The purpose of our life is the well–being of our microflora?
The optimal age of death was determined by human microbes
Evolution has changed the microflora (the community of microbes inhabiting the human body) in such a way as to spare children and gradually kill the elderly – thanks to this, microorganisms have achieved the optimal size and well-being of their hosts' population. In other words, people rarely live to 120 years because of the evolutionary adaptation mechanisms of bacteria living in symbiosis with them, suggested the American microbiologist Martin Blaser. By increasing the risk of death for people coming out of reproductive age, microbes contribute to optimal population growth of their hosts. A mathematical model developing this hypothesis was presented by scientists in the journal mBio (Martin J. Blasera, Glenn F. Webb, Host Demise as a Beneficial Function of Indigenous Microbiota in Human Hosts), and it is briefly reported in a press release from Vanderbilt University (Early human populations may have been shaped by bacteria the body hosts).
The human microflora contains about 100 trillion cells – ten times more than the cells of the body itself. In recent years, scientists have pointed out the importance of microflora in human life: the impact of these microbes is not limited to digestion, but concerns brain development, sexual life and immunity.
Blazer began to think about the influence of microflora on the age structure of the population as a result of many years of studying the bacterium Helicobacter pylori, which lives in the stomach of more than half of the world's population. Most of the time, H.pylori does not harm its hosts, and even helps them: in 1996, Blazer found out that it regulates the level of acidity in the stomach. However, with age, the risk of stomach cancer increases dramatically, the main cause of which is the same H.pylori. "I thought: a real symbiote keeps you alive while you're young and kills you when you get old. This is not very good for you personally, but it is useful for the whole species," the scientist said. That is, the evolution of the microflora had to select the bacteria that keep the entire population in optimal condition, even if it harms the health of individual individuals.
Diagram from an article in mBio – VM
To test his hypothesis, Blazer turned to mathematician Glenn Webb for help, and they began modeling the effects of pathogens of various types on a hypothetical population of ancient people (hunter-gatherers). Scientists divided the latter into three groups – children, people of reproductive age and the elderly. Then they included the risk factor of shigella (one of the causative agents of dysentery) – infant mortality increased sharply, and as a result, the population disappeared. When they modeled mortality from a type of H. pylori microorganism (the risk of which increases with age), the proportion of old people in the population decreased, which freed up a lot of resources for the development of young people. The result is a more stable growth and stability of the population. And if you double childbearing, you get an unstable population: then growing, then dying out under the influence of environmental factors. Finally, even with a small increase in the proportion of healthy old people in the population, resources began to decline rapidly, and, again, extinction occurred.
By "knocking out" aging individuals, the microflora (at least in part) created the demographic structure of Homo optimal for its own survival. However, now with the increase in life expectancy in civilized societies, the evolutionary advantage has begun to bring harm. Older people suffer from a variety of degenerative diseases (like Alzheimer's disease), and their microbes play a significant role in the development of these ailments, Blazer said. That is, if earlier microbes killed old people, now, thanks to the achievements of civilization, they only reduce their quality of life.
Portal "Eternal youth" http://vechnayamolodost.ru19.12.2014