Category Archives: Anthropology and Geoarchaeology

Neanderthal development

Despite the lingering public image that Neanderthals were not as bright as fully modern humans some had significantly larger brains than we do, albeit with most of the difference being in the rear part of the brain region. So they may have had different powers, such as enhanced vision and awareness of position (proprioception). Because there are few cranial fossils of immature Neanderthals and, for them, little evidence of ages, not much is known about how they developed from birth. A common assumption has been that because their brain was larger post-natal development much have been faster than in modern humans. Set against our slow post-natal development and the faster pace in chimpanzees this assumption has been used in support of limited Neanderthal cognitive abilities.

The El Sidron Neanderthal boy, including a reconstruction of his skull and brain cast. (credit: Antonio Rosas, Museo Nacional de Ciencias Naturales, Madrid, Spain)

The El Sidron cave in Asturias region of northern Spain has yielded fossil remains of a dozen Neanderthals dated at between 49 and 37 ka, the time when anatomically modern humans were also present in Europe. They are among the best studied examples of this human group. Three were of boys, the best preserved of whom is estimated to have died at 7.7 years old from analysis of his dental development (Rosas, A. and 10 others 2017. The growth pattern of Neandertals, reconstructed from a juvenile skeleton from El Sidrón (Spain). Science, v. 357, p. 1282-1287; doi:10.1126/science.aan6463) Analysis of signs of the maturation stage that he had reached, including that of his brain, show no fundamental difference from modern human juveniles in his overall pace of growth. Other workers have found that a similarly aged Homo erectus boy from Kenya had indeed developed more quickly than modern human juveniles.

It’s not much to go on, but the El Sidron boy supports the view that Neanderthals were not much different from us.

You can find more information on migration of modern humans here.

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Ancient footprints

To see traces of where our forebears walked, such as the famous Australopithecus afarensis trackway at Laetoli in Tanzania, the footprints of Neanderthal children in 350 ka old Italian volcanic ash (The first volcanologists? Earth Pages March 2003) or even those of Mesolithic families in estuarine mud is about as heart stopping as it gets for a geologist. But imagine the astonishment of members of a multinational team working on Miocene shore-line sediments on Crete when they came upon a bedding surface covered with what are almost certainly the footprints of another bipedal animal from 5.7 Ma ago (Gierliński, G.D. et al. 2017. Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete? Proceedings of the Geologists’ Association, online; https://doi.org/10.1016/j.pgeola.2017.07.006). Trackways preserve a few moments in time, however old they are and the chances of their being preserved are very small, yet they can supply information that is lost from even the best preserved fossil, such as gait, weight, speed and so forth.

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Track bearing surface; (b) two footprints in 5.7 Ma old Miocene sediments at Trachilos, Crete (credit: Gierliński, G.D. et al. 2017; Figures 2 and 8)

The tracks clearly indicate that whatever left them was bipedal and lacked claws, and closely resemble those attributed to A. afarensis at Laetoli in a 3.7 Ma old volcanic ash. What they do not resemble closely are those of non-hominin modern primates, such as chimpanzees. They are diminutive compared with adult modern human prints, being about 12.5 cm long (equivalent to a UK child’ shoe size 4 – US size 4.5, EU 20) and about a third to half the size of those at Laetoli. Were they around the age of those at Laetoli or younger there seems little doubt that they would be widely interpreted as being of hominin origin. But being from an island in the Mediterranean as well as far from sites in Africa that have yielded Miocene hominins (Ardipithecus kadabba from Ethiopia, Orrorin from Kenya and Sahelanthropus from Chad),  such an interpretation is bound to create controversy. Somewhat less controversial might be to regard them as having been created by a late-Miocene primate that convergently evolved a hominin-like upright gait and foot. Being preserved in what seem to be coastal marine sediments, there is probably little chance of body fossils being preserved in the exposed horizon. Since foot bones are so fragile, even if a primate fossil is discovered in the late Miocene of Crete the chances of resolving the issue are pretty remote. Yet fossil primate specialists will undoubtedly beat a well-trodden path to the Trachilos site near Kissamos on Crete

Early modern humans in Sumatra before the Toba eruption

In late July 2017 news emerged that modern humans first reached Australia at least 65 thousand years ago. Confirming that the date of departure from Africa to end up in SE Asia and Australasia was  considerable earlier than previously believed, deposits in Sumatra that contain remains of early Home sapiens have yielded even older ages (Westaway, K.E. and 22 others 2017. An early modern human presence in Sumatra 73,000–63,000 years ago. Nature v. 548 online; doi:10.1038/nature23452). This resulted from a re-examination of material from the Padang Caves first excavated more than a century ago by Eugène Dubois, famous for his discovery in Java of the first H. erectus remains. A richly fossiliferous breccia in the Lida Ajer cave yielded a fauna characteristic of a rainforest biome and included two teeth that Dubois considered to be human. Several later palaeontologists confirmed his identification as have hominin specialists in the present Australian-Indonesian-American-British-Dutch-German team. The fossil assemblage has long suggested great antiquity for the site, but only now has it been dated precisely. The dating employed three methods: optically stimulated luminescence dating of quartz grains from the breccia (85±25 to 62±5  ka); uranium-series dating of speleothem including fragments of hollow ‘soda-straw’ stalactites(84±1 to 71±7 ka); uranium-series dating of gibbon and orangutan teeth found together with the human teeth (86±13 to 76±7 ka). Statistical analysis of the age data suggests 73 to 63 ka for the fauna, with a maximum age for deposition of the breccia of 84±1 ka.

Satellite image of Lake Toba, the site of a VE...

Satellite image of Lake Toba in NW Sumatra (at centre), the site of the largest volcanic eruption during the history of human evolution ~71,600 years ago (credit: Wikipedia)

Stone tools which may have been carried by anatomically modern humans into the area have previously been used to suggest a minimum date of the arrival of migrants, though they may have been carried by ­H. erectus. Remarkably, such tools have been found beneath a thick bed of volcanic ash found throughout southern Asia and in Indian Ocean sediment cores. This has been dated at 71.6 ka and represents the explosive collapse of the caldera now containing Lake Toba in NW Sumatra that was the largest volcanic event in the entire history of the genus Homo. The new age data from Lida Ajer suggests that modern humans were present in its vicinty before the eruption, a view also supported by ‘molecular-clock’ dating of the range of mitochondrial DNA carried by living SE Asian people (79 to 75 ka). So, despite the stupendous magnitude of the Toba eruption is seems likely that some of the migrants survived.  Together with the dating of the earliest Australians the Sumatran evidence is at odds with the view, widely held by palaeoanthropologists, that the ‘Out of Africa’ exodus began by crossing the Straits of Bab el Mandab between 74 and 58 ka when global sea-level fell markedly during marine oxygen-isotope Stage 4 (MIS4). A problem with that hypothesis has been that climatic and ecological conditions in southern Asia during MIS4 were unfavourable. But is seems that modern humans were already there and capable of adapting to both the climate shift and to the devastation undoubtedly caused by Toba.

New dates for earliest human occupation of Australia

When modern humans first reached Australia has an importance beyond the starting date for the island continent’s archaeology and confirmation that their ancestors are the oldest known migrants from Africa. The first native Australians carried within their genome important information about the minimum date at which some non-Africans interbred with more archaic Neanderthal and Denisovan humans, traces of whose DNA are are present in that of living Australian aborigines. Most dating of when modern humans first reached different parts of the non-African world has relied on the radiocarbon method, which is suspect from beyond 40 to 45 ka as 14C produced earlier has decayed to levels that are now below the practical limit of detection and measurement. It is therefore no accident that the bulk of ‘first-arrival’ dates for Eurasia and Australasia are around 45 ka. In fact, any accurate age, however old, for the earliest skeletal remains only indicates the minimum date of arrival until other remains are discovered.

Reliable dating of earlier events in the Pleistocene relies on other methods, the most important for settings other than speleothem from caves being optically stimulated luminescence (OSL) applied to soil minerals that estimates their time of burial. Briefly, molecules of soil grains made of a mineral such as quartz are ‘charged-up’ with energy by radiation emitted by unstable isotopes in the soil. Exposure to light releases that stored energy in the form of luminescence. Measuring the amount of luminescence emitted by optically stimulated grains therefore gives a measure of the time since they were buried and ceased to be exposed to sunlight.

Madjedbebe rock shelter

The Madjedbebe rock shelter in Arnhem Land, Northern Territories, Australia. (Credit: Chris Clarkson, University of Queensland)

A re-evaluation of the Madjedbebe site in the Northern Territory, widely accepted as having yielded Australia’s oldest artefacts in 1989, takes back human occupation more than 20 thousand years before previous estimates (Clarkson and 27 others 2017. Human occupation of northern Australia by 65, 000 years ago. Nature, v.  547, p. 306-310; doi:10.1038/nature22968). The soil profile in the Madjedbebe rock shelter turns out to be littered with artefacts – including hearths, tools and blocks of ochre and reflective mica pigments, plus remnants of plant foods – to a depth of ~2.5 m, with three particularly dense accumulations. Carbon-rich remains are also present throughout the profile which provided a means of accurate calibration and confirmation of OSL dates back as far as the radiocarbon method allows, giving confidence in the older OSL dates that extend to 65.0±5.7 ka in the earliest zone of dense artefact finds. Because the modern DNA of Australia’s first native people shows no sign of mixture with other modern humans, this places the timing of modern human interbreeding with archaic people before this time. The age also predates the range when the continent’s megafauna began to decline to eventual extinction, which supports the view that it was anthropogenic.

See also: Marean, C.W. 2017. Early signs of human presence in Australia. Nature, v.  547, p. 285-287; doi:10.1038/547285a.

Origin of anatomically modern humans

How evolution proceeds and species arise are affected by many different processes. But, if members of every generation of the clade that led from the probable common ancestor of ourselves, Neanderthals, Denisovans and other hominins of the last 700 ka or so – widely thought to have been Homo heidelbergensis­ – were found as perfectly preserved fossils they would show gradually shifting anatomical features that from time to time and place to place would diverge to lead to different species. If, also, every specimen was accurately dated then there would be the last part of the human evolutionary bush laid out in a 3-D graphic. That is never going to be possible, of course. Human fossils are rare and there are few of them that are well-preserved. So the field of human origins throws up surprises on a regular basis, and if palaeoanthropologists were more dogmatic than most of them actually are there would be equally regular, public displays of the eating of hats.

As regards early modern H. sapiens, fossils from a couple of sites in Ethiopia have been the oldest known, at between 160 to 195 ka, for the last 15 years. However, in the 1960s quarry workers at Jebel Irhoud in SW Morocco exposed the infill of a cave network in which were found numerous items of the Levallois stone-tool technology, some human bone fragments that included a brain case and many dismembered and cut bones of prey animals. Initially they were thought to date from about 40 ka and to represent an African form of Neanderthals. Subsequently, re-evaluation of the remains revealed a greater likelihood that they were from modern humans, but too young to be of great interest. An upgraded date of ~160 ka caused them to be considered  as peripheral to the core group of Ethiopian early modern humans. DNA analyses then suggested modern humans to have split from Neanderthals about 500 ka ago. Members of the French-Moroccan team that did the original work, accompanied by other scientists, recently re-excavated the site and exhumed a much richer fossil haul that pin-pointed an anatomically modern human (AMH) provenance, albeit with some archaic characteristics (Hublin, J.-J. and 10 others, 2017. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature, v. 546, p. 289-294; doi:10.1038/nature22336), which can be referred to as ‘pre-modern’ H. sapiens. The bombshell stemming from their work was the precise dating of the fossils and their stratigraphic context by other members of the team (Richter, D. and 11 others. The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age. Nature, v. 546, p. 293-296; doi:10.1038/nature22335), which yielded 315±34 ka from fire-heated flint fragments and 286±32 ka from a human tooth. Both dates are far older than the previously accepted maximum of 200 ka for AMH.

The early evolution of fully modern humans seems to have spanned the whole of Africa, rather than being set in an Ethiopian heartland, a view partly supported by a fragmentary 260 ka fossil from South Africa bearing close resemblance to the Moroccan individuals. Interestingly, Levallois stone tools, as their name suggests, are widespread in both Africa and Europe at around 300 ka, although that is not proof that AMH migrated out of Africa around 300 ka, for Neanderthals may also have been using a similar flint flaking method (another space to be watched).

See also:  Stringer C. & Galway-Witham, J., 2017. On the origin of our species.  Nature, v. 546, p. 212-215; doi:10.1038/nature 546212a.

You can find more information on migration of modern humans here.

Homo naledi: an anti-climax

In September 2015 a barrage of publicity announced the remarkable unearthing of the remains of 15 diminutive hominins, dubbed Homo nadeli, from the floor sediments of an almost inaccessible South African cave, part of the equally hyped ‘Cradle of Humankind’ UNESCO World Heritage Site near Johannesburg. An international team of lithe women speleo-archaeologists was recruited for the excavation, for which the original discoverers were incapably burly. The remains included numerous examples of still articulated intricate bones, such as those of feet and hands, and none show signs of dismemberment by large scavengers. Indeed the discovery chamber was so far from the cave entrance that such animals probably were unaware of their presence. These features and the sheer complexity of the system strongly suggested that cadavers had been deliberately taken to the chamber; implying that the deep penetration had been accomplished using fire-brand illumination. What seized the headlines was the possibility of ritual burial, although sanitary disposal or panicked refuge from predators seem equally, if not more likely.

Lee Burger and the reconstructed skull of Homo naledi

Now yet more fossils have been reported from a separate chamber at a crawling distance about 150 m away from the original but closer to the system’s main entrance (~85 m). These add at least other 3 individuals to the H. nadeli association, with sufficient similarity to indicate that all 18 belong to H. naledi. This wealth of detail enabled the team of authors (Hawks, J. and 37 others 2017. New fossil remains of Homo naledi from the Lesedi Chamber, South Africa. eLife, v. 6, online; http://dx.doi.org/10.7554/eLife.24232) to perform a detailed comparative anatomic analysis of the species. The results are a mosaic, showing some post-cranial affinities with australopithecines, H. habilis, H.floresiensis, H. erectus, Neanderthals and anatomically modern humans, and others, such as the hands and shoulders, that are not well matched with other hominins. Their crania show a similar broad spectrum of resemblances, and as regards dentition they are distinctly primitive. They are also on the small-brained side of the hominin clade. Despite the astonishing abundance of fossil material, not a single artifact was found in the cave system, despite the apparent similarity of its hands to those of ourselves and Neanderthals.

With plenty of scope for speculation, H. nadeli remains enigmatic. The big question looming over the 2015 announcement of the species was its age, the discovers suggesting about 2 Ma, and placing on the direct line of human descent. On the same day as the fossil description there appeared a multi-method dating analysis (Dirks, P.H.G.M. and 19 others 2017. eLife, v. 6, online; http://dx.doi.org/10.7554/eLife.24231.001), which showed that with little doubt that the H. nadeli association was deposited between 236 ka and 335 ka; around the time when anatomically modern humans first emerged and stone tools had undergone a >2 Ma technological evolution. To me, the only sensible conclusion at present is that H. nadeli is another addition to the 6 species living and in some cases coexisting across the late Pleistocene world, and that expansion of ideas beyond that must await DNA analysis; a definite possibility considering the age of the fossils, their seemingly good preservation in a relatively dry cave system and the new possibility of cave soils as well as bones yielding genetic materials. The leader of the research team, Lee Berger of the University of the Witwatersrand now maintains, together with four other members of the research team, that H. nadeli may be a coelacanth-like survivor of Homo’s earliest diversification and that ‘we cannot exclude that this lineage was responsible for the production of Acheulean or Middle Stone Age tool industries’.

Barras, C. 2017. Homo naledi is only 250,000 years old – here’s why that matters. New Scientist, 6 May 2017 Issue

Sample, I. 2017. New haul of Homo naledi bones sheds surprising light on human evolution. The Guardian, 9 May 2017

Detecting the presence of hominins in ancient soil samples

Out on the plains countless herbivores fertilise the ground by continual urination and defecation. A friend’s sheep are doing just that in the small field that came with my current home while they are keeping the grass under control.  Millions of hectares of prime agricultural land in China are kept fertile through disposal of human night soil from ‘honey wagons’ every day; it is even fed to fishes in small ponds. Such a nice economy also donates the DNA of the animal and plant inhabitants to the soil system. In 2015 analysis of environmental DNA from permafrost in Siberia and Alaska produced ‘bar codes’ for the now vanished ecosystems of what was  mammoth steppe during the climate decline to the last glacial maximum and the subsequent warming. The study revealed mammoth and pre-Columbian horse DNA and changes in the steppe vegetation, from which it was concluded that the steppe underwent regional extinction pulses of its megafauna linked to rapid climate ups and downs connected with Dansgaard-Oeschger cycles. It was but a small step to see the potential for studying distribution and timing of various hominins’ occupation of caves from the soils preserved within them, without depending on generally very rare occurrences of human skeletal remains.

Tourists at the entrance to Denisova Cave, Rus...

Tourists at the entrance to Denisova Cave, Russia (credit: Wikipedia)

The Max Planck Institute for Evolutionary Anthropology in Leipzig, now famous for extracting DNA from Neanderthal, Denisovan and possibly H. antecessor fossils, has applied the environmental DNA approach to sediments from 7 caves in France, Belgium, Spain, Croatia and Russia that span the period from 550 to 14 ka (Slon, V. and 30 others 2017.  Neandertal and Denisovan DNA from Pleistocene sediments. Science, v. 356 (online publication); doi:10.1126/science.aam9695). The sites had previously yielded fossils and/or artefacts. All of them contained mitochondrial DNA from diverse large mammals, four including archaic human genetic material supplied by Neanderthal individuals and Denisovans in the case of the Denisova cave. A key finding was Neanderthal mtDNA in one sedimentary layer that contained no skeletal remains – decay of a body was probably not involved. In two cases the DNA was from more than one individual. A variety of tests showed that surprisingly large quantities of DNA survive in soil and that it is spread evenly in sediment rather than being present in spots – an indication of derivation from urine, excreta or decayed soft tissue.

Although the study does not add to knowledge of hominin genetics, it confirms that the methodology is sufficiently advanced and efficient to detect hominin presence in fossil-free sediment. So this approach seems set to become a standard for many sites, such as that from California reported in the previous post, which suggest a human influence, or any cave sediments for that matter. Although skeletal remains are essential for reconstruction of bodily characteristics, hominin phylogeny seems set to cut loose from fossils. Hitherto suspected species’ presence in the time period where DNA analysis is feasible may be detected, such as Asian H. erectus. It may become possible to map or extend the geographic ranges of Denisovans and Neanderthals. Perhaps species new to science will emerge.

More on late Pleistocene hominin genetics here

Wade, E. 2017. DNA from cave soil reveals ancient human occupants. Science, v. 356, p. 363.

Wade, E. 2017. DNA from cave soil reveals ancient human occupants. Science, v. 356, p. 363.

Pre-sapiens hominins reached North America?

In 1991-2 palaeontologists excavated a site near San Diego, California where broken bones had been found. These turned out to be the disarticulated remains of an extinct mastodon. One feature of the site was the association of several large cobbles with bones of large limbs that seemed to have been smashed either to extract marrow or as source of tool-making material. The cobbles showed clear signs or pounding, such as loss of flakes – one flake could be fitted exactly to a scar in a cobble – pitted surfaces and small radiating fractures. The damage to one cobble suggested that it had been used as an anvil, the others being hammer stones.  Broken pieces of rock identical to the hammer stones were found among the heap of bones. No other artefacts were found, and the bones show no sign of marks left by cutting meat from them with stone tools. The breakage patterns of the bones included spiral fractures that experimental hammering of large elephant and cow bones suggest form when bone is fresh. Other clear signs of deliberate breakage are impact notches and small bone flakes. Two detached, almost spherical heads of mastodon femora suggest that marrow was the target for the hammering and confirmed the breakage was deliberate.

Mastodon.

Artist’s impression of American mastodon. (credit: Wikipedia)

Since the sediment stratum in which the remains occurred consists of fine sands and silt, typical of a low-energy river system, the chances that the cobbles had been washed into association with the mastodon are very small. The interpretation of the site is that it was the result of opportunistic exploitation of a partial carcase of a young adult mastodon by humans. In the early 1990s attempts were made to date the bones using the radiocarbon method, but failed due to insufficient preserved collagen. That the site may have been much older than the period of known occupation of North America by ancestors of native people (post 14.5 ka) emerged from attempts at optically stimulated luminescence dating of sand grains that can suggest the age of burial. These suggested burial by at least 60 to 70 ka ago. It was only when the uranium-series disequilibrium method was used on bone fragments that full significance of the site emerged. The results indicated that they had been buried at 130.7±9.4 ka (Holen, S.R. and 10 others 2017. A 130,000-year-old archaeological site in southern California, USA. Nature, v.  544, p. 479—493; doi:10.1038/nature22065 – full paper and supplements available free)

Not only is the date almost ten times that of the earliest widely accepted signs of Homo sapiens in the Americas, the earliest anatomically modern humans known to have left Africa are around the same age, but restricted to the Levant. The earliest evidence that modern humans had reached East Asia and Australasia through their eastward migration out of Africa is no more than 60 ka. The date from southern California is around the start of the interglacial (Eemian) before the one in which we live now. It may well have been possible then, as ~14 ka ago, to walk across the Bering Straits due to low sea level, or even by using coast-hugging boats – hominins had reached islands in the Mediterranean and the Indonesian peninsula certainly by 100 ka, and probably earlier. But whoever exploited the Californian mastodon marrow must have been cold-adapted to achieve such a migration. While the authors speculate about ‘archaic’ H. sapiens the best candidates would have been hominins known to have been present in East Asia: H. erectus, Neaderthals and the elusive Denisovans.

Surely there will be reluctance to accept such a suggestion without further evidence, such as tools and, of course, hominin skeletal remains. But these long-delayed findings seem destined to open up a new horizon for American palaeoanthropology, at least in California.

You can find more information on hominin migration here.

https://www.newscientist.com/article/2129042-first-americans-may-have-been-neanderthals-130000-years-ago/

Yukon colonised during Last Glacial Maximum

For many years anthropologists were certain that the Americas remained outside the human realm until the great icecap of North America had begun to melt decisively. This view stemmed partly from the only conceived route being across the exposed floor of the Bering Sea when sea-level had fallen to leave it as a landmass known as Beringia. The other literal stumbling block had been the glacial blockage of the only lowland corridor from Alaska to the Great Plains which roughly follows the Alberta – British Columbia border in Canada. There is abundant evidence that the corridor did not become ice-free until about 13 ka, an important fact that for a long while bolstered the Clovis-First hypothesis, from the eponymous and highly distinctive stone tools that date back to just after that time. After a long, sturdy rearguard action by its devotees that view was transcended by finds of earlier tools with dates as old as 15.5 ka that extend close to the southernmost tip of South America. Studies of Y-chromosome DNA from living First Nations men that suggested that all early Americans stemmed from 4 separate colonising populations who may have entered via Beringia by different routes, including along the Pacific coast. A possible common ancestor of all native Americans has turned up from the mitochondrial and Y-chromosome DNA of a fossil skeleton from near Lake Baikal in Siberia who lived about 24 ka ago. But yet another twist has emerged from the Yukon Territory of Northern Canada.

Beringia Land Bridge. Animated gif of its prog...

Beringia Land Bridge. Animation of its development from 21.000 BC to modern times.(Photo credit: Wikipedia)

Since 1987 it has been known that animal bones with clear signs of butchery occurred in the Bluefish Cave on the Yukon – Alaska border. Dating of the bones by the 14C method seemed to support human occupation there during the Last Glacial Maximum; highly controversial at the time, in the absence of any other sites of that age in the whole Americas. The material has now been re-examined and dated by a more advanced radiocarbon method (Bourgeon, L. et al. 2017. Earliest human presence in North America dated to the Last Glacial Maximum: new radiocarbon dates from Bluefish Caves, Canada. PLoS ONE, v. 12; doi:10.1371/journal.pone.0169486). This work has confirmed the earlier view since the ages of bones range from 24 to 12 ka. But the discovery of what seems long-term occupation under the most arduous glacial conditions is not the only outcome of the research. One hypothesis for the genetic diversity among living indigenous people of the Americas is that their forebears, the first people of the Americas, may have been from genetically isolated populations stranded on Beringia, yet surviving eventually to migrate southward once climate warmed. The ‘Beringian standstill hypothesis’ suggest that the small population underwent genetic drift for about eight thousand years, their descendants inheriting the genetic diversity produced by this process. Bluefish Cave is probably where some of those pioneers waited-out the Ice Age

Neanderthals and dental hygiene

Teeth are the most likely parts of skeletons to survive for long periods because of their armour by a layer of enamel made of hydroxyapatite (Ca5(PO4)3(OH)). Dental enamel is the hardest material in the bodies of vertebrate animals and lies midway between fluorite and feldspar on Moh’s scale of hardness (value 5). Like the mineral apatite, teeth survive abrasion, comminution and dissolution for long periods in the surface environment. Subdivision of fossil hominin species and even among different groups of living humans relies to a marked extent on the morphology of their teeth’s biting and chewing surface. Although there are intriguing examples in Neolithic jawbones of dental cavities having been filled it is rather lack of attention to teeth that characterises hominin fossils. As well as horrifying signs of mandibular erosion due to massive root abscesses, a great many hominin remains carry large accumulations of dental plaque or calculus made of mineralised biofilm laid down by oral bacteria. Even assiduous brushing only delays the build up. Grisly as this inevitability might seem, plaque is an excellent means of preserving not only the bacteria but traces of what an individual ate. As fossil DNA is a guide to ancestry and relatedness among fossil hominins, so far going back to about 430 ka in the case of a Spanish Homo heidelburgensis, plaque potentially may reveal details of diet and to some extent social behaviour elaborating beyond the possibilities presented by carbon isotopes and dental wear patterns.

Plaque deposits have already shown that Neanderthals had a very varied vegetable diet and that they cooked their food, the sugars thereby released encouraging bacterial biofilms. There have even been hints that they used medicinal herbs, such as yarrow and chamomile. Now a large multinational team of scientists has taken this fascinating line of study a step further using short DNA fragments to identify the actual oral microbes and even plant and animal species that dominated the diets of 8 cave-dwelling Neanderthals found in Spain, Belgium and Italy (Weyrich, L.S. and 30 others 2017. Neanderthal behaviour, diet, and disease inferred from ancient DNA in dental calculus. Nature, v. 543; online doi:10.1038/nature21674). The Spanish individuals found in El Sidrón cave seem to have been mainly vegetarian (mushrooms, pine nuts and edible moss) whereas two from the Spy cave in Belgium feasted on wooly rhinoceros and mouflon sheep. One of the El Sidrón Neanderthals had a dental abscess, and was probably in great pain, and whose calculus contained evidence of ingestion of tissue from poplar trees, known to contain salicylic acid (the active ingredient in aspirin): an example of self-medication. The unfortunate individual was also suffering from acute diarrhoea brought on by a eukaryote parasite (microsporidium). Astonishingly, DNA from several plant fungi, including Penicillium rubens (penicillin) also occurred in this individual’s calculus, from eating mouldy plant material: predating modern antibiotics by more than forty-five thousand years!

More predictable findings from the unfortunate El Sidrón individual was a spectrum of common plaque colonising bacteria. But another surprise was Methanobrevibacter oralis, an archaea common in the human mouth ecosystem, for which a complete genome was reconstructed. It is different from that in the Methanobrevibacter oralis found in living humans and the team were able to use a molecular clock approach to date the divergence between the two sub-species. This seems to have occurred between 112-143 ka ago, long after the divergence of Neanerthals and anatomically modern humans, judged to be around 450 to 750 ka ago. The authors suggest that ‘commensal microbial species were transferred between the two hosts during subsequent interactions, potentially in the Near East’. Two alternative ‘interactions’ occurred to one commentator: kissing or exchange of chewed food (Callaway, E, 2017. Plaque DNA hints at Neanderthal lifestyle. Nature, v. 543, p. 163). Intriguingly the date, albeit imprecise, overlaps with estimates for the timing of Neanderthal – modern human interbreeding as the latter began to leave Africa: not only do living non-Africans share genes with Neanderthals, the may also share saliva and oral bacteria.

For more information on recent human evolution see here.