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.

Socioeconomic benefits and limited parent-offspring disagreement in arranged marriages in Nepal

Mate preferences probably evolved to increase fitness; however, studies using arranged and non-arranged marriage as proxies for limited and free mate choice (respectively) do not find any reproductive differences. We explore why arranged and non-arranged marriages are an imperfect proxy for limited and free-choice matings and what fitness effects different marriage types could produce. Data from focus group discussions with men and women in Nepal show that there are three spouse choice categories with differing levels of parental influence over mate choice, reinforcing that arranged and non-arranged are not dichotomous. Discussions also show that parents and offspring, especially sons, may be more aligned in in-law/mate preferences than expected, demonstrating the need to establish clear domains of parent-offspring disagreement over spouse choice in the community before investigating fitness. Several social and financial benefits that are only available to arranged couples in this community were detected, and these benefits could compensate for any costs of not choosing a spouse independently. These benefits of arranged marriage are more salient for women than for men. These discussions indicate that predictions about the effects of spouse choice on fitness outcomes may differ for men and women and depend on community-specific socioeconomic benefits.

From little girls to adult women: Changes in age at marriage in Scheduled Castes from Madhya Pradesh and Uttar Pradesh, India

BACKGROUND

Research confirms the negative relationship between early marriage and mothers' and children's health outcomes. This is why studies of the changes in age at marriage are an important task from the point of view of the health status and well-being of a mother and her offspring, especially in groups represented by extremely disadvantaged social strata in India. The results of such studies may influence the future family planning policy in the country.

OBJECTIVES

This study aims to investigate the trend of age at marriage among the Scheduled Castes (SCs) women from two Indian states: Madhya Pradesh and Uttar Pradesh relative to the level of education and also to socioeconomic changes in the states. These states manifest the highest proportion of girls getting married below the age of 18 years-far above the proportion observed in entire India.

METHODS

Women from Scheduled Caste, N = 1,612, aged 25-65, born in 1950-1990 were investigated. A modern semiparametric regression approach was used. To capture the relationship between age at marriage and year of birth, categories of women's level of education (illiterate; primary: 1st-5th standards; middle school: 6th-8th standards; high school: 9th-10th standards; higher secondary: 11th-12th standards), and categories of the profession (women working in the agricultural sector or the non-agricultural sector), flexible framework of the Generalized Additive Model (GAM) was applied.

RESULTS

A significant impact of the cohort defined by the year of birth (<0.001), and women's education (<0.001) on age at marriage was noted, while the influence of women's occupation was not significant (p = 0.642). Mean age at marriage differed significantly with different education level. Women who graduated from primary school married 0.631 years later on average than illiterate ones, while those who graduated from middle schools, high schools (9th-10th standards) and higher secondary schools married significantly later than illiterate ones by 1.454 years and 2.463 years, respectively. Age at marriage increased over time: from slightly above 15 years in the cohort of illiterate women born in 1950 to almost 19 years in quite well-educated women born in 1990. The average age at marriage estimated for four education levels in 1990 ranged between 16.39 years (95%CI: 15.29-17.50) in the group of illiterate women and 18.86 years (95%CI: 17.76-19.95) in women graduated from high and higher secondary schools.

CONCLUSION

The rise of age at marriage can be partly explained by the increase of females enrolled in schools, the alleviation of poverty, and the implementation of social programs for women.

The impact of market integration on arranged marriages in Matlab, Bangladesh

Success in marriage markets has lasting impacts on women's wellbeing. By arranging marriages, parents exert financial and social powers to influence spouse characteristics and ensure optimal marriages. While arranging marriages is a major focus of parental investment, marriage decisions are also a source of conflict between parents and daughters in which parents often have more power. The process of market integration may alter parental investment strategies, however, increasing children's bargaining power and reducing parents' influence over children's marriage decisions. We use data from a market integrating region of Bangladesh to (a) describe temporal changes in marriage types, (b) identify which women enter arranged marriages and (c) determine how market integration affects patterns of arranged marriage. Most women's marriages were arranged, with love marriages more recent. We found few predictors of who entered arranged vs. love marriages, and family-level market integration did not predict marriage type at the individual level. However, based on descriptive findings, and findings relating women's and fathers' education to groom characteristics, we argue that at the society-level market integration has opened a novel path in which daughters use their own status, gained via parental investments, to facilitate good marriages under conditions of reduced parental assistance or control.

Fitness consequences of cousin marriage: a life-history assessment in two populations

Cousin marriage, a spousal union between close kin, occurs at high frequencies in many parts of the world. The rates of cousin marriage in humans are concordant with empirical studies that challenge the traditionally held view that reproduction with kin is generally avoided in animals. Similarly, some theoretical models in animal behaviour show that inbreeding avoidance is more constrained than previously thought. Such studies highlight the importance of quantifying the costs and benefits of reproduction among close kin over the whole life-course. Here, we use genealogical data from two human populations with high frequencies of cousin marriage (the Dogon from Mali, and the Ancien Régime nobility from Europe) to estimate these potential costs and benefits. We compare age-specific fertility and survival curves, as well as the projected growth rates, of subpopulations of each marriage type. Fitness costs of cousin marriage are present in terms of reduced child survival (in both populations), while benefits exist as increased fertility for men (in the Dogon) and for women (in the Ancien Régime nobility). We also find some differences in the projected growth rates of lineages as a function of marriage type. Finally, we discuss the trade-offs that might shape marriage decisions in different ecological conditions.

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.

Different predictors of intimate partner and natal family violence against women

Background

Violence against women is often studied in the context of violence from intimate partners. However, women receive violence from a wider range of individuals—such as their natal kin—including their siblings, parents, uncles and cousins. Applying insights from evolutionary theory, we examine whether cousin marriage, which has been hypothesized to both reduce the risk of partner violence but increase the risk of natal family violence, associates differently with each type of violence. Second, we test whether common risk factors for partner violence, such as wealth, associate similarly with natal violence.

Methodology

We analyse over 16 000 Jordanian women from three cohorts of the Jordan Demographic Health Surveys. Predictor variables include type of cousin marriage (patrilateral or matrilateral), education, wealth, number of children, urban living and polygyny. Outcome variables include whether a woman’s husband or her natal family has ever been physically violent towards her.

Results

Being married to a patrilateral cousin but not a matrilateral cousin is associated with a reduced risk of reporting intimate partner violence (IPV). By contrast being married to a matrilateral cousin but not a patrilateral one is associated with a reduced risk of reporting natal family violence. As expected, wealth is negatively associated with reporting partner violence, but we find no association with reports of natal family violence. Finally, individuals with more children are more likely to report IPV.

Conclusions and implications

Findings indicate the importance of distinguishing between types of cousin marriage and highlight substantial differences in risk factors for intimate partner compared to natal family violence.

Lay Summary

Sociodemographic risk factors, such as wealth, may associate differently with intimate partner and natal family violence. Results suggest that whether cousin marriage is protective of violence may depend on the type of cousin and secondly, that violence can have fitness relevant outcomes.

Social support, nutrition and health among women in rural Bangladesh: complex tradeoffs in allocare, kin proximity and support network size

Malnutrition among women of reproductive age is a significant public health concern in low- and middle-income countries. Of particular concern are undernutrition from underweight and iron deficiency, along with overweight and obesity, all of which have negative health consequences for mothers and children. Accumulating evidence suggests that risk for poor nutritional outcomes may be mitigated by social support, yet how social support is measured varies tremendously and its effects likely vary by age, kinship and reproductive status. We examine the effects of different measures of social support on weight and iron nutrition among 677 randomly sampled women from rural Bangladesh. While we find that total support network size mitigates risk for underweight, other results point to a potential tradeoff in the effects of kin proximity, with nearby adult children associated with both lower risk for underweight and obesity and higher risk for iron deficiency and anaemia. Social support from kin may then enhance energy balance but not diet quality. Results also suggest that a woman's network of caregivers might reflect their greater need for help, as those who received more help with childcare and housework had worse iron nutrition. Overall, although some findings support the hypothesis that social support can be protective, others emphasize that social relationships often have neutral or negative effects, illustrating the kinds of tradeoffs expected from an evolutionary perspective. The complexities of these effects deserve attention in future work, particularly within public health, where what is defined as 'social support' is often assumed to be positive. This article is part of the theme issue 'Multidisciplinary perspectives on social support and maternal-child health'.

Married Too Young? The Behavioral Ecology of ‘Child Marriage’

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.

When marital institutions break down: Impact and adaptation among the Enga of Papua New Guinea

Institutions to regulate marriage and sexual mores are nearly universal across human societies to assure production and reproduction and weave the fabric of society. The stakeholders are many. What happens when marital traditions break down in times of rapid change? Taking a long-term perspective, we will first look at developments in marital institutions that occurred after the arrival of the sweet potato (ca. 400 BP) among the Enga of Papua New Guinea. Next, we will document changes in recent marital practices of 402 Enga women collected in 2007. With data from 270 public forums in customary courts applying restorative justice between 2008 and 2019, we will consider (a) the impact of the breakdown of marital institutions and (b) responses to adapt norms to new practices. In the absence of regulation by 'traditional' institutions, individuals pursue their own interests and passions with negative outcomes for families and communities. Communities, non-governmental organisations, churches and government throughout Papua New Guinea are seeking to adapt norms to new conditions. We consider both norm change resulting from community action via customary courts and what communities strive to preserve. Cultural institutions and accompanying norms are important factors in assuring production and reproduction; however, they can instill attitudes that inhibit adaptation.

Genetic and reproductive consequences of consanguineous marriage in Bangladesh

Introduction

This study aimed to assess the prevalence, sociodemographic factors, reproductive consequences, and heritable disease burdens associated with consanguineous marriage (CM) in Bangladesh.

Methods

A total of 7,312 families, including 3,694 CM-families, were recruited from 102 locales of 58 districts of Bangladesh. Using a standard questionnaire, we collected medical history and background sociodemographic data of these families. Family history was assessed by pedigree analysis. Fertility, mortality, secondary sex ratio, selection intensity, lethal equivalents were measured using standard methods.

Results

The mean prevalence of CM in our studied population was 6.64%. Gross fertility was higher among CM families, as compared to the non-CM families (p < 0.05). The rate of under-5 child (U5) mortality was significantly higher among CM families (16.6%) in comparison with the non-CM families (5.8%) (p < 0.01). We observed a persuasive rise of abortion/miscarriage and U5 mortality rates with the increasing level of inbreeding. The value of lethal equivalents per gamete found elevated for autosomal inheritances as compared to sex-linked inheritance. CM was associated with the incidence of several single-gene and multifactorial diseases, and congenital malformations, including bronchial asthma, hearing defect, heart diseases, sickle cell anemia (p < 0.05). The general attitude and perception toward CM were rather indifferent, and very few people were concerned about its genetic burden.

Conclusion

This study highlights the harmful consequences of CM on reproductive behavior and the incidence of hereditary conditions. It essences the need for genetic counseling from premarital to postnatal levels in Bangladesh.

Prevalence and determinants of consanguineous marriage and its types in India: evidence from the National Family Health Survey, 2015-2016

The aim of the present study was to estimate the prevalence and examine the determinants of consanguineous marriage types in India. Data for 456,646 ever-married women aged 15-49 years were analysed from the National Family Health Survey (NFHS)-4 conducted in 2015-16. The overall prevalence of consanguineous marriage was 9.9%; the South region (23%) and North-East region (3.1%) showed the highest and lowest prevalences, respectively. Muslims had a higher prevalence (15%) than Hindus (9%). The prevalence of first cousin marriage (8.7%) was more than that of second cousin (0.7%) and of uncle-niece marriages (0.6%). Women living in urban areas and in nuclear families, having a higher level of education and belonging to affluent families were less likely to marry their cousins (p < 0.01). Women living in the South region of the country were more likely to marry their cousins, as well as uncles (p < 0.001). Close scrutiny of the trends in the results (odds ratios) revealed no clear relationship between socioeconomic condition and consanguineous marriage. The study results suggest that religion and north-south regional dichotomy in culture largely determine consanguineous marriage rather than socioeconomic condition in India.

Human niche, human behaviour, human nature

The concept of a 'human nature' or 'human natures' retains a central role in theorizing about the human experience. In Homo sapiens it is clear that we have a suite of capacities generated via our evolutionary past, and present, and a flexible capacity to create and sustain particular kinds of cultures and to be shaped by them. Regardless of whether we label these capacities 'human natures' or not, humans occupy a distinctive niche and an evolutionary approach to examining it is critical. At present we are faced with a few different narratives as to exactly what such an evolutionary approach entails. There is a need for a robust and dynamic theoretical toolkit in order to develop a richer, and more nuanced, understanding of the cognitively sophisticated genus Homo and the diverse sorts of niches humans constructed and occupied across the Pleistocene, Holocene, and into the Anthropocene. Here I review current evolutionary approaches to 'human nature', arguing that we benefit from re-framing our investigations via the concept of the human niche and in the context of the extended evolutionary synthesis (EES). While not a replacement of standard evolutionary approaches, this is an expansion and enhancement of our toolkit. I offer brief examples from human evolution in support of these assertions.