The New Science of Practical Wisdom [Texte]
Jeste et al.
Perspectives in biology and medicine, 2019
Wisdom is associated with positive life outcomes including better health, well-being, happiness, life satisfaction, and resilience. Wisdom tends to increase with active aging, facilitating a contribution of wise grandparents to promoting fitness of younger kin. Despite the loss of their own fertility and physical health, older adults help enhance their children’s and grandchildren’s well-being, health, longevity, and fertility-the « grandmother hypothesis » of wisdom.
Do post-menopausal women provide more care to their kin?: evidence of grandparental caregiving from two large-scale national surveys [Abstract]
Hofer et al.
Evolution and human behavior, 2019
Results from both studies revealed that (even when controlling statistically for age, health, financial resources, and other pertinent variables), post-menopausal women devoted more time to grandparental caregiving. This effect was specific to kin care: Menopause status was not as strongly related to a measure of non-kin-directed altruistic behavior (time spent volunteering).
Postreproductive killer whale grandmothers improve the survival of their grandoffspring [Texte]
Nattras et al.
Here, we test the grandmother effect in resident killer whales, where females can live for decades after their last reproductive event. We show that grandmothers increase the survival of their grandoffspring, and these effects are greatest when grandmothers are no longer reproducing. These findings can help explain why killer whales have evolved the longest postreproductive life span of all nonhuman animals.
Using Geographic Distance as a Potential Proxy for Help in the Assessment of the Grandmother Hypothesis [Texte]
Engelhardt et al.
Current biology, 2019
Reproductive success was higher when grandmothers were alive.
Grandmother effects decreased with grandmother-daughter geographic distance
Crucial Contributions: A Biocultural Study of Grandmothering During the Perinatal Period
Scelza & Hinde
Human Nature, 2019
These findings demonstrate that the role of grandmother can be crucial, even when alloparenting is common and breastfeeding is frequent and highly visible. Situated within the broader anthropological and clinical literature, these findings substantiate the claim that humans have evolved in an adaptive sociocultural perinatal complex in which grandmothers provide significant contributions to the health and well-being of their reproductive-age daughters and grandchildren.
Limits to Fitness Benefits of Prolonged Postreproductive Lifespan in Women [Texte]
Chapman et al.
Current biology, 2019
The presence of maternal grandmothers aged 50–75 increased grandchild survival after weaning, confirming the fitness advantage of post-reproductive lifespan. However, co-residence with paternal grandmothers aged 75+ was detrimental to grandchild survival, with those grandmothers close to death and presumably in poorer health particularly associated with lower grandchild survival. The age limitations of gaining inclusive fitness from grandmothering suggests that grandmothering can select for post-reproductive longevity only up to a certain point.
Mammalian brain development and our grandmothering life history [PDF]
Hawkes & Finlay
Physiology & behavior, 2018
Among mammals, including humans, adult brain size and the relative size of brain components depend precisely on the duration of a highly regular process of neural development. Much wider variation is seen in rates of body growth and the state of neural maturation at life history events like birth and weaning. Large brains result from slow maturation, which in humans is accompanied by weaning early with respect to both neural maturation and longevity. The grandmother hypothesis proposes this distinctive combination of life history features evolved as ancestral populations began to depend on foods that just weaned juveniles couldn’t handle. Here we trace possible reciprocal connections between brain development and life history, highlighting the resulting extended neural plasticity in a wider cognitive ecology of allomaternal care that distinguishes human ontogeny with consequences for other peculiarities of our lineage.
Postreproductive lifespans are rare in mammals [PDF]
Ellis et al.
Ecology and evolution, 2017
despite considerable interest, the taxonomic prevalence of post-reproductive stages remains unclear and debated. In this study we use life tables constructed from published data on wild populations of mammals, and statistical measures of post-reproductive lifespans, to distinguish true post-reproductive stages from artefacts of senescence and demography in 52 species. We find post-reproductive stages are rare in mammals and are limited to humans and a few species of toothed whales.
Caregiving within and beyond the family is associated with lower mortality for the caregiver: A prospective study [Texte]
Hillbrand et al.
Evolution & human behavior, 2017
Survival analyses based on data from the Berlin Aging Study revealed that mortality hazards for grandparents who provided non-custodial childcare were 37% lower than for grandparents who did not provide childcare and for non-grandparents.
Do post-reproductive aged females promote maternal health? Preliminary evidence from historical populations [Texte]
Gemmil & Catalano
Evolution, medicine & public health, 2017
Results suggest that the presence of older women in a population may enhance population health by reducing mortality among women who face high risk of maternal death, although additional research is needed to determine if this relationship is causal.
Nearby grandmother enhances calf survival and reproduction in Asian elephants [Texte]
Lahdenperä et al.
we found that grandcalves from young mothers (<20 years) had 8 times lower mortality risk if the grandmother resided with her grandcalf compared to grandmothers residing elsewhere. Resident grandmothers also decreased their daughters’ inter-birth intervals by one year. In contrast to the hypothesis predictions, the grandmother’s own reproductive status did not modify such grandmother benefits. That elephant grandmothers increased their inclusive fitness by enhancing their daughter’s reproductive rate and success irrespective of their own reproductive status suggests that fitness-enhancing grandmaternal effects are widespread and challenge the view that grandmother effects alone select for menopause coupled with long post-reproductive lifespan.
Mate Choice and the Origin of Menopause [Texte]
Morton et al.
Classic theory, involving a one-sex (female) model of human demography, suggests that genes imparting deleterious effects on post-reproductive survival will accumulate. Thus, a ‘death barrier’ should emerge beyond the maximum age for female reproduction. Under this scenario, few women would experience menopause (decreased fertility with continued survival) because few would survive much longer than they reproduced. However, no death barrier is observed in human populations. Subsequent theoretical research has shown that two-sex models, including male fertility at older ages, avoid the death barrier. Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility and thus produce a menopausal period. Our model requires neither the initial assumption of a decline in older female fertility nor the effects of inclusive fitness through which older, non-reproducing women assist in the reproductive efforts of younger women. Our model helps to explain why such effects, observed in many societies, may be insufficient factors in elucidating the origin of menopause.
Increased Longevity Evolves from Grandmothering [Texte]
Kim et al. (Hawkes)
Proceedings of the Royal Society B: Biological Sciences, 2012
Grandmothers can support only one dependent at a time and do not care selectively for their daughters’ offspring. They must take the oldest juveniles still relying on mothers; and infants under the age of 2 years are never eligible for subsidy. Our model includes no assumptions about brains, learning or pair bonds. Grandmother effects alone are sufficient to propel the doubling of life spans in less than sixty thousand years.
Alternatives to the Grandmother Hypothesis. A Meta-Analysis of the Association Between Grandparental and Grandchild Survival in Patrilineal Populations [PDF]
Strassmann & Garrard
Human nature, 2011
We conducted a meta-analysis of 17 studies that tested for an association between grandparental survival and grandchild survival in patrilineal populations. Using two different methodologies, we found that the survival of the maternal grandmother and grandfather, but not the paternal grandmother and grandfather, was associated with decreased grandoffspring mortality.
Cooperative breeding in South American hunter–gatherers [Texte]
Hill & Hurtado
Proceedings of the Royal Society B: Biological Sciences, 2009
Here, we show in two hunter–gatherer societies of South America that each breeding pair with dependent offspring on average obtained help from approximately 1.3 non-reproductive adults. Young married males and unmarried males of all ages were the main food providers, accounting for 93–100% of all excess food production available to breeding pairs and their offspring. Thus, each breeding pair with dependants was provisioned on average by 0.8 adult male helpers. The data provide no support for the hypothesis that post-reproductive females are the main provisioners of younger reproductive-aged kin in hunter–gatherer societies. Demographic and food acquisition data show that most breeding pairs can expect food deficits owing to foraging luck, health disabilities and accumulating dependency ratio of offspring in middle age, and that extra-pair provisioning may be essential to the evolved human life history.
Beyond the Grandmother Hypothesis: Evolutionary Models of Human Longevity [PDF] (chapitre de livre)
Gurven & Kaplan
In The cultural context of aging, 2008
An evolutionary perspective on the origin and ontogeny of menopause [PDF]
Barry X. Kuhle
I put forward the « absent father hypothesis » proposing that reduced paternal investment linked with increasing maternal age was an additional impetus for the evolution of menopause. Reduced paternal investment was linked with increasing maternal age because men died at a younger age than their mates and because some men were increasingly likely to defect from their mateships as their mates aged.
Menopause and post-generative longevity: Testing the ‘stopping-early’ and ‘grandmother’ hypotheses [PFD]
Grainger & Beise
Max Planck institute, 2004
Marlowe proposes that extended life span was selected for early in human evolutionary history but that the primary selection pressure was the improved status and mating opportunities that age affords men.
[…] it may pay to cease reproduction at the point when the risk of maternal mortality (death caused by pregnancy or birth)reaches a certain threshold. This hypothesis has become known as the ‘mothering’ or‘stopping-early’ hypothesis and has received wide support.
[…] Father’s are not expected, from an evolutionary point of view, to be the most dependable helpers given their lack of certainty regarding relatedness to offspring. Hawkes et al therefore propose that human females evolved longevity past the age of reproductive-senescence in order to help their daughters raise grandoffspring, an idea that has become known as ‘the grandmotherhypothesis’.
[…] if post-generative women also decrease their grandoffsprings’ mortality by 10%, and increase their daughters’ fertility by 10%, then women who experience menopause have greater reproductive fitness than those who do not.
[…]Hawkes (2002) does argue that it would be physiologically possible for reproductive life span to be expanded if there were sufficient selection pressure.
[…]grandmothers seem to have only a very limited effect on the fertility of their daughters, but a significant influence on the survival of grandoffspring.
[…] While there may never have been any pressure to increase numbers of offspring born, there is surely constant pressure to reduce offspring mortality and thus achieve the optimal number of offspring with minimal loss. The results of the present study suggest that this pressure may have been great enough to result in the evolution of post-generative longevity.
[…] In conclusion, if one accepts that it is post-generative life span, rather than menopause, that is the anomaly in human life history requiring explanation, the results of the current models provide support for the grandmother hypothesis, but little support for the stopping-early hypothesis.
The grandmother effect [PDF]
Why do women live long past the age of child-bearing? Contrary to common wisdom, this phenomenon is not new, and is not due to support for the elderly. Rather, grannies have a lot to offer their grandchildren.
Menopause: why does fertility end before life? [PDF]
M. Lahdenperä et al.
A Critique of the Grandmother Hypotheses: Old and New
Jocelyn Scott Peccei
American Journal of Human Biology, 2001
The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis—the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved
from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females. In the old grandmother hypothesis, menopause is an adaptation facili-
tating grandmothering; it is about stopping early in order to create a postreproductive lifespan. In the new grandmother hypothesis, grandmothering is an adaptation facilitating increased longevity, and menopause is a byproduct. This paper reviews and critically evaluates the evidence for and against both hypotheses, focusing on key predictions of each. If menopause is the result of selection for
increased maternal investment, this involved mainly mothers, not grandmothers.
The patriarch hypothesis [PDF]
Human Nature, 2000
Adaptive explanations of menopause offered thus far turn on women’s long-term investment in offspring and grandoffspring, all variations on the grandmother hypothesis. Here, I offer a very different explanation. The patriarch hypothesis proposes that once males became capable of maintaining high status and reproductive access beyond their peak physical condition, selection favored the extension of maximum life span in males. Because the relevant genes were not on the Y chromosome, life span increased in females as well. However, the female reproductive span was constrained by the depletion of viable oocytes, which resulted in menopause.
Grandmothering and the evolution of Homo erectus [PDF]
O’Connell et al.
Journal of Human Evolution, 1999
Despite recent, compelling challenge, the evolution of Homo erectus is still commonly attributed to big game hunting and/or scavenging and family provisioning by men. Here we use a version of the ‘‘grand-mother’’ hypothesis to develop an alternative scenario, that climate-driven adjustments in female foraging and food sharing practices, possibly involving tubers, favored significant changes in ancestral life history, morphology, and ecology leading to the appearance, spread and persistence of H. erectus. Available paleoclimatic, environmental, fossil and archaeological data are consistent with this proposition; avenues for further critical research are readily identified. This argument has important implications for widely-held ideas about the recent evolution of long human lifespans, the prevalence of male philopatry among ancestral hominids, and the catalytic role of big game hunting and scavenging in early human evolution.
Grandmothering, menopause, and the evolution of human life histories [PDF]
Hawkes et al.
Long postmenopausal lifespans distinguish humans from all other primates. This pattern may have evolved with mother–child food sharing, a practice that allowed aging females to enhance their daughters’ fertility, thereby increasing selection against senescence.
A hypothesis for the origin and evolution of menopause [Abstract]
Jocelyn Scott Peccei
Natural selection favored females who became prematurely infertile, as the escalating cost of raising each offspring led to maternal depletion and made it more profitable in terms of lifetime reproductive success to continue investing in existing offspring rather than attempting late pregnancies. Results of a mathematical model are presented which show that reproductive senescence can be advantageous even when maximum potential lifespan is only 50 years, if the premature cessation of reproduction allows females to moderately increase the survival and fertility of their existing subadult offspring. These findings suggest that menopause could have originated as much as 1.5 million years ago, and that if menopause is indeed such an old trait, it was more likely the result of selective pressure on females to invest more in their own children, as opposed to their grandchildren.
Menopause: A Comparative Life History Perspective [PDF]
Pavelka & Fedigan
Yearbook of physical anthropology, 1991
As a life history characteristic of human females, menopause is universal, it occurs halfway through the maximum lifespan of the
species, and it consistently occurs at approximately age 50 in different populations. Menopause is fundamentally distinct from the reproductive senescence that has been described for a very small number of very old individual alloprimates. Menopause is not a recent historical artifact. As a species universal showing little variation in occurrence across contemporary populations, it must be understood in evolutionary terms. Supporters of the “grandmother hypothesis” explain menopause as a n adaptive feature in itself. Others see menopause as a byproduct of the increased lifespan of
Homo sapiens. Plieotropy theory may help to explain menopause in broader mammalian terms.
The evolution of premature reproductive senescence and menopause in human females [PDF]
Hill & Hurtado
Human nature, 1991
Ache data do not support the proposition that females can gain greater fitness benefits in old age by helping kin rather than continuing to reproduce. Nevertheless, one crucial parameter in the model, when adjusted to the highest value within the measured 95% confidence interval, would lead to the evolution of reproductive senescence at about 53 years of age. Further investigation is necessary to determine whether the kin selection hypothesis of menopause can account for its current maintenance in most populations.
Pleiotropy, natural selection, and the evolution of senescence [1ère page] [PDF]
George C. Williams
Vulgarisation, réseaux sociaux
Un bon article, présentant les controverses :
How Much Did Grandmothers Influence Human Evolution? [Texte]
Smithsonian magazine, 2021
Sievert argues that as the human lifespan potential became longer and longer, the female body did not simultaneously evolve to make enough eggs to keep up. The maximum potential lifespan, therefore, grew to outpace egg production.
Evolutionary Math and Just-So Stories [Texte]
Quanta Magazine, 2018
Evolutionary stories like the grandmother hypothesis are easy to construct from mathematical models, but how well do they reflect reality?
Présentation honnête :