James E. Coxworth

Grandmothers and the evolution of human longevity: A review of findings and future directions

Women and female great apes both continue giving birth into their forties, but not beyond. However humans live much longer than other apes do. Even in hunting and gathering societies, where the mortality rate is high, adult life spans average twice those of chimpanzees, which become decrepit during their fertile years and rarely survive them. Since women usually remain healthy through and beyond childbearing age, human communities include substantial proportions of economically productive postmenopausal women. A grandmother hypothesis8–12 may explain why greater longevity evolved in our lineage while female fertility still ends at ancestral ages. This hypothesis has implications for the evolution of a wide array of human features. Here we review some history of the hypothesis, recent findings, and questions for ongoing research.

Family Provisioning Is Not the Only Reason Men Hunt

Gurven and Hill (2009) ask, “Why do men hunt?” As they say, “The observation that men hunt and women gather supported the simplistic view of marriage as a cooperative enterprise. Greater sophistication suggests that males may often be motivated by mating and status rather than offspring investment” (p. 60). We agree (e.g., Hawkes 1990, 1991; Hawkes et al. 1991, 2001a, 2001b). This is the revision we first proposed nearly 20 years ago (Hawkes 1990) and have elaborated several times since. Having endorsed our point, Gurven and Hill then reject it, expressing continuing confidence in the idea that “men’s food production efforts are mainly motivated by a concern for familial welfare” (p. 68). Their rejection of our argument and related reaffirmation of conventional wisdom stem from a misunderstanding of data from the Paraguayan Ache and Tanzanian Hadza and a failure to appreciate the importance of other sources of information. We elaborate this critique on four key points.

Grandmothering drives the evolution of longevity in a probabilistic model.

We present a mathematical model based on the Grandmother Hypothesis to simulate how human post-menopausal longevity could have evolved as ancestral grandmothers began to assist the reproductive success of younger females by provisioning grandchildren. Grandmothers׳ help would allow mothers to give birth to subsequent offspring sooner without risking the survival of existing offspring. Our model is an agent-based model (ABM), in which the population evolves according to probabilistic rules governing interactions among individuals. The model is formulated according to the Gillespie algorithm of determining the times to next events. Grandmother effects drive the population from an equilibrium representing a great-ape-like average adult lifespan in the lower twenties to a new equilibrium with a human-like average adult lifespan in the lower forties. The stochasticity of the ABM allows the possible coexistence of two locally-stable equilibria, corresponding to great-ape-like and human-like lifespans. Populations with grandmothering that escape the ancestral condition then shift to human-like lifespan, but the transition takes longer than previous models (Kim et al., 2012). Our simulations are consistent with the possibility that distinctive longevity is a feature of genus Homo that long antedated the appearance of our species.

Grandmothering life histories and human pair bonding

Significance Pair bonds are universal in human societies and distinguish us from our closest living relatives. They characteristically involve men’s proprietary claims over women—mate guarding—which in animals generally is both predicted and observed to be more frequent when sex ratios in the fertile ages are male-biased. A marked male bias in the fertile ages evolved in our lineage as longevity increased without an extension of female fertility. We compare the sex-ratio shift in simulations of the grandmother hypothesis to demographic data from chimpanzees and human hunter–gatherers then connect the expanded proportions of older men to benefits for mate guarding, the evolution of pair bonds, and the long recognized importance of male alliances in human social life. The evolution of distinctively human life history and social organization is generally attributed to paternal provisioning based on pair bonds. Here we develop an alternative argument that connects the evolution of human pair bonds to the male-biased mating sex ratios that accompanied the evolution of human life history. We simulate an agent-based model of the grandmother hypothesis, compare simulated sex ratios to data on great apes and human hunter–gatherers, and note associations between a preponderance of males and mate guarding across taxa. Then we explore a recent model that highlights the importance of mating sex ratios for differences between birds and mammals and conclude that lessons for human evolution cannot ignore mammalian reproductive constraints. In contradiction to our claim that male-biased sex ratios are characteristically human, female-biased ratios are reported in some populations. We consider the likelihood that fertile men are undercounted and conclude that the mate-guarding hypothesis for human pair bonds gains strength from explicit links with our grandmothering life history.

Brief communication: Adrenal androgens and aging: Female chimpanzees (Pan troglodytes) compared with women.

Ovarian cycling continues to similar ages in women and chimpanzees yet our nearest living cousins become decrepit during their fertile years and rarely outlive them. Given the importance of estrogen in maintaining physiological systems aside from fertility, similar ovarian aging in humans and chimpanzees combined with somatic aging differences indicates an important role for nonovarian estrogen. Consistent with this framework, researchers have nominated the adrenal androgen dehydroepiandrosterone (DHEA) and its sulfate (DHEAS), which can be peripherally converted to estrogen, as a biomarker of aging in humans and other primates. Faster decline in production of this steroid with age in chimpanzees could help explain somatic aging differences. Here, we report circulating levels of DHEAS in captive female chimpanzees and compare them with published levels in women. Instead of faster, the decline is slower in chimpanzees, but from a much lower peak. Levels reported for other great apes are lower still. These results point away from slowed decline but toward increased DHEAS production as one of the mechanisms underlying the evolution of human longevity.

Blood cell telomere lengths and shortening rates of chimpanzee and human females

Slower rates of aging distinguish humans from our nearest living cousins. Chimpanzees rarely survive their forties while large fractions of women are postmenopausal even in high‐mortality hunter–gatherer populations. Cellular and molecular mechanisms for these somatic aging differences remain to be identified, though telomeres might play a role. To find out, we compared telomere lengths across age‐matched samples of female chimpanzees and women.

Religiosity, Spirituality, and Psychological Distress in African-Americans at Risk for Having a Hereditary Cancer Predisposing Gene Mutation

Elevated psychological distress has been observed among people at increased risk for familial cancer. Researchers consider religiosity and spirituality (RS) to be positive coping mechanisms associated with reduced psychological distress. Relatively little is known about the impact of RS on genomic health issues. The objectives of our study were: (1) describe the prevalence of RS and depressive symptoms and (2) explore how RS relates to psychological distress in a cohort of individuals with a ≥25% prior probability of a genetic predisposition to cancer. Participants (n = 99) were drawn from an African‐American, Louisiana‐based kindred with a mutation at the BRCA1 locus. This analysis reports findings from a survey assessing RS and the use of three types of religious coping styles: collaborative, self‐directing, and deferring. Clinically significant depressive symptoms were relatively high (27%); with females (33%) more likely than males (17%) to report symptoms (P < 0.01). The majority of participants reported being highly religious. The most commonly employed religious problem solving style used by participants was collaborative (

Age-related decline in ovarian follicle stocks differ between chimpanzees (Pan troglodytes) and humans

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Increased longevity evolves from grandmothering

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Exploring attitudes, beliefs, and communication preferences of Latino community members regarding BRCA1/2 mutation testing and preventive strategies.

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