What process primarily caused the frequency of the white coat gene to increase beyond its natural equilibrium?

Deliberate human selection and artificial breeding in captivity.

The population structure of white tigers today is largely a product of human activity, specifically captive breeding programs that began in the mid-20th century. In the wild, natural selection restricts the gene's frequency because the trait offers no survival advantage. However, when zoos and private breeders began prioritizing the aesthetic rarity of the white coat, the evolutionary pressure inverted entirely. This process, known as artificial selection, actively favored any animal expressing or carrying the recessive gene, leading to intentional breeding decisions that rapidly and artificially inflated the gene's frequency far beyond what environmental constraints would naturally allow.