"Due to penguins being fish eaters, the absence of the umami taste is particularly perplexing," explained study leader Jianzhi "George" Zhang, a professor in the department of ecology and evolutionary biology. Penguins consume fish, so one would assume they would require the umami receptor genes, yet they do not possess them. Zhang added, "These results are both surprising and puzzling and we do not have a definitive explanation for them. However, we have a few theories." He believes that the changes in sensory perception are linked to ancient climate cooling events in Antarctica, where penguins originated. The primary hypothesis is that the genes were lost due to cold Antarctic temperatures affecting taste perception. Vertebrates typically have five basic tastes: sweet, sour, salty, bitter, and umami. Previous genetic research indicated that the sweet taste receptor gene is not present in the genomes of any birds examined so far. For this study, Zhang and his team closely examined data from Adelie and emperor penguins. They also analyzed tissue samples from other bird species. They discovered that all penguin species lack functional genes for the receptors of sweet, umami, and bitter tastes. In the Adelie and emperor genomes, umami and bitter taste receptor genes have turned into "pseudogenes," which are genetic sequences resembling a gene but unable to encode proteins. On the other hand, non-penguin bird species contain genes for umami and bitter tastes but lack receptors for the sweet taste. The authors concluded that umami and bitter tastes were lost in the common ancestor of all penguins, while the sweet taste was lost earlier. Penguins emerged in Antarctica after splitting from tubenose seabirds around 60 million years ago, with major penguin groups diverging from each other about 23 million years ago. "The loss of taste likely occurred during that 37-million-year period, which included periods of significant climate cooling in Antarctica," Zhang explained. The study will be published in the journal Current Biology.