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How are mule deer and black-tailed deer related?

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male white-tailed deer — deer Male white-tailed deer (*Odocoileus virginianus*).

Mule deer and black-tailed deer are not separate species; rather, they are the same species, Odocoileus hemionus. The black-tailed deer (O. hemionus columbianus) is specifically classified as a subspecies of the mule deer.12

The relationship between them is rooted in their evolutionary history. The black-tailed deer is considered the more primitive and ancestral form. In contrast, the mule deer is a more recent development that appears to have arisen from the hybridization of female white-tailed deer and male black-tailed deer. This is evidenced by the fact that the mule deer’s mitochondrial DNA, which is inherited maternally, is closely related to that of the white-tailed deer rather than the ancestral black-tailed deer.1

While they share the same species, they occupy different ranges: the mule deer is found across western North America, while the black-tailed deer is primarily found along the Pacific coast from Alaska to northern California.1