Wednesday, August 22, 2012

Evolution favoured menopause to reduce competition

Once a woman hits the menopause, she is no longer fertile, effectively ending her capabilities of reproduction. Evolutionists have wondered why something like the menopause exists. Surely it has no evolutionary benefit to keep an organism alive that has no ability to reproduce, one would think. However, there have been some theories regarding the potential benefits, and an international group of scientists performed experiments to see if one of them holds any truth. They found that the menopause reduces competition in families, especially between in-laws.

Reproduction
A study was conducted to assess the effects of women rearing children late in life. Specifically, they looked at what happened when a mother gives birth to a child at the same time as her daughter-in-law. The information was collected from church data and revolved around births and deaths in families in the years between 1700 and 1900. They looked at older data in order to exclude the confounding effects of modern healthcare.

Survival
When comparing survival rates, the scientists found that an older mother and a daughter-in-law both having a child at approximately the same time has unwanted effects. Children growing up in such conditions were found twice as likely to die before the age of 15, when compared to conditions where the older mother would not have another child of her own, and instead would 'just' be the grandmother. The decreased survival rate is attributed to increased competition, as such conditions would increase conflicts between the in-laws. Additionally, a grandmother without children of her own to take care of would increase support for other children.

Grandmother Hypothesis
The findings add to an existing hypothesis regarding the menopause, which is known as the Grandmother Hypothesis. It argues that keeping members of a species alive after their fertile period offers benefits for the offspring that already exist. Instead of producing new offspring, resources could be devoted to keeping the existing children alive. This would be especially relevant for human beings, as our babies need a lot of time before they can survive independently, meaning that aid from grandma would be beneficial. Of course, nowadays we have healthcare and social services, but evolution did not have time yet to take this into account.

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