the Persian word tigra ('pointed or sharp') and the Avestan word tigrhi ('arrow'), perhaps referring to the speed of the tiger's leap, although these words are not known to have any meanings associated with tigers. The generic name Panthera is derived from the Latin word panthera and the Ancient Greek word πάνθηρ ('panther'). Taxonomy In 1758, Carl Linnaeus described the tiger in his work Systema Naturae and gave it the scientific name Felis tigris. In 1929, the British taxonomist Reginald Innes Pocock subordinated the species under the genus Panthera using the scientific name Panthera tigris. Subspecies Following Linnaeus's first descriptions of the species, several tiger specimens were described and proposed as subspecies. The validity of several tiger subspecies was questioned in 1999. Most putative subspecies described in the 19th and 20th centuries were distinguished on basis of fur length and colouration, striping patterns and body size, hence characteristics that vary widely within populations. Morphologically, tigers from different regions vary little, and gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two tiger subspecies as valid, namely P. t. tigris in mainland Asia, and P. t. sondaica in the Greater Sunda Islands. This two-subspecies proposal was reaffirmed in 2015 by a comprehensive analysis of morphological, ecological and molecular traits of all putative tiger subspecies using a combined approach. The authors proposed recognition of only two subspecies, namely P. t. tigris comprising the Bengal, Malayan, Indochinese, South Chinese, Siberian and Caspian tiger populations of continental Asia, and P. t. sondaica comprising the Javan, Bali and Sumatran tiger populations of the Sunda Islands. The continental nominate subspecies P. t. tigris constitutes two clades: a northern clade composed of the Siberian and Caspian tiger populations, and a southern clade composed of all other mainland populations. The authors of the 2015 study noted that this two-subspecies reclassification will affect tiger conservation management. It would make captive breeding programs and future re-wilding of zoo-born tigers easier, as one tiger population could then be used to bolster the population of another population. However, there is the risk that the loss of subspecies uniqueness could negatively impact protection efforts for specific populations. In 2017, the Cat Classification Task Force of the IUCN Cat Specialist Group revised felid taxonomy in accordance with the two-subspecies proposal of the comprehensive 2015 study, and recognized the tiger populations