The genetic component of life expectancy
"From the perspective of a biologist and a medic, ultimately, the life expectancy of a person
it is determined by a triad: type, heredity, lifestyle and living conditions." Academician V.V. Frolkis
Genetic regulation of individual development (ontogenesis) is associated with the sequential implementation of various genetic programs in time, ending with the death of an individual.
At the same time, the final stages of ontogenesis in a number of organisms are not always preceded by prolonged aging. Such examples are known both in the plant kingdom and in the animal kingdom: pink salmon die after spawning; bee drones die immediately after fertilization of females; mayflies generally live one day and do not even eat; bamboo can reproduce vegetatively for up to 20 years, but, starting sexual reproduction, dries up within a few days after seed maturation; mexican agave blooms in the tenth year and dries up after the appearance of the fruit. These data suggest the possible existence of genetic programs operating at the late stages of ontogenesis preceding death. However, in most organisms, the final stages of ontogenesis are associated with the aging process.
Life expectancy is a fairly stable species trait. At the same time, even very close species can differ significantly in life expectancy. For example, the degree of homology of the human and chimpanzee genomes is 98%, but this does not equalize their life expectancy. If a person can live up to 120 years, then the age of a chimpanzee does not reach 60 years. Life expectancy is one of the quantitative characteristics of the species. The phenotype - the value of the life span of an individual of a given species – is the result of the manifestation of the genotype in certain environmental conditions. Accordingly, the life expectancy of an individual of a species, like any other species trait, is determined by the norm of the reaction of its genotype, i.e., the limits of the modification variability of the organism (the limits of variation of the trait). The range of this variability is the difference between the shortest lifespan (the lower bound of the reaction rate) and the longest lifespan (the upper bound of the reaction rate).
A real assessment of this range is rather difficult, since "it is not known which limits of the reaction norm in relation to life expectancy can be considered as variants of the norm, and which are deviations from it" (B.A. Kaurov). Nevertheless, since the value of life expectancy is a species trait, then within the normal response of this trait, an individual should have time to develop all its main species characteristics and bring its offspring to its independent existence. For a person, this lower limit can be taken for 40-45 years. Accordingly, beyond the upper species limit there will be the maximum possible duration of an individual of the species in its natural habitat without artificially changing its genotype, and it corresponds to approximately 110-120 years.
The existence of a correlation between the longevity of offspring and parents is indicated by the presence of a certain genetic conditioning of the rate of aging. For example, the descendants of centenarians were four times more likely to live 85 years or more than the children of those who died before the age of 73. It is possible to assess the heritability of a person's longevity by observing members of the same family. At the same time, using the heritability coefficient, it is possible to assess the impact of people's lifestyle on the amount of population variability. A study of longevity in twins has shown that the heritability of life expectancy in humans does not exceed 50%. A number of authors have shown that the heritability coefficient of life expectancy increases with age. So, if for the age group of 6-28 years it is no more than 0.06, for people older than 60 years, the coefficient value increases to 0.34. Such an increase in the heritability coefficient occurs, apparently, because during the aging process, genotypes are selected for survival. At the same time, the greater the age to which individuals live, the narrower the spectrum of the corresponding genotypes, i.e. with age there is a kind of concentration of certain genotypes.
The conducted studies indicate that the range of population variability of life expectancy in humans, due to environmental changes, is quite high, despite its decrease with age. This suggests that the reserves for increasing the number of people with a longer life expectancy have not been exhausted. In order to reach the upper limit of the individual norm of life expectancy response, optimal environmental impact on the body is necessary from the early stages of ontogenesis, starting with embryonic development.
Nevertheless, due to the extreme genotypic diversity of the human population, the main difficulty arises: which lifestyle is the best in terms of longevity of an individual, and whether it will adversely affect other indicators of the vital activity of the organism. It is necessary to think about this at the moment, when, as the methodology of genetic engineering improves, attempts to interfere with the human genotype in order to increase his life expectancy will become more active.