Welcome to the St. Patrick’s Day special edition of Four Stone Hearth 88. 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 Martin Rundkvist. The next issue will be hosted at the Greg Laden’s blog on 31 March.
Online Degrees.net has posted their 100 best blogs for anthropology students. It is a wonderful resource that I recommend checking out. Now on with this round of carnival posts.
Over at Testimony of the spade, Magnus Reuterdahl reflects on how extant abbeys can give us a greater appreciation for those which over time have falling into ruin.
Martin Rundkvist over at Aardvarchaeology, has mixed feelings about his Magnum opus entitled “Domed oblong brooches of Vendel Period Scandinavia.” Martin relays how sticking to your “scholarly ideals” is not always the easiest road to career advancement.
In a recent post, I discuss the trend towards decreased head size starting around 30,000 years ago, which continues today.
Carl Feagans at ahotcupofjoe looks at the dispersal of early Homo out of Africa.
Last year, amidst much media fanfare everybody came to know about our 47 million year old purported ancestor “Ida”. This was indeed a spectacularly preserved fossil specimen, which preserved the outline of the body as well as the stomach contents. However, the scientific community at the time aired scepticism about the claim that it was on the evolutionary line that led to us. Many palaeontologists and primatologists were quick to point out that this primate looked more lemur-like. Well, it turns out that they were right. In a paper published in the Journal of Human Evolution shows that this species, Darwinius masillae, belonged to an extinct branch of primates, most closely related to lemurs and lorises. Brian Switek of the Laelaps gives a synopsis of the paper, while Eric Michael Johnson at Primate Diaries gives a very accessible account of the whole affair.
John Hawks is a fly on the wall at a symposium on genetics and genealogy of the African Diaspora. He reports on Fatimah Jackson’s genetic work in Africa and African-Americans, in particular the idea of “ethnogenetic layering”.
Raymond Ho at the Prancing Papio blog has a review of a paper on the changing mating systems in Sichuan snub-nosed monkeys. The pieces offers some plausible evolutionary reasons for the shift from polygynous to polygamous mating systems.
Valerie Williamson writes about Siberian languages, which are on the verge of extinction. The race is on for linguists to document these languages before they disappear completely.
Krystal, over at Anthropology in Practice, talks about a street vendor in her city that has started to take coffee orders via text message. Is this merely a fad or society simply adapting to our greater reliance on digital media?
Ronald Kephart a.k.a. the Cranky Linguist reports on the educational malpractice of teaching religion as science at Liberty University.
Eric Michael Johnson reports on the Itineraries of Exchange symposium. This piece gives us an insight how indigenous groups have managed to maintain traditions and self-determination in the face persecution, racism, and exploitation.
Also check out Eric’s article on Coca Cola’s over-exploitation of water resources in India. It seems that the slogan “Good Till the Last Drop” has a more pernicious meaning.
A Very Remote Period Indeed has a wonderfully titled piece “Mad Neanderthals, peer review and scholarly publication”. Controversy has surrounded the journal Medical Hypotheses since its very conception. This journal is unique in that it doesn’t have a peer review system, while promoting controversial and thought-provoking ideas. However, Julien Riel-Salvatore tells of the comment he published in this journal in response to an article that proposed that Spongiform Encephalopathies may have led to the demise of the Neanderthals. Julien does not think the biggest problem is with the journal’s incredibly low standards but rather with the academic publishing house Elsevier, who by purchasing Medical Hypotheses has given it an air of legitimacy.
That’s it for another edition of Four Stone Hearth. Happy St. Patrick’s Day to one and all!
Golden snub nosed monkey from artsonearth,
CocaColaIndia by Carlos Latuff under the Wikimedia Commons licence.
Marilyn Monroe reading James Joyce. Flickr creative commons licensed content by user I, Puzzled.
The Times article forwards a number of the various hypotheses about why brain size has decreased. Antoine Balzeau reasons that “the cerebellum — a brain structure linked to language and concentration — appears to take up a larger proportion of the head now than in the time of Cro Magnon 1.” While it is true that the cerebellum is proportionally larger in modern humans, it is proportionally smaller than in apes, by around 20%. We still don’t know enough about brain function to be able to say what advantage, if any, a larger cerebellum would give us.
Second up, is the suggestion that big heads are somehow an adaptation to cold climate. There are a number of problems with this idea. If having a large skull is an adaptation to cold environments we would expect to see such traits peaking in the aftermath of the Last Glacial Maximum around 20,000 years ago, many millennia after Cro-Magnon walked the earth. As a general rule people living in Arctic regions tend to have more rounded heads, unlike the long headed Cro-Magnon. What’s more, the limbs of Cro-Magnon and their kin are quite long, contradicting Allen’s Rule which predicts that species will evolve smaller appendages as an adaptation to colder climes. Their body type also differs markedly from that of Neandertals, for whom there is a better case to made of being cold-adapted.
The article goes on to suggest diet as a driving force behind the decrease in head size. Cranial robusticity has indeed been shown to correlate with diet. It is important, however, to make the distinction between cranial size and robusticity. While the two are related they do not necessarily go hand in hand. While the Gravettian populations were undoubtedly more robust than most modern-day populations, they are not especially robust when compared to the Mesolithic populations of Téviec and Hoëdic or modern Aboriginal Australian or Fuegian populations. It is also unclear what dietary innovation could account for the decrease in head size. We have unambiguous evidence for the control of fire at around 250,000 years ago, while agriculture did not appear until around 10,000 years ago. The dates just don’t add up.
The article suggest one more hypothesis for the downsizing of the brain: “… with high infant mortality, only the toughest survived — and the toughest tended to have big heads.” Infant mortality is an ever-present problem for humans because bipedalism has constrained the size of the birth canal. If anything, giving birth to a larger headed children is going to lead to increased mortality for both the mother and child. Indeed, natural selection has restricted in utero brain growth in humans, with a large proportion of brain development occurring outside of the womb. In most non-human primates, the brain is close to adult size by the first year of life. In humans, on the other hand, near-adult brain size is not reached until about ten years of age.
Perhaps, the best explanation for the larger head size of our ancestors is one that the authors failed to mention – allometry. Bigger animals have bigger brains. While the cranial capacity for modern humans is large for a primate of our size, it is still only about a quarter of the size of that of an elephant. The decrease in brain size during the late Pleistocene was also accompanied by a decrease in body size. In other primates that show a decrease in brain size, there is an accompanying decrease in body size. Having a larger brain comes at a cost. The brain is a greedy glucose-guzzling tissue. The is possible that our smaller brain has allowed us to reallocate energy for other bodily functions.
References and further reading
Henneberg M. Evolution of the human brain: is bigger better?. Clin Exp Pharmacol Physiol 1998, 25:745-749.
Schaaffhausen H. On the crania of the most Ancient Races of Man. Müllers Archiv 1858:453.
I will be hosting a St. Patrick’s Day special edition of Four Stone Hearth on Wednesday, March 17th. Four Stone Hearth is a fortnightly anthropology blog carnival. If you have read or written any interesting blog posts on archaeology, socio-cultural anthropology, bio-physical anthropology or linguistic anthropology in the last few weeks, please email me a link and I’ll be sure to include them.
The Online Degrees.net blog has compiled a comprehensive list of the 100 Best Blogs for Anthropology Students. This is a fantastic resource for anybody interested in anthropology.
The premises of the Paleo diet raise some interesting questions that are well worth exploring. For instance, are we really better adapted to the Palaeolithic than the modern era and which aspects of the Palaeolithic does the Paleo diet reference? Many proponents ask the question “who ever heard of a fat caveman?”, as if the answer is somehow inferred. While it is seems be the case that the average Palaeolithic human had a brawnier body than the average modern human, we should not confuse correlation with causation. A better question to ask is whether the “caveman” physique is due solely to diet or are there other factors at play?
While certain human adaptations undoubtedly arose during the Palaeolithic, these are likely to be no more or less important than the adaptations of preceding and subsequent periods in our evolutionary history. Most of our genes evolved a long time before our ancestors were recognisable as primates, never mind humans. Moreover, humans continue to adapt to their diet today. Lactose tolerance is a good example of a trait that arose in many populations of humans after the Palaeolithic. Evolution exists on a continuum; it didn’t start and end sometime during the Palaeolithic.
The Palaeolithic covers a period of around 2.5 million years, as well as an immense geographic range. Moreover, many species of humans lived in very diverse environments during this time. Proponents of the Paleo diet rarely specify what period and indeed which populations or species they use as their model. Food procurement methods changed dramatically over this time period. Over the course of the Palaeolithic, humans shifted from mostly scavenging their meat to systematic hunting. Even among modern hunter-gatherers there is great dietary variation. For instance, the diets of Inuits and Aboriginal Australians couldn’t be more different. Another consideration is that humans have been selectively breeding plants and animals over many millennia. Many of the domesticated varieties we see today are unrecognisable from their wild ancestors. As such, while the Paleo diet recommends greater reliance on meats and non-cultivated plants, it should be kept in mind that these probably bear little resemblance to the wild species our ancestors ate.
The limb bones of the early Upper Palaeolithic Gravettian people are not only large but also have massive muscle attachments. Early humans were physically fit not only because of their diet but in large part due to their high mobility. Hunting and foraging expeditions would have required these groups to cover large distances. Demographic pressures impinging on these small bands of humans would also have further encouraged greater mobility.
It is not disputed that the diet of early hunter-gatherers was much more varied than that of their agricultural counterparts. Early agriculturalists often had an over reliance on few food types, leading to various nutritional deficiencies and generally poorer health. However, there is little reason why this should be the case today. Our shops and markets are packed with varieties of food that our ancestors would be only able to dream off.
Many of the recommendations of the Paleo diet are sensible, such as eating less processed foods, decreasing our sugar intake and increasing our dietary fibre. In this regard, the Paleo diet is on par with most governmental dietary recommendations. Why the need to dress it up in some romanticised account of how our ancestors ate? I will concede that versions of the Paleo diet are probably healthier than the diets most of us adhere to. However, the reasoning behind it is based on an immutable view of human prehistory, coupled with some poor evolutionary thinking.
Above photo modified from original by Lord Jim under creative commons license.
However, what happened Matt is much more disturbing. It has been long known that sauropods have a swelling in the sacral region, leading some people to suggest that it may have functioned as a second brain. This idea has been thoroughly debunked. When Matt was asked to comment on this here is how the original unedited conversation went down:
”Ok one of the curious things about sauropods is that they did have a swelling in the spinal cord in the neighbourhood of their pelvis. And for a while it was thought that may be this was sort of like a second brain to help control the back half of the body. Erm there are a couple of misconceptions there. One is that most animals control large part of their body with their spinal cord. If you’re going through day to day operations like just walking down the street and your minds on something else your brain isn’t even involved in very much controlling your body. A lot of that is a reflex arc that’s controlled by your spinal cord. So it’s not just dinosaurs that are controlling their body with their spinal cord, it’s all animals. Now the other thing about this swelling at the base of the tail is we find the same thing in birds and its called the glycogen body. It’s a big swelling in the spinal cord that has glycogen which is this very energy rich compound that animals use to store energy. Problem is we don’t even know what birds are doing with their glycogen bodies. Er the function is mysterious – we don’t know if the glycogen is supporting their nervous system – if its there to be mobilised, help drive their hind limbs or the back half of their body and until we find out what birds are doing with theirs we have very little hope of knowing what dinosaurs were doing with their glycogen bodies.”
I can only imagine the shock Matt experienced when this got edited down to:
“This was sort of like a second brain to help control the back half of the body.”
This is not what he said at all. In fact, he said the exact opposite, even going so far as to give the reasons why this is a discredited theory. Not only is this downright dishonest on the part of the producers, it also calls into question the credibility of this professional scientist. More generally, it gives legitimacy to the ‘second brain’ hypothesis in the eyes of the public. Understandably, enraged by what he saw, Matt sent an email form Dangerous Ltd, the production company who were responsible for filming the documentary. He received a reply that amounted to a nopology, even having the audacity to say: “we were simply working on the show ever aware of the demands of our audience.” And what about presenting the facts or fairly representing the views of the scientists?
Thankfully, this story has a happy ending. Matt talked to a person high up at the Discovery Channel, who promised that the egregious portion would be promptly removed. Unfortunately, this misrepresentation of a scientist is not an isolated case and we would do well to understand why this happens and what can be done to prevent it. The first thing we should remember is that documentaries are, first and foremost, made for entertainment. As a result, most are written by screenwriters and have a predetermined script. One would think that the scientific facts write themselves but this is sadly not the case. It is the job of the film crew to interview specialists, all the time being conscious of the preplanned plot. Scientists should not be afraid to ask to see an outline of the plot. That way they have an idea of what pieces of information the production team are after. When documentary makers interview scientists they are generally looking for snippets that will propel the storyline. This is the reason why hours of footage eventually get edited down to mere seconds. Naturally, the more time you spend talking the greater the chances of something making it into the finally cut. However, this also means that there is more material that can be taken out of context. It is in the interviewee’s best interest to keep the conversation from wandering off course. This can be achieved by negotiating an hourly fee with the production company prior to any interview. Scientists shouldn’t be shy about demanding money for their time. Film crews will often have a budget for this but are normally not very forthcoming in divulging this information. As long as the film crew are cognisant of their budget, they are more likely to cut to the chase earlier on, rather than fishing around for juicy quotes.
While it is tempting for experts to point out the flaws in refuted hypotheses, they are perhaps better off biting their tongues. This way, their words cannot be contorted to suggest that they are in fact a proponent of a viewpoint they firmly disagree with. However, if you are cornered into giving an opinion on a contrary idea it is perhaps best to let your body do the talking. If you can visibly demonstrate your disdain for a particular idea through your facial expressions, it makes it much harder for the editors to later manipulate your words in such a way that they contradict your body language. This requires scientists to really show and perhaps exaggerate their emotions, but heck, if one truly loves their profession that shouldn’t be too difficult to accomplish.
It is important that scientists speak out against any media distortions of science. It is likely that Dangerous Ltd. felt some heat from the negative reaction of bloggers and commentators, subsequent to Matt’s initial blog post. If we don’t take a stand, we are simply emboldening sloppy science communication. We should email, phone, or write to these companies and let them know that we are not happy with how science is being misrepresented. As a last resort one may consider taking legal action. While scientists give up many of their privileges once they sign a release form, slander is still slander, and as such is subject to legal action.
Good science doesn’t need to be dressed up or distorted, most especially when we are talking about dinosaurs. While some may cringe at the very thought, scientists more than ever before need to become media-saavy. The media is ultimately interested in a great story and will go to extreme lengths to get it. The case of Matt is not new and their will be many more cases like it to come. Only by being more aware of how the media operates can scientists be equipped to deal with such future misrepresentations.
Lies, damned lies, and Clash of the Dinosaurs
Clash of the Dinosaurs: Dangerous Ltd document their own dishonest editing
Clash of the Dinosaurs: The Discovery Channel steps up
A scientist is QUOTE MINED on a Discovery dinosaur documentary
This abstract from a 1961 paper made me smile:
Casey AE, Franklin RB. 1961. Cork-kerry Irish compared anthropometrically with 139 modern and ancient peoples. Irish Journal of Medical Science. 36 (9).
Chinese scientists say that a recently discovered partial jaw from Guangxi challenges the ‘out of Africa’ model of modern human origins, while lending support to the multiregional hypothesis. The 110,000 year-old mandible is described as having a chin that juts “ever so slightly outward.” These scientists assert that the presence of chin shows that there was significant gene flow between populations of modern Homo sapiens and archaic Homo.
Wu Xinzhi of the Chinese Academy of Sciences had the following to say about the find:
It is interesting to note Xinzhi’s use of the past simple tense to suggest that this is a closed case. Far from it! Palaeoanthropological theory has moved on from the multiregional sensu stricto versus ‘out of Africa’ sensu stricto dichotomy that predominated the discussion during the latter half of the last century. Nevertheless, the question of how much gene flow, if any, took place between modern and archaic Homo is still very much a debated issue.
At this stage you may be wondering why there has been such furore over a chinned jaw. As long ago as 1775, Johann Friedrich Blumenbach commented on the uniqueness of the modern human chin:
The distinctive modern human chin develops through the combination of bone deposition on the inferior part of the jaw and resorption around the alveolar region. In other primates the entire jaw undergoes deposition. The modern human chin is characterised as having a central keel, with hollowed out depressions (known as mental fossae) to either side, together with a protruding inferior portion. This distended mental protuberance and lateral extremities make up the mental trigone, giving the chin the appearance of an inverted T. It is the combination of all these anatomical features that make up the prototypal modern chin. However, chins show great variability, with some modern humans not having any.
This variability is also extends to earlier hominins. The Middle Pleistocene fossils from the Sima de los Huesos have been described as having chins, and even well-developed mental trigones. Among Pleistocene hominins, Neandertals appear to have the most divergent pattern from the modern configuration, universally lacking the inverted T and mental fossae. While it has been argued that the Neandertal mandibles from the Croatian site of Vindija show the development of incipient chins, this has not been borne out by later analyses.
Some of the ‘modern’ Klasies River Mouth mandibles do not have developed mental trigones, midline keel or a thickening of the inferior margin. However, the modern designation of this material is controversial with these fossils showing a mosaic of both archaic and modern features. Similarly, the modern humans from Qafzeh show variable expression of the inverted T and mental fossae, with no indication of these features in the Skhūl specimens. The 700-800,000 year-old Tighenif mandibles show a surprisingly modern configuration complete with central keel, a thickened inferior portion, and the development of a triangular protuberance. The presence of a chin in these specimens could represent a synapomorphy with modern humans.
Based on the archaeological record, it appears that modern humans left Africa some time around 100,000 years ago. Among the oldest undisputed modern human remains in China come from Zhoukoudian Cave at around 35,000 years BP. The possibly earlier fossil from Liujiang is marred with dating problems. In order for the Chinese scientists’ assertion to hold, it would require an even earlier exit from Africa or expansive gene flow between modern humans living in Africa and archaic humans in Asia; claims for which the evidence is currently lacking. Future analyses of the specimens will determine whether these chins have a truly modern form or whether the pattern is more like the non-homologous protruding inferior jaws seen in other archaic specimens. Alternatively, if these specimens end up being the result of convergent evolution it would raise questions about the functional significance of a chin. Finally, if these fossils show a pattern similar to the one seen in the Tighenif fossils it may suggest that they belong to the same clade.
References and further reading
Ahern JC (1993). The Transitional Nature of the Late Neandertal Mandibles from Vindija Cave, Croatia. M.A. thesis. Department of Anthropology, Northern Illinois University.
Blumenbach, JF (1978). The anthropological treatises of Johann Friedrich Blumenbach / translated and edited from the Latin, German, and French originals by Thomas Bendyshe. Boston : Longwood Press.
Hawks, J (2009). It came from Guangxi.
McKenna, P (2009). Chinese challenge to ‘out of Africa’ theory. New Scientist.
Rosas, A. (1995). Seventeen new mandibular specimens from the Atapuerca/Ibeas Middle Pleistocene hominids sample. J. hum. Evol. 28, 533–559.
Schwartz JH, Tattersall I (2000). The human chin revisited: what is it and who has it? J Hum Evol 38:367-409.
Schwartz JH, Tattersall I (2002) The Human Fossil Record, Vol. 1: Craniodental Morphology of Genus Homo (Europe) Wiley-Liss: New York.
Stone R (2009). Signs of Early Homo sapiens in China? Science 326 (5953) p 655.
Above image: Institute of Vertebrate Palaeontology and Palaeoanthropology, Chinese Academy of Sciences.
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 erectusis 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.
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).
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.
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.