its top 100 science stories of the year, even before our December paper came out -- mainly on the strength of the paper by Scott Williamson and colleagues from earlier this year. And "Human genetic variation" was Science's "Breakthrough of the Year" -- most of that variation representing recent 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. Puzzling, isn't it? But then, considering the trouble with Neandertal contamination reported in August, maybe we're better off leaving the early Upper Paleolithic alone for a while.
• 7. The mitochondrial history of human dispersals will become more and more detailed, but no paper will test against other loci. D'oh! Reading this one a year later, it's pretty obvious that I should have included Y chromosome in this one, since those two get compared all the time! Proofread, Hawks!
• 6. Another (yes, another) paper about the chimpanzee-human divergence will peg it between 5 and 7 million years ago. Will they never tire of these? Hobolth et al. (2007, PLoS Genet 3:e7) pegged the divergence at 4.1 million years. That's too recent to fit my prediction. Instead, I have to turn to Ebersberger et al. (2007, Mol Biol Evol 24:2276), who placed the divergence at 5.7 million years ago. Both estimates are too recent for Sahelanthropus, which the geneticists have started to figure out....
• 5. Three papers with new Ethiopian fossils. The last few years, one annual Ethiopian find seemed to be predictable enough. So I figured, why not three? We got a not-nearly-noted-enough paper this summer by Gen Suwa and colleagues descringing the Konso Homo erectus remains. Then, Suwa brought us Chororapithecus -- hey, I didn't say "hominid!" That's two. But despite the long-ago announcement of the Woranso-Mille skeleton, its appearance in a meetings abstract and a mid-summer press release about further Mille fossils, all we got from the peer review system is a lousy faunal list. Well, the faunal list does include the hominids. Should it count as a "paper with new Ethiopian fossils?" I'll say yes -- hey, unlike Aramis, at least the Mille fossils are new!
• 4. Another early Upper Paleolithic specimen will emerge from a museum collection. The only bizarre thing about this one was the location: South Africa. Hoffmeyr may not be that convincing as a European early Upper Paleolithic skull, but it was sure sold that way. Weird.
• 3. A big year for Miocene apes, which will look increasingly important in the story of human brain evolution. No brains, but it sure was a big year for Miocene apes, with two significant East African discoveries claiming to push back the timeline of African ape divergence.
• 2. Maturation rate in early Homo becomes a dead issue, because of the variation in dental and skeletal maturation in living people. Wishful thinking. Still, did Tanya Smith (2007) breathe new life into perikymata? Let's just say that unresolved questions remain.
• 1. The year will end without a single new hominid species having been named. This one was like dodging a bullet, since new species riffle out of paleoanthropologists' minds all the time. From 2001 to 2006, there were six (six!). In 2007, none.
• BONUS: A dramatic development in the problem of pre-2.0-million-year-old Homo. Rats.

OK, that's seven out of ten. It's beyond belief that I did better in the top five than the bottom five -- I picked those because they were far out there. I mean, really -- a new Upper Paleolithic specimen from a museum collection? After Muierii, that's like calling lightning to strike twice. But there it is, and in January, no less.

I'm clearly going to have to pick stranger predictions this year. And I'll have to be careful about that "dramatic development" line -- I mean, it's appropriately Delphic, but what is it supposed to mean, really? I wonder whether "operatic development" might be better.

And do I dare call down my non-lightning strike for a third year? It's ruining my percentage! It's starting to reek of desperation -- I mean, it starts to look like the stopped watch effect even if it happens.

Oh, well. I mean, those are just the risks of predictions, right? Suppose in the preseason I had picked Kansas to win the Orange Bowl!

• 10. A dramatic development in the Sahelanthropus story.
• 9. Both major-party candidates for the 2008 U.S. Presidential election will accept evolution.
• 8. This year's featured piece of anatomy: the femur.
• 7. No new hobbits, at least, not from Flores.
• 6. An incisive example of introgression in East Asia.
• 5. A viral insertion in the human genome will tell us about a disease of the australopithecines.
• 4. Another language gene joins FoxP2. No word on whether Neandertals have the human version.
• 3. Homo habilis: an endangered species?
• 2. This year, something new from three A's: A. afarensis. A. africanus. Atapuerca.
• 1. Oh, and one more A. Ardipithecus.
• BONUS: A big, big year for Neandertals. I mean, besides the election.

There you have it. I'm not sure which of these is the riskiest, but I'm sure they're more out on a limb than last year!

John Kappelman was kind enough to send me a preprint of the report on the new Turkish Middle Pleistocene specimen. The specimen consists of frontal and parietal fragments from a single skull, and comes from a travertine quarry outside the town of Kacabaş, western Turkey. The skull was found in the course of quarrying activities, and may be the first hominid specimen to have been "reduced to a standard rough-cut tile thickness of about 35 mm."

The paper reports a date estimate of 490 ± 0.05 to 510 ± 0.05 kyr, based on thermoluminescence of travertine. The paper contains some pictures of the specimen, description of its anatomy, and evidence for the presence of tuberculosis.

I review these elements below.

Is it Homo erectus?

At 500,000 years old, the specimen is just the right age to be in the middle of a taxonomic mess. Many agree that the roughly contemporary Zhoukoudian sample should be referred to H. erectus. But there are other alternatives. Some people contribute a number of penecontemporary samples to "Homo heidelbergensis", or alternatively to "archaic Homo sapiens". Among these, the Bodo skull is earlier at 600,000 years old, and arguably so is the Sima de los Huesos sample (Bischoff et al. 2003, 2007). So in terms of time, this specimen might qualify for any number of names.

Kappelman and colleagues include this paragraph, which I think is an admirable discussion of the problem:

The most conservative approach is to provisionally attribute the Kocabaş specimen to H. erectus but the combination of features in the Kocabas hominin highlights the ongoing controversy about whether Pleistocene hominins attributed to the genus Homo represent a polytypic species with an Old World range (Asfaw et al., 2002) or instead provide evidence for multiple lineages with more limited temporal and geographical distributions (Schwartz, 2004). A single specimen clearly cannot answer this question, and it seems likely that the ongoing controversy will extend past the sample traditionally referred to H. erectus and on into that referred to H. heidelbergensis.

The problem of taxonomy is confounded with geography. Ultimately, whether this specimen looks like Homo erectus depends on whether it looks more like contemporary East Asians (e.g., Zhoukoudian, or possibly Sambungmachan), or whether instead it looks like contemporary Europeans or Africans (e.g., Bodo).

But this is to some extent complicated by variability within the western sample. Consider, the African Middle Pleistocene includes large skulls like Bodo and Kabwe but also small ones like Ndutu and Salé. Europe has Petralona, but also Steinheim. With this specimen, only the top of the skullcap is preserved, so the comparisons will be heavily dependent on size: browridge size, bone thickness and robusticity, and measured frontal breadth and length. The essential question is whether it is more like the contemporary Asian or African/European samples.

The frontal fragment includes the lateral two-thirds of the supraorbital torus, which is relatively uniform in thickness to its lateralmost extent. The browridge is very thick -- nearly as thick as Kabwe, and substantially thicker than any of the Zhoukoudian specimens. The frontal squama slopes posteriorly -- with less of a frontal boss than most of the Chinese specimens. This makes the supratoral sulcus relatively slight.

The minimum frontal breadth as reconstructed (by mirroring) is fairly narrow -- it is comparable to OH 9 or Sangiran 17. Kappelman and colleagues give a nice graph of this dimension compared to estimated cranial breadth and supraorbital torus thickness. With a vault thickness of 10 mm at bregma, the skull is relatively thick but inside the ranges of both contemporary Asian and African samples.

So, is the Kacabaş skull more like Asians or Africans? Metrically, Kappelman et al. show that the skull is a lot like the Zhoukoudian L3 skull, OH 9, and Sangiran 17. I could see more comparisons (and I am a bit curious about the way the orbital breadth compares to the other samples) but Kappelman et al. have done a nice job of presenting the skull and their description of the supraorbital region is quite detailed. The overall morphology of the specimen and its size are very comparable to Zhoukoudian, so it is fair to refer the skull to Homo erectus.

Compared to most of the Middle Pleistocene Africans and Europeans it is small -- but then, the sample did not include some very small crania like Ndutu or Salé.

On the other hand, there are those who would assign these small African crania to H. erectus. In other words, both taxonomy and geography are confounded by size!

In terms of this specimen, the morphology is more similar to Zhoukoudian, but it is not so very different from Kabwe or Bodo, other than its smaller size. If we approach the skull with the hypothesis that it is part of a West Asian population intermediate between Middle Pleistocene East Asians, Africans, and Europeans, I don't see anything to disprove that hypothesis.

Tuberculosis

I think the absolute coolest part of the paper is its demonstration of cranial lesions attributable to tuberculosis. They provide microscopic views of the lesions and detail why they are consistent with the disease. I'm no paleopathologist, but it looks like a solid case to me.

The discussion of the paper considers why the specimen might have faced an unusual risk of TB, focusing on the possibility of vitamin D deficiency. The authors suggest that a dark-skinned, presumably African population of H. erectus may have moved north into temperate latitudes, where lower UV radiation levels caused vitamin D deficiency. In theory, low vitamin D levels may have an immunosuppressive effect, possibly increasing the risk or severity of TB. The paper discusses the increased incidence of TB in dark-skinned immigrants to Europe as support for this hypothesis.

Personally, I think this section was unnecessary. The fact stands on its own: the individual suffered from TB, by no means an uncommon disease in historic human populations. There has been no shortage of light-skinned TB sufferers. While it is possible that dark-skinned people have an higher intrinsic risk, there are other factors such as access to health care that may contribute to this risk as well. Most important, there is really no reason to suppose that a 500,000-year-old Turkish hominid need have been dark-skinned. Indeed, the presence of at least one light pigmentation variant in Neandertals plainly shows that we can assume nothing about earlier hominids.

The idea that tuberculosis is a very old hominid disease has gained currency in the last few years. Older molecular analyses made this hypothesis seem unlikely -- most pathogenic strains of Mycobacterium tuberculosis stem from a common ancestor sometime during the last 20,000-35,000 years. This passage from Gutierrez et al. (2005) describes the history:

Members of the Mycobacterium tuberculosis complex (MTBC), the agents responsible for tuberculosis, are among the most successful human pathogens. The MTBC as defined here comprises the so-called M. tuberculosis, M. bovis, M. microti, M. africanum, M. pinnipedii, and M. caprae species. Although the members of the MTBC display different phenotypic characteristics and mammalian host ranges, they represent one of the most extreme examples of genetic homogeneity, with about 0.01%-0.03% synonymous nucleotide variation and no significant trace of genetic exchange among them. Therefore, it is believed that the members of the MTBC are the clonal progeny of a single successful ancestor, resulting from a recent evolutionary bottleneck that occurred 20,000 to 35,000 y ago.

However, Gutierrez and colleagues studied several strains of "smooth" bacilli from East Africans, finding that these were distant relatives of the MTBC strains, with a divergence around 3 million years ago. The usual hypothesis had been that TB was a zoonotic pathogen, possibly from cattle, which entered humans recently. But the presence of TB-related bacilli in humans suggests instead that TB is an old hominid pathogen, and that a particularly virulent strain may have spread recently through the human population, spreading from people into cattle and other domesticates. That may seem surprising (how exactly did it spread from humans into seals, one may ask?), but all of the identified animal forms are pathogenic in humans under some circumstances, and the majority of human cases come from three different bacterial species -- M. tuberculosis, M. bovis, and M. africanum.

The hypothesis of an old hominid-specific strain of TB has been challenged (Smith 2006), mainly because working out divergence times and relationships among reticulating bacterial strains is complicated. Gutierrez and colleagues defended their hypothesis in a reply, but this problem clearly is not yet settled. Actually finding the disease in such an ancient specimen pretty much brings closure to the initial question of whether TB is old, but doesn't yet tell us whether the particular phylogenetic scenario really happened.

I think tuberculosis is especially likely to be an old human pathogen, because it has a number of characteristics that would facilitate its survival in small-scale hunter-gatherer societies. Infections last a long time and they are symptomatic for a large proportion of that time. The primary mode of infection is respiratory, and the bacteria are easily spread. Present-day tuberculosis is predominantly a crowd disease -- spreading quickly in crowded cities. But if Gutierrez and colleagues are correct about the smooth bacilli being an ancestral form of the bacterium, this earlier form may not have been as dependent on population density for its spread.

Other pathogens with these characteristics are also candidates for old Pleistocene human diseases. My favorite at the moment is pertussis (whooping cough), which Diavatopoulos and colleagues (2005) showed may have diverged from an old, human-specific strain of Bordetella bronchiseptica. It has nothing to do with this specimen, but the common thread of diseases suitable for spread in Pleistocene humans may give us some things to look for in terms of ancient genetic adaptations to disease.

References:

Bischoff JL, Shamp DD, Aramburu A, Arsuaga JL, Carbonell E, Bermudez de Castro JM. 2003. The Sima de los Huesos hominids date to beyond U/Th equilibrium (>350 kyr) and perhaps to 400-500 kyr: new radiometric dates. J Archaeol Sci 30:275-280. doi:10.1006/jasc.2002.0834

Bischoff JL, Williams RW, Rosenbauer RJ, Aramburu A, Arsuaga JL, Garcia N, Cuenca-Bescós G. 2007. High-resolution U-series dates from the Sima de los Huesos hominids yields 600 kyrs: implications for the evolution of the early Neanderthal lineage. J Archaeol Sci 34:763-770. doi:10.1016/j.jas.2006.08.003

Diavatopoulos DA, Cummings CA, Schouls LM, Brinig MM, Relman DA, Mooi FR. 2005. Bordetella pertussis, the Causative Agent of Whooping Cough, Evolved from a Distinct, Human-Associated Lineage of B. bronchiseptica. PLoS Pathog 1: e45. doi:10.1371/journal.ppat.0010045

Kappelman J, Alçiçek MC, Kazancı N, Schultz M, Özkul M, Şen Ş. 2007. First Homo erectus from Turkey and implications for migrations into temperate Eurasia. Am J Phys Anthropol (in press) doi:10.1002/ajpa.20739

Gutierrez MC, Brisse S, Brosch R, Fabre M, Omaïs B, Marmiesse M, Supply P, Vincent V. 2005. Ancient Origin and Gene Mosaicism of the Progenitor of Mycobacterium tuberculosis. PLoS Pathogens 1:e5. doi:10.1371/journal.ppat.0010005

Smith NH. 2006. A re-evaluation of M. prototuberculosis. PLoS Pathogens 2:e98. doi:10.1371/journal.ppat.0020098

Based on a press release from John Kappelman, this is pretty interesting:

Although most scientists believe tuberculosis emerged only several thousand years ago, new research from The University of Texas at Austin reveals the most ancient evidence of the disease has been found in a 500,000-year-old human fossil from Turkey.

...

The researchers identified this specimen of Homo erectus as a young male based on aspects of the cranial suture closure, sinus formation and the size of the ridges of the brow. They also found a series of small lesions etched into the bone of the cranium whose shape and location are characteristic of the Leptomeningitis tuberculosa, a form of tuberculosis that attacks the meninges of the brain.

I'll have quite a bit more on this when the paper becomes available (in AJPA); most tuberculosis strains in living people originated within the last 35,000 years, but a couple of years ago it was suggested that these stem from a much older bacillus species in hominids.

There's a lot of fluff in the press release about skin pigmentation, vitamin D and depressed immune systems. It's just fluff -- we don't know what color these hominids were, and there are plenty of light-skinned people in the world with tuberculosis. I don't see why finding tuberculosis roughly 500,000 years earlier than ever before isn't interesting enough!

I missed this in Science last week:

As Indonesia's "king of paleoanthropology," Teuku Jacob ruled over a vital collection of hominid fossils....On 17 October, at the age of 76, the professor emeritus and former rector of Gadjah Mada University in Yogyakarta died of liver problems.

Jacob studied fossil hominids under famed paleontologist G. H. R. von Koenigswald, then found and was curator of many important specimens, particularly of Homo erectus. He was a key figure in the Indonesian independence movement, making nationalist radio broadcasts after World War II during the country's 4-year fight for independence from the Dutch.

(via Palanthsci)

Science's Michael Balter reviews the recent Cambridge conference on "Global Origins and Development of Seafaring". The article begins with a suggestion that the first inhabitants of Flores floated there on vegetation rafts by accident -- channel crossings being otherwise impossible for Lower Paleolithic hominids:

"Flores is the exception that proves the rule in terms of when seafaring really began," says Atholl Anderson, a prehistorian at the Australian National University (ANU) in Canberra. [Jon] Erlandson agrees: "Otherwise, H. erectus should have colonized Australia and the surrounding islands."

It mostly seems to be about Wallacea, Sahul, and Melanesia.

The article features a disagreement concerning the colonization of these regions. Some think that island colonizations started before seafaring technology was quite ready for prime time. In that scenario, the initial habitation of parts of Wallacea along with Australia and New Guinea was a sort of accidental chain of small founding events, possibly as early as 60,000 years ago or earlier.

The opposing viewpoint holds that these islands (and continent) were inhabited relatively late and quite suddenly, by people who had developed an advanced seafaring skill. Balter quotes University of Utah archaeologist Jim O'Connell to good effect:

In the last few years, O'Connell, together with archaeologist Jim Allen of La Trobe University in Bundoora, Australia, has argued from a detailed analysis of radiocarbon dates for a "short chronology" that puts the occupation of Sahul no earlier than about 50,000 years ago. He pointed out that by 45,000 years ago modern humans had colonized a number of islands between Sunda and Sahul, called the Wallacean Archipelago, which stretched at least 1000 kilometers even when sea levels were at their lowest. Reaching many of these islands required sea crossings of 30 to 70 kilometers, sometimes against the currents. Most animals from Asia never achieved these crossings, implying that humans must have used technology to do it. That 5000 years of colonization, O'Connell said, represented a relatively short "archaeological instant."

O'Connell also argues that some of the island sites before 40,000 years ago include deep-water fish, suggesting relatively advanced ocean-going boats at that time -- something I noted in a post on the East Timor site, Jerimalai.

Which side is right? I don't know, but it's good that they are formulating hypotheses this way, involving the technological trajectory, genetic constraints on small populations, and various ecological parameters.

References:

Balter M. 2007. In search of the world's most ancient mariners. Science 318:388-389. doi:10.1126/science.318.5849.388

From p. 48 of P. V. Tobias, Dart, Taung, and the Missing Link, Witwatersrand University Press, Johannesburg:

All fossil hominid discoveries up to 1925 had bearings on the evolution of established and unequivocal hominids; they had illustrated teh changes that had occurred along the way from incontrovertible earlier hominids (like Homo erectus of Java) to later hominids (like Neandertal and Cro-Magnon men). Australopithecus imported an entirely new dimension into the picture: it opened a window, not on to the evolution of established hominids, but on to human emergence -- the very roots of the family of hominids from non-hominid predecessors. It posed such questions as these: What are the features that distinguish hominids from other primate families? Which of the hallmarks of mankind were the first to appear and when did they arise? How were the different traits that characterize the human family related to one another? -- such traits as uprightness and bipedal locomotion, reduced canines, brain enlargement and structural re-arrangement, the human grasping and manipulating hand, human communication, human material culture including tool-making activities?

These were the kinds of questions which Dart's discovery and what he made of it compelled upon the world of science. Countless new areas of investigation were opened up -- even if the motivation was the felt need to repudiate Dart's claims! Dart's plunge into ancestral waters took the twentieth century to the very fountainhead where one could plumb the depths of human genesis.

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:

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.

In case you're following the debate about Homo habilis limb proportions, there's a new contribution by Martin Haeusler and Henry McHenry in the JHE holding pen. They examined the partial KNM-ER 3735 skeleton.

KNM-ER 3735 is often assigned to Homo habilis, but it's not exactly an easy diagnosis. There are a few pieces of the skull preserving anatomy, including the cheek, frontal and temporal. Here's what Bernard Wood (1991) had to say about the skeleton:

The form of the mandibular fossa and malar region virtually preclude this specimen from being attributed to A. boisei. Its general affinities are with Homo. 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.

Provisional taxonomic assessment: Homo sp. indet.

Well, that's not exactly a rousing endorsment. You can see the problem --- and it's a common tale for hominid fossils. It has a smaller brain than early H. erectus (that would be the "frontal looks like KNM-ER 1813 bit). But its cranial bones are thick. The most complete of the bones in the skeleton is a radius, but it's not complete. The best bone for estimating joint surface area is the sacrum; a femur shaft is there, but it falls short of the midshaft length.

And there's a problem: the radius seems pretty big, but the sacrum is little. If it were a human, the radius looks like it came from a body twice the size of the sacrum. There's something going on here. Previous work has assumed that the sacrum is more likely reflective of the size of the body, and the radius is therefore big compared to a small body mass. Maybe that means more climbing, leading to a greater role in weight support for the arms. Or maybe it means a retention of more apelike proportions.

This is a frustrating literature to follow, because pretty much every other early specimen except Lucy (AL 288-1) and the Nariokotome skeleton (KNM-WT 15000) present exactly the same problem. You can't estimate limb sizes very accurately from small pieces of bone. And you can't estimate proportions accurately at all without estimates of size. Plus, it's not clear that you can interpret limb proportions without a decent estimate of body mass. Two years ago, there was a huge go-around about the limb proportions of OH 62. Like KNM-ER 3735, it looks to have a relatively large arm compared to its body. Or maybe the legs are short. Or maybe the estimates are bad. You get the picture. So everybody has a different clever statistical transformation to try to make these fossils comparable to each other. I have no argument with any of the work; but it seems like the error involved in these assessments of proportions is pretty large relative to the information content of the bones.

Here's some of the conclusion from Haeusler and McHenry:

Our analyses suggest that the idea that KNM-ER 3735 had more primitive body proportions than A.L. 288-1 (e.g., Leakey et al., 1989) needs to be refined. We found a unique but distinct mosaic of modern and ape-like limb proportions in the two early hominid species. H. habilis shares a gracile humerus and radius and a small base of the hand phalanges with the earlier A.L. 288-1 and modern humans. In addition, other characteristics, including the relatively small size of the sacrum and a robust midshaft of the phalanges, are common to both early hominids and extant great apes. Surprisingly, however, those upper limb proportions that differ between the two fossil species, such as a robust scapula, a long radial neck, and a long forearm, are all more ape-like in H. habilis.

In KNM-ER 3735, the shoulder muscles that originate on the scapula (trapezius, deltoid, supraspinatus, and infraspinatus) as well as the biceps brachii were, therefore, probably not only more powerful than in modern humans, but also stronger than in A.L. 288-1. On the other hand, the extraordinarily short lever arm of A.L. 288-1's biceps muscle, the minute elbow size, and the small radial head may indicate a weaker arboreal component in its behavioral repertoire than in H. habilis. However, in the absence of modern correlates, caution is needed with respect to possible behavioral implications of the different forearm proportions in the two species.

They also note the Homo-like anatomy of the femur shaft, including a marked pilaster.

Seth Dobson (2005) claimed that that the sacrum of STW 431 (A. africanus) is also small -- it certainly yields a small mass estimate compared to other elements of the skeleton. Heck, all of the early hominid sacra yield small mass estimates. Well, you can see it's confusing.

References:

Haeusler M, McHenry HM. 2007. Evolutionary reversals of limb proportions in early hominids? Evidence from KNM-ER 3735. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.06.001

Dobson SD. 2005. Are the differences between Stw 431 (Australopithecus africanus) and A.L. 288-1 (A. afarensis) significant? J Hum Evol 49:143-154. doi:10.1016/j.jhevol.2005.04.001

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've read through the new paper by Martinón-Torres et al., on Eurasian continuity in the Middle Pleistocene. They've put out an interesting hypothesis, with some support from previous work, but ultimately I think their methods are too weak to test it.

The press coverage of the paper so far (e.g., this AP article) has been a little confusing, because it misses this point: this paper is not about modern human origins, it's about much earlier evolutionary relationships. National Geographic News resorts to the always-safe:

The finding suggests that the hominid family tree could be much more complex than previously thought.

Ah, so that's what it means! More complex than previously thought! Why isn't there ever a story that makes things simpler than previously thought? I mean, isn't it a sign of a failed science if you have to add complexity to your hypothesis every time you make a new observation? It's like Ptolemaic paleoanthropology!

Anyway, enough of that rant. Let's look at what the paper really says, which is much more interesting than the press! Here's the abstract:

A common assumption in the evolutionary scenario of the first Eurasian hominin populations is that they all had an African origin. This assumption also seems to apply for the Early and Middle Pleistocene populations, whose presence in Europe has been largely explained by a discontinuous flow of African emigrant waves. Only recently, some voices have speculated about the possibility of Asia being a center of speciation. However, no hard evidence has been presented to support this hypothesis. We present evidence from the most complete and up-to-date analysis of the hominin permanent dentition from Africa and Eurasia. The results show important morphological differences between the hominins found in both continents during the Pleistocene, suggesting that their evolutionary courses were relatively independent. We propose that the genetic impact of Asia in the colonization of Europe during the Early and Middle Pleistocene was stronger than that of Africa.

OK, so this is about the initial colonization of Europe and the subsequent evolutionary trends in Europe, Asia, and Africa. The observation is that European teeth show a continued similarity to Asians during the Middle Pleistocene, and there is no evidence that European teeth evolved in the direction of Africans during that time period.

Why is that interesting? Two reasons:

1. The hypothesis directly conflicts with the idea that Middle Pleistocene Europeans were linked to Africans. A large number of anthropologists have been pushing the European-African link, under the old hypothesis that these ancient people belonged to a species that was distinct from East Asians. The European-African clade in this hypothesis is often called Homo heidelbergensis; the Asian clade remains Homo erectus.

2. The hypothesis also seems to conflict with genetic data, which suggest that the relationship of European and African hominids is more recent than the early Middle Pleistocene. In particular, the genetic divergence time between human and Neandertal genomes appears to date to more recently than 700,000 years ago (Green et al. 2006, Noonan et al. 2006), which means that the population divergence must be still more recent. Also, Alan Templeton's papers (e.g., 2002, 2006) claim evidence for migrations from Africa into Europe and Asia during the Middle Pleistocene. Those claims are consistent with the Neandertal genome data, as far as we know it, and they suggest gene flow from Africa into Eurasia.

So, the authors ought to deal with these issues. They do so in their discussion, which in this short paper is one long paragraph. I'm quoting it here in full to comment on the details:

If the population of the Eurasian continent during the Early and
Middle Pleistocene was mainly the result of several out-of-Africa incursions, we should have found African influences in the morphology of the Eurasian populations. However, the continuity of the "Eurasian dental pattern" from the Early Pleistocene until the appearance of the Upper Pleistocene Neanderthals suggests that the evolutionary courses of the Eurasian and the African continents were relatively independent for a long period and that the impact of Asia in the colonization of Europe was stronger than that of Africa.

That is the conclusion of the analysis, in brief. The strength of the conclusion depends on the power of the analytical methods to detect gene flow based on morphological similarities. More on that below.

This finding does not necessarily imply that there was not genetic flow between continents, but emphasizes that this interchange could have been both ways (25, 26).

This seems a little misleading. They have no particular evidence of gene flow from Eurasia to Africa (that would be the "both ways"). Nor do they have evidence in their analysis of gene flow from Africa to Eurasia, after the initial colonization. So they don't have any evidence for gene flow at all. So the finding doesn't emphasize anything about gene flow, other than that the teeth don't show obvious evidence for it.

Around 1 Ma, hominins appear to have dispersed into temperate latitudes as far north as 40 - 45° N (27-29), not only from Africa, but also within Eurasia (29 - 31). These populations were probably descendants of an ancient out-of-Africa exodus, rather than a later one at the end of the Early Pleistocene (30).

This is an important assertion. Other workers have emphasized the similarities of some African fossils to East Asian fossils (mainly from Java, plus Gongwangling in China) in the late Early Pleistocene. That has always been the case with OH 9, and it influenced the description of the Daka and Buia crania as well. The question is how early Asian populations became morphologically distinctive. Here, the authors argue that it was very early, without substantial signs for later interaction, which in the context of the cranial comparisons is now an extreme claim.

In addition, a recent study on the European Lower Pleistocene hominin populations has revealed a possible Eurasian origin for these groups (32).

This refers to the description of the ATD6-96 mandible, which contains an earlier assertion about Asian-European connections. I return to this below.

Furthermore, it has been pointed out that during the Middle Pleistocene there was hardly any faunal exchange bet ween East Africa and the Levant (33) and that the desert between the Sahara and Arabia was an important barrier at that time (26), therefore contributing to the isolation of both continents.

This is an important argument in support of their hypothesis. If movement between Africa and Eurasia was difficult during this time span, that reinforces their claim, and makes it less plausible that there were large-scale dispersals out of Africa during the Middle Pleistocene. That leaves us with a mention of a major exception to their proposed pattern: the evolution of humans in the Late Pleistocene:

With the exception of the SAP [i.e., H. sapiens] out-of Africa dispersion based mainly on genetic data (2), the history of human populations in Eurasia may not have been the result of a few high-impact replacement waves of dispersals from Africa, but a much more complex puzzle of dispersals and contacts among populations within and outside continents. In the light of these results, we propose that Asia has played an important role in the colonization of Europe, and that future studies on this issue are obliged to pay serious attention to the "unknown" continent (Martinón-Torres et al. 2007:3).

The citation of the ATD6-96 mandible leads us to a passage from that earlier paper (Carbonell et al. 2005), which also describes the hypothesis that the founding population of Europe was Asian. Remember that this research group calls the Gran Dolina sample, Homo antecessor, and they initially had written that this species probably colonized Europe from Africa in the late Lower Pleistocene. Here's the relevant paragraph from the cited paper (Carbonell et al. 2005):

The differences in dimensions and robustness between the TD6 mandibles and the East and North African mandibles cast doubt on the African origin of H. antecessor. In contrast, our comparative analysis suggests looking toward the Asian continent. In this respect, it is relevant to mention some data that remained unpublished in 1997, when the new species was named (10), and that are relevant to this discussion. The partial cranium Nanjing I, recovered in 1993-1994 from the Hulu Cave (Tangshan Hill, eastern central China), shows clear modern midfacial traits similar to those observed in the specimen ATD6-69 (19). Wang and Tobias (20) also found similarities between Nanjing I and the Zhoukoudian hominins. Geochronological dates, combined with ecological and paleoclimatic evidence, indicate that the Nanjing skull is ~600 thousand years old (21). Furthermore, the Locality 1 levels at Zhoukoudian, which yielded most hominin specimens, are now considered at least 800 thousand years old (22). Thus, these Chinese hominins may be contemporaneous with or slightly younger than the TD6 hominins. If the Gran Dolina and Chinese populations are phylogenetically related, they should share a common ancestor that also had a modern midfacial pattern and a gracile mandible. In the cranium, this hypothetical common ancestor would have had a low and flat temporal squama, and an unfused styloid process. These traits would have been retained in the Asian hominins but lost in the TD6 hominins, who exhibit a fused styloid process, a convex temporal squama, and probably a significant increase in cranial capacity (19). The Ceprano calvaria (Italy), which has been tentatively assigned to H. antecessor (23), exhibits a convex temporal squama and a cranial capacity of about 1,057 ml (24). Interestingly, TD6 and Zhoukoudian are the only hominins that have a zygomaxillary tubercle before the Upper Pleistocene (19).

So that provides cranial and mandibular evidence of an Asia-Europe connection, supporting the dental evidence provided in the current paper. Still, that evidence is from the initial founding of Europe in the Early Pleistocene and doesn't necessarily apply to the trends during the Middle Pleistocene.

After working through the data supplements for the paper, I think that the analysis is much weaker in statistical power than it could be. In their analysis, they disregard much of the variation within these ancient samples and focus on the differences between samples according to their scoring methods. This may reveal the broad relationships among samples -- if we disregard the possibility of selected parallelisms -- but it does not say anything about the possibility of gene flow among the samples.

Indeed, the result of their analysis (a dendrogram, or branching tree) is quite incapable of showing genetic exchanges at all. It can only show branching events, which means that the result will show either an exclusive relationship between Europeans and Asians, or an exclusive relationship between Europeans and Africans, but never a mixed relationship.

The only result in the paper that indicates a European-Asian relationship is from their cladistic analysis of a subset of the data. And it isn't especially strong evidence, since the Middle Pleistocene Africans are limited to the relatively early sites of Rabat and Tighenif (Ternifine). Granted, the later sample is also small in number, but this isn't really a test of relationships; it's more of a suggestion.

The phenogram inexplicably omits Middle and Lower Pleistocene Africans entirely, and considers only australopithecines and habilines as the African sample.

So, at the moment I consider this to be a very interesting hypothesis in search of a good test. There is no test of gene flow here, just an assertion. Yet, the cranial comparisons give the assertion some plausibility -- and remember, another idea out there is the hypothesis that early Homo originated in Asia and migrated to Africa later.

I think that these topics together constitute the important problem in early human relationships right now, so I'll be writing some more about them. There are many additional interesting facts to consider...

References:

Martinón-Torres M, Bermúdez de Castro JM, Gómez-Robles A, Arsuaga JL, Carbonell E, Lordkipanidze D, Manzi, G, Margvelashvili A. 2007. Dental evidence on the hominin dispersals during the Pleistocene. Proc Nat Acad Sci USA (early) doi:10.1073/pnas.0706152104

Stringer C. 2002. Modern human origins: progress and prospects. Phil Trans Roy Soc Lond B 357:563-579. doi:10.1098/rstb.2001.1057

Rightmire GP. 1998. Human evolution in the Middle Pleistocene: the role of Homo heidelbergensis. Evol Anthropol 6:218-227. doi:10.1002/(SICI)1520-6505(1998)6:6<218::AID-EVAN4>3.0.CO;2-6

Carbonell E and 19 others. 2005. An Early Pleistocene hominin mandible from Atapuerca-TD6, Spain. Proc Nat Acad Sci USA 102:5674-5678. doi:10.1073/pnas.0501841102

Bruner E, Manzi G. 2005. CT-based description and phyletic evaluation of the archaic human calvarium from Ceprano, Italy. Anat Rec A 285A:643-657. doi:10.1002/ar.a.20205

I always get the most interesting mail right after any kind of news interview. Here's the best from last week:

I am wondering, after reading your comments in a news article about the origins of mankind, what makes anyone in your field of study believe that mankind originated on this planet? No one to date has, to the best of my knowledge, made any verifiable direct links to homo erectus, or any other of the monkeys from several million years ago. In fact, Homo Sapiens can only be traced back a few hundred thousand years before the link disappears with no further direct trace.

I would like to submit to you that Earth has been invaded five (5) times by humanoids from different civilizations. Evidence from these invasions is evident if you would care to look outside your own little nook. Wake up young man, and study what is in front of your eyes. The evidence is in South America, Northern Africa (Sahara region), China/Mongolia, and believe it or not, the South Pole.