In fact, the gastrointestinal function of vegetarian animals is very strong, and there is no problem in digesting meat. Moreover, there is no strict boundary between the eating habits of most animals in nature (especially between vegetarians and omnivores). Many vegetarian animals, such as cattle, sheep, deer, horses and donkeys, can eat meat, and some people have indeed witnessed them eating meat. Animals such as hippos or reindeer take the initiative to prey (but strictly speaking, their predatory behavior is essentially different. Hippos are so aggressive that they may eat intruders after killing them. Usually, even if they eat meat, it is ready-made; Reindeer will prey on lemmings or young birds to fill their stomachs.

Even carnivores eat plants in some cases. For example, wolves eat fruits when food is scarce, while bears are vegetarians (in fact, bears are closer to omnivores, and some ancient Xiong Ke animals such as cave bears are totally vegetarians in classification. The giant panda is an exception. This guy is a carnivore in classification, but he doesn't like meat because he can't taste it because of genetic mutation. However, similar to the situation of vegetarians eating meat, carnivores are mostly used to supplement substances that are not available or have little content in ordinary food (vegetarians eat meat mainly for salt and protein, while carnivores eat for vitamins), or they have to eat other things to satisfy their hunger because of food shortage. Aside from these two aspects, carnivores will only be vegetarian when they need to treat diseases (looking for plants that can be used as medicine, mainly to help digestion or induce vomiting).

Another point, from the perspective of biological evolution, carnivores also appeared first. One of the important reasons is that plants are indeed more difficult to digest than meat. According to the evolution law from simple to complex, early heterotrophic animals must have preyed on other animals for a living.

Look at humans again. All primates, including humans, are omnivores in essence, not vegetarians. Monkeys have the ability and behavior to prey on other animals from the beginning, just because their constitution does not allow them to make too many predatory actions (too big animals can't catch them, and too small animals don't often meet them). But some very small primates often prey on insects. At the level of apes (orangutans, gorillas, etc.). ), there are more predatory behaviors (because they have a larger range of activities, stronger bodies and better brains than monkeys, so it is easier to catch other animals). But because it is easier to get plant food in their living environment, there is little demand for hunting (but some apes hunt in an organized way). At the level of human beings (including all kinds of apes and extinct human subspecies), due to the increase of their range of activities, they may sometimes not be able to obtain easily picked plant food, and they also need better bodies and brains to compete with new competitors in the new living environment. At this time, the demand for meat will naturally increase (if they want to grow meat, they must have enough protein, which is why vegetarians eat more frequently than carnivores. There are too few protein in plants), and in this case, the more convenient stones and branches may not be easy to find (among other things, have you ever tried to kill mosquitoes or cockroaches in your daily life, but you can't find a convenient guy at the moment? Although the purpose is different, primitive people will encounter similar situations and often encounter them. This is one of the reasons why early humans gradually learned to make tools. With better weapons, it is easier to get bigger prey. The proportion of meat in primitive people's food gradually increased. Therefore, it is definitely not that human beings are vegetarian but want to eat meat, but because they have been omnivores since monkeys, but with evolution, meat is more and more easily obtained by human beings.