Tag: Neanderthal

Sophisticated Neanderthal art now established

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The first detailed description and analysis of the amazing cave paintings of Western Europe that have been attributed to anatomically modern humans (AMH) were made in the early 20th century by the Jesuit priest Abbé Henri Breuil. As well as that those of Lascaux and Altamira, which have been dated, many works in Spanish caves have not. Art ascribed to AMH includes figurative work depicting a wide range of Late Pleistocene animals, abstract and perhaps symbolic designs, and ‘signatures’ of individual people in the form of direct prints or stencils of hands. The earliest known graphic work made by modern humans is a 100 ka-old baton of ochre with a zig-zag set of sharp incisions found with ochre-filled shells possibly for body painting at Blombos Cave in South Africa.

Evidence for pre-AMH work in Europe is sparse and widely  judged to be ambiguous; for instance 50 ka-old ochre-stained and pierced shells associated with Neanderthal remains in Spain.  Hints at even earlier origins for art lie in the geometrically etched bivalve shells excavated by Eugene Dubois at the site in Java where he discovered Homo erectus crania in 1891. They have recently been dated at around half a million years old.  Occasionally, radiometric dating of drawings has revealed quite meagre red dots that are slightly older than the widely accepted date of first entry of AMH into Europe (~40-45 ka) and may have been made by Neanderthals. Of course, there are many European cave paintings associated with dates earlier than the extinction of Neanderthals (around 30 ka) that may have been made by them, but which are generally ascribed to AMH by assuming that only our species has the wit to make them.  Even the sophisticated Châtelperronian stone tools and rough ornaments associated with undeniable Neanderthal remains are considered by many paleoanthropologists to show skills copied from AMH.

This AMH-centric view of art depends on two outlooks: simple prejudice that any beings markedly different in appearance from us were intellectually inferior – generally condemned as racist if applied to different groups of living humans; lack of incontrovertible and unambiguous evidence to the contrary. Both are set to be rigorously challenged by the growing use of sophisticated radiometric U-Th dating of the thin films of chemically precipitated calcite (flowstone or speleothem) that often coat the walls of caves and are at least as old as the art that they cover. A German-Spanish-British team has applied the technique to artwork and painted stalactites on the walls of three caves in Spain known to have been occupied by hominins over the last 100 ka (Hoffmann, D.L and 13 others 2018. U-Th dating of carbonate crusts reveals Neandertal origin of Iberian cave art. Science, v. 359, p. 912-915; doi: 10.1126/science.aap7778. See also: Appenzeller, T. 2018. Europe’s first artists were Neandertals. Science, v. 359, p.852-853; doi: 10.1126/science.359.6378.852). One cave that was analysed is that at La Pasiega in Cantabria whose art was sketched by Abbé Breuil. The team’s results are dramatic: all the dated samples pre-date 40 Ka, the oldest at 79.66±14.90 ka being from La Pasiega. Precisely dated art includes hand stencils, painted stalactites, geometric patterns and line drawings of animals. Many of the caves’ artworks remain to be dated, including some well-executed animals and strange, possibly symbolic designs.

Symbolic Neanderthal art in La Pasiega cave, Spain – left: recent photograph; right: sketch produced Abbé Breuil in 1913. The red, ladder-like symbol has a minimum age of 64 ka but it is unclear if the animals and other symbols were painted later. (credit: Hoffmann et al. 2018, Supplementary Data Figure S4)

The implications of this work are far-reaching. Handprints and stencils are common throughout the archives of European cave art and seem generally to be the oldest at each site. The dating method is yet to applied to the bulk of cave art, much of which is encased in speleothem, so it is quite possible that ‘dual authorship’ may be discovered in some caves. It now seems clear that Neanderthals invented permanent art independently of AMH, and since art is a form of communication that has implications for the ability to speak as well as to think ‘outside-the-box’. The 177 ka corral-like enclosures made of stalactites and associated hearths deep within Bruniquel Cave seem more likely to have ritual significance, far from the light of day, for the Neanderthals that made them. The finds throw doubt on the implausibility of Neanderthal invention of so-called ‘transitional’ technologies, such as the Châtelperronian. Finally, fully modern humans in Africa and Neanderthals in Europe were doing much the same things over roughly the same time period; genetically and physically they parted company about 450 to 400 ka ago; both were capable of artistic symbolism and fulfilled that potential. That implies that their common ancestor may have passed on the proclivity, as might their predecessor H. erectus who created the etched mollusc shells of Trinil half a million years ago.

More on Neanderthals, Denisovans and AMH genetic relatedness

Editorial from the Guardian Newspaper 26 February 2018.

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Neanderthal development

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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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Detecting the presence of hominins in ancient soil samples

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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.

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

Pre-sapiens hominins reached North America?

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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.

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

Denisovan(?) remains in the garden

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On the edge of the small town of Lingjing near Xuchang City in Henan Province, China, local people have long practiced intensive vegetable gardening because the local soil is naturally irrigated by the water table beneath the flood plain deposits of the Yinghe River. In the mid 1960s, around a small spring, they began to find dozens of small stone tools together with animal bones. Only in 2005, after the spring had stopped flowing, did systematic excavation begin (Li, Z.-Y. et al. 2017. Late Pleistocene archaic human crania from Xuchang, China. Science, v. 355, p. 969-972; doi: 10.1126/science.aal2482) About 3.5 m below the surface tools and bone fragments, including one with a carved representation of a bird, occurred just above the base of the modern soil profile. Radiocarbon dating of charcoal from the layer clustered around 13 500 years ago, just before the start of the Younger Dryas cooling episode; probably products of modern humans, although no human remains were found in the layer. Continued excavation penetrated sediments free of fossils and tools down to a depth of 8 m, when stone tools and bone fragments began to turn up again through the lowest 2 m of sediment. Optically stimulated luminescence (OSL) dating of mineral grains, which shows the last time that sediments were exposed to sunlight, produced much older dates between 78 to 123 ka. The thousands of stone flakes and cores, and cut marks on the animal bones found through the fossil-rich layer suggests that this was a site long used for tool making and food preparation, that had begun in the last interglacial period. Among the bones were fragments of the crania of as many as five individual humans.

Who were they? Their age range is tens of thousands of years before anatomically modern humans began to migrate into east Asia, so they are likely to have been an earlier human group. Homo erectus is known to have inhabited China since as early as 1.6 Ma ago and may be a possibility. The other possible group are the Denisovans, known only from their DNA in a small finger bone from a cave in eastern Siberia. Fragments of Denisovan DNA are famously present in that of many living indigenous people from eastern Asia, Melanesia and the Americas, but hardly at all in west Asians and Europeans. They also interbred with Neanderthals and may share a common ancestor with us and them, who lived about 700 ka ago.

Map showing the proportion of the genome inferred to be Denisovan in ancestry in diverse non-Africans. The color scale is not linear to allow saturation of the high Denisova proportions in Oceania (bright red) and better visualization of the peak of Denisova proportion in South Asia. (Credit: Sankararaman et al./Current Biology 2016; http://dx.doi.org/10.1016/j.cub.2016.03.037)
Map showing the proportion of the genome inferred to be Denisovan in ancestry in non-Africans. The color scale ranges from black – 0, through greens – present to red – highest . (Credit: Sankararaman et al./Current Biology 2016; http://dx.doi.org/10.1016/j.cub.2016.03.037)

Unfortunately the human bones are completely fragmented and lack any teeth, jaw bones or elements of the face. However, the Chinese-US team used sophisticated computer refitting of CT-scanned fragments to reconstruct two of the crania, revealing one individual with prominent brow ridges and a flat-topped skull extended towards the back, similar to that of Neanderthals but with a much larger brain than H. erectus. The semi-circular canals associated with the ears, but used in balancing, are well preserved and also resemble those of Neanderthals. Yet east Asia has yielded not a single Neanderthal fossil. Could these be the elusive Denisovans? Even if more diagnostic bones turn up, especially teeth, such is the state of late hominin taxonomy that only DNA will provide definitive results: the Denisovans are defined entirely by DNA. The authors, perhaps wisely, do not speculate, but others may not be able to resist the temptation.

For more information on recent human evolution see here.

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Gibbons, A. 2017. Close relative of Neandertals unearthed in China. Science, v. 355, p. 899; doi: 10.1126/science.355.6328.899

Neanderthal culture confirmed

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The Châtelperronian material culture represents the earliest sign of the Upper Palaeolithic in Europe and its products span a period from about 45 to 40 ka. It includes stone tools, such as points and long, thin blades with a single cutting edge and a blunt back, reminiscent of a modern knife, and others with notched, or denticulate edges that resemble saw blades. A great many of the tools, including ivory and bone ones, are probably designed for working and stitching skins. But the most revealing worked objects are animal teeth, shells and fossils that are either bored or grooved to be strung together. The best have been found in the Grotte du Renne in eastern France. The most controversial aspect of the Châtelperronian is that its artefacts are sometimes found with the fossil remains of Neanderthals who had previously produced less sophisticated, Mousterian tools since around 160 ka. The controversy centres on whether or not Neanderthals created the Châtelperronian culture, and if so, did they develop them independently or through cultural exchange with or copying from the newly arrived anatomically modern humans (AMH).

Science Magazine
Châtelperronian ornaments from the Grotte du Renne eastern France, probably parts of a necklace. (Credit: ©Marian Vanhaeren, CNRS, University of Bordeaux)

The Grotte du Renne material is especially rich in ornaments, but insufficient fossil material is present to tell from anatomical characteristics whether or not they were made by AMH or Neanderthals. It has now become possible using traces of bone proteins to detect hominin bone fragments and DNA to assess which group is implicated (Welker, F. and 127 others, 2016. Palaeoproteomic evidence identifies archaic hominins associated with the Châtelperronian at the Grotte du Renne. Proceedings of the National Academy of Science, www.pnas.org/cgi/doi/10.1073/pnas.1605834113). Analyses of mtDNA and radiometric dating of the bones that yielded it show that the Grotte du Renne tools and ornaments link with Neanderthals who lived there about 37 ka ago. Interestingly, the stratigraphic horizon beneath the definite Neanderthal occupation level contains their earlier, Mousterian artefacts. So it seems that they developed new manufacturing techniques and material culture. Yet, the findings do not resolve the issue of independent invention or copying AMH methodology.

Importantly, Grotte du Renne shows that Neanderthals, even if they copied AMH techniques, were capable of appreciating, producing and using personal ornamentation: they could learn and transmit ideas. In that respect, here is support for the notion that, apart from significant anatomical differences from AMH they were not that different intellectually.

More on Neanderthals, Denisovans and anatomically modern humans

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Wade, L. 2016. Neandertals made jewelry, proteins confirm. Science, v. 353, p. 1350.

Breaking news: Cave structures made by Neanderthals

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Neanderthals were well equipped and undoubtedly wore clothing, made shelters, hunted, used fire and famously lived in caves. Deliberate burial of their dead, in some cases arguably with remains of flowers, indicates some form of ritual and belief system. Those in Spain wore necklaces and pendants of bivalve shells, some of which retain evidence of having been painted. Excavators there even found a paint container and painting tools made of small bones from a horse’s foot. The container and tools retain traces of the common iron colorants goethite, jarosite and hematite. One large, perforated scallop shell, perhaps used as a pectoral pendant, shows that its white interior was painted to match its reddish exterior. Given the evidence for adornment by earlier hominins, to find that Neanderthals created art should not be surprising. In May 2016 it emerged that about 177 thousand years ago and earlier, they had broken stalagmites off the cave roof to create curious semi-circular structures in Bruniquel Cave near Montauban in southern France (Jaubert, J. and 19 others, 2016. Early Neanderthal constructions deep in Bruniquel Cave in southwestern France. Nature, v. 533,  online publication, doi:10.1038/nature18291). Each of the structures contains incontrovertible evidence that fires were made within them. Rather than being near the well-lit cave entrance the structures are more than 300 m deep within the cave system surrounded by spectacular stalagmites and stalactites that are still in place. Were the structures younger than 42 ka they would probably have been attributed to the earliest anatomically modern Europeans and to some ritual function. Instead they were made during the climatic decline to the last but one glacial maximum.

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Neanderthals built mystery underground circles 175,000 years ago

 

Neanderthal news

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Increasingly sophisticated analysis of existing genomes from Neanderthal and Denisovan fossil bone, together with new data on single-chromosome DNA extracted from Croatian and Spanish Neanderthals continues to break new ground.

Artistic reconstruction of Neanderthal woman (credit: Natural History Museum, http://www.nhm.ac.uk/natureplus/blogs/tags/human_evolution)
Artistic reconstruction of Neanderthal woman (credit: Natural History Museum, http://www.nhm.ac.uk/natureplus/blogs/tags/human_evolution)

According to genome comparison between a Siberian specimen and modern humans, a population from which Neanderthals emerged separated from that which led to anatomically modern humans (AMH) sometime between 550 and 765 ka, although the fossil record can only confirm that divergence was before 430 ka. The comparison famously showed that Neanderthals contributed to modern, non-African humans between 47 and 75 ka, that is after the exodus of AMH from Africa that spread our species throughout all continents except Antarctica. This genetic exchange is thought to have taken place somewhere in the Middle East, which seems to have been a major staging post for our spread further east and also westward to Europe. A similar indication of liaison between Denisovans and AMH migrants is restricted to modern Melanesians, and probably took place in eastern Asia before 45 ka, when modern people began crossing from Eurasia to New Guinea and Australia. Neanderthal-Denisovan comparison suggests that those distinct groups separated between 380 and 470 ka ago (recently revised from an earlier estimate).

In both cases the gene flow was from the older groups to humans. Further examination of Siberian Neanderthal genomes now indicates that a reverse exchange occurred more than 100 ka ago (Kuhlwilm, M. and 21 others 2016. Ancient gene flow from early modern humans into Eastern Neanderthals. Nature, v. 530, p. 429-433). But the single-chromosome DNA from Croatian and Spanish Neanderthals shows no such sign This instance of two-way exchange is significant in another way: it took place before direct evidence of the generally accepted departure of African migrants to populate the rest of the world. At about 100 ka there is fossil evidence of possible AMH-Neanderthal cohabitation of the Levant, followed by a period with fossil evidence for Neanderthal presence there but not modern humans. Because stone tools from northern Arabia are dated as far back as 125 ka and closely resemble those associated with archaic modern humans, there is a possibility that AMH migration was far earlier than previously thought and passed through the Levant en route to points east.

Another tantalizing aspect of Neanderthal-modern human genetics is the tangible legacy of interbreeding with non-African humans. The first sign was that the gene (mc1r) that confers red hair on those of us blessed, or otherwise, with it may have Neanderthal origins, thus making us extremely proud of that heritage. The same gene is implicated in northern modern humans having developed pale skin, which might embarrass ‘white supremacists’! Similar studies in Svante Paabo’s lab at the Max Planck Institute for Evolutionary Anthropology in Leipzig also suggested 15 genome regions that include those involved in energy metabolism, possibly associated with type 2 diabetes; cranial shape and cognitive abilities, perhaps linked to Down’s syndrome, autism and schizophrenia; wound healing; skin, sweat glands, hair follicles and skin pigmentation; and barrel chests. There is more…

Joshua Akey of the University of Washington, Seattle, and evolutionary genomicist Tony Capra of Vanderbilt University in Nashville hit on the idea of ‘mining’ archived genetic information from more than 28 thousand living people for traces of 6000 Neanderthal DNA variants and comparing the results with physical traits and diseases logged in the human database (reported by Gibbons, A. 2016. Neanderthal genes linked to modern diseases. Science, v. 351, p. 648-9). On the plus side, Neanderthal ancestry may help boost immune responses to fungi, parasites and bacteria. Inheritance of enhanced blood coagulation, although greatly assisting recovery from wounds and hemorrhage when giving birth, confers a proclivity to heart attacks and strokes. Neanderthals also passed on ‘weak bladders’, solar keratoses that confer skin cancer risk, a tendency to malnutrition from modern diets low on meat and nuts, depression triggered by jet lag(!) and even a tendency to nicotine addiction. But a ‘pure’ line of modern human descent, shared by most Africans, also has its positive and negative heritable traits.

More on Neanderthals, Denisovans and anatomically modern humans

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Our ancestors parted from other humans earlier than expected

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Despite the excitement raised by the discovery of remnants of 15 individuals of Homo naledi in a South African Cave the richest trove of hominin fossils remains that of Sima de los Huesos (‘pit of bones’) in northern Spain. In 2013 bone found in that cave from one of 28 or more individuals of what previous had been regarded as H. heidelbergensis, dated at around 400 ka, yielded mitochondrial DNA. It turned out to have affinities with mtDNA of both Neanderthals and Denisovans, especially the second. The data served to further complicate the issue of our origins, but were insufficient to do more than throw some doubt on the significance of H. heidelbergensis as a distinct species: nuclear DNA would do better, it was hoped by the palaeo-geneticists of the Max Planck Institute for Evolutionary Anthropology in Leipzig. Now a small fragment of those data (about 1 tro 2 million base pairs) have been presented to a London meeting of the European Society for the Study of Human Evolution – though not yet in a peer-reviewed journal. Anne Gibbons summarised the formal presentation in the 18 September 2015 issue of Science (Gibbons, Ann 2015. Humanity’s long, lonely road. Science, v. 349, p. 1270).

English: Cranium 5 is one of the most importan...
One of the best preserved discoveries in the Sima de los Huesos, Atapuerca (Spain). (credit: Wikipedia)

The partial nuclear DNA is a great deal more like that of Neanderthals from much more recent times than it is of either Denisovans and modern humans. It seems most likely that the Sima de los Huesos individuals are early Neanderthals, which implies that the Neanderthal-Denisovan split was earlier than 400 ka. That might seem to be just fine, except for one thing: Neanderthal and Denisovan DNA are much more closely related to each other than to that of ourselves. That implies that the last common ancestor of the two archaic human species must have split from the ancestral line leading to modern humans even further back in time: maybe 550 to 765 ka ago and 100 to 400 ka earlier than previously surmised. This opens up several interesting possibilities for our long and separate development. Since Neanderthals and perhaps Denisovans emigrated from Africa to Eurasia several glacial cycles ago, maybe people genetically en route to anatomically modern humans did so too. The Neanderthal and Denisovan genomes suggest that they interbred with each other and that could have been at any time after the genetic split between them. Famously, they also interbred with direct ancestors of living Eurasians, but there is no genetic sign of that among living Africans. The evidence suggests that the insertion of archaic genetic material was into new migrants from Africa around 100 to 60 ka ago at different points along their routes to Europe and East Asia. But, obviously, it is by no means clear cut what passed between all three long-lived groups nor when. It is now just as possible that surviving, earlier Eurasians on the road to modern humans passed on their own inheritance from relationships with Neanderthal and Denisovan to newcomers from Africa. But none of these three genetic groups ever made their way back to Africa, until historic times.

More on Neanderthals, Denisovans and anatomically modern humans

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Human-Neanderthal cohabitation of the Levant

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The earliest known remains of anatomically modern humans outside of Africa were found unearthed from the Skhul and Qafzeh caves in what is now northern Israel. Their context was that of deliberate burial at a time when climate was cooling from the last interglacial, between 90 to 120 ka. The Levant was also the repository for a number of well-preserved Neanderthal skeletons, most dating to between 35-65 ka, including ten individuals at Shanidar in today’s northern Iraq, some of whom were also deliberately buried including one whose grave reputedly contained evidence for a floral tribute. The 25 ka gap between the two populations has previous been regarded as evidence for lack of contact between them. However, the Tabun Cave in modern Israel has yielded tools attributed to Neanderthal Mousterian culture that may indicate their intermittent presence from 200 to 45 ka, and fossils of two individuals dated at ~122 and ~90 ka. The remains at Skhul and Qafzeh are significantly more rugged or robust than African contemporaries and have been considered possible candidates for Neanderthal-modern human hybrids. But whatever their parentage, it seems they became extinct as the climate of the Levant dried to desert conditions around 80 ka.

View of the exterior of Shanidar Cave, taken d...
Entrance to the Shanidar Cave, northern Iraq, occupied by Neanderthals between 35-65 ka (credit: Wikipedia)

A more promising overlap between modern human and Neanderthal occupation comes with the discovery by a group of Israeli, US, Canadian, German and Austrian scientists of a much younger anatomically modern human cranium from the Manot Cave, also in northern Israel (Herschkovitz, I. and 23 others 2015. Levantine cranium from Manot Cave (Israel) foreshadows the first European modern humans. Nature (online) doi:10.1038/nature14134). The cranium has a U-Th radiometric age of ~55 ka, well within the time span of Neanderthal occupation. Moreover, Manot Cave is one of a cluster of occupied sites in northern Israel, with separations of only a few tens of kilometres: undoubtedly, this individual and companions more than likely met Neanderthals. The big question, of course, is did the neighbours interbreed? If so the Levant would be the confirmed as the probable source of hybridisation to which the DNA of non-African living humans points. There may be a insuperable difficulty in taking this further: it is thought that the high temperatures of the region, despite its dryness, may have destroyed any chance of reconstructing ancient genomes. Yet one of the first Neanderthal bones to yield useful genetic material was from Croatia, which is not a great deal cooler in summer.

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