Pandas Evolved to be Lazy with Their Diet of Bamboo

Why are giant pandas able to survive only on bamboo? Other bears have to rely on protein sources, while pandas stick to a vegetarian diet. Now, scientists have discovered that pandas manage this diet because they essentially evolved to be extremely lazy.

The researchers actually followed five captive and three wild giant pandas for about a year. They used GPS trackers and also analyzed the pandas' poop, looking for specific chemicals. This revealed the amount of energy that the pandas spent each day. Surprisingly, though, the pandas only seemed to expend about 38 percent of the energy that an animal with the same body mass would require.

"Pandas save a lot of energy by being frugal with the energy they spend on physical activity," said John Speakman, one of the study's lead authors, in an interview with BBC News. "We found that their low metabolism is correlated with very low levels of thyroid hormones, which was linked to a genetic mutation in the thyroid synthesis pathway that is unique to the panda."

The researchers also pointed out that the size of the panda's brain, liver and kidney is relatively small compared to other bears. This could contribute to the panda's low energy demands.

In fact, the metabolism of the panda is equal to that of the three-toed sloth and slower than that of the koala. The only known mammals to have a lower daily energy usage than the giant panda are the Australian rock rat and the golden mole.

These findings reveal exactly how pandas manage to function without high-energy foods. More specifically, it reveals that, in fact, these bears essentially evolved to be lazy.

The findings are published in the journal Science.

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