However, the physical characteristics of herbivores usually help them to eat hard, fibrous plant substances, because the digestive system of herbivores contains bacteria that decompose enzymes needed for cellulose. Once these celluloses are decomposed, protein, sugar and fat stored in plant cells can be obtained and converted into body muscles.
In addition, most herbivores have wide molars, which can help them grind leaves and grass. Animals like cattle also have ruminant system, and it is precisely because of the existence of ruminant system that cattle can decompose plant cellulose more comprehensively and thoroughly.
In order to digest plant matter, ruminants have more than one stomach cavity, but four. When ruminants chew and swallow grass, leaves and other substances, they will first enter the first cavity of the stomach, stay there and soften. At this time, special bacteria will break down food. When the food is soft enough, the animal will chew the food again, decompose various substances in the plant again, and then the animal will swallow the ruminant again and enter the second stomach cavity.
The chemicals in the second gastric cavity further digest plant substances and then enter the third gastric cavity circulation. After the first three steps, the digested food will enter the fourth stomach cavity, which is equivalent to the human stomach. The process of rumination can be simply understood as that a food is digested four times, and the process is like a fermentation chamber. In addition to treating plant cell walls, there will be a fermentation process to absorb food nutrients to the maximum extent.
In addition to the ruminant system, the intestines of cattle are much longer than those of humans. A mature cow has a small intestine 45 meters long and a total capacity of nearly 70 liters. The digestive products entering the small intestine are mixed with the secretions of pancreas and liver, so that the pH value is increased from 2.5 to 7-8 to ensure the normal work of the enzyme. In addition, there are many "finger-like" protrusions called villi on the wall of cattle intestine, which increase the intestinal surface area and help to absorb nutrients.
However, eating grass is not only time consuming, but also difficult to digest. Many herbivores depend on grass for most of their food, but grass does not contain protein like meat, so herbivores must eat grass for most of the day to get enough protein and other nutrients. For example, besides cattle, elephants need to eat about 130 kg (300 kg) of food every day. It takes a long time to eat so many leaves and grass, so elephants sometimes eat 18 hours a day, while circus elephants always look skinny because they don't have enough time to eat.
Finally, biological evolution is fair, and human beings can have developed muscles themselves. For example, when our ancestors lived in the jungle, their limbs were muscular because they had to run and hunt, run to avoid wild animals and exercise for a long time. However, after human beings stand at the top of the food chain with their clever brains, their exercise level is weakened and they do more lying, lying and waiting. Therefore, today's human beings usually look potbellied and have low muscle level. Unless you love sports and fitness, you will gain weight.