The five major tastes—sweet, sour, salty, umami (or savory), and bitter—were long assumed to be universal. Each flavor delivers important information to its taster: sweet fruits are generally ripe and safe to eat but bitter foods may be poison and probably shouldn’t be ingested.

Scientists believed that the ability to taste bitterness was crucial to survival. And while that may still be true for most species, being unable to taste bitterness might be an advantage for the snow monkeys of Kii, Japan.

Researchers at Kyoto University conducted genetic tests on more than 600 snow monkeys, or macaques, from around Japan. They found that macaques from the Kii region were far more likely than their compatriots to have lost the gene that enables them to taste bitterness.

And the Kii snow monkeys' loss of the gene over generations means that their inability to taste bitterness was somehow an asset and that monkeys without the gene were more likely to survive and reproduce.

Analyzed by itself, this regional genetic quirk doesn’t make much sense. But the researchers realized that the super-bitter fruit Citrus tachibana had originated in the Kii region. Local monkeys would have been at quite an advantage if they could eat the fruit.

In recent years, scientists have discovered that animals have a range of tasting abilities. Penguins can’t taste bitter, sweet, or umami flavors. Cats are especially sensitive to bitter foods, which may explain their reputation as picky eaters. Frogs have more bitter taste receptors than chickens.

Like so many other things in science and in life, taste is complicated.