Maternal Time Allocation in Two Cooperative Childrearing Societies

Music production and its role in coalition signaling during foraging contexts in a hunter-gatherer society

Music is a cultural activity universally present in all human societies. Several hypotheses have been formulated to understand the possible origins of music and the reasons for its emergence. Here, we test two hypotheses: (1) the coalition signaling hypothesis which posits that music could have emerged as a tool to signal cooperative intent and signal strength of alliances and (2) music as a strategy to deter potential predators. In addition, we further explore the link between tactile cues and the propensity of mothers to sing toward infants. For this, we investigated the singing behaviors of hunter-gatherer mothers during daily foraging trips among the Mbendjele BaYaka in the Republic of the Congo. Although singing is a significant component of their daily activities, such as when walking in the forest or collecting food sources, studies on human music production in hunter-gatherer societies are mostly conducted during their ritual ceremonies. In this study, we collected foraging and singing behavioral data of mothers by using focal follows of five BaYaka women during their foraging trips in the forest. In accordance with our predictions for the coalition signaling hypothesis, women were more likely to sing when present in large groups, especially when group members were less familiar. However, predictions of the predation deterrence hypothesis were not supported as the interaction between group size and distance from the village did not have a significant effect on the likelihood of singing. The latter may be due to limited variation in predation risk in the foraging areas, because of the intense bush meat trade, and hence, future studies should include foraging areas with higher densities of wild animals. Lastly, we found that mothers were more likely to sing when they were carrying infants compared to when infants were close, but carried by others, supporting the prediction that touch plays an important prerequisite role in musical interaction between the mother and child. Our study provides important insight into the role of music as a tool in displaying the intent between or within groups to strengthen potentially conflict-free alliances during joint foraging activities.

Shodagor women cooperate across domains of work and childcare to solve an adaptive problem

Across human societies, women's economic production and their contributions to childcare are critical in supporting reproductive fitness for themselves, their spouses and children. Yet, the necessity of performing both work and childcare tasks presents women with an adaptive problem in which they must determine how best to allocate their time and energy between these tasks. Women often use cooperative relationships with alloparents to solve this problem, but whether or not women cooperate across different domains (e.g. work and childcare) to access alloparents remains relatively under-explored. Using social network data collected with Shodagor households in Bangladesh, we show that women who need childcare help in order to work draw on cooperative work partners as potential alloparents, and that all women rely heavily on kin, but not reciprocal cooperation for childcare help. These results indicate that Shodagor women strategize to create work and childcare relationships in ways that help solve the adaptive problem they face. We discuss the implications of our results and the example provided by Shodagor women for a broader understanding of women's cooperative relationships, including the importance of socio-ecological circumstances and gendered divisions of labour in shaping women's cooperative strategies. This article is part of the theme issue 'Cooperation among women: evolutionary and cross-cultural perspectives'.

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.

Are fathers a good substitute for mothers? Paternal care and growth rates in Shodagor children

Biparental care is a hallmark of human social organization, though paternal investment varies between and within societies. The facultative nature of paternal care in humans suggests males should invest when their care improves child survival and/or quality, though testing this prediction can be challenging because of the difficulties of empirically isolating paternal effects from those of other caregivers. Additionally, the broader context in which care is provided, vis-à-vis care from mothers and others, may lead to different child outcomes. Here, we examine the effects of paternal care on child growth among Shodagor fisher-traders, where fathers provide high levels of both additive and substitutive care, relative to mothers. We modeled seasonal z-scores and velocities for height, weight, and body mass index (BMI) outcomes using linear mixed models. Our evidence indicates that, as predicted, the context of paternal care is an important predictor of child outcomes. Results show that environmental seasonality and alloparental help contribute to a nuanced understanding of the impact of Shodagor paternal care on child physiology.

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.

Comparing the Self-Reported Health, Happiness, and Marital Happiness of a Multinational Sample of Consensually Non-Monogamous Adults with Those of the U.S. General Population: Additional Comparisons by Gender, Number of Sexual Partners, Frequency of Sex, and Marital Status

The primary objective of this cross-sectional study was to examine the associations of self-reported health, happiness, marital happiness, frequency of sexual activity, and number of partners from a multinational survey of individuals who are consensually non-monogamous (CNM) or open to being CNM, completed in 2012 with 4062 respondents. We compared data from this survey with the 2010-2014 US General Social Surveys (GSS). This study explored these variables and their predictors by gender (including 612 non-binary-gendered CNM individuals), marital status, number of partners, sexual frequency, age, education, and income and were broken down by behavioral sexual orientation, marital status, and other relevant categories. Respondents in our CNM sample generally reported being as healthy (sometimes healthier; e.g., all respondents M-W Z = 7.66, p < .001, η² = 0.007), happy (frequently happier; e.g., multiple-partnered Z = 15.43, p < .001, η² = 0.069), happy in their marriages (in some cases happier; e.g., multiple-partnered females Z = 2.61, p = .009, η² = 0.067), and reported having more frequent sexual activity (e.g., all Z = 29.54, p < .001, η² = 0.094) with more partners (e.g., all Z = 60.75, p < .001, η² = 0.393) compared to corresponding individuals within the GSS. This study contributes to knowledge about commonalities and differences between the general population and those who are CNM regarding health, happiness, and happiness in marriage, including differences in optimal number of sexual partners and sexual frequency.

Biological constraints and socioecological influences on women's pursuit of risk and the sexual division of labour

Evolutionary treatments of women's work and the sexual division of labour derive from sexual selection theory and focus on an observed cross-cultural trend: tasks performed by women tend to be more compatible with childcare and produce less economic risk than tasks performed by men. Evolutionary models emphasize biological sex differences and opportunity costs to understand this pattern of behaviour, yet deviations remain poorly understood. We examine variation in women's work among Shodagor fisher-traders in Bangladesh with the goal of explaining such deviations related to women's work. First, we demonstrate that women's trading produces higher variance returns than men's work - a pattern not previously quantified. Next, we test predictions from the economy of scale model to understand the socioecological circumstances associated with trading. We suggest that relaxing model assumptions around biological constraints may elucidate key circumstances under which members of one gender should systematically engage in work that is incompatible with childcare and/or produces higher levels of economic risk. Results indicate that biological sex differences are insufficient to explain gendered patterns of behaviour but removal of childcare constraints and comparative advantages related to opportunity costs can explain adherence to and deviation from trends in women's work and the division of labour.

Harsh environments promote alloparental care across human societies

Alloparental care is central to human life history, which integrates exceptionally short interbirth intervals and large birth size with an extended period of juvenile dependency and increased longevity. Formal models, previous comparative research, and palaeoanthropological evidence suggest that humans evolved higher levels of cooperative childcare in response to increasingly harsh environments. Although this hypothesis remains difficult to test directly, the relative importance of alloparental care varies across human societies, providing an opportunity to assess how local social and ecological factors influence the expression of this behaviour. We therefore, investigated associations between alloparental infant care and socioecology across 141 non-industrialized societies. We predicted increased alloparental care in harsher environments, due to the fitness benefits of cooperation in response to shared ecological challenges. We also predicted that starvation would decrease alloparental care, due to prohibitive energetic costs. Using Bayesian phylogenetic multilevel models, we tested these predictions while accounting for potential confounds as well as for population history. Consistent with our hypotheses, we found increased alloparental infant care in regions characterized by both reduced climate predictability and relatively lower average temperatures and precipitation. We also observed reduced alloparental care under conditions of high starvation. These results provide evidence of plasticity in human alloparenting in response to ecological contexts, comparable to previously observed patterns across avian and mammalian cooperative breeders. This suggests convergent social evolutionary processes may underlie both inter- and intraspecific variation in alloparental care.

Infant allocare in traditional societies

Across human societies infants receive care from both their mothers and others. Reproductive cooperation raises two important questions: how does allocare benefit mothers and infants, and why do caretakers help mothers when they could spend their time in other, perhaps more valuable ways? We use behavioral and biological data from three small-scale societies to evaluate 1) how allocare affects a nursing mother's time, 2) whether a mother's birth interval length, surviving fertility and infant weight vary as a function of the childcare help that she receives, and 3) the opportunity cost for helpers to spend time caring for children. Across our hunter-gatherer and agricultural samples we find that on average mothers provide 57% of the direct care that an infant receives and allocaretakers 43% (±20%). Model results show that for every 10% increase in allocare the probability that a mother engages in direct care diminishes by 25%, a potential savings of an estimated 165 kcals per day. While allocare has a significant immediate impact on mother's time, no detectable effect on delayed fitness measures (birth interval and surviving fertility) or on infant weight status was evident. Cross culturally we find that other than mothers, siblings spend the most time caretaking infants, and they do so without compromising the time that they might otherwise spend in play, economic activities or education. The low opportunity cost for children to help offers an alternative explanation why juveniles are common caretakers in many societies, even in the absence of delayed indirect fitness benefits. While we expect specific patterns to vary cross culturally, these results point to the importance of infant allocare and its immediate time benefits for mothers to maintain flexibility in balancing the competing demands to support both older and younger children.

Shodagor Family Strategies : Balancing Work and Family on the Water

The Shodagor of Matlab, Bangladesh, are a seminomadic community of people who live and work on small wooden boats, within the extensive system of rivers and canals that traverse the country. This unique ecology places particular constraints on family and economic life and leads to Shodagor parents employing one of four distinct strategies to balance childcare and provisioning needs. The purpose of this paper is to understand the conditions that lead a family to choose one strategy over another by testing predictions about socioecological factors that impact the sexual division of labor, including a family’s stage in the domestic cycle, aspects of the local ecology, and the availability of alloparents. Results show that although each factor has an impact on the division of labor individually, a confluence of these factors best explains within-group, between-family differences in how mothers and fathers divide subsistence and childcare labor. These factors also interact in particular ways for Shodagor families, and it appears that families choose their economic strategies based on the constellation of constraints that they face. The results of these analyses have implications for theory regarding the sexual division of labor across cultures and inform how Shodagor family economic and parenting strategies should be contextualized in future studies.

BaAka women's health and subsistence practices in transitional conservation economies: Variation with age, household size, and food security

OBJECTIVES

Using ethnographic interviews and biological measures, this article investigates changing health and nutrition of a hunter-gatherer population transitioning from a forest-based subsistence system to a horticultural and market-driven lifestyle.

METHODS

This study represents biological and dietary recall data for adult female foragers (18+; n = 60) across two villages, Mossapoula (MS) and Yandoumbé (YDBE), in the Dzanga Sangha Protected Areas (APDS), Central African Republic (CAR). Standard anthropometric measurements (height, weight, skinfolds) and hemoglobin values were collected to assess short-term nutritional status.

RESULTS

BMI was similar across all three age classes in YDBE, but differed amongst women of MS (ANOVA; F = 6.34, df = 30, P = 0.005).Values were lowest among the older women in older age class 3 who also had the greatest number of dependents. Overall SS values were significantly negatively correlated with the number of biological children (r = -0.33, P = 0.01) in both villages.

CONCLUSIONS

Here, we identify older BaAka women, caring for their own children and grandchildren, as particularly vulnerable to economic changes and food insecurity. We found older women, especially those in a community with greater restrictions on access to forest resources to have more dependents, reduced market integration, and low BMI relative to younger women in the population. Am. J. Hum. Biol. 28:453-460, 2016. © 2015 Wiley Periodicals, Inc.

Stay Close to Me

Our study examines stranger anxiety and maternal beliefs about child development in a traditional society living in an adverse socio-political situation. Thirty Bedouin mothers from the “unrecognized” villages in the Naqab and their 1-year-old children participated in our study, which utilized a mixed-method approach. First, we observed children’s stranger anxiety in everyday situations and examined their mothers’ ethnotheories via questionnaires and interviews. Second, we conducted a focus group discussion about stranger anxiety. The data revealed an emphasis on the cultural model of hierarchical relatedness, reflecting traditional values. Although multiple childcare arrangements created an expectation that Bedouin children would adjust easily to strangers, more than half of the Bedouin children showed stranger anxiety. Based on the focus group findings, we attribute the high levels of stranger anxiety to the adverse socio-political situation. Our study highlights the impact of the socio-political context on children’s stranger anxiety and their mothers’ belief systems. The findings show that definitions of security can take very different forms, depending also on the socio-political situation. Accordingly, parental and child behaviors can carry different meanings.

Cooperative breeding and Aka children's nutritional status: is flexibility key?

Research suggests that nonmaternal caregivers (allomothers) offer essential assistance through caregiving and provisioning, helping to support lengthy child development. Here, we examine the role of allomothers and the broader social and sharing network on Aka forager children's anthropometrics. We hypothesize that nonmaternal investors strategically target their assistance when it is most needed and when it will have the greatest effect. We evaluate children's nutritional status using WHO standards [weight-for-age (WAZ), height-for-age (HAZ), and weight-for-height (WHZ)] during four periods of child development [early infancy (birth to <9 months), mobility to weaning (9 to <36 months), early childhood (36 to <72 months), and middle childhood (72 to <120 months); N = 127]. We explore the effects of allomothers and the social network across these different risk periods and examine whether the broader social network buffers the loss of a primary allomother. ANOVA results suggest that girls may be experiencing some growth faltering, while boys start smaller and remain small across these stages. We used OLS multiple regression models to evaluate the effects of sex, camp composition, risk periods, and allomothers' presence on WAZ, HAZ, and WHZ. Grandmothers are the most influential allomother, with their effect most evident during the 9 to <36 month period. Camp size was also associated with greater WAZ, suggesting that children residing in small camps may be disadvantaged. Our findings also indicate that, under specific residence patterns, cooperative child rearing networks buffer the loss of a grandmother. Overall, our results suggest the importance of social networks to children's nutritional status and that individuals target investment to critical phases.

Born Both Ways: The Alloparenting Hypothesis for Sexual Fluidity in Women

Given the primacy of reproduction, same-sex sexual behavior poses an evolutionary puzzle. Why would selection fashion motivational mechanisms to engage in sexual behaviors with members of the same sex? We propose the alloparenting hypothesis, which posits that sexual fluidity in women is a contingent adaptation that increased ancestral women's ability to form pair bonds with female alloparents who helped them rear children to reproductive age. Ancestral women recurrently faced the adaptive problems of securing resources and care for their offspring, but were frequently confronted with either a dearth of paternal resources due to their mates' death, an absence of paternal investment due to rape, or a divestment of paternal resources due to their mates' extra-pair mating efforts. A fluid sexuality would have helped ancestral women secure resources and care for their offspring by promoting the acquisition of allomothering investment from unrelated women. Under this view, most heterosexual women are born with the capacity to form romantic bonds with both sexes. Sexual fluidity is a conditional reproductive strategy with pursuit of men as the default strategy and same-sex sexual responsiveness triggered when inadequate paternal investment occurs or when women with alloparenting capabilities are encountered. Discussion focuses on (a) evidence for alloparenting and sexual fluidity in humans and other primates; (b) alternative explanations for sexual fluidity in women; and (c) fourteen circumstances predicted to promote same-sex sexual behavior in women.

Household Task Delegation among High-Fertility Forager-Horticulturalists of Lowland Bolivia

Human kin cooperation is universal, leading researchers to label humans as "cooperative breeders." Despite widespread interest in human cooperation, there has been no systematic study of how household economic decision making occurs. We document age and sex profiles of task delegation by parents to children ages 4-18 among Bolivian forager-horticulturalists. We test for sex differences in the probability of delegation and examine whether tasks are more likely delegated as household labor demand increases. We also test whether food acquisition tasks are more likely delegated to higher producers. We find mixed support for the prediction that girls are more likely delegated domestic and alloparenting tasks than boys (n = 173 children). Both sexes are more likely delegated tasks during rice harvest months; number of coresident young children is also associated with greater probability of delegated allocare, although the effect retains significance for girls only. For both sexes, father absence is associated with greater probability of delegation, particularly for food acquisition tasks. Children delegated rice harvesting achieve 45% higher mean daily caloric returns from harvesting than children not delegated harvesting. Our results therefore suggest that delegation increases household economic efficiency. We find mixed support for the hypothesis that delegation prepares children for sex-specific adult roles.

Cooperative breeding and maternal energy expenditure among Aka foragers

OBJECTIVES

Previous research among foragers and theory suggests that nonmaternal caregivers offer essential assistance, which supports female reproduction and the costs associated with lengthy child development. Mothers' face trade-offs in energy allocation between work and childcare, particularly when mothers have an infant. These trade-offs likely have crucial impacts on the pace of reproduction and child health. Caregivers can help mothers with childcare or they can reduce a mother's nonchildcare workload. If caregivers assist mothers by substituting childcare, then maternal energy expenditure (EE) in other work activities should increase. If caregivers assist mothers by substituting labor, then maternal EE in work activities should decrease when caregivers are present.

METHODS

Utilizing detailed, quantitative behavioral observations and EE data, we test these propositions with data from 28 Aka forager mothers with children <35 months old. We isolate paternal, grandmaternal, and other caregiver effects on maternal EE and childcare in multivariate analyses.

RESULTS

Our results show that caregivers (largely grandmothers) significantly reduce mothers' work EE by as much 216 kcal across a 9-hour observation period, while fathers and juveniles appear to increase maternal EE. Direct childcare from grandmothers decreases maternal direct care by about one-to-one indicating a labor substitution. Direct childcare from fathers decreases maternal care by almost 4 to 1, resulting in a net reduction of total direct care from all caregivers.

CONCLUSIONS

Our results indicate that there are multiple pathways by which helpers offset maternal work/childcare trade-offs.

The foundation of kinship: households

Men's hunting has dominated the discourse on energy capture and flow in the past decade or so. We turn to women's roles as critical to household formation, pair-bonding, and intergenerational bonds. Their pivotal contributions in food processing and distribution likely promoted kinship, both genetic and affinal, and appear to be the foundation from which households evolved. With conscious recognition of household social units, variable cultural constructions of human kinship systems that were sensitive to environmental and technological conditions could emerge. Kinship dramatically altered the organization of resource access for our species, creating what we term "kinship ecologies." We present simple mathematical models to show how hunting leads to dependence on women's contributions, bonds men to women, and bonds generations together. Kinship, as it organized transfers of food and labor energy centered on women, also became integrated with the biological evolution of human reproduction and life history.

Physical activity in an indigenous Ecuadorian forager-horticulturalist population as measured using accelerometry

OBJECTIVE

Minimal information on physical activity is available for non-Western populations undergoing the transition to a market economy. This is unfortunate given the importance of these data for understanding health issues such as the global obesity epidemic. We consider the utility of using accelerometry technology to examine activity patterns and energy use regulation among indigenous Shuar, an Ecuadorian forager-horticulturalist population undergoing economic and lifestyle change. We investigate sex differences in Shuar activity patterns and the effects of reproductive status on activity. Finally, we discuss the potential of accelerometry use in human biology research.

METHODS

Physical activity levels were measured using Actical accelerometers in 49 indigenous Shuar adults (23 males, 26 females) from a rural Ecuadorian community. Female participants were in various reproductive states including pregnant, lactating, and nonpregnant/nonlactating.

RESULTS

Activity counts (AC), activity energy expenditure (AEE), and physical activity levels (PAL) were significantly higher (P < 0.05) in males than females. Significant differences in energy expenditure were found among pregnant or lactating females and males with pregnant or lactating partners (P < 0.001). Males with pregnant or lactating partners also had significantly higher activity levels than did other men (P < 0.01).

CONCLUSIONS

Shuar activity levels are relatively low compared to other non-Western populations. Despite increasing market integration, pregnant and lactating females seem to be adopting a strategy noted in other subsistence populations where male participation in subsistence activities increases to compensate for their partners' elevated reproductive costs. Despite certain limitations, use of accelerometry in human biology research shows promise.