The tiger, a large felid belonging to the mammalian order Carnivora, is characterized by its light yellow or brownish-yellow fur with black stripes, a rounded head with short ears,

black markings on the back of the ears with a prominent white spot in the center, robust and powerful limbs, and a thick, elongated tail with black rings and a black tip.

However, not all species with "tigers" in their name are tigers. For example, the saber-toothed tiger commonly seen in documentaries refers to a group of fossil felids known as the Machairodontinae subfamily, characterized by well-developed saber-like canine teeth. Additionally, species like the Yangtze tiger, despite their name, are not true tigers and may have closer relationships with lions instead.

On October 25, 2018, a study utilizing population genomics methods depicted the most comprehensive evolutionary history of tigers to date, unraveling the genetic basis of their natural selection and ecological adaptation. It confirmed the classification of extant tigers into six subspecies, including the Bengal tiger and the Malayan tiger, resolving decades-long disputes over tiger subspecies delineation and laying a scientific foundation for global tiger conservation strategies.

The study analyzed 32 samples with known geographic origins, conducting whole-genome sequencing with an average coverage depth of tenfold, identifying approximately 1.8 million polymorphic loci.

Results indicated that tigers as a species have a history spanning 2 to 3 million years, but modern tigers exhibit low levels of genomic polymorphism, with a common ancestor dating back only around 110,000 years ago, suggesting at least one population bottleneck during the Late Pleistocene.

Nonetheless, phylogenetic and population genetic analyses revealed significant genetic differentiation among regional tiger populations, indicating historical isolation and limited gene flow. Consequently, the study advocated for the recognition of six distinct subspecies of extant wild tigers: the Sumatran tiger, Bengal tiger, Indochinese tiger, Malayan tiger, Siberian tiger, and South China tiger.

Factors such as Late Pleistocene climatic fluctuations, the eruption of the Mount Toba supervolcano on Sumatra, and dynamic ice-age dynamics likely contributed to repeated population divergences and the formation of the current geographic distribution patterns of tiger subspecies.

Tiger populations in different regions face varying natural selection pressures due to their respective ecological environments, potentially leading to further genetic differentiation. Through whole-genome scans, this study identified several genomic regions possibly associated with the tiger's adaptive evolution. Particularly, the ADH7 gene and its adjacent segments, associated with body size development, exhibited strong positive selection signals in the Sumatran tiger population.

Compared to other subspecies, the Sumatran tiger is smaller in size, likely due to the scarcity of large ungulate prey species on Sumatra and the smaller size of available prey such as muntjac. This finding provides the first insights into the genetic mechanisms underlying intraspecific adaptive evolution in tigers.

This study is poised to profoundly reshape the subspecies classification and conservation landscape of tigers worldwide, influencing the formulation of conservation strategies for both wild and captive tigers. It has garnered attention and coverage from major international news outlets such as the New York Times upon its publication.