Menopause: another possible reason
Anna Govorova, Infox.ru
One of the most unpleasant and incomprehensible events in a woman's life — menopause — has received a new explanation. Scientists blame the stopping of the "birthing mechanism" of daughters-in-law who fought for power in a primitive family.
Only in humans, the phenomenon of the occurrence of menopause exists everywhere: about 50 years, normal healthy women lose the ability to procreate. Over the next ten years or so, a woman's reproductive system stops working.
Menopause is a mystery. A woman loses 20-30 years of her life, during which she can transfer her genetic material to new generations. This is a huge waste by evolutionary standards. It is obvious to scientists that the pressure of natural selection must be very strong, because there is not a single woman in the world who would avoid menopause. That is, there is clear evolutionary evidence that menopause has existed for a long time.
Everywhere in the animal world, the aging of the reproductive system occurs in parallel with the aging of other systems and organs. With age, the intensity of cardiac activity is disrupted and decreases, hearing and vision gradually deteriorate, and eventually reproductive ability is lost. Things are different for people. By the age of 50, women abruptly stop ovulation and estrogen synthesis. In developed countries, the average female life expectancy is 80 years, and by the age of 60, more than 99% of women become unable to procreate.
The maternal hypothesisScientists believe, and it is really obvious, that it is better for a mother to avoid the risk associated with the birth of a child and concentrate on raising children who have already been born.
After all, our children need at least ten years to become more or less independent. There is no doubt that orphans have less chance of surviving and that having a child is always a risk. A woman who dies during childbirth does not allow at least two or three more children to be born. At the same time, early termination of reproductive function makes it impossible for two or three children to be born, too. And this is the gap of the maternal hypothesis. The question is why menopause happens so early. After all, most women still have a lot of energy to raise grandchildren up to their puberty.
The "grandmother" hypothesisThe hypothesis suggests that a healthy grandmother helps her genes survive by taking care of several generations of descendants.
A woman passes on 50% of her genes to her child and 25% to her grandchildren. And this is a great contribution in an evolutionary sense. But whether it can compensate for the transfer of genetic information to children that she could bear herself is unclear.
In May, Kim Hill from Arizona National University and Magdalena Hurtado from The University of New Mexico in Albuquerque compared the genetic benefits of grandmothers and moms over the same period. And it turned out that the difference is insignificant. And it does not explain at all why the reproductive period stops so early.
A new hypothesis of "generational competition" and mother-in-law-daughter-in-law interactionDr. Kant and his colleague Rufus Johnston from the University of Cambridge noticed a striking omission of all previous theories.
None of them considered the role of other women in the family or group. Scientists believe that competition between women of different age groups is the key to understanding the causes of menopause.
Although mothers, as a rule, live to the reproductive age of their daughters, they themselves are capable of childbearing for a very narrow period, if we consider the time interval when their daughters are reproductively active. This distinguishes humans from primates. In primates, mothers and daughters often bear cubs at the same time. But the reproductive division of generations is characteristic of many other mammals — for example, in rodents, younger and more competitive females forbid older ones to have offspring.
Based on behavioral patterns in mammals, Dr. Kant and Johnston suggested that the mismatch of reproductive periods in humans mitigates the conflict between generations, weakening competition.
The idea was developed, and scientists began to study models of interaction between women in the social environment of the family. Based on the assessment of mitochondrial DNA and Y-chromosome analysis, scientists have suggested that our ancestors harassed women who came to them from other groups in every possible way. This pattern of behavior persists in most cases to this day. So, older women compete with young women who come from nowhere and for no reason. But these women are young and independent. With age, a woman's dependence on a new family increases more and more — family ties, psychological, social and material dependence appear, and now a woman from another family dictates behavior to new relatives. This is the daughter—in-law - the son's wife. And she doesn't want to compete with anyone. Her genes turn out to be more important for evolution. Dr. Kant and Jonathan believes that this model is the key to solving the mystery of the appearance of menopause.
The same thing, apparently, can happen if there are only daughters in the family. It's just that then conflicts begin even earlier, with a transitional period. However, the authors do not write about this – perhaps this will be the topic of their next work.
You can get acquainted with the calculations of scientists in an article that was published in the NewScientist magazine for December 11.
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