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
It is thought the Eurasian brown bears which colonized America were tundra-adapted (as many grizzlies are today in North America) and the species is sometimes found around sub-Arctic ice fields. This is indicated by brown bears in the Chukotka Peninsula on the Asian side of the Bering Strait, which are the only Asian brown bears to live year-round in lowland tundra like their North American cousins. Genetics relay that two separate radiations led to today's North American brown bears, one a coastal form that led to the Kodiak bear (from "U. a. beringianus" or a common ancestor) and one an interior form that led to the grizzly bear (from "U. a. lasiotus" or a common ancestor). In Arctic areas, the potential habitat of the brown bear is increasing. The warming of that region has allowed the species to move farther north into what was once exclusively the domain of the polar bear (potentially another offshoot of a radiation of coastal brown bears). In non-Arctic areas, habitat loss is blamed as the leading cause of endangerment, followed by hunting.