Riddles of pandas: why predatory bears switched to bamboo

Pandas are so unusual and so different from their closest relatives that they confuse biologists. Despite the fact that Chinese scientists with their international colleagues have been studying pandas for decades, there are still enough questions that cannot be answered. One of them is the strange food specialization of animals. After all, pandas, just like polar bears or grizzlies, belong to the bear family, but at the same time they eat exclusively bamboo. Moreover, not so long ago it became clear that their body is not adapted for such a plant-based diet, since the absorption of bamboo is extremely low.

In the digestive system of pandas, like many other animals, microorganisms live, which are involved in the digestion of incoming food. Each species has its own special composition of microflora, which corresponds to one or another type of food. Herbivorous ungulates will have one composition of microorganisms, while predatory leopards will have a completely different composition. But, as it turned out, pandas do not fit into this rule.

A group of researchers from Shanghai University managed to establish that the composition of the intestinal microflora in large pandas, as well as the enzymes secreted by the body, are not suitable for the full digestion of bamboo leaves and stems. For this reason, of the enormous amount of bamboo that pandas absorb during daylight hours, only about 17% is absorbed by their body. Judging by the composition of microorganisms, bamboo bears should be omnivores or even full-fledged predators, but not strict vegetarians sitting on a mono-diet.

Scientists believe that the ancestors of bamboo bears really were omnivores, as well as brown bears, in the diet of which there is food of both animal and plant origin. But about 2 million years ago, pandas had to become exclusively herbivorous and concentrate on one plant. For this reason, their body has acquired a number of evolutionary adaptations, from the sixth finger on the front paws to the special structure of the stomach, protected from damage by bamboo stems. In addition, bamboo bears, sitting on an extremely low-calorie diet, were able to reduce their metabolism so much that they spend 2 times less energy during the day than their closest relatives with the same mass.

But at the same time, the pandas still have much from their predatory ancestors. For example, the structure of the teeth of these animals betrays recent predators in them, and the features of the digestive system and metabolism allow us to conclude that pandas are halfway to real vegetarians. Most likely, they lost their place in the food chain to more powerful and fit fellow predators. Due to high competition, they had to switch to a bamboo diet and begin to evolve in accordance with it. But this process dragged on for several million years and, apparently, has not yet been completed.