The grandmother hypothesis is meant to explain why menopause, rare in mammal species, arose in human evolution, and how late life infertility could actually confer an evolutionary advantage. The hypothesis suggests that this is because of risks associated with pregnancy and childbirth and the relative importance of parental investment to the human species. Grandmotherly investment may also be important in the few other animals which experience menopause, such as whales. Kristen Hawkes originated the hypothesis, and C.G. Williams was the first to posit that menopause may be protective. Menopause (also known as the Change of life or climacteric) is a stage of the human female reproductive cycle that occurs as the ovaries stop producing estrogen, causing the reproductive system to gradually shut down. ... Human evolution is a multidisciplinary scientific inquiry which seeks to understand and describe the origin and development of humanity. ... A pregnant woman Pregnancy is the process by which a mammalian female carries a live offspring from conception until it develops to the point where the offspring is capable of living outside the womb. ... Childbirth in a hospital. ... Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. ...
Both pregnancy and childbirth are extremely detrimental to the health and longevity of women. Pregnancy increases a woman’s caloric intake requirements and childbirth exposes women, especially older women, to deadly infections. For these reasons physical anthropologists think that older women in primitive times were less productive child bearers than younger women.
It is conceivable that older mothers that lost their procreative viability were able to spend more of their time helping, protecting and teaching their children and grandchildren. Such an investment of time is referred to by behaviorists as parental investment. Experiments and natural observation have shown that those animals that have had time invested in them by family members, in the form of protection and teaching, are much more likely to live to the age at which they are able to reproduce.
On average, prehistoric women who experienced menopause may have lived longer lives and were better able to spend time supporting their children and their grandchildren. The progeny of these menopausal women benefited from additional parental investment and were therefore more likely to live to procreate. These progeny also benefited from inheriting their mother’s genes because these genes caused them to experience menopause and have more prosperous progeny of their own. This rationale is used by anthropologists to provide an evolutionary theory of menopause which holds that menopause in modern women is a remnant of a protective adaptation that allowed older females to better focus their maternal resources.
Grandma earns her stripes - The "grandmotherhypothesis" - an evolutionary explanation of the menopause - fits most of the demographic facts, says a population geneticist, whose mathematical model of the hypothesis supports the idea that the fitness of a population is maximized if women stop reproducing and help to raise their grandchildren instead.
The "grandmotherhypothesis" - an evolutionary explanation of the menopause - fits most of the demographic facts, says a population geneticist, whose mathematical model of the hypothesis supports the idea that the fitness of a population is maximized if women stop reproducing and help to raise their grandchildren instead.
Their main finding supports the grandmotherhypothesis, and has to do with a tradeoff between fertility and survival across generations: for each additional child born to a mother who already has a daughter of reproductive age, their model predicts a cost to the daughter of two children.
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