How much does family matter? Cooperative breeding and the demographic transition

Effects of family socioeconomic status on the self-expectations of children under grandparenting in China

Introduction

The increasing expansion of grandparenting necessitates further study of the effects of grandparenting on child development. This study investigated the relationship between family socioeconomic status (SES) and children's self-expectations in households involving grandparenting, using data from the "China Family Panel Studies" (CFPS). The CFPS is a national, large-scale, multidisciplinary social tracking survey conducted by the Institute of Social Science Survey (ISSS) at Peking University.

Methods

The analysis drew on data from 4,946 children aged 6-16 and their families, collected from CFPS2016 to CFPS2018. To determine whether grandparenting was involved, responses from the Children's parents' questionnaire were used. Any caregiving arrangement involving grandparents-whether during the day, at night, or both-was classified as grandparenting. Correlational and hierarchical regression analyses were conducted to examine the association between family SES and children's self-expectations.

Results

The findings revealed a significant negative correlation between family SES and children's self-expectations, including its various dimensions, in both groups of families. Additionally, family SES was found to negatively predict children's self-expectations. A potential explanation for this result is that children from low-income families may have a stronger desire to improve their environmental and social circumstances, fostering greater internal motivation and higher self-expectations. In comparison to families without grandparenting, those with grandparenting had significantly lower family SES, children's self-expectations, parent-child communication, and parental marital status, with more students studying in non-elite schools. Parent-child communication and residential areas for children can positively predict children's self-expectations in both groups of families.

Discussion

These findings highlight the significance of family SES and the influence of multiple factors for raising the self-expectations of children under grandparenting. Thus, to improve the quality of life for children under grandparent care and promote their physical and mental health requires a multi-level approach involving the state, society, and individuals within the family.

Fertility Behavior in the Context of Polygyny in Pakistan With the Moderating Effect of Household Wealth Status Evidences From Demographic and Health Survey 2017-18

INTRODUCTION

Fertility and population dynamics in Pakistan play a critical role in shaping the country's socio-economic development. High fertility rates contribute to rapid population growth and pose significant challenges to healthcare, education, and resource management. This study investigates the relationship between polygyny and fertility, with the moderating effect of household wealth status.

METHOD

The study utilizes data from the "Demographic and Health Survey 2017-18". It implies zero-truncated negative binomial regression, interaction effect, marginal analysis, and propensity score matching techniques. The total number of samples size is 50 495 women including 48 699 belonging to polygynous and 1796 with monogamous families.

RESULTS

Polygynous unions are generally associated with higher fertility rates than their monogamous counterparts, as indicated by an IRR of 1.03 (CI: 1.00-1.05). This finding is further supported by propensity score matching, controlling for household wealth status, education, husband's education, residency, and region. After accounting for these demographic factors, the analysis reveals that polygynous families, on average, have 14% more children than monogamous families. Additionally, the relationship between polygyny and fertility is influenced by household wealth status.

CONCLUSION

While the household wealth index typically shows a negative association with fertility, this pattern does not apply to polygynous families, where wealthier households tend to have more children than monogamous ones. This interaction between wealth and polygyny highlights a complex dynamic, suggesting that wealth amplifies fertility within polygynous unions, diverging from the general trend of declining fertility with increasing wealth.

Towards more horizontality in families? Sibling associations in socio-economic status in the Barcelona area in the sixteenth to nineteenth centuries

This paper explores the shift in family influence on socio-economic outcomes, focusing on sibling relationships, from the sixteenth to the nineteenth centuries in the Barcelona area. Our findings reveal a diminishing role of vertical ties (parents-children) and an increasing significance of horizontal ties (between siblings). Specifically, brothers who were first in the sibling group to marry exerted more influence on socio-economic persistence over time, aligning with the changes in familial dynamics since proto-industrialization. Gender dynamics highlight the influence of first-married brothers' influence, although first-married sisters were also significantly associated with non-first-married siblings' social mobility. The intensification of horizontal ties is seen as a cooperative model among siblings, challenging the notion of a complete loss of family influence during industrialization. The study contributes nuance to modernization theory by highlighting the enduring importance of kinship in industrial periods, especially among siblings.

Close and more distant relatives are associated with child mortality risk in historical Finland

Humans are characterised as cooperative breeders, as not only the parents but also other members of the social group take part in raising offspring. The individuals who invest most in childrearing are usually the more closely related individuals. However, most studies have concentrated on close kin and the effects of more distant kin remain unknown. Here, we investigated the associations of child mortality (<5 years, n = 32,000 children) with the presence of 36 different types of relatives, divided by lineage and sex, in a historical Finnish population. We found that the presence and greater number of several paternal relatives were associated with an increase in child mortality and many of these associations were seen among the wealthiest families, due to inheritance practices and shared resources. The presence of the maternal grandmother was associated with a decrease in child mortality and the most among poorer families, who probably needed the grandmother's contribution more than the wealthy. Our results bring new insights into the importance of kin and suggest that relatives can provide support or other resources but also compete for limited resources and care. The results give a broader perspective of human family life and increase understanding of the evolution of cooperative breeding.

The Effect of Parental Caregiving on the Fertility Expectations of Adult Children

Previous research has highlighted the positive impact of parents on their adult children's fertility plans through childcare, but the association between parental health and fertility expectations remains unclear. Thus, this paper offers a novel perspective on the issue of family support by investigating how caregiving responsibilities toward elderly parents affect adult children's decision to have a child. Using a long panel dataset for Australia, we examine whether adult children changed their fertility expectations after becoming care providers to their parents. To address issues of unobserved heterogeneity and selection into parenthood and caregiving, we employ generalized difference-in-differences models. Results show a 7% decrease in fertility expectations within two years of becoming a parental caregiver, with a stronger effect over time, consistent across genders and more pronounced for respondents with one child. These findings suggest that interventions aimed at reducing the caregiver burden could provide an opportunity to positively influence fertility levels.

Grandmotherhood is associated with reduced OXTR DNA methylation

In mammals, both parental and alloparental care are associated with increased brain oxytocin signaling. Grandmothers are important alloparents in many human families. Based on animal model research showing that peripheral Oxtr methylation is associated with Oxtr expression in the nucleus accumbens, we investigated whether grandmaternal caregiving is associated with lower peripheral OXTR methylation. Results reveal several regions within OXTR where grandmothers have lower DNA methylation compared with non-grandmother controls, and no regions where grandmothers have higher OXTR DNA methylation. Among grandmothers, OXTR methylation was most strongly correlated with the grandmother's assessment of the degree of positive feelings between her and the grandchild, which in turn predicted caregiving engagement. Although there was little evidence that grandmaternal OXTR methylation modulated grandmaternal neural responses to viewing photos of the grandchild within brain regions involved in caregiving motivation, it was negatively correlated with the neural response to an unknown grandchild. Thus, while OT signaling may not be essential for activating grandmaternal brain reward systems in our low-stress experimental context, it may support caregiving motivation towards unrelated children. Future longitudinal research should determine whether the transition to grandmotherhood is associated with a reduction in OXTR methylation.

Grandmothers - a cultural resource for women and children's health and well-being across the life cycle

Grandmothers exist in all societies. Especially in the non-western Majority World, where Elders are both highly respected and responsible for transmitting their knowledge to younger generations, there is extensive anecdotal evidence of Grandmothers' role in health promotion and healing. However, due to Eurocentric and reductionist views of families and communities, in the extensive past research on maternal, child and adolescent health issues across Africa, Asia, Latin America and the Middle East, and in Indigenous societies in North America, Australia and New Zealand, scant attention has been given to the role of Grandmothers. This paper addresses this oversight and supports the imperative to decolonize health promotion in the non-western world by building on non-western worldviews, roles and values. Based on an eclectic body of both published and gray literature, this review presents extensive evidence of Grandmothers' involvement across the life cycle of women and children and of the similar core roles that they play across cultures. While in some cases Grandmothers have a negative influence, in most cases their involvement and support to younger women and children is beneficial in terms of both their advisory and their caregiving roles. For future research and interventions addressing maternal, child and adolescent health, the conclusions of this review provide strong support for: adoption of a family systems framework to identify both gender-specific and generation-specific roles and influence; and the inclusion of Grandmothers in community health promotion programs dealing with different phases of the life cycle of women and children.

Cross-cousin marriage among Tsimane forager-horticulturalists during demographic transition and market integration

Although still prevalent in many human societies, the practice of cousin marriage has precipitously declined in populations undergoing rapid demographic and socioeconomic change. However, it is still unclear whether changes in the structure of the marriage pool or changes in the fitness-relevant consequences of cousin marriage more strongly influence the frequency of cousin marriage. Here, we use genealogical data collected by the Tsimane Health and Life History Project to show that there is a small but measurable decline in the frequency of first cross-cousin marriage since the mid-twentieth century. Such changes are linked to concomitant changes in the pool of potential spouses in recent decades. We find only very modest differences in fitness-relevant demographic measures between first cousin and non-cousin marriages. These differences have been diminishing as the Tsimane have become more market integrated. The factors that influence preferences for cousin marriage appear to be less prevalent now than in the past, but cultural inertia might slow the pace of change in marriage norms. Overall, our findings suggest that cultural changes in marriage practices reflect underlying societal changes that shape the pool of potential spouses.

Investment by maternal grandmother buffers children against the impacts of adverse early life experiences

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.

Projections of human kinship for all countries

Demographers have long attempted to project future changes in the size and composition of populations, but have ignored what these processes will mean for the size, composition, and age distribution of family networks. Kinship structures matter because family solidarity-a crucial source of informal care for millions of people around the world-is conditional on kin being alive. Here, we present innovative projections of biological kin for the 1950 to 2100 period and discuss what they imply for the availability of informal care. Overall, we project that the number of living kin for individuals will decline dramatically worldwide. While a 65-yo woman in 1950 could expect to have 41 living kin, a 65-yo woman in 2095 is projected to have just 25 [18.8 to 34.7] relatives (lower and upper 80% projection intervals). This represents a 38% [15 to 54] global decline. The composition of family networks is also expected to change, with the numbers of living grandparents and great-grandparents markedly increasing, and the numbers of cousins, nieces and nephews, and grandchildren declining. Family networks will age considerably, as we project a widening age gap between individuals and their kin due to lower and later fertility and longer lifespans. In Italy, for example, the average age of a grandmother of a 35-yo woman is expected to increase from 77.9 y in 1950 to 87.7 y [87.1 to 88.5] in 2095. The projected changes in kin supply will put pressure on the already stretched institutional systems of social support, as more individuals age with smaller and older family networks.

A data-driven approach shows that individuals' characteristics are more important than their networks in predicting fertility preferences

People's networks are considered key in explaining fertility outcomes-whether people want and have children. Existing research on social influences on fertility is limited because data often come from small networks or highly selective samples, only few network variables are considered, and the strength of network effects is not properly assessed. We use data from a representative sample of Dutch women reporting on over 18 000 relationships. A data-driven approach including many network characteristics accounted for 0 to 40% of the out-of-sample variation in different outcomes related to fertility preferences. Individual characteristics were more important for all outcomes than network variables. Network composition was also important, particularly those people in the network desiring children or those choosing to be childfree. Structural network characteristics, which feature prominently in social influence theories and are based on the relations between people in the networks, hardly mattered. We discuss to what extent our results provide support for different mechanisms of social influence, and the advantages and disadvantages of our data-driven approach in comparison to traditional approaches.

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

BACKGROUND

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.

METHODS

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.

RESULTS

In all, 57 116 children were included in the analysis, of which 7% died before age 5 y. Person-months were generated for the children, which produced 2.7 million records, with about 487 800 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.

CONCLUSIONS

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.

Concordance and determinants of mothers' and children's diets in Nigeria: an in-depth study of the 2018 Demographic and Health Survey

OBJECTIVES

Improving the diversity of the diets in young children 6-23 months is a policy priority in Nigeria and globally. Studying the relationship between maternal and child food group intake can provide valuable insights for stakeholders designing nutrition programmes in low-income and middle-income countries.

DESIGN

We examined the relationship between maternal and child dietary diversity among 8975 mother-child pairs using the Nigeria 2018 Demographic and Health Survey (DHS). We assessed concordance and discordance between maternal and child food group intake using the McNemar's χ2 test, and the determinants of child minimum dietary diversity (MDD-C) including women MDD (MDD-W) using hierarchical multivariable probit regression modelling.

SETTING

Nigeria.

PARTICIPANTS

8975 mother-child pairs from the Nigeria DHS.

PRIMARY AND SECONDARY OUTCOME MEASURES

MDD-C, MDD-W, concordance and discordance in the food groups consumed by mothers and their children.

RESULTS

MDD increased with age for both children and mothers. Grains, roots and tubers had high concordance in mother-child dyads (90%); discordance was highest for legumes and nuts (36%), flesh foods (26%), and fruits and vegetables (39% for vitamin-A rich and 57% for other). Consumption of animal source food (dairy, flesh foods, eggs) was higher for dyads with older mothers, educated mothers and more wealthy mothers. Maternal MDD-W was the strongest predictor of MDD-C in multivariable analyses (coef 0.27; 95% CI 0.25 to 0.29, p<0.000); socioeconomic indicators including wealth (p<0.000), mother's education (p<0.000) were also statistically significant in multivariable analyses and rural residence (p<0.000) was statistically significant in bivariate analysis.

CONCLUSION

Programming to address child nutrition should be aimed at the mother-child dyad as their food consumption patterns are related and some food groups appear to be withheld from children. Stakeholders including governments, development partners, non-governmental organizations, donors and civil society can act on these findings in their efforts to address undernutrition in the global child population.

Sibling competition, dispersal and fitness outcomes in humans

Determining how sibling interactions alter the fitness outcomes of dispersal is pivotal for the understanding of family living, but such studies are currently scarce. Using a large demographic dataset on pre-industrial humans from Finland, we studied dispersal consequences on different indicators of lifetime reproductive success according to sex-specific birth rank (a strong determinant of dispersal in our population). Contrary to the predictions of the leading hypotheses, we found no support for differential fitness benefits of dispersal for either males or females undergoing low vs. high sibling competition. Our results are inconsistent with both hypotheses that family members could have different fitness maximizing strategies depending on birth rank, and that dispersal could be mainly driven by indirect fitness benefits for philopatric family members. Our study stresses the need for studying the relative outcomes of dispersal at the family level in order to understand the evolution of family living and dispersal behaviour.

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.

Cooperation and partner choice among Agta hunter-gatherer children: An evolutionary developmental perspective

Examining development is essential for a full understanding of behaviour, including how individuals acquire traits and how adaptive evolutionary forces shape these processes. The present study explores the development of cooperative behaviour among the Agta, a Filipino hunter-gatherer population. A simple resource allocation game assessing both levels of cooperation (how much children shared) and patterns of partner choice (who they shared with) was played with 179 children between the ages of 3 and 18. Children were given five resources (candies) and for each was asked whether to keep it for themselves or share with someone else, and if so, who this was. Between-camp variation in children's cooperative behaviour was substantial, and the only strong predictor of children's cooperation was the average level of cooperation among adults in camp; that is, children were more cooperative in camps where adults were more cooperative. Neither age, sex, relatedness or parental levels of cooperation were strongly associated with the amount children shared. Children preferentially shared with close kin (especially siblings), although older children increasingly shared with less-related individuals. Findings are discussed in terms of their implications for understanding cross-cultural patterns of children's cooperation, and broader links with human cooperative childcare and life history evolution.

Post-marital residence patterns and the timing of reproduction: evidence from a matrilineal society

Humans exhibit a broad range of post-marital residence patterns and there is growing recognition that post-marital residence predicts women's reproductive success; however, the nature of the relationship is probably dependent on whether co-resident kin are cooperators or competitors. Here, we explore this relationship in a Tibetan population, where couples practice a mixture of post-marital residence patterns, co-residing in the same village with the wife's parents, the husband's parents or endogamously with both sets of parents. Using detailed demographic data from 17 villages we find that women who live with only their own parents have an earlier age at first birth (AFB) and age at last birth (ALB) than women who live with only their parents-in-law. Women who co-reside with both sets of parents have the earliest AFB and ALB. However, those with co-resident older siblings postponed reproduction, suggestive of competition-related delay. Shifts to earlier reproductive timing were also observed in relation to the imposition of family planning policies, in line with Fisherian expectations. Our study provides evidence of the costs and benefits to women's direct fitness of co-residing with different kin, against a backdrop of adaptive responses to cultural constraints on completed fertility.

Intergenerational Support and Second-Child Fertility Intention in the Chinese Sandwich Generation: The Parallel Mediation Model of Double Burnout

In 2013, the Chinese government implemented a two-child policy to increase the country's fertility rate. However, the persistently low rates necessitated other measures to boost fertility. This study empirically investigated the association between intergenerational support and second-child fertility intention in the Chinese sandwich generation and demonstrated the mediating role of parental burnout and burnout in caring for grandparents. Survey data collected at Time 1, Time 2, and Time 3 included 2939 participants from different regions of China. Before analyzing the data, coarsened exact matching and propensity score matching was conducted to reduce sampling bias. Regression analysis results indicated that intergenerational support has a significant total positive effect on second-child fertility intention. Furthermore, mediation path analysis revealed that parental burnout and burnout in caring for grandparents play significant but opposite directional mediating roles in the association between intergenerational support and second-child fertility intention. Sensitivity analysis using different calipers yielded similar results. These results indicated that second-child fertility intention can be increased among the Chinese sandwich generation with intergenerational support, by mitigating parental burnout. However, intergenerational support did not alleviate burnout in caring for grandparents in the sandwich generation; therefore, formal older adult care policies are required to help the sandwich generation experience lower burnout, while receiving intergenerational support.

Sedentarization and maternal childcare networks: role of risk, gender and demography

Women cooperate over multiple domains and while research from western contexts portrays women's networks as limited in size and breadth, women receive help, particularly with childcare, from a diverse range of individuals (allomothers). Nonetheless, little exploration has occurred into why we see such diversity. Wide maternal childcare networks may be a consequence of a lack of resource accumulation in mobile hunter-gatherers-where instead households rely on risk-pooling in informal insurance networks. By contrast, when households settle and accumulate resources, they are able to retain risk by absorbing losses. Thus, the size and composition of mothers' childcare networks may depend on risk-buffering, as captured by mobile and settled households in the Agta, a Philippine foraging population with diverse lifestyles. Across 78 children, we find that childcare from grandmothers and sisters was higher in settled camps, while childcare from male kin was lower, offering little support for risk-buffering. Nonetheless, girls' workloads were increased in settled camps while grandmothers had fewer dependent children, increasing their availability. These results point to gender-specific changes associated with shifting demographics as camps become larger and more settled. Evidently, women's social networks, rather than being constrained by biology, are responsive to the changing socioecological context. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

Girls in early childhood increase food returns of nursing women during subsistence activities of the BaYaka in the Republic of Congo

Nursing mothers face an energetic trade-off between infant care and work. Under pooled energy budgets, this trade-off can be reduced by assistance in food acquisition and infant care tasks from non-maternal carers. Across cultures, children also often provide infant care. Yet the question of who helps nursing mothers during foraging has been understudied, especially the role of children. Using focal follow data from 140 subsistence expeditions by BaYaka women in the Republic of Congo, we investigated how potential support from carers increased mothers' foraging productivity. We found that the number of girls in early childhood (ages 4–7 years) in subsistence groups increased food returns of nursing women with infants (kcal collected per minute). This effect was stronger than that of other adult women, and older girls in middle childhood (ages 8–13 years) and adolescence (ages 14–19 years). Child helpers were not necessarily genetically related to nursing women. Our results suggest that it is young girls who provide infant care while nursing mothers are acquiring food—by holding, monitoring and playing with infants—and, thus, that they also contribute to the energy pool of the community during women's subsistence activities. Our study highlights the critical role of children as carers from early childhood.

Religiosity is associated with greater size, kin density, and geographic dispersal of women's social networks in Bangladesh

Human social relationships, often grounded in kinship, are being fundamentally altered by globalization as integration into geographically distant markets disrupts traditional kin based social networks. Religion plays a significant role in regulating social networks and may both stabilize extant networks as well as create new ones in ways that are under-recognized during the process of market integration. Here we use a detailed survey assessing the social networks of women in rural Bangladesh to examine whether religiosity preserves bonds among kin or broadens social networks to include fellow practitioners, thereby replacing genetic kin with unrelated co-religionists. Results show that the social networks of more religious women are larger and contain more kin but not more non-kin. More religious women's networks are also more geographically diffuse and differ from those of less religious women by providing more emotional support, but not helping more with childcare or offering more financial assistance. Overall, these results suggest that in some areas experiencing rapid social, economic, and demographic change, religion, in certain contexts, may not serve to broaden social networks to include non-kin, but may rather help to strengthen ties between relatives and promote family cohesion.

Fertility intentions to have a second or third child under China's three-child policy: a national cross-sectional study

STUDY QUESTION

What proportion of people want to have a second or third child after the enactment of the three-child policy in China?

SUMMARY ANSWER

Under the three-child policy, fertility intention to have a second child was ∼60% (56% of women vs 65% of men), and fertility intention to have a third child was 13% (10% of women vs 17% of men) among the Chinese population.

WHAT IS KNOWN ALREADY

The Chinese government announced the three-child policy on 31 May 2021, allowing all couples to have up to three children. At present, there is a lack of national surveys on the fertility intentions of women and men to have a second or third child under the three-child policy in China.

STUDY DESIGN, SIZE, DURATION

In June 2021, a national cross-sectional survey including 9243 respondents aged 18-49 years was conducted online from 31 provinces in China's mainland using a random sampling method.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data on the intention to have a second or third child were collected by anonymous questionnaire. Descriptive statistics were performed to assess fertility intentions. Multivariate and multinomial logistic regression analyses were used to assess the association between fertility intentions and the investigated factors.

MAIN RESULTS AND THE ROLE OF CHANCE

Approximately 60% (5493/9243) of the investigated people (55.6% women vs 64.7% men) intended to have a second child, and 13.0% (1203/9243) of them (10.0% women vs 17.1% men) intended to have a third child under China's three-child policy. For non-child respondents, 46.8% of women and 60.4% of men intended to have a second child. For one-child respondents, 47.8% of women and 53.8% of men intended to have a second child. For two-child respondents, 14.4% of women and 25.9% of men intended to have a third child. The mean desired family size was 1.58 children per woman, which was lower than the 1.76 children per man. Notably, the age-specified fertility intentions of men were always higher than those of women. Women with a college or higher degree (adjusted odds ratio [aOR] 0.60, 95% CI 0.42-0.88) and a high-middle (aOR 0.71, 95% CI 0.53-0.95) or high (aOR 0.64, 95% CI 0.48-0.85) household income, as well as men living in urban areas (aOR 0.71, 95% CI 0.58-0.87) and having a high-middle household income (aOR 0.68, 95% CI 0.52-0.90), were associated with a lower intention to have a third child (all P < 0.05). In contrast, men of public service personnel had a higher intention to have a third child than factory workers (aOR 1.44, 95% CI 1.02-2.04, P < 0.05). Meanwhile, approximately one out of five two-child respondents intended to have a third child, while one out of four two-girl respondents (aOR 2.09, 95% CI 1.44-3.04) were willing to have a third child with a strong preference for boys (12.7% for boys vs 2.7% for girls). Economic and childrearing barriers were the leading barriers to having one more child.

LIMITATIONS, REASONS FOR CAUTION

The online survey might limit the representativeness of the present study's sample. A large sample size was enrolled and a random sampling method was used to increase the sample diversity and representativeness.

WIDER IMPLICATIONS OF THE FINDINGS

This study will assist in estimating the impact on population demographic of the three-child policy in China. Multiple efforts are needed to create a fertility-friendly environment for couples, thereby increasing fertility intentions to have one more child and increasing fertility rates.

STUDY FUNDING/COMPETING INTEREST(S)

No funding. The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Fertility Dynamics and Life History Tactics Vary by Socioeconomic Position in a Transitioning Cohort of Postreproductive Chilean Women

Globally, mortality and fertility rates generally fall as resource abundance increases. This pattern represents an evolutionary paradox insofar as resource-rich ecological contexts can support higher numbers of offspring, a component of biological fitness. This paradox has not been resolved, in part because the relationships between fertility, life history strategies, reproductive behavior, and socioeconomic conditions are complex and cultural-historically contingent. We aim to understand how we might make sense of this paradox in the specific context of late-twentieth-century, mid–demographic transition Chile. We use distribution-specific generalized linear models to analyze associations between fertility-related life-history traits—number of offspring, ages at first and last reproduction, average interbirth interval, and average number of live births per reproductive span year—and socioeconomic position (SEP) using data from a cohort of 6,802 Chilean women born between 1961 and 1970. We show that Chilean women of higher SEP have shorter average interbirth intervals, more births per reproductive span year, later age at first reproduction, earlier ages at last reproduction, and, ultimately, fewer children than women of lower SEP. Chilean women of higher SEP consolidate childbearing over a relatively short time span in the middle of their reproductive careers, whereas women of lower SEP tend to reproduce over the entirety of their reproductive lifespans. These patterns may indicate that different SEP groups follow different pathways toward declining fertility during the demographic transition, reflecting different life-history trade-offs in the process.

Matrilateral bias of grandparental investment in grandchildren persists despite the grandchildren's adverse early life experiences

Evolutionary theory predicts a downward flow of investment from older to younger generations, representing individual efforts to maximize inclusive fitness. Maternal grandparents and maternal grandmothers (MGMs) in particular consistently show the highest levels of investment (e.g. time, care and resources) in their grandchildren. Grandparental investment overall may depend on social and environmental conditions that affect the development of children and modify the benefits and costs of investment. Currently, the responses of grandparents to adverse early life experiences (AELEs) in their grandchildren are assessed from a perspective of increased investment to meet increased need. Here, we formulate an alternative prediction that AELEs may be associated with reduced grandparental investment, as they can reduce the reproductive value of the grandchildren. Moreover, we predicted that paternal grandparents react more strongly to AELEs compared to maternal grandparents because maternal kin should expend extra effort to invest in their descendants. Using population-based survey data for English and Welsh adolescents, we found evidence that the investment of maternal grandparents (MGMs in particular) in their grandchildren was unrelated to the grandchildren's AELEs, while paternal grandparents invested less in grandchildren who had experienced more AELEs. These findings seemed robust to measurement errors in AELEs and confounding due to omitted shared causes.

Testing the buffering hypothesis: Breastfeeding problems, cessation, and social support in the UK

OBJECTIVES

Physical breastfeeding problems can lead women to terminate breastfeeding earlier than planned. In high-income countries such as the UK, breastfeeding problems have been attributed to the cultural and individual "inexperience" of breastfeeding, ultimately leading to lower breastfeeding rates. Yet, cross-cultural evidence suggests breastfeeding problems still occur in contexts where breastfeeding is common, prolonged, and seen publicly. This suggests breastfeeding problems are not unusual and do not necessarily lead to breastfeeding cessation. As humans evolved to raise children cooperatively, what matters for breastfeeding continuation may be the availability of social support during the postnatal period. Here, we test the hypothesis that social support buffers mothers from the negative impact breastfeeding problems have on duration.

METHODS

We run Cox models on a sample of 565 UK mothers who completed a retrospective online survey about infant feeding and social support in 2017-2018.

RESULTS

Breastfeeding problems were important predictors of cessation; however, the direction of the effect was dependent on the problem type and type of support from a range of supporters. Helpful support for discomfort issues (blocked ducts, too much milk) was significantly associated with reduced hazards of cessation, as predicted. However, helpful support for reported milk insufficiency was assoicated with an increased hazard of cessation.

CONCLUSIONS

Experiencing breastfeeding problems is the norm, but its impact may be mitigated via social support. Working from an interdisciplinary approach, our results highlight that a wide range of supporters who provide different types of support have potential to influence maternal breastfeeding experience.

How a pregnant woman's relationships with her siblings relate to her mental health: a prenatal allocare perspective

BACKGROUND

In cooperatively breeding species, individuals may promote their inclusive fitness through allomothering. Humans exhibit some features of cooperative breeding, and previous studies have focused on allomothering by grandparents and juvenile siblings in the postnatal period. We hypothesize that a pregnant woman's relationships with her siblings (offspring's maternal aunts and uncles) are beneficial for maternal affect in ways that can enhance the siblings' inclusive fitness. Maternal affect during pregnancy is a salient target of allocare given the detrimental effects of antepartum mood disorders on birth and infant outcomes.

METHODOLOGY

We test our hypotheses in a cohort of pregnant Latina women in Southern California (N = 201). Predictor variables of interest include number of siblings a participant has, if she has sisters, frequency of seeing siblings, and frequency of communication with siblings. Outcome variables measuring maternal affect include depression, state anxiety, pregnancy-related anxiety and perceived stress.

RESULTS

Having at least one sister and greater frequency of communication with siblings were associated with fewer depressive symptoms during pregnancy. No significant associations were found between sibling variables and other measures of affect.

CONCLUSION AND IMPLICATIONS

Results suggest that how frequently you communicate with, and not how often you see, siblings could be protective against risk of antepartum depression. Sibling allomothering could impart effects through social-emotional support rather than instrumental support, as a strategy to benefit the prenatal environment in which future nieces and nephews develop. Allomothering may be particularly important in cultural contexts that value family relationships. Future studies should investigate other communities.

The Influence of Kin Proximity on the Reproductive Success of American Couples, 1900-1910

Children require a large amount of time, effort, and resources to raise. Physical help, financial contributions, medical care, and other types of assistance from kin and social network members allow couples to space births closer together while maintaining or increasing child survival. We examine the impact of kin availability on couples' reproductive success in the early twentieth-century United States with a panel data set of over 3.1 million couples linked between the 1900 and 1910 U.S. censuses. Our results indicate that kin proximity outside the household was positively associated with fertility, child survival, and net reproduction, and suggest that declining kin availability was an important contributing factor to the fertility transition in the United States. We also find important differences between maternal and paternal kin inside the household-including higher fertility among women residing with their mother-in-law than among those residing with their mother-that support hypotheses related to the contrasting motivations and concerns of parents and parents-in-law.

The neural correlates of grandmaternal caregiving

In many societies, grandmothers are important caregivers, and grandmaternal investment is often associated with improved grandchild well-being. Here, we present, to our knowledge, the first study to examine grandmaternal brain function. We recruited 50 grandmothers with at least one biological grandchild between 3 and 12 years old. Brain function was measured with functional magnetic resonance imaging as grandmothers viewed pictures of their grandchild, an unknown child, the same-sex parent of the grandchild, and an unknown adult. Grandmothers also completed questionnaires to measure their degree of involvement with and attachment to their grandchild. After controlling for age and familiarity of stimuli, viewing grandchild pictures activated areas involved with emotional empathy (insula and secondary somatosensory cortex) and movement (motor cortex and supplementary motor area). Grandmothers who more strongly activated areas involved with cognitive empathy (temporo-parietal junction and dorsomedial prefrontal cortex) when viewing pictures of the grandchild desired greater involvement in caring for the grandchild. Finally, compared with results from an earlier study of fathers, grandmothers more strongly activated regions involved with emotional empathy (dorsal anterior cingulate cortex, insula and secondary somatosensory cortex), and motivation (nucleus accumbens, ventral pallidum and caudate nucleus). All in all, our findings suggest that emotional empathy may be a key component of grandmaternal responses to their grandchildren.

Does Transition to Retirement Promote Grandchild Care? Evidence From Europe

Evolutionary theory posits that grandparents can increase their inclusive fitness by investing in their grandchildren. This study explored whether the transition to retirement affected the amount of grandchild care that European grandparents provided to their descendants. Data from five waves of the longitudinal Survey of Health, Aging, and Retirement in Europe collected between 2004 and 2015 from 15 countries were used. We executed within-person (or fixed-effect) regression models, which considered individual variations and person-specific changes over time. It was detected that transition to retirement was associated with increased grandchild care among both grandmothers and grandfathers. However, the effect of retirement was stronger for grandfathers than for grandmothers. Moreover, transition to retirement was associated with increased grandchild care among both maternal and paternal grandparents, but there was no significant difference between lineages in the magnitude of the effect of transition to retirement on grandchild care. In public debate retirees are often considered a burden to society but the present study indicated that when grandparents retire, their investment in grandchildren increased. The findings are discussed with reference to key evolutionary theories that consider older adults' tendency to invest time and resources in their grandchildren.

Rethinking the Fertility Transition in Rural Aragón (Spain) Using Height Data

Based on an analysis of the life trajectories of 2510 conscripts and their families from a Spanish rural area in the period 1835–1977, this paper studies the development of the fertility transition in relation to height using bivariate analyses. The use of heights is an innovative perspective of delving into the fertility transition and social transformation entailed. The results confirm that the men with a low level of biological well-being (related to low socio-economic groups) were those who started to control their fertility, perhaps due to the effect that increased average family size had on their budget. The children of individuals who controlled their fertility were taller than the children of other families. Therefore, the children of parents who controlled their fertility experienced the largest intergenerational increase in height (approximately 50% higher). This increase could be due to the consequence of a greater investment in children (Becker’s hypothesis) or a greater availability of resources for the whole family (resource dilution hypothesis).

One but not two grandmothers increased child survival in poorer families in west Bohemian population, 1708–1834

Human childrearing is characterized by cooperative care and grandmothers are usually the most prominent alloparents. Nevertheless, it has been argued that limited resources may intensify competition among kin. The effect of grandmothers’ presence on child survival may thus crucially depend on the family’s socioeconomic status. We evaluate the impact of grandmothers’ presence on child survival using a large historical dataset from eighteenth to nineteenth-century western Bohemia (N = 6880) and assess the effects of socioeconomic status. We employed a varying effects model conditioned on relatedness between individuals because of possible genetically transmitted benefits. Proportional hazards showed that grandmothers had little or no impact on child survival in families of high and medium socioeconomic status (farmers and cottagers, respectively), whereas in families with the lowest socioeconomic status (lodgers), grandmothers’ presence increased the survival probability of children up to five years of age. The beneficial effect of grandmaternal care was strongest between the first and second years of life. Importantly, though, in families with low socioeconomic status, we also observed lower survival chances of children when both grandmothers lived in the same village. These findings suggest that the balance between kin cooperation in childrearing and competition over resources may depend on resource availability.

Engaging family members in maternal, infant and young child nutrition activities in low- and middle-income countries: A systematic scoping review

The influence of fathers, grandmothers and other family members on maternal, infant and young child nutrition practices has been well documented for decades, yet many social and behavioural interventions continue to reach only mothers. While recent guidelines recommend involving fathers, grandmothers and other family members in maternal and child nutrition, we lack a comprehensive review of interventions that have engaged them. This scoping review aimed to address this gap by describing social and behavioural interventions to engage family members in maternal and child nutrition in low- and middle-income countries. We systematically searched PubMed, Scopus, Web of Science, Global Health and CINAHL for peer-reviewed studies meeting inclusion criteria. We screened 6,570 abstracts, evaluated 179 full-text articles, and included 87 articles from 63 studies. Studies reported a broad range of approaches to engage fathers, grandmothers and other family members to support maternal nutrition (n = 6); breastfeeding (n = 32); complementary feeding (n = 6) and multiple maternal and child nutrition practices (n = 19). Interventions were facility and community based; included individual and group-based interpersonal communication, community mobilization, mass media and mHealth; and reached mothers and family members together or separately. Most interventions were located within the health sector; rare exceptions included nutrition-sensitive agriculture, social protection, early child development and community development interventions. Few interventions addressed gender norms, decision-making, and family dynamics or described formative research or theories informing intervention design. These diverse studies can shed light on innovative programme approaches to increase family support for maternal and child nutrition.

The male breadwinner nuclear family is not the 'traditional' human family, and promotion of this myth may have adverse health consequences

The importance of social support for parental and child health and wellbeing is not yet sufficiently widely recognized. The widespread myth in Western contexts that the male breadwinner-female homemaker nuclear family is the 'traditional' family structure leads to a focus on mothers alone as the individuals with responsibility for child wellbeing. Inaccurate perceptions about the family have the potential to distort academic research and public perceptions, and hamper attempts to improve parental and child health. These perceptions may have arisen partly from academic research in disciplines that focus on the Western middle classes, where this particular family form was idealized in the mid-twentieth century, when many of these disciplines were developing their foundational research. By contrast, evidence from disciplines that take a cross-cultural or historical perspective shows that in most human societies, multiple individuals beyond the mother are typically involved in raising children: in evolutionary anthropology, it is now widely accepted that we have evolved a strategy of cooperative reproduction. Expecting mothers to care for children with little support, while expecting fathers to provide for their families with little support, is, therefore, likely to lead to adverse health consequences for mothers, fathers and children. Incorporating evidence-based evolutionary, and anthropological, perspectives into research on health is vital if we are to ensure the wellbeing of individuals across a wide range of contexts. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Children are important too: juvenile playgroups and maternal childcare in a foraging population, the Agta

Non-maternal carers (allomothers) are hypothesized to lighten the mother's workload, allowing for the specialized human life history including relatively short interbirth intervals and multiple dependent offspring. Here, using in-depth observational data on childcare provided to 78 Agta children (a foraging population in the northern Philippines; aged 0-6 years), we explore whether allomaternal childcare substitutes and decreases maternal childcare. We found that allomother caregiving was associated with reduced maternal childcare, but the substitutive effect varied depending on the source and type of care. Children-only playgroups consistently predicted a decrease in maternal childcare. While grandmothers were rarely available, their presence was negatively associated with maternal presence and childcare, and grandmothers performed similar childcare activities to mothers. These results underscore the importance of allomothering in reducing maternal childcare in the Agta. Our findings suggest that flexibility in childcare sources, including children-only playgroups, may have been the key to human life-history evolution. Overall, our results reinforce the necessity of a broad conceptualization of social support in human childcare. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Who cares for women with children? Crossing the bridge between disciplines

It has long been acknowledged that women with children require social support to promote their health and wellbeing, as well as that of their children. However, the dominant conceptualizations of support have been heavily influenced by Western family norms. The consequence, at best, has been to stifle our understanding of the nature and consequences of support for mothers and children. At worst, it has led to systematic discrimination negatively impacting maternal-child health. To fully engage with the complexities of social support, we must take multidisciplinary or interdisciplinary approaches spanning diverse cultural and geographical perspectives. However, multidisciplinary knowledge-processing can be challenging, and it is often unclear how different studies from different disciplines relate. To address this, we outline two epistemological frameworks-the scientific approach and Tinbergen's four questions-that can be useful tools in connecting research across disciplines. In this theme issue on 'Multidisciplinary perspectives on social support and maternal-child health', we attempt to foster multidisciplinary thinking by presenting work from a diverse range of disciplines, populations and cultures. Our hope is that these tools, along with papers in this issue, help to build a holistic understanding of social support and its consequences for mothers and their children. Overall, a multidisciplinary perspective points to how the responsibility of childrearing should not fall solely onto mothers. Indeed, this multidisciplinary issue demonstrates that successful childrearing is consistently an activity shared beyond the mother and the nuclear family: an insight that is crucial to harnessing the potential of social support to improve maternal-child health. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Childcare support and child social development in Japan: investigating the mediating role of parental psychological condition and parenting style

In humans, support from partners and alloparents is crucial for successful child-rearing and optimal child development. However, the complex relationships among childcare support, children's outcomes and parental characteristics have not been fully examined. We investigate how three sources of partner and alloparental support-partner's childcare participation, support from children's grandparents and support from non-kin-can be associated with child social development. We hypothesize that the associations between childcare support from partners/alloparents and child social development are partly mediated by parental psychological condition and parenting style. To test this, we conducted path analyses on online survey data collected in 2016 from parents of 3- to 5-year-old children in Japan. We found no evidence that childcare support had direct positive effects on child social development. Rather, the benefit of childcare support was mediated by its effects on parental psychological condition and parenting style, which in turn improved children's outcomes. At the same time, we found some evidence that greater availability of childcare support was directly associated with more behavioural difficulties in children. Our findings reveal the complex pathways between childcare support, parental characteristics and children's outcomes in Japan, showing potential mechanisms behind parental and alloparental effects in industrialized populations. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Does Parental Investment Shape Adult Children's Fertility Intentions? Findings From a German Family Panel

Parents can play an important role in the childbearing plans of adult children. However, studies testing whether changes in parental investment are associated with subsequent changes in fertility intentions over time are lacking. We investigated whether parental investment, measured as contact frequency, emotional closeness, financial support, and childcare, is associated with adult children's intentions to have a first and a second, or subsequent, child within the next 2 years. These associations were studied in four different parent-adult child dyads based on the sex of parents and adult children (i.e, mother-daughter, mother-son, father-daughter, father-son). The participants are from the German Family Panel, which is a longitudinal survey of younger and middle-aged adults with eight follow-up waves. We exploited within-person (or fixed-effect) regression models, which concentrated an individual's variation over time (i.e., whether changes in parental investment frequencies are associated with subsequent changes in adult children's fertility intentions). It was detected that increased emotional closeness between fathers and daughters was associated with increased adult daughter's intentions to have a first child but father-daughter contact decreased daughter's intentions to have another child, and maternal financial support decreased son's intentions to have a first child. Overall, statistically nonsignificant associations outweighed significant ones. Although it is often assumed that parental investment is an important factor influencing the childbearing decisions of adult children, the present findings indicate that parental investment may not increase adult children's intentions to have a/another child in Germany.

The Impact of Grandparental Death on the Fertility of Adult Children

The increasingly central role of vertical family kinship in Western societies underscores the potential value of intergenerational linkages that tie grandparents to the fertility of their adult children. Recent research has examined the changing demography of grandparenthood and the roles fulfilled by living grandparents, but the complex implications of grandparental death-a key feature of intergenerational linkages over the life course-have drawn less attention. In this article, we explore whether and how childbearing of adult women is affected by the death of grandparents-their own parent(s) or their spouse's parent(s). We develop a novel conceptual framework that presents the pathways of influence and considers the overall impact of grandparental death on childbearing of adult children. We then estimate fixed-effects models to identify causal relationships between grandparental death and childbearing, using linked micro-level census and population register data from Israel for the period 1986-2014. We find that grandparental death leads to a reduction of approximately 5 percentage points in the five-year probability of childbirth. The effects of grandparental death are negative across all parities examined and are broadly similar across grandparent's gender and kinship relation. Additional effects are identified, including how the impact of grandparental death varies with time since the previous birth as well as residential proximity prior to death. We explain how our findings regarding the effect of grandparental death offer insight into the role of living grandparents. Our results suggest that policy-makers concerned with low fertility should explore mechanisms that reinforce potential sources of support from grandparents.

Mother’s Partnership Status and Allomothering Networks in the United Kingdom and United States

In high-income, low-fertility (HILF) settings, the mother’s partner is a key provider of childcare. However, it is not clear how mothers without partners draw on other sources of support to raise children. This paper reports the findings from a survey of 1532 women in the United Kingdom and the United States, in which women described who provided childcare for a focal child and how frequently they did so. We use multivariate Bayesian regression models to explore the drivers of support from partners, maternal kin, and other allomothers, as well as the potential impact of allomothering on women’s fertility. Relative to mothers who are in a stable first marriage or cohabitation, mothers who are unpartnered rely more heavily on fewer maternal kin, use more paid help, and have networks which include more non-kin helpers. Repartnered mothers received less help from their partners in the UK and less help from maternal kin in both countries, which US mothers compensated for by relying on other helpers. While repartnered mothers had higher age-adjusted fertility than women in a first partnership, allomaternal support was not clearly related to the mother’s fertility. These findings demonstrate the importance of partners but also of allomothering more broadly in HILF settings.

Communication Across Maternal Social Networks During England's First National Lockdown and Its Association With Postnatal Depressive Symptoms

Postnatal/postpartum depression (PND/PPD) had a pre-COVID-19 estimated prevalence ranging up to 23% in Europe, 33% in Australia, and 64% in America, and is detrimental to both mothers and their infants. Low social support is a key risk factor for developing PND. From an evolutionary perspective this is perhaps unsurprising, as humans evolved as cooperative childrearers, inherently reliant on social support to raise children. The coronavirus pandemic has created a situation in which support from social networks beyond the nuclear family is likely to be even more important to new mothers, as it poses risks and stresses for mothers to contend with; whilst at the same time, social distancing measures designed to limit transmission create unprecedented alterations to their access to such support. Using data from 162 mothers living in London with infants aged ≤6 months, we explore how communication with members of a mother's social network related to her experience of postnatal depressive symptoms during the first "lockdown" in England. Levels of depressive symptoms, as assessed via the Edinburgh Postnatal Depression Scale, were high, with 47.5% of the participants meeting a ≥11 cut-off for PND. Quasi-Poisson regression modelling found that the number of network members seen in-person, and remote communication with a higher proportion of those not seen, was negatively associated with depressive symptoms; however, contact with a higher proportion of relatives was positively associated with symptoms, suggesting kin risked seeing mothers in need. Thematic qualitative analysis of open text responses found that mothers experienced a burden of constant mothering, inadequacy of virtual contact, and sadness and worries about lost social opportunities, while support from partners facilitated family bonding. While Western childrearing norms focus on intensive parenting, and fathers are key caregivers, our results highlight that it still "takes a village" to raise children in high-income populations and mothers are struggling in its absence.

Fertility intentions and outcomes in Indonesia: Evolutionary perspectives on sexual conflict

Differential fertility preferences for men and women may provide insights into human sexual conflict. We explore whether pairbonded couples have different preferences for future offspring, which socioecological factors are associated with these preferences, and who achieves their desired fertility over time. We utilise the Indonesia Family Life Survey (IFLS), a longitudinal survey which collected data from 1993 to 2015, to compare desired future fertility for 9655 couples and follow couples who had divergent preferences. The majority of couples (64.8%) want the same number of future offspring. In 20.7% of couples, husbands want more future offspring than their wives, while the reverse occurs in 14.5% of couples. Living in villages with the husband's or the wife's parent(s) is associated with having divergent preferences for future offspring, where there is a higher likelihood that women prefer more offspring than their husbands. When examining fertility outcomes, women, particularly those who marry at older ages, are more likely to achieve their desired preference. Contrary to previous research, we do not find that living near one's natal kin or having increased autonomy increases an individual's likelihood of achieving desired fertility outcomes.

Offspring fertility and grandchild survival enhanced by maternal grandmothers in a pre-industrial human society

Help is directed towards kin in many cooperative species, but its nature and intensity can vary by context. Humans are one of few species in which grandmothers invest in grandchildren, and this may have served as an important driver of our unusual life history. But helping behaviour is hardly uniform, and insight into the importance of grandmothering in human evolution depends on understanding the contextual expression of helping benefits. Here, we use an eighteenth-nineteenth century pre-industrial genealogical dataset from Finland to investigate whether maternal or paternal grandmother presence (lineage relative to focal individuals) differentially affects two key fitness outcomes of descendants: fertility and survival. We found grandmother presence shortened spacing between births, particularly at younger mother ages and earlier birth orders. Maternal grandmother presence increased the likelihood of focal grandchild survival, regardless of whether grandmothers had grandchildren only through daughters, sons, or both. In contrast, paternal grandmother presence was not associated with descendants' fertility or survival. We discuss these results in terms of current hypotheses for lineage differences in helping outcomes.

Cultural change beyond adoption dynamics: Evolutionary approaches to the discontinuation of contraception

Numerous evolutionary mechanisms have been proposed for the origins, spread and maintenance of low fertility. Such scholarship has focused on explaining the adoption of fertility-reducing behaviour, especially the use of contraceptive methods. However, this work has yet to engage fully with the dynamics of contraceptive behaviour at the individual level. Here we highlight the importance of considering not just adoption but also discontinuation for understanding contraceptive dynamics and their impact on fertility. We start by introducing contemporary evolutionary approaches to understanding fertility regulation behaviours, discussing the potential for integrating behavioural ecology and cultural evolution frameworks. Second, we draw on family planning studies to highlight the importance of contraceptive discontinuation owing to side-effects for understanding fertility rates and suggest evolutionary hypotheses for explaining patterns of variation in discontinuation rates. Third, we sketch a framework for considering how individual flexibility in contraceptive behaviour might impact the evolution of contraceptive strategies and the demographic transition. We argue that integrating public health and evolutionary approaches to reproductive behaviour might advance both fields by providing (a) a predictive framework for comparing the effectiveness of various public health strategies and (b) a more realistic picture of behaviour by considering contraceptive dynamics at the individual level more explicitly when modelling the cultural evolution of low fertility.

Grandmothers - a neglected family resource for saving newborn lives

Across the globe, the well-being of newborns is significantly influenced by the knowledge and practices of family members, yet global health policies and interventions primarily focus on strengthening health services to save newborn lives. Predominant approaches to promote newborn survival in non-western cultures across the Global South are based on a western, nuclear family model and ignore the roles of caregivers within wider family systems, whose attitudes and practices are determined by culturally prescribed strategies. In this paper, I review evidence of a neglected facet of newborn care, the role and influence of senior women or grandmothers.Based on a family systems frame, I reviewed research from numerous settings in Africa, Asia and Latin America that provides insight into family roles related to newborn care, specifically of grandmothers. I identified primarily published studies which provide evidence of grandmothers' role as culturally designated and influential newborn advisors to young mothers and direct caregivers. Research from all three continents reveals that grandmothers play similar core roles in newborn care while their culturally specific practices vary. This review supports two main conclusions. First, future newborn research should be conceptualised within a family systems framework that reflects the structure and dynamics of non-western collectivist cultures. Second, newborn interventions should aim not only to strengthen health services but also influential family caregivers, particularly grandmothers and the indigenous social support networks of which they are a part, in order to improve family-level newborn practices and save newborn lives.

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.

How evolutionary behavioural sciences can help us understand behaviour in a pandemic

The COVID-19 pandemic has brought science into the public eye and to the attention of governments more than ever before. Much of this attention is on work in epidemiology, virology and public health, with most behavioural advice in public health focusing squarely on 'proximate' determinants of behaviour. While epidemiological models are powerful tools to predict the spread of disease when human behaviour is stable, most do not incorporate behavioural change. The evolutionary basis of our preferences and the cultural evolutionary dynamics of our beliefs drive behavioural change, so understanding these evolutionary processes can help inform individual and government decision-making in the face of a pandemic. Lay summary: The COVID-19 pandemic has brought behavioural sciences into the public eye: Without vaccinations, stopping the spread of the virus must rely on behaviour change by limiting contact between people. On the face of it, "stop seeing people" sounds simple. In practice, this is hard. Here we outline how an evolutionary perspective on behaviour change can provide additional insights. Evolutionary theory postulates that our psychology and behaviour did not evolve to maximize our health or that of others. Instead, individuals are expected to act to maximise their inclusive fitness (i.e, spreading our genes) - which can lead to a conflict between behaviours that are in the best interests for the individual, and behaviours that stop the spread of the virus. By examining the ultimate explanations of behaviour related to pandemic-management (such as behavioural compliance and social distancing), we conclude that "good of the group" arguments and "one size fits all" policies are unlikely to encourage behaviour change over the long-term. Sustained behaviour change to keep pandemics at bay is much more likely to emerge from environmental change, so governments and policy makers may need to facilitate significant social change - such as improving life experiences for disadvantaged groups.