ON THE NATURE OF THE AGING PROCESS

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Abstract
It is assumed that among the 15,000 genes, there are perhaps 3000 genes which are important for the functioning of the somatic cells of the adult. These are designated as "vegetative genes" and a mutant form of such a gene is called a "fault." In the course of aging, a somatic cell remains functional as long as, out of each pair of homologous vegetative genes, at least 1 of the 2 genes is competent and active, and the cell ceases to be functional when both genes are out of action. Accordingly, when a chromosome suffers an "aging hit," the cell will cease to be functional if the homologous chromosome has either previously suffered an aging hit or if it carries a fault. According to the author''s theory, the elementary step in the process of aging is an aging hit which "destroys" a chromosome of the somatic cell, in the sense that it renders all genes carried by that chromosome inactive. The aging hits are random events, and the probability that a chromosome of a somatic cell suffers such a hit per unit time remains constant throughout life. The rate at which chromosomes of a somatic cell suffer such hits is a characteristic of the species and does not vary appreciably from individual to individual. As a result of an aging process of this nature, the number of the somatic cells of an individual organism which have "survived" up to a given age decreases with age at an accelerating rate. The theory postulates that when f, the surviving fraction of the somatic cells of an individual approaches a certain critical value f then the probability that that individual may die within a period of 1 year will come close to 1. On this basis the theory establishes a relationship between the surviving fraction of the somatic cells and the age of death of the individual. Because the young mammalian organism may be assumed to have a large functional reserve, it may be assumed that the surviving fraction of the somatic cells of an individual may fall substantially before the organism loses its capacity to live, perhaps to a value somewhere between 1/3 and 1/12. According to the views adopted here, the main reason why some adults live shorter lives and others live longer is the difference in the number of faults they have inherited. One of the basic results of the theory is that an individual whose genetic make-up contains 1 fault more than another individual has a life expectancy which is shorter by r, the basic time interval of the aging process.

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