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Urbanization in low and middle-income nations is characterized by economic and demographic shifts largely understood to be beneficial to women’s empowerment. These changes include increased education and wage-labor opportunities, a disruption of traditional patrilocal residence systems, and reductions in spousal age gap and fertility. However, such changes may drive a “violence backlash,” with men increasing intimate partner violence (IPV) in efforts to challenge women’s shifting status. To date, tests of this idea primarily relate to women’s changing economic status, with less known about the demographic correlates of IPV in urbanizing settings. Addressing this, we conducted a cross-sectional study of IPV behavior and attitudes in an urbanizing community in Mwanza, northern Tanzania ( n = 317). Consistent with a violence backlash, IPV was reported more often among women educated at higher levels than their husband, and women earning similar, rather than lower, wages to their husband were more likely to report that he condones IPV. These findings were independent of women’s absolute education and income. Furthermore, less frequent paternal kin contact, and relatively small spousal age gaps, generally understood to boost women’s empowerment, were associated with an increased risk of experiencing IPV. Less frequent paternal kin contact was also associated with an increased likelihood that a husband condones IPV. Contrary to our predictions, relatively lower fertility, generally linked to higher women’s empowerment, did not predict IPV behavior and women with high, rather than low, fertility were more likely to report that their husband condones IPV. Overall, our results support the notion of a violence backlash corresponding to economic changes for women that accompany urbanization. In contrast, demographic changes associated with urbanization have more variable relationships. Drawing on these results, we suggest future research avenues for better understanding the vulnerability of women to IPV in urbanizing settings.

Research centres in low- and middle-income countries are routinely circumvented in the production of cross-cultural research on human behaviour. Where local contributions are made, collaboration is rarely equitable and often uncredited in co-authorship. Efforts to decolonize the social sciences will remain inadequate until these norms are overturned.

The marriage of older men to younger women is common across cultures. On one hand, husband-older marriage may serve the interests of both sexes, a conclusion broadly consistent with reported gender differences in mate preferences. On the other hand, men alone may benefit from such marriages at a cost to women if seniority enables men to exert dominance in conflicts of interest. Indeed, in public health large spousal age gaps are generally deemed “pathological”, both as a cause and consequence of gender inequalities harmful to women. We investigate these alternative models of spousal age gap using data from a cross-sectional survey of women in Mwanza, northwestern Tanzania (n = 993). Consistent with the notion that spousal age gaps are a product of sexual conflict, women typically married with a larger age gap than stated ideals. However, adjusting for potential confounds, spousal age gap was not associated with fertility or the risk of divorce. Furthermore, women's mental health and autonomy in household decision-making was higher in husband-older marriages compared to rare cases of same-age or wife-older marriage. Beyond this comparison, the magnitude of spousal age gaps was unrelated to either measure of women's wellbeing among the overwhelming majority of marriages where the husband was older. Together these findings suggest husband-older marriage does not influence marital stability, relatively large spousal age gaps are neither especially costly nor beneficial to women, and that alternative sociodemographic factors are more important in driving variation in women's wellbeing and reproductive success in this context. Our results support neither a model of mutual benefits, nor a pathological conceptualization of spousal age gaps. We conclude by both encouraging evolutionary human scientists to engage more fully with models of sexual conflict in future studies of marriage and mating, and suggesting that public health scholars consider more neutral interpretations of spousal age differences.

Global health studies typically characterise adolescent marriage as a fundamental risk to female wellbeing. In contrast, ethnographic research among communities 'at risk' identifies that early marriage is often viewed as an opportunity weighed against locally feasible alternatives. Addressing this contradiction, we document perceived risks and opportunities of marriage, positioning them among wider concerns facing female adolescents in north-western Tanzania. On the basis of these data, we then provide recommendations for global efforts to end the marriage of minors. Thirteen focus groups and 26 in-depth interviews were conducted in 2019 with female adolescents, young women and men, and parents of female adolescents from a semi-urban community where adolescent marriage is normative. Data were compiled to synthesise narratives of adolescent risk and opportunity. Marriage was viewed as an opportunity for adolescent girls, bringing benefits such as increased social status. Risks sometimes outweighed benefits of marriage, but marriage remained desirable when structural constraints, like poverty, limited feasible alternatives and when adolescents faced similar risks, like pregnancy, outside of marriage. We conclude that remaining unmarried does not shield adolescents from adversity, and campaigns targeting adolescent marriage via criminalisation, without diminishing other risks of adolescence, may further limit rather than expand options for adolescent girls.

To determine the frequency, impact, and factors associated with self-reported neurobehavioural disability (NBD) in individuals with stroke. A secondary aim was to examine the course of self-reported NBD over time and associations with outcomes.Eighty-seven participants admitted for inpatient rehabilitation post-stroke completed the St Andrew's-Swansea Neurobehavioural Outcome Scale. Demographic and stroke details and measures of functional disability, cognitive impairment, mood, and self-rated impact of NBD symptoms were completed. Twenty-seven participants and 19 close-others were reassessed three to six months following discharge.Overall reporting of neurobehavioural problems was infrequent. The domains of interpersonal and cognitive difficulties were the most commonly identified but were still only reported occasionally. However, even mild NBD was significantly correlated with negative impact. Greater self-reported NBD was significantly correlated with greater functional dependence, anxiety, and depression during inpatient rehabilitation. Self-reports of NBD remained stable over time and, at follow-up, was significantly correlated with depressive symptoms both in participants with stroke and close-others.In survivors of stroke, self-report of NBD is associated with poor outcomes in function, anxiety, and depression. These findings highlight the importance of routine and comprehensive assessment and intervention to manage NBD following stroke.IMPLICATIONS FOR REHABILITATIONDespite relatively infrequent self-reporting, presence of NBD remained stable across a six month follow-up period following rehabilitation which highlights the potential persistent nature of these difficulties.Even mild levels of self-reported NBD were associated with emotional distress in both stroke survivors and their significant others indicating a need for relevant interventions to support long-term outcomes.Routine screening for the presence of NBD is recommended to facilitate early detection and intervention to optimise post-stroke recovery.

Despite evidence of the efficacy of telerehabilitation post-stroke, uptake has lagged behind the development of available technology, slowed by low confidence in user experience. We aimed to explore the issue of acceptability by characterizing the experience of telerehabilitation for service providers and consumers of a memory rehabilitation program. Semi-structured interviews were conducted with nine clinicians (

Global health interventions increasingly target the abolishment of ‘child marriage’ (marriage under 18 years, hereafter referred to as ‘early marriage’). Guided by human behavioural ecology theory, and drawing on focus groups and in-depth interviews in an urbanising Tanzanian community where female early marriage is normative, we examine the common assumption that it is driven by the interests and coercive actions of parents and/or men. We find limited support for parent–offspring conflict. Parents often encouraged early marriages, but were motivated by the promise of social and economic security for daughters, rather than bridewealth transfers alone. Moreover, forced marriage appears rare, and adolescent girls and young women (AGYW) were active agents in the transition to marriage, sometimes marrying against parental wishes. Support for gendered conflict was stronger. AGYW were described as being lured into unstable relationships by men misrepresenting their long-term intentions. Community members voiced concerns over these marriages. Overall, early marriage appears rooted in limited options, encouraging strategic, but risky choices on the marriage market. Our results highlight plurality and context dependency in drivers of early marriage, even within a single community. We conclude that engaging with the importance of context is fundamental in forging culturally sensitive policies and programs on early marriage.

Purpose: To investigate the level of agreement of neurobehavioral disability following stroke.Methods: Stroke patients and nurses were recruited from an inpatient neurorehabilitation facility. In t...

Approximately 40% of women in sub-Saharan Africa marry before their eighteenth birthday1. Within the international development sector, this phenomenon is referred to as 'child marriage', widely equated to forced marriage, and recognized as damaging to multiple dimensions of female well-being1,2. An escalating global campaign to end early marriage typically assumes that its high prevalence is driven by a conflict of interests between parents and daughters, with parents coercing daughters to marry early for the parents' economic benefit3. However, a parent-offspring conflict model of early marriage has not been explicitly tested. Here we present a study of marriage transitions in rural Tanzania, where marriage before or just after 18 years of age is normative. Consistent with parental coercion, we find that bridewealth transfers are highest for younger brides. However, autonomy in partner choice is very common at all ages, relationships between age at marriage and female well-being are largely equivocal, and women who marry early achieve relatively higher reproductive success. We conclude that, in contexts in which adolescents have autonomy in marriage choices and in which marriage promotes economic and social security, early marriage may be better understood as serving the strategic interests of both parents and daughters.

A global campaign to end “child marriage” has emerged over the last decade as part of growing international commitments to address gender inequities and improve female wellbeing. Campaigns typically assert that young brides have negligible autonomy in the marriage process and that marrying under 18 years has resolutely negative impacts on wellbeing. Yet, surprisingly few studies explore local attitudes towards marriage and its timing within contexts where early marriage is most common. As such our understanding of motivations and potential conflicts of interest leading female adolescents into marriage remain poorly informed by viewpoints of people purportedly at risk. We present an exploratory study of attitudes to early marriage in northwestern Tanzania where marriage before or shortly after 18 years is normative. We use focus group discussions, complimented by a survey of 993 women, to investigate local views on marriage. We explore (i) why people marry, (ii) when marriage is deemed appropriate, and (iii) who guides the marriage process. Contrary to dominant narratives in the end child marriage movement, we find that women are frequently active rather than passive in the selection of when and who to marry. Furthermore, marriage is widely viewed as instrumental in acquiring social status within one’s local community. Our conclusions illuminate why rates of early marriage remain high despite potential negative wellbeing consequences and increasingly restrictive laws. We discuss our results in relation to related qualitative studies in other cultural contexts and consider the policy implications for current efforts to limit early marriage in Tanzania and beyond.

Background The concept of ‘child marriage’ in global health distinguishes ostensibly harmful from healthy ages to marry at a universally-applied threshold of 18-years. With intensifying efforts to end child marriage, targeted communities are increasingly asked to change their perception of such marriages from relatively benign to profoundly problematic. The objective of this study is to understand how this shift in perception is navigated by adolescent girls and young women (AGYW). Methods Using qualitative data collected in 2019 from a semi-urban community in Tanzania where marriage under 18-years is common and campaigns to end child marriage ongoing, we contrast reports of lived experiences of marriage under 18-years among AGYW to views of child marriage as an abstract concept. Thirteen in-depth interviews with AGYW, as part of a wider qualitative study, were recorded, transcribed, and analyzed using a framework analysis approach. Results While many AGYW had heard of child marriage, the concept was routinely conflated with forced marriage, which is rare in the community, and non-marital teenage sex and pregnancy, which are common. As a likely consequence, participants disagreed on whether or not child marriage occurs locally. Furthermore, accounts of real-life marriages under 18 sometimes aligned with, but often departed from, common narratives about the purported causes and harmful consequences inherent to the global health concept of child marriage. Conclusions We argue that engaging with diverse local views and experiences of marrying young is essential to producing culturally-sensitive, effective initiatives addressing the vulnerabilities of female adolescence.

Rehabilitation of memory remains an unmet need for many stroke survivors. Telehealth methods may provide a solution, however evidence supporting the efficacy of remotely-delivered therapy is needed. A non-concurrent multiple baseline design was used with randomized onset of intervention across five individuals with chronic stroke-related memory complaints. A six-week compensatory memory skills programme was delivered individually via internet videoconferencing. Target behaviours of frequencies of self-reported lapses of everyday and prospective memory were measured weekly across baseline, intervention, and follow-up phases. A secondary outcome of functional goal attainment was measured once per phase, with participants setting two personal rehabilitation goals. Data were analysed visually and statistically. Improvements in memory functioning were statistically significant on at least one measure of target behaviour for four out of five participants at intervention or follow-up. Visual evidence of level change indicated at least modest improvements for all participants by follow-up. All participants attained at least one functional goal by follow-up. High rates of treatment adherence and participant satisfaction were observed. Technological issues were minimal and did not impact content delivery or engagement. These results provide preliminary support for the efficacy of a telehealth-delivered rehabilitation programme in improving memory function and achieving memory-related goals for stroke survivors.

Achieving gender equality fundamentally requires a transfer of power from men to women. Yet data on men's support for women's empowerment (WE) remains scant and limited by reliance on self-report methodologies. Here, we examine men's support for WE as a sexual conflict trait, both via direct surveys (n = 590) and indirectly by asking men's wives (n = 317) to speculate on their husband's views. Data come from a semi-urban community in Mwanza, Tanzania. Consistent with reduced resource competition and increased exposure to relatively egalitarian gender norms, higher socioeconomic status predicted greater support for WE. However, potential demographic indicators of sexual conflict (high fertility, polygyny, large spousal age gap) were largely unrelated to men's support for WE. Contrasting self- and wife-reported measures suggests that men frequently exaggerate their support for women in self-reported attitudes. Discrepancies were especially pronounced among men claiming the highest support for WE, but smallest among men who held a professional occupation and whose wife participated in wage labour, indicating that these factors predict genuine support for WE. We discuss the implications of these results for our understanding of both individual variation and patriarchal gender norms, emphasising the benefits of greater exchange between the evolutionary human sciences and global health research on these themes.

Objective: Memory problems are commonly reported following stroke; however, the specific nature and frequency of memory complaints experienced by stroke survivors has not been sufficiently ...

Objective:Rehabilitation of memory after stroke remains an unmet need. Telehealth delivery may overcome barriers to accessing rehabilitation services.Method:We conducted a non-randomized intervention trial to investigate feasibility and effectiveness of individual telehealth (internet videoconferencing) and face-to-face delivery methods for a six-week compensatory memory rehabilitation program. Supplementary analyses investigated non-inferiority to an existing group-based intervention, and the role of booster sessions in maintaining functional gains. The primary outcome measure was functional attainment of participants’ goals. Secondary measures included subjective reports of lapses in everyday memory and prospective memory, reported use of internal and external memory strategies, and objective measures of memory functioning.Results:Forty-six stroke survivors were allocated to telehealth and face-to-face intervention delivery conditions. Feasibility of delivery methods was supported, and participants in both conditions demonstrated treatment-related improvements in goal attainment, and key subjective outcomes of everyday memory, and prospective memory. Gains on these measures were maintained at six-week follow-up. Short-term gains in use of internal strategies were also seen. Non-inferiority to group-based delivery was established only on the primary measure for the telehealth delivery condition. Booster sessions were associated with greater maintenance of gains on subjective measures of everyday memory and prospective memory.Conclusions:This exploratory study supports the feasibility and potential effectiveness of telehealth options for remote delivery of compensatory memory skills training after a stroke. These results are also encouraging of a role for booster sessions in prolonging functional gains over time.

Evolutionary demography predicts that variation in reproductive timing stems from socio-ecologically contingent trade-offs between current and future reproduction. In contemporary high-income societies, the costs and benefits of current reproduction are likely to vary by socioeconomic status (SES). Two influential hypotheses, focusing on the parenthood ‘wage penalty’, and responses to local mortality have separately been proposed to influence the timing of parenthood. Economic costs of reproduction (i.e. income loss) are hypothesized to delay fertility, especially among high childhood SES individuals who experience greater opportunities to build capital through advantageous education and career opportunities. On the other hand, relatively low childhood SES individuals experience higher mortality risk, which may favour earlier reproduction. Here, we examine both hypotheses with a representative register-based, multigenerational dataset from contemporary Finland (N= 47 678). Consistent with each hypothesis, the predicted financial cost of early parenthood was smaller, and mortality among close kin was higher for individuals with lower childhood SES. Within the same dataset, lower predicted adulthood income and more kin deaths were also independently associated with earlier parenthood. Our results provide a robust demonstration of how economic costs and mortality relate to reproductive timing. We discuss the implications of our findings for demographic theory and public policy.

Background: A global campaign to eradicate ‘child marriage’ (Methods: We surveyed USA nationals via the online survey platform MTurk. Participants provided sociodemographic information and answered ten questions about their understanding of child marriage. To identify potential misconceptions and inaccurate beliefs we present descriptive statistics for participant responses paired with correct answers where available.Results: 609 participants provided data for analysis. 59% were women, with a mean age of 37 years, just over half (55%) were university educated, and the majority (79%) were currently employed. Half of those surveyed mistakenly believed that the cut-off for child marriage is younger than the legal threshold of 18 years, and nearly three-quarters incorrectly believed that most child marriages occur at 15 years or below (child marriage primarily takes place in later adolescence). The large majority of participants incorrectly believed that child marriage is illegal throughout the United States (it’s illegal in only two states), and mistakenly believed that child marriage primarily takes place among Muslim-majority regions of the Middle East and North Africa (it is most common in sub Saharan Africa and South Asia). Participants tended to substantially overestimate the prevalence of child marriage in both the USA and abroad.Conclusions: These findings suggest that public understanding of child marriage is not only poor, but also shaped by wider misperceptions of both relatively high and low-income nations. Organizations seeking to empower girls and young women by reducing child marriage need to be cautious of these misunderstandings, and wary of the potential for their own activities to seed misinformation. For example, we suggest the terminology ‘child marriage’, as opposed to ‘teen marriage’ or ‘adolescent marriage’, may contribute to widespread confusion about the typical ages at which child marriages occur.

Variation in parental care by child's sex is evident across cultures. Evolutionary theory provides a functional explanation for this phenomenon, predicting that parents will favour specific children if this results in greater fitness payoffs. Here, we explore evidence for sex-biased parental care in a high-fertility, patriarchal and polygynous population in Tanzania, predicting that both mothers and fathers will favour sons in this cultural setting. Our data come from a cross-sectional study in rural northwestern Tanzania, which included surveys with mothers/guardians of 808 children under age 5. We focus on early childhood, a period with high mortality risk which is fundamental in establishing later-life physical and cognitive development. Examining multiple measures of direct/physical care provision (washing, feeding, playing with, supervising, co-sleeping and caring when sick), we demonstrate that fathers favour sons for washing, feeding and supervising, while maternal care is both more intensive and unrelated to child sex. We find no difference in parental care between girls and boys regarding the allocation of material resources and the duration of breastfeeding; or in terms of parental marital and co-residence status. This bias towards sons may result from higher returns to investment for fathers than mothers, and local gender norms about physical care provision.

For girls and women, marriage under 18 years is commonplace in many low-income nations today and was culturally widespread historically. Global health campaigns refer to marriage below this threshold as ‘child marriage’ and increasingly aim for its universal eradication, citing its apparent negative wellbeing consequences. Here, we outline and evaluate four alternative hypotheses for the persistence of early marriage, despite its associations with poor wellbeing, arising from the theoretical framework of human behavioral ecology. First, early marriage may be adaptive (e.g., it maximizes reproductive success), even if detrimental to wellbeing, when life expectancy is short. Second, parent–offspring conflict may explain early marriage, with parents profiting economically at the expense of their daughter’s best interests. Third, early marriage may be explained by intergenerational conflict, whereby girls marry young to emancipate themselves from continued labor within natal households. Finally, both daughters and parents from relatively disadvantaged backgrounds favor early marriage as a ‘best of a bad job strategy’ when it represents the best option given a lack of feasible alternatives. The explanatory power of each hypothesis is context-dependent, highlighting the complex drivers of life history transitions and reinforcing the need for context-specific policies addressing the vulnerabilities of adolescence worldwide.

Economic and evolutionary models of parental investment often predict education biases toward earlier-born children, resulting from either household resource dilution or parental preference. Previous research, however, has not always found these predicted biases—perhaps because in societies where children work, older children are more efficient at household tasks and substitute for younger children, whose time can then be allocated to school. The role of labor substitution in determining children’s schooling remains uncertain, however, because few studies have simultaneously considered intrahousehold variation in both children’s education and work. Here, we investigate the influence of coresident children on education, work, and leisure in northwestern Tanzania, using detailed time use data collected from multiple children per household (n = 1,273). We find that age order (relative age, compared with coresident children) within the household is associated with children’s time allocation, but these patterns differ by gender. Relatively young girls do less work, have more leisure time, and have greater odds of school enrollment than older girls. We suggest that this results from labor substitution: older girls are more efficient workers, freeing younger girls’ time for education and leisure. Conversely, relatively older boys have the highest odds of school enrollment among coresident boys, possibly reflecting traditional norms regarding household work allocation and age hierarchies. Gender is also important in household work allocation: boys who coreside with more girls do fewer household chores. We conclude that considering children as both producers and consumers is critical to understanding intrahousehold variation in children’s schooling and work.

Approximately 40% of women in sub-Saharan Africa marry before their eighteenth birthday

Background: Researchers from a variety of disciplines have presented data indicating that polygynous marriage is damaging to child health. This work has been used to support the classification of polygyny as a 'harmful cultural practice' and to advocate for marital reform across sub-Saharan Africa. Objective: We present a critical review of studies of polygyny and child health, highlighting issues of context and variation. We also consider methodological limitations of the existing literature. Methods: We describe key features of African polygyny, variation in its form, and the pathways through which polygyny has been hypothesized to influence child health. We then review the available empirical evidence, focusing on cross-national studies utilizing the Demographic and Health Surveys and relatively small-scale studies based on more specific socioecological settings (e.g., among particular ethnic groups). Conclusions: We conclude that (i) heterogeneity in the impact of polygyny on child health should be anticipated a priori given substantial variety in its form, locally available alternatives, and the wider context of the practice; (ii) available evidence suggests that polygyny is most frequently associated with poor child health, but there are also instances where polygyny appears inconsequential or even beneficial to children; and (iii) methodological shortcomings are rife across the literature, severely undermining our ability to make causal inferences from observed relationships between polygyny and child health. Contribution: Theoretical and empirical considerations imply that a singular health consequence of polygyny does not apply across all ecological and cultural settings. We encourage a more nuanced stance on polygyny in future academic and policy discourse.

© 2016 Wiley Periodicals, Inc. Objectives: The importance of fathers in ensuring child health in rural developing populations is questioned by anthropologists and population health scientists. Existing literature focuses on paternal death and child mortality. A relative lack of studies consider alternative forms of father absence and/or more subtle health outcomes. Here we determine the frequency and form of father absence in northern Tanzania, and its relationship to household food security, wealth, and child anthropometric status. Methods: We conducted a cross-sectional survey of 3136 children under 5 years of age from 56 villages. Using multilevel regression we contrast children residing with both parents to those that (i) have experienced paternal death, (ii) reside with their mother but not their living father and (iii) are fostered apart from both living parents. Results: Of the total, 3.5% of children had experienced paternal death. Thirteen percent resided with their mother but away from their living father. Supporting data indicate such cases primarily reflect parental divorce/separation, extra-marital birth, or polygynous fathers residing with an alternative cowife. Paternal death and residing apart from one's living father was associated with lower food security and/or relative poverty and there is suggestive evidence that children in such circumstances achieve lower height-for-age. Six percent of children were fostered, usually with grandparents, and were comparable to children residing with both parents in terms of household food security, wealth, and anthropometric status. Conclusion: Our results highlight diversity in the form and consequences of father absence. We discuss limitations of the current study and wider literature on fatherhood and make suggestions for future research.

Human behavioral ecology (HBE) is the study of human behavior from an adaptive perspective. It focuses in particular on how human behavior varies with ecological context. Although HBE is a thriving research area, there has not been a major review published in a journal for over a decade, and much has changed in that time. Here, we describe the main features of HBE as a paradigm and review HBE research published since the millennium. We find that the volume of HBE research is growing rapidly, and its composition is changing in terms of topics, study populations, methodology, and disciplinary affiliations of authors. We identify the major strengths of HBE research as its vitality, clear predictions, empirical fruitfulness, broad scope, conceptual coherence, ecological validity, increasing methodological rigor, and topical innovation. Its weaknesses include a relative isolation from the rest of behavioral ecology and evolutionary biology and a somewhat limited current topic base. As HBE continues to grow, there is a major opportunity for it to serve as a bridge between the natural and social sciences and help unify disparate disciplinary approaches to human behavior. HBE also faces a number of open questions, such as how understanding of proximate mechanisms is to be integrated with behavioral ecology's traditional focus on optimal behavioral strategies, and the causes and extent of maladaptive behavior in humans. © 2013 © The Author 2013. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.

LETTER LETTER REPLY TO RIEGER AND WAGNER: Context matters when studying purportedly harmful cultural practices David W. Lawson a,1 , Susan James b , Esther Ngadaya c , Bernard Ngowi c , Sayoki G. M. Mfinanga c , and Monique Borgerhoff Mulder b,d Rieger and Wagner (1) present three lines of cri- tique. First, Rieger and Wagner (1) argue that our (2) demonstration that polygyny predicts higher child weight-for-height z-scores (WHZ) in two out of three ethnic groups practicing polygyny should be disre- garded because of inadequacies of this measure. We defend our use of WHZ because: (i) although no mea- sure is perfect, many studies unequivocally confirm that WHZ is a useful indicator of acute malnutrition, highly predictive of child mortality (3); and (ii) regard- less of construct validity, WHZ scores have guided the international development sector for decades, our primary audience in addressing claims that po- lygyny is universally harmful. We also emphasize that our interpretation that polygyny may, in certain contexts, serve female interests rests not only on differences in WHZ, but also on our demonstration that (male-headed) polygynous households are rel- atively food secure and wealthy compared with monogamous households. Second, Rieger and Wagner (1) write that we dem- onstrate that child height-for-age z-scores (HAZ) are “systematically and negatively correlated with polygyny both at the individual and the village levels” (1), and that although our individual-level comparisons are sta- tistically nonsignificant, this can be attributed to small sample size because their study of polygyny across 26 African nations revealed a statistically significant nega- tive correlation at a similar magnitude (4). This critique fundamentally misses our central conclusion: context matters when studying purportedly harmful cultural practices. At the village level, the association between polygyny prevalence and child HAZ is accounted for by underlying contextual differences in ecological vulner- ability (rainfall) and socioeconomic marginalization (ed- ucation). At the individual level, our estimates are based on a specific area of Tanzania, and so cannot be mean- ingfully contrasted with Wagner and Rieger’s (4) esti- mate based on Africa as a whole. Indeed, consistent with our analysis (2), Wagner and Rieger’s cross-national study identifies considerable heterogeneity, with confi- dence intervals crossing zero for 15 of 26 countries and a positive (statistically nonsignificant) association be- tween polygyny and HAZ in Tanzania (ref. 4, p 17). Africa is a diverse continent and polygyny a diverse in- stitution, encompassing variable norms of residence, resource sharing, and spousal recruitment (5). A true understanding of polygyny can only be gained by ac- knowledging this diversity and designing analyses that take context into account (2). Third, Rieger and Wagner (1) suggest our analyses (2) are flawed because we don’t include interactions with child age. Reanalyzing our data selecting only children over 30 mo, Rieger and Wagner (1) report a negative association between polygyny and HAZ. However, our data are not suitable to test for age de- pendencies, which can only be confidently assessed via longitudinal analysis. Furthermore to achieve ade- quate sample size, Rieger and Wagner resort to (i) pooling data across ethnic groups, and so cannot rule out confounding with ethnicity, and (ii) crude compar- isons neglecting wife rank (proxied by household head sex) that proved crucial in our original analysis. Notably, once adjusted for village differences, Rieger and Wagner’s (1) effect estimate also falls short of standard levels of statistical significance (i.e., P < 0.05). We also observe a double standard: Wagner and Rieger’s (4) own cross-national study of polygyny neglects age interactions. In studying “harmful cul- tural practices” it is vital that we apply equivalent stan- dards of evidence independent of whether results meet or contradict conventional expectation. a Department of Population Health, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom; b Savannas Forever Tanzania, Arusha, Tanzania; c National Institute for Medical Research, Muhimbili Medical Research Centre, Dar es Salaam, 11101, Tanzania; and Department of Anthropology, University of California, Davis, CA 95616 Author contributions: D.W.L., S.J., E.N., B.N., S.G.M.M., and M.B.M. designed research; D.W.L. analyzed data; D.W.L. and M.B.M. wrote the paper; and S.J., E.N., B.N., and S.G.M.M. collected data. The authors declare no conflict of interest. To whom correspondence should be addressed. Email: david.lawson@lshtm.ac.uk. d www.pnas.org/cgi/doi/10.1073/pnas.1601420113 PNAS Early Edition | 1 of 2

The idea that trade-offs between offspring quantity and quality shape reproductive behaviour has long been central to economic perspectives on fertility. It also has a parallel and richer theoretical foundation in evolutionary ecology. We review the application of the quantity–quality trade-off concept to human reproduction, emphasizing distinctions between clutch size and lifetime fertility, and the wider set of forces contributing to fertility variation in iteroparous and sexually reproducing species like our own. We then argue that in settings approximating human evolutionary history, several factors limit costly sibling competition. Consequently, while the optimization of quantity–quality trade-offs undoubtedly shaped the evolution of human physiology setting the upper limits of reproduction, we argue it plays a modest role in accounting for socio-ecological and individual variation in fertility. Only upon entering the demographic transition can fertility limitation be clearly interpreted as strategically orientated to advancing offspring quality via increased parental investment per child, with low fertility increasing descendant socio-economic success, although not reproductive success. We conclude that existing economic and evolutionary literature has often overemphasized the centrality of quantity–quality trade-offs to human fertility variation and advocate for the development of more holistic frameworks encompassing alternative life-history trade-offs and the evolved mechanisms guiding their resolution.

Evolutionary models of human reproduction argue that variation in fertility can be understood as the local optimization of a life-history trade-off between offspring quantity and ‘quality’. Child survival is a fundamental dimension of quality in these models as early-life mortality represents a crucial selective bottleneck in human evolution. This perspective is well-rehearsed, but current literature presents mixed evidence for a trade-off between fertility and child survival, and little empirical ground to evaluate how socioecological and individual characteristics influence the benefits of fertility limitation. By compiling demographic survey data, we demonstrate robust negative relationships between fertility and child survival across 27 sub-Saharan African countries. Our analyses suggest this relationship is primarily accounted for by offspring competition for parental investment, rather than by reverse causal mechanisms. We also find that the trade-off increases in relative magnitude as national mortality declines and maternal somatic (height) and extrasomatic (education) capital increase. This supports the idea that socioeconomic development, and associated reductions in extrinsic child mortality, favour reduced fertility by increasing the relative returns to parental investment. Observed fertility, however, falls considerably short of predicted optima for maximizing total offspring survivorship, strongly suggesting that additional unmeasured costs of reproduction ultimately constrain the evolution of human family size.

Polygyny is cross-culturally common and a topic of considerable academic and policy interest, often deemed a harmful cultural practice serving the interests of men contrary to those of women and children. Supporting this view, large-scale studies of national African demographic surveys consistently demonstrate that poor child health outcomes are concentrated in polygynous households. Negative population-level associations between polygyny and well-being have also been reported, consistent with the hypothesis that modern transitions to socially imposed monogamy are driven by cultural group selection. We challenge the consensus view that polygyny is harmful, drawing on multilevel data from 56 ethnically diverse Tanzanian villages. We first demonstrate the vulnerability of aggregated data to confounding between ecological and individual determinants of health; while across villages polygyny is associated with poor child health and low food security, such relationships are absent or reversed within villages, particularly when children and fathers are coresident. We then provide data indicating that the costs of sharing a husband are offset by greater wealth (land and livestock) of polygynous households. These results are consistent with models of polygyny based on female choice. Finally, we show that village-level negative associations between polygyny prevalence, food security, and child health are fully accounted for by underlying differences in ecological vulnerability (rainfall) and socioeconomic marginalization (access to education). We highlight the need for improved, culturally sensitive measurement tools and appropriate scales of analysis in studies of polygyny and other purportedly harmful practices and discuss the relevance of our results to theoretical accounts of marriage and contemporary population policy.

Evolutionary models of parental investment often assume that negative effects of competition between offspring (i.e., quantity-quality trade-off effects) will be most apparent under conditions of resource scarcity. However, improvements in resource access associated with “modernization” may reduce levels of extrinsic environmental risk, creating a stronger association between parental investment and offspring success. Here we provide evidence that a rural development initiative in Ethiopia is associated with increased levels of parental investment in offspring status and increased levels of competition for this investment between siblings. Villages with access to an improved water supply, which have reduced levels of childhood mortality, are associated with higher investments in education, and the likelihood of offspring education is more determined by position within the family, compared to neighboring villages without access to water taps. However, there is no evidence of higher parental investment of base-level resources directly related to child health (indicated by childhood vaccination rates). Educational investment may be more sensitive to mortality changes, despite being costly and “surplus” to essential functions, because it has the potential to introduce the greatest economic payoffs for children, e.g., from jobs in an emerging wage-labour market. While tap villages are currently associated with a higher birth rate, we anticipate that in time, and with improved access to family planning, fertility will drop in response to shifts in environmental risk and improved pay-offs to strategies of high parental investment. These villages may be experiencing the initial stages of a demographic transition to small family sizes.

The social and health sciences have often emphasised the negative impacts of large sibship size and late birth order on childhood. For example, it is now well established that, other things being equal, children in large families and/or with many older siblings, receive lower allocations of care time from both parents, are more likely to grow up in conditions of economic hardship, and, as a likely consequence, exhibit relatively poor educational and physical health outcomes. Few researchers have, however, quantitatively assessed how siblings may influence indicators of mental health, where it is conceivable that social interactions with siblings may have a positive influence. Here, using data from a large British cohort survey (the Avon Longitudinal Study of Parents and Children), we explored the effects of sibling configuration on the Strengths and Difficulties Questionnaire, as a multidimensional index for mental health problems. We demonstrate a significant socio-economic gradient in mental health between the ages of three and nine years, but little evidence for negative effects of large sibship size. Rerunning this analysis to examine birth order, a much clearer pattern emerged; the presence of older siblings was associated with relatively good mental health, while the presence of younger siblings was associated with relatively poor mental health. This suggests that being born into a large family, providing the child is not joined by subsequent siblings, may carry important benefits unconsidered by past research. We discuss possible interpretations of this pattern and the wider implications for understanding the family context of child development.

Evolutionary and economic models of the family propose that parents face a fundamental trade-off between fertility and investment per offspring. However, tests of this hypothesis have focused primarily on offspring outcomes rather than direct measures of parental investment. Existing studies of parenting also suffer a number of methodological problems now recognized as common sources of error in sociodemographic studies. Here, we present a more definitive picture of the effects of family structure on parental care by analyzing an extensive longitudinal dataset of contemporary British families (the Avon Longitudinal Study of Parents and Children). Unlike other studies, we simultaneously track maternal and paternal behaviors within the same family and consider variation both across time and between distinct population subgroups. Parental investment was measured as frequency of engagement in key care activities over the first decade of life. For both parents, larger family size was traded off against investment per offspring, representing the strongest explanatory variable considered in our analysis. However, contrary to the predictions of traditional quantity–quality trade-off models, increasing family socioeconomic status did not alleviate this effect. In fact, for paternal care in particular, increases in wealth and education created stronger trade-offs. We also demonstrate that large sibships were particularly costly for later-born offspring. Sex of siblings did not influence parental care, however maternal investment was biased towards daughters and paternal investment biased towards sons. Unrelated father figures were also associated with lower investment from both parents. Results are discussed in relation to parental investment theory and evolutionary models of modern low fertility.

Background Life history theory and resource dilution models of the family suggest that siblings may present a threat to healthy development because they compete for resources that parents have available to invest in individual offspring. Using data from a large cohort study of contemporary British families (ALSPAC), we test this hypothesis using childhood growth trajectories as a biomarker for health status. Methods Incorporating time-varying measures of changing family structure and socio-economic environment, this study represents the first true longitudinal analysis of family configuration effects on human growth. Using separate multi-variate multi-level models we estimate the effect of sibling number and sibling age and sex on height from birth to 10 years. Results Adjusting for family level socio-economic factors, the presence of siblings is associated with deficits in height across the study period. At the largest comparison, we estimate that compared with only children, children with four siblings have a reduced birth length by � 8.7 mm (95% confidence interval (CI): � 14.8 to � 2.6) and a reduced rate of growth by � 2.3 mm per year (95% CI: � 3.8 to � 0.8), leading to a deficit of 31.5 mm by age 10. Older siblings are associated with larger lasting negative consequences on height than younger siblings. We find no difference in the height of children in relation to the sex of siblings. Conclusions Even in the relatively wealthy, well-nourished conditions of modern Western society, children are not buffered from the health costs of reduced parental investment. Later-born children appear worst affected by within family resource division.

Kanazawa (2007) proposes the ‘evolutionary psychological imagination’ (p.7) as an authoritative framework for understanding complex social and public issues. As a case study of this approach, Kanazawa addresses acts of international terrorism, specifically suicide bombings committed by Muslim men. It is proposed that a comprehensive explanation of such acts can be gained from taking an evolutionary perspective armed with only three points of cultural knowledge: 1. Muslims are exceptionally polygynous, 2. Muslim men believe they will gain reproductive access to 72 virgins if they die as a martyr and 3. Muslim men have limited access to pornography, which might otherwise relieve the tension built up from intra-sexual competition. We agree with Kanazawa that evolutionary models of human behaviour can contribute to our understanding of even the most complex social issues. However, Kanazawa’s case study, of what he refers to as ‘World War III’, rests on a flawed theoretical argument, lacks empirical backing, and holds little in the way of explanatory power.

In this chapter, we consider what evolutionary anthropology contributes to the study of population health, focusing specifically on family structure and its relationship to child and adult physical health. Evolutionary anthropologists have now built a substantial body of literature on relationships between family structure and various dimensions of human wellbeing, particularly in the context of small-scale ‘traditional’ societies and developing rural communities most at risk of poor health outcomes. Crucially, they have also constructed theoretical models to account for variation in key dimensions of family structure in relation to individual, ecological, and cultural factors. Thus, evolutionary anthropologists have much to say, not only about the extent to which specific family structures may influence health but also why certain family forms may persist or change across time and space. Here, focusing on studies primarily conducted in sub-Saharan Africa, we review the literature on three interrelated dimensions of family structure and their relationship to health: (1) family size, (2) polygynous versus monogamous marriage, and (3) the role of extended kin. Using these examples, we highlight the theoretical and empirical contributions of evolutionary anthropology and draw out implications for population policy and related initiatives seeking to improve family health in the developing world.

The idea that symmetry in facial traits is associated with attractiveness because it reliably indicates good physiological health, particularly to potential sexual partners, has generated an extensive literature on the evolution of human mate choice. However, large-scale tests of this hypothesis using direct or longitudinal assessments of physiological health are lacking. Here, we investigate relationships between facial fluctuating asymmetry (FA) and detailed individual health histories in a sample ( n = 4732) derived from a large longitudinal study (Avon Longitudinal Study of Parents and Children) in South West England. Facial FA was assessed using geometric morphometric analysis of facial landmark configurations derived from three-dimensional facial scans taken at 15 years of age. Facial FA was not associated with longitudinal measures of childhood health. However, there was a very small negative association between facial FA and IQ that remained significant after correcting for a positive allometric relationship between FA and face size. Overall, this study does not support the idea that facial symmetry acts as a reliable cue to physiological health. Consequently, if preferences for facial symmetry do represent an evolved adaptation, then they probably function not to provide marginal fitness benefits by choosing between relatively healthy individuals on the basis of small differences in FA, but rather evolved to motivate avoidance of markers of substantial developmental disturbance and significant pathology.

© 2014 Lawson et al. The Maasai of northern Tanzania, a semi-nomadic ethnic group predominantly reliant on pastoralism, face a number of challenges anticipated to have negative impacts on child health, including marginalisation, vulnerabilities to drought, substandard service provision and on-going land grabbing conflicts. Yet, stemming from a lack of appropriate national survey data, no large-scale comparative study of Maasai child health has been conducted. Savannas Forever Tanzania surveyed the health of over 3500 children from 56 villages in northern Tanzania between 2009 and 2011. The major ethnic groups sampled were the Maasai, Sukuma, Rangi, and the Meru. Using multilevel regression we compare each ethnic group on the basis of (i) measurements of child health, including anthropometric indicators of nutritional status and self-reported incidence of disease; and (ii) important proximate determinants of child health, including food insecurity, diet, breastfeeding behaviour and vaccination coverage. We then (iii) contrast households among the Maasai by the extent to which subsistence is reliant on livestock herding. Measures of both child nutritional status and disease confirm that the Maasai are substantially disadvantaged compared to neighbouring ethnic groups, Meru are relatively advantaged, and Rangi and Sukuma intermediate in most comparisons. However, Maasai children were less likely to report malaria and worm infections. Food insecurity was high throughout the study site, but particularly severe for the Maasai, and reflected in lower dietary intake of carbohydrate-rich staple foods, and fruits and vegetables. Breastfeeding was extended in the Maasai, despite higher reported consumption of cow's milk, a potential weaning food. Vaccination coverage was lowest in Maasai and Sukuma. Maasai who rely primarily on livestock herding showed signs of further disadvantage compared to Maasai relying primarily on agriculture. We discuss the potential ecological, socioeconomic, demographic and cultural factors responsible for these differences and the implications for population health research and policy.

Evolutionary anthropology presents a powerful theoretical framework to understand how both current environments and legacies of past selection shape human behavioural and cultural diversity. Combining ethnographic, economic and demographic methods, this integrative and pluralistic field has provided new insights into the ultimate motivations and proximate pathways that guide human adaptation and variation. In recent years, anthropologists and related social scientists have also begun to explore how evolutionary theory may be used as a tool to address questions of public health and social policy relevance. This marks a watershed development in evolutionary approaches to human behaviour, as the field moves beyond purely academic boundaries and into the realm of applied social science. As a species, we are currently experiencing dramatic shifts in our lifestyle, family structure, diet and health and global contact. ‘Applied evolutionary anthropology’ (AEA) can provide new insights into the causes and the consequences of such human behavioural shifts by studying populations at the cusp of these transitions. It also holds great, largely untapped, potential to guide the design, implementation and evaluation of effective social and public health policy. This edited volume reviews the current state of the emerging field of AEA, highlighting the work of a number of interdisciplinary evolutionary scientists studying contemporary world issues. In this chapter, we briefly introduce the objectives and main contributions of AEA, and discuss the key research themes explored both in this book and the wider literature.