Acheulean

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Acheulean

Geographical range	Africa, Europe, and Asia
Period	Lower Paleolithic
Dates	1.76–0.13 Mya
Type site	Saint-Acheul (Amiens)
Preceded by	Oldowan
Followed by	Mousterian, Clactonian, Micoquien

Acheulean hand-axes from Kent. The types shown are (clockwise from top) cordate, ficron, and ovate.

 

Depiction of a Terra Amata hut in Nice, France as postulated by Henry de Lumley dated to 400 thousand years ago. Acheulean-culture shelter construction has been discovered in Japan dating back to 500 thousand years ago.

 

Acheulean (/əˈʃuːliən/; also Acheulian and Mode II), from the French acheuléen, is an archaeological industry of stone tool manufacture characterized by distinctive oval and pear-shaped "hand-axes" associated with Homo erectus and derived species such as Homo heidelbergensis. 

Acheulean tools were produced during the Lower Palaeolithic era across Africa and much of West Asia, South Asia, and Europe, and are typically found with Homo erectus remains. It is thought that Acheulean technologies first developed about 1.76 million years ago, derived from the more primitive Oldowan technology associated with Homo habilis. The Acheulean includes at least the early part of the Middle Paleolithic. Its end is not well defined, depending on whether Sangoan (also known as "Epi-Achaeulean") is included, it may be taken to last until as late as 130,000 years ago. In Europe and Western Asia, early Neanderthals adopted Achaeulean technology, transitioning to Mousterian by about 160,000 years ago.

History of research

The type site for the Acheulean is Saint-Acheul, a suburb of Amiens, the capital of the Somme department in Picardy, where artifacts were found in 1859.

John Frere is generally credited as being the first to suggest a very ancient date for Acheulean hand-axes. In 1797, he sent two examples to the Royal Academy in London from Hoxne in Suffolk. He had found them in prehistoric lake deposits along with the bones of extinct animals and concluded that they were made by people "who had not the use of metals" and that they belonged to a "very ancient period indeed, even beyond the present world". His ideas were, however, ignored by his contemporaries, who subscribed to a pre-Darwinian view of human evolution.

Later, Jacques Boucher de Crèvecœur de Perthes, working between 1836 and 1846, collected further examples of hand-axes and fossilised animal bone from the gravel river terraces of the Somme near Abbeville in northern France. Again, his theories attributing great antiquity to the finds were spurned by his colleagues, until one of de Perthe's main opponents, Dr Marcel Jérôme Rigollot, began finding more tools near Saint Acheul. Following visits to both Abbeville and Saint Acheul by the geologist Joseph Prestwich, the age of the tools was finally accepted.

In 1872, Louis Laurent Gabriel de Mortillet described the characteristic hand-axe tools as belonging to L'Epoque de St Acheul. The industry was renamed as the Acheulean in 1925.

Dating the Acheulean

An Acheulean handaxe, Haute-Garonne France – MHNT

 

Providing calendrical dates and ordered chronological sequences in the study of early stone tool manufacture is often accomplished through one or more geological techniques, such as radiometric dating, often potassium-argon dating, and magnetostratigraphy. From the Konso Formation of Ethiopia, Acheulean hand-axes are dated to about 1.5 million years ago using radiometric dating of deposits containing volcanic ashes. Acheulean tools in South Asia have also been found to be dated as far as 1.5 million years ago. However, the earliest accepted examples of the Acheulean currently known come from the West Turkana region of Kenya and were first described by a French-led archaeology team. These particular Acheulean tools were recently dated through the method of magnetostratigraphy to about 1.76 million years ago, making them the oldest not only in Africa but the world. The earliest user of Acheulean tools was Homo ergaster, who first appeared about 1.8 million years ago. Not all researchers use this formal name, and instead prefer to call these users early Homo erectus.

From geological dating of sedimentary deposits, it appears that the Acheulean originated in Africa and spread to Asian, Middle Eastern, and European areas sometime between 1.5 million years ago and about 800 thousand years ago. In individual regions, this dating can be considerably refined; in Europe for example, it was thought that Acheulean methods did not reach the continent until around 500,000 years ago. However more recent research demonstrated that hand-axes from Spain were made more than 900,000 years ago.

Relative dating techniques (based on a presumption that technology progresses over time) suggest that Acheulean tools followed on from earlier, cruder tool-making methods, but there is considerable chronological overlap in early prehistoric stone-working industries, with evidence in some regions that Acheulean tool-using groups were contemporary with other, less sophisticated industries such as the Clactonian and then later with the more sophisticated Mousterian, as well. It is therefore important not to see the Acheulean as a neatly defined period or one that happened as part of a clear sequence but as one tool-making technique that flourished especially well in early prehistory. The enormous geographic spread of Acheulean techniques also makes the name unwieldy as it represents numerous regional variations on a similar theme. The term Acheulean does not represent a common culture in the modern sense, rather it is a basic method for making stone tools that was shared across much of the Old World.

The very earliest Acheulean assemblages often contain numerous Oldowan-style flakes and core forms and it is almost certain that the Acheulean developed from this older industry. These industries are known as the Developed Oldowan and are almost certainly transitional between the Oldowan and Acheulean.

Acheulean stone tools

Stages

In the four divisions of prehistoric stone-working, Acheulean artefacts are classified as Mode 2, meaning they are more advanced than the (usually earlier) Mode 1 tools of the Clactonian or Oldowan/Abbevillian industries but lacking the sophistication of the (usually later) Mode 3 Middle Palaeolithic technology, exemplified by the Mousterian industry.

The Mode 1 industries created rough flake tools by hitting a suitable stone with a hammerstone. The resulting flake that broke off would have a natural sharp edge for cutting and could afterwards be sharpened further by striking another smaller flake from the edge if necessary (known as "retouch"). These early toolmakers may also have worked the stone they took the flake from (known as a core) to create chopper cores although there is some debate over whether these items were tools or just discarded cores.

The Mode 2 Acheulean toolmakers also used the Mode 1 flake tool method but supplemented it by using bone, antler, or wood to shape stone tools. This type of hammer, compared to stone, yields more control over the shape of the finished tool. Unlike the earlier Mode 1 industries, it was the core that was prized over the flakes that came from it. Another advance was that the Mode 2 tools were worked symmetrically and on both sides indicating greater care in the production of the final tool.

Mode 3 technology emerged towards the end of Acheulean dominance and involved the Levallois technique, most famously exploited by the Mousterian industry. Transitional tool forms between the two are called Mousterian of Acheulean Tradition, or MTA types. The long blades of the Upper Palaeolithic Mode 4 industries appeared long after the Acheulean was abandoned.

As the period of Acheulean tool use is so vast, efforts have been made to classify various stages of it such as John Wymer's division into Early Acheulean, Middle Acheulean, Late Middle Acheulean and Late Acheulean for material from Britain. These schemes are normally regional and their dating and interpretations vary.

In Africa, there is a distinct difference in the tools made before and after 600,000 years ago with the older group being thicker and less symmetric and the younger being more extensively trimmed.

Manufacture

The primary innovation associated with Acheulean hand-axes is that the stone was worked symmetrically and on both sides. For the latter reason, handaxes are, along with cleavers, bifacially worked tools that could be manufactured from the large flakes themselves or from prepared cores.

Tool types found in Acheulean assemblages include pointed, cordate, ovate, ficron, and bout-coupé hand-axes (referring to the shapes of the final tool), cleavers, retouched flakes, scrapers, and segmental chopping tools. Materials used were determined by available local stone types; flint is most often associated with the tools but its use is concentrated in Western Europe; in Africa sedimentary and igneous rock such as mudstone and basalt were most widely used, for example. Other source materials include chalcedony, quartzite, andesite, sandstone, chert, and shale. Even relatively soft rock such as limestone could be exploited. In all cases the toolmakers worked their handaxes close to the source of their raw materials, suggesting that the Acheulean was a set of skills passed between individual groups.

Some smaller tools were made from large flakes that had been struck from stone cores. These flake tools and the distinctive waste flakes produced in Acheulean tool manufacture suggest a more considered technique, one that required the toolmaker to think one or two steps ahead during work that necessitated a clear sequence of steps to create perhaps several tools in one sitting.

A hard hammerstone would first be used to rough out the shape of the tool from the stone by removing large flakes. These large flakes might be re-used to create tools. The tool maker would work around the circumference of the remaining stone core, removing smaller flakes alternately from each face. The scar created by the removal of the preceding flake would provide a striking platform for the removal of the next. Misjudged blows or flaws in the material used could cause problems, but a skilled toolmaker could overcome them.

Once the roughout shape was created, a further phase of flaking was undertaken to make the tool thinner. The thinning flakes were removed using a softer hammer, such as bone or antler. The softer hammer required more careful preparation of the striking platform and this would be abraded using a coarse stone to ensure the hammer did not slide off when struck.

Final shaping was then applied to the usable cutting edge of the tool, again using fine removal of flakes. Some Acheulean tools were sharpened instead by the removal of a tranchet flake. This was struck from the lateral edge of the hand-axe close to the intended cutting area, resulting in the removal of a flake running along (parallel to) the blade of the axe to create a neat and very sharp working edge. This distinctive tranchet flake can be identified amongst flint-knapping debris at Acheulean sites.

Use

Acheulean hand-axe from Egypt. Found on a hill top plateau, 1400 feet above sea level, 9 miles NNW of the city of Naqada, Egypt. Paleolithic. The Petrie Museum of Egyptian Archaeology, London

 

Loren Eiseley calculated that Acheulean tools have an average useful cutting edge of 20 centimetres (8 inches), making them much more efficient than the 5-centimetre (2 in) average of Oldowan tools.

Use-wear analysis on Acheulean tools suggests there was generally no specialization in the different types created and that they were multi-use implements. Functions included hacking wood from a tree, cutting animal carcasses as well as scraping and cutting hides when necessary. Some tools, however, could have been better suited to digging roots or butchering animals than others.

Alternative theories include a use for ovate hand-axes as a kind of hunting discus to be hurled at prey. Puzzlingly, there are also examples of sites where hundreds of hand-axes, many impractically large and also apparently unused, have been found in close association together. Sites such as Melka Kunturé in Ethiopia, Olorgesailie in Kenya, Isimila in Tanzania, and Kalambo Falls in Zambia have produced evidence that suggests Acheulean hand-axes might not always have had a functional purpose.

Recently, it has been suggested that the Acheulean tool users adopted the handaxe as a social artifact, meaning that it embodied something beyond its function of a butchery or wood cutting tool. Knowing how to create and use these tools would have been a valuable skill and the more elaborate ones suggest that they played a role in their owners' identity and their interactions with others. This would help explain the apparent over-sophistication of some examples which may represent a "historically accrued social significance".

One theory goes further and suggests that some special hand-axes were made and displayed by males in search of mate, using a large, well-made hand-axe to demonstrate that they possessed sufficient strength and skill to pass on to their offspring. Once they had attracted a female at a group gathering, it is suggested that they would discard their axes, perhaps explaining why so many are found together.

Hand-axe as a left over core

Stone knapping with limited digital dexterity makes the center of gravity the required direction of flake removal. Physics then dictates a circular or oval end pattern, similar to the handaxe, for a leftover core after flake production. This would explain the abundance, wide distribution, proximity to source, consistent shape, and lack of actual use, of these artifacts.

Money

Mimi Lam, a researcher from the University of British Columbia, has suggested that Acheulean hand-axes became "the first commodity: A marketable good or service that has value and is used as an item for exchange."

Distribution

The geographic distribution of Acheulean tools – and thus the peoples who made them – is often interpreted as being the result of palaeo-climatic and ecological factors, such as glaciation and the desertification of the Sahara Desert.

Acheulean Biface from Saint Acheul

 

Acheulean stone tools have been found across the continent of Africa, save for the dense rainforest around the River Congo which is not thought to have been colonized by hominids until later. It is thought that from Africa their use spread north and east to Asia: from Anatolia, through the Arabian Peninsula, across modern day Iran and Pakistan, and into India, and beyond. In Europe their users reached the Pannonian Basin and the western Mediterranean regions, modern day France, the Low Countries, western Germany, and southern and central Britain. Areas further north did not see human occupation until much later, due to glaciation. In Athirampakkam at Chennai in Tamil Nadu the Acheulean age started at 1.51 mya and it is also prior than North India and Europe.

Until the 1980s, it was thought that the humans who arrived in East Asia abandoned the hand-axe technology of their ancestors and adopted chopper tools instead. An apparent division between Acheulean and non-Acheulean tool industries was identified by Hallam L. Movius, who drew the Movius Line across northern India to show where the traditions seemed to diverge. Later finds of Acheulean tools at Chongokni in South Korea and also in Mongolia and China, however, cast doubt on the reliability of Movius's distinction. Since then, a different division known as the Roe Line has been suggested. This runs across North Africa to Israel and thence to India, separating two different techniques used by Acheulean toolmakers. North and east of the Roe Line, Acheulean hand-axes were made directly from large stone nodules and cores; while, to the south and west, they were made from flakes struck from these nodules.

Biface (trihedral) Amar Merdeg, Mehran, National Museum of Iran

Acheulean tool users

For further details of the known environment and people during the time when Acheulean tools were being made, see Palaeolithic and Lower Palaeolithic.

 

Most notably, however, it is Homo ergaster (sometimes called early Homo erectus), whose assemblages are almost exclusively Acheulean, who used the technique. Later, the related species Homo heidelbergensis (the common ancestor of both Neanderthals and Homo sapiens) used it extensively. Late Acheulean tools were still used by species derived from H. erectus, including Homo sapiens idaltu and early Neanderthals.

The symmetry of the hand-axes has been used to suggest that Acheulean tool users possessed the ability to use language; the parts of the brain connected with fine control and movement are located in the same region that controls speech. The wider variety of tool types compared to earlier industries and their aesthetically as well as functionally pleasing form could indicate a higher intellectual level in Acheulean tool users than in earlier hominines. Others argue that there is no correlation between spatial abilities in tool making and linguistic behaviour, and that language is not learned or conceived in the same manner as artefact manufacture.

Lower Palaeolithic finds made in association with Acheulean hand-axes, such as the Venus of Berekhat Ram, have been used to argue for artistic expression amongst the tool users. The incised elephant tibia from Bilzingsleben in Germany, and ochre finds from Kapthurin in Kenya and Duinefontein in South Africa, are sometimes cited as being some of the earliest examples of an aesthetic sensibility in human history. There are numerous other explanations put forward for the creation of these artefacts, however; and there is no unequivocal evidence of human art until around 50,000 years ago, after the emergence of modern Homo sapiens.

The kill site at Boxgrove in England is another famous Acheulean site. Up until the 1970s these kill sites, often at waterholes where animals would gather to drink, were interpreted as being where Acheulean tool users killed game, butchered their carcasses, and then discarded the tools they had used. Since the advent of zooarchaeology, which has placed greater emphasis on studying animal bones from archaeological sites, this view has changed. Many of the animals at these kill sites have been found to have been killed by other predator animals, so it is likely that humans of the period supplemented hunting with scavenging from already dead animals.

Excavations at the Bnot Ya'akov Bridge site, located along the Dead Sea rift in the southern Hula Valley of northern Israel, have revealed evidence of human habitation in the area from as early as 750,000 years ago. Archaeologists from the Hebrew University of Jerusalem claim that the site provides evidence of "advanced human behavior" half a million years earlier than has previously been estimated. Their report describes an Acheulean layer at the site in which numerous stone tools, animal bones, and plant remains have been found.

Azykh cave located in Azerbaijan is another site where Acheulean tools were found. In 1968, a lower jaw of a new type of hominid was discovered in the 5th layer (so-called Acheulean layer) of the cave. Specialists named this type “Azykhantropus”.

Only limited artefactual evidence survives of the users of Acheulean tools other than the stone tools themselves. Cave sites were exploited for habitation, but the hunter-gatherers of the Palaeolithic also possibly built shelters such as those identified in connection with Acheulean tools at Grotte du Lazaret and Terra Amata near Nice in France. The presence of the shelters is inferred from large rocks at the sites, which may have been used to weigh down the bottoms of tent-like structures or serve as foundations for huts or windbreaks. These stones may have been naturally deposited. In any case, a flimsy wood or animal skin structure would leave few archaeological traces after so much time. Fire was seemingly being exploited by Homo ergaster, and would have been a necessity in colonising colder Eurasia from Africa. Conclusive evidence of mastery over it this early is, however, difficult to find.

Neanderthal behavior

From Wikipedia, the free encyclopedia

A Mousterian tool retoucher on a bone-shaft from the French site of La Quina, used to modify stone tools.

 

Almost everything about Neanderthal behaviour is controversial. From their physiology, Neanderthals are presumed to have been omnivores, but animal protein formed the majority of their dietary protein, showing them to have been apex predators and not scavengers [DJS -- I don't see the logic in this claim]. Some studies suggest they cooked vegetables.

The quality of stone tools at archaeological sites suggests Neanderthals were good at "expert" cognition, a form of observational learning and practice acquired through apprenticeship that relies heavily on long-term procedural memory. Neanderthal toolmaking changed little over hundreds of thousands of years. The lack of innovation was said to imply they may have had a reduced capacity for thinking by analogy and less working memory. The researchers further speculated that Neanderthal behaviour would probably seem neophobic, dogmatic and xenophobic to modern humans. A 2018 open access paper discussed, in light of recent developments in the fields of paleogenetics and paleoanthropology, whether or not Neanderthals were rational. The authors' argument focuses on the genetic evidence that supports interbreeding with Homo sapiens, language acquisition (including the FOXP2 gene), archaeological signs of cultural development and potential for cumulative cultural evolution.

Few Neanderthals lived past 35.

Language

The hyoid bone and larynx in a modern human.

 

It is not known whether Neanderthals were anatomically capable of speech and whether they actually spoke. A once-widely believed theory that the Neanderthal vocal tract was different from that of living humans and so probably could not speak is now discredited. The only bone in the vocal tract is the hyoid but is so fragile that no Neanderthal hyoid was found until 1983, when excavators discovered a well-preserved one on Neanderthal Kebara 2, Israel. It was largely similar to that of living humans. Although the original excavators claimed that the similarity of this bone with that of living humans implied Neanderthals were anatomically capable of speech, it is not possible to reconstruct the vocal tract with information supplied by the hyoid. In particular, it does not allow to determine whether the larynx of its owner was in a low-lying position, a feature considered important in producing speech.

A 2013 study on the Kebara hyoid used X-ray microtomography and finite element analysis to conclude that the Neanderthal hyoid showed microscopic features more similar to a modern human's hyoid than to a chimpanzee hyoid. To the authors, that suggested the Neanderthal hyoid was used similarly to that in living humans, that is, to produce speech. Yet, because the authors did not compare the microscopic structure of the Kebara 2 hyoid with that of speech-hindered living humans, the result is not yet conclusive. 

Although some researchers believe Neanderthal tool-making is too complex for them not to have had language, toolmaking experiments of Levallois technology, the most common Neanderthal toolmaking technique, have found that living humans can learn it in silence.

Neanderthals had the same DNA-coding region of the FOXP2 gene as living humans, but are different in one position of the gene's regulatory regions, and the extent of FOXP2 expression might hence have been different in Neanderthals. Although the gene appears necessary for language—living humans who don't have the normal human version of the gene have serious language difficulties—it is not necessarily sufficient. It is not known whether FOXP2 evolved for or in conjunction with language, nor whether there are other language-related genes that Neanderthals may or may not have had. Similarly, the size and functionality of the Neanderthal Broca's and Wernicke's areas, used for speech generation in modern humans, is debated.

In 1998, researchers suggested Neanderthals had a hypoglossal canal at least as large as humans, suggesting they had part of the neurological requirements for language. The canal carries the hypoglossal nerve, which controls the muscles of the tongue, necessary to produce language. However, a Berkeley research team showed no correlation between canal size and speech, as a number of extant non-human primates and fossilized australopithecines have larger hypoglossal canals.

The morphology of the outer and middle ear of Homo heidelbergensis, the Neanderthal's ancestor, suggests they had an auditory sensitivity similar to modern humans and different from chimpanzees.

Tools

Neanderthal and early anatomically modern human archaeological sites show a more simple toolkit than those found in Upper Paleolithic sites, produced by modern humans after about 50,000 BP. In both early anatomically modern humans and Neanderthals, there is little innovation in the toolkit.

Tools produced by Middle Palaeolithic humans in Eurasia (both Neanderthals and early modern humans) are known as Mousterian. These were often produced using soft hammer percussion, with hammers made of materials like bones, antlers, and wood, rather than hard hammer percussion, using stone hammers. A result of this is that their bone industry was relatively simple. They routinely made stone implements. Neanderthal tools consisted of stone-flakes and task-specific hand axes, many of which were sharp.

There is evidence for violence among Neanderthals. The 40,000-year-old Neanderthal skull of St. Césaire has a healed fracture in its cranial vault likely caused by something sharp, suggesting interpersonal violence. The wound healed and the Neanderthal survived.

Whether they had projectile weapons is controversial. They seem to have had wooden spears, but it is unclear whether they were used as projectiles or as thrusting spears. Wood implements rarely survive, but several 320,000-year-old wooden spears about 2-metres in length were found near Schöningen, northern Germany, and are believed to be the product of the older Homo heidelbergensis species.

Neanderthals used fire on occasion, but it is not certain whether they were able to produce it. They may have used Pyrolusite (manganese dioxide) to accelerate the combustion of wood. "With archaeological evidence for fire places and the conversion of the manganese dioxide to powder, [it has been argued] that Neanderthals at Pech-de-l’Azé I used manganese dioxide in fire-making and produced fire on demand." MnO₂ lowers the combustion temperature of wood from 350 degrees Celsius to 250 degrees Celsius and is common in Neanderthal archaeological sites.

Neanderthals produced birch tar through the dry distillation of birch bark.

Pendants and other jewelry showing traces of ochre dye and of deliberate grooving have also been found in one single stratigraphically disturbed Neanderthal archaeological layer, but whether these items were ever in the hands of Neanderthals or were mixed into their archaeological layers from overlying modern human ones is debated.

Burial claims

A claimed Neanderthal burial at Kebara Cave (Carmel Range, Israel). Thermoluminescence dates place Neanderthal levels at Kebara at ca. 60,000 BP. Skeleton of an adult man nicknamed Moshe (25–35 years old, height 1.70 m) found in 1983

No claim of a deliberate Neanderthal burial is universally accepted. An interpretation of pre-Neanderthal Shanidar IV as having been ritually buried with flowers has been seriously questioned, and to Paul B. Pettitt, convincingly eliminated: "A recent examination of the microfauna from the strata into which the grave was cut suggests that the pollen was deposited by the burrowing rodent Meriones tersicus (Persian jird), which is common in the Shanidar microfauna and whose burrowing activity can be observed today".

Diet

Traces of fossilized plants have been extracted from Neanderthal teeth found in Belgium and Iraq suggesting they mostly consumed plants. Nonetheless, preliminary studies indicated that Neanderthals obtained protein in their diet from animal sources. Evidence based on isotope studies shows that at least some Neanderthals may have eaten meat.

Neanderthals hunted large animals, such as the mammoth. However, they are believed to have practiced cannibalism or ritual defleshing. This hypothesis was formulated after researchers found marks on Neanderthal bones similar to the bones of a dead deer butchered by Neanderthals.

Neanderthal bones from various sites (Combe-Grenal and Abri Moula in France, Krapina in Croatia and Grotta Guattari in Italy) have all been cited as bearing cut marks made by stone tools. However, the results of technological tests have revealed varied causes. 

Re-evaluation of these marks using high-powered microscopes, comparisons to contemporary butchered animal remains, and recent ethnographic cases of excarnation mortuary practises have shown that perhaps this was a case of ritual defleshing.

• At Grotta Guattari, the apparently purposefully widened base of the skull (for access to the brain) has been shown to be caused by carnivore action, with hyena tooth marks found on the skull and mandible.
• According to some studies, fragments of bones from Krapina show marks similar to those on bones from secondary burials at a Michigan ossuary (14th century AD), and are indicative of removing the flesh of a partially decomposed body.
• According to others, the marks on the bones found at Krapina are indicative of defleshing, although whether this was for nutritional or ritual purposes cannot be determined with certainty.

Evidence of cannibalism includes:

• Analysis of bones from Abri Moula in France does seem to suggest cannibalism was practiced here. Cut-marks are concentrated in places expected in the case of butchery, instead of defleshing. Additionally the treatment of the bones was similar to that of roe deer bones, assumed to be food remains, found in the same shelter.
• At El Sidron in Northern Spain, scientists have found evidence pointing to the cannibalism of 12 individuals by what is hypothesized to have been a neighboring group of Neanderthals. According to Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona, the individuals (three children aged from two to nine, three teenagers, and six adults) appear to have been "killed and eaten, with their bones and skulls split open to extract the marrow, tongue and brains." Scientists believe that the lack of any evidence of a fire makes it likely that the event happened in winter, during times when food was scarce.

Evidence indicating cannibalism would not distinguish Neanderthals from modern humans, which are known to have practiced cannibalism or mortuary defleshing (e.g., the sky burial of Tibet).

Claims of art and adornment

Upon Higham et al.'s (2010) publication of new radiocarbon dates shedding doubt on the association of Châtelperronian beads with Neanderthals, Paul Mellars wrote that “the single most impressive and hitherto widely cited pillar of evidence for the presence of complex ‘symbolic’ behavior among the late Neanderthal populations in Europe has now effectively collapsed”. This conclusion, however, is controversial, and others such as Jean-Jacques Hublin and colleagues have re-dated more material and used proteomic evidence to restate the challenged association with Neanderthal. 

There exists a very large number of other claims of Neanderthal art, adornment, and structures. These are often taken literally by the media as showing Neanderthals were capable of symbolic thought, or "mental equals" to anatomically modern humans. As evidence of symbolism, none of them are widely accepted, although the same is true for Middle Palaeolithic anatomically modern humans. Among many others:

• Pigmented shells from Murcia, Spain, were argued in 2009 to be Neanderthal make-up containers.
• Bird bones were argued to show evidence for feather plucking in a 2012 study examining 1,699 ancient sites across Eurasia, which the authors controversially took to mean Neanderthals wore bird feathers as personal adornments.
• Deep scratches were found in 2012 on a cave floor underlying Neanderthal layer in Gorham's Cave, Gibraltar, which some have controversially interpreted as art.
• Two 176,000-year-old stalagmite ring structures, several metres wide, were reported in 2016 more than 300 metres from the entrance within Bruniquel Cave, France. The authors claim artificial lighting would have been required as this part of the cave is beyond the reach of daylight and that the structures had been made by early Neanderthals, the only humans in Europe at this time.

Interbreeding between archaic and modern humans

From Wikipedia, the free encyclopedia

A model of the phylogeny of H. sapiens over the last 600,000 years (vertical axis). The horizontal axis represents geographic location; the vertical axis represents time in thousands of years ago. Homo heidelbergensis is shown as diverging into Neanderthals, Denisovans and H. sapiens. With the expansion of H. sapiens after 200 kya, Neanderthals, Denisovans and unspecified archaic African hominins are displayed as again subsumed into the H. sapiens lineage. Possible admixture events involving certain modern populations in Africa are also shown.

 

There is evidence for interbreeding between archaic and modern humans during the Middle Paleolithic and early Upper Paleolithic. The interbreeding happened in several independent events that included Neanderthals, Denisovans, as well as several unidentified hominins. 

In Eurasia, interbreeding between Neanderthals and Denisovans with modern humans took place several times. The introgression events into modern humans is estimated to have happened about 47,000–65,000 years ago with Neanderthals and about 44,000–54,000 years ago with Denisovans. Neanderthal-derived DNA was found in the genome of contemporary populations in Europe and Asia. It accounted for 1–4% of modern genomes, although estimates may vary. Neanderthal-derived ancestry is absent from most modern populations in sub-Saharan Africa, while Denisovan-derived ancestry is absent from modern populations in Western Eurasia and Africa. However, in Africa, archaic alleles consistent with several independent admixture events in the subcontinent have been found. It is currently unknown who these archaic African hominins were.

The highest rates of Denisovan admixture has been found in Oceanian and certain Southeast Asian populations, with an estimated 4–6% of the genome of modern Melanesians being derived from Denisovans for example. In addition, Denisovan-derived ancestry has been found in very low trace amounts in mainland Asia, with a relative elevated Denisovan ancestry in South Asian populations. Regarding Neanderthal admixture, it is found in all non-African groups but varies slightly between populations. It is highest in East Asians, intermediate in Europeans, and lower in Southeast Asians. According to some evidence, it is also lower in Melanesians compared to both East Asians and Europeans. However, some research finds higher Neanderthal admixture in Oceanians, as well as in Native American groups, than in Europeans (though not higher than in East Asians).

Although the narratives of human evolution are often contentious, DNA evidence shows that human evolution should not be seen as a simple linear or branched progression, but a mix of related species. In fact, genomic research has shown that hybridization between substantially diverged lineages is the rule, not the exception, in human evolution. Furthermore, it is argued that hybridization was an essential driving force in the emergence of modern humans.

Neanderthals

Genetics

Proportion of admixture

On 7 May 2010, following the genome sequencing of three Vindija Neanderthals, a draft sequence of the Neanderthal genome was published and revealed that Neanderthals shared more alleles with Eurasian populations (e.g. French, Han Chinese, and Papua New Guinean) than with sub-Saharan African populations (e.g. Yoruba and San). According to Green et al. (2010), the observed excess of genetic similarity is best explained by recent gene flow from Neanderthals to modern humans after the migration out of Africa. They estimated the proportion of Neanderthal-derived ancestry to be 1–4% of the Eurasian genome. Prüfer et al. (2013) estimated the proportion to be 1.5–2.1% for non-Africans, which was revised in 2017 to a higher 1.8–2.6% for non-Africans outside Oceania. Lohse and Frantz (2014) infer a higher rate of 3.4–7.3% in Eurasia. Prüfer et al. (2017) noted that East Asians carry more Neandertal DNA (2.3–2.6%) than Western Eurasians (1.8–2.4%).

Introgressed genome

About 20% of the Neanderthal genome has been found introgressed or assimilated in the modern human population (by analyzing East Asians and Europeans), but the figure has also been estimated at about a third.

Subpopulation admixture rate

A higher Neanderthal admixture was found in East Asians than in Europeans, which is estimated to be about 20% more introgression into East Asians. This could possibly be explained by the occurrence of further admixture events in the early ancestors of East Asians after the separation of Europeans and East Asians, dilution of Neanderthal ancestry in Europeans by populations with low Neanderthal ancestry from later migrations, or natural selection that may have been relatively lower in East Asians than in Europeans. Studies simulating admixture models indicate that a reduced efficacy of purifying selection against Neanderthal alleles in East Asians could not account for the greater proportion of Neanderthal ancestry of East Asians, thus favoring more-complex models involving additional pulses of Neanderthal introgression into East Asians. Such models show a pulse to ancestral Eurasians, followed by separation and an additional pulse to ancestral East Asians. It is observed that there is a small but significant variation of Neanderthal admixture rates within European populations, but no significant variation within East Asian populations.

Genomic analysis suggests that there is a global division in Neanderthal introgression between Sub-Saharan African populations and other modern human groups (including North Africans) rather than between African and non-African populations. North African groups share a similar excess of derived alleles with Neanderthals as do non-African populations, whereas Sub-Saharan African groups are the only modern human populations that generally did not experience Neanderthal admixture. The Neanderthal genetic signal among North African populations was found to vary depending on the relative quantity of autochthonous North African, European, Near Eastern and Sub-Saharan ancestry. Using f4 ancestry ratio statistical analysis, the Neanderthal inferred admixture was observed to be: highest among the North African populations with maximal autochthonous North African ancestry such as Tunisian Berbers, where it was at the same level or even higher than that of Eurasian populations (100–138%); high among North African populations carrying greater European or Near Eastern admixture, such as groups in North Morocco and Egypt (∼60–70%); and lowest among North African populations with greater Sub-Saharan admixture, such as in South Morocco (20%). Quinto et al. (2012) therefore postulate that the presence of this Neanderthal genetic signal in Africa is not due to recent gene flow from Near Eastern or European populations since it is higher among populations bearing indigenous pre-Neolithic North African ancestry. Low but significant rates of Neanderthal admixture has also been observed for the Maasai of East Africa. After identifying African and non-African ancestry among the Maasai, it can be concluded that recent non-African modern human (post-Neanderthal) gene flow was the source of the contribution since around an estimated 30% of the Maasai genome can be traced to non-African introgression from about 100 generations ago.

Distance to lineages

Presenting a high-quality genome sequence of a female Altai Neanderthal, it has been found that the Neanderthal component in non-African modern humans is more related to the Mezmaiskaya Neanderthal (Caucasus) than to the Altai Neanderthal (Siberia) or the Vindija Neanderthals (Croatia). By high-coverage sequencing the genome of a 50,000-year-old female Vindija Neanderthal fragment, it was later found that the Vindija and Mezmaiskaya Neanderthals did not seem to differ in the extent of their allele-sharing with modern humans. In this case, it was also found that the Neanderthal component in non-African modern humans is more closely related to the Vindija and Mezmaiskaya Neanderthals than to the Altai Neandertal. These results suggest that a majority of the admixture into modern humans came from Neanderthal populations that had diverged (about 80–100kya) from the Vindija and Mezmaiskaya Neanderthal lineages before the latter two diverged from each other.

Analyzing chromosome 21 of the Altai (Siberia), El Sidrón (Spain), and Vindija (Croatia) Neanderthals, it is determined that—of these three lineages—only the El Sidrón and Vindija Neanderthals display significant rates of gene flow (0.3–2.6%) into modern humans, suggesting that the El Sidrón and Vindija Neanderthals are more closely related than the Altai Neanderthal to the Neanderthals that interbred with modern humans about 47,000–65,000 years ago. Conversely, it is also determined that significant rates of modern human gene flow into Neanderthals occurred—of the three examined lineages—for only the Altai Neanderthal (0.1–2.1%), suggesting that modern human gene flow into Neanderthals mainly took place after the separation of the Altai Neanderthals from the El Sidrón and Vindija Neanderthals that occurred roughly 110,000 years ago. The findings show that the source of modern human gene flow into Neanderthals originated from a population of early modern humans from about 100,000 years ago, predating the out-of-Africa migration of the modern human ancestors of present-day non-Africans.

Mitochondrial DNA and Y chromosome

No evidence of Neanderthal mitochondrial DNA has been found in modern humans. This suggests that successful Neanderthal admixture happened in pairings with Neanderthal males and modern human females. Possible hypotheses are that Neanderthal mitochondrial DNA had detrimental mutations that led to the extinction of carriers, that the hybrid offspring of Neanderthal mothers were raised in Neanderthal groups and became extinct with them, or that female Neanderthals and male Sapiens did not produce fertile offspring.

As shown in an interbreeding model produced by Neves and Serva (2012), the Neanderthal admixture in modern humans may have been caused by a very low rate of interbreeding between modern humans and Neanderthals, with the exchange of one pair of individuals between the two populations in about every 77 generations. This low rate of interbreeding would account for the absence of Neanderthal mitochondrial DNA from the modern human gene pool as found in earlier studies, as the model estimates a probability of only 7% for a Neanderthal origin of both mitochondrial DNA and Y chromosome in modern humans.

Reduced contribution

There is a presence of large genomic regions with strongly reduced Neanderthal contribution in modern humans due to negative selection, partly caused by hybrid male infertility. These large regions of low Neanderthal contribution were most-pronounced on the X chromosome—with fivefold lower Neanderthal ancestry compared to autosomes. They also contained relatively high numbers of genes specific to testes. This means that modern humans have relatively few Neanderthal genes that are located on the X chromosome or expressed in the testes, suggesting male infertility as a probable cause. It may be partly affected by hemizygosity of X chromosome genes in males.

Deserts of Neanderthal sequences may also be caused by genetic drift involving intense bottlenecks in the modern human population and background selection as a result of strong selection against deleterious Neanderthal alleles. The overlap of many deserts of Neanderthal and Denisovan sequences suggests that repeated loss of archaic DNA occur at specific loci.

It has also been shown that Neanderthal ancestry has been selected against in conserved biological pathways, such as RNA processing.

Consistent with the hypothesis that purifying selection has reduced Neanderthal contribution in present-day modern human genomes, Upper Paleolithic Eurasian modern humans (such as the Tianyuan modern human) carry more Neanderthal DNA (about 4–5%) than present-day Eurasian modern humans (about 1–2%).

Rates of selection against Neanderthal sequences varied for European and Asian populations.

Changes in modern humans

In Eurasia, modern humans acquired adaptive introgression from archaic humans, which provided a source of advantageous genetic variants that are adapted to local environments and a reservoir for additional genetic variation. Adaptive introgression from Neanderthals have targeted genes involved with keratin filaments, sugar metabolism, muscle contraction, body fat distribution, enamel thickness, oocyte meiosis, as well as brain size and functioning. There are signals of positive selection, as the result of adaptation to diverse habitats, in genes involved with variation in skin pigmentation and hair morphology. In the immune system, introgressed variants have heavily contributed to the diversity of immune genes, of which there's an enrichment of introgressed alleles that suggest a strong positive selection.

Genes affecting keratin were found to have been introgressed from Neanderthals into modern humans (shown in East Asians and Europeans), suggesting that these genes gave a morphological adaptation in skin and hair to modern humans to cope with non-African environments. This is likewise for several genes involved in medical-relevant phenotypes, such as those affecting systemic lupus erythematosus, primary biliary cirrhosis, Crohn's disease, optic disk size, smoking behavior, interleukin 18 levels, and diabetes mellitus type 2.

Researchers found Neanderthal introgression of 18 genes—several of which are related to UV-light adaptation—within the chromosome 3p21.31 region (HYAL region) of East Asians. The introgressive haplotypes were positively selected in only East Asian populations, rising steadily from 45,000 years BP until a sudden increase of growth rate around 5,000 to 3,500 years BP. They occur at very high frequencies among East Asian populations in contrast to other Eurasian populations (e.g. European and South Asian populations). The findings also suggests that this Neanderthal introgression occurred within the ancestral population shared by East Asians and Native Americans.

Evans et al. (2006) had previously suggested that a group of alleles collectively known as haplogroup D of microcephalin, a critical regulatory gene for brain volume, originated from an archaic human population. The results show that haplogroup D introgressed 37,000 years ago (based on the coalescence age of derived D alleles) into modern humans from an archaic human population that separated 1.1 million years ago (based on the separation time between D and non-D alleles), consistent with the period when Neanderthals and modern humans co-existed and diverged respectively. The high frequency of the D haplogroup (70%) suggest that it was positively selected for in modern humans. The distribution of the D allele of microcephalin is high outside Africa but low in sub-Saharan Africa, which further suggest that the admixture event happened in archaic Eurasian populations. This distribution difference between Africa and Eurasia suggests that the D allele originated from Neanderthals according to Lari et al. (2010), but they found that a Neanderthal individual from the Mezzena Rockshelter (Monti Lessini, Italy) was homozygous for an ancestral allele of microcephalin, thus providing no support that Neanderthals contributed the D allele to modern humans and also not excluding the possibility of a Neanderthal origin of the D allele. Green et al. (2010), having analyzed the Vindija Neanderthals, also could not confirm a Neanderthal origin of haplogroup D of the microcephalin gene.

It has been found that HLA-A*02, A*26/*66, B*07, B*51, C*07:02, and C*16:02 of the immune system were contributed from Neanderthals to modern humans. After migrating out of Africa, modern humans encountered and interbred with archaic humans, which was advantageous for modern humans in rapidly restoring HLA diversity and acquiring new HLA variants that are better adapted to local pathogens.

It is found that introgressed Neanderthal genes exhibit cis-regulatory effects in modern humans, contributing to the genomic complexity and phenotype variation of modern humans. Looking at heterozygous individuals (carrying both Neanderthal and modern human versions of a gene), the allele-specific expression of introgressed Neanderthal alleles was found to be significantly lower in the brain and testes relative to other tissues. In the brain, this was most pronounced at the cerebellum and basal ganglia. This downregulation suggests that modern humans and Neanderthals possibly experienced a relative higher rate of divergence in these specific tissues.

Furthermore, correlating the genotypes of introgressed Neanderthal alleles with the expression of nearby genes, it is found that archaic alleles contribute proportionally more to variation in expression than nonarchaic alleles. Neanderthal alleles affect expression of the immunologically genes OAS1/2/3 and TLR1/6/10, which can be specific to cell-type and is influenced by environmental stimuli.

Studying the high-coverage female Vindija Neanderthal genome, Prüfer et al. (2017) identified several Neanderthal-derived gene variants, including those that affect levels of LDL cholesterol and vitamin D, and has influence on eating disorders, visceral fat accumulation, rheumatoid arthritis, schizophrenia, as well as the response to antipsychotic drugs.

Examining European modern humans in regards to the Altai Neanderthal genome in high-coverage, results show that Neanderthal admixture is associated with several changes in cranium and underlying brain morphology, suggesting changes in neurological function through Neanderthal-derived genetic variation. Neanderthal admixture is associated with an expansion of the posterolateral area of the modern human skull, extending from the occipital and inferior parietal bones to bilateral temporal locales. In regards to modern human brain morphology, Neanderthal admixture is positively correlated with an increase in sulcal depth for the right intraparietal sulcus and an increase in cortical complexity for the early visual cortex of the left hemisphere. Neanderthal admixture is also positively correlated with an increase in white and gray matter volume localized to the right parietal region adjacent to the right intraparietal sulcus. In the area overlapping the primary visual cortex gyrification in the left hemisphere, Neanderthal admixture is positively correlated with gray matter volume. The results also show evidence for a negative correlation between Neanderthal admixture and white matter volume in the orbitofrontal cortex.

In Papuans, assimilated Neanderthal inheritance is found in highest frequency in genes expressed in the brain, whereas Denisovan DNA has the highest frequency in genes expressed in bones and other tissues.

Population substructure theory

Although less parsimonious than recent gene flow, the observation may have been due to ancient population sub-structure in Africa, causing incomplete genetic homogenization within modern humans when Neanderthals diverged while early ancestors of Eurasians were still more closely related to Neanderthals than those of Africans to Neanderthals. On the basis of allele frequency spectrum, it was shown that the recent admixture model had the best fit to the results while the ancient population sub-structure model had no fit–demonstrating that the best model was a recent admixture event that was preceded by a bottleneck event among modern humans—thus confirming recent admixture as the most parsimonious and plausible explanation for the observed excess of genetic similarities between modern non-African humans and Neanderthals. On the basis of linkage disequilibrium patterns, a recent admixture event is likewise confirmed by the data. From the extent of linkage disequilibrium, it was estimated that the last Neanderthal gene flow into early ancestors of Europeans occurred 47,000–65,000 years BP. In conjunction with archaeological and fossil evidence, the gene flow is thought likely to have occurred somewhere in Western Eurasia, possibly the Middle East. Through another approach—using one genome each of a Neanderthal, Eurasian, African, and chimpanzee (outgroup), and dividing it into non-recombining short sequence blocks—to estimate genome-wide maximum-likelihood under different models, an ancient population sub-structure in Africa was ruled out and a Neanderthal admixture event was confirmed.

Morphology

The early Upper Paleolithic burial remains of a modern human child from Abrigo do Lagar Velho (Portugal) features traits that indicates Neanderthal interbreeding with modern humans dispersing into Iberia. Considering the dating of the burial remains (24,500 years BP) and the persistence of Neanderthal traits long after the transitional period from a Neanderthal to a modern human population in Iberia (28,000–30,000 years BP), the child may have been a descendant of an already heavily admixed population.

The remains of an early Upper Paleolithic modern human from Peștera Muierilor (Romania) of 35,000 years BP shows a morphological pattern of European early modern humans, but possesses archaic or Neanderthal features, suggesting European early modern humans interbreeding with Neanderthals. These features include a large interorbital breadth, a relatively flat superciliary arches, a prominent occipital bun, an asymmetrical and shallow mandibular notch shape, a high mandibular coronoid processus, the relative perpendicular mandibular condyle to notch crest position, and a narrow scapular glenoid fossa.

The modern human Oase 2 skull (cast depicted), found in Peştera cu Oase, displays archaic traits due to possible hybridization with Neanderthals.

 

The early modern human Oase 1 mandible from Peștera cu Oase (Romania) of 34,000–36,000 ¹⁴C years BP presents a mosaic of modern, archaic, and possible Neanderthal features. It displays a lingual bridging of the mandibular foramen, not present in earlier humans except Neanderthals of the late Middle and Late Pleistocene, thus suggesting affinity with Neanderthals. Concluding from the Oase 1 mandible, there was apparently a significant craniofacial change of early modern humans from at least Europe, possibly due to some degree of admixture with Neanderthals.

The earliest (before about 33 ka BP) European modern humans and the subsequent (Middle Upper Paleolithic) Gravettians, falling anatomically largely inline with the earliest (Middle Paleolithic) African modern humans, also show traits that are distinctively Neanderthal, suggesting that a solely Middle Paleolithic modern human ancestry was unlikely for European early modern humans.

A late-Neanderthal jaw (more specifically, a corpus mandibulae remnant) from the Mezzena rockshelter (Monti Lessini, Italy) shows indications of a possible interbreeding in late Italian Neanderthals. The jaw falls within the morphological range of modern humans, but also displayed strong similarities with some of the other Neanderthal specimens, indicating a change in late Neanderthal morphology due to possible interbreeding with modern humans.

The Manot 1, a partial calvaria of a modern human that was recently discovered at the Manot Cave (Western Galilee, Israel) and dated to 54.7±5.5 kyr BP, represents the first fossil evidence from the period when modern humans successfully migrated out of Africa and colonized Eurasia. It also provides the first fossil evidence that modern humans inhabited the southern Levant during the Middle to Upper Palaeolithic interface, contemporaneously with the Neanderthals and close to the probable interbreeding event. The morphological features suggest that the Manot population may be closely related or given rise to the first modern humans who later successfully colonized Europe to establish early Upper Palaeolithic populations.

History

The interbreeding has been discussed ever since the discovery of Neanderthal remains in the 19th century, though earlier writers believed that Neanderthals were a direct ancestor of modern humans. Thomas Huxley suggested that many Europeans bore traces of Neanderthal ancestry, but associated Neanderthal characteristics with primitivism, writing that since they "belong to a stage in the development of the human species, antecedent to the differentiation of any of the existing races, we may expect to find them in the lowest of these races, all over the world, and in the early stages of all races".

Hans Peder Steensby in the 1907 article Racestudier i Danmark ("Race studies in Denmark") rejected that Neanderthals were ape-like or inferior, and, while emphasizing that all modern humans are of mixed origins, suggested interbreeding as the best available explanation of a significant number of observations which by then were available.

In the early twentieth century, Carleton Coon argued that the Caucasoid race is of dual origin consisting of Upper Paleolithic (mixture of H. sapiens and H. neanderthalensis) types and Mediterranean (purely H. sapiens) types. He repeated his theory in his 1962 book The Origin of Races.

Denisovans

Genetics

The Denisovan genome was sequenced from the distal manual phalanx fragment (replica depicted) found in the Denisova cave.

Proportion of admixture

It has been shown that Melanesians (e.g. Papua New Guinean and Bougainville Islander) share relatively more alleles with Denisovans when compared to other Eurasians and Africans. It estimated that 4% to 6% of the genome in Melanesians derives from Denisovans, while no other Eurasians or Africans displayed contributions of the Denisovan genes. It has been observed that Denisovans contributed genes to Melanesians but not to East Asians, indicating that there was interaction between the early ancestors of Melanesians with Denisovans but that this interaction did not take place in the regions near southern Siberia, where as-of-yet the only Denisovan remains have been found. In addition, Aboriginal Australians also show a relative increased allele sharing with Denisovans, compared to other Eurasians and African populations, consistent with the hypothesis of increased admixture between Denisovans and Melanesians.

Reich et al. (2011) produced evidence that the highest presence of Denisovan admixture is in Oceanian populations, followed by many Southeast Asian populations, and none in East Asian populations. There is significant Denisovan genetic material in eastern Southeast Asian and Oceanian populations (e.g. Aboriginal Australians, Near Oceanians, Polynesians, Fijians, eastern Indonesians, Philippine Mamanwa and Manobo), but not in certain western and continental Southeast Asian populations (e.g. western Indonesians, Malaysian Jehai, Andaman Onge, and mainland Asians), indicating that the Denisovan admixture event happened in Southeast Asia itself rather than mainland Eurasia. The observation of high Denisovan admixture in Oceania and the lack thereof in mainland Asia suggests that early modern humans and Denisovans had interbred east of the Wallace Line that divides Southeast Asia according to Cooper and Stringer (2013).

Skoglund and Jakobsson (2011) observed that particularly Oceanians, followed by Southeast Asians populations, have a high Denisovans admixture relative to other populations. Furthermore, they found possible low traces of Denisovan admixture in East Asians and no Denisovan admixture in Native Americans. In contrast, Prüfer et al. (2013) found that mainland Asian and Native American populations may have a 0.2% Denisovan contribution, which is about twenty-five times lower than Oceanian populations. The manner of gene flow to these populations remains unknown. However, Wall et al. (2013) stated that they found no evidence for Denisovan admixture in East Asians.

Findings indicate that the Denisovan gene flow event happened to the common ancestors of Aboriginal Filipinos, Aboriginal Australians, and New Guineans. New Guineans and Australians have similar rates of Denisovan admixture, indicating that interbreeding took place prior to their common ancestors' entry into Sahul (Pleistocene New Guinea and Australia), at least 44,000 years ago. It has also been observed that the fraction of Near Oceanian ancestry in Southeast Asians is proportional to the Denisovan admixture, except in the Philippines where there is a higher proportional Denisovan admixture to Near Oceanian ancestry. Reich et al. (2011) suggested a possible model of an early eastward migration wave of modern humans, some who were Philippine/New Guinean/Australian common ancestors that interbred with Denisovans, respectively followed by divergence of the Philippine early ancestors, interbreeding between the New Guinean and Australian early ancestors with a part of the same early-migration population that did not experience Denisovan gene flow, and interbreeding between the Philippine early ancestors with a part of the population from a much-later eastward migration wave (the other part of the migrating population would become East Asians).

Finding components of Denisovan introgression with differing relatedness to the sequenced Denisovan, Browning et al. (2018) suggested that at least two separate episodes of Denisovan admixture has occurred. Specifically, introgression from two distinct Denisovan populations is observed in East Asians (e.g. Japanese and Han Chinese), whereas South Asians (e.g. Telugu and Punjabi) and Oceanians (e.g. Papuans) display introgression from one Denisovan population.

Exploring derived alleles from Denisovans, Sankararaman et al. (2016) estimated that the date of Denisovan admixture was 44,000–54,000 years ago. They also determined that the Denisovan admixture was the greatest in Oceanian populations compared to other populations with observed Denisovan ancestry (i.e. America, Central Asia, East Asia, and South Asia). The researchers also made the surprising finding that South Asian populations display an elevated Denisovan admixture (when compared to other non-Oceanian populations with Denisovan ancestry), albeit the highest estimate (which are found in Sherpas) is still ten times lower than in Papuans. They suggest two possible explanations: There was a single Denisovan introgression event that was followed by dilution to different extents or at least three distinct pulses of Denisovan introgressions must have occurred.

It has been shown that Eurasians have some but significantly lesser archaic-derived genetic material that overlaps with Denisovans, stemming from the fact that Denisovans are related to Neanderthals—who contributed to the Eurasian gene pool—rather than from interbreeding of Denisovans with the early ancestors of those Eurasians.

The skeletal remains of an early modern human from the Tianyuan cave (near Zhoukoudian, China) of 40,000 years BP showed a Neanderthal contribution within the range of today's Eurasian modern humans, but it had no discernible Denisovan contribution. It is a distant relative to the ancestors of many Asian and Native American populations, but post-dated the divergence between Asians and Europeans. The lack of a Denisovan component in the Tianyuan individual suggests that the genetic contribution had been always scarce in the mainland.

Reduced contribution

There are large genomic regions devoid of Denisovan-derived ancestry, partly explained by infertility of male hybrids, as suggested by the lower proportion of Denisovan-derived ancestry on X chromosomes and in genes that are expressed in the testes of modern humans.

Changes in modern humans

Exploring the immune system's HLA alleles, it has been suggested that HLA-B*73 introgressed from Denisovans into modern humans in western Asia due to the distribution pattern and divergence of HLA-B*73 from other HLA alleles. Even though HLA-B*73 is not present in the sequenced Denisovan genome, HLA-B*73 was shown to be closely associated to the Denisovan-derived HLA-C*15:05 from the linkage disequilibrium. From phylogenetic analysis, however, it has been concluded that it is highly likely that HLA-B*73 was ancestral.

The Denisovan's two HLA-A (A*02 and A*11) and two HLA-C (C*15 and C*12:02) allotypes correspond to common alleles in modern humans, whereas one of the Denisovan's HLA-B allotype corresponds to a rare recombinant allele and the other is absent in modern humans. It is thought that these must have been contributed from Denisovans to modern humans, because it is unlikely to have been preserved independently in both for so long due to HLA alleles' high mutation rate.

Tibetan people received an advantageous EGLN1 and EPAS1 gene variant, associated with hemoglobin concentration and response to hypoxia, for life at high altitudes from the Denisovans. The ancestral variant of EPAS1 upregulates hemoglobin levels to compensate for low oxygen levels—such as at high altitudes—but this also has the maladaption of increasing blood viscosity. The Denisovan-derived variant on the other hand limits this increase of hemoglobin levels, thus resulting in a better altitude adaption. The Denisovan-derived EPAS1 gene variant is common in Tibetans and was positively selected in their ancestors after they colonized the Tibetan plateau.

Archaic African hominins

Rapid decay of fossils in Sub-Saharan African environments makes it currently unfeasible to compare modern human admixture with reference samples of archaic Sub-Saharan African hominins.

From three candidate regions with introgression found by searching for unusual patterns of variations (showing deep haplotype divergence, unusual patterns of linkage disequilibrium, and small basal clade size) in 61 non-coding regions from two hunter-gatherer groups (Biaka Pygmies and San who have significant admixture) and one West African agricultural group (Mandinka, who don't have significant admixture), it is concluded that roughly 2% of the genetic material found in the Biaka Pygmies and San was inserted into the human genome approximately 35,000 years ago from archaic hominins that separated from the ancestors of the modern human lineage around 700,000 years ago. A survey for the introgressive haplotypes across many Sub-Saharan populations suggest that this admixture event happened with archaic hominins who once inhabited Central Africa.

Researching high-coverage whole-genome sequences of fifteen Sub-Saharan hunter-gatherer males from three groups—five Pygmies (three Baka, a Bedzan, and a Bakola) from Cameroon, five Hadza from Tanzania, and five Sandawe from Tanzania—there are signs that the ancestors of the hunter-gatherers interbred with one or more archaic human populations, probably over 40,000 years ago. Analysis of putative introgressive haplotypes in the fifteen hunter-gatherer samples suggests that the archaic African population and modern humans diverged around 1.2 to 1.3 million years ago.

Xu et al. (2017) analyzed the evolution of the Mucin 7 protein in the saliva of modern humans and found evidence that an unidentified ghost population of archaic African humans may have contributed DNA, with an estimated coalescence time to modern humans of about 4.5 million years BP, into the gene pool of modern Africans (e.g. African-American, African-Caribbean, Esan, Gambian, Luhya, Mende, and Yoruba people).

Related studies

In February 2019, scientists discovered evidence, based on genetics studies using artificial intelligence (AI), that suggest the existence of an unknown human ancestor species, not Neanderthal, Denisovan or human hybrid (like Denny), in the genome of modern humans.