Neandertal - Wisent.jpg

Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While the "causes of Neanderthal disappearance about 40,000 years ago remain highly contested," demographic factors such as small population size, inbreeding and genetic drift, are considered probable factors. Other scholars have proposed competitive replacement, assimilation into the modern human genome (bred into extinction), great climatic change, disease, or a combination of these factors.

It is unclear when the line of Neanderthals split from that of modern humans; studies have produced various intervals ranging from 315,000 to more than 800,000 years ago. The date of divergence of Neanderthals from their ancestor ''H. heidelbergensis'' is also unclear. The oldest potential Neanderthal bones date to 430,000 years ago, but the classification remains uncertain. Neanderthals are known from numerous fossils, especially from after 130,000 years ago. The type specimen, Neanderthal 1, was found in 1856 in the Neander Valley in present-day Germany. For much of the early 20th century, European researchers depicted Neanderthals as primitive, unintelligent, and brutish. Although knowledge and perception of them has markedly changed since then in the scientific community, the image of the unevolved caveman archetype remains prevalent in popular culture.

Neanderthal technology was quite sophisticated. It includes the Mousterian stone-tool industry and ability to create fire and build cave hearths, make the adhesive birch bark tar, craft at least simple clothes similar to blankets and ponchos, weave, go seafaring through the Mediterranean, and make use of medicinal plants, as well as treat severe injuries, store food, and use various cooking techniques such as roasting, boiling, and smoking. Neanderthals made use of a wide array of food, mainly hoofed mammals, but also other megafauna, plants, small mammals, birds, and aquatic and marine resources. Although they were probably apex predators, they still competed with cave bears, cave lions, cave hyaenas, and other large predators. A number of examples of symbolic thought and Palaeolithic art have been inconclusively attributed to Neanderthals, namely possible ornaments made from bird claws and feathers or shells, collections of unusual objects including crystals and fossils, engravings, music production (possibly indicated by the Divje Babe flute), and Spanish cave paintings contentiously dated to before 65,000 years ago. Some claims of religious beliefs have been made. Neanderthals were likely capable of speech, possibly articulate, although the complexity of their language is not known.

Compared with modern humans, Neanderthals had a more robust build and proportionally shorter limbs. Researchers often explain these features as adaptations to conserve heat in a cold climate, but they may also have been adaptations for sprinting in the warmer, forested landscape that Neanderthals often inhabited. Nonetheless, they had cold-specific adaptations, such as specialised body-fat storage and an enlarged nose to warm air (although the nose could have been caused by genetic drift). Average Neanderthal men stood around and women tall, similar to pre-industrial modern humans. The braincases of Neanderthal men and women averaged about and respectively, which is within the range of the values for modern humans. The Neanderthal skull was more elongated and had smaller parietal lobes and cerebellum, morphological traits used to assign specimens to species.

The total population of Neanderthals remained low, proliferating weakly harmful gene variants, and precluding effective long-distance networks. Despite this, there is evidence of regional cultures and thus of regular communication between communities. They may have frequented caves, and moved between them seasonally. Neanderthals lived in a high-stress environment with high trauma rates, and about 80% died before the age of 40. The 2010 Neanderthal genome project's draft report presented evidence for interbreeding between Neanderthals and modern humans. It possibly occurred 316–219 thousand years ago, but more likely 100,000 years ago and again 65,000 years ago. Neanderthals also appear to have interbred with Denisovans, a different group of archaic humans, in Siberia. Around 1–4% of genomes of Eurasians, Australo-Melanesians, Native Americans, and North Africans is of Neanderthal ancestry, while the inhabitants of sub-Saharan Africa have only 0.3% of Neanderthal genes, save possible traces from early Sapiens-to-Neanderthal gene flow and/or more recent back-migration of Eurasians to Africa. In all, about 20% of distinctly Neanderthal gene variants survive today. Although many of the gene variants inherited from Neanderthals may have been detrimental and selected out, Neanderthal introgression appears to have affected the modern human immune system,
and is also implicated in several other biological functions and structures, but a large portion appears to be non-coding DNA.

Taxonomy

Etymology

Neanderthals are named after the Neandertal Valley in which the first identified specimen was found. The valley was spelled ''Neanderthal'' and the species was spelled ''Neanderthaler'' in German until the spelling reform of 1901. The spelling ''Neandertal'' for the species is occasionally seen in English, even in scientific publications, but the scientific name, ''H. neanderthalensis'', is always spelled with ''th'' according to the principle of priority. The vernacular name of the species in German is always ''Neandertaler'' ("inhabitant of the Neander Valley"), whereas ''Neandertal'' always refers to the valley. The valley itself was named after the late 17th century German theologian and hymn writer Joachim Neander, who often visited the area. His name in turn means ‘new man’, being a learned Graecization of the German surname ''Neumann''.

''Neanderthal'' can be pronounced using the (as in ) or the standard English pronunciation of ''th'' with the fricative / θ/ (as ).

Neanderthal 1, the type specimen, 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 specimen to the entire species, and formally recognising it as distinct from humans—was first proposed by Irish geologist William King in a paper read to the 33rd British Science Association in 1863. However, in 1864, he recommended that Neanderthals and modern humans be classified in different genera as he compared the Neanderthal braincase to that of a chimpanzee and argued that they were "incapable of moral and theistic">theism.html" ;"title="/nowiki>theism">theisticconceptions".

Research history

The first Neanderthal remains—Engis 2 (a skull)—were discovered in 1829 by Dutch naturalist Philippe-Charles Schmerling in the Schmerling Caves, Grottes d'Engis, Belgium, but he thought it was a fossil modern human skull. In 1848, Gibraltar 1 from Forbes' Quarry was presented to the Gibraltar Scientific Society by their Secretary Lieutenant Edmund Henry Réné Flint, but was also thought to be a modern human skull. In 1856, local schoolteacher Johann Carl Fuhlrott recognised bones from Kleine Feldhofer Grotte in Neander Valley—Neanderthal 1 (the holotype specimen)—as distinct from modern humans, and gave them to German anthropologist Hermann Schaaffhausen to study in 1857. It comprised the cranium, thigh bones, right arm, left humerus and ulna, left ilium (hip bone), part of the right shoulder blade, and pieces of the ribs. Following Charles Darwin's '' On the Origin of Species'', Fuhlrott and Schaaffhausen argued the bones represented an ancient modern human form; Schaaffhausen, a social Darwinist, believed that humans linearly progressed from savage to civilised, and so concluded that Neanderthals were barbarous cave-dwellers. Fuhlrott and Schaaffhausen met opposition namely from the prolific pathologist Rudolf Virchow who argued against defining new species based on only a single find. In 1872, Virchow erroneously interpreted Neanderthal characteristics as evidence of senility, disease, and malformation instead of archaicness, which stalled Neanderthal research until the end of the century.

By the early 20th century, numerous other Neanderthal discoveries were made, establishing ''H. neanderthalensis'' as a legitimate species. The most influential specimen was La Chapelle-aux-Saints 1 ("The Old Man") from La Chapelle-aux-Saints, France. French palaeontologist Marcellin Boule authored several publications, among the first to establish palaeontology as a science, detailing the specimen, but reconstructed him as slouching, ape-like, and only remotely related to modern humans. The 1912 'discovery' of Piltdown Man (a hoax), appearing much more similar to modern humans than Neanderthals, was used as evidence that multiple different and unrelated branches of primitive humans existed, and supported Boule's reconstruction of ''H. neanderthalensis'' as a far distant relative and an evolutionary dead-end. He fuelled the popular image of Neanderthals as barbarous, slouching, club-wielding primitives; this image was reproduced for several decades and popularised in science fiction works, such as the 1911 ''The Quest for Fire'' by J.-H. Rosny aîné and the 1927 '' The Grisly Folk'' by H. G. Wells where they are depicted as monsters. In 1911, Scottish anthropologist Arthur Keith reconstructed La Chapelle-aux-Saints 1 as an immediate precursor to modern humans, sitting next to a fire, producing tools, wearing a necklace, and having a more humanlike posture, but this failed to garner much scientific rapport, and Keith later abandoned his thesis in 1915.

By the middle of the century, based on the exposure of Piltdown Man as a hoax as well as a reexamination of La Chapelle-aux-Saints 1 (who had osteoarthritis which caused slouching in life) and new discoveries, the scientific community began to rework its understanding of Neanderthals. Ideas such as Neanderthal behaviour, intelligence, and culture were being discussed, and a more humanlike image of them emerged. In 1939, American anthropologist Carleton Coon reconstructed a Neanderthal in a modern business suit and hat to emphasise that they would be, more or less, indistinguishable from modern humans had they survived into the present. William Golding's 1955 novel '' The Inheritors'' depicts Neanderthals as much more emotional and civilised. However, Boule's image continued to influence works until the 1960s. In modern-day, Neanderthal reconstructions are often very humanlike.

Hybridisation between Neanderthals and early modern humans had been suggested early on, such as by English anthropologist Thomas Huxley in 1890, Danish ethnographer Hans Peder Steensby in 1907, and Coon in 1962. In the early 2000s, supposed hybrid specimens were discovered: Lagar Velho 1 and Muierii 1. However, similar anatomy could also have been caused by adapting to a similar environment rather than interbreeding. Neanderthal admixture was found to be present in modern populations in 2010 with the mapping of the first Neanderthal genome sequence. This was based on 3 specimens in Vindija Cave, Croatia, which contained almost 4% archaic DNA (allowing for near complete sequencing of the genome). However, there was approximately 1 error for every 200 letters (base pairs) based on the implausibly high mutation rate, probably due to the preservation of the sample. In 2012, British-American geneticist Graham Coop hypothesised that they instead found evidence of a different archaic human species interbreeding with modern humans, which was disproven in 2013 by the sequencing of a high-quality Neanderthal genome preserved in a toe bone from Denisova Cave, Siberia.

Classification

Neanderthals are hominids in the genus '' Homo'', humans, and generally classified as a distinct species, ''H. neanderthalensis'', although sometimes as a subspecies of modern human as ''H. sapiens neanderthalensis''. This would necessitate the classification of modern humans as '' H. sapiens sapiens''.

A large part of the controversy stems from the vagueness of the term "species", as it is generally used to distinguish two genetically isolated populations, but admixture between modern humans and Neanderthals is known to have occurred. However, the absence of Neanderthal-derived patrilineal Y-chromosome and matrilineal mitochondrial DNA (mtDNA) in modern humans, along with the underrepresentation of Neanderthal X chromosome DNA, could imply reduced fertility or frequent sterility of some hybrid crosses, representing a partial biological reproductive barrier between the groups, and therefore species distinction. In 2014 geneticist Svante Pääbo summarised the controversy, describing such "taxonomic wars" as unresolvable, "since there is no definition of species perfectly describing the case".

Neanderthals are thought to have been more closely related to Denisovans than to modern humans. Likewise, Neanderthals and Denisovans share a more recent last common ancestor (LCA) than to modern humans, based on nuclear DNA (nDNA). However, Neanderthals and modern humans share a more recent mitochondrial LCA (observable by studying mtDNA). This likely resulted from an interbreeding event subsequent to the Neanderthal/Denisovan split which introduced another mtDNA line. This involved either introgression coming from an unknown archaic human into Denisovans, or introgression from an earlier unidentified modern human wave from Africa into Neanderthals.

Evolution

It is largely thought that ''H. heidelbergensis'' was the last common ancestor of Neanderthals, Denisovans, and modern humans before populations became isolated in Europe, Asia, and Africa, respectively. The taxonomic distinction between ''H. heidelbergensis'' and Neanderthals is mostly based on a fossil gap in Europe between 300 and 243 thousand years ago during marine isotope stage 8. "Neanderthals", by convention, are fossils which date to after this gap. However, 430,000-year old bones at Sima de los Huesos could represent early Neanderthals or a closely related group, and the 400,000-year old Aroeira 3 could represent a transitional phase. Ancestral and derived morphs could have lived concurrently. It is also possible that there was gene flow between Western Europe and Africa during the Middle Pleistocene, obscuring Neanderthal characteristics in such specimens, namely from Ceprano, Italy, and Sićevo Gorge, Serbia. The fossil record is much more complete from 130,000 years ago onwards, and specimens from this period make up the bulk of known Neanderthal skeletons. Dental remains from the Italian Visogliano and Fontana Ranuccio sites indicate that Neanderthal dental features had evolved by around 450–430 thousand years ago during the Middle Pleistocene.

There are two main hypotheses regarding the evolution of Neanderthals following the Neanderthal/human split: two-phase and accretion. Two-phase argues that a single major environmental event—such as the Saale glaciation—caused European ''H. heidelbergensis'' to increase rapidly in body size and robustness, as well as undergoing a lengthening of the head (phase 1), which then led to other changes in skull anatomy (phase 2). However, Neanderthal anatomy may not have been driven entirely by adapting to cold weather. Accretion holds that Neanderthals slowly evolved over time from the ancestral ''H. heidelbergensis'', divided into four stages: early-pre-Neanderthals (MIS 12, Elster glaciation), pre-Neanderthals '' sensu lato'' (MIS 11– 9, Holstein interglacial), early Neanderthals (MIS 7– 5, Saale glaciation–Eemian), and classic Neanderthals ''sensu stricto'' (MIS 4–3, Würm glaciation).

Numerous dates for the Neanderthal/human split have been suggested. The date of around 250,000 years ago cites "'' H. helmei''" as being the last common ancestor (LCA), and the split is associated with the Levallois technique of making stone tools. The date of about 400,000 years ago uses ''H. heidelbergensis'' as the LCA. Estimates of 600,000 years ago assume that "''H. rhodesiensis''" was the LCA, which split off into modern human lineage and a Neanderthal/''H. heidelbergensis'' lineage. 800,000 years ago has ''H. antecessor'' as the LCA, but different variations of this model would push the date back to 1 million years ago. However, a 2020 analysis of ''H. antecessor'' enamel proteomes suggests that ''H. antecessor'' is related but not a direct ancestor. DNA studies have yielded various results for the Neanderthal/human divergence time, such as 538–315, 553–321, 565–503, 654–475, 690–550, 765–550, 741–317, and 800–520 thousand years ago; and a dental analysis concluded before 800,000 years ago.

Neanderthals and Denisovans are more closely related to each other than they are to modern humans, meaning the Neanderthal/Denisovan split occurred after their split with modern humans. Assuming a mutation rate of 1 × 10⁻⁹ or 0.5 × 10⁻⁹ per base pair (bp) per year, the Neanderthal/Denisovan split occurred around either 236–190 or 473–381 thousand years ago respectively. Using 1.1 × 10⁻⁸ per generation with a new generation every 29 years, the time is 744,000 years ago. Using 5 × 10⁻¹⁰ nucleotide sites per year, it is 616,000 years ago. Using the latter dates, the split had likely already occurred by the time hominins spread out across Europe, and unique Neanderthal features had begun evolving by 600–500 thousand years ago. Before splitting, Neanderthal/Denisovans (or "Neandersovans") migrating out of Africa into Europe apparently interbred with an unidentified "superarchaic" human species who were already present there; these superarchaics were the descendants of a very early migration out of Africa around 1.9 mya.

Demographics

Range

Pre- and early Neanderthals, living before the Eemian interglacial (130,000 years ago), are poorly known and come mostly from Western European sites. From 130,000 years ago onwards, the quality of the fossil record increases dramatically with classic Neanderthals, who are recorded from Western, Central, Eastern, and Mediterranean Europe, as well as Southwest, Central, and Northern Asia up to the Altai Mountains in southern Siberia. Pre- and early Neanderthals, on the other hand, seem to have continuously occupied only France, Spain, and Italy, although some appear to have moved out of this "core-area" to form temporary settlements eastward (although without leaving Europe). Nonetheless, southwestern France has the highest density of sites for pre-, early, and classic Neanderthals.

The southernmost find was recorded at Shuqba Cave, Levant; reports of Neanderthals from the North African Jebel Irhoud and Haua Fteah have been reidentified as ''H. sapiens''. Their easternmost presence is recorded at Denisova Cave, Siberia 85°E; the southeast Chinese Maba Man, a skull, shares several physical attributes with Neanderthals, although these may be the result of convergent evolution rather than Neanderthals extending their range to the Pacific Ocean. The northernmost bound is generally accepted to have been 55°N, with unambiguous sites known between 50– 53°N, although this is difficult to assess because glacial advances destroy most human remains, and palaeoanthropologist Trine Kellberg Nielsen has argued that a lack of evidence of Southern Scandinavian occupation is (at least during the Eemian interglacial) due to the former explanation and a lack of research in the area. Middle Palaeolithic artefacts have been found up to 60°N on the Russian plains, but these are more likely attributed to modern humans. A 2017 study claimed the presence of ''Homo'' at the 130,000 year old Californian Cerutti Mastodon site in North America, but this is largely considered implausible.

It is unknown how the rapidly fluctuating climate of the last glacial period (Dansgaard–Oeschger events) impacted Neanderthals, as warming periods would produce more favourable temperatures but encourage forest growth and deter megafauna, whereas frigid periods would produce the opposite. However, Neanderthals may have preferred a forested landscape. Populations may have peaked in cold but not extreme intervals, such as marine isotope stages 8 and 6 (respectively 300 and 191 thousand years ago during the Saale glaciation). It is possible their range expanded and contracted as the ice retreated and grew respectively to avoid permafrost areas, residing in certain refuge zones during glacial maxima. In 2021, Israeli anthropologist Israel Hershkovitz and colleagues suggested the 140 to 120 thousand years old Israeli Nesher Ramla remains, which feature a mix of Neanderthal and more ancient '' H. erectus'' traits, represent one such source population which recolonised Europe following a glacial period.

Population

Like modern humans, Neanderthals probably descended from a very small population with an effective population—the number of individuals who can bear or father children—of 3,000 to 12,000 approximately. However, Neanderthals maintained this very low population, proliferating weakly harmful genes due to the reduced effectivity of natural selection.
Various studies, using mtDNA analysis, yield varying effective populations, such as about 1,000 to 5,000; 5,000 to 9,000 remaining constant; or 3,000 to 25,000 steadily increasing until 52,000 years ago before declining until extinction. Archaeological evidence suggests that there was a tenfold increase in the modern human population in Western Europe during the period of the Neanderthal/modern human transition, and Neanderthals may have been at a demographic disadvantage due to a lower fertility rate, a higher infant mortality rate, or a combination of the two. Estimates giving a total population in the higher tens of thousands are contested. A consistently low population may be explained in the context of the " Boserupian Trap": a population's carrying capacity is limited by the amount of food it can obtain, which in turn is limited by its technology. Innovation increases with population, but if the population is too low, innovation will not occur very rapidly and the population will remain low. This is consistent with the apparent 150,000 year stagnation in Neanderthal lithic technology.

In a sample of 206 Neanderthals, based on the abundance of young and mature adults in comparison to other age demographics, about 80% of them above the age of 20 died before reaching 40. This high mortality rate was probably due to their high-stress environment. However, it has also been estimated that the age pyramids for Neanderthals and contemporary modern humans were the same. Infant mortality was estimated to have been very high for Neanderthals, about 43% in northern Eurasia.

Anatomy

Build

Neanderthals had more robust and stockier builds than typical modern humans, wider and barrel-shaped rib cages; wider pelvises; and proportionally shorter forearms and forelegs.

Based on 45 Neanderthal long bones from 14 men and 7 women, the average height was for males and for females. For comparison, the average height of 28 males and 10 females Upper Palaeolithic humans is respectively and , although this decreases by nearer the end of the period based on 21 males and 15 females; and the average in the year 1900 was and , respectively. The fossil record shows that adult Neanderthals varied from about in height, although some may have grown much taller (73.8 to 184.8 cm based on footprint length and from 65.8 to 189.3 cm based on footprint width). For Neanderthal weight, samples of 26 specimens found an average of for males and for females. Using , the body mass index for Neanderthal males was calculated to be 26.9–28.2, which in modern humans correlates to being overweight. This indicates a very robust build. The Neanderthal LEPR gene concerned with storing fat and body heat production is similar to that of the woolly mammoth, and so was likely an adaptation for cold climate.

The neck vertebrae of Neanderthals are longer and thicker than those of (most) modern humans, leading to stability, possibly due to different head shape and size. Although the Neanderthal thorax (where the ribcage is) was similar in size to modern humans, the longer and straighter ribs would have equated to a widened mid-lower thorax and stronger breathing in the lower thorax, which are indicative of a larger diaphragm and possibly greater lung capacity. The lung capacity of Kebara 2 was estimated to have been , compared to the average human capacity of for males and for females. The Neanderthal chest was also more pronounced (expanded front-to-back, or antero-posteriorly). The sacrum (where the pelvis connects to the spine) was more vertically inclined, and was placed lower in relation to the pelvis, causing the spine to be less curved (exhibit less lordosis) and to fold in on itself somewhat (to be invaginated). In modern populations, this condition affects just a proportion of the population, and is known as a lumbarized sacrum. Such modifications to the spine would have enhanced side-to-side (mediolateral) flexion, better supporting the wider lower thorax. It is claimed by some that this feature would be normal for all ''Homo'', even tropically-adapted ''Homo ergaster'' or ''erectus'', with the condition of a narrower thorax in most modern humans being a unique characteristic.

Body proportions are usually cited as being "hyperarctic" as adaptations to the cold, because they are similar to those of human populations which developed in cold climates—the Neanderthal build is most similar to that of Inuit and Siberian Yupiks among modern humans—and shorter limbs result in higher retention of body heat. Nonetheless, Neanderthals from more temperate climates—such as Iberia—still retain the "hyperarctic" physique. In 2019, English anthropologist John Stewart and colleagues suggested Neanderthals instead were adapted for sprinting, because of evidence of Neanderthals preferring more warmer wooded areas over the colder mammoth steppe, and DNA analysis indicating a higher proportion of fast-twitch muscle fibres in Neanderthals than in modern humans. He explained their body proportions and greater muscle mass as adaptations to sprinting as opposed to the endurance-oriented modern human physique, as persistence hunting may only be effective in hot climates where the hunter can run prey to the point of heat exhaustion ( hyperthermia). They had longer heel bones, reducing their ability for endurance running, and their shorter limbs would have reduced moment arm at the limbs, allowing for greater rotational force at the wrists and ankles without extra exertion of the rotating muscles at the elbows and knees by increasing the speed at which the muscles contracted, causing faster acceleration. In 1981, American palaeoanthropologist Erik Trinkaus made note of this alternate explanation, but considered it less likely.

Face

Neanderthals had a staightened chin, sloping forehead, and projecting nose, which also started somewhat higher on the face than in most modern humans. The Neanderthal skull is typically more elongated and less globular than that of most modern humans, and features much more of an occipital bun, or "chignon", a protrusion on the back of the skull, although it is within the range of variation for humans who have it. It is caused by the cranial base and temporal bones being placed higher and more towards the front of the skull, and a flatter skullcap. They also had larger eyes likely to adapt to the low-light environment.

The projected Neanderthal nose and paranasal sinuses have generally been explained as having warmed air as it entered the lungs and retained moisture ("nasal radiator" hypothesis); If their noses were wider, it would differ to the generally narrowed shape in cold-adapted creatures, and that it would have been caused instead by genetic drift. Also, the sinuses reconstructed wide are not grossly large, being comparable in size to those of modern humans. However, if sinus size is not an important factor for breathing cold air, then the actual function would be unclear, so they may not be a good indicator of evolutionary pressures to evolve such a nose. Further, a computer reconstruction of the Neanderthal nose and predicted soft tissue patterns shows some similarities to those of modern Arctic peoples, potentially meaning the noses of both populations convergently evolved for breathing cold, dry air.

Neanderthals featured a rather large jaw which was once cited as a response to a large bite force evidenced by heavy wearing of Neanderthal front teeth (the "anterior dental loading" hypothesis), but similar wearing trends are seen in contemporary humans. It could also have evolved to fit larger teeth in the jaw, which would better resist wear and abrasion, and the increased wear on the front teeth compared to the back teeth probably stems from repetitive use. Neanderthal dental wear patterns are most similar to those of modern Inuit. The incisors are large and shovel-shaped, and, compared to modern humans, there was an unusually high frequency of taurodontism, a condition where the molars are bulkier due to an enlarged pulp (tooth core). Taurodontism was once thought to have been a distinguishing characteristic of Neanderthals which lent some mechanical advantage or stemmed from repetitive use, but was more likely simply a product of genetic drift. The bite force of Neanderthals and modern humans is now thought to be about the same, about and in modern human males and females, respectively.

Brain

The Neanderthal braincase averages 1,640 cc for males and 1,460 cc for females, which is significantly larger than the averages for all groups of extant humans; for example, modern European males average and females . For 28 modern human specimens from 190 to 25 thousand years ago, the average was about disregarding sex, and modern human brain size is suggested to have decreased since the Upper Palaeolithic. The largest Neanderthal brain, Amud 1, was calculated to be , one of the largest ever recorded in hominids. Both Neanderthal and human infants measure about .

The Neanderthal skull is distinctively elongated, a characteristic shape known as "en bombe," with smaller parietal lobes and a smaller cerebellum, areas implicated in tool use, visuospatial integration, numeracy, creativity, higher-order conceptualization, muscle memory, and possibly language, attention, working memory, social abilities, and episodic memory. Neanderthal brains also have larger occipital lobes (relating to the classic occurrence of an occipital bun in Neanderthal skull anatomy), likely an adaptation to lower light conditions in Europe that implies internal differences in the proportionality of brain-internal regions, relative to ''Homo sapiens,'' consistent with external measurements obtained with fossil skulls. Their brains also have larger temporal lobe poles, wider orbitofrontal cortex, and larger olfactory bulbs, suggesting potential differences in language comprehension and associations with emotions ( temporal functions), decision making (the orbitofrontal cortex), and sense of smell (olfactory bulbs). Their brains also show different rates of brain growth and development. Such differences, while slight, would have been visible to natural selection and may underlie and explain differences in the material record in things like social behaviors, technological innovation, and artistic output.

Hair and skin colour

The lack of sunlight most likely led to the proliferation of lighter skin in Neanderthals, although it has been recently claimed that light skin in modern Europeans was not particularly prolific until perhaps the Bronze Age. Genetically, BNC2 was present in Neanderthals, which is associated with light skin colour; however, a second variation of BNC2 was also present, which in modern populations is associated with darker skin colour in the UK Biobank. DNA analysis of three Neanderthal females from southeastern Europe indicates that they had brown eyes, dark skin color, and brown hair; with one having red hair. "According to this method, all three Neandertals had a dark complexion and brown eyes, and although one was red-haired, two sported brown locks"

In modern humans, skin and hair colour is regulated by the melanocyte-stimulating hormone—which increases the proportion of eumelanin (black pigment) to phaeomelanin (red pigment)—which is encoded by the MC1R gene. There are five known variants in modern humans of the gene which cause loss-of-function and are associated with light skin and hair colour, and another unknown variant in Neanderthals (the R307G variant) which could be associated with pale skin and red hair. The R307G variant was identified in a Neanderthal from Monti Lessini, Italy, and possibly Cueva del Sidrón, Spain. However, as in modern humans, red was probably not a very common hair colour because the variant is not present in many other sequenced Neanderthals.

Metabolism

Maximum natural lifespan and the timing of adulthood, menopause, and gestation were most likely very similar to modern humans. However, it has been hypothesised, based on the growth rates of teeth and tooth enamel, that Neanderthals matured faster than modern humans although this is not backed up by age biomarkers. The main differences in maturation are the atlas bone in the neck as well as the middle thoracic vertebrae fused about 2 years later in Neanderthals than in modern humans, but this was more likely caused by a difference in anatomy rather than growth rate.

Generally, models on Neanderthal caloric requirements report significantly higher intakes than those of modern humans because they typically assume Neanderthals had higher basal metabolic rates (BMRs) due to higher muscle mass, faster growth rate, and greater body heat production against the cold; and higher daily physical activity levels (PALs) due to greater daily travelling distances while foraging. However, using a high BMR and PAL, American archaeologist Bryan Hockett estimated that a pregnant Neanderthal would have consumed 5,500 calories per day, which would have necessitated a heavy reliance on big game meat; such a diet would have caused numerous deficiencies or nutrient poisonings, so he concluded that these are poorly warranted assumptions to make.

Neanderthals may have been more active during dimmer light conditions rather than broad daylight because they lived in regions with reduced daytime hours, hunted large game (such predators typically hunt at night to enhance ambush tactics), and had large eyes and visual processing neural centres. Genetically, colour blindness (which may enhance mesopic vision) is typically correlated with northern-latitude populations, and the Neanderthals from Vindija Cave, Croatia, had some substitutions in the Opsin genes which could have influenced colour vision. However, the functional implications of these substitutions are inconclusive. Neanderthal-derived alleles near ASB1 and EXOC6 are associated with being an evening person, narcolepsy, and day-time napping.

Pathology

Neanderthals suffered a high rate of traumatic injury, with an estimated 79–94% of specimens showing evidence of healed major trauma, of which 37–52% were severely injured, and 13–19% injured before reaching adulthood. One extreme example is Shanidar 1, who shows signs of an amputation of the right arm likely due to a nonunion after breaking a bone in adolescence, osteomyelitis (a bone infection) on the left clavicle, an abnormal gait, vision problems in the left eye, and possible hearing loss (perhaps swimmer's ear). In 1995, Trinkaus estimated that about 80% succumbed to their injuries and died before reaching 40, and thus theorised that Neanderthals employed a risky hunting strategy ("rodeo rider" hypothesis). However, rates of cranial trauma are not significantly different between Neanderthals and Middle Palaeolithic modern humans (although Neanderthals seem to have had a higher mortality risk), there are few specimens of both Upper Palaeolithic modern humans and Neanderthals who died after the age of 40, and there are overall similar injury patterns between them. In 2012, Trinkaus concluded that Neanderthals instead injured themselves in the same way as contemporary humans, such as by interpersonal violence. A 2016 study looking at 124 Neanderthal specimens argued that high trauma rates were instead caused by animal attacks, and found that about 36% of the sample were victims of bear attacks, 21% big cat attacks, and 17% wolf attacks (totalling 92 positive cases, 74%). There were no cases of hyaena attacks, although hyaenas still nonetheless probably attacked Neanderthals, at least opportunistically. Such intense predation probably stemmed from common confrontations due to competition over food and cave space, and from Neanderthals hunting these carnivores.

Low population caused a low genetic diversity and probably inbreeding, which reduced the population's ability to filter out harmful mutations ( inbreeding depression). However, it is unknown how this affected a single Neanderthal's genetic burden and, thus, if this caused a higher rate of birth defects than in modern humans. It is known, however, that the 13 inhabitants of Sidrón Cave collectively exhibited 17 different birth defects likely due to inbreeding or recessive disorders. Likely due to advanced age (60s or 70s), La Chapelle-aux-Saints 1 had signs of Baastrup's disease, affecting the spine, and osteoarthritis. Shanidar 1, who likely died at about 30 or 40, was diagnosed with the most ancient case of diffuse idiopathic skeletal hyperostosis (DISH), a degenerative disease which can restrict movement, which, if correct, would indicate a moderately high incident rate for older Neanderthals.

Neanderthals were subject to several infectious diseases and parasites. Modern humans likely transmitted diseases to them; one possible candidate is the stomach bacteria '' Helicobacter pylori''. The modern human papillomavirus variant 16A may descend from Neanderthal introgression. A Neanderthal at Cueva del Sidrón, Spain, shows evidence of a gastrointestinal ''Enterocytozoon bieneusi'' infection. The leg bones of the French La Ferrassie 1 feature lesions that are consistent with periostitis—inflammation of the tissue enveloping the bone—likely a result of hypertrophic osteoarthropathy, which is primarily caused by a chest infection or lung cancer. Neanderthals had a lower cavity rate than modern humans, despite some populations consuming typically cavity-causing foods in great quantity, which could indicate a lack of cavity-causing oral bacteria, namely ''Streptococcus mutans''.

Two 250,000-year-old Neanderthaloid children from Payré

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