Study leader Jianzhi "George" Zhang, a professor in the department of ecology and evolutionary biology, stated that the absence of umami taste receptors in penguins, who are fish eaters, is particularly perplexing. Despite the expectation that penguins would have these genes due to their diet, they do not. Zhang finds these findings surprising and puzzling, with the leading hypothesis being that the genes were lost due to cold Antarctic temperatures interfering with taste perception. Penguins, as well as other non-penguin bird species, lack functional genes for sweet, umami, and bitter tastes. Penguins likely lost umami and bitter tastes in their common ancestor, while the sweet taste was lost earlier. The study suggests that this taste loss occurred during a 37-million-year span of dramatic climate cooling in Antarctica, when penguins originated from tubenose seabirds around 60 million years ago. The research will be published in the journal Current Biology.