The early signs of counting and arithmetic?

Three earlier articles in Earth-logs originally focussed on what I supposed to be ‘ancient abstract art’.  One highlighted a clam shell that bears carefully etched V-shapes found at the type locality for Asian Homo erectus at Trinil on the Solo River, Java, dated between 430 and 540 ka. Another is about parallel lines etched on a piece of defleshed bone from China dated at 78 to 123 ka, which may be a Denisovan artefact. The most complex is a piece of ochre found in the coastal Blombos Cave 300 km east of Cape Town, South Africa in association with tools ascribed to early modern humans who lived there about 73 ka ago. Fascinating as they seemed at the time, they may hold much greater significance about early-human cognitive powers than about mere decoration. That is thanks to recent evaluation of other simple artefacts made of lines and notches by anthropologists, cognitive scientists and psychologists. Their work is summarised in a recent Nature Feature by Colin Barras (Barras, C. 2021. How did Neanderthals and other ancient humans learn to count? Nature, v. 594, p. 22-25; DOI: 10.1038/d41586-021-01429-6). The European Research Council recently allocated a €10 million grant to foster research into ‘when, why and how number systems appeared and spread’.

Examples of ancient ‘abstract’ art. Top – V-shaped features inscribed on 430-540 ka freshwater clam from Java; Middle – parallel lines etched through red ochre to show white bone, from a possible Denisovan site in China; Bottom – complex inscription on a tablet of iron-rich silcrete from South Africa

Straight lines and patterns made from them are definitely deliberate, whatever their antiquity. In recent times, such devices have been used by artists to render mental images, moods and thoughts as simplified abstractions: hence ‘abstract’ art, such as that of Piet Mondrian and Kazimir Malevich. The term also applies to the dribbles and drabbles of Jackson Pollock and many more styles. But these works are a very recent evolutionary development out of earlier schools of art. So deliberate geometric shapes and arrangements of lines that are many millennia old cannot simply be termed ‘abstract art’. It is certainly not easy to see how they evolved into the magnificence of Palaeolithic figurative cave art that started at least 40 thousand years ago; Yet they are not ‘doodles’. Being so deliberate suggests that they represented something to their makers. The question is, ‘What?’

The research summarised by Barras is mainly that of Francisco d’Errico of The University of Bordeaux, France and colleagues from Canada and Italy (d’Errico, F. et al. 2018. From number sense to number symbols. An archaeological perspective. Philosophical Transactions of the Royal Society B, v. 373, article 2160518; DOI: 10.1098/rstb.2016.0518). They focused their work on two remarkable artefacts. The oldest (72 to 60 ka), from a cave near Angoulême in France, is a fragment of a hyena’s thigh bone that carries nine notches. It is associated with stone tools almost certainly made by Neandethals. The other, from the Border Cave rock shelter in KwaZulu-Natal in South Africa, is a 44 to 42 ka old baboon’s shin bone, which carries a row of 29 prominent notches, and a number of less distinct, roughly parallel scratches. The rock shelter contains remains of anatomically modern humans and a very diverse set of other artefacts that closely resemble some used by modern San people.

Top: notched hyena femur bone fragment associated with Neanderthal tools from SW France. Bottom: notched baboon shin bone from Border Cave, South Africa. Scale bars(Credit: F. d’Errica and L. Backwell)

Microscopic examination of the notches made by a Neanderthal suggest that all 9 notches were cut at the same time, using the same stone blade. Those on the Border Cave shin bone suggest that they were made using four distinctly different tools on four separate occasions. Are both objects analogous to tally sticks; i.e. to count or keep a record of things as an extension to memory? There are other known examples, such as a 30 ka-old  wolf’s radial bone from the Czech Republic having notches in groups of five, suggesting a record of counting on fingers. Yet very similar devices, made in recent times by the original people of Australia, were not used for keeping count, but to help travellers commit a verbal message to memory enabling them to recount it later.

Do read Barras’s summary and the original paper by d’Errico et al. to get an expanded notion of the arguments being debated. They emerge from the truly novel idea that just because the makers of such objects lived tens or even hundreds of thousands of years ago that doesn’t make them intellectually lacking. Imagining in the manner of Victorian scientists that ancient beings such as Neanderthals and H. erectus must have been pretty dim is akin to the prejudice of European colonialists that people of colour or with non-European cultures were somehow inferior, even non-human. To me it is admirable that the European Research Council has generously funded further research in this field at a time when research funding in the UK, especially for the disciplines involved, has been decimated by those who demanded an exit from the EU.

The older Trinil and Blombos patterns appear yet more sophisticated. The pattern on the latter looks very like the kind of thing that someone in a prison cell might draw to keep track of time. It also incorporates the zig-zag element engraved on the Trinil clam shell. Remember that the word ‘Exchequer’ is derived from a tax audit during the reign of Henry I of England that was conducted on a counting board whose surface had a checked pattern

CSI and detecting the presence of ancient humans

Enter a room, even for a few minutes, and dead skin cells will follow you like an invisible cloud to settle on exposed surfaces. Live there and a greyish white, fluffy dust builds up in every room. Even the most obsessive cleaning will not remove it, especially under a bed or on the bathroom floor. Consider a cave as a home, but one without vacuum cleaners, any kind of sanitation, paper tissues, panty liners, nappies or wet wipes. For pre-modern human dwellings can be added snot, fecal matter, sweat, urine, menstrual blood and semen among all the other detritus of living. A modern crime-scene investigator would be overwhelmed by the sheer abundance of DNA from the host of people who had once dwelt there. CSI works today as much because most homes are pretty clean and most people are fastidious about personal hygene as because of the rapidly shrinking lower limit of DNA detection of the tools at its disposal. Except, that is, when someone from outside the home commits a criminal offence: burglary, GBH, rape, murder. We have all eagerly watched ‘police operas’ and in the absence of other evidence the forensic team generally gets its perpetrator, unless they did the deed wearing a hazmat suit, mask, bootees and latex gloves.

Artistic impression of Neanderthal extended-family life in a cave (credit: Tyler B. Tretsven)

Since 2015 analysis of environmental DNA from soils has begun to revolutionise the analysis of ancient ecosystems, including the living spaces of ancient humans (see: Detecting the presence of hominins in ancient soil samples, April 2017). It is no longer necessary to find tools or skeletal remains of humans to detect their former presence and work out their ancestry. DNA sequencing of soil samples, formerly discarded from archaeological sites, can now detect former human presence in a particular layer, as well as that of other animals. In many cases the ‘signal’ pervades the layer rather than occurring in a particular spot, as expected from shed skin cells and bodily fluids. The first results were promising but only revealed mitochondrial DNA. Now the technique has extended to nuclear DNA: the genome (Vernot, B. and 33 others 2021. Unearthing Neanderthal population history using nuclear and mitochondrial DNA from cave sediments. Science, v. 372, article eabf1667; DOI: 10.1126/science.abf1667). Benjamin Vernot and colleagues from 7 countries collected and analysed cave soils from three promising sites with tangible signs of ancient human occupation. Two of them were in Siberia and had previously yielded Neanderthal and Denisovan genomes from bones. The other is part of the Atapuerca cave complex of NW Spain that had not. The Russian caves yielded DNA from more than 60 samples, 30 being nuclear DNA consistent with that from actual Neanderthal and Denisovan bones found in the caves. Galería de las Estatuas cave in Spain presented a soil profile spanning about 40 thousand years from 112 to 70 ka.

Teasing-out nuclear DNA from soil is complicated, from both technical and theoretical standpoints. So being able to match genomes from soil and bone samples in the Russian caves validated the methodology. The Spanish samples could then be treated with confidence. Galería de las Estatuas revealed the presence of Neanderthals throughout its 40 ka soil profile, but also a surprise. The older DNA was sufficiently distinct from that from later levels to suggest that two different populations had used the cave as a home, the original occupants being replaced by another genetically different group around 100 to 115 ka ago. The earlier affinity was with the ancestors of sequenced Neanderthal remains from Belgium, the later with those from Croatia. That time is at the end of the last (Eemian) interglacial episode, so one possibility is a population change driven by climatic deterioration. This success is sure to encourage other re-examinations of caves all over the place. That is, if there is the analyical capacity to perform such painstaking work in greater volume and at greater pace. Like many other palaeo-genomic studies, this one has relied heavily on the analytical facilities pioneered and developed by Svante Paäbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Covid has forced genetics to the front page for a year and more. And it has led to many advances in anlytical techniques, particularly in their speed. It would nice to think that a dreadful experience may end-up with positive benefits for understanding the full history of humanity.

Relationships between modern humans and Neanderthals

Before 40 thousand years (ka) ago Europe was co-occupied by Neanderthals and anatomically modern humans (AMH) for between five to seven thousand years; about 350 generations – as long as the time since farming began in Neolithic Britain to the present day. Populations of both groups were probably low given their dependence on hunting and foraging during a period significantly colder than it is now. Crude estimates suggest between 3,000 to 12,000 individuals in each group; equivalent to the attendance at a single English Football League 2 match on a Covid-free winter Saturday afternoon. Moving around Europe south of say 55°N, their potential range would have been around 5 million square kilometres, which very roughly suggests that population density would be one person for every 200 km2. That they would have moved around in bands of, say, 10 to 25 might seem to suggest that encounters were very infrequent. Yet a hybrid Neanderthal-Denisovan female found in Siberia yielded DNA that suggested a family connection with Croatia, 5,000 km away (see: Neanderthal Mum meets Denisovan Dad, August 2018); early humans moved far and wide.

The likely appearances of Neanderthals and anatomically modern humans when they first met between 50 and 40 thousand years ago. (Credit: Jason Ford, New York University)

A sparsely populated land can be wandered through with little fear other than those of predators, sparse resources or harsh climate and lack of shelter. But it still seems incredible for there to have been regular meetings with other bands. But that view leaves out knowledge of good places to camp, hunt and forage that assure shelter, water, game and so forth, and how to get to them – a central part of hunter-gatherers’ livelihoods. There would have been a limited number of such refuges, considerably increasing chances of meeting. Whatever the physiognomic differences between AMH and Neaderthals, and they weren’t very striking, meeting up of bands of both human groups at a comfortable campsite would be cause for relief, celebration, exchanges of knowledge and perhaps individuals of one group to partner members of the other.

As well as that from Neanderthals, ancient DNA from very early European AMH remains has increasingly been teased out. The latest comes from three individuals from Bacho Kiro Cave in Bulgaria dated to between 45.9 to 42.6 ka; among the earliest known, fully modern Europeans. One had a Neanderthal ancestor less than six generations removed (perhaps even a great-great grandparent 60 years beforehand). Because of the slight elapsed time, the liaison was probably in Europe, rather than in the Middle East as previously suggested for insertion of Neanderthal genes into European ancestry. The genetic roots of the other two families stemmed back seven to ten generations – roughly 100 to 150 years (Hajdinjak, M. and 31 others 2021. Initial Upper Palaeolithic humans in Europe had recent Neanderthal ancestryNature, v. 592, p. 253–257; DOI: 10.1038/s41586-021-03335-3). The interpretation of these close relationships stems from the high proportion of Neanderthal DNA (3 to 4 %) in the three genomes. The segments are unusually lengthy, which is a major clue to the short time since the original coupling; inherited segments tend to shorten in successive generations. The groups to which these AMH individuals belonged did not contribute to later Eurasian populations, but link to living East Asians and Native Americans. They seem to have vanished from Europe long before modern times. The same day saw publication of a fourth instance of high Neanderthal genetic content (~3 %) in an early European’s genome, extracted from a ~45 ka female AMH from Zlatý kůň (Golden Horse) Cave in Czechia (Prüfer, K. and 11 others 2021. A genome sequence from a modern human skull over 45,000 years old from Zlatý kůň in Czechia. Nature Ecology & Evolution  DOI: 10.1038/s41559-021-01443-x). In her case, too, the Neanderthal DNA segments are unusually lengthy, but indicate 70 to 80 generations (~2,000 to 3,000 years) had elapsed. Her DNA also suggests that she was dark-skinned and had brown hair and brown eyes. Overall her genetics, too, do not have counterparts in later European AMH. The population to which she belonged may have migrated westwards from the Middle East, where one of her ancestors had mated with a Neanderthal, perhaps as long as 50 ka ago. But that does not rule out her group having been in Europe at that time. A later modern human, dated at 42 to 37 ka, is a young man from the Petştera cu Oase cave in Romania, whose forbears mixed with Neanderthals. His genome contains 6.4% of Neanderthal DNA, suggesting that his Neanderthal ancestor lived a mere 4 to 6 generations earlier, most likely in Europe, and was perhaps one of the last of that group.

The data suggest that once modern humans came into contact with their predecessors in the Middle East and Europe, mixture with Neanderthals was ‘the rule rather than the exception’. Yet their lack of direct relationship to later Europeans implies that AMH colonisation of Europe occurred in successive waves of people, not all of whom survived. As Palaeolithic specialist Chris Stringer of the Natural History Museum in London cautions, of these multiple waves of incomers ‘Some groups mixed with Neanderthals, and some didn’t. Some are related to later humans and some are not’. Even five thousand years after ‘first contact’, relations of modern humans with Neanderthals remained ‘cordial’, to say the least, including with the last few before their extinction.

See also: Gibbons, A. 2021. More than 45,000 years ago, modern humans ventured into Neanderthal territory. Here’s what happened next. Science, v. 372, News article; DOI: 10.1126/science.abi8830. Callaway, E. 2021. Oldest DNA from a Homo sapiens reveals surprisingly recent Neanderthal ancestry. Nature, v. 592, News article; DOI: 10.1038/d41586-021-00916-0. Genomes of the earliest Europeans (Science Daily, 7 April 2021). Bower, B. 2021 Europe’s oldest known humans mated with Neandertals surprisingly often (ScienceNews, 7 April 2021)

Magnetic reversal and demise of the Neanderthals?

A rumour emerged last week that the Neanderthals met their end as one consequence of an extraterrestrial, possibly even extragalactic influence. Curiously, it stems from a recent discovery in New Zealand, where of course Neanderthals never set foot and nor did anatomically modern humans, the ancestors of Maori people, until a mere 800 years ago. It started with an ancient log from a kauri tree (Agathis australis), a species that Maoris revere. Found in excavations of boggy ground, the log weighed about 60 tons, so it was a valuable commodity, especially as it is illegal to fell living kauri trees. The wood is unaffected by burial and insect attack, has a regular grain and colour throughout, so is ideal for monumental Maori sculpture. Such swamp kauri also preserves their own life history in annual growth rings, and the log in question has 1700 of them. Using growth rings to chart climate variation gives the most detailed records of the recent past, provided the wood can be dated. Matching growth ring records from several trees of different ages is key to charting local climate with annual precision over several millennia.

An ancient kauri tree log recovered by swampland excavations in New Zealand. (Credit: Jonathan Palmer, in Voosen 2021)

Radiocarbon dating indicates that this particular kauri tree was growing around 42 thousand years ago. That is close to the upper limit for using 14C concentration in organic matter to determine age because the isotope has a short half-life (5730 years). In this case samples of the log would contain only about 0.7 % of its original complement of radioactive carbon. Cosmic rays generate 14C when they hit nitrogen atoms in the atmosphere and it enters COand thus the carbon cycle. Carbon dioxide taken up by photosynthesis to contribute carbon to plants contains only about one part per trillion of 14C. Consequently wood as ancient as that in the kauri log contains almost vanishingly small amounts, yet it can still be measured using mass spectrometry to yield an accurate radiometric age.

The particularly interesting thing about the 42 ka date is that it coincides with the timing of the last reversal of the Earth’s magnetic field, known as the Laschamps event. The kauri tree bears detailed witness through its growth rings to the environmental effects of a decrease in that field to almost zero as the poles flipped. The bulk of cosmic rays are normally deflected away from the Earth by the geomagnetic field, but during a reversal a great many more pass through the atmosphere, the most energetic reaching the surface and the biosphere. The kauri growth rings record fluctuations in the generation of 14C by their passage and thereby the geomagnetic field strength, which was only 6% of normal levels from 42.3 to 41.6 ka (Cooper, A. and 32 others  2021. A global environmental crisis 42,000 years ago. Science, v. 371, p. 811-818; DOI: 10.1126/science.abb8677). This coincided with an unrelated succession of periods of low solar activity and a reduced solar ‘wind’, which also provides some cosmic-rayprotection when activity is at normal levels; a ‘double whammy’. One consequence would have been destruction of stratospheric ozone by cosmic rays and thus increased ultraviolet exposure at ground level.

Combined with the highly precise growth-ring dating, the climatic changes over the 1700 year lifetime of the kauri tree can be linked to other records of environmental change. These include glacial ice- and lake-bed cores together with stalactite layers. Apparently, the Laschamps geomagnetic reversal coincided with abrupt shifts in wind belts and precipitation, perhaps triggering major droughts in the southern continents. Highly plausible, but some of the other speculations are less certain. For instance, some time around 42 ka, but far from well-established, Australia’s marsupial megafauna experienced major extinctions, the Neanderthals disappear from the fossil record and modern humans started decorating caves in Europe (20 ka after they did in Indonesia). In fact, speculation becomes somewhat silly, with suggestions that early Europeans went to live in caves because of increased exposure to UV (they knew, did they, while Neanderthals didn’t?), their painting and, by implication, their entire culture shifting through the shock and awe of mighty displays of the aurora borealis. Just because the number 42 is (or was), according to the late Douglas Adams’s Hitchhiker’s Guide to the Galaxy, ‘the answer to life, the universe and everything’, the authors tag the episode as the ‘Adams Event’. In their summary for The Conversation they include an animation with a quintessential Stephen Fry narrative, which Earth-logs readers can judge for themselves. Perhaps ‘Lockdown Trauma’ has a lot more to answer for, other than upsurges in Zoom conferences, knitting and gourmet experimentation …

See also: Voosen, P. 2021. Kauri trees mark magnetic flip 42,000 years ago. Science, v. 371, p. 766; DOI: 10.1126/science.371.6531.766

How like the Neanderthals are we?

An actor made-up to resemble a Neanderthal man in a business suit traveling on the London Underground. (Source: screen-grab from BBC2 Neanderthals – Meet Your Ancestors)

In the most basic, genetic sense, we were sufficiently alike for us to have interbred with them regularly and possibly wherever the two human groups met. As a result the genomes of all modern humans contain snips derived from Neanderthals (see: Everyone now has their Inner Neanderthal; February 2020). East Asian people also carry some Denisovan genes as do the original people of Australasia and the first Americans. Those very facts suggest that members of each group did not find individuals from others especially repellent as potential sexual partners! But that covers only a tiny part of what constitutes culture. There is archaeological evidence that Neanderthals and modern humans made similar tools. Both had the skills to make bi-faced ‘hand axes’ before they even met around 45 to 40 ka ago.  A cave (La Grotte des Fées) near Châtelperron to the west of the French Alps that was occupied by Neanderthals until about 40 ka yielded a selection of stone tools, including blades, known as the Châtelperronian culture, which indicates a major breakthrough in technology by their makers. It is sufficiently similar to the stone industry of anatomically modern humans (AMH) who, around that time, first migrated into Europe from the east (Aurignacian) to pose a conundrum: Did the Neanderthals copy Aurignacian techniques when they met AMH, or vice versa? Making blades by splitting large flint cores is achieved by striking the cores with just a couple of blows with a softer tool. At the very least Neanderthals had the intellectual capacity to learn this very difficult skill, but they may have invented it (see: Disputes in the cavern; June 2012). Then there is growing evidence for artistic abilities among Neanderthals, and even Homo erectus gets a look-in (see: Sophisticated Neanderthal art now established; February 2018).

Reconstructed burial of a Neanderthal individual at La Chappelle-aux-Saints (Credit: Musée de La Chapelle-aux-Saints, Corrèze, France)

For a long time, a pervasive aspect of AMH culture has been ritual. Indeed much early art may be have been bound up with ritualistic social practices, as it has been in historic times. A persuasive hint at Neanderthal ritual lies in the peculiar structures – dated at 177 ka – found far from the light of day in the Bruniquel Cave in south-western France (see: Breaking news: Cave structures made by Neanderthals; May 2016). They comprise circles fashioned from broken-off stalactites, and fires seem to have been lit in them. The most enduring rituals among anatomically modern humans have been those surrounding death: we bury our dead, thereby preserving them, in a variety of ways and ‘send them off’ with grave goods or even by burning them and putting the ashes in a pot. A Neanderthal skeleton (dated at 50 ka) found in a cave at La Chappelle-aux-Saints appears to have been buried and made safe from scavengers and erosion. There are even older Neanderthal graves (90 to 100 ka) at Quafzeh in Palestine and Shanidar in Iraq, where numerous individuals, including a mother and child, had been interred. Some are associated with possible grave goods, such as pieces of red ochre (hematite) pigment, animal body parts and even pollen that suggests flowers had been scattered on the remains. The possibility of deliberate offerings or tributes and even the notion of burial have met with scepticism among some palaeoanthropologists. One reason for the scientific caution is that many of the finds were excavated long before the rigour of modern archaeological protocols

Recently a multidisciplinary team involving scientists from France, Belgium, Italy, Germany, Spain and Denmark exhaustively analysed the context and remains of a Neanderthal child found in the La Ferrassie cave (Dordogne region of France) in the early 1970s  (Balzeau, A. and 13 others 2020. Pluridisciplinary evidence for burial for the La Ferrassie 8 Neandertal childScientific Reports, v. 10, article 21230; DOI: 10.1038/s41598-020-77611-z). Estimated to have been about 2 years old, the child is anatomically complete. Bones of other animals found in the same deposit were less-well preserved than those of the child, adding weight to the hypothesis that a body, rather than bones, had been buried soon after death. Luminescence dating of the sediments enveloping the skeleton is considerably older than the radiocarbon age of one of the child’s bones. That is difficult to explain other than by deliberate burial. It is almost certain that a pit had been dug and the child placed in it, to be covered in sediment. The skeleton was oriented E-W, with the head towards the east. Remarkably, other Neanderthal remains at the La Ferrassie site also have heads to the east of the rest of their bones, suggesting perhaps a common practice of orientation relative to sunrise and sunset.

It is slowly dawning on palaeoanthropologists that Neanderthal culture and cognitive capacity were not greatly different from those of anatomically modern humans. That similar beings to ourselves disappeared from the archaeological record within a few thousand years of the first appearance of AMH in Europe has long been attributed to what can be summarised as the Neanderthals being ‘second best’ in many ways. That may not have been the case. Since the last glaciation something similar has happened twice in Europe, which analysis of ancient DNA has documented in far more detail than the disappearance of the Neanderthals. Mesolithic hunter-gatherers were followed by early Neolithic farmers with genetic affinities to living people in Northern Anatolia in Turkey – the region where growing crops began. The DNA record from human remains with Neolithic ages shows no sign of genomes with a clear Mesolithic signature, yet some of the genetic features of these hunter-gatherers still remain in the genomes of modern Europeans. Similarly, ancient DNA recovered from Bronze Age human bones suggests almost complete replacement of the Neolithic inhabitants by people who introduced metallurgy, a horse-centred culture and a new kind of ceramic – the Bell Beaker. This genetic group is known as the Yamnaya, whose origins lie in the steppe of modern Ukraine and European Russia. In this Neolithic-Bronze Age population transition the earlier genomes disappear from the ancient DNA record. Yet Europeans still carry traces of that earlier genetic heritage. The explanation now accepted by both geneticists and archaeologists is that both events involved assimilation and merging through interbreeding. That seems just as applicable to the ‘disappearance’ of the Neanderthals

See also: Neanderthals buried their dead: New evidence (Science Daily, 9 December 2020)

Further back in the Eurasian human story

About 800 to 950 thousand years (ka) ago the earliest human colonisers of northern Europe, both adults and children, left footprints and stone tools in sedimentary strata laid down by a river system that then drained central England and Wales. The fossil flora and fauna at the Happisburgh (pronounced ‘Haze-burra’) site in Norfolk suggest a climate that was somewhat warmer in summers than at present, with winter temperatures about 3°C lower than now: similar to the climate in today’s southern Norway. At that time the European landmass extended unbroken to the western UK, so any hunter-gatherers could easily follow migrating herds and take advantage of seasonal vegetation resources. These people don’t have a name because they left no body fossils. A group known from their fossils as Homo antecessor had occupied Spain, southern France and Italy in slightly earlier times (back to 1200 ka). Since the discovery of their unique mix of modern and primitive traits, they have been regarded as possible intermediaries between H. erectus and H. heidelbergensis – once supposed to be the predecessor of Neanderthals and possibly anatomically modern humans (AMH). Since the emergence about 10 years ago of ancient genomics as the prime tool in examining human ancestry the picture has been shown to be considerably more complex. Not only had AMH interbred with Neanderthals and Denisovans, those two groups were demonstrably interfertile too, and a complex web of such relationships had been pieced together by 2016. But there has been a new development.

700 ka Homo erectus from Java: a possible Eurasian ‘super-archaic’ human (credit: Gibbons 2020)

Population geneticists at the University of Utah, USA, have devised sophisticated means of making more of the detailed ATCG nucleotide sequences in ancient human DNA, despite there being very few full genomes of Neanderthals and Denisovans (Rogers, A.R. et al. 2020. Neanderthal-Denisovan ancestors interbred with a distantly related hominin. Science Advances, v. 6, article eaay5483; DOI: 10.1126/sciadv.aay5483). In Earth-logs you may already have come across the idea of the ancestral ‘ghosts’ that are represented by unusual sections of genomes from living West African people. Those sections seem likely to have resulted from interbreeding with an unknown archaic population – i.e. neither Neanderthal nor Denisovan. It now seems that both Neanderthal and Denisovan genomes also show traces of such introgression with ‘ghost’ populations during much earlier times. The ancestors of both these groups separated from the lineage that led to AMH perhaps 750 ka ago. Rogers et al. refer to the earliest as ‘neandersovans’ and consider that they split into the two groups after they entered Eurasia, at some time before 600 ka – perhaps around 740 ka. This division may well have occurred as a result of a population of ‘neandersovans’ having spread over the vastness of Eurasia and growing genetic isolation. The reanalysis of both sets of genomes show evidence of a ‘neandersovan’ population crash before the split. Thereafter, the early Neanderthal population may have risen to around 16 thousand then slowly declined to ~3400 individuals.

A ‘state-of-play’ view of human interbreeding in Eurasia since 2 Ma ago (credit: Gibbons 2020)

However, the ‘neandersovans’ did not enter a new continent devoid of hominins, for as long ago as 1.9 Ma archaic H. erectus had arrived from Africa.  Both Neanderthal and Denisovan genomes record the presence of sections of ‘super-archaic’ DNA, which reflect early  interbreeding with earlier Eurasian populations. Indeed, Denisovans seem to have repeated their ancestors’ sexual exploits, once they became a genetically distinct group.  From the ‘ghost’ DNA fragments Rogers et al. conclude that the ‘super-archaics’ separated from other humans about two million years ago. They were descended from the first ‘Out-of-Africa’ wave of humans, represented by the fossils humans from Dmanisi in Georgia (see First out of Africa, November 2003 and An iconic early human skull,  October 2013 in Earth-logs Human evolution and migrations). A measure of the potential of novel means of analysing available ancient human DNA is the authors’ ability even to estimate the approximate population size of the interbreeding ‘super-archaic’ group at 20 to 50 thousand. Long thought to be impossible, it now seems possible to penetrate back to the very earliest human genetics, and the more DNA that can be teased out of other Neanderthal and Denisovan fossils the more we will know of our origins.

See also: Gibbons, A. 2020. Strange bedfellows for human ancestors. Science, v. 367, p. 838–839; doi:10.1126/science.367.6480.838

Life with the Neanderthals

From Robinson Crusoe’s discovery of Friday’s footprint on his desert island to Mary Leakey’s unearthing of a 3.6 Ma old trackway left by two adults and a juvenile of the hominin species Australopithecus afarensis at Laetoli in Tanzania, such tangible signs of another related creature have fostered an eerie thrill in whoever witnesses them. Other ancient examples have turned up, such as the signs of mud trampled by 800 ka humans (H. antecessor?) at Happisburgh, Norfolk, UK (see Traces of the most ancient Britons, February 2014). From a purely scientific standpoint, footprints provide key evidence of foot anatomy, gait, travel speed, height, weight, and the number of individuals who contributed to a trackway. At Le Rozel on the Cherbourg Peninsula in Normandy, France – about 30 km west of the D-Day landing site at Utah beach – Yves Roupin, an amateur archaeologist, discovered a footprint on the foreshore in the 1960s close to the base of a thick sequence of late-Pleistocene dune sediments exposed below a rocky cliff. Fifty years later, rapid onset of wind and tidal erosion threatened to destroy the site, so excavations and scientific analysis began. This involved excavation of thick overburden on an annual basis to expose as much of five footprint-bearing horizons as possible (about 90 m2).

Le Rozel
The Le Rozel excavation, with weighted plastic sheets to protect the site from erosion between visits (credit: Dominique Cliquet)

More and more prints emerged, each photographed and modelled in 3-D, with the best being preserved as casts using a flexible material, similar to that used by dentists (Duveau, J. eyt al. 2019. The composition of a Neandertal social group revealed by the hominin footprints at Le Rozel (Normandy, France). Proceedings of the National Academy of Sciences. 9 September 2019; DOI: 10.1073/pnas.1901789116). At the end of the excavation hundreds of prints had been found and recorded. They had been preserved in wet sand, probably deposited in an interdune pond. Luminescence dating of sand grains revealed that the footprints were produced around 80 ka ago, 35 ka before Europe was occupied by anatomically modern humans. Scattered around the site are numerous fossils of butchered prey animals, together with stone tools typical of Neanderthal technology.

Such a large number of footprints presented a unique opportunity to analyse the social structure of the Neanderthal group that produced them, for they came in many different sizes. During the very short period in which they were produced and buried by wind-blown sand, an estimated 10 to 13 individuals had crossed and re-crossed the site – there may have been more individuals who didn’t happen to cross the wet patch But the evidence suggests that children and adolescents, one of whom may have been as young as 2 years, predominated. Two or three with the biggest feet were probably adults as tall as 1.9 metres – about 20 cm taller that the average for modern human males. That is surprising for Neanderthals who are widely believed to have been more stocky. The fact that footprints occur in 5 horizons suggests that the band, or perhaps family, found the site to be good for occupation. Wider hypotheses are a little shaky. Did Neanderthals have large families? Does the predominance of children and adolescents indicate that they died young? But perhaps children stayed close to habitations with just a few ‘minders’, while other adults went off hunting and foraging. Were the kids playing?

Neanderthal demographics and their extinction

About 39 thousand years ago all sign of the presence of Neanderthal bands in their extensive range across western Eurasia disappears. Their demise occurred during a period of relative warmth (Marine-Isotope Stage-3) following a cold period at its worst around 65 ka (MIS-4). They had previously thrived since their first appearance in Eurasia at about 250 ka, surviving at least two full glacial cycles. Their demise occurred around 5 thousand years after they were joined in western Eurasia by anatomically modern humans (AMH). During their long period of habitation they had adapted well to a range of climatic zones from woodland to tundra. During their overlap both groups shared much the same food resources, dominated by large herbivores whose numbers burgeoned during the warm period, with the difference that Neanderthals seemed to have depended on ranges centred on fixed sites of habitation while AMH maintained a nomadic lifestyle. Having shared a common African ancestry about 400 thousand years ago, DNA studies  have revealed that the two populations interbred regularly, probably in the earlier period of overlap in west Asia from around 120 thousand years ago and possibly in Europe too after 44 ka. Considering their previous tenacity, how the Neanderthals met their end is something of a mystery. It may have been a result of competition for resources with AMH, which could be countered by the increase in food resources. Maybe physical conflict was involved, or perhaps disease imported with AMH from warmer climes. Genetic absorption through interbreeding of a small population with a larger one of AMH is a possibility, although DNA evidence is lacking. An inability to adapt to climate change contradicts the Neanderthals long record and their disappearance during MIS-3. Previous population estimates of changing Neanderthal populations in the Iberian Peninsula (see Fig. 2 in Roberts, M.F. & Bricher, S.E 2018. Modeling the disappearance of the Neanderthals using principles of population dynamics and ecology. Journal of Archaeological Science, v. 100, p.16-31; DOI: 10.1016/j.jas.2018.09.012) show decline from about 70,000 to 20,000 before MIS-4, then recovery to about 40,000 before the arrival of AMH at 44 ka followed by a decline to extinction thereafter. Roberts and Bricher developed a model for investigating demographics from archaeological evidence that is neutral as regards any particular hypothesis for Neanderthal extinction.

Nea family
Artistic reconstruction of Neanderthal family group (credit: Nikola Solic, Reuters)

Continue reading “Neanderthal demographics and their extinction”

Neanderthal Mum meets Denisovan Dad

Two bone fragments from the Denisova Cave – the former abode of an 18th century Russian hermit called Denis – in the Altai region of Siberia yielded ancient  DNA. One matches that from previously analysed Neanderthal remains and the other a genome that could only be ascribed to a hitherto unknown ancient-human population, now known as the Denisovans. Since their discovery further analysis of both modern and ancient DNA has shown that modern humans living outside of Africa contain a few percent of DNA from both ancient-human groups. Soon after leaving Africa some of their ancestors interbred with both; indeed a 40 ka-old modern-human jaw from Romania revealed genetic evidence that the individual had a Neanderthal great-great grandparent. Their descendants spread far and wide to populate Eurasia, Australasia and the Americas. Using the ancient DNA to peer back in time suggests that Neanderthals and Denisovans diverged from a common ancestor between 470 and 380 ka, itself having split from modern-human ancestry between 770 to 550 ka. Denisovan DNA also contains evidence that its ancestry included segments that could only have come from a totally unknown hominin species. Interestingly, DNA from the Neanderthal bone fragment found at Denisova contains fragments from an anatomically modern-human.

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

With such riches from tiny fragments of human bones unearthed from the Denisova Cave, it is no surprise that the team led by Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has subsequently analysed others that showed signs of human proteins. The latest ‘takes the biscuit’. A fragment of limb bone from someone who was at least 13 years old yielded DNA commensurate with their having been the child of a Neanderthal mother and a Denisovan father (Slon, V. and 18 others 2018. The genome of the offspring of a Neanderthal mother and a Denisovan father. Nature, v. 560, published on-line; doi: 10.1038/s41586-018-0455-x). Their child was a girl, who has been nicknamed ‘Denny’ by the team, though ‘Denise’ might seem more appropriate. The only clues to what her father, or any Denisovan, might have looked like stem from a few teeth and a skull fragment from the cave that have yielded Denisovan DNA. The teeth are much larger and the skull fragment is thicker than those of Neanderthals, suggesting that Denisovans were distinctly bigger and more robust than even the sturdy Neanderthals.

The father came from a population related to a later Denisovan found in the cave – the first to be sequenced. This suggests long-term occupancy of the area by Denisovans. But his genome also carries traces of Neanderthal ancestry. Surprisingly, the mother is more closely related to Croatian Neanderthals, rather than to an earlier Neanderthal found in the cave. Neanderthals were clearly capable of migrating between Europe and eastern Eurasia; more than 5000 km in this case. Even though very few archaic humans have been genetically sequenced it is beginning to look as if genetic mixing between diverse hominin groups in the last half million years was common, when they actually met. A custom of marrying outside a closely related group (exogamy) has been popular throughout recorded history; indeed it makes sound genetic sense. With the tiny human population density during the Late Pleistocene, it may then have been cause for mutual celebration.  As documented in Chapters 2 and 3 of David Reich’s Who We Are and How We Got Here (Oxford University Press, 2018) human origins since about 470 ka until the present chart a history of episodic migrations and genetic mixing that certainly makes nonsense of earlier ideas of ‘racial purity’ and casts doubt even on the term ‘species’ as regards members of the genus Homo.

If we are ever to discover who the Denisovans were and what they looked like, the evidence is likely to come from East Asia at latitudes where climate favours preservation of DNA. Advanced sequencing equipment and techniques are now operational in China, where suspected Denisovan remains have been found

See also: Warren, M. 2018. First ancient-human hybrid. Nature, v. 560, p. 417-418; doi: 10.1038/d41586-018-06004-0); Sample, I. 2018. Offspring of Neanderthal and Denisovan identified for first time. The Guardian (22 August 2918).

A revised and updated edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Neanderthals on the BBC

Since it began in 2000 Earth-Pages News has been covering the emergent science concerning the Neanderthals. To say that it has been a fertile field would be a considerable understatement, and I am certain that it will continue to be so. The first EPN item to mention them concerned the British Channel 4 TV documentary Neanderthals. In it I quoted Steve Jones FRS, former Head of the Department of Genetics, Evolution and Environment at University College London, who is always good for a humorous take on his science, and much more besides. ‘If you met an unwashed Cro Magnon dressed in a business suit on the Underground, you would probably change seats.  If you met a similarly garbed Neanderthal, you would undoubtedly change trains’. That they had the build of world-champion freestyle wrestlers, beetling brows and extremely large noses was illustrated in the programme by reconstructions based on their skeletal remains; yes, they did look  dangerous. But Jones’s theory is put to the test with a suitably attired actor made up as a Neanderthal man in new two-part series on BBC2, Neanderthals – Meet Your Ancestors (follow the link to watch the first programme – you need to create an account at BBC iPlayer and claim that you do have a British TV licence). Some commuters did give the chap a slightly worried glance, but there was not a rush for the doors. Ella Al-Shamahi, one of the presenters, even commented that some of her friends may well have actively sought a date with him! He certainly did not seem out of place in cosmopolitan London, and the same might be said for a cattle auction in rural Cumbria. On the New York subway he would undoubtedly have been ignored. Steve Jones was wrong!

An actor made-up to resemble a Neanderthal man in a business suit traveling on the London Underground. (Source: screen-grab from BBC2 Neanderthals – Meet Your Ancestors)

We now know that the majority of people who live on the planet today have Neanderthal segments in their genome. So between 80 and 30 ka ago to dally with Neanderthals and vice versa was as acceptable as it might be today, if they were around; probably more so, considering the amount of their DNA that is retained 2000 generations after the last possible contact. Most of the discoveries concerning Neanderthals that EPN has covered over the last 17 years are used by the two programmes to arrive at the best concept to date of just who Neanderthals were and what they were able to do.

The first episode focuses on the use of skeletal remains to visualise male and female Neanderthals, using digital techniques of forensic face and body reconstruction. Over several hundred thousand years their physiology had adapted to the fluctuating conditions of western Asia and Europe, including repeated cold episodes that ranged from full glacials to interstadials. They had also adapted to forest ecosystems where hunting would have relied on ambushing prey. Their build was suited to bursts on sprinting, probably faster than Usain Bolt could manage at his best. But they were not built for the kind of endurance needed by evolving modern humans in Africa to chase down prey in savannah scrub until they succumb to heat exhaustion. Interestingly, the right, upper-arm bones of male Neanderthals are more robust than those on the left, muscle attachment scars revealing that in life they developed large biceps, probably to use spears in powerful upward lunges into the underside of large prey, such as mammoths and aurochs. They were close-combat experts and carry the signs of injury that every such hunt would have risked. However, the series goes beyond reconstruction, by using the power of CGI motion-capture techniques developed for modern animated films and games. Actors perform the moves, and are morphed to accommodate Neanderthal physique and probable gait in the resulting action sequences – fearsomely and convincingly realistic. Analysis of a single complete hyoid bone (the hard component of the ‘voice box’ and ‘Adam’s Apple’) digitally inserted into reconstruction of the Neanderthal neck, and digital reconstruction of their possible vocal range results in demonstration of how close to human pronunciation they could have been, albeit with a pronounced distortion of the vowel Aah but almost indistinguishable for other vowels. Their faces were capable of much the same range of expressions as ours.

The second episode, available on BBC iPlayer after Sunday 20 May 2018, focuses on the genetic relations between us and Neanderthals. We gained both advantages and sets-back. It also uses what evidence there is to investigate just how like us they were in their social and intellectual behaviour. It seems they were doing OK in the grim climatic scenario of the run-up to the last glacial maximum, but succumbed to extinction during the ten thousand years following the permanent entry of anatomically modern humans into Europe and western Asia after 40 ka. Why did that happen? Every human outside  sub-Saharan Africa contains Neanderthal genes: on average about 2%. Yet each of us contains a different set, so that up to 70% of the full Neanderthal genome remains in humanity as a whole. Is it possible that they could be reconstructed? Crucially, should that ever be attempted it would pose a huge moral dilemma.

To read more on the evolutionary relationships between modern humans and Neanderthals click here.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook