棕熊
There are many methods used by scientists to define bear species and subspecies, as no one method is always effective. Brown bear taxonomy and subspecies classification has been described as "formidable and confusing," with few authorities listing the same specific set of subspecies. Genetic testing is now perhaps the most important way to scientifically define brown bear relationships and names. Generally, genetic testing uses the word clade rather than species because a genetic test alone cannot define a biological species. Most genetic studies report on how closely related the bears are (or their genetic distance). There are hundreds of obsolete brown bear subspecies, each with its own name, and this can become confusing; Hall (1981) lists 86 different types, and even as many as 90 have been proposed. However, recent DNA analysis has identified as few as five main clades which contain all extant brown bears, while a 2017 phylogenetic study revealed nine clades, including one representing polar bears. , 15 extant or recently extinct subspecies were recognized by the general scientific community.