Neanderthal

Name

The species is named after one of the first sites where its fossils were discovered in the 19th century, about 12 km (7 mi) east of Düsseldorf, Germany, in the Feldhofer Cave, located in the Düssel River's Neander valley. Thal is an older spelling of the German word Tal (with the same pronunciation), which means "valley" (cognate with English dale).

Neanderthal 1 was known as the "Neanderthal cranium" or "Neanderthal skull" in anthropological literature, and the individual reconstructed on the basis of the skull was occasionally called "the Neanderthal man". The binomial name Homo neanderthalensis – extending the name "Neanderthal man" from the individual type specimen to the entire species – was first proposed by the Anglo-Irish geologist William King in 1864, although that same year King changed his mind and thought that the Neanderthal fossil was distinct enough from humans to warrant a separate genus. Nevertheless, King's name had priority over the proposal put forward in 1866 by Ernst Haeckel, Homo stupidus. The practice of referring to "the Neanderthals" and "a Neanderthal" emerged in the popular literature of the 1920s.

The German pronunciation of Neanderthaler or Neandertaler is [neˈandɐˌtʰaːlɐ] in the International Phonetic Alphabet. In British English, "Neanderthal" is pronounced with the /t/ as in German, but different vowels (IPA: /niːˈændərtɑːl/). In layman's American English, "Neanderthal" is pronounced with a /θ/ (the voiceless th as in thin) and /ɔ/ instead of the longer British /aː/ (IPA: /niːˈændərθɔːl/), although scientists typically use the /t/ as in German.

Classification

Scientists to this day debate over whether Neanderthals should be classified as a distinct species - Homo neanderthalensis - or as Homo sapiens neanderthalensis, the latter placing Neanderthals as a subspecies of H. sapiens. During the early 20th century the prevailing view was heavily influenced by Arthur Keith and Marcellin Boule, who wrote the first scientific description of a nearly complete Neanderthal skeleton. Senior members of their respective national paleontological institutes and among the most eminent paleoanthropologists of their time, both men argued that this "primitive" Neanderthal could not be a direct ancestor of modern man. This idea was reflected in an erroneous and inaccurate reconstruction of the Neanderthal findings of La Chapelle-aux-Saints, mounted in a crooked pose with a deformed and heavily curved spine and legs buckled.

During the 1930s scholars Ernst Mayr, George Gaylord Simpson and Theodosius Dobzhansky reinterpreted the existing fossil record and came to different conclusions. Neanderthal man was classified as Homo sapiens neanderthalensis - an early subspecies contrasted with what was now called Homo sapiens sapiens. The obviously unbroken succession of fossil sites of both subspecies in Europe was considered evidence that there was a slow and gradual evolutionary transition from Neanderthals to modern humans. Contextual interpretations of similar excavation sites in Asia lead to the hypothesis of multiregional origin of modern man in the 1980s.

Current views

Current scientific ideas hold that both species evolved from a common African ancestor: Homo erectus. Fossil and tool finds support the idea that during the first migration wave around 2 million years ago, small groups of Homo erectus left Africa via the Levant and the Black Sea area into Georgia (fossils of Dmanisi) and possibly via north-west Africa towards southern Spain. The 1.2-million-year-old fragmented finds in Spain are referred to as Homo antecessor by their discoverers, and considered to be the ancestors of Neanderthal. This interpretation, however, is controversial.

Some 600,000 years ago a second propagation wave of African Homo erectus took place. Skulls from that period found in Spain for example, suggest a brain volume of between 1100 and 1450 cm³. The brain volume of fossils from the first propagation wave is however estimated only to be slightly above 1000 ccm. Homo erectus that arrived in Europe in the second wave of colonization developed into Neanderthals through the intermediate Homo heidelbergensis. Since about 200,000 years ago in Africa the so-called early anatomically modern humans descended from the local Homo erectus through the intermediate Homo rhodesiensis. Evidence from mitochondrial DNA studies has been interpreted as evidence that Neanderthals were not a subspecies of H. sapiens. Others, for example University of Cambridge Professor Paul Mellars, say "no evidence has been found of cultural interaction".

The period when the Neanderthal lineage separated from the lineage that led to modern man remains debated. In 2010 a period between 440,000 and 270,000 years B.P. was calculated by the molecular clock method. However, the reliability of molecular clocks is questionable as dating determined by stratigraphic methods varies considerably from those determined using the molecular clock. In 2012 recalculation of the mutation rates revealed evidence of a much earlier separation: between 800,000 and 400,000 years ago.

Origin

The first representatives of the genus Homo with proto-Neanderthal traits are believed to have existed in Eurasia as early as 350,000–600,000 years ago with the first "true Neanderthals" appearing between 200,000 and 250,000 years ago. The exact date of their extinction had been disputed but in 2014, a team led by Thomas Higham of the University of Oxford used an improved radiocarbon dating technique on material from 40 archaeological sites to show that Neanderthals died out in Europe between 41,000 and 39,000 years ago, with the last group disappearing from southern Spain 28,000 years ago. Radiocarbon dating performed on charcoal in Gorham's Cave in Gibraltar in 2006 suggests that Neanderthals lived there 24,000 to 28,000 years ago. This coincides with the start of a very cold period in Europe and is 5,000 to 18,000 years after Homo sapiens reached the continent.

Comparison of the DNA of Neanderthals and Homo sapiens suggests that they diverged from a common ancestor between 350,000 and 400,000 years ago. This ancestor was probably Homo heidelbergensis. Heidelbergensis originated between 800,000 and 1,300,000 years ago, and continued until about 200,000 years ago. It ranged over Eastern and South Africa, Europe and Western Asia. Between 350,000 and 400,000 years ago the African branch is thought to have started evolving towards modern humans and the Eurasian branch towards Neanderthals. Scientists do not agree when Neanderthals can first be recognised in the fossil record, with dates ranging between 200,000 and 300,000 years BP.

Discovery

Neanderthal skulls were first discovered in the Engis Caves (the partial skull dubbed Engis 2) (fr), in what is now Belgium (1829) by Philippe-Charles Schmerling and in Forbes' Quarry, Gibraltar, dubbed Gibraltar 1 (1848), both prior to the type specimen discovery in a limestone quarry of the Neander Valley in Erkrath near Düsseldorf in August 1856, three years before Charles Darwin's On the Origin of Species was published.

The type specimen, dubbed Neanderthal 1, consisted of a skull cap, two femora, three bones from the right arm, two from the left arm, part of the left ilium, fragments of a scapula, and ribs. The workers who recovered this material originally thought it to be the remains of a bear. They gave the material to amateur naturalist Johann Carl Fuhlrott, who turned the fossils over to anatomist Hermann Schaaffhausen.

To date, the bones of over 400 Neanderthals have been found.

Timeline of research

Habitat and range

Early Neanderthals lived in the last glacial period for a span of about 100,000 years. Because of the damaging effects the glacial period had on the Neanderthal sites, not much is known about the early species. Countries where their remains are known include most of Europe south of the line of glaciation, roughly along the 50th parallel north. This includes most of Western Europe, Central Europe, the Carpathians, and the Balkans, some sites in Ukraine and in western Russia, Central and Northern Asia up to the Altai Mountains, and Western Asia from the Levant up to the Indus River. The Bontnewydd Palaeolithic site at Denbighshire, North Wales is the most north-western site of Neanderthal remains and one of the oldest remains in Britain (230,000 years ago). It is estimated that the total Neanderthal population across this habitat range numbered at around 70,000 at its peak.

Neanderthal fossils have not been found to date in Africa, but there have been finds close to North Africa, both on Gibraltar and in the Levant. At some Levantine sites, Neanderthal remains date from after the same sites were vacated by modern humans. Mammal fossils of the same time period show cold-adapted animals were present alongside these Neanderthals in this region of the Eastern Mediterranean. This implies Neanderthals were better adapted biologically to cold weather than modern humans and at times displaced them in parts of the Middle East when the climate got cold enough. However this has been disputed recently through studies of their cranial morphology and sinuses. Some scholars have also posited that Neanderthals could be an Asian species which expanded into Europe, making Neanderthals a tropical species rather than cold adaptive.

Homo sapiens appears to have been the only human type in the Nile River Valley during these periods, and Neanderthals are not known to have ever lived south-west of present-day Israel. When climate change caused warmer temperatures, the Neanderthal range likewise retreated to the north, along with the cold-adapted species of mammals. Apparently these weather-induced population shifts took place before modern people secured competitive advantages over the Neanderthal, as these shifts in range took place well over ten thousand years before modern people totally replaced the Neanderthal, despite the recent evidence of some successful interbreeding.

Separate developments in the human line, in other regions such as Southern Africa, somewhat resembled the Eurasian Neanderthals, but these people were not Neanderthals. One such example is Rhodesian Man (Homo rhodesiensis), who existed long before any classic Eurasian Neanderthals, but had a more modern set of teeth. Some H. rhodesiensis populations appeared to be on the road to modern H. sapiens sapiens. At any rate, the populations in Eurasia underwent increasing "Neanderthalization" over time. Some have suggested that H. rhodesiensis in general was ancestral to both modern humans and Neanderthals, and that at some point the two populations went their separate ways, but this argument presupposes that H. rhodesiensis existed around 600,000 years ago.

To date, no intimate connection has been found between these similar archaic people and the Eurasian Neanderthals, at least during the same time as H. rhodesiensis seems to have lived about 600,000 years ago, long before the time of classic Neanderthals. This said, some researchers think that H. rhodesiensis may have lived much later than this period, depending on the method used to date the fossils, so this question remains open to debate. Some H. rhodesiensis features, like the large brow ridge, may have been caused by convergent evolution.

It appears incorrect, based on present research and known fossil finds, to refer to any fossils outside Eurasia as true Neanderthals. They had a known range that possibly extended as far east as the Altai Mountains, but not farther to the east or south, and apparently not into Africa. At any rate, in North-East Africa the land immediately south of the Neanderthal range was possessed by modern humans Homo sapiens idaltu or Homo sapiens, since at least 160,000 years before the present. 160,000-year-old hominid fossils at Jebel Irhoud in Morocco were previously thought to be Neanderthal, but it is now clear that they are early modern humans.

Classic Neanderthal fossils have been found over a large area, from northern Germany to Israel and Mediterranean countries like Spain and Italy in the south and from England and Portugal in the west to Uzbekistan in the east. This area probably was not occupied all at the same time. The northern border of their range, in particular, would have contracted frequently with the onset of cold periods. On the other hand, the northern border of their range as represented by fossils may not be the real northern border of the area they occupied, since Middle Palaeolithic-looking artifacts have been found even farther north, up to 60° N, on the Russian plain. Recent evidence has extended the Neanderthal range by about 1,250 miles (2,010 km) east into southern Siberia's Altai Mountains.

Anatomy

Neanderthal anatomy differed from modern humans in that they had a more robust build and distinctive morphological features, especially on the cranium, which gradually accumulated more derived aspects as it was described by Marcellin Boule, particularly in certain isolated geographic regions. These include shorter limb proportions, a wider, barrel-shaped rib cage, a reduced chin, and a large nose, which was much larger in both length and width, and started somewhat higher on the face, than in modern humans. Evidence suggests they were much stronger than modern humans, with particularly strong arms and hands, while they were comparable in height; based on 45 long bones from at most 14 males and 7 females, Neanderthal males averaged 164–168 cm (65–66 in) and females 152–156 cm (60–61 in) tall. Samples of 26 specimens in 2010 found an average weight of 77.6 kg (171 lb) for males and 66.4 kg (146 lb) for females. A 2007 genetic study suggested some Neanderthals may have had red hair and blond hair, along with a light skin tone.

Gregory Cochran and Henry Harpending in the book "The 10,000 year explosion," investigated whether it is accurate to depict Neanderthals as having hair pattens similar to Homo Sapiens. They concluded that, "We don’t yet know for sure, but it seems likely that, as part of their adaptation to cold, Neanderthals were furry. Chimpanzees have ridges on their finger bones that stem from the way that they clutch their mother’s fur as infants. Modern humans don’t have these ridges, but Neanderthals do." (Cochran, G. & H. Harpending (2009).

In 'The Spread of Modern Humans in Europe; 2002 John F Hoffecker, writes "Neanderthal sites show no evidence of tools for making tailored clothing. There are only hide scrapers, which might have been used to make blankets or ponchos. This is in contrast to Upper Paleolithic (modern human) sites, which have an abundance of eyed bone needles and bone awls Moreover, microwear analysis of Neanderthal hide scrapers shows that they were used only for the initial phases of hide preparation, and not for the more advanced phases of clothing production ."

A 2013 study of Neanderthal skulls suggests that their eyesight may have been better than that of modern humans, owing to larger eye sockets and larger areas of the brain devoted to vision.

Neanderthals are known for their large cranial capacity, which at 1600 cm³ is larger on average than that of modern humans. One study has found that Neanderthal brains were more asymmetric than other hominid brains. In 2008, a group of scientists produced a study using three-dimensional computer-assisted reconstructions of Neanderthal infants based on fossils found in Russia and Syria. It indicated that Neanderthal and modern human brains were the same size at birth, but that by adulthood, the Neanderthal brain was larger than the modern human brain. They had almost the same degree of encephalization (i.e. brain to body size ratio) as modern humans.

Behavior

Neanderthals made advanced tools, apparently kindled fire on demand, may have had a language (the nature of which is debated and likely unknowable), and lived in complex social groups. The Molodova I archaeological site in eastern Ukraine suggests some Neanderthals built dwellings using animal bones. A building was made of mammoth skulls, jaws, tusks and leg bones, and had 25 hearths inside.

Circumstantial evidence suggests Neanderthals may have been building some form of watercraft since the Middle Paleolithic. Scientists have speculated that these watercraft may have been similar to dugout canoes, which are among the oldest known boats in the archaeological record. Mousterian stone tools discovered on the southern Ionian Islands suggests that Neanderthals were sailing the Mediterranean Sea as early as 110,000 years ago. Quartz hand-axes, three-sided picks, and stone cleavers from Crete have also been recovered that date back about 170,000 years ago.

It was once thought that Neanderthals lacked the sophistication for hunting, perhaps scavenging meat from carcasses, but increasing evidence suggests they were apex predators, capable of bringing down a wide range of prey from red deer, reindeer, ibex and wild boar, to larger animals such as aurochs and even, on occasion, mammoth, straight-tusked elephant and rhinoceros. However, while they were largely carnivorous, new studies indicate Neanderthals also had cooked vegetables in their diet. In 2010, an isotope analysis of Neanderthal teeth found traces of cooked vegetable matter, and more recently a 2014 study of Neanderthal coprolites (fossilized feces) found substantial amounts of plant matter, contradicting the earlier belief they were exclusively (or almost exclusively) carnivorous. A dental analysis of specimens from Spy, Belgium and El Sidrón, Spain by an international team, published in 2017 in Nature revealed, that these Neanderthals "had a wide-ranging diet", even claiming the "Neanderthals from El Sidrón showed no evidence of meat eating" at all while living on "a mixture of forest moss, pine nuts and a mushroom known as split gill".

The size and distribution of Neanderthal sites, along with genetic evidence, suggests Neanderthals lived in much smaller and more sparsely distributed groups than their Homo sapiens contemporaries. Some experts suggest that this disparity alone was a major contributing factor to their ultimate replacement by Homo sapiens, which may have outnumbered them by as much as 9 to 1 according to some estimates. Their lower population density may have also increased Neanderthal susceptibility to mutations caused by inbreeding.

The bones of twelve Neanderthals were discovered at El Sidrón cave in the Atapuerca Mountains of Spain. They are believed to be a social group which was massacred about 50,000 years ago, and analysis of the mtDNA shows that the three adult males belonged to the same maternal lineage, while the three adult females belonged to different ones. This suggests a social structure where males remained in the same social group and females "married" out.

The bones of the El Sidron group show signs of defleshing, suggesting that they were victims of cannibalism, and as their bones also show signs that they suffered from food shortage, they may have been victims of "survival cannibalism" by another Neanderthal group. The St. Césaire 1 skeleton discovered in 1979 at La Roche à Pierrot, France, showed a healed fracture on top of the skull apparently caused by a deep blade wound. Researchers have taken this as evidence of the presence of interpersonal violence among the Neanderthals.

In 2016, Jacques Jaubert and colleagues reported the discovery of 176,000 year old stalagmite constructions 336 meters deep in Bruniquel Cave near Bruniquel in south-western France. There were two annular (ring) structures, one 6.7 by 4.5 metres, and the other 2.2 by 2.1, with one to four layers of aligned broken stalagmites, and short pieces within the layers to support them. There were also four stack structures, two within the large ring and two outside it. Artificial lighting would have been required as the cave is far beyond the reach of daylight, and 57 of the stalagmite pieces are reddened and 66 blackened by fire. Burnt organic material was also found. The researchers concluded that the constructions must have been made by early Neanderthals, as they were the only human species in the area at the time. The elaborate structures show that the Neanderthals had a more sophisticated level of social organisation than previously thought possible.

Background

Early investigations concentrated on mitochondrial DNA (mtDNA), which, owing to strictly matrilineal inheritance and subsequent vulnerability to genetic drift, is of limited value in evaluating the possibility of interbreeding of Neanderthals with Cro-Magnon people.

In 1997, geneticists were able to extract a short sequence of DNA from Neanderthal bones. The extraction of mtDNA from a second specimen was reported in 2000, and showed no sign of modern human descent from Neanderthals.

In July 2006, the Max Planck Institute for Evolutionary Anthropology and 454 Life Sciences announced that they would sequence the Neanderthal genome over the next two years. This genome was expected to be roughly the size of the human genome, three-billion base pairs, and share most of its genes. It was hoped the comparison would expand understanding of Neanderthals, as well as the evolution of humans and human brains.

Svante Pääbo has tested more than 70 Neanderthal specimens. The Neanderthal genome is almost the same size as the human genome and is identical to ours to a level of 99.7% by comparing the accurate order of the nitrogenous bases in the double nucleotide chain. From mtDNA analysis estimates, the two species shared a common ancestor about 500,000 years ago. An article appearing in the journal Nature has calculated the species diverged about 516,000 years ago, whereas fossil records show a time of about 400,000 years ago. A 2007 study pushes the point of divergence back to around 800,000 years ago.

Edward Rubin of the Lawrence Berkeley National Laboratory states recent genome testing of Neanderthals suggests human and Neanderthal DNA are some 99.5% to nearly 99.9% identical.

Interbreeding with modern humans

On 16 November 2006, Lawrence Berkeley National Laboratory issued a press release suggesting Neanderthals and ancient humans probably did not interbreed. Edward M. Rubin, director of the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the Joint Genome Institute (JGI), sequenced a fraction (0.00002) of genomic nuclear DNA (nDNA) from a 38,000-year-old Vindia Neanderthal femur. They calculated the common ancestor to be about 353,000 years ago, and a complete separation of the ancestors of the species about 188,000 years ago.

Their results show the genomes of modern humans and Neanderthals are at least 99.5% identical, but despite this genetic similarity, and despite the two species having coexisted in the same geographic region for thousands of years, Rubin and his team did not find any evidence of any significant interbreeding between the two. Rubin said, "While unable to definitively conclude that interbreeding between the two species of humans did not occur, analysis of the nuclear DNA from the Neanderthal suggests the low likelihood of it having occurred at any appreciable level."

In 2008 Richard E. Green et al. from Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, published the full sequence of Neanderthal mitochondrial DNA (mtDNA) and suggested "Neanderthals had a long-term effective population size smaller than that of modern humans."

In the same publication, it was disclosed by Svante Pääbo that in the previous work at the Max Planck Institute, "Contamination was indeed an issue," and they eventually realized that 11% of their sample was modern human DNA. Since then, more of the preparation work has been done in clean areas and 4-base pair 'tags' have been added to the DNA as soon as it is extracted so the Neanderthal DNA can be identified.

With 3 billion nucleotides sequenced, analysis of about ⅓ showed no sign of admixture between modern humans and Neanderthals, according to Pääbo. This concurred with the work of Noonan from two years earlier. The variant of microcephalin common outside Africa, which was suggested to be of Neanderthal origin and responsible for rapid brain growth in humans, was not found in Neanderthals. Nor was the MAPT variant, a very old variant found primarily in Europeans.

However, an analysis of a first draft of the Neanderthal genome by the same team released in May 2010 indicates interbreeding may have occurred. "Those of us who live outside Africa carry a little Neanderthal DNA in us," said Pääbo, who led the study. "The proportion of Neanderthal-inherited genetic material is about 1 to 4 percent. It is a small but very real proportion of ancestry in non-Africans today," says Dr. David Reich of Harvard Medical School, who worked on the study. This research compared the genome of the Neanderthals to five modern humans from China, France, sub-Saharan Africa, and Papua New Guinea. The finding is that about 1 to 4 percent of the genes of the humans outside sub-Saharan Africa came from Neanderthals, compared to the baseline defined by the two sub-Saharan Africans.

This indicates a gene flow from Neanderthals to modern humans, i.e., interbreeding between the two populations. Since the three non-African genomes show a similar proportion of Neanderthal sequences, the interbreeding must have occurred early in the migration of modern humans out of Africa, perhaps in the Middle East. No evidence for gene flow in the direction from modern humans to Neanderthals was found. Gene flow from modern humans to Neanderthals would not be expected if contact occurred between a small colonizing population of modern humans and a much larger resident population of Neanderthals. A very limited amount of interbreeding could explain the findings, if it occurred early enough in the colonization process.

It is suggested that 20 percent of Neanderthal DNA survived in modern humans, notably expressed in the skin, hair, and diseases of the modern people. Modern human genes involved in making keratin—the protein found in skin, hair, and nails—have specially high levels of Neanderthal DNA. For example, around 66% of East Asians contain the Neanderthal skin gene, while 70% of Europeans contain the Neanderthal gene which affects skin colour. POU2F3 is found in around 66 percent of East Asians, while the Neanderthal version of BNC2, which affects skin color, among other traits, is found in 70 percent of Europeans. Neanderthal are the variants in genes that affect the risk of several diseases, including lupus, biliary cirrhosis, Crohn's disease, and type 2 diabetes. 8% of Neanderthal DNA comes from unknown species, tantalizing hints of unknown groups from Asia and Africa that left genes in Denisovans and modern humans, respectively. 17% of the genes of Denisovians and Neanderthals are shared. According to a research led by an Oxford scientist, it is possible that the gene causing red hair in modern humans is inherited from the Neanderthals, which is up to 100,000 years old, although a different mutation on Neanderthals was found in the MRC1 gene than on modern humans.

While interbreeding is viewed as the most parsimonious interpretation of the genetic discoveries, the authors point out they cannot conclusively rule out an alternative scenario, in which the source population of non-African modern humans was already more closely related to Neanderthals than other Africans were, because of ancient genetic divisions within Africa. Other studies carried out since the sequencing of the Neanderthal genome have cast doubt on the level of admixture between Neanderthals and modern humans, or even as to whether the species interbred at all. One study has asserted that the presence of Neanderthal or other archaic human genetic markers can be attributed to shared ancestral traits between the species originating from a 500,000-year-old common ancestor.

Among the genes shown to differ between present-day humans and Neanderthals were RPTN, SPAG17, CAN15, TTF1, FOXP2 and PCD16.

More recent research suggests that Neanderthal–Homo sapiens interbreeding appears to have occurred asymmetrically among the ancestors of modern-day humans, and that this is a possible rationale for differing frequencies of Neanderthal-specific DNA in the genomes of modern humans. In 2015, researchers Benjamin Vernot and Joshua Akey at the University of Washington conclude in a paper in the American Journal of Human Genetics that the relatively greater quantity of Neanderthal-specific DNA in the genomes of individuals of East Asian descent (than those of European descent) cannot be explained by differences in selection. They further suggest that "two additional demographic models, involving either a second pulse of Neandertal gene flow into the ancestors of East Asians or a dilution of Neandertal lineages in Europeans by admixture with an unknown ancestral population" are parsimonious with their data. Similar conclusions were reached in a paper published in the same publication by researchers Bernard Kim and Kirk Lohmueller at UCLA: "Using simulations of a broad range of models of selection and demography, we have shown that this hypothesis [that the greater proportion of Neandertal ancestry in East Asians than in Europeans is due to the fact that purifying selection is less effective at removing weakly deleterious Neandertal alleles from East Asian populations] cannot account for the higher proportion of Neandertal ancestry in East Asians than in Europeans. Instead, more complex demographic scenarios, most likely involving multiple pulses of Neandertal admixture, are required to explain the data."

In a subsequent interview, Dr. Lohmueller did note that these findings go against the commonly-held perception that Neanderthals were mostly localized to modern-day Europe and western Asia: "It’s very hard to put these findings into spatial context. The key idea is that there would have to have been some additional interbreeding events involving East Asians, but not Europeans. These interbreeding events could have been directly between Neanderthals and East Asians, maybe in some other indirect way." Vernot also noted that "[H]umans have been constantly migrating throughout their history - this makes it hard to say exactly where interactions with Neanderthals occurred. It's possible, for example, that all of the interbreeding with Neanderthals occurred in the Middle East, before the ancestors of modern non-Africans spread out across Eurasia. In the model from the paper, the ancestors of all non-Africans interbred with Neanderthals, and then split up into multiple groups that would later become Europeans, East Asians. Shortly after they split up, the ancestors of East Asians interbred with Neanderthals just a little bit more."

Studies published in March 2016 suggest that modern humans bred with hominins, including Neanderthals, on multiple occasions. Another study in April 2016 found differences between Homo sapiens and Neanderthal Y chromosomes that, they postulated, could cause female Homo Sapiens to miscarry male babies that had Neanderthal fathers. This could explain why no modern man had to date been found with a Neanderthal Y chromosome. Melanesians and Australoid populations show evidence of only one interbreeding event, possibly ~100,000 years ago, occurring in the Middle East, Europeans show a second event, which may also be of Middle Eastern origin, occurring possibly 50,000 years ago, while East Asians show an additional third interbreeding event possibly 30,000 years ago occurring in Siberia. Evidence that Neanderthal genomic material is often found amongst genes of the immune system suggests that some of the interbreeding may have secured resistance to diseases that Neanderthal populations had bred resistance to.

In 2016 researchers reported that they had found Human DNA in the genome of a female Neanderthal from the Altai mountains region near the border between Mongolia and Russia. They calculated that the mating must have taken place about 100,000 years ago.

Epigenetics

In April 2014, a first glimpse into the epigenetics of the Neanderthal was obtained with the publication of the full DNA methylation of the Neanderthal and the Denisovan. The reconstructed DNA methylation map allowed researchers to assess gene activity levels throughout the Neanderthal genome and compare them to modern humans. One of the major findings focused on the limb morphology of Neanderthals. Gokhman et al. found that changes in the activity levels of the HOX cluster of genes were behind many of the morphological differences between Neanderthals and modern humans, including shorter limbs, curved bones and more.

Extinction hypotheses

According to a 2014 study by Thomas Higham and colleagues of organic samples from European sites, Neanderthals died out in Europe between 41,000 and 39,000 years ago, and Homo sapiens arrived in Mediterranean Europe between 45,000 and 43,000 years ago, so the two different human populations shared Europe for several thousand years. The exact nature of biological and cultural interaction between Neanderthals and other human groups has been contested.

Possible scenarios for the extinction of the Neanderthals are:

1. Neanderthals were a separate species from modern humans, and became extinct (because of climate change or interaction with modern humans) and were replaced by modern humans moving into their habitat between 45,000 and 40,000 years ago. Jared Diamond has suggested a scenario of violent conflict and displacement.
2. Neanderthals were a contemporary subspecies that bred with modern humans and disappeared through absorption (interbreeding theory).
3. Volcanic catastrophe: see Campanian Ignimbrite Eruption

As Paul Jordan notes: "A natural sympathy for the underdog and the disadvantaged lends a sad poignancy to the fate of the Neanderthal folk, however it came about." Jordan, though, does say that there was perhaps interbreeding to some extent, but that populations that remained totally Neanderthal were probably out-competed and marginalized to extinction by the Aurignacians.

Climate change

About 55,000 years ago, the weather began to fluctuate wildly from extreme cold conditions to mild cold and back in a matter of a few decades. Neanderthal bodies were well suited for survival in a cold climate—their barrel chests and stocky limbs stored body heat better than the Cro-Magnons. However, the rapid fluctuations of weather caused ecological changes to which the Neanderthals could not adapt; familiar plants and animals would be replaced by completely different ones within a lifetime. Neanderthals' ambush techniques would have failed as grasslands replaced trees. Neanderthals died out in Europe between 41,000 and 39,000 years ago which coincides with the start of a very cold period. Raw material sourcing and the examination of faunal remains by Adler et al. (2006) in the southern Caucasus region suggest that modern humans may have had a survival advantage during this period, being able to use social networks to acquire resources from a greater area. They found that in both the Late Middle Palaeolithic and Early Upper Palaeolithic more than 95% of stone artifacts were drawn from local material, suggesting Neanderthals were restricted to more local resources. Furthermore, excavations at Ortvale Klde Rockshelter discovered that there was a clear break between the Late Middle Paleolithic and the Early Upper Paleolithic lithic assemblages, which were attributed to Neanderthals and modern humans respectively. This would suggest that modern humans came in and replaced Neanderthals, rather than a slow shift or integration occurring in this region.

Studies on Neanderthal body structures have shown that they needed more energy to survive than any other species of hominid. Their energy needs were up to 100 to 350 kcal (420 to 1,460 kJ) more per day comparing to projected anatomically modern human males weighing 68.5 kg (151 lb) and females 59.2 kg (131 lb). When food became scarce, this difference may have played a major role in the Neanderthals' extinction.

Coexistence with Homo sapiens

In November 2011 tests conducted at the Oxford Radiocarbon Accelerator Unit in England on what were previously thought to be Neanderthal baby teeth, which had been unearthed in 1964 from the Grotta del Cavallo in Italy, were identified as the oldest modern human remains discovered anywhere in Europe, dating from between 43,000 and 45,000 years ago. Given that the 2014 study by Thomas Higham of Neanderthal bones and tools indicates that Neanderthals died out in Europe between 41,000 and 39,000 years ago, the two different human populations shared Europe for as long as 5,000 years. The exact nature of biological and cultural interaction between Neanderthals and other human groups has been contested.

Modern humans co-existed with them in Europe starting around 45,000 years ago and perhaps even earlier. Neanderthals inhabited that continent for a long period of time before the arrival of modern humans. H. sapiens may have introduced a disease that contributed to the extinction of Neanderthals, and that may be added to other recent explanations for their extinction. When Neanderthal ancestors left Africa roughly 100,000 years earlier they adapted to the pathogens in their European environment, unlike modern humans who adapted to African pathogens. This transcontinental movement is known as the Out of Africa model. If contact between humans and Neanderthals occurred in Europe and Asia the first contact may have been devastating to the Neanderthal population, because they would have had little if any immunity to the African pathogens. More recent historical events in Eurasia and the Americas show a similar pattern, where the unintentional introduction of viral, or bacterial pathogens to unprepared populations has led to mass mortality and local population extinction. The most well-known example of this is the arrival of Christopher Columbus to the New World, which brought and introduced foreign diseases when he and his crew arrived to a native population who had no immunity.

Anthropologist Pat Shipman, of Pennsylvania State University, suggested that domestication of the dog could have played a role in Neanderthals' extinction.

Interbreeding hypotheses

An alternative to extinction is that Neanderthals were absorbed into the Cro-Magnon population by interbreeding. This would be counter to strict versions of the Recent African Origin, since it would imply that at least part of the genome of Europeans would descend from Neanderthals.

Hans Peder Steensby, while strongly emphasising that all modern humans are of mixed origins, proposed the interbreeding hypothesis in 1907, in the article Race studies in Denmark. He held that this would best fit current observations, and attacked the widespread idea that Neanderthals were ape-like or inferior.

The most vocal proponent of the hybridization hypothesis is Erik Trinkaus of Washington University. Trinkaus claims various fossils as products of hybridized populations, including the child of Lagar Velho, a skeleton found at Lagar Velho in Portugal. In a 2006 publication co-authored by Trinkaus, the fossils found in 1952 in the cave of Peștera Muierii, Romania, are likewise claimed as descendants of previously hybridized populations.

Genetic research has asserted that some admixture took place. The genomes of all non-Africans include portions that are of Neanderthal origin, due to interbreeding between Neanderthals and the ancestors of Eurasians in Northern Africa or the Middle East prior to their spread. Rather than absorption of the Neanderthal population, this gene flow appears to have been of limited duration and limited extent. An estimated 1 to 4 percent of the DNA in Europeans and Asians (French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with Sub-Saharan Africans (Yoruba people and San probands). Ötzi the iceman, Europe's oldest preserved mummy, was found to possess an even higher percentage of Neanderthal ancestry. 2014 findings suggest there may be even more Neanderthal genes in non-African humans than previously expected: approximately 20% of the Neanderthal gene pool was present in a broad sampling of non-African individuals, though each individual's genome was on average only 2% Neanderthal.

2012 genetic studies seem to suggest that modern humans may have mated with "at least two groups" of ancient humans: Neanderthals and Denisovans. Some researchers suggest admixture of 3.4–7.9% in modern humans of non-African ancestry, rejecting the hypothesis of ancestral population structure. Detractors have argued and continue to argue that the signal of Neanderthal interbreeding may be due to ancient African substructure, meaning that the similarity is only a remnant of a common ancestor of both Neanderthals and modern humans and not the result of interbreeding. John D. Hawks has argued that the genetic similarity to Neanderthals may indeed be the result of both structure and interbreeding, as opposed to just one or the other.

While some modern human nuclear DNA has been linked to the extinct Neanderthals, no mitochondrial DNA of Neanderthal origin has been detected, which in primates is always maternally transmitted. This observation has prompted the hypothesis that whereas female humans interbreeding with male Neanderthals were able to generate fertile offspring, the progeny of female Neanderthals who mated with male humans were either rare, absent or sterile. However, some researchers have argued that there is evidence of possible interbreeding between female Neanderthals and male modern humans.

Notable specimens

Chronology

This section describes bones with Neanderthal traits in chronological order.

Mixed with H. heidelbergensis traits

Typical H. neanderthalensis traits

Homo sapiens with some neanderthal-like archaic traits

Popular culture

Neanderthals have been portrayed in popular culture including appearances in literature, visual media and comedy, often in an unflattering and inaccurate light.

Early artistic reconstructions mostly presented Neanderthals as beastly creatures, emphasizing hairiness and rough, dark complexion.