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. 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.

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).

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.

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.



Above photos modified from originals by erix! and fangleman under creative commons license.

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

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.

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.

Welcome to Four Stone Hearth number 75. Four Stone Hearth is a fortnightly anthropology blog carnival. Topics covered span the four major fields of anthropology: archaeology, socio-cultural anthropology, bio-physical anthropology and linguistic anthropology. If you would like to host the carnival, please write to . The next issue will be hosted at the Afarensis blog on 23 September. So without further preamble, let's get on with the show.

Archaeology
Martin Rundkvist talks about his experience digging at a Middle Neolithic coastal site in Sweden. Among the finds were small potsherds and a fine example of Pitted Ware.

A recent article in the journal Nature reports on the "oldest handaxes" in Europe. John Hawks gives his interpretation regarding the significance of these bifaces, suggesting that although Lower Pleistocene hominins had the technology to produce bifacial handaxes, they were not a necessity.


Biological anthropology
Anybody who has been following anthropology news for the past few weeks will be well aware of the spirited reaction that a recent editorial in Scientific American generated. The article calls for the adoption of more open practices with regard to accessing human fossils. I have written a piece where I give my own take on the issue.

Matthew Wolf-Meyer reviews Jonathan Marks' latest book "Why I am not a scientist". Jonathan Marks is a controversial anthropologist, who sticks to his guns in this, his latest work. Ever thought provoking, Marks is bound to stir up some debate among anthropologists and scientists alike.

There has been a lot of debate regarding whether Central European farmers were the descendants of indigenous hunter-gathers or the result of a demic diffusion from the southeast. Dienkes reports on a new study which suggests that Central European farmers were in fact probably not descended from local hunter-gatherer groups.

Stephen Wang asks the age old question of how similar Neandertals were to us and how they thought about the world.


Linguistic anthropology
The Innovation in Teaching blog explains the concept of a “focused gathering”, a term coined by anthropologist Clifford Geertz. The post goes on to discuss how this concept helps us better think about classroom dynamics.


Socio-cultural anthropology
Over at Neuroanthropology, Daniel Lende has a revealing piece which looks at food crises in Lesotho and the role funerals play in coping with these food shortages. In another post Daniel takes on the recent "research" by researchers Ogi Ogas and Sai Gaddam, which is plagued by poor methodologies and a pseudoscientific approach to neuroscience. Greg Downey follows this up with his own take on some of the methodological flaws of the investigators, principally their inflexibility in the face of contradictory evidence.

Rex over at the Savage Minds blog suggests that the real question anthropologists should ask regarding internet addiction is not whether it exists but rather "how and in what forms do preexisting cultural structures predispose people to think something is true?"

Greg Laden debunks the fallacy that culture overrides biology. This part of a larger series on the common misperceptions that people have regarding biology.

Idris Mootee thinks that industrial designers need to think like cultural anthropologists. He uses the example of how different cultures adopt their own particular posture while sitting. By being aware of this, designers can better accommodate the needs of the end user. Joana Breidenbach of the Culture Matters blog is of a similar opinion:


Lian explores the the archaeology of the worship of Celtic deities in Roman Britain.

Lorenz at the antropologi blog reviews Thomas Hylland Eriksen's new book "Engaging Anthropology". In it, he addresses the question of why anthropologists fail to engage the general public. In a similar piece that appeared in Times Higher Education, anthropologist Nancy Scheper-Hughes asserts that part of the problem may lie with universities:


Anna Barros shows how trends are subject to selection. She demonstrates how memes can be transmitted from person to person and how they respond to selection pressures.


One more thing…
Each of the four fields of anthropology can offer us a glimpse into our past. Perhaps more importantly, they can take us on a journey and show us the steps which got us to where we are today. Photography offers yet another way of archiving the past. To use the clichéd metaphor – photographs are moments frozen in time. A Flickr photostream by Jason Powell wonderfully bridges the gap between the past and the present, through the medium of photography. Enjoy!

A recent article in Scientific American has generated a lot of buzz in the anthropology blogosphere. The piece discusses the problems of accessing human fossil remains, reopening the discussion on how open anthropology needs to be. The reason why data acquisition is such a problem in palaeoanthropology is captured in the opening sentence of an article Stephen Jay Gould and David Pilbeam wrote for Science:


Whenever supply cannot keep up with demand, you can be sure that problems will follow. (Many parents have learned this to their chagrin, when they find out that the Christmas toy du jour, their beloved child so wanted, is sold out.) Each newly unearthed fragment of human bone represents yet another valuable piece in the ever-growing jigsaw puzzle that is our evolutionary history. The study of primary data is of prime importance in paleoanthropology. As a result, a conflict arises, due to the need to study fossils and the limited access placed upon them. Restricted access occurs for a number of reasons, ranging from valid concerns over the fragility of a particular specimen, to scientists reaping the benefits of a research monopoly.

There is an unwritten rule in palaeoanthropology that the discoverers of a fossil have the exclusive rights to publish the initial monograph describing their specimen. Palaeoarchaeologists invest a lot of resources, time and effort in recovering fossils. They will often literally risk body and limb. Dehydration, food poisoning, snake bites, diseases and infections are but some of the hazards field archaeologists face. When they are not digging they are often engaged in the unenviable task of writing grants for their projects. It is understandable that they are wary of outsiders who expect free access to their hard-won prizes.

Ancient fossils usually come out of the ground highly fragmented and in a poor state of preservation. Much time is required to clean, preserve and reconstruct them before conducting a phylogenetic analysis. While many people have focused on the fact that certain specimens have taken an exhorbitant amount of time to describe, thus holding up the process of peer validation, it must also be kept in mind that these represent only a small fraction of the total human fossil record. While it of the utmost importance to make fossils available to outside investigators in a timely fashion, it is perhaps not the most fruitful or constructive area in which to be directing our attention.

Conflicts arise between researchers who want to access fossil material and curators who are genuinely concerned about the wear and tear that these fossils have endured through repeated handling. Curators will often direct researchers to others who have already measured the material in question, to avoid the redundant repetition of measurements. It is often at this point that researchers can come up against a brick wall, with peers who are unwilling to relinquish their valued data. Like the fossils themselves, unique data is a precious commodity and alas is necessary for publication. For good or for ill, peer-reviewed publications are placed in high regard in the anthropological world. Its role when it comes to job-seeking or tenure cannot be underestimated. An incredible amount of data has been collected through the years on ancient human remains but they are rarely put in the public domain. A noteworthy exception is the data on some 3,000 skulls from 17 worldwide populations, measured and made freely available by the eminent anthropologist William W. Howells (pdf file). The Howells' dataset is perhaps that man's most lasting legacy, at least in the sheer number of times his data have been used and referenced. Similarly, we need to place great value on other researchers who make their data available and this should be taken into consideration in matters of career advancement. At a minimum, the sharing of data should be deemed equivalent to research publication.

Positive steps have been taken in the ensure more data is made available. The US National Science Foundation encourage applicants to make provisions to make data available after the research has been completed. The NSF states that:


Anthropologists who fail to comply with these recommendations may have subsequent grant proposals turned down on these grounds. There is an ever-growing number of high quality casts and 3D images of fossils becoming available. Taphonomic processes may deform the fossilised bone and filling in gaps has often required a liberal amount of guesswork. 3D images often allow for better reconstructions of the original specimens, due to the ability to interpolate absent regions and more readily pinpoint and correct deformation. Research centres have woken up to the fact that collaborative projects tend to have a greater synergy due to their symbiotic nature. For palaeoanthropology to become a truly open discipline, it will not only need researchers to be more freehanded with their data, but will require funding agencies, universities and research centres to incentivise such actions.

Related reading
Fossil access editorial @ John Hawks weblog.

Science Suffers From The Idiots At Scientific American @ Anthropology.net.

Take your time @ A Primate of Modern Aspect.

Delson et al. Databases, data access, and data sharing in paleoanthropology: First steps. Evol. Anthropol. (2007) vol. 16 (5).

Gibbons. Glasnost for Hominids: Seeking Access to Fossils. Science (2002) vol. 297 pp. 1464-1468.

Mafart. Human fossils and paleoanthropologists: a complex relation. Journal of Anthropological Sciences (2008) vol. 86 pp. 201-204.

Pilbeam and Gould. Size and Scaling in Human Evolution. Science (1974) vol. 186 ( 4167), 892-901.

Tattersall and Schwartz. Is paleoanthropology science? Naming new fossils and control of access to them. Anat Rec (2002) vol. 269 (6) pp. 239-41.

Above photo by Simon Strandgaard under creative commons license.

The 74th Four Stone Hearth anthropology blog carnival is available over at Adam Henne’s Natures/Cultures blog. Catch up on the latest on anthropology blogging. The next Four Stone Hearth will be hosted here on the 9th of September. Send any anthropology submission for the upcoming carnival to or (be sure to replace [AT] with @ in the email addresses).

The early Lower Palaeolithic remains from Ceprano and Monte Poggiolo show that humans arrived in the Italian peninsula sometime prior to 700,000 years ago. However, it is not until the Aurignacian period (~ 38,000-30,000 BP*) of the Upper Palaeolithic that we see signs of widespread occupation. The earliest Aurignacian seems to occur in northern Italy, before expanding southwards (Mussi 1990). The people of the Aurignacian exploited very diverse habitats in both lowland and mountainous areas, as well as on the island of Sicily.

Extrapolating from data by Bocquet-Appel et al. (2005) it is possible that the population of Italy did not exceed 1,000 inhabitants. While this figure is little more than a best guess, it still gives us an idea of the fragile nature of these groups, who were living constantly on the edge of extinction. With such small numbers inbreeding can become a serious problem. However, studies of European Upper Palaeolithic people find them to be surprisingly homogenous as a whole, which would suggest a significant amount of gene flow between far-flung populations (Henke 1989, 1991). In order to understand how mating systems would have operated during the Early Upper Palaeolithic researchers have looked to modern hunter-gatherer groups. Such studies have found hunter-gatherers to have less group closure than agriculturalists. This would have been an important survival strategy for the hunter-gatherer groups of the Upper Palaeolithic, especially when faced with unpredictable environmental conditions and already constrained mating networks. This open network is also reflected in the material culture from this period. Venus figurines, dating chiefly from the Gravettian period, have been found over an area of approximately 2000 km, spanning from modern day Russia in the Northeast to Spain in the Southwest. The Italian Venuses from Savignano, Balzi Rossi and Parabita show the same female form, with an enlarged midsection, pronounced buttocks, large breasts and voluminous thighs, characteristic of the vast majority of these figurines. This suggests that there was an extensive flow of people and ideas during the Early Upper Palaeolithic. This is further supported by the transport of exotic materials, such as flint and shells over distances of several hundred kilometres.

At around 29,000 years ago, the Italian archaeological record falls silent. This hiatus seems to last for around two millennia. Mussi (2000) suggests that Italy may have become a "demographic trap", due to the combination of low population numbers and small group sizes, leading to the eventual extinction of the Aurignacian people.

Based on their assemblages, is believed that the Gravettian people were a new group, who likely entered the Italian peninsula from south-eastern France. As climatic conditions worsen, more exotic artefacts begin to appear in the archaeological record. A major concentration of sites date to around 25,000 BP, suggesting the arrival of immigrants from northern Europe coinciding with the onset of the Last Glacial Maximum. As new people entered Italy, they had to adapt to strange environments and a more limited variety of animals. We no longer find high altitude sites like in the Aurignacian. This shift to lower altitudes is undoubtedly due to the advancing ice. There is evidence of decreased mobility during the Last Glacial Maximum, which continues until the Mesolithic period (Holt 2003). This may reflect a move to more closed systems, as regionalisation grew due to the ever-increasing population density and greater competition over territories. The burial practices, art, and personal adornments of the Early Upper Palaeolithic, which paralleled those from the rest of the continent disappear at the height of the Last Glacial Maximum, further reflecting a shift to more closed social networks. As temperatures begin to improve towards the end of the Last Glacial Maximum, these cultural artefacts reappear in abundance, once again mirroring the styles and practices seen elsewhere in Europe.

Sicily comes in for special attention. The island has long been of interest to anthropologists, who saw the it as a stepping stone between North Africa and Europe. Ferembach (1986) postulated that Sicily may have served as an entry point for the North African Aterians (or their ancestors) around 50,000 years ago, who later became the "Cro-Magnon race". However, this idea finds little archaeological or skeletal support. Evidence of occupation prior to the Last Glacial Maximum in Sicily is patchy at best. At the site of Fontana Nuova, Aurignacian tools and isolated fragments of human bone have been found and estimated to date to around 30,000 years ago, making it the earliest record of occupation for the island (Chilardi et al 1996). However, it is the only evidence we have for the colonisation of the island during the Aurignacian and it is not until the Epigravettian (~20,000-10,000 BP) that we have further evidence of humans in Sicily. This suggests that the earliest settlers probably went extinct due their small numbers, limited resources and restricted gene flow with the mainland. It also reflects the pattern seen in the rest of Italy, since there are no Aurignacian sites known after 30,000 BP.

At the site of Grotta di San Teodoro the skeletal remains of seven individuals were found, making it the single largest Upper Palaeolithic sample in Sicily. An unpublished direct AMS 14C date situates the skeletal remains at around 14,800 BP (D’Amore et al. 2009). A recent craniometric study of the San Teodoro skeletons shows that they have higher affinities with the Late Upper Palaeolithic and Mesolithic populations, rather than Early Upper Palaeolithic ones (ibid.). These results suggest one of two possible scenarios (a) an early arrival with gene flow, thus explaining the homogeneity with the mainland Italian groups or (b) the late arrival of the direct descendants of the San Teodoro population on the island of Sicily. At the time of the Last Glacial Maximum there was probably a land bridge between Sicily and the Italian mainland, with sea levels being some 120 metres lower. The appearance of exotic faunal evidence further suggest this land connection. While Sicily was occupied as early as the Aurignacian, it may not have been until the Late Epigravettian that the island had a stable population able to overcome the threat of extinction. Like the rest of Italy, Sicily gives us a unique insight the challenges faced by Europe’s latest inhabitants.

*BP is used to indicated uncalibrated radiometric years before present.

References
Bocquet-Appel et al. Estimates of Upper Palaeolithic meta-population size in Europe from archaeological data. Journal of Archaeological Science (2005) vol. 32 (11) pp. 1656-1668.

Chilardi S, Frayer DW, Gioia P, Macchiarelli R, Mussi M (1996) Fontana Nuova di Ragusa (Sicily, Italy): southernmost Aurignacian site in Europe 70: 553-563.

D'Amore G, Marco SD, Tartarelli G, Bigazzi R, Sineo L (2009) Late Pleistocene human evolution in Sicily: comparative morphometric analysis of Grotta di San Teodoro craniofacial remains 56: 537-550.

Ferembach. Les Hommes du Paléolithique Supérieur. Autour du Bassin Méditerraneen. L'Anthropologie (1986) vol. 90 (3) pp. 579-587.

Henke W (1991) Biological Distances in Late Pleistocene and Early Holocene Human Populations in Europe. In: Variability and Evolution. Poznan, Poland: Miskiewicz University Press. pp. 39-64.

Henke (1989) Jungpaläolithiker und Mesolithiker: Beiträge zur Anthropologie. Habilitationsschrift, FB Biologie, Mainz, 1701 S.

Holt BM (2003) Mobility in Upper Paleolithic and Mesolithic Europe: Evidence from the lower limb. Am. J. Phys. Anthropol.

Mussi (1990) Continuity and change in Italy at the Last Glacial Maximum.. In: Soffer, Gamble, editors. The world at 18000: high latitudes. London: . pp. 126-147.

Mussi M (2000) Heading south: the gravettian colonisation of Italy. In: Roebroeks, Mussi, Svoboda, Fennema, editors. Hunters of the Golden Age: The Mid Upper Palaeolithic of Eurasia 30,000–20,000 BP. Leiden: Leiden University Press. pp. 355-374.

Certain anatomical features of the human skeleton are known to vary with geography and climate. To what extent each variable contributes to our physical makeup is less clear. The problem is that populations with similar climate are geographically close to one another. Even if we find shared traits among populations from similar climates it may be just as a result of geographic proximity (and thus clinal gene flow), rather than shared common ancestry.

As I mentioned in my previous post, anthropologists often compared cranial data to matched microsatellite datasets. However, it is rarely possible to get an exact match between the cranial and microsatellite populations. The anthropologist will instead use populations that are genetically similar and which may or may not be representative of the target population. Another option is to substitute microsatellite data with geographic distances, since studies have found a strong correlation between genetic distance and geographic distance (Manica et al. 2005; Ramachandran et al. 2005; Romero et al. 2008). This allows us to get around the need to match phenotypic data with genetic datasets.

A recent paper by Betti et al. used geographic distance as a proxy for neutral genetic distance. They set out to test the extent to which cranial differences can be explained by geographic proximity, by comparing pairwise phenotypic distances among populations and pairwise geographic distances using isolation by distance (IBD) models, as well as comparing pairwise cranial distances with climatic variables after correcting for IBD. Geographic distances were calculated as the shortest distance over land between populations while avoiding areas greater than 2000 metres above sea level. Intercontinental land bridges were also factored into their model.

Their study found geographic distance (and by extension genetic distance) to be a strong predictor of cranial variation. Minimum and maximum temperatures were also a significant predictor of cranial differentiation but not as strong as geographic distance. It also appears that much of this climate-related variation is influenced by the populations from exceptionally cold climates. A previous study by Roseman also found that populations living in extremely cold climates showed greater selection. Betti et al. suggest that this may be due to culture acting as an environmental buffer, with the buffer breaking down at extremely cold climates, after which cranial plasticity takes over.

Since climate and geographic distance covary, not considering isolation by distance leads to an overestimation of the effect of climate on cranial differences between populations. Not surprisingly facial traits showed the strongest correlation with climate. In summary, this study suggests that cranial measurements are predominately influenced by neutral evolutionary processes, especially in populations that do not live in extremely cold climates.

References:
Betti et al. 2009. The relative role of drift and selection in shaping the human skull. Am. J. Phys. Anthropol. in press.

Manica A, Prugnolle F, Balloux F. 2005. Geography is a better determinant of human genetic differentiation than ethnicity. Hum Genet 118:366–371.

Ramachandran S, Deshpande O, Roseman CC, Rosenberg NA, Feldman MW, Cavalli-Sforza LL. 2005. Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa. Proc Natl Acad Sci USA 102:15942–15947.

Romero IG, Manica A, Goudet J, Handley LL, Balloux F. 2008. How accurate is the current picture of human genetic variation? Heredity 102:120–126.



Above photo by jacorbett70 under creative commons license.