100 best anthropology blogs

The Online Degrees.net blog has compiled a comprehensive list of the 100 Best Blogs for Anthropology Students. This is a fantastic resource for anybody interested in anthropology.
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Paleo diet

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For many people the new year represents an occasion to set the clock back to zero and make a fresh start. We invariably eat too much during the festive season, only later to feel remorse for our gluttonous ways. With the new year comes the renewed goal of losing some of the extra padding. There are no end of miraculous sounding diets which promise to convert fat to flat. Among the various in vogue diets is the so-called Paleo diet (short for Paleolithic diet), also known as the caveman diet. The central premise behind the Paleo diet is that many human adaptations evolved during the Palaeolithic, and as such, we are maladapted to the modern world in which we find ourselves.

The premises of the Paleo diet raise some interesting questions that are well worth exploring. For instance, are we really better adapted to the Palaeolithic than the modern era and which aspects of the Palaeolithic does the Paleo diet reference? Many proponents ask the question “who ever heard of a fat caveman?”, as if the answer is somehow inferred. While it is seems be the case that the average Palaeolithic human had a brawnier body than the average modern human, we should not confuse correlation with causation. A better question to ask is whether the “caveman” physique is due solely to diet or are there other factors at play?

While certain human adaptations undoubtedly arose during the Palaeolithic, these are likely to be no more or less important than the adaptations of preceding and subsequent periods in our evolutionary history. Most of our genes evolved a long time before our ancestors were recognisable as primates, never mind humans. Moreover, humans continue to adapt to their diet today. Lactose tolerance is a good example of a trait that arose in many populations of humans after the Palaeolithic. Evolution exists on a continuum; it didn’t start and end sometime during the Palaeolithic.

The Palaeolithic covers a period of around 2.5 million years, as well as an immense geographic range. Moreover, many species of humans lived in very diverse environments during this time. Proponents of the Paleo diet rarely specify what period and indeed which populations or species they use as their model. Food procurement methods changed dramatically over this time period. Over the course of the Palaeolithic, humans shifted from mostly scavenging their meat to systematic hunting. Even among modern hunter-gatherers there is great dietary variation. For instance, the diets of Inuits and Aboriginal Australians couldn’t be more different. Another consideration is that humans have been selectively breeding plants and animals over many millennia. Many of the domesticated varieties we see today are unrecognisable from their wild ancestors. As such, while the Paleo diet recommends greater reliance on meats and non-cultivated plants, it should be kept in mind that these probably bear little resemblance to the wild species our ancestors ate.

The limb bones of the early Upper Palaeolithic Gravettian people are not only large but also have massive muscle attachments. Early humans were physically fit not only because of their diet but in large part due to their high mobility. Hunting and foraging expeditions would have required these groups to cover large distances. Demographic pressures impinging on these small bands of humans would also have further encouraged greater mobility.

It is not disputed that the diet of early hunter-gatherers was much more varied than that of their agricultural counterparts. Early agriculturalists often had an over reliance on few food types, leading to various nutritional deficiencies and generally poorer health. However, there is little reason why this should be the case today. Our shops and markets are packed with varieties of food that our ancestors would be only able to dream off.

Many of the recommendations of the Paleo diet are sensible, such as eating less processed foods, decreasing our sugar intake and increasing our dietary fibre. In this regard, the Paleo diet is on par with most governmental dietary recommendations. Why the need to dress it up in some romanticised account of how our ancestors ate? I will concede that versions of the Paleo diet are probably healthier than the diets most of us adhere to. However, the reasoning behind it is based on an immutable view of human prehistory, coupled with some poor evolutionary thinking.


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Above photo modified from original by Lord Jim under creative commons license.
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Dangerous quote mines: a cautionary tale

matt_wedel
Mathew John Wedel (right) is a palaeontologist who specialises in sauropod dinosaurs. Recently, he was invited to be a talking head for Discovery Channel’s new series, Clash of the Dinosaurs. In the making of such shows, experts are often interviewed for hours on end about a variety of topics, which is later edited down to little more than a pithy one-liner. Sound bites are anathema to the complexity of science. Scientists often feel hard done by, after spending hours doing to their best to explain the science, to see it condensed down to a few words.

However, what happened Matt is much more disturbing. It has been long known that sauropods have a swelling in the sacral region, leading some people to suggest that it may have functioned as a second brain. This idea has been thoroughly debunked. When Matt was asked to comment on this here is how the original unedited conversation went down:
”Ok one of the curious things about sauropods is that they did have a swelling in the spinal cord in the neighbourhood of their pelvis. And for a while it was thought that may be this was sort of like a second brain to help control the back half of the body. Erm there are a couple of misconceptions there. One is that most animals control large part of their body with their spinal cord. If you’re going through day to day operations like just walking down the street and your minds on something else your brain isn’t even involved in very much controlling your body. A lot of that is a reflex arc that’s controlled by your spinal cord. So it’s not just dinosaurs that are controlling their body with their spinal cord, it’s all animals. Now the other thing about this swelling at the base of the tail is we find the same thing in birds and its called the glycogen body. It’s a big swelling in the spinal cord that has glycogen which is this very energy rich compound that animals use to store energy. Problem is we don’t even know what birds are doing with their glycogen bodies. Er the function is mysterious – we don’t know if the glycogen is supporting their nervous system – if its there to be mobilised, help drive their hind limbs or the back half of their body and until we find out what birds are doing with theirs we have very little hope of knowing what dinosaurs were doing with their glycogen bodies.”

I can only imagine the shock Matt experienced when this got edited down to:
“This was sort of like a second brain to help control the back half of the body.”

This is not what he said at all. In fact, he said the exact opposite, even going so far as to give the reasons why this is a discredited theory. Not only is this downright dishonest on the part of the producers, it also calls into question the credibility of this professional scientist. More generally, it gives legitimacy to the ‘second brain’ hypothesis in the eyes of the public. Understandably, enraged by what he saw, Matt sent an email form Dangerous Ltd, the production company who were responsible for filming the documentary. He received a reply that amounted to a nopology, even having the audacity to say: “we were simply working on the show ever aware of the demands of our audience.” And what about presenting the facts or fairly representing the views of the scientists?

Thankfully, this story has a happy ending. Matt talked to a person high up at the Discovery Channel, who promised that the egregious portion would be promptly removed. Unfortunately, this misrepresentation of a scientist is not an isolated case and we would do well to understand why this happens and what can be done to prevent it. The first thing we should remember is that documentaries are, first and foremost, made for entertainment. As a result, most are written by screenwriters and have a predetermined script. One would think that the scientific facts write themselves but this is sadly not the case. It is the job of the film crew to interview specialists, all the time being conscious of the preplanned plot. Scientists should not be afraid to ask to see an outline of the plot. That way they have an idea of what pieces of information the production team are after. When documentary makers interview scientists they are generally looking for snippets that will propel the storyline. This is the reason why hours of footage eventually get edited down to mere seconds. Naturally, the more time you spend talking the greater the chances of something making it into the finally cut. However, this also means that there is more material that can be taken out of context. It is in the interviewee’s best interest to keep the conversation from wandering off course. This can be achieved by negotiating an hourly fee with the production company prior to any interview. Scientists shouldn’t be shy about demanding money for their time. Film crews will often have a budget for this but are normally not very forthcoming in divulging this information. As long as the film crew are cognisant of their budget, they are more likely to cut to the chase earlier on, rather than fishing around for juicy quotes.

While it is tempting for experts to point out the flaws in refuted hypotheses, they are perhaps better off biting their tongues. This way, their words cannot be contorted to suggest that they are in fact a proponent of a viewpoint they firmly disagree with. However, if you are cornered into giving an opinion on a contrary idea it is perhaps best to let your body do the talking. If you can visibly demonstrate your disdain for a particular idea through your facial expressions, it makes it much harder for the editors to later manipulate your words in such a way that they contradict your body language. This requires scientists to really show and perhaps exaggerate their emotions, but heck, if one truly loves their profession that shouldn’t be too difficult to accomplish.

It is important that scientists speak out against any media distortions of science. It is likely that Dangerous Ltd. felt some heat from the negative reaction of bloggers and commentators, subsequent to Matt’s initial blog post. If we don’t take a stand, we are simply emboldening sloppy science communication. We should email, phone, or write to these companies and let them know that we are not happy with how science is being misrepresented. As a last resort one may consider taking legal action. While scientists give up many of their privileges once they sign a release form, slander is still slander, and as such is subject to legal action.

Good science doesn’t need to be dressed up or distorted, most especially when we are talking about dinosaurs. While some may cringe at the very thought, scientists more than ever before need to become media-saavy. The media is ultimately interested in a great story and will go to extreme lengths to get it. The case of Matt is not new and their will be many more cases like it to come. Only by being more aware of how the media operates can scientists be equipped to deal with such future misrepresentations.

Related reading
Lies, damned lies, and Clash of the Dinosaurs
Clash of the Dinosaurs: Dangerous Ltd document their own dishonest editing
Clash of the Dinosaurs: The Discovery Channel steps up
A scientist is QUOTE MINED on a Discovery dinosaur documentary


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Irish Neandertals!

This abstract from a 1961 paper made me smile:

Living Cork-Kerry Irish were compared with 139 modern and ancient peoples using 36 factors, 14 blood groups, 3 skin, hair and eye pigmentations and 22 physical measurements. The method was a form of multiple correlation in which the class interval for each factor was one-half the standard deviation, and numerical values allocated to each half-standard deviation. The Irish, Northern Scots, Icelanders, S.W. Norse, N. Dutch and Frisians form a racial entity with 97 per cent. inter-correlation and very little change during the past 1,000–4,000 years. There is a high correlation with the ancient Scythians substantiating the Irish legends of descent from the kings of Scythia. There is a substantial mixture of upper palaeolithic and Neanderthal man in the north-western perimeter of Europe, exemplified by the people of Cork and Kerry, a mixture not shared by the American Indians, the Australian Aborigines, and by the Bushmen and Pygmies of Africa. There is a good possibility that the large frame, red hair, blue eyes and white skin of West Europe was contributed by upper palaeolithic and Neanderthal men.

Casey AE, Franklin RB. 1961. Cork-kerry Irish compared anthropometrically with 139 modern and ancient peoples. Irish Journal of Medical Science. 36 (9).
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One chin does not a modern human make

Guangxi chins
Chinese scientists say that a recently discovered partial jaw from Guangxi challenges the ‘out of Africa’ model of modern human origins, while lending support to the multiregional hypothesis. The 110,000 year-old mandible is described as having a chin that juts “ever so slightly outward.” These scientists assert that the presence of chin shows that there was significant gene flow between populations of modern Homo sapiens and archaic Homo.

Wu Xinzhi of the Chinese Academy of Sciences had the following to say about the find:
”The finding was strong evidence to prove the multiregional model, and from this evidence, it was significant to solve the academic dispute between 'the multiregional mode' and 'out of Africa theory’”.
It is interesting to note Xinzhi’s use of the past simple tense to suggest that this is a closed case. Far from it! Palaeoanthropological theory has moved on from the multiregional sensu stricto versus ‘out of Africa’ sensu stricto dichotomy that predominated the discussion during the latter half of the last century. Nevertheless, the question of how much gene flow, if any, took place between modern and archaic Homo is still very much a debated issue.

At this stage you may be wondering why there has been such furore over a chinned jaw. As long ago as 1775, Johann Friedrich Blumenbach commented on the uniqueness of the modern human chin:
In the animals there is scarcely a particular chin which can be considered as comparable to that of man: and in those men who, as is often said, seem to have something apish in their countenance, this generally resides in a deeply-retreated chin.
The distinctive modern human chin develops through the combination of bone deposition on the inferior part of the jaw and resorption around the alveolar region. In other primates the entire jaw undergoes deposition. The modern human chin is characterised as having a central keel, with hollowed out depressions (known as mental fossae) to either side, together with a protruding inferior portion. This distended mental protuberance and lateral extremities make up the mental trigone, giving the chin the appearance of an inverted T. It is the combination of all these anatomical features that make up the prototypal modern chin. However, chins show great variability, with some modern humans not having any.

This variability is also extends to earlier hominins. The Middle Pleistocene fossils from the Sima de los Huesos have been described as having chins, and even well-developed mental trigones. Among Pleistocene hominins, Neandertals appear to have the most divergent pattern from the modern configuration, universally lacking the inverted T and mental fossae. While it has been argued that the Neandertal mandibles from the Croatian site of Vindija show the development of incipient chins, this has not been borne out by later analyses.

Some of the ‘modern’ Klasies River Mouth mandibles do not have developed mental trigones, midline keel or a thickening of the inferior margin. However, the modern designation of this material is controversial with these fossils showing a mosaic of both archaic and modern features. Similarly, the modern humans from Qafzeh show variable expression of the inverted T and mental fossae, with no indication of these features in the Skhūl specimens. The 700-800,000 year-old Tighenif mandibles show a surprisingly modern configuration complete with central keel, a thickened inferior portion, and the development of a triangular protuberance. The presence of a chin in these specimens could represent a synapomorphy with modern humans.

Based on the archaeological record, it appears that modern humans left Africa some time around 100,000 years ago. Among the oldest undisputed modern human remains in China come from Zhoukoudian Cave at around 35,000 years BP. The possibly earlier fossil from Liujiang is marred with dating problems. In order for the Chinese scientists’ assertion to hold, it would require an even earlier exit from Africa or expansive gene flow between modern humans living in Africa and archaic humans in Asia; claims for which the evidence is currently lacking. Future analyses of the specimens will determine whether these chins have a truly modern form or whether the pattern is more like the non-homologous protruding inferior jaws seen in other archaic specimens. Alternatively, if these specimens end up being the result of convergent evolution it would raise questions about the functional significance of a chin. Finally, if these fossils show a pattern similar to the one seen in the Tighenif fossils it may suggest that they belong to the same clade.


References and further reading
Ahern JC (1993). The Transitional Nature of the Late Neandertal Mandibles from Vindija Cave, Croatia. M.A. thesis. Department of Anthropology, Northern Illinois University.

Blumenbach, JF (1978). The anthropological treatises of Johann Friedrich Blumenbach / translated and edited from the Latin, German, and French originals by Thomas Bendyshe. Boston : Longwood Press.

Hawks, J (2009). It came from Guangxi.

McKenna, P (2009). Chinese challenge to 'out of Africa' theory. New Scientist.

Rosas, A. (1995). Seventeen new mandibular specimens from the Atapuerca/Ibeas Middle Pleistocene hominids sample. J. hum. Evol. 28, 533–559.

Schwartz JH, Tattersall I (2000). The human chin revisited: what is it and who has it? J Hum Evol 38:367-409.

Schwartz JH, Tattersall I (2002) The Human Fossil Record, Vol. 1: Craniodental Morphology of Genus Homo (Europe) Wiley-Liss: New York.

Stone R (2009). Signs of Early Homo sapiens in China? Science 326 (5953) p 655.


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Above image: Institute of Vertebrate Palaeontology and Palaeoanthropology, Chinese Academy of Sciences.
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Full frontal hominins

modern skull
One of the most visually striking differences between modern humans and other hominins is the shape of the forehead. The frontal bone of the forehead serves two primary functions: it houses the frontal lobes of the brain in the anterior cranial fossa and also forms the orbital roof. When the orbits are positioned anterior to the frontal lobes, a supraorbital torus or brow ridge, forms in order to bridge the gap. This is particularly the case in archaic members of the genus Homo, whose brain cases are positioned well behind their faces.

The incredible brow ridges of Homo erectus is perhaps this species most salient physical feature.
Homo erectus
They possess a flattened forehead with a bar-like brow ridge over the eye sockets. The supraorbital torus is continuous and thickened laterally, which in turn is associated with a pinching of the orbital breadth behind the eye sockets, known as postorbital constriction. In H. erectus, the supraorbital torus is separated from the frontal squama by a depression called the posttoral sulcus. While most Erectines conform to this general bauplan, there is a lot of regional variation in the exact form of the torus.

Neandertals are characterised by their long, large, low and wide skull. They have a double-arched browridge above the orbits, which angles backward on the sides of the face. It is depressed along the middle by the presence of a supraglabellar fossa. Compared to H. erectus, Neandertals have a more vertical and rounded forehead, with a less pronounced supraorbital torus.

Modern humans have a vertical forehead, due to in no small part to the expansion of the front part of the brain. Unlike in other hominins, the frontal lobes sit directly above the orbits, negating the need for a supraorbital torus. Instead, we tend to have relatively lightly developed superciliary arches. In present day populations, large supraorbitals are generally seen in individuals that have both robust and narrow skulls. Supraorbital ridges can also occur in cases of neurodevelopmental disorders, such as microcephaly, in which case normal orbital size is combined with smaller cerebral size. The presence of a supraorbital torus in the hominin Homo floresiensis was one of the traits that some researchers used to suggest that these dwarf humans were in fact microcephalic Homo sapiens.

basicranial_flexion_thumb
Modern adult humans have the most flexed basicranium of any mammal. This is due largely to us having a more vertically oriented sphenoid bone. A more flexed cranial base repositions the face directly below the anterior cranial fossa, while a more extended cranial base results in greater facial prognathism. In turn, the combination of an extended cranial base and facial forwardness influences the development of the supraorbital region. Early modern human skulls, such as Skhūl V and Dar es-Soltan, have prominent brow ridges. The development of large supraorbitals in these specimens results from greater cranial base angulation. In this regard, the development of the supraorbital region in some early modern humans does not result from neuro-orbital disjunction like in archaic humans, but primarily because of their more extended cranial base.

While much has been written about the non-metric variation of the frontal in hominins, there is little in the way of metric analyses, due to the bone's lack of cranial landmarks. Sheela Athreya recently carried out a quantitative study of the frontal bones of various Pleistocene hominins. She collected outlines along the sagittal and parasagittal planes of the bone. Based on her analyses, specimens were classified as either Early Pleistocene, Homo erectus, Middle Pleistocene, Neandertal or anatomically modern Homo sapiens.

The highest classification accuracy was along the midsagittal plane, with a success rate of a mere 68%. In other words, using this technique almost one-third of specimens were misclassified. A well-seasoned palaeoanthropologist would have a much higher success rate using only non-metric traits. The key to identifying which species a particular frontal bone comes from involves looking at the totality of features along the entire length of the torus and surrounding bone. It is likely that if each of the curves were combined in a multivariate analysis they would have yielded a much higher classificatory success rate. Linear measurements along a curve only capture two dimensions of the frontal form, thereby losing a lot of information contained in the third dimension. A better approach would be to digitise a three-dimensional dense point cloud along the entire bone and to analyse the region using geometric morphometrics. However, such equipment is expensive and not available in most anthropology departments.

Perhaps the most important outcome of this study was that it quantitatively confirmed some of the general characteristics of the frontal form of Homo, that have been previously described qualitatively. These include the fact that most of the variation in the frontal bone between Pleistocene groups is along the midsagittal plane. The study additionally found Homo erectus to differ from all other groups in the projection of the glabellar region. Finally, it identified modern humans as differing from all other groups in the curvature of the forehead, as well as the prominence of the lateral supraorbital torus. This confirms what many palaeoanthropologists have been saying for a long time – the lack of a supraorbital torus in modern humans is a uniquely derived feature.


References

Athreya, S. A comparative study of frontal bone morphology among Pleistocene hominin fossil groups, J Hum Evol (2009), doi:10.1016/j.jhevol.2009.09.003.

Lahr, MM. The Evolution of Modern Human Diversity : A Study on Cranial Variation . Cambridge; New York : Cambridge University Press, 1996.

Lieberman, Daniel E, Osbjorn M Pearson, and Kenneth M Mowbray. "Basicranial Influence on Overall Cranial Shape." Journal of Human Evolution 38 (2000): doi:10.1006/jhev.1999.0335.

Martin RD, MacLarnon AM, Phillips JL, Dussebieux L, Williams PR, Dobyns WV. 2006a. Comment on ‘‘The brain of LB1, Homo floresiensis.’’ Science 312:999b.

Trinkaus. Modern Human versus Neandertal Evolutionary Distinctiveness. Current Anthropology (2006) vol. 47 (4) pp. 597-620.

Trinkaus. European early modern humans and the fate of the Neandertals. Proceedings of the National Academy of Sciences (2007) 104 (18) pp. 7367-7372.

Above photos modified from originals by
missmareck and arnybo under creative commons license.
Image of lateral dissected skull by
dollinjune14, via deviantART (modified from original).


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Did Neandertals and modern humans interbreed?

Neandertal
Ever since William King proposed the taxonomic designation Homo neanderthalensis in 1864, there has been intense debate as to whether Neandertals represent a distinct species from us. Species, as defined by the biological species concept, are populations of organisms that can potentially interbreed and have fertile offspring. It is believed that the lineage leading to Neandertals and modern humans split sometime around 500,000 years ago. For most of their existence Neandertals and early modern humans were geographically isolated (and by extension reproductively isolated) from one another. The big question is whether they could have produced viable offspring when they met.

woman
Today, most researchers acknowledge that some sexual encounters could have occurred between Neandertals and modern humans. The more interesting question is how common were these encounters and did they leave their mark on the modern gene pool. Undoubtedly, modern humans and Neandertals would have recognised each other as fellow humans but this does not mean that they would have acted humanely to each another. Countless social and psychological studies have shown humans to have a very strong "us versus them" mentality, that no doubt also existed in our ancestors. It is unlikely that modern humans and Neandertals had an easy relationship. Most sexual encounters that took place between the two were likely opportunistic and probably involved enslavement and rape.


The morphological evidence

Palaeoanthropologists generally have little problem seperating Neandertals and modern humans based on their gross morphologies. However, some of the earliest modern humans from central Europe have traits that have been seen as evidence for continuity between them and Neandertals. These fossils, particularly those from Peştera cu Oase in Romania and Mladeč in the Czech Republic, have been touted as exemplars for modern-Neandertal admixture. These specimens show traits that are seen in high frequencies in Neandertals, such as bunning of the occipital and the presence of a suprainiac fossa.

However, many researchers have questioned whether these traits are in fact distinctly Neandertal. For instance, the form of the occipital seems to be different in early Upper Palaeolithic populations, leading many to favour the term hemibun to describe the shape of the occipital in early Europeans. Lieberman and colleagues has gone as far as to suggest that the buns seen in these two groups are not homologous. Similarly, it has been argued that the shape of the suprainiac fossa is distinct in early modern Europeans compared to Neandertals.

A palpable difficulty in assessing proposed Neandertal traits in early modern humans is that both groups shared similar niches and some traits may be the result of lifetime behavioural adaptations or convergent evolution. Indeed, the shared robustness of these early humans is likely due to the higher physical activities of these Late Pleistocene groups than during later period.


The genetic evidence

Mitochondrial DNA (mtDNA) has some characteristics that make it ideal for analyses of ancient specimens. MtDNA is found in abundance – cells can have thousands of copies of mtDNA, while only containing two copies of nuclear DNA. Moreover, its structure and location within the cell make it more resistant to decay. All the studies of Neandertal mtDNA to date cluster outside the range for modern human mtDNA variation. However, the mitochondria contain only a small part of the total DNA that make up a genome. The possibility that Neandertal genes could show up somewhere else in the genome cannot be ruled out.

The recent announcement by Svante Pääbo that he is sure that Neandertals and modern humans had sex is quite a bold pronouncement coming from a scientist. It raises the question of whether this ascertain is based on some hard evidence they found while sequencing the Neandertal genome. It is possible that if there was some Neandertal genes passed on to the first moderns in Europe, they could have got eliminated from the subsequent gene pool as population sizes fluctuated during the more severe climatic episodes. A more likely scenario is that Pääbo's team found evidence of modern introgression in the Neandertal genome. In all likelihood the incoming modern humans were more numerous than the Neandertals, thereby absorbing the endemic populations through genetic swamping.


References

Caspari RE. 1991. The evolution of the posterior cranial vault in the central European Upper Pleistocene. PhD dissertation. Ann Arbor, MI: University of Michigan.

King, W., 1864. The reputed fossil man of Neanderthal. Quarterly Journal of Science 1, 88–97.

Krings et al. 1997. Neandertal DNA sequences and the origin of modern humans. Cell vol. 90 (1) pp. 19-30.

Krings M, Capelli C, Tschentscher F, et al. 2000. A view of Neandertal genetic diversity. Nat Genet 26, 144–146.

Lieberman et al. 2000. Basicranial influence on overall cranial shape. J. Hum. Evol. vol. 38 (2) pp. 291-315.

Nara MT. 1994. Etude de la variabilité de certainscaractères métriques et morphologiques des Néandertaliens. Bordeaux: Thèse de Docteur.

Pääbo S, Poinar H, Serre D, et al. 2004. Genetic analyses from ancient DNA. Ann Rev Genet 38, 645–679.


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Above photos modified from originals by erix! and fangleman under creative commons license.
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John Hawks on Ardipithecus

Razib Khan of the Gene Expression blog interviews John Hawks regarding the significance of Ardipithecus ramidus.




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Homo heidelbergensis and the muddle in the middle

Craneo_5
Michael Balter reports for Science on a recent conference held in Gibraltar entitled Human Evolution 150 Years After Darwin [1]. Gibraltar holds a special place in palaeoanthropologists' hearts. Not only is it the place where the first Neandertal were discovered in 1848, it is also seems to have been among the last refugia of this species, prior to their disappearance some 30,000 years ago. Charles Darwin got to see the original Gibraltar specimen in 1864, which perhaps influenced him to comment on the "well developed and capacious" braincase of Neandertals in The Descent of Man [2].

At the conference, much attention was focused on the Middle Pleistocene "muddle in the middle" [3], particularly the role of Homo heidelbergensis in hominin evolution. While H. heidelbergensis possesses both archaic and derived traits intermediate between H. erectus and later members of the Homo genus, it lacks uniquely derived traits or autapomorphies, which are a prerequisite for defining a species.

H. heidelbergensis has traits that have been interpreted as nascent Neandertal autapomorphies, leading some researchers to propose that there was a continuous evolution of Neandertals [4-6]. This accretion model would make H. heidelbergensis a chronospecies on the continuum of the Neandertal lineage, a view championed by Jean-Jacques Hublin. The accretion model proposes that Neandertals evolved by anagenesis, i.e. non-branching evolutionary change.

Another scenario views both the European and African H. heidelbergensis as a single species, and the last common ancestor of both Neandertals and modern humans. Alternatively, H. heidelbergensis could have become isolated in Europe and evolved into Neandertals, while the African populations led to modern humans.

During the conference, Ian Tattersall noted that while the accretion model explains some of the variation in the Middle Pleistocene, it cannot account for some outliers, such as the 28 or so specimens that have been recovered from the Sima de los Huesos in Atapuerca, Spain. Tattersall is not the first author to call the accretion model into question [7]. Recent dates have placed the Sima fossils at just over half-a-million years old. Based on the dissimilarity between these fossils and the penicontemporaneous H. heidelbergensis from the rest of Europe, Tattersall proposes that two hominin lineages coexisted in Europe before the arrival of H. sapiens. He suggests that one line (which may include the Sima specimens) led to the Neandertals, while the branch which included H. heidelbergensis went extinct. If Tattersall is correct it would mean that the Sima fossils, which are currently classified as H. heidelbergensis, must be designated another name.

Hublin is to his guns and doesn't see any need to reclassify the Sima material. He goes as far as to suggest binning the species name H. heidelbergensis altogether and instead reassigning all these Middle Pleistocene fossils as H. neanderthalensis. Whatever the outcome is in this debate, it appears that hominin evolution in the Middle Pleistocene is more complex than we have previously suspected.

References

1. Balter M. New work may complicate history of Neandertals and H. sapiens. Science 2009; 326:224-5.

2. Darwin C. The descent of man, and selection in relation to sex. New York, A. L. Burt; 1874.

3. Butzer KW, Isaac GL, International Congress of Anthropological and Ethnological Sciences 9C1. After the Australopithecines : stratigraphy, ecology, and culture, change in the Middle Pleistocene . The Hague : Mouton ; Chicago : distributed in the USA and Canada by Aldine; 1976.

4. Hublin. Paleogeography, and the evolution of the Neandertals. In: Akazawa, Aoki, Bar-Yosef, Eds. Neandertals and Modern Humans in Western Asia. New York: Plenum Press; 1998:295-310.

5. Hublin. Climatic Changes, Paleogeography, and the Evolution of the Neandertals. In: Akazawa, Aoki, Bar-Yosef, Eds. Neandertals and Modern Humans in Western Asia. New York: Plenum Press; 1998:295-310.

6. Martinón-Torres M, Bastir M, Bermúdez de Castro JM, Gómez A, Sarmiento S, Muela A, Arsuaga JL. Hominin lower second premolar morphology: evolutionary inferences through geometric morphometric analysis. J Hum Evol 2006; 50:523-33.

7. Hawks JD, Wolpoff MH. The accretion model of Neandertal evolution. Evolution 2001; 55:1474-85.


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The pelvis of Ardipithecus ramidus

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One of the anatomical features that sets humans apart from other living primates is the shape of our pelvis. The shift from a quadrupedal aboreal lifestyle to habitually walking on two legs requires a substantial reconfiguration of the hip region. The 4.4 million year old Ardipithecus ramidus fossil remains give us a glimpse of what the one of the earliest members of the hominin lineage looked like. While the feet of Ar. ramidus show that it was still adapted to life in the trees, the pelvis shows significant adaptations to walking upright on two legs.

The gluteus maximus, which is a relatively minor muscle in quadrupeds has been reconfigured into the largest muscle in humans, in order to stabilize the pelvis and trunk in an upright position. The derived nature of the ilium of Ar. ramidus suggests that the enlargement of the gluteal maximus had already begun. The craniocaudal height of the pelvis is also reduced, which would have lowered the relatively long trunk's centre of mass. This would have allowed for more stable bipedal locomotion.

However, the ischium is quite primitive compared to the ilia, likely to accommodate the large hindlimb musculature required for tree climbing. The two best preserved australopithicine pelves, AL 288-1 and Sts 14, both have short ischia, like those seen in modern humans. The preserved portion of the ischial ramus in Ar. ramidus is significantly larger than that found in any of the Australopithecines. A long ischium creates a greater moment arm suggesting that Ar. ramidus had relatively powerful hamstrings, a trait that is common in tree-dwelling primates.

The configuration of the ARA-VP-6/500 pelvis suggests that lower lumbars were probably posteriorly positioned, allowing for lordosis of the spine. A reduction in iliac height would have further facilitated lordosis. Lordosis positions the spine to a more forward position, so that it directly overlies the hips during erect posture. Lower spinal lordosis would have allowed the full extension of the hips and knee during extended bipedal locomotion.

Ar. ramidus was quite capable of bipedal locomotion, as attested to by the morphology of its pelvis and foot. However, its large thigh muscles and its prehensile big toe show that it was still very much adapted to arboreal life. Ar. ramidus shares arboreal adaptations that were probably present in the human-chimp last common ancestor, as well as bipedal adaptations that are so characteristic of hominins. Ar. ramidus appears to have been an arboreal ape with bipedal adaptations, rather than a biped with arboreal adaptations. It is not until almost half-a-million years later, with the arrival of Australopithecus afarensis, that we find a truly habitual bipedal hominin.


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