Theory of disposable soma

The theory of disposable soma , sometimes the theory of expendable soma ^[1] ( English Disposable soma theory ) is an evolutionary - physiological model that attempts to explain the evolutionary origin of the aging process. The theory was proposed in 1977 by Thomas Kirkwood , then an employee of the British National Institute for Biological Standards and Control, in his review article ^[2] . This theory asks how the body should manage its own resources (in the first version of the theory, it was only energy) between the support and repair of soma and other functions necessary for survival. The need for a compromise in the use of these resources arises due to the limited resources and the need to choose the best way to use them.

This theory was proposed in an attempt to create an evolutionary structure for understanding the existence and variations in the aging process that is universal for all living organisms ^{[2] [3]} . She suggests that individuals should invest the livelihood and reparation of their soma in accordance with their expectations regarding future life expectancy and breeding opportunities. However, the individual's expectations of future life support prospects and the probability of reproduction are not constant. For different species, and sometimes even for different individuals within the boundaries of the species, therefore, it is necessary to maintain your soma for different periods of time. The theory of a one-time catfish provides that species and populations that on average have a small number of external threats and low reproduction rates should invest a lot more in protecting their soma than species and populations that expect a short lifespan and rapid reproduction. When organisms get into protected conditions and are exempt from natural selection , the differences in the repair and support of the catfish manifest as interspecific and interpopulation differences in the rate of aging and maximum longevity .

The theory is supported by the result of observation of wild animal populations in nature, which shows that the number and activity of predators affect the survival strategy of a population. For example, studies of guppy populations have shown the evolution of life expectancy, which manifests itself very quickly in response to changes in mortality ^[4] . Representatives of the guppy population, which grows under conditions of increased mortality, are smaller in size, grow faster, reproduce at an earlier age, and allocate more resources for reproduction than guppies who live in conditions of low external mortality ^[5] . In addition, it was suggested that one of the reasons why birds and bats live longer than land animals of similar size is that, thanks to the ability to fly, they were freed from much of the evolutionary pressure from predators experienced by land animals. ^[6] . Another study, which confirmed some of the fundamentals of the theory, was carried out on two populations of virgin possums ^{[7] [8]} . One population of possums, found on the island of Sapelo ( Georgia ) does not have natural land predators, the other, found in the mainland of the state, is pursued by pumas , foxes and red-haired lynxes . As a result, it was found that the island population gives birth to fewer cubs than the continental group, and generally survives until the second breeding season, receiving a second opportunity for breeding. Representatives of this group are smaller in size, have a 25% longer average life expectancy and 50% longer maximum life expectancy than the continental group.

It is important to note that, since the theory of one-time soma considers only the evolutionary aspects of aging, the relationship between consumption, reproduction and aging is considered in terms of the final result, and not specific mechanisms. If an individual animal has the ability to breed, it cannot expect biological immortality, since it only needs to maintain its som to such a level that the average individual within the population can survive for the time required to obtain the required number of offspring. However, the lack of opportunities for reproduction can have a positive effect on aging and longevity ^{[9] [10]} . This does not mean that there is a link between the premonition of life support, reproduction, support for the catfish and longevity, the theory of one-time catfish provides only a compromise between support for the catfish and reproduction, mediating in which is the process of resource allocation. The theory suggests two reasons for changing organisms. First, an increase in the expectation of mortality in an adult state should lead to a decrease in soma support. If the body does not expect to live long, it has less need to protect itself. Secondly, an increase in the expectation of the reproduction rate should lead to a decrease in the support of the catfish, since individuals provide for the shortage of resources necessary for the reproduction.

The theory of a one-time soma does not postulate any specific support mechanisms for soma, and therefore is compatible with most mechanistic models of aging, such as the accumulation of somatic mutations, altered proteins, mitochondrial theory, free-radical theory, etc. ^[11] . In addition, the species that have the lowest mortality from external causes and low reproduction rates also have the best protection against oxidative stress and, as a result, mutations and damage to proteins ^{[12] [13]} . For example, DNA repair (repair) is much worse in rodents than in primates ^[14] , and somatic cells of mice are much more susceptible to oxidative stress caused by chemical methods than cells of long-lived mammals ^[15] . Kidney epithelial cells of relatively durable birds are also more resistant to chemical and radiation damage than the corresponding cells of mice ^[16] .

In general, the theory of a one-time soma provides a useful evolutionary structure for understanding the aging process. A large number of indirect evidence supports this theory, but detailed experimental studies are still lacking.