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About this sample
About this sample
Words: 511 |
Page: 1|
3 min read
Published: Apr 11, 2019
Words: 511|Page: 1|3 min read
Published: Apr 11, 2019
The grandmother hypothesis tries to explain the existence of menopause in human females. Unlike human males, who do not have the biological equivalent of menopause, females typically end menstruation around the age of 51 and no longer have the ability to bear children. The evolutionary cost of an non-reproducing older female is large to a group. The grandmother hypothesis gives us an explanation on why a costly individual would live on in a group with the reasoning being the value of offspring care by the grandmother far outweighs the cost of their presence in the group.
Anthropologist Kristen Hawkes explains that humans tend to have an age pyramid with an uncharacteristically large percentage of the pyramid filled by females past the reproducing age. Menopause, which is when females stop menstruating and can no longer give birth, happens on average at 51 years old. Compared to our closest living ancestor, the chimpanzees, there are virtually no female chimpanzees that live past menopause. Humans are unique in this respect and the grandmother hypothesis theorizes that females that live past menopause continue to live to help their daughters raise children.
Along with the chimpanzee data, there is strong evidence when you look at the age breakdowns of modern hunter gatherer populations. Despite the average lifespan of the Aché people of Paraguay being 37, about a third of the adult women live past menopause. Similar numbers are found with the Hadza of Tanzania and the ǃKung people of Namibia. Compared to the males who are mainly responsible for hunting and preventing predators or other human enemies to threaten the wellbeing of the group, females raise offspring. Grandmothers can help raise children, which gives the daughter more energy to invest in giving birth and raising additional children. It is reasonable to say the direct offspring care provided by the grandmothers gives ample reason for the uncharacteristically long lifespan of females.
Menopause requires an explanation as human males do not have a biological equivalent. Additionally, women are born with a finite number of eggs, as opposed to males who continuously produce sperm throughout their lifetime. Part of the grandmother hypothesis is that along with slower aging in females, menopause was a biological feature of evolution to prevent grandmothers from continuing to produce their own offspring, so they could focus on helping raise their daughter’s offspring. Raising additional offspring along with your grandchildren is simply too costly and it is better served in invest resources in raising grandchildren. Menopause prevented females from continuing to reproduce past 50 and the evolutionary theory of kin selection provides enough incentive for the grandmother because the grandchild shares her genes.
The grandmother hypothesis remains a hypothesis at this point, but it does provide a compelling case for why grandmothers and menopause exist. Menopause exists to prevent further reproduction and more investment in the grandchildren incentivized by kin selection. It seems obvious in modern times why grandmothers are so important, but evolutionarily wouldn’t have made much sense in our ancestral past.
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