There are many intestinal bacteria in the human body, as many as one trillion. It can be said that there are as many intestinal bacteria as there are cells in our body. Some of these bacteria come from food and the external environment, these are just passers-by in the intestines, and some are "old acquaintances" who have accompanied us since ancient times.

Scientists have found that the history of these old-fashioned intestinal bacteria knowing us can be traced back to the Australopithecus period in southern Africa. About 654.38+00 million years ago, Australopithecus africanus split into two groups. One group evolved into gorillas, some in the other group evolved into humans, and the rest evolved into chimpanzees and bonobos.

The ancestors of these bacteria lived in the intestines of African apes and differentiated with the differentiation of African apes. To some extent, they have evolved with us so far, which is the evolutionary history of our human beings and the evolutionary history of intestinal bacteria.

Similarly, the evolutionary history of apes can also be explored through the intestinal bacteria of apes. In 20 10, scientists drew the genealogy map of intestinal bacteria of apes for the first time, and found that they propagated and evolved simultaneously with their respective "hosts". For example, the intestinal bacteria of three subspecies of African chimpanzees are very similar to each other, and the similarity is higher than that of bonobos.

In this way, with the development and reproduction of human beings, intestinal bacteria are constantly developing and reproducing. Although invisible to the naked eye, they are there and have been with us for thousands of years.

An indispensable companion for human beings.

To some extent, the companionship of intestinal bacteria to human beings is a biological relationship. * * * is a very common phenomenon in nature, and many animals and microorganisms are interrelated. For example, aphids and Brucella provide an essential nutrient for aphids, but aphids themselves cannot get these nutrients from food. Similarly, aphids provide Brucella with nutrients that Brucella itself cannot produce, thus maintaining the survival of bacteria. Aphids and Brucella have a very long history, as early as 250-200 million years ago, when dinosaurs just appeared. Since then, aphids and Brucella have been born together, and they have been born perfectly until today.

In addition, Brucella only lives in aphids, not in other places. They spread from the mother of aphids to eggs and then to reproductive larvae. This kind of life has been passed down from generation to generation. This is a mutually beneficial relationship, so is intestinal bacteria and humans, but compared with aphids and Brucella, the relationship between humans and intestinal bacteria is slightly different.

Some human intestinal bacteria can participate in the metabolism of sugar and protein and promote the absorption of mineral elements such as iron and zinc. Some can synthesize a variety of vitamins, such as vitamin B 1, B2 and other B vitamins, and can also use protein residue to synthesize a variety of amino acids, such as aspartic acid and phenylalanine. Some can attract water and promote fecal excretion; Some can improve the immune function of the body and inhibit the reproduction of pathogenic bacteria in the intestine. Intestinal bacteria play an important role in human life and health and are of great significance to human survival. We need intestinal bacteria.

However, intestinal bacteria may not need humans. They decompose food in human intestines, and they do get the nutrients needed to sustain life, but human intestines are just one of the ecosystems in which they live, not just our intestines. Scientists have collected many fecal samples of apes and humans from all over the world. After analysis, it is found that some human intestinal bacteria can "move", that is, they can be transferred from us to chimpanzees or from chimpanzees to gorillas. For example, bacteria of Chaetomium family often have such transfer. After research, scientists believe that they can be transferred between different species, perhaps because they can produce a hard and cold-resistant spore, so that bacteria can survive outside the intestine. In fact, many intestinal bacteria can produce spores, so scientists speculate that it may be normal for bacteria to "move" back and forth between different living bodies.

Accompanied by humans and intestinal bacteria, both sides benefit, but bacteria can leave the human body and continue to live in other organisms, and once there is no bacteria in the human body to decompose and digest food, the consequences will be unimaginable.

Will the longest companionship end?

These intestinal bacteria have been with us since humans appeared. But today, this situation is quietly changing.

Scientists have found that some bacterial species still live in gorillas, chimpanzees and bonobos, but their species have changed greatly in the human body. For example, in Europe and North America, those bacteria have disappeared in human intestines, but in rural areas of Malawi, an East African country, people still have these bacteria.

This may be due to the great changes in human diet and hygiene in recent hundreds of years, especially in developed areas of the world. In other words, inadvertently, we expelled some intestinal bacteria that have been with us for a long time.

So why did these bacteria disappear? There may be two reasons. On the one hand, antibiotics and other drugs are widely used in modern industrialized society to interfere with and expel some intestinal bacteria. On the other hand, scientists have found from archaeological research that the reduction of bacterial species in human intestines began not only in modern times, but in ancient times. At that time, humans were still in the era of hunting and gathering, and the types of intestinal bacteria were less than those of chimpanzees and gorillas at the same time. There are fewer kinds of intestinal bacteria in modern European and North American urban residents than in ancient times. Maybe when humans started cooking food, the number of bacteria began to decrease. Therefore, scientists speculate that perhaps because of the change of food types, the types of intestinal bacteria have also changed accordingly, and some of them are no longer needed.

If so, do these disappearing bacteria have an impact on human health? Scientists infer that since these bacteria have been with us for a long time, they must play an important role, perhaps helping us digest food, perhaps helping us maintain our immune system and so on. Without them, people may have some health problems. This may explain why the incidence of obesity, inflammation and immune diseases is rising gradually.

However, to some extent, this inference is too hasty. After all, the current research sample only contains four kinds of primate intestinal bacteria. In the follow-up research, scientists will start from two aspects. On the one hand, they will deeply study the whole genome of intestinal bacteria and investigate their development and changes; On the other hand, the research sample is extended to other primates, such as monkeys. At that time, maybe we can get a definite answer.

This article comes from the article 12, 20 16 of The Mystery of Science.