Large bear native to Eurasia and North America
 ;templatestyles src="Template:Taxobox/core/styles.css" / ;
The brown bear (Ursus arctos) is a large bear native to Eurasia and North America. Of the land carnivorans, it is rivaled in size only by its closest relative, the polar bear, which is much less variable in size and slightly bigger on average. The brown bear is a sexually dimorphic species, as adult males are larger and more compactly built than females. The fur ranges in color from cream to reddish to dark brown. It has evolved large hump muscles, unique among bears, and paws up to wide and long, to effectively dig through dirt. Its teeth are similar to those of other bears and reflect its dietary plasticity.
Throughout the brown bear's range, it inhabits mainly forested habitats in elevations of up to . It is omnivorous, and consumes a variety of plant and animal species. Contrary to popular belief, the brown bear derives 90% of its diet from plants. When hunting, it will target animals as small as insects and rodents to those as large as moose or muskoxen. In parts of coastal Alaska, brown bears predominantly feed on spawning salmon that come near shore to lay their eggs. For most of the year, it is a usually solitary animal that associates only when mating or raising cubs. Females give birth to an average of one to three cubs that remain with their mother for 1.5 to 4.5 years. It is a long-lived animal, with an average lifespan of 25 years in the wild. Relative to its body size, the brown bear has an exceptionally large brain. This large brain allows for high cognitive abilities, such as tool use. Attacks on humans, though widely reported, are generally rare.
While the brown bear's range has shrunk, and it has faced local extinctions across its wide range, it remains listed as a least concern species by the International Union for Conservation of Nature (IUCN) with a total estimated population in 2017 of 110,000. Populations that were hunted to extinction in the 19th and 20th centuries are the Atlas bear of North Africa and the Californian, Ungavan and Mexican populations of the grizzly bear of North America. Many of the populations in the southern parts of Eurasia are highly endangered as well. One of the smaller-bodied forms, the Himalayan brown bear, is critically endangered: it occupies only 2% of its former range and is threatened by uncontrolled poaching for its body parts. The Marsican brown bear of central Italy is one of several currently isolated populations of the Eurasian brown bear and is believed to have a population of only about 50 bears.
The brown bear is considered to be one of the most popular of the world's charismatic megafauna. It has been kept in zoos since ancient times, and has been tamed and trained to perform in circuses and other acts. For thousands of years, the brown bear has had a role in human culture, and is often featured in literature, art, folklore, and mythology.
Etymology.
The brown bear is sometimes referred to as the , from Middle English. This name originated in the fable "History of Reynard the Fox", translated by William Caxton, from the Middle Dutch word or , meaning "brown". In the mid-19th-century United States, the brown bear was given the nicknames "Old Ephraim" and "Moccasin Joe".
The scientific name of the brown bear, "Ursus arctos", comes from the Latin , meaning "bear", and the Greek /, also meaning "bear".
Evolution and taxonomy.
Taxonomy and subspecies.
Carl Linnaeus scientifically described the species under the name "Ursus arctos" in the 1758 edition of "Systema Naturae". Brown bear taxonomy and subspecies classification has been described as "formidable and confusing", with few authorities listing the same set of subspecies. There are hundreds of obsolete brown-bear subspecies. As many as 90 subspecies have been proposed. A 2008 DNA analysis identified as few as five main clades, which comprise all extant brown bear species, while a 2017 phylogenetic study revealed nine clades, including one representing polar bears. As of 2005[ [update]], 15 extant, or recently extinct, subspecies were recognized by the general scientific community.
DNA analysis shows that, apart from recent, human-caused population fragmentation, brown bears in North America are generally part of a single interconnected population system, with the exception of the population (or subspecies) in the Kodiak Archipelago, which has probably been isolated since the end of the last Ice Age. These data demonstrate that "U. a. gyas", "U. a. horribilis", "U. a. sitkensis", and "U. a. stikeenensis" are not distinct or cohesive groups, and would more accurately be described as ecotypes. For example, brown bears in any particular region of the Alaska coast are more closely related to adjacent grizzly bears than to distant populations of brown bears.
The history of the bears of the Alexander Archipelago is unusual in that these island populations carry polar bear DNA, presumably originating from a population of polar bears that was left behind at the end of the Pleistocene, but have since been connected with adjacent mainland populations through the movement of males, to the point where their nuclear genomes indicate more than 90% brown bear ancestry. MtDNA analysis revealed that brown bears are apparently divided into five different clades, some of which coexist or co-occur in different regions.
Evolution.
The brown bear is one of eight extant species in the bear family Ursidae and of six extant species in the subfamily Ursinae. 
The brown bear is thought to have evolved from the Etruscan bear ("Ursus etruscus") in Asia during the early Pliocene. A genetic analysis indicated that the brown bear lineage diverged from the cave bear species-complex approximately 1.2–1.4 million years ago, but did not clarify if "U. savini" persisted as a paraspecies for the brown bear before perishing. The oldest brown bear fossils occur in Asia from about 500,000 to 300,000 years ago. They entered Europe 250,000 years ago and North Africa shortly after. Brown bear remains from the Pleistocene period are common in the British Isles, where, amongst other factors, they may have contributed to the extinction of cave bears ("Ursus spelaeus").
Brown bears first emigrated to North America from Eurasia via Beringia during the Illinoian Glaciation. Genetic evidence suggests that several brown bear populations migrated into North America, aligning with the glacial cycles of the Pleistocene. The founding population of most North American brown bears arrived first, with the genetic lineage developing around ~177,000 BP. Genetic divergences suggest that brown bears first migrated south during MIS-5 (~92,000–83,000 BP), upon the opening of the ice-free corridor, After a local extinction in Beringia ~33,000 BP, two new but closely related lineages repopulated Alaska and northern Canada from Eurasia after the Last Glacial Maximum ( ;25,000 BP).
Brown-bear fossils discovered in Ontario, Ohio, Kentucky, and Labrador show that the species occurred farther east than indicated in historic records. In North America, two types of the subspecies "Ursus arctos horribilis" are generally recognized—the coastal brown bear and the inland grizzly bear.
Hybrids.
A grizzly–polar bear hybrid is a rare ursid hybrid resulting from a crossbreeding of a brown bear with a polar bear. It has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid was confirmed by testing the DNA of a strange-looking bear that had been shot in the Canadian Arctic, and seven more hybrids have since been confirmed in the same region, all descended from a single female polar bear. Previously, the hybrid had been produced in zoos and was considered a "cryptid" (a hypothesized animal for which there is no scientific proof of existence in the wild). Analyses of the genomes of bears have shown that introgression between species was widespread during the evolution of the genus "Ursus", including the introgression of polar-bear DNA introduced to brown bears during the Pleistocene.
Description.
Size.
The brown bear is the most variable in size of modern bears. The typical size depends upon which population it is from, as most accepted subtypes vary widely in size. This is in part due to sexual dimorphism, as male brown bears average at least 30% larger than females in most subtypes. Individual bears vary in size seasonally, weighing the least in spring due to lack of foraging during hibernation, and the most in late fall, after a period of hyperphagia to put on additional weight to prepare for hibernation.
Brown bears generally weigh , with males outweighing females. They have a head-and-body length of and a shoulder height of . The tail is relatively short, as in all bears, ranging from in length. The smallest brown bears, females during spring among barren-ground populations, can weigh so little as to roughly match the body mass of males of the smallest living bear species, the sun bear ("Helarctos malayanus"), while the largest coastal populations attain sizes broadly similar to those of the largest living bear species, the polar bear. Brown bears of the interior are generally smaller, being around the same weight as an average lion, at an average of in males and in females, whereas adults of the coastal populations weigh about twice as much. The average weight of adult male bears, from 19 populations, was found to be while adult females from 24 populations were found to average .
Coloration.
Brown bears are often not fully brown. They have long, thick fur, with a moderately elongated mane at the back of the neck which varies somewhat across bear types. In India, brown bears can be reddish with silver-tipped hairs, while in China, brown bears are bicolored, with a yellowish-brown or whitish collar across the neck, chest, and shoulders. Even within well-defined subspecies, individuals may show highly variable hues of brown. North American grizzlies can be from dark brown (almost black) to cream (almost white) or yellowish-brown and often have darker-colored legs. The common name "grizzly" stems from their typical coloration, with the hairs on their back usually being brownish-black at the base and whitish-cream at the tips, giving them their distinctive "grizzled" color. Apart from the cinnamon subspecies of the American black bear ("U. americanus cinnamonum"), the brown bear is the only modern bear species to typically appear truly brown. The brown bear's winter fur is very thick and long, especially in northern subspecies, and can reach at the withers. The winter hairs are thin, yet rough to the touch. The summer fur is much shorter and sparser, with its length and density varying among geographic ranges.
Cranial morphology and size.
Adults have massive, heavily built, concave skulls, which are large in proportion to the body. The projections of the skull are well developed. Skull lengths of Russian brown bears tend to be for males, and for females. Brown bears have the broadest skull of any extant ursine bear. The width of the zygomatic arches in males is , and in females. Brown bears have strong jaws: the incisors and canine teeth are large, with the lower canines being strongly curved. The first three molars of the upper jaw are underdeveloped and single-crowned with one root. The second upper molar is smaller than the others, and is usually absent in adults. It is usually lost at an early age, leaving no trace of its alveolus in the jaw. The first three molars of the lower jaw are very weak, and are often lost at an early age. The teeth of brown bears reflect their dietary plasticity and are broadly similar to those of other bears. They are reliably larger than teeth of American black bears, but average smaller in molar length than those of polar bears.
Claws and feet.
Brown bears have large, curved claws, with the front ones being larger than the back. They may reach and measure along the curve. Compared with the American black bear ("Ursus americanus"), the brown bear has longer and stronger claws, with a blunt curve. Due to their claw structure, in addition to their excessive weight, adult brown bears are not able to climb trees as well as black bears. In rare cases adult female brown bears have been seen scaling trees. The claws of a polar bear are quite different, being notably shorter but broader with a strong curve and sharper point. The species has large paws; the rear feet measure long, while the forefeet tend to measure 40% less. Brown bears are the only extant bears with a hump at the top of their