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.

Palaeoanthropologist Darren Curnoe (2009) gives the following biological definition of the term ‘robust’:

…a descriptive anatomical term referring to individuals, complexes, organs, structures or traits which are heavily built, rugged, well defined or corpulent.

Bones tend to more robust where muscles, tendons or ligaments insert into the periosteum. When these insertion sites are subjected to stress, blood flow increases. This in turn stimulates the production of osteoblasts, which lay down extra bone. With respect to the skull the term robust is generally used to refer to so-called superstructures, such as the supraorbital ridges, occipital crests or zygomaxillary tuberosities. Anthropologists often classify robusticity based on the relative expression of a particular trait, or indeed its absence. Given that robusticity is related to physical stress, traits tend to be more pronounced in males and in certain populations (e.g. Aboriginal Australians and Fuegians).

The retention of robust features in certain populations, particularly Aboriginal Australians, has been used to support the multiregional hypothesis of human origins (e.g. Wolpoff et al. 2001; Frayer et al., 1993). On the other hand, proponents of a replacement model see robust traits (e.g. in Australian Aboriginal populations) as retained plesiomorphies and argue that these traits cannot be used to show continuity (Lieberman 2000). In response, many multiregionalists have revised their position to suggest that the reduction of the browridge in later Neandertals, such as St Césaire and Vindija, represents a synapomorphy between Neandertals and modern humans, likely due to interbreeding. The underlying assumption here is that these robust traits have a strong genetic component. Furthermore, there is a notable decrease in cranial robusticity from the early Upper Palaeolithic to late Upper Palaeolithic. It has been suggested that this may reflect changes in diet. Transition from hunter-gather to agricultural lifestyle is associated with a reduction in cranial robusticity, although correlation does not necessarily prove causation. However, not all hunter-gather groups are universally more robust than argriculturalists, which might suggest some other factors at play.

A recent in press paper by Baab et al. sets out to examine the possible mechanisms behind robust cranial characters. The null hypothesis in their study is that neutral evolutionary processes (e.g. genetic drift) were responsible for the pattern of cranial robusticity in modern humans - the rejection of which would suggest selection acting on these traits. To test the null hypothesis of neutral evolution of cranial robusticity Mahalonobis D² distances for robust characters were compared to Ddm distances derived from microsatellite data. Microsatellites are useful in reconstructing evolutionary relationships due to their unusually high mutation rates, which result in largely selectively neutral polymorphisms.

Of the variables examined, only cranial shape was significantly correlated with robusticity, while cranial size, climate and neutral genetic distances were not. This is at odds with an earlier study by Mirazón Lahr and Wright (1996) (1996) who found the strongest correlation between cranial robusticity and cranial size. This finding may be due to use of geometric morphometrics by Baab and colleagues, which is better at separating size and shape compared to the linear morphometrics used by Mirazón Lahr and Wright (1996).

Cranial robusticity was not correlated with neutral genetic distances, suggesting that neutral evolutionary processes (e.g. genetic drift) were not responsible for the pattern of cranial robusticity in the populations studied. As noted by the authors, this finding could also be explained by a non-perfect match of populations among some of the cranial and molecular samples. In studies such as this one, it is often difficult to find an exact match between the populations from which we derive our cranial and molecular data. In such cases, we are left with the choice of eliminating samples or using another genetically similar population. The authors choose the latter but neither option is ideal and both have their own disadvantages. Unfortunately, the reason for including Upper Palaeolithic and Neolithic samples in this study is never fully explained and the assumption that modern genetic populations are appropriate proxies for such populations is never justified. Setting this aside, the findings of this study caution the use of robust traits in constructing phylogenetic relationships in modern humans.

The strongest correlations were found between cranial robusticity and either cranial or masticatory shape. This lends support to the hypothesis that robusticity is in some part functionally determined. The study also found crania with more prognathic faces, longer skulls, expanded glabellar and occipital regions to be more robust. Mirazón Lahr and Wright (1996) noted a similar tendency of longer skulls to have superstructures, while further emphasising their tendency to be associated with narrow skulls and a large palatal region.

While most of the robust variables in this study were areas of muscle insertions, the supraorbital region has a distinct aetiology. While many have interpreted the supraorbital region as an area of stress reinforcement in the skull (the so-called beam model) which is strongly influenced by mastication (Endo 1966, 1970; Russell 1985), there is a strong evidence to suggest that this is not its primary purpose. Supraorbital development begins early in life, suggesting that the supraorbital ridge may be part of the overall craniofacial complex and is likely under genetic control. While the beam model is intuitive, it is unsupported by empirical data. Hylander and colleagues (Hylander et al. 1991a, 1991b, 1992; Hylander and Ravosa 1992) conducted in vivo strain gauge experiments in different primates to assess the amount of strain magnitudes generated during mastication. They found these levels to be low to induce bone deposition in all the species they studied, even when chewing hard food. Moreover, anthropoids do not show a correlation between the browridge and the moment arms of the masticatory muscles, as the beam model would predict (Ravosa 1991). These researchers adopt the model proposed by Moss and Young (1960), which views supraorbital development as the result of placement of the brain and eyes. They postulated that the reduction of the brow ridge in modern humans was related to the expansion of the frontal lobe in our species. In hominins with orbits positioned well in front of the frontal lobes, as in chimpanzees or the erectines, the space between the orbits and the brain case is bridged by a brow ridge. If the supraorbital region is under genetic control, as the research of Hylander and Ravosa suggests, it would be of interest to examine this region in isolation to assess if it correlates with neutral evolutionary processes, particularly in light of a recent paper by Von Cramen-Taubedal which found the shape of the frontal bone to be consistent with neutral genetic expectation.

References

Baab KL, SE Freidline, SL Wang, T Hanson. 2009. Relationship of cranial robusticity to cranial form, geography and climate in Homo sapiens (in press). Am. J. Phys. Anthropol.

Curnoe D. 2009. Possible causes and significance of cranial robusticity among Pleistocene-Early Holocene Australians. Journal of Archaeological Science (2009) vol. 36 (4): 980-990.

Endo B. 1966. Experimental studies on the mechanical significance of the form of the human facial skeleton. J Faculty Sci Univ Tokyo (Section V, Anthropol) 3:1–106.

Endo B. 1970. Analysis of stress around the orbit due to masseter and temporalis muscles respectively. J Anthropol Soc Nippon 78:251–266.

Frayer DW, MH Wolpoff, AG Thorne, FH Smith, GG Pope. Theories of modern human origins: the paleontological test. American Anthropologist (1993) vol. 95 (1): 14-50.

Hylander WL, Picq PG, Johnson KR. 1991a. Masticatory–stress hypotheses and the supraorbital region of primates. Am J Phys Anthropol 86:1–36.

Hylander WL, Picq PG, Johnson KR. 1991b. Function of the supraorbital region of primates. Arch Oral Biol 36:273– 281.

Hylander WL, Ravosa MJ. 1992. An analysis of the supraorbital region of primates: a morphometric and experimental approach. In: Smith P, Tchernov E,
editors. Structure, function and evolution of teeth. Tel Aviv: Freund Publishing. p 223–255.

Lieberman, DE. (2000) Ontogeny, homology, and phylogeny in the Hominid craniofacial skeleton: the problem of the browridge. In P. O'Higgins and M. Cohn (eds.) Development, Growth and Evolution: implications for the study of hominid skeletal evolution. London: Academic Press, pp. 85-122.

Moss ML, RW Young. 1960. A functional approach to craniology. Am. J. Phys. Anthropol. 18:281-292.

Mirazón Lahr M, RVS Wright. 1996. The question of robusticity and the relationship between cranial size and shape in Homo sapiens. Journal of Human Evolution.

Ravosa MJ. 1991. Interspecific perspective on mechanical and nonmechanical models of primate circumorbital morphology. Am J Phys Anthropol. 86(3):369-96.

Russell MD. 1985. The Supraorbital Torus:" A Most Remarkable Peculiarity". Current Anthropology. vol. 26 (3) pp. 337

Wolpoff MH, J Hawks, DW Frayer, K Hunley. 2001. Modern Human Ancestry at the Peripheries: A Test of the Replacement Theory. Science. vol. 291 (5502):293-297.



Above photo modified from original by Thomas Hawk under creative commons license.

Among this week’s new videos from TED, was a talk given by Elaine Morgan – the chief promoter of the Aquatic Ape Hypothesis (AAH). The AAH was first formulated by Alister Hardy and is the idea that human evolution went through an aquatic stage, which in turn explains many of the features of the human physiology. For anybody with a poor understanding of evolutionary biology the AAH arguments can seem quite compelling. Instead of repeating the numerous reasons why the AAH fails (Jim Moore has an entire website dedicated to this), I wish to address some of the specific arguments made in this video.

Morgan starts off my stating that "… there's one aspect of this story which they [evolutionists] have thrown no light on and they seem anxious to skirt around and step over it and talk about something else. So I'm going to talk about it. It's the question of why are we so different from the chimpanzees?". Either Morgan has not been reading the hundreds of research papers that have addressed these important questions or she is trying to hoodwink her audience. Palaeoanthropologists and primatologists have long recognised the value of studying human and chimp differences in order to understand our shared evolutionary history. In fact, it is impossible to talk about functional anatomy and phylogenetic history in humans without reference to our closest extinct and living hominin relatives.

She continues: "Yet when you look at the phenotypes. There's a chimp, there's a man. They're astoundingly different. No resemblance at all." I am hearing this correctly? No resemblance at all? Even a five year old can see the striking similarities between chimpanzees and humans. To suggest that there is “no resemblance at all” is laughable. It was the similarities of humans to other non-human primates that led Charles Darwin to argue for common ancestry between humans and the great apes. Even without the fossil record and the unambiguous molecular evidence, the morphological similarities alone would be enough to suggest a shared common ancestry of chimps and humans.

Throughout the talk she constantly refers to humans as naked, as if to suggest we are hairless. One need only look at a shirtless Alec Baldwin, Robin Williams or Andy Garcia to know this is not the case. While it is true that humans are less hairy than the rest of our primate kin there are far more compelling hypotheses to explain our lack of hair (thermoregulation, defence against parasites or sexual selection). She claims that hairlessness is an aquatic trait when in fact most aquatic/semi-acquatic mammals are in fact hairy. Otters, polar bears, seals, and walruses are but some examples that spring to mind.

Regarding the failed savannah hypothesis of bipedalism Morgan has this to say: "What do scientists do when a paradigm fails… carry on as though nothing had ever happened… If they haven't got a paradigm they can't ask the questions… The only other option open to them is to stop asking the questions. So that is what they have done now. That is why you don't hear them talking about it."

When paradigms fail science marches on. When was the last time you heard a scientist defending the merits of Lamarckism, psychoanalysis and phrenology? Morgan is correct that the savannah hypothesis doesn’t weigh up against the evidence but she mistakenly claims that the anthropologists haven’t let go of this idea. The savannah hypothesis was formulated in a time when there was a dearth of palaeoecological data for the most important African archaeological sites. As more data came in, anthropologists changed their models correspondingly. No serious anthropologist still adheres to the savannah hypothesis. Morgan chooses to ignore this fact, instead preferring the easier route of attacking a strawman. In the references section below, you will find just a spattering of the work anthropologists have been doing on palaeoecological reconstructions of the environments occupied by our forebearers. These papers address the very questions Morgan asserts that scientists have stopped asking. Does she not read the anthropological literature or does she just choose to ignore it? She implies that because the savannah hypothesis is false it somehow offers support to the AAH. In fact, the consensus opinion suggests that neither savannah nor aquatic environments were very important in the early stages of human evolution, but rather our hominin ancestors exploited wood and forest habitats. A number of anthropologists have proposed an arboreal origin of hominin bipedality (Crompton 2008; Pickerford 2006; Senut 2003, 2006). In fact, the best known human ancestor Lucy shows clear arboreal adaptations.

Morgans proceeds by stating that "there is only one circumstance in which they always, all of them [non human primates], walk on two legs and that is when they are wading through water." Contrary to Morgan’s claim, the data have shown apes to be bipedal more often on land than in the water.

She follows this up by saying that the fat in humans is similar to that seen in aquatic mammals. Humans have a similar number of fat cells compared with other primates. The increased subcutaneous fat seen in humans is most likely a result of diet rather than an evolutionary adaptation. Non-human primate obesity is well documented, particularly in primates kept in captivity (Videan 2007; Altmann et al 1993; Kemnitz et al 1989; Schwartz et al 1993). Moreover, the distribution of fat in humans runs contrary to need aquatic mammals have for streamlining.

Ten minutes into the talk she states that "the only creatures that have got conscious control of their breath are the diving animals and the birds". Humans are not the only non-aquatic mammal which can hold its breath. Various monkeys, for instance, can and do hold their breath, as well as dogs.

Finally, she asserts that "we are streamlined." Humans are anything but streamlined. Our motion in the water is generally quite wasteful. Ask any swimming coach. Fish have a fusiform shape (tapered at both ends), which is ideal for moving through the water with the least amount of resistance. Let’s put this into perspective. The sailfish records speeds of up to 116 km/hr (72 mph), while Michael Phelps can average a measly about 6.5 km/hr (4 mph) on a good day! Our body shape is a consequence of our adaptation to bipedalism, the requirements of childbirth in women, sexual dimorphism and sexual selection.

While I generally enjoy listening to the speakers at TED, I think this is an idea NOT worth spreading.

References

Altmann J, Alberts SC, Altmann SA, Roy SB (2002) Dramatic change in local climate patterns in the Amboseli Basin, Kenya. Afr J Ecol 40, 248–251.

Altmann J, Schoeller D, Altmann SA, Muruthi P, Sapolsky RM (1993) Body size and fatness of free-living baboons reflect food availability and activity levels. Am J Primatol 30: 149–61.

Andrews P (1996) Palaeoecology and hominoid palaeoenviron-ments. Biol Rev 71, 257–300.

Andrews P, Humphrey L (1999) African Miocene environments and the transition to early hominines. In African Biogeography, Climate Change and Early Hominid Evolution (eds Bromage TG, Schrenk F), pp. 282–300. New York: Oxford University Press.

Andrews P (2007) The biogeography of hominid evolution. J Biogeogr 34, 381–382.

Andrews P, Kelley J (2007) Middle Miocene dispersals of apes. Folia Primatol 78, 328–343.

Andrews P, Bamford M (2008) Past and present vegetation ecology of Laetoli, Tanzania. J Hum Evol 54, 78–98.

Codron D, Luyt J, Lee-Thorp JA, Sponheimer M, De Ruiter D, Codron J (2005) Utilization Of Savanna-Based Resources By Plio-Pleistocene Baboons. S Afr J Sci 101, 245–248.

Crompton RH, EE Vereecke, SKS Thorpe (2008) Locomotion and posture from the common hominoid ancestor to fully modern hominins, with special reference to the last common panin/hominin ancestor. J Anat 212, 501–543.

Demenocal PB (2004) African Climate Change And Faunal Evolution During The Pliocene-Pleistocene. Earth Planet Sci Lett 220, 3–24.

Denton G (1999) Cenozoic climate change. In African Biogeography, Climate Change and Early Hominid Evolution (eds Bromage TG, Schrenk F), pp. 94–114. New York: Oxford University Press.

Dowsett HJ, Barron JA, Poore RZ, et al. (1999) Middle Pliocene paleoenvironmental reconstruction: PRISM2. US Geol Surv, Reston, Va, Open File Rep 99–535.

Elton S (2000) Ecomorphology and evolutionary biology of African Cercopithecoids: providing an ecological context for hominin evolution. PhD dissertation, University of Cambridge.

Jacobs BF (2004) Palaeobotanical studies from tropical Africa: relevance to the evolution of forest, woodland and savannah biomes. Phil Trans R Soc Lond B359, 1573–1583.

Kemnitz JW, Goy RW, Flitsch TJ, Lohmiller JJ, Robinson JA (1989) Obesity in male and female rhesus monkeys: fat distribution, glucoregulation, and serum androgen levels. J Clin Endocrinol Metab 69:287–93.

Kingston J, Harrison T (2007) Isotopic dietary reconstructions of Pliocene herbivores at Laetoli: implications for hominin paleo- ecology. Palaeogeog Palaeoclimatol Palaeoecol 243, 272–306.

Kovarovic KM, Andrews P, Aiello L (2002). The palaeoecology of the Upper Ndolanya Beds, Laetoli, Tanzania. J Hum Evol 43, 395–418.

Pickford M (2006) Paleoenvironments, Paleoecology, Adaptations and the Origins of Bipedalism in Hominidae. In Human Origins and Environmental Backgrounds (eds Ishida H, Tuttle RH, Pick- ford M, Ogihara M, Nakatsukasa M), pp. 175–198. Heidelberg: Springer.

Schwartz SM, Kemnitz JW, Howard CF Jr (1993) Obesity in free-ranging rhesus macaques. Int J Obes 17:1–9.

Senut B (2003) Palaeontological approach to the evolution of hominid bipedalism: the evidence revisited. Cour Forsch-Inst Senkenberg 243, 125–134.

Senut B (2006) Arboreal Origins of Bipedalism. In Human Origins and Environmental Backgrounds (eds Ishida H, Tuttle RH, Pickford M, Ogihara N, Nakatsukasa M), pp. 199–208. Heidelberg: Springer.

Sikes N (1999) Plio-Pleistocene floral context and habitat prefer- ences of sympatric hominid species in East Africa. In African Bio- geography, Climate Change and Early Hominid Evolution (eds Bromage TG, Schrenk F), pp. 301–315. New York: Oxford Univer- sity Press.

Videan EN, J Fritz, J Murphy (2007) Development of guidelines for assessing obesity in captive chimpanzees (Pan troglodytes). Zoo Biology 26: 93–104.

Vincens A, Garcin Y, Buchet G. (2007) Influence of rainfall seasonality on African lowland vegetation during the Late Quaternary: pollen evidence from Lake Masoko, Tanzania. J Biogeogr 34, 1274–1288.

WoldeGabriel G, Haile-Selassie Y, Renne P, et al. (2001) Geology and palaeontology of the Late Miocene Middle Awash valley, Afar rift, Ethiopia. Nature 412, 175–178.