Giant pandas have been called many things: adorable, clumsy, even “evolutionary dead-ends.” It’s not hard to see why some people think they shouldn’t still be around. They’re bears that don’t act like bears. They have a digestive system built for meat, yet they eat almost nothing but bamboo. They spend most of the day sitting, chewing, and resting. It seems like a survival strategy that shouldn’t work. And yet, pandas have managed to hang on.

This is a 100-kilogram (220-pound) bear that eats almost nothing but bamboo. The plant is tough, low in nutrients, and pandas aren’t well equipped to digest it. Their ancestors were carnivorous bears, and they still have the same basic digestive anatomy: a short, simple stomach with no specialized chambers to break down plant fiber. Even their gut microbes resemble those of other meat-eaters.

Because of that, pandas absorb only about 17 percent of the nutrients in the bamboo they eat. The rest passes through undigested. Some adults defecate up to 40 times a day, working like bamboo-processing machines just to keep going.