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Father absence in early life has been shown to be associated with accelerated reproductive development in girls. Evolutionary social scientists have proposed several adaptive hypotheses for this finding. Though there is variation in the detail of these hypotheses, they all assume that family environment in early life influences the development of life-history strategy, and, broadly, that early reproductive development is an adaptive response to father absence. Empirical evidence to support these hypotheses, however, has been derived from WEIRD (Western, Educated, Industrialized, Rich and Democratic) populations. Data from a much broader range of human societies are necessary in order to properly test adaptive hypotheses. Here, we review the empirical literature on father absence and puberty in both sexes, focusing on recent studies that have tested this association beyond the WEIRD world. We find that relationships between father absence and age at puberty are more varied in contexts beyond WEIRD societies, and when relationships beyond the father–daughter dyad are considered. This has implications for our understanding of how early-life environment is linked to life-history strategies, and for our understanding of pathways to adult health outcomes, given that early reproductive development may be linked to negative health outcomes in later life This article is part of the theme issue ‘Developing differences: early-life effects and evolutionary medicine’.

What motivates grandparents to their altruism? We review answers from evolutionary theory, sociology, and economics. Sometimes in direct conflict with each other, these accounts of grandparental investment exist side-by-side, with little or no theoretical integration. They all account for some of the data, and none account for all of it. We call for a more comprehensive theoretical framework of grandparental investment that addresses its proximate and ultimate causes, and its variability due to lineage, values, norms, institutions (e.g., inheritance laws), and social welfare regimes. This framework needs to take into account that the demographic shift to low fecundity and mortality in economically developed countries has profoundly altered basic parameters of grandparental investment. We then turn to the possible impact of grandparental acts of altruism, and examine whether benefits of grandparental care in industrialized societies may manifest in terms of less tangible dimensions, such as the grandchildren's cognitive and verbal ability, mental health, and well-being. Although grandparents in industrialized societies continue to invest substantial amounts of time and money in their grandchildren, we find a paucity of studies investigating the influence that this investment has on grandchildren in low-risk family contexts. Under circumstances of duress – for example, teenage pregnancy or maternal depression – there is converging evidence that grandparents can provide support that helps to safeguard their children and grandchildren against adverse risks. We conclude by discussing the role that grandparents could play in what has been referred to as Europe's demographic suicide.

Across human cultures, grandparents make a valued contribution to the health of their families and communities. Moreover, evidence is gathering that grandparents have a positive impact on the development of grandchildren in contemporary industrialized societies. A broad range of factors that influence the likelihood grandparents will invest in their grandchildren has been explored by disciplines as diverse as sociology, economics, psychology and evolutionary biology. To progress toward an encompassing framework, this study will include biological relatedness between grandparents and grandchildren, a factor central to some discipline's theoretical frameworks (e.g., evolutionary biology), next to a wide range of other factors in an analysis of grandparental investment in contemporary Europe. This study draws on data collected in the Survey of Health, Ageing and Retirement in Europe from 11 European countries that included 22,967 grandparent-child dyads. Grandparents reported biological relatedness, and grandparental investment was measured as the frequency of informal childcare. Biological and non-biological grandparents differed significantly in a variety of individual, familial and area-level characteristics. Furthermore, many other economic, sociological, and psychological factors also influenced grandparental investment. When they were controlled, biological grandparents, relative to non-biological grandparents, were more likely to invest heavily, looking after their grandchildren almost daily or weekly. Paradoxically, however, they were also more likely to invest nothing at all. We discuss the methodological and theoretical implications of these findings across disciplines.

This chapter review the evidence that humans receive important help from other individuals in raising children, by drawing together empirical evidence that the availability of family members affects child health and wellbeing and female fertility rates. In the first section we will concentrate on the evidence for the effects of kin on child well-being in pre-demographic transition societies. In the second section we will tackle the effects of kin on children in post-transition societies. Finally, in the third section we will present evidence that kin may affect fertility rates. Adapted from the source document.

There is growing evidence that the reproductive schedules of female mammals can be affected by conditions experienced during early development, with low parental investment leading to accelerated life-history strategies in the offspring. In humans, the relationships between early-life conditions and timing of puberty are well studied, but much less attention has been paid to reproductive behaviour. Here, we investigate associations between early-life conditions and age at first pregnancy (AFP) in a large, longitudinally studied cohort of British women (n = 4553). Low birthweight for gestational age, short duration of breastfeeding, separation from mother in childhood, frequent family residential moves and lack of paternal involvement are all independently associated with earlier first pregnancy. Apart from that of birthweight, the effects are robust to adjustment for family socioeconomic position (SEP) and the cohort member's mother's age at her birth. The association between childhood SEP and AFP is partially mediated by early-life conditions, and the association between early-life conditions and AFP is partially mediated by emotional and behavioural problems in childhood. The overall relationship between early-life adversities and AFP appears to be approximately additive.

Exogenous shocks during sensitive periods of development can have long-lasting effects on adult phenotypes including behavior, survival and reproduction. Cooperative breeding, such as grandparental care in humans and some other mammal species, is believed to have evolved partly in order to cope with challenging environments. Nevertheless, studies addressing whether grandparental investment can buffer the development of grandchildren from multiple adversities early in life are few and have provided mixed results, perhaps owing to difficulties drawing causal inferences from non-experimental data. Using population-based data of English and Welsh adolescents (sample size ranging from 817 to 1197), we examined whether grandparental investment reduces emotional and behavioral problems in children resulting from facing multiple adverse early life experiences (AELEs), by employing instrumental variable regression in a Bayesian structural equation modeling framework to better justify causal interpretations of the results. When children had faced multiple AELEs, the investment of maternal grandmothers reduced, but could not fully erase, their emotional and behavioral problems. No such result was observed in the case of the investment of other grandparent types. These findings indicate that in adverse environmental conditions the investment of maternal grandmothers can improve child wellbeing.

Background With an increasing number of grandparents providing care to their grandchildren, calls have been made for these caregivers to be considered important stakeholders in encouraging children’s engagement in health-promoting behaviors, such as physical activity. Understanding the perspectives of grandparents who provide care is crucial to informing efforts that aim to increase children’s physical activity, yet little is understood about their perceptions of specific barriers and enablers to promoting children’s physical activity and reducing screen time. The present study sought to explore these perceptions. Methods Semi-structured focus groups and individual interviews were conducted with grandparents who reported providing care to a grandchild aged 3 to 14 years. A total of 20 grandparents were sampled (mean age = 67.8 years). Data were subjected to reflexive thematic analysis. Results Key reported barriers to physical activity included (i) the effort (physical and logistical) and financial cost associated with organizing physical activities, (ii) grandparents’ age and mobility issues (e.g., due to injury or illness), (iii) caring for children of different ages (e.g., older children having different physical activity interests than younger children), and (iv) a local environment that is not conducive to physical activity (e.g., lack of appropriate facilities). Barriers to reducing screen time included (i) parents sending children to care with electronic devices and (ii) children’s fear of missing out on social connection that occurs electronically. Strategies and enablers of physical activity included (i) integrating activity into caregiving routines (e.g., walking the dog), (ii) involving grandchildren in decision making (e.g., asking them in which physical activities they wish to engage), (iii) encouraging grandchildren to engage in activity with other children, and (iv) creating a physical and social environment that supports activity (e.g., owning play equipment). A common strategy for reducing screen time was the creation of a home environment that is not conducive to this activity (e.g., removing electronic devices from view). Conclusions Findings suggest that grandparents may benefit from resources that assist them to identify activities that are inexpensive and require minimal effort to organize. Activities that account for grandparents’ age and health status, as well as any environmental barriers, are likely to be well-received.

From changing diapers and minding the kids when school is out to providing support when they set fire to the carpet, grandparents can be invaluable to have around. What motivates grandparents to lend a hand? Several disciplines have offered answers. The most important accounts come from life-history theory and evolutionary psychology, sociology, and economics. These accounts exist side-by-side, but there is little theoretical integration among them. But regardless of whether grandparental investment is traced back to ancestral selection pressure or attributed to an individual grandparent's values or norms, one important question is, What impact does it have in industrialized, low-fertility, low-mortality societies? We briefly review the initial evidence concerning the impact of grandparental investment in industrialized societies and conclude that in difficult circumstances, grandparents can provide the support that safeguards their grandchildren's development. Additional cross-disciplinary research to examine the effects of intergenerational transfers in our evolutionarily unique environment of grandparenthood is needed.

Cultural, ecological, familial and physiological factors consistently influence fertility behaviours, however, the proximate psychological mechanisms underlying fertility decisions in humans are poorly understood. Understanding the psychological mechanisms underlying human fertility may illuminate the final processes by which some of these known predictors have their influence. To date, research into the psychological mechanisms underlying fertility has been fragmented. Aspects of reproductive psychology have been examined by researchers in a range of fields, but the findings have not been systematically integrated in one review. We provide such a review, examining current theories and research on psychological mechanisms of fertility. We examine the methods and populations used in the research, as well as the disciplines and theoretical perspectives from which the work has come. Much of the work that has been done to date is methodologically limited to examining correlations between ecological, social and economic factors and fertility. We propose, and support with examples, the use of experimental methods to differentiate causal factors from correlates. We also discuss weaknesses in the experimental research, including limited work with non-WEIRD (western, educated, industrialized, rich and democratic) populations.

•Explores anecdotal evidence that grandparents could influence paediatric vaccine uptake.•Reviews articles that suggest grandparents influence parents’ decision to vaccinate children.•Currently there is no direct evidence that grandparents influence parents’ vaccination decisions.•Articles reviewed highlight indirect evidence of grandparental influence on parents’ decisions.•Highlights grandparents’ attitudes and beliefs are echoed in parents’ decision to vaccinate. The global reduction in childhood infectious diseases since the 1960s is primarily due to the success of extensive worldwide immunisation campaigns. However, the universal vaccination coverage program appears to have lost momentum in the wake of negative, unfounded claims about the safety of vaccines. While parents of the 21st century have little first-hand knowledge of devastating childhood diseases, grandparents are more likely to remember family and community members who were afflicted. In the current age of vaccine hesitancy and science scepticism, where research-informed arguments are not always persuasive, grandparents, through their experience of the diseases, may positively influence paediatric vaccine uptake. This paper reviews the literature investigating potential direct or indirect influences of grandparents on parents’ decisions to vaccinate their children. A database search using the keywords immunisation, vaccination, children and grandparents resulted in 1988 articles. Titles were screened for relevance and seventy-seven results were retained. After the abstracts were read, only five articles that either explored paediatric vaccines, factors promoting and/or inhibiting paediatric vaccine use and decision-making strategies were reviewed. One paper located through Google Scholar, which failed to show up on database searches, was also retained for a total of six papers. While none of the six papers set out to explore the impact of grandparents on vaccine uptake, they found that grandparents were involved to varying degrees in paediatric vaccine uptake within young families. The research clearly showing that grandparents, and older people more generally, promote vaccination uptake is not currently available. The dearth of literature shows the need for research exploring the perceived and real influences of grandparents on childhood vaccination. This will establish whether grandparents’ memory and knowledge of preventable childhood infectious diseases could be harnessed as a public health measure to counteract the current, ill-informed, negative attention on paediatric vaccines.