From the evolutionary point of view, if the individual life span of any kind of organism is extended indefinitely, it will be unfavorable to the survival of that kind of organism. Monkeys live in the forest and eat fruit for a living. If they all live forever and reproduce at the same time, then in a few generations, all the forests on the earth will be crowded with monkeys, all the fruits will be eaten, and finally everyone will die together. The destruction of forests will destroy other links in the biosphere and cause a series of vicious reactions. This kind of disaster will not happen because all living things have acquired a genetic characteristic in the long-term evolution process and set a limit. Once this limit is reached, organisms will stop growing, aging and dying, thus limiting the life span of each individual to a certain limit. This is the basis that every living thing has a certain natural life span.

Life span is the inherent survival process of all living things in nature. All living things have a certain natural life span, and different species have different life spans, which is determined by genetic factors. Chinese medicine believes that the length of a person's life is determined in the mother's womb. For example, Zhang Jingyue said, "Madam's biological quality was born at the beginning of her life, so she has a certain number. It seems that she is not strong in manpower. The first thing is to get it all. If you can stay together, you will live longer. If you lose it all, you can't be worse if you raise it. " Xu Ling's fetus also said: "When he was born, he already had a definite point. The so-called success is also full of energy. If you don't see it, you can't have it. Attached to qi and blood, slaughtered before qi and blood. It was fixed when it was formed. "

While affirming the existence of objective laws such as age, minute and number, TCM literature also points out the important role of people's subjective initiative. For example, Zhang Jingyue's explanation of "there is a destiny every year" in Ling Shu is: "The so-called heaven can conquer man, and man can conquer heaven". The key to human success lies in keeping healthy.

Recently, some scientists have suggested that people's life span is like the area of a plane triangle, and the factors affecting life span are the three sides of the "life triangle". If a person's life span is compared to a triangle, its bottom is the genetic factors of parents (innate endowments), and the other two sides are the factors of acquired environment. The longer the three sides of a triangle are, the larger its area is. If a person has the genetic factor of longevity given by his parents, then the bottom of his "life triangle" is long; If environmental factors such as food, clothing, housing, transportation, spirit, climate and topography are also beneficial to him, then the two adjacent sides are also long, and his "triangle of life" is large, which means that he will live a long life. On the contrary, the smaller the area of the "life triangle", the shorter the life span.

The foundation of the triangle of life is very important. Humans have long-lived families and short-lived families, and their genetic factors are obvious. For example, among 53 long-lived elderly people in Bama County, China, 365,438+0 people have relatives who live long. Similarly, genetic factors are also obvious in short-lived families. If there is Weiner syndrome, its symptoms are white hair (or shedding), cataract, scleroderma and premature aging. This disease is hereditary and will lead to short life. People will die in three years. Of course, genetic factors are not the only factor in the length of life. The two sides of the triangle-acquired environment, aftercare and other factors also play an important role. In other words, congenital endowment factors are important to people's life span, but if health care is proper, it can also make up for the deficiency of congenital endowment. Therefore, in the process of studying longevity, both congenital factors and acquired factors can not be ignored.