The Grandmother Hypothesis

This entry was written by Margot Schneider as part of a project done in BIAN 2133 ‘Human Reproductive Strategies’ at The Australian National University in 2019 Semester 2.


The Grandmother Hypothesis aims to explain why human females have a long period of infertility before death; menopause (Krasheninnikova, 2019). While men produce sperm until their dying days, women have a set number of oocytes, with accelerated depletion by age 50 (Peccei, 2001). The grandmother hypothesis is an adaptive view that senescence of female reproduction increases fitness of older females (Ward, et al., 2009). Krasheninnikova (2019), states that there is only supporting evidence for maternal grandmothers helping daughters, believing that paternal uncertainty is the cause of this. While this hypothesis exists to explain the onset of human menopause, other long lived mammals also go through it: many species of whales experience a long post reproductive life span, with the females living much longer than males (Péron, et al., 2019). There is a certain amount of controversy around this hypothesis with Peccei (2001) believing that menopause is a by-product of living longer and increased dependency of young, this is the non-adaptive view. This short essay will outline the supporting evidence for the grandmother hypothesis in humans, the importance of non-human mammalian comparisons, as well as the conflicting opinions around this theory.

Main Text

Helping Grandchildren Increases Grandmothers Fitness

Menopause from an evolutionary standpoint should be maladaptive, a shorter reproductive life span would negatively impact fitness (Krasheninnikova, 2019). However, if older mothers in the community assist their daughters, then the grandchildren have a higher chance of surviving, this allows the mother to have children more frequently: increasing fitness (Hawkes & Coxworth, 2013). This phenomenon is stronger between maternal grandmothers, as there is certainty in shared genes. The strongest evidence surrounding the Grandmother Hypothesis is the Hadza population, a group of hunter gatherers of East Africa (Krasheninnikova, 2019; Hawkes & Coxworth, 2013; Peccei, 2001). Older Women have the knowledge and skill to find and process higher quality foods than the younger population. The Hadza people became heavily reliant on tubers as grasslands became more abundant: a niche was opened for the older women. Mother with young chidren were not well suited to collect these tubers, yet grandmothers with no young children had the time to do so. Peccei (2001), states that the Hadza childrens weight is correlated with the grandmothers foraging time. The Hadza population is a direct example of post-menopausal women positivily influencing the success of future generations.

Intergenerational reproductive conflict

Intergenerational reproductive conflift (IRC) is another adaptive explantion for the existence of post menopausal women (Lahdenpera, et al., 2012). IRC helps to explain that while decreasing fertility is not the most benefical in terms of fitness, it removes the breeding competion between a grandmother and her daughter. Explaining that a grandmothers resources would be better spent helping her daughter, which will increase the grandmothers fitness, avoiding direct competetion with her daughter. IRC’s explanation for the grandmother’a hypothesis places an emphasis on the negative conotation of “the mother in law”, due to paternal uncertainty in the animal kingdom. Indicating that the presence of paternal grandmothers will most likely have no impact at all or is sometimes hindering.

Menopause in other long lived mammals: whales

Humans are not the only mammal to go through menopause, which has been documented in at least 4 species of whales: toothed whales, killer whales, short finned pilot whales and the fake killer whale (Péron, et al., 2019). Female Killer whales can live to 90, with about 50% surviving past menopause, yet male killer whales die around 50. Killer whales have a strong matrilineal social structure, the males provide no care to their offspring. Killer whales, like humans, are dependent on their mothers until reproductive maturity. This raises opposing ideas to the grandmother’s hypothesis, whereby we stop reproducing so that we are alive long enough to look after our last-born child. With the benefit of grandmothers being a secondary benefit to this phenomenon. In killer whales, it is thought that grandmother’s share knowledge of the best feeding locations, however the only age group with statistically significant benefits from a grandmother’s presence is newly weaned whales, at about 3 years of age.

Alternative mechanisms

While the grandmother hypothesis aims to explain the evolution of menopause, the contrary argument is that menopause is a by-product of our increased life span (Peccei, 2001). Many other theories exist to explain human menopause: the mother hypothesis states that by ending reproductive abilities early, humans avoid risky pregnancies and energy can be placed on existing young (Ward, et al., 2009). Ward et al. (2009), also detail the mutation accumulation hypothesis, whereby menopause is a by-product due to physiological deterioration as we age. One of the main issues with the grandmother hypothesis is the lack of explanation for continued spermatogenesis in males, and the help provided by other family members not just grandmother’s in human societies (Krasheninnikova, 2019). Therefore, many believe that the mother hypothesis makes more sense, women’s fertility ends so that there is enough time to look after the last-born child, however this hypothesis like the grandmother hypothesis does not explain everything.

Chimpanzees and humans

Female Humans, and other long lived mammals have a long post reproductive senescence life span however, our closest living relative the Chimpanzee often dies while they are still cycling, raising questions about the history of human somatic aging (Hawkes & Coxworth, 2013). Dehydroepiandrosterone sulphate (DHEAS) can be used as a biomarker for aging in primates, with DHEAS levels being three times higher in human females than chimpanzee females, this increased production could help explain females increased lifespan compared with other apes. This opens research doors into adrenal androgens and life history traits, and could help provide a genetic backing to the grandmother hypothesis.


The Grandmother Hypothesis is an adaptive view, that ending female reproductive abilities early, helps to increase fitness in older women. Evidence suggests this only applies to maternal grandmothers due to paternal uncertainty. The children of the East African Hadza population benefit from the foraging of the grandmothers is their community, whereby the fitness of the grandmothers is increased by providing food to their daughters and grandchildren. Intergeneration reproductive conflict is also hypothesised to be a reason for early reproductive senescence avoiding direct competition between generations. However, many believe there is little evidence for the grandmother hypothesis believing that the benefits are merely secondary to our increased life span. Menopause is not a uniquely human life history trait, whales experience menopause and understanding this mechanism could give us an insight into its development. Similarly, chimpanzees often die while they are still cycling, and more research needs to be done comparing this mechanism in humans and chimpanzees to understand the evolution of menopause.

Literature Cited

Lahdenpera, M., Gillespie, D., Lummaa, V. & Russell, A. 2012. Severe intergenerational reproductive conflict and theevolution of menopause. Ecological Letters, 15, 1283-1290.

Hawkes, K. & Coxworth, J. 2013. Grandmothers and the Evolution of Human Longevity: A Review of Findings and Future Directions. Evolutionary Anthropology, 22, 294-302.

Krasheninnikova, A. 2019. Grandmother Hypothesis. Encyclopedia of Animal Cognition and Behavior, 1-4.

Peccei, J. 2001. A Critique of the Grandmother Hypotheses: Old and New. American Journal of Human Biology, 13, 434-452.

Péron, G. et al. 2019. Does grandparental care select for a longer lifespan in non-human mammals. Biological Journal of the Linnean Society, 20, 1-13.

Ward, E. et al. 2009. The role of menopause and reproductive senescence in a long-lived social mammal. Frontiers in Zoology, 6(4), 1-10.

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