Neanderthal anatomy

Neanderthal anatomy is characterised by a long, flat skull and a stocky body plan. When first discovered, Neanderthals were thought to be anatomically comparable to Aboriginal Australians, in accord with historical race concepts. As more fossils were discovered in the early 20th century, French palaeontologist Marcellin Boule defined them as a slouching, apelike species; a popular image until the middle of the century. Neanderthal features gradually accreted in European populations over the Middle Pleistocene, driven by natural selection in a cold climate, as well as genetic drift when populations crashed during glacial periods. This culminated in the "classical Neanderthal" anatomy by the Last Interglacial.

The Neanderthal skull is distinctive by namely a rounded supraorbital torus (brow ridge), large orbits (eye sockets) and nose, and an occipital bun at the back of the skull. The jaws and teeth are strong, which may have been a response to habitual heavy loading of the front teeth. The body is typically short and stocky, with an average size of 165 cm (5 ft 5 in) and 78 kg (172 lb) for males, and 155 cm (5 ft 1 in) and 66 kg (146 lb) for females. Short limbs may be an adaptation to the cold climate (Allen's rule) or to improve sprinting efficiency.

The brain is large, averaging 1,640 cc (100 cu in) in males and 1,460 cc (89 cu in) in females, larger than the average of any living population. The Neanderthal brain was organised much differently than the modern human brain, especially in regions related to cognition and language, which may be implicated in Neanderthal behaviour and the poorer evidence of material culture compared to Cro-Magnons.

Neanderthals may have developed mesopic vision in low-light conditions, and a stronger respiratory system to fuel a comparatively faster metabolism. It is unclear if Neanderthals could produce speech at the same level as modern humans. Neanderthal skin and hair colour may have ranged from dark to light. Red hair seems to have been a rare trait. Neanderthals may have had a faster growth rate than modern humans. Neanderthals suffered extensively from traumatic injury and major physical trauma, possibly as a consequence of risky hunting strategies and animal attacks. They also maintained a low population and genetic diversity, leading to inbreeding depression.

When the first Neanderthal fossil, Neanderthal 1 (a skullcap), was discovered in 1856, initial reactions characterised it as belonging to a brutish, savage race of man. The low braincase and flattened forehead were often cited as evidence of its primitiveness, as classic markers of the lower races, in accord with historical race concepts. Consequently, the Neanderthal skull was often anatomically compared to most notably Aboriginal Australians, who were considered the most primitive race alive. German pathologist Rudolf Virchow 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 described him as a hairy, slouching, ape-like creature; a reconstruction which would endure until around the middle of the 20th century. By this point, several fossils from across the Old World were classified as "Neanderthaloid", a type of transitional fossil in human evolution halfway between Homo erectus and Homo sapiens. The modern anatomical definition of "Neanderthal" was formalised with the popularisation of cladistics in the late 1970s.

The Neanderthal skull is distinguished namely by a flat and broad skullcap, rounded supraorbital torus (the brow ridges), high orbits (eye sockets), a broad nose, mid-facial prognathism (the face projects far from the base of the skull), an "en bombe" (bomb-like) skull shape when viewed from the back, and an occipital bun at the back of the skull. The occipital bun, or "chignon", is within the range of variation for modern humans who have it. In Neanderthals, it is caused by the high and anterior (more forward) positions of the cranial base and temporal bones, in combination with a flatter skullcap.

In Neanderthals, the zygomatic arches (cheekbones) are positioned in a rearward location relative to modern humans, while the maxilla (upper jaw) and nasal bones are positioned in a more forward direction. The front (anterior) teeth are characterised by their large size, strong and bulging tooth roots, and tooth wearing (especially on the lower front teeth). The upper incisors are shovel-shaped. There is a large retromolar space (gap behind the molars). Especially in Europe, Neanderthals had a high frequency of taurodontism, a condition where the molars are bulkier due to an enlarged pulp (tooth core). In modern populations the trait has an incidence rate of about 5%, but a weaker form of taurodontism (hypotaurodontism) is somewhat common in some European H. heidelbergensis populations, especially at the Sima de los Huesos site.