Study leader Jianzhi "George" Zhang, a professor in the department of ecology and evolutionary biology, expressed confusion regarding the loss of the umami taste in penguins, as they are fish eaters. Despite the expectation that penguins would possess umami receptor genes, they do not. Zhang believes this sensory change may be linked to ancient climate cooling events in Antarctica, where penguins originated. The study found that all penguin species lack functional genes for sweet, umami, and bitter tastes, with umami and bitter taste receptor genes becoming pseudogenes in Adelie and emperor penguins. Non-penguin birds, on the other hand, have genes for umami and bitter tastes but lack sweet taste receptors. The researchers suggest that the loss of umami and bitter tastes in penguins likely occurred in their common ancestor around 37 million years ago, during periods of dramatic climate cooling in Antarctica. The study will be published in the journal Current Biology.