Grandmother Hypothesis Research Articles

Grandparents' social capital hypothesis: Relationships with grandparents and young adults' trust through kinship support

AbstractObjectiveThe current research investigated how relationships with grandparents were associated with young adults' trust levels.BackgroundTo complement the grandmother hypothesis that explains the adaptiveness of human longevity from the perspective of instrumental contributions, a “grandparents' social capital hypothesis” was proposed, indicating that grandparents benefit social capital construction for their grandchildren, the effect of which could be symbolic for young adults. Older adults, who tend to have high levels of trust and the connections within extended family, could have positive impacts on young adults' trust.MethodUsing convenience sampling, we surveyed 314 Chinese young adults on quality and quantity of their interactions with grandparents, kinship support, and their generalized trust and particularized trust toward relatives through trust games. Path analysis was used to analyze the data.ResultsQuality of the relationship with grandparents, rather than quantity of contact with them, was related to young adults' higher levels of particularized and generalized trust. Kinship support mediated the associations between high‐quality relationships with grandparents and young adults' particularized trust, as well as generalized trust.ConclusionGrandparents could play a symbolic role in social capital accumulation for young adults through the mediation effect of kinship support.ImplicationsThese findings provide new evidence supporting older adults' constructive role in human societies and shed light on possible strategies to cultivate social capital in the communities.

Impact of kinship support on child mortality in the Upper East Region of Ghana: assessing the Grandmother Hypothesis.

The grandmother is an important kin member whose contribution to childcare and survival has been recognized in the literature, hence the Grandmother Hypothesis. This article examines the effect of the presence of a grandmother on child mortality. Data were obtained from the Navrongo Health and Demographic Surveillance System, located in the Upper East Region of Ghana. Children born between January 1999 and December 2018 were included in the analysis. Person-months lived for each child were generated. The multilevel Poisson regression technique was employed to investigate the effect of a grandmother on child survival. In all, 57116 children were included in the analysis, of which 7% died before age 5y. Person-months were generated for the children, which produced 2.7 million records, with about 487800 person-years. After controlling for confounders, results showed that children in households with paternal grandmothers are 11% less likely to die compared with those without paternal grandmothers. However, when other confounders were taken into accounts, the beneficial effect of maternal grandmothers disappeared. We conclude that the presence of grandmothers improves child survival, thus sustaining the Grandmother Hypothesis. The experiences of these grandmothers should be tapped to improve child survival, particularly in rural areas.

Grandparental co-residence and grandchild survival: the role of resource competition in a pre-industrial population.

Although grandparents are and have been important alloparents to their grandchildren, they are not necessarily only beneficial but can also compete with grandchildren over limited resources. Competition over parental care or other resources may exist especially if grandparents live in the same household with grandchildren and it can be dependent on grandchild age. By utilizing demographic data collected from historic population registers in Finland between 1761 and 1895 (study sample n = 4041) we investigate whether grandparents living in the same household with grandchildren are detrimental or beneficial for grandchild survival. Having a living but not co-residing grandmother or grandfather were both associated with better survival whereas having a co-resident grandfather was associated with lower chance to survive for infants (age < 1 year). Separating the effect between maternal and paternal grandparents and grandmothers and grandfathers revealed no differences in the effects between lineages. Negative effect of having a co-residing grandfather was not significant when grandfathers were separated for lineage specific models. These results implicate that accounting for the co-residence status and child's age, grandparents were mostly beneficial when not co-residing with very young children and that having a co-residing grandfather at that age could be associated with lower chances to survive. Predictions made by grandmother hypothesis and resource competition both received support. The results presented here also offered comparison points to preindustrial and contemporary three-generational families.

Justice for the Menopause: A Research Agenda

&#x0D; &#x0D; &#x0D; Menopause is defined by its relationship to menstruation––it is the cessation of menstruation. Medical texts identify menopause as part of the cycle of “decay” associated with female reproductive functions; early menopause is often a dreaded result of various medical treatments and a sign of disfunction.&#x0D; It turns out that only three types of animals experience menopause: killer whales, short-finned pilot whales, and humans, while other animals can reproduce until death. Although the precise relationship between evolutionary theory and the physical development of human menopause is still uncertain, scientists and anthropologists suggest that the “grandmother hypothesis” provides a partial explanation: older women, who can no longer produce their own children, ensure their genetic legacy by playing a critical role in helping to feed, raise, and nurture their grandchildren.&#x0D; &#x0D; &#x0D; &#x0D; The average woman will spend almost as many years “post-menopause” as they will menstruating, and they may spend four years (or more) experiencing perimenopausal symptoms, the transition time between “normal” menstruation and menopause. But legal issues relating to perimenopause, menopause, and post-menopause are just beginning to surface, prompted by the movement towards menstrual justice, feminist jurisprudence, and developments in the law of aging.&#x0D; This Essay is an initial effort to catalogue various legal approaches to menopause and to set out areas for further analysis. It briefly explores cultural images of menopause and post-menopausal women, including the ubiquitous hot flashes; analyzes potential legal claims for menopausal justice; and suggests the interrelationship between such approaches and social attitudes towards menopause. It suggests that “normalizing” menopause––acknowledging its realities––is one means for removing the associated stigma and “disabilities” and might result in reinterpreting existing laws and guiding future legal reforms.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Reevaluating the grandmother hypothesis.

Menopause is an evolutionary mystery: how could living longer with no capacity to reproduce possibly be advantageous? Several explanations have been offered for why female humans, unlike our closest primate relatives, have such an extensive post-reproductive lifespan. Proponents of the so-called "grandmother hypothesis" suggest that older women are able to increase their fitness by helping to care for their grandchildren as allomothers. This paper first distinguishes the grandmother hypothesis from several other hypotheses that attempt to explain menopause, and then develops a formal model by which these hypotheses can be compared and tested by empirical researchers. The model is then modified and used to respond to a common objection to the grandmother hypothesis: that human fathers, rather than grandmothers, are better suited to be allomothers due to their physical strength and a high incentive to invest in their own children. However, fathers-unlike maternal grandmothers-can never be sure that the children they are caring for are their own. Incorporating paternity uncertainty into the model demonstrates the conditions under which the grandmother hypothesis is more plausible than a hypothesis that focuses on the contributions of men.

Ongoing selection for a uniquely human null allele of SIGLEC12 in world-wide populations may protect against the risk of advanced carcinomas.

The CD33-related subset of Siglecs (Sialic Acid binding Immunoglobulin superfamily Lectins) are well-known signaling receptors on immune cells, but Siglec-XII is also expressed on epithelial cell surfaces.1, 2 A point mutation eliminating the canonical sialic acid-binding function of Siglec-XII is unique to humans2, 3 and fixed in all populations worldwide. We and others reported a further polymorphic frameshift mutation in the human SIGLEC12 gene that appears to be undergoing selection favoring a null and/or truncated allele in all human populations.1, 4, 5 Individuals who have an ancestral SIGLEC12 allele with an intact open reading frame appear more prone to develop advanced carcinomas.6 The likely mechanism involves aberrant signaling via recruitment of the SHP2 phosphatase to the cytosolic tail of the dysfunctional Siglec-XII. We appreciate the strongly supportive and positive comments by Voskarides7 about our article published in this journal,6 which suggested that human-specific polymorphic pseudogenization of SIGLEC12 protects against advanced cancer progression. Voskarides appropriately emphasizes the relevance of George Williams' classic theory of “antagonistic pleiotropy”,8 in which selection for an allele's beneficial effects in early life can have deleterious consequences in late life.9 A 2018 meta-analysis of 247 Genome-Wide Association Studies (GWAS) identified an association between 1377 cancer-associated genes in populations living in extremely cold environments and very high altitudes.10-12 It is suggested that genetic variants that contributed to the survival of early humans living in these extreme environments are now associated with cancer incidence in contemporary populations, that is, the accumulation of deleterious mutations in tumor-suppressor, apoptosis, and cell cycle regulation genes.7 In response to the interesting commentary which compares our discovery with previous examples of antagonistic pleiotropy, we should emphasize that our findings on Siglec-XII are somewhat different from these instances. First, we report selection for the null alleles of SIGLEC12 in all human populations. Second, SIGLEC12 expression is not associated with the incidence or risk for carcinomas. Rather, the null state is associated with a decrease in advanced carcinomas commonly found in humans.1, 6, 13 Third, unlike the genes discussed by Voskarides, many of which are extensively studied and fundamental to cancer biology, Siglec-XII has received very little attention to date. Moreover, our studies represent the first implications of SIGLEC12 in human cancer, with currently unknown potential impact on cancer biology, prevention, and therapy. Despite the above differences between our findings6 and those of Voskarides, we believe his perspective gives some useful additional clues. First, the deleterious SIGLEC12 mutation is not fully studied and understood under stressful conditions. It might be that the status of SIGLEC12 in populations living in extreme vs non-extreme conditions is different, following the trend shown for tumor-suppressor and DNA repair genes. Our data also shows that unlike the other examples, Siglec-XII seems to be a suitable prognostic marker. In a large cohort study of late-stage colon cancer patients, we found that Siglec-XII non-expressors had a two fold higher survival than expressors.6 Siglec-XII also has the potential to be a therapeutic target, as we previously also showed that it undergoes rapid endocytosis upon binding a Siglec-XII antibody, allowing selective delivery of a conjugated toxin.1 In keeping with the conventional theory, Voskarides also emphasizes that it is very hard for natural selection to eliminate mutations that cause cancer after the end of reproductive age. With SIGLEC12, ongoing selection for the null state might be an example of a “less-is-more” evolutionary scenario, where losing expression of the full-length protein is beneficial under current selective pressures.6, 14, 15 It is also potentially an example of selection for prolonged post-reproductive life span, a trait that is unique to humans among all land mammals. Indeed, it is consistent with the grandmother hypothesis, which posits that post-reproductive individuals (predominantly grandmothers) can improve the survival of helpless younger kin.16-18 In this regard, we have reported one example of a uniquely human allele of CD33 that protects against cognitive decline during the post-reproductive lifespan of humans.19, 20 Overall, we believe that the scenario with Siglec-XII is different from other cancer genes undergoing positive selection, but further studies are needed.

Grandmaternal investment and early childhood injury: the role of X-chromosomal relatedness

Evolutionary theory posits that grandmothers can increase their inclusive fitness by investing time and resources in their grandchildren. According on the X-linked grandmother hypothesis, the asymmetric inheritance of X-chromosomes should be responsible for the biased effect of the investment by maternal and paternal grandmothers towards granddaughters and grandsons. The British Millennium Cohort Study (n=4445 children) was used to investigate the association between grandmaternal childcare and children's injuries between the ages of 9 months and 3 years. Support was found for the X-linked grandmother hypothesis predicting that the investment of paternal grandmothers benefits more granddaughters than grandsons, the investment of paternal grandmothers benefits granddaughters more than the investment of maternal grandmothers, and the investment of maternal grandmothers is similarly associated with the injuries of granddaughters and grandsons. However, no support was found for the prediction that maternal grandmothers benefit more grandsons than paternal grandmothers. Thus, some, although not univocal, evidence for the prediction that X-chromosomal relatedness shapes the grandmaternal effect on child outcomes was found.

The Centrality of Ancestral Grandmothering in Human Evolution.

When Fisher, Williams, and Hamilton laid the foundations of evolutionary life history theory, they recognized elements of what became a grandmother hypothesis to explain the evolution of human postmenopausal longevity. Subsequent study of modern hunter-gatherers, great apes, and the wider mammalian radiation has revealed strong regularities in development and behavior that show additional unexpected consequences that ancestral grandmothering likely had on human evolution, challenging the hypothesis that ancestral males propelled the evolution of our radiation by hunting to provision mates and offspring. Ancestral grandmothering has become a serious contender to explain not only the large fraction of post-fertile years women live and children's prolonged maturation yet early weaning; it also promises to help account for the pair bonding that distinguishes humans from our closest living evolutionary cousins, the great apes (and most other mammals), the evolution of our big human brains, and our distinctive preoccupation with reputations, shared intentionality and persistent cultural learning that begins in infancy.

Grandparenthood from the Evolutionary Perspective

Abstract Humans belong to the few species in which females and males live for a relatively long time after the end of their reproductive period. In this paper, I present theoretical concepts explaining the relatively long post-reproductive life span of humans and the menopause: the grandmother hypothesis and the diet, intelligence and longevity model (also known as the embodied capital model). The grandmother hypothesis, offering an evolutionary explanation of the menopause, shows that throughout most of the human history, childrearing has been a cooperative endeavour. In all societies across the world, mothers, fathers, grandparents, and other family members cooperate in networks consisting of kins and non-kins in order to assist with child rearing. The paper also argues how ethnographic research can contribute to the testing of evolutionary theories of grandparenthood in contemporary societies.

A mathematical model for the effects of grandmothering on human longevity.

Although females in human and the great ape populations reach the end of fertility at similar ages (approximately 45 years), female humans often live well beyond their post-fertile years, while female primates typically die before or shortly after the end of fertility. The grandmother hypothesis proposes that the care-giving role provided by post-fertile females contributed to the evolution of longevity in human populations. When post-fertile females provide care for weaned infants, mothers are able to have their next baby sooner without compromising the chances of survival of their previous offspring. Thus, the post-menopausal longevity that is unique to human populations may be an evolutionary adaptation. In this work, we construct, simulate, and analyze an ordinary differential equations mathematical model to study the grandmother hypothesis. Our model describes the passage of the individuals of a population through five life stages in the cases with and without grandmothering. We demonstrate via numerical simulation of the mathematical model that grandmothering care is sufficient to significantly increase adult life expectancy. We also investigate the relationship between the number of weaned infants that a post-fertile female can care for at a given time and the steady-state age distributions of a population.

Social evolution in Plio-Pleistocene hominins: Insights from hamadryas baboons and paleoecology

Reconstructions of hominin evolution have long benefited from comparisons with nonhuman primates, especially baboons and chimpanzees. The hamadryas baboon (Papio hamadryas) is arguably one of the best such models, as it exhibits both the male kin bonding and the cross-sex pair bonding thought to have been important in hominin evolution. Here we link processes of behavioral evolution in hamadryas baboons with those in a Plio-Pleistocene hominin, provisionally identified as Homo erectus (sensu lato) – a pivotal species in that its larger body and brain size and wider ranging patterns increased female costs of reproduction, increasing the importance of sociality. The combination of these higher costs of reproduction and shifts in diet and food acquisition have previously been argued to have been alleviated either via strengthening of male-female bonds (involving male provisioning and the evolution of monogamy) or via the assistance of older, post-reproductive females (leading to post-reproductive longevity in females, i.e., the grandmother hypothesis). We suggest that both arrangements could have been present in Plio-Pleistocene hominins if they lived in multilevel societies. Here we expand on our earlier scenario with two sets of recent data in support of it, (1) archaeological data from the 2 million year old Oldowan site of Kanjera South, Kenya and other sites that are suggestive of tool dependent foraging on nutrient dense resources (animal carcasses and plant underground storage organs), cooperation, and food sharing; and (2) a pattern of genetic variation in hamadryas baboons that suggests the operation of kin selection among both males and females at multiple levels of society. Taken together, these two sets of data strengthen our model and support the idea of a complex society linked by male-male, male-female, and female-female bonds at multiple levels of social organization in Plio-Pleistocene hominins.

MATHEMATICAL MODELLING OF THE EVOLUTION OF HUMAN BEHAVIOURS AND STRATEGIC CHOICE

Evolutionary anthropology seeks answers to the eternal philosophical question: how have we come to be? Studies in evolutionary anthropology attempt to explain the evolution of uniquely human behaviours by investigating the mechanisms that drive different trajectories. In this thesis dynamic mathematical models are built to investigate the tradeoffs defining divergent evolutionary pathways of strategic choice. This is done by comparing evolutionary equilibria at great ape-like and hunter-gatherer-like life histories. One investigation considers the evolution of pair bonding in humans. Mate guarding that pays off in increased likelihood of obtaining paternities outperforms strategies of paternal care at hunter-gatherer-like male-biased sex ratios while multiple mating is the evolutionary equilibrium at chimpanzee-like female-biased sex ratios. This demonstrates the promise of mate guarding as a pathway to social monogamy and links male reproductive strategies to the grandmother hypothesis through sex ratio dependence. Competition and care as male reproductive strategies are then investigated more generally in an ordinary differential equation model. Equilibria depend on life history and benefit parameters. An integro-difference equation model that explores the effect of non-parental imitation on the coevolution of low fertility at high socio-economic status is also given, applying Darwinian selection to a contemporary case of cultural evolution. This thesis shows that competitive strategies often pay off at human-like parameters despite the possibility of increased offspring survivorship through care. However, coexistence or persistence of a non-competitive strategy may also occur under specific parameters. Uncovering drivers of the evolution of different male reproductive strategies is important for guiding further research and shedding light on why we are so different from other great apes.

Does grandparental care select for a longer lifespan in non-human mammals?

Abstract Several non-human mammalian species provide grandparental care but remain fertile until death, unlike our species. This might call into question the ‘grandmother hypothesis’ that the ability to provide grandparental care, associated with an increase in the cost of breeding with age, promote the early cessation of reproduction. Here, we analyse individual longevity records from non-human mammals to determine whether the few species with grandparental care also stand out among mammals in terms of age-specific survival patterns. Indeed, females of species with grandparental care lived on average 43% longer than males (range: 24–61%), compared with 12% in other polygynous species (95% quantile: −8 to 30%), because of low baseline mortality rates and delayed onset of actuarial senescence. We discuss this finding with respect to the ‘stopping early’ vs. ‘living longer’ debate. We review the role of the environmental context and of the decrease in offspring performance with maternal age (Lansing effect). We formalize the idea of a continuum of parental–grandparental allocation instead of a discrete switch to grandparental care only. Lastly, we suggest that the evolution of menopause has been driven by different forces in different species.

Transition to Grandparenthood and Subjective Well-Being in Older Europeans: A Within-Person Investigation Using Longitudinal Data.

The transition to grandparenthood, that is the birth of the first grandchild, is often assumed to increase the subjective well-being of older adults; however, prior studies are scarce and have provided mixed results. Investigation of the associations between grandparenthood and subjective well-being, measured by self-rated life satisfaction, quality of life scores, and depressive symptoms, used the longitudinal Survey of Health, Ageing and Retirement in Europe from 13 countries, including follow-up waves between 2006 and 2015 (n = 64,940 person-observations from 38,456 unique persons of whom 18,207 had two or more measurement times). Both between-person and within-person (or fixed-effect) regression models were executed, where between-person associations represent results across individuals, that is, between grandparents and non-grandparents; within-person associations represent an individual's variation over time, that is, they consider whether the transition to grandparenthood increases or decreases subjective well-being. According to the between-person models, both grandmothers and grandfathers reported higher rate of life satisfaction and quality of life than non-grandparents. Moreover, grandmothers reported fewer depressive symptoms than women without grandchildren. The within-person models indicated that entry into grandmotherhood was associated with both improved quality of life scores and improved life satisfaction. These findings are discussed with reference to inclusive fitness theory, parental investment theory, and the grandmother hypothesis.

Low Evolutionary Selection Pressure in Senescence Does Not Explain the Persistence of Aβ in the Vertebrate Genome.

The argument is frequently made that the amyloid-β protein (Aβ) persists in the human genome because Alzheimer’s disease (AD) primarily afflicts individuals over reproductive age and, therefore, there is low selective pressure for the peptide’s elimination or modification. This argument is an important premise for AD amyloidosis models and therapeutic strategies that characterize Aβ as a functionless and intrinsically pathological protein. Here, we review if evolutionary theory and data on the genetics and biology of Aβ are consistent with low selective pressure for the peptide’s expression in senescence. Aβ is an ancient neuropeptide expressed across vertebrates. Consistent with unusually high evolutionary selection constraint, the human Aβ sequence is shared by a majority of vertebrate species and has been conserved across at least 400 million years. Unlike humans, the overwhelming majority of vertebrate species do not cease reproduction in senescence and selection pressure is maintained into old age. Hence, low selective pressure in senescence does not explain the persistence of Aβ across the vertebrate genome. The “Grandmother hypothesis” (GMH) is the prevailing model explaining the unusual extended postfertile period of humans. In the GMH, high risk associated with birthing in old age has lead to early cessation of reproduction and a shift to intergenerational care of descendants. The rechanneling of resources to grandchildren by postreproductive individuals increases reproductive success of descendants. In the GMH model, selection pressure does not end following menopause. Thus, evolutionary models and phylogenetic data are not consistent with the absence of reproductive selection pressure for Aβ among aged vertebrates, including humans. Our analysis suggests an alternative evolutionary model for the persistence of Aβ in the vertebrate genome. Aβ has recently been identified as an antimicrobial effector molecule of innate immunity. High conservation across the Chordata phylum is consistent with strong positive selection pressure driving human Aβ’s remarkable evolutionary longevity. Ancient origins and widespread conservation suggest the human Aβ sequence is highly optimized for its immune role. We detail our analysis and discuss how the emerging “Antimicrobial Protection Hypothesis” of AD may provide insights into possible evolutionary roles for Aβ in infection, aging, and disease etiology.

Life-History Evolution: Grandmothering in Space and Time

The evolutionary puzzle of the extended post-reproductive life of female humans has been explained by indirect fitness benefits gained by grandmothers helping raise their grandchildren. Two new studies support this 'grandmother hypothesis' and explore its limits in space and time.

Using Geographic Distance as a Potential Proxy for Help in the Assessment of the Grandmother Hypothesis

Life-history theory predicts that selection could favor the decoupling of somatic and reproductive senescence if post-reproductive lifespan (PRLS) provides additional indirect fitness benefits [1, 2]. The grandmother hypothesis proposes that prolonged PRLS evolved because post-reproductive grandmothers gain inclusive fitness benefits by helping their daughters and grandchildren [3, 4]. Because most historical human data do not report direct evidence of help, we hypothesized that geographic distance between individuals may be inversely related to their capacity to help. Using anexceptionally detailed dataset of pre-industrial French settlers in the St. Lawrence Valley during the 17th and 18th centuries, we assessed the potential for grandmothers to improve their inclusive fitness by helping their descendants, and we evaluated how this effect varied with geographic distance, ranging between 0 and 325km, while accounting for potential familial genetic and environmental effects [5-9]. Grandmothers (F0) who were alive allowed their daughters (F1) to increase their number of offspring (F2) born by 2.1 and to increase their number of offspring surviving to 15 years of age by 1.1 compared to when grandmothers were dead. However, the age at first reproduction was not influenced by the life status (alive or dead) of grandmothers. As geographic distance increased, the number of offspring born and lifetime reproductive success decreased, while the age at first reproduction increased, despite the grandmother being alive in these analyses. Our study suggests that geographic proximity has the potential to modulate inclusive fitness, supporting the grandmother hypothesis, and to contribute to our understanding of the evolution of PRLS.

An expanded theory of Alzheimer's caregiving.

The ancient and cross-culturally prevalent pattern of caregiving suggests that long-term caregiving is species characteristic for humans. If so, then an evolutionary account of the adaptation(s) that underwrite this caregiving is necessary, particularly for the one-sided and long-term nature of Alzheimer's caregiving. Four standard evolutionary explanations are evaluated: kin selection theory, the grandmother hypothesis, direct reciprocity, and indirect reciprocity. Each is found inadequate to explain caregiving because of the lack of reproductive benefits. These evolutionary accounts also assume that relationships are only valuable to the degree that they provide benefits and that relationship partners are predominantly motivated by self-interest. Attachment provides another explanation, which evolved initially to ensure infant protection and nurturance, but was exapted for important adult relationships. Attachment relationships naturally include caregiving and engender long-term relational commitment. Yet attachment theory is ambiguous about whether relationships are maintained for the sake of security benefits or because they have inherent value. This ambiguity undermines the explanatory value of attachment theory for Alzheimer's caregiving. Therefore, a shared identity theory is offered that highlights the inherent value of the relationship and the loved one, transcending the predominant focus on beneficial individual outcomes. The theory emphasizes the frequent human motivation to benefit others because of their mutual commitment, shared identity, and shared goals. The conclusion is that fully understanding and supporting the arduous efforts of caregiving for loved ones with Alzheimer's requires psychologists to fully appreciate and support the deep and meaningful motivations that often inspire the humanity seen in caregiving. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The New Science of Practical Wisdom.

Wisdom has been discussed for centuries in religious and philosophical texts. It is often viewed as a fuzzy psychological construct analogous to consciousness, stress, and resilience. This essay provides an understanding of wisdom as a scientific construct, based on empirical research starting in the 1970s. The focus is on practical rather than theoretical wisdom. While there are different conceptualizations of wisdom, it is best defined as a complex human characteristic or trait with specific components: social decision-making, emotional regulation, prosocial behavior (such as empathy and compassion), self-reflection, acceptance of uncertainty, decisiveness, and spirituality. These psychological processes involve the fronto-limbic circuitry. 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. Wisdom has important implications at individual and societal levels and is a major contributor to human thriving. We need to place a greater emphasis on promoting wisdom through our educational systems from elementary to professional schools.

Why does women's fertility end in mid-life? Grandmothering and age at last birth

Great apes, the other living members of our hominid family, become decrepit before the age of forty and rarely outlive their fertile years. In contrast, women – even in high mortality hunter-gatherer populations – usually remain healthy and productive well beyond menopause. The grandmother hypothesis aims to account for the evolution of this distinctive feature of human life history. Our previous mathematical simulations of that hypothesis fixed the end of female fertility at the age of 45, based on the similarities among living hominids, and then modeled the evolution of human-like longevity from an ancestral state, like that of the great apes, due only to grandmother effects. A major modification here allows the age female fertility ends to vary as well, directly addressing a version of the question, influentially posed by GC Williams six decades ago: Why isn't menopause later in humans? Our model is an agent-based model (ABM) that accounts for the coevolution of both expected adult lifespan and end of female fertility as selection maximizes reproductive value. We find that grandmother effects not only drive the population from an equilibrium representing a great ape-like longevity to a new human-like longevity, they also maintain the observed termination of women's fertility before the age of 50.