"Because penguins are fish eaters, the absence of the umami taste is particularly perplexing," said study leader Jianzhi "George" Zhang, professor in the department of ecology and evolutionary biology. Penguins typically eat fish, so one would assume that they would possess the umami receptor genes; however, they do not. Zhang stated that these findings are surprising and puzzling, with no clear explanation. He believes that the sensory changes may be linked to ancient climate cooling events in Antarctica where penguins originated. The leading theory is that the genes were lost due to cold Antarctic temperatures affecting taste perception. Previous genetic studies have shown that birds do not have the sweet taste receptor gene. In this study, Zhang and colleagues examined Adelie and emperor penguins, as well as other closely related bird species, and found that penguins lack functional genes for sweet, umami, and bitter tastes. The umami and bitter taste receptor genes in Adelie and emperor penguins have become "pseudogenes," meaning they resemble a gene but cannot encode proteins. Non-penguin birds, on the other hand, have genes for umami and bitter tastes but lack receptors for sweet taste. The researchers concluded that penguins lost umami and bitter tastes in their common ancestor, which likely occurred during a 37-million-year period that included dramatic climate cooling in Antarctica. The study will be published in the journal Current Biology.