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Read aloud From a biological point of view, the climacteric is a mystery: In the second trimester of life, it ends the fertility of women, whereas men remain fertile for their entire lives. There are also few parallels in the animal kingdom: As a rule, the females are capable of reproduction until death. So how it comes to the phenomenon in humans is so far misunderstood. Now, Canadian researchers have developed a new explanatory model for female loss of fertility. According to them, men are the culprits: their preference for young female partners has led to an accumulation of mutations in the course of evolution leading to infertility in older women. The climacteric refers to the time of the hormonal change before and after the last menstrual period, which also marks the last ovulation. Thereafter, the fertile phase of a woman's life is over, though often decades of life follow. The predominant explanation for this phenomenon so far is the so-called "grandmother hypothesis". It states that women beyond menopause benefit from their experiences the survival of the clan and thus their own genes: they ensure by the careful care of their children and grandchildren more healthy offspring than by the birth of other own children. However, from an evolutionary point of view, the researchers around Rama Singh from McMaster University in Hamilton find this explanatory model questionable: "Selection in the context of evolution produces fertility and not the opposite, " says Singh.

The researchers have now developed computer models that show that the cause of menopause could simply be men's preference for young women. This factor did not select fertility in older women. Thus, mutations could accumulate in the genetic material of humans, which induce infertility in women in advanced age, the scientists explain. According to her computer models, menopause, without the factor of sexual preference of men to young women, would not exist at all: "Like men, they would maintain their reproductive ability throughout their lives, " says Singh. Theoretically, even a reverse scenario would have been possible in the course of evolution: "If women had chosen only young men as partners, this would have led to male infertility from a certain age, " said the evolutionary biologist.

The researchers' new explanatory model makes it clear that biological phenomena such as the climacteric do not always have to serve a purpose. While the preference of men for young women offers them advantages in reproductive success, according to the new hypothesis, menopause would only be a concomitant of this sexual selection and not itself an advantage in the struggle for survival. Whether this really is the case, but remains open. The causes or possible functions of the climacteric can be scientifically difficult to grasp and therefore hardly clarify. Presumably, the supporters of the "grandmother's hypothesis" will not give up and will soon present new evidence for their explanatory model.

Rama Singh (McMaster University, Hamilton) et al .: PLoS Comput Biol, doi: 10.1371 / journal.pcbi.1003092 © science.de - Martin Vieweg Display

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