In-law infighting boosted evolution of menopause


Conflict between women and their daughters-in-law could be a factor in explaining an evolutionary puzzle — the human menopause. 

Humans, pilot whales and killer whales are the only animals known to stop being able to reproduce long before they die. In terms of evolution, where passing on your genes is the main reason for living, the menopause remains puzzling.

Now, using a large data set from Finland, researchers have for the first time been able to test a hypothesis that competition between different generations of genetically unrelated breeding women could have promoted the evolution of the menopause. The results are published today in Ecology Letters1.

Mirkka Lahdenperä, an ecologist at the University of Turku in Finland, and her colleagues used data from meticulous birth, death and marriage records kept by the Lutheran church in the country between 1702 and 1908. As they dug into the data, the researchers found that the chances of children dying increased when mothers-in-law and daughters-in-law gave birth around the same time. For children of the older women, survival dropped by 50%. For children of the daughters-in-law, it dropped by 66%. However, if mothers and daughters had children at the same time, the survival of those children wasn’t affected.

The results suggest that it would be beneficial to stop having children once your daughter-in-law entered the fray. “We were surprised that the result was so strong,” says Andrew Russell, an ecologist at the University of Exeter, UK, who was part of the research team. He suggests that perhaps in-laws fought over food for their children instead of cooperating as mothers and daughters might.

Written By: Katharine Sanderson
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  1. The in-law fighting interpretation of the data is not convincing. If there is such conflict, elimination of the women having passed reproductive age would be an effective solution. The grandmother hypothesis seems plausible. If I remember correctly, this hypothesis is supported by a study of south american tribes.

  2. I think the grandmother hypothesis makes much more sense, especially when examining other menopausal females, like orcas, and seeing that they don’t have mothers-in-law. Older females are really important in terms of pod leadership, and having them around to support daughters with calves is probably a huge benefit.

  3. An interesting argument but I’m not convinced. The main assumption appears to be that data collected over the last 300 years can be extrapolated to early humans. I’m not sure there is any evidence that suggests the family and social units of early humans are the same size or functioned the same way as modern humans.   Child mortality is also affected by the pathogens which we acquired from animals this would have to be factored in and I’d venture that the menopause evolved before the domestication of animals. 

  4. I’d always thought it was a precaution against genetic damage to womens’ egg stocks accumulated over time causing resources to be used on malformed infants where they could be used on healthy ones instead. I’m not sure how you’d demonstrate that, though.

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