Why are the old women alive
Alexey Petrov, "Newspaper.Ru»Women live long enough to raise children, not grandchildren.
Scientists have found strong evidence against the "grandmother hypothesis", which explains why women continue to live after menopause. The "hypothesis of motherhood", which explains both long life and menopause itself, received support.
Anthropologists around the world still cannot figure out whether a person's ability to live significantly longer than his reproductive period is a by-product of evolution or whether it has become a property of independent selection during the evolutionary struggle for survival.
Scientists know that in the wild, an individual, as a rule, ages quickly and dies after crossing the age threshold separating the fertile period from unproductive old age. Beyond the reproductive age, natural selection in its primitive sense ceases to work: animals and plants are no longer able to transmit to their offspring the signs that affect survival. Therefore, there is no mechanism that cleanses the gene pool of a species from inevitably accumulating mutations that manifest themselves at a more than mature age.
When applied to a person, this question concerns primarily women. In men, the ability to conceive decreases gradually, so it is even difficult to determine where the threshold is. However, the female menopause leads to a complete hormonal restructuring of the body and makes further reproduction impossible, and the occurrence of this phenomenon is still not fully justified from an evolutionary point of view.
To explain the evolutionary prerequisites for such a device of the female body, scientists have put forward two theories. The most common is the so-called grandmother's theory, expressed at one time by the British mathematician William Hamilton. Within the framework of his theory, Hamilton justified the high life expectancy not only of the female half of the human population, but also of the male.
He suggested that the key factor determining the long life of people is the ability of grandmothers to live to a ripe old age, surrounding their growing grandchildren with care and attention in their old age. Thus, these young people gain more comfortable living conditions during the development period and gain competitive evolutionary advantages over those whose grandmothers passed away early.
As a result, life expectancy, especially in economically developed countries, is showing monotonous growth these days, and people from generation to generation live significantly longer, further and further delaying death from the end of childbearing age.
The controversy surrounding the "grandmother's hypothesis" does not abate. For example, a recent statistical study has demonstrated that in some cases, high life expectancy is directly related to late fatherhood. In this regard, scientists have suggested that men who have become fathers again, whose age has passed the fifth, and sometimes the sixth decade, pass on to their daughters and sons the so-called "longevity genes". However, scientists did not reveal the actual genetic background at that time.
The so-called theory of motherhood, which considers the long post-productive period of women's life as an evolutionary achievement of many millennia of human history, also competes with Hamilton's theory. According to this hypothesis, this period in women is designed to accumulate physical resources to help their own children, already born, but unable to enter adulthood. It is in such a restructuring that the meaning of menopause consists.
American scientists have managed to find statistical data that, in their opinion, refute the "grandmother's hypothesis".
In the new work, the researchers relied on statistical data on the fate of mothers and grandmothers from various families who lived in the central regions of Costa Rica in the period from 1500 to 1900. The article by anthropologist Lorena Madrigal from the University of South Florida and Mauricio Melendez-Obando from the Costa Rican Academy of Sciences has been accepted for publication in the American Journal of Physical Anthropology.
Scientists believe that the validity of the "grandmother's hypothesis" could show a good correlation between the life expectancy of women in the post-productive period and the number of grandchildren brought to her by her daughters. On the contrary, the validity of the hypothesis of motherhood, in turn, would have to mean a proportional ratio between the number of children and life expectancy after menopause.
The results are not in favor of the first option.
The "grandmother's hypothesis" seems to be fundamentally wrong, since scientists observed the smaller the number of grandchildren in the family, the more venerable the age of grandmothers was. The direct conclusion of the study is that a longer post–productive period in women negatively affects the fertility of their daughters.
Anthropologists also failed to identify any noticeable ability of the "longevity genes" to be inherited.
However, these results probably cannot be considered a direct confirmation of the theory of motherhood. However, its main competitor, the "grandmother's hypothesis", which still remains the most popular, has been dealt a serious blow.
Portal "Eternal youth" www.vechnayamolodost.ru
13.03.2008