Study leader Jianzhi "George" Zhang, a professor in the department of ecology and evolutionary biology, expressed surprise at the lack of umami taste receptors in penguins, given their diet of fish. Zhang suspects that ancient climate cooling events in Antarctica may have caused the loss of these genes in penguins. Penguins, unlike other birds, lack functional genes for sweet, umami, and bitter tastes. This taste loss likely occurred during the 37-million-year span of penguin evolution, which included periods of dramatic climate cooling in Antarctica.