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You’d think that if your maker sentenced you to eat raw fish—forever—you’d at least be able to taste it. Pity the poor penguin, then: According to a new study published Monday in the journal Current Biology, penguins, unlike other birds, can’t perceive bitterness or even umami, the “fleshy” flavor associated with meat and fish.

Evolutionary geneticist Jianzhi “George” Zhang and his team at the University of Michigan analyzed publicly available genetic data, plus genetic data gleaned from tissue samples at the University of Michigan Museum of Zoology, from five penguin species—Adelie, Emperor, Chinstrap, Rockhopper, and King. They compared the five genomes to those of 22 non-penguin bird species. They found that all five types of penguin lacked functional genes for recognizing sweet, umami, and bitter tastes, leaving just salty and sour to work with. To penguins, the whole world has the flavor profile of a jar of pickles. By contrast, the 22 other species—including tubenose seabirds, penguins’ closest living relatives—possessed the genes for umami and bitter tastes. (Except for hummingbirds, birds cannot sense sweetness.)

Zhang was surprised by these birds’ simple palettes, but especially by their inability to taste umami, a savory, meaty “fifth” taste recognized by scientists and foodies alike as distinct from the four others. It’s found in mushrooms, tomatoes, beef, pork, and fish, which constitute most if not all of a penguin’s diet. “The umami taste would presumably be helpful for sensing a fish’s good taste,” Zhang told ���Ϲ���.

The going hypothesis, says Zhang, is that penguins lost a key bitter and umami taste receptor, called Trpm5, during a particularly frosty period in Antarctica some 60 million to 23 million years ago. Scientists believe that Trpm5 is sensitive to cold temperatures; over time, the frigid climate caused mutations to accumulate in the gene, degrading the ability to savor fleshy flavors. And since the lack of taste receptors seems to be uniform across penguin species, the gene must have been lost by a common penguin ancestor, the study says.

The genetic analysis is just the first step. To confirm the findings, scientists will have to run some behavioral tests to gauge the birds’ ability to distinguish tastes. Even if their tongues do have limited processing power, the birds don’t seem to mind much—a typical Emperor Penguin scarfs down nearly 10lbs. of fish a day.