Asian black bear
Biologically and morphologically, Asiatic black bears represent the beginning of the arboreal specializations attained by sloth bears and sun bears. Asiatic black bears have karyotypes nearly identical to those of the five other ursine bears, and, as is typical in the genus, they have 74 chromosomes. From an evolutionary perspective, Asiatic black bears are the least changed of Old World bears, with certain scientists arguing that it is likely that all other lineages of ursine bear stem from this species. Scientists have proposed that Asiatic black bears are either a surviving, albeit modified, form of "Ursus etruscus", specifically the early, small variety of the Middle Villafranchian (Upper Pliocene to Lower Pleistocene) or a larger form of "Ursus minimus", an extinct species that arose 4,000,000 years ago. With the exception of the age of the bones, it is often difficult to distinguish the remains of "Ursus minimus" with those of modern Asiatic black bears.
Brown bear
Brown bears are thought to have evolved from "Ursus etruscus" in Asia. The brown bear, per Kurten (1976), has been stated as "clearly derived from the Asian population of "Ursus savini" about 800,000 years ago; spread into Europe, to the New World." 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 fossils positively identified as from this species occur in China from about 0.5 million years ago. Brown bears entered Europe about 250,000 years ago and North Africa shortly after. Brown bear remains from the Pleistocene period are common in the British Isles, where it is thought they might have outcompeted giant cave bears ("Ursus spelaeus"). The species entered Alaska 100,000 years ago, though they did not move south until 13,000 years ago. It is speculated that brown bears were unable to migrate south until the extinction of the much larger giant short-faced bear ("Arctodus simus").