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.
Kodiak bear
Physiologically, the Kodiak bear is very similar to the other brown bear subspecies, such as the mainland grizzly bear ("Ursus arctos horribilis") and the now-extinct California grizzly bear ("U. a. californicus"†), with the main difference being in size. While there is generally much variation in size between brown bears in different areas, most usually weigh between 115 and 360 kg (254 and 794 lb). The Kodiak bear, on the other hand, commonly reaches sizes of , and has even been known to exceed weights of . Despite this large variation in size, the diet and lifestyle of the Kodiak bear does not differ greatly from that of other brown bears.