structural:summarization
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 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 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.