Economist
Mothers-in-law are the subject of countless jokes. However, behind the humor may be a harsh reality. An article in the journal Ecology and Sociobiology Behavioral by Jan Beiss of the Max Planck Institute for Demographic Research in Rostock, and Eckart Walland of the University of Giessen in Germany, suggests that at least in the past, the mother-in-law may have had a lethal effect on her daughter-in-law's children.
Dr. Bays and Dr. Walland collected data on infant mortality from church records in the district of Krumhorn in Germany. They examined the records of more than 23 families, who lived between 1720 and 1874. They found that when the paternal grandmother was alive when the baby was born, the chance that the baby would die in the first month of life was double compared to a baby whose paternal grandmother had already died. The question of whether the grandmother lived in the same house as the child had no effect on his chances of survival.
The maternal grandmothers, on the other hand, had no effect in the first month, but they had a considerable effect when it comes to improving the child's chances later on. The chances of a six-month-old child reaching his first birthday were 60 percent higher if the maternal grandmother was alive.
This finding makes a lot of sense from an evolutionary point of view. The first finding, however, does not make sense. After all, the paternal grandmother has a genetic interest in her son's children living for a long time - just like the maternal grandmother. This is provided, of course, that they are really her son's children. The maternal grandmother is the only one who can be absolutely sure that the baby is indeed her grandchild. The paternal grandmother, on the other hand, cannot be sure: it is possible that her son's wife grew horns for him. So the best explanation the two researchers came up with is that mothers-in-law bully their daughters-in-law in some way to prevent extramarital matings. Such harassment may have a harmful effect on the woman's fetus if she is pregnant, and it is likely that this effect will manifest itself early in the child's life.
If we learn from the jokes, the common opinion is that such bullying by the mother-in-law does exist. But there is not much evolutionary logic in "guarding" a pregnant woman from such matings, since she cannot conceive again. So the influence of the mother-in-law still remains a mystery.
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