New Dmanisi skull
So far only short items in the Georgian media, evidently based on a press release. The longest story is in the English language Messenger, but there are no new details (most of the article is about what has long been out of the ground).
That's never stopped be before, though, so let's have at it:
Yet another skull of a pre-historic man has been found by archaeologists in Dmanisi, researchers announced on Friday, August 5.
"This is a unique discovery, presumably dating back 1.8 million years ago," Minister of Culture, Sport and Monument Protection Giorgi Gabashvili said on Friday.
He noted it has been the fifth scull of the ancient Europeans discovered in Dmanisi over the last five years. "We can finally conclude now that people were living 1 million years ago jointly, in an organized way in Dmanisi," the minister said.
In other words, no new information. The skull in Lordkipanidze's hands in the photo is D3444, reported last year. Neither the date nor the number of individuals is news. Everything else is 1.8 million already, and they already had five individuals (D2280, D2282 (+ D211), D2700 (+ D2735), D3444 (+D3900), and D2600). All of these except the last include a skull; D2600 is only a mandible.
And what a mandible it is! Its corpus height is well over 50 percent greater than the other mandibles (It is illustrated in the supplementary material to Vekua et al. 2002). Its teeth are correspondingly large. No known early Homo skull can yet match it for sheer size -- the closest might be Sangiran 17, although it would appear to lack the huge ramus height.
Could the new skull be the match for D2600? That would be pretty interesting. A tiny hint in the article might suggest it isn't:
As of Friday the skull had not been extracted from the ground and the minister of culture commented that the archaeologists have not decided yet if the skill [sic] belongs to a pre-historic man or woman.
Well, if it were a match for D2600, there would be little doubt on that score. But it's probably just boilerplate -- how would a minister know, anyhow?
I'll be following the story.
Meanwhile, there's this:
Gabashvili also announced that the site will take on modern significance on August 13 when Dmanisi will host the so-called pre-historic games organized by the National Museum of Georgia.
"There will be competitions in, for example, lighting a fire or making primitive hunting tools," the minister explained. The games will be open to international participants and interested people can contact the National Museum.
You know, in principle it should be much easier to train for this stuff than the Olympics, since we have a long history of selection that ought to make us good at them. Unless you're Scottish. Then I suppose selection was for caber-tossing.
References:
Vekua A et al. 2002. A new skull of early Homo from Dmanisi, Georgia. Science 297:85-89. Abstract
Dmanisi paleoecology
I'm mining the data supplements from the Dmanisi postcrania paper for interesting stuff. There is a section (Supplement 4) on the paleoecology, which evaluates the site in terms of the faunal list:
The combination of topographic and vertebrate palaeontological information allows to infer a differentiated landscape pattern. Over a distance of a few kilometres, the landscape character changed from a flat and fairly wet river valley with gallery forests (indicated especially by the frequently recorded Eucladoceros and the elaphine deer Cervus abesalomi) to flanking slopes with shrub vegetation of varying densities, turning into dry meadows in the southerly exposed areas with more intense insolation. Extended tree savannah to open grasslands characterised the higher ground out of the valley. In addition to savannahs, semidesert-like rocky terrains existed on the lava outcrops in the vicinity of the site. Testudo graeca and Hystrix refossa indicate temperate climatic parameters.
Supplement 3 concerns the faunal resemblances with other geographic regions: they conclude that the greatest similarity is with Europe, and faunal similarities with Africa are
mainly due to the co-occurrence of common carnivore genera (e.g. Homotherium, Megantereon, Panthera) or, among herbivores, widespread genera like Equus.
Homotherium and Megantereon are the sabretooths.
References:
Lordkipanidze D and 17 others. 2007. Postcranial evidence from early Homo from Dmanisi, Georgia. Nature 449:305-310. doi:10.1038/nature06134
News flash: Dmanisi hominids were not short
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.
Caring for the edentulous
One of the features of the National Geographic (April 2005) article on Dmanisi is the discussion of the necessity of other people to aid and care for the old and infirm. The skull D3444 is an old adult individual, with no teeth remaining and the alveolar surfaces of the jaws nearly completely resorbed. This means that the individual lived without functional teeth for a period of time extending well beyond a year, and possibly to several years.
The article quotes some of the researchers working on the fossils about the importance of the condition of this individual:
In the survival of the old man, "we're looking at perhaps the first sign of truly human behavior in one of our ancestors," says [David] Lordkipanidze. It could be a glimpse of a new level of planning and sharing, adds Philip Rightmire, an anthropologist at Binghamton University in New York State who is one the Dmanisi research team. "Seeing this at the very dawn of Homo, our own genus," he says, "may be the most exciting thing of all." (Fischman 2005:19)
The idea is that a person who could not chew could not survive on his or her own. So he or she (I'm sticking to "he or she" until I see more information about D3444; it is more robust than the two females, but not extremely so) needed help from other people, in this story. The interesting aspect of this specimen is that it is so much older than the next oldest specimens with comparably extensive tooth loss, which are all Neandertals. Dmanisi does appear to considerably extend the time period over which we have evidence for human survival in the face of extensive disability; at least in terms of dental function.
There has been some criticism of the idea that tooth loss is a necessary indicator of care from other individuals.
The observation of old, edentulous individuals in a number of species of primates has formed the basis of a disagreement about the importance of such individuals for inferring the behavioral capacities of early hominids. This literature is reviewed by Cuozzo and Sauther (2004), and includes two examinations of the Aubesier 11 Neandertal by Lebel and Trinkaus and two critiques by David DeGusta. The gist of the argument is a discussion of whether any wild primates are observed to be missing as many teeth as certain Neandertal specimens (particularly Aubesier 11, but one may also include Monte Circeo, La Chapelle-aux-Saints, and possibly others who retain a higher proportion than Aubesier 11).
In my view, the actual proportion of missing teeth is much less important than the overall view of the function of the dentition. A chimpanzee with no functional occlusion is certainly almost as poorly off as a Neandertal with no teeth at all, even if many teeth are still present.
As an example, here is a shot of a female chimpanzee palate in the CMNH collection:
This is one out of around fifty wild-shot chimpanzees, a collection that is biased toward younger individuals than would have died natural deaths. The mandible retains the premolars and molars, although only one incisor, so the individual had essentially no functional dental occlusion. All chewing capacity was tooth against gum. As such, this chimpanzee wasn't quite as poorly off as the D3444 individual, but was certainly comparable in terms of dental dysfunction. There are several chimpanzee crania in this collection that are missing a few teeth, although none as extensive as this one (1).
But I don't think this line of argument is particularly productive, because it evades the central issue: do rare individuals ever allow any inferences about the social attributes of ancient humans? The edentulous hominids are evidence of the extreme end of a range of variation in life history traits. DeGusta (2002, 2003) essentially argues that the extreme end for Middle Pleistocene humans is not greatly different, if at all, from that in other primate species. I am sympathetic with that view, but I don't think it goes far enough to answer the problem. For one thing, the data as they stand indicate that Neandertals actually did survive with worse health status than other primates. This is not only true of tooth loss (where the difference is quite minor) but also bone breakage, arthritis, cranial injuries, and other assessments of both trauma and chronic health conditions. For earlier humans, the data are sparser, but these people had their problems also, as evidenced by D3444 and specimens like KNM-ER 1808. I suspect that the sample of Early Pleistocene hominids as it stands is not significantly different from Neandertals in health (although it is significantly different in longevity). So we cannot let the matter rest on the idea that other primates are like early humans in end-of-life health status; it is quite likely that early humans were not very much like any other primate.
DeGusta (2003) includes another objection to the assumption that edentulous individuals indicate care from other individuals:
Lebel and Trinkaus (2003) and Lebel et al. (2001) fail to suggest any reason why Aubesier 11 would have been unable to obtain or manually process soft foods on his/her own, rather than relying on conspecifics to do so. There is no evidence of any condition, or even advanced age, that would have precluded Aubesier 11 from doing so. So even granting the rest of their argument, Aubesier 11 cannot be used as evidence of conspecific care (92).
To take the position that these individuals are strong evidence of social behavior is to make several assumptions:
- That a change in the average pattern of behavior highly affects the extreme end of the range of life history.
- That it is social interaction and not some other behavioral or life history change (e.g. diet, disease, day range, secondary altriciality) that is responsible for the difference.
- That the end of the range is sampled adequately to make such inferences.
I think all these assumptions are unwarranted.
In the case of life history variation, I think that the survival of a small number of individuals under extraordinary circumstances says little about the habitual capabilities of a species. The difference between extraordinary and ordinary is one of sampling density. One individual out of a sample of five may be entirely normal, or a one-in-hundreds freak occurrence. Ten individuals out of fifty, while the same proportion of a sample, clearly are not exceptional.
In any population, some individuals are likely to survive under circumstances that would usually be fatal. For example, food availability varies greatly both from place to place and from year to year. Although the odds of mortality are higher for older adults, in practical terms these odds fluctuate along with ecological conditions. There are likely to be periods of years when a very low proportion of older individuals die, and some survive with infirmities that are extreme for their population. Older edentulous individuals who are otherwise healthy have a number of advantages. These range from a relatively high social status (and thereby a claim on food noticed by others) to extensive knowledge of food sources and other ecological needs, to a greater ability to evade or resist predators.
We can ask a more basic question. Is antemortem tooth loss in humans evidence of aid from other individuals? A high proportion of older adult humans today lack functional dentitions. In industrialized societies and to a great extent elsewhere, these people make use of artificial dentitions, which we can presume were not part of the technological repertoire of Early Pleistocene humans. But dentures and other dental appliances are unavailable to a substantial proportion of edentulous humans today, for economic and other cultural reasons. These people do not starve; instead they use extensive extraoral processing to enable the consumption of a relatively normal diet. This does not require, although it sometimes involves, the assistance of other people.
Certainly the present-day situation is different from that experienced by the Dmanisi hominids, or even Neandertals for that matter. Edentulous people today are greatly aided by the consumption of a high-starch diet of grains, tubers, or other stored vegetables that can be reduced with long cooking to a paste or mush. But among living people such a diet is routine, and long survival after the loss of a functional dentition is very common. In Pleistocene humans, such survival was almost certainly exceptional, as argued by the low proportion of edentulous remains.
It is no great stretch to think that an occasional older person might have put together a diet for several years that would allow survival without teeth. Such a diet need not have been steady or nutritionally complete. We can imagine the life of such a person, possibly with long stretches of hunger punctuated by a rare full meal on soft plant foods, honey, organ meat from an animal, or chunks of flesh painstakingly sliced thin with a stone flake. We do not even need to imagine that such foods would have been cooked, as supported by the survival of edentulous, non-cooking primates.
Tooth loss and selection
There is another, possibly more interesting, question arising from this specimen. Presumably the dentition is adapted to the life history of a species. Long-lived species have teeth that last a long time; short-lived species need not have teeth that last as long. Under some circumstances, there is value to having teeth that have thinner enamel (and therefore wear more rapidly), are smaller (and therefore wear more rapidly), or otherwise do not last as long. Smaller teeth may allow the application of greater masticatory force to certain kinds of food items (such as pliable plant or animal muscle fibers). Thinner enamel allows an enamel/dentine wear gradient that maintains greater occlusal topography for more effective shearing of food. But such teeth are not well-suited to a long lifespan unless the rate of attrition can be reduced by diet choice. These contrary influences on tooth form lead to different stable equilibria in different species, depending upon their life history and diet.
The interesting question is the strength of selection resulting from loss of dental function in old individuals. These people survive for some length of time with compromised teeth. Although the causes of tooth loss and extreme dental wear are not always the same, both factors lead to a reduction in dental function. This is especially true for old people who have had lives leading to high degrees of attrition or dental disease; which may occur more or less depending on the prevailing environmental conditions, social status of the individual, and possibly dietary preferences.
Notes:
1. As an interesting aside, I scored dental wear in over 100 male gorillas from this collection, and I do not remember that any of them had any significant number of teeth missing. This recollection accords with the data presented by Cuozzo and Sauther (2004), where they find no gorillas out of 65 that have more than 40 percent of their teeth missing. [UPDATE 4/26/05: A reader points out that these observations come from Nancy Lovell's (1990) work, cited by Cuozzo and Sauther (2004).] To be honest, I don't remember there being a single specimen missing that many teeth, although I deliberately excluded specimens with missing teeth from my own wear sample so I surely don't remember them as well as the ones I used.
References:
Cuozzo FP, Sauther ML. 2004. Tooth loss, survival, and resource use in wild ring-tailed lemurs (Lemur catta): Implications for inferring conspecific care in fossil hominids. J Hum Evol 46:623-631.
DeGusta D. 2002. Comparative skeletal pathology and the case for conspecific care in middle Pleistocene hominids. J Archaeol Sci 29:1435-1438.
DeGusta D. 2003. Aubesier 11 is not evidence of Neanderthal conspecific care. J Hum Evol 45:91-94.
Fischman J. 2005. Family ties: Dmanisi find. National Geographic April, 2005:17-27.
Lovell NC. 1990. Patterns of Injury and Illness in Great Apes: A Skeletal Analysis. Smithsonian Institution Press, Washington DC.
Lebel S, Trinkaus E. 2002. Middle Pleistocene human remains from the Bau de l'Aubesier. J Hum Evol 43:659-685.
Lebel S, Trinkaus E, Faure M, Fernandez P, Guérin C, Richter D, Mercier N, Valladas H, Wagner G. 2001. Comparative morphology and paleobiology of middle Pleistocene human remains from the Bau de l'Aubesier, Vaucluse, France. Proc Natl Acad Sci U S A 98:11097-11102.
Dmanisi in National Geographic
The article in the April 2005 National Geographic about Dmanisi has some interesting details that have not been made public before. The feature of the article is the D3444 skull, which I discuss in this post. But there are other points of interest.
The most significant is the short mention of the estimated stature of the Dmanisi partial skeletons. National Geographic says these are four feet seven inches, or 140 cm. To put this in perspective, the estimated adult height of KNM-WT 15000 is 180 cm or taller; the estimated height of AL 288-1 (Lucy) is 105 cm. The estimated stature for the KNM-ER 1472 femur, which is often assigned to H. rudolfensis and assumed to relate to the same population as the KNM-ER 1470 skull, is around 160 cm. So the Dmanisi hominids not only had habiline-sized brains; they also had habiline-sized bodies. Which makes them much more australopithecine-like than almost everyone had expected early humans to be.
There will be a lot of rewriting when these facts become official. Since the discovery of the Nariokotome specimen (KNM-WT 15000), there has been an emerging narrative of the evolution of early Homo. In this story, several anatomical and behavioral changes were confluent at a central speciation event that led to large-bodied Homo. These range from simple anatomical correlates, such as an increase in brain size, to far-flung behavioral inferences, such as the advent of menopause. All of these interpretations rest on the assumption that several behavioral and anatomical changes were coincident with the evolution of large body size. All of them now are thrown into question.
The other interesting feature is the John Gurche reconstructions of the Dmanisi crania. There is a multimedia presentation of the reconstruction of this and the other Dmanisi skulls at the National Geographic website. Like his other work, these are the best anatomical reconstructions of early Homo I've seen. I do wonder about the noses, though.
Hands down, palms forward
I've seen the "palms facing forward" quote in a few news reports about last week's Dmanisi postcrania paper. It's pretty nonsensical when you see it devoid of context. Consider Bruce Bower's Science News article:
However, the arms of Dmanisi hominids appear more like those of australopithecines, an earlier line of hominids. For instance, unlike people, the new specimens have upper arms that are straight rather than slightly curved, their shoulders are relatively narrow, and their palms are oriented forward rather than inward.
This is quite a vision, isn't it? How exactly is that humerus curved, again? And they stand with their palms forward? What?
OK, so it's tough to give a description of humeral torsion while making it sound important. Your humerus has two ends. The proximal end, called the head, attaches to your shoulder; the distal end is part of your elbow joint. When you are born, the head of your humerus faces toward the back (posteriorly). As you grow up, the humerus twists, so that the head faces inward toward your body (medially). The amount of twist is called the torsion; it is measured relative to the cross-section of the distal end of the humerus.
Nobody really knows what purpose is served by this twisting growth pattern. Presumably, the twisting adjusts for a change in the orientation of the shoulder joint, although that growth pattern has yet to be documented. But humans are more twisted than apes, and low humeral torsion is the key link that people are pointing out between Dmanisi and Homo floresiensis. So the articles are forced to describe it somehow. As a paleoanthropologist, I'm used to describing skeletal changes in punchy ways. Humeral torsion is a challenge -- without a really clear explanation of its function, it is hard to describe it in concrete, memorable terms.
Where does the "palms-forward" interpretation come from? We can trace it to Daniel Lieberman's commentary:
In modern humans, the elbow joint is typically rotated relative to the shoulder joint, so that the forearm naturally hangs with the palms facing inwards; but the new Dmanisi humeri lack torsion, so their palms would have been oriented more forwards. Lack of humeral torsion, a highly plastic and variable feature, suggests something different about the shoulder in these specimens.
Now, I'm sure that most of my readers will be scratching their heads over this one. People carry their hands palm-inward not because the humerus is twisted, but because the radius is habitually rotated across the ulna. That's the same reason why my hands are currently palm-downward on the computer keyboard. The humeral torsion is entirely irrelevant to the palm position when the arms are "naturally hanging" -- I can assure you, all of my children walk with their palms facing inward, despite the fact that their adult humeral torsion hasn't developed.
And of course, if humeral torsion is really about the orientation of the shoulder joint, as Lieberman suggests, then it really has no importance to the function of the elbow at all -- different torsion values would maintain the same lower arm mechanics with different shoulder orientations.
Still, neither the function nor adaptive value of humeral torsion are obvious. As Lieberman mentions, the trait is variable -- Larson and colleagues (2007) reported ranges in recent human populations extending from less than 110° to more than 170°. The value for the adult Dmanisi D4507 humerus is 110°, at the very lowest end of the modern human range; the value for the subadult D2680 is 104°. Humeral torsion continues to increase until age 16 in living people, although most change occurs before age 8 (Edelson 2000).
Larson et al. (2007) suggest that low humeral torsion is related to a short clavicle -- the idea being that the shoulder joint (glenoid fossa) was anteriorly (forward) placed, and the head of the humerus therefore had to face more posteriorly. I'm not sure that explains the low torsion at Dmanisi, since the Dmanisi clavicles aren't especially short -- like the long bones, they are right in the middle of the modern human range. But they might have had an anteriorly-facing glenoid fossa even if their clavicles weren't short, and given the low humeral torsion I suppose they probably did.
None of this means that the Dmanisi people or any other early hominids stood with their palms forward. Paleoanthropologists usually do a really good job of describing anatomy in down-to-earth terms, but humeral torsion seems to be a challenge!
References:
Edelson G. 2000. The development of humeral head retroversion. J Shoulder Elbow Surg 9:316-318. doi:10.1067/mse.2000.106085
Lieberman DE. 2007. Homing in on early Homo. Nature 449:291-292. doi:10.1038/449291a
Larson SG, Jungers WL, Morwood MJ, Sutikna T, Saptomo EW, Duw RA, Djubiantono T. 2007. Homo floresiensis and the evolution of the hominin shoulder. J Hum Evol (in press) doi:10.1016/j.jhevol.2007.06.003
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks