Intention versus behaviour in parental sex preferences among the Mukogodo of Kenya

Do Social Pensions Affect the Physical and Mental Health of Rural Children in China? An Intergenerational Care Perspective

Research Purpose: This study aimed to explore the effect of China’s New Rural Pension (NRP) on the physical and mental health of rural children from the perspective of intergenerational care, and to examine whether family childcare types and the child’s gender affect the relationships between social pensions and the physical and mental health of rural children. Methods: We used data from the 2016 China Family Panel Studies (CFPS) of the China Social Science Survey Center, a nationally representative sample at the individual, family, and county levels from 25 provinces (cities and districts) in China. A total of 2142 sets of valid samples of children, the elderly, family economic and social conditions, and basic family information were retained after data screening. The regression discontinuity (RD) method was employed for the statistical analyses. Results: The NRP had a significant effect on both the mental health (β = −2.818, p < 0.1) and physical health (β = −2.214, p < 0.1) of rural children. This effect varied with the family childcare type and child’s gender. Conclusions: We reveal a positive effect of the NRP on the physical and mental health of rural children. Therefore, the establishment of a social pension system may be used as an effective approach to enhance the health of rural children. The impact of the NRP on the physical and mental health of children differs with the family childcare type and their gender, which should be taken into consideration when using social pensions to enhance child health.

Field evidence for two paths to cross-cultural competence: implications for cultural dynamics

Interaction between members of culturally distinct (ethnic) groups is an important driver of the evolutionary dynamics of human culture, yet relevant mechanisms remain underexplored. For example, cultural loss resulting from integration with culturally distinct immigrants or colonial majority populations remains a topic whose political salience exceeds our understanding of mechanisms that may drive or impede it. For such dynamics, one mediating factor is the ability to interact successfully across cultural boundaries (cross-cultural competence). However, measurement difficulties often hinder its investigation. Here, simple field methods in a uniquely suited Amazonian population and Bayesian item-response theory models are used to derive the first experience-level measure of cross-cultural competence, as well as evidence for two developmental paths: cross-cultural competence may emerge as a side effect of adopting out-group cultural norms, or it may be acquired while maintaining in-group norms. Ethnographic evidence suggests that the path taken is a likely consequence of power differences in inter- vs intra-group interaction. The former path, paralleling language extinction, may lead to cultural loss; the latter to cultural sustainability. Recognition of such path-dependent effects is vital to theory of cultural dynamics in humans and perhaps other species, and to effective policy promoting cultural diversity and constructive inter-ethnic interaction.

Fathers favour sons, mothers don't discriminate: Sex-biased parental care in northwestern Tanzania

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.

Sexual conflict and the Trivers-Willard hypothesis: Females prefer daughters and males prefer sons

Because parental care is expected to depend on the fitness returns generated by each unit of investment, it should be sensitive to both offspring condition and parental ability to invest. The Trivers-Willard Hypothesis (TWH) predicts that parents who are in good condition will bias investment towards sons, while parents who are in poor condition will bias investment towards daughters because high-quality sons are expected to out-reproduce high quality daughters, while low-quality daughters are expected to out-reproduce low quality sons. We report results from an online experiment testing the Trivers-Willard effect by measuring implicit and explicit psychological preferences and behaviorally implied preferences for sons or daughters both as a function of their social and economic status and in the aftermath of a priming task designed to make participants feel wealthy or poor. We find only limited support for predictions derived from the TWH and instead find that women have strong preferences for girls and men have preferences for boys.

Gender and birth order as determinants of parental behaviour

This study analyses the effect of gender and birth order of fifty-eight 3-month-old first- and laterborn boys and girls on parental treatment. Presence of parents, maternal primary care, and maternal and paternal facial exchange with the baby were assessed during videotaped observation sessions equivalent to a full day. The data reveal a sound birth rank effect, indicating that firstborns are preferred over laterborns in several respects: presence of mothers, presence of fathers, and father’s face-to-face behaviour when the mother is also present. With respect to gender differences, mothers prefer their daughters in terms of presence and primary care. Fathers prefer their sons in terms of presence. Unexpectedly, fathers prefer their daughters in terms of face-to-face exchange. The social context of fathers’ and mothers’ joint presence reveals the only interaction effect between gender and birth order with the preference of firstborn boys. The findings are related to previous research results as well as evolutionary considerations about parental investment.

Preferential parental investment in daughters over sons

Female-biased parental investment is unusual but not unknown in human societies. Relevant explanatory models include Fisher's principle, the Trivers-Willard model, local mate and resource competition and enhancement, and economic rational actor models. Possible evidence of female-biased parental investment includes sex ratios, mortality rates, parents' stated preferences for offspring of one sex, and direct and indirect measurements of actual parental behavior. Possible examples of female-biased parental investment include the Mukogodo of Kenya, the Ifalukese of Micronesia, the Cheyenne of North America, the Herero of southern Africa, the Kanjar of south Asia, the Mundugumor of New Guinea, contemporary North America, and historical Germany, Portugal, and the United States.

Access to resources shapes maternal decision making: evidence from a factorial vignette experiment

The central assumption of behavioral ecology is that natural selection has shaped individuals with the capacity to make decisions that balance the fitness costs and benefits of behavior. A number of factors shape the fitness costs and benefits of maternal care, but we lack a clear understanding how they, taken together, play a role in the decision-making process. In animal studies, the use of experimental methods has allowed for the tight control of these factors. Standard experimentation is inappropriate in human behavioral ecology, but vignette experiments may solve the problem. I used a confounded factorial vignette experiment to gather 640 third-party judgments about the maternal care decisions of hypothetical women and their children from 40 female karo Batak respondents in rural Indonesia. This allowed me to test hypotheses derived from parental investment theory about the relative importance of five binary factors in shaping maternal care decisions with regard to two distinct scenarios. As predicted, access to resources--measured as the ability of a woman to provide food for her children--led to increased care. A handful of other factors conformed to prediction, but they were inconsistent across scenarios. The results suggest that mothers may use simple heuristics, rather than a full accounting for costs and benefits, to make decisions about maternal care. Vignettes have become a standard tool for studying decision making, but have made only modest inroads to evolutionarily informed studies of human behavior.

Socioeconomic status determines sex-dependent survival of human offspring

In a polygynous African society, rich men have much more life time offspring than women through the marriage of multiple wives. In line with evolutionary predictions, we found that in rich households more newborn sons were registered, sons had lower mortality and higher body weight. Conscious or unconscious, this maximizes reproductive output.

Background and objectives: In polygynous societies, rich men have many offspring through the marriage of multiple wives. Evolutionary, rich households would therefore benefit more from sons, and according to the Trivers–Willard hypothesis, parents invest more in offspring of the sex that has the best reproductive prospects. We determined the sex differences in number of offspring, sex ratio of offspring, offspring survival and offspring weight in rich and poor households in a polygynous population.

Methodology: We studied a population of 28 994 individuals in Northern Ghana during an 8-year prospective follow-up. We determined the fertility rate for both men and women, sex ratio of 3511 newborn offspring and offspring survival in 16 632 offspring up to reproductive age (≤18 years). Also, we collected 9842 weight measurements of 1470 offspring up to the age of 3 years from growth charts of local clinics.

Results: In rich households, men have a lifetime number of 6.0 offspring, while for women this was 3.1. In line with evolutionary predictions, the male:female sex ratio was higher in rich households (0.52; poor households 0.49), sons had lower mortality in rich households (hazard ratio male versus female 1.06, P = 0.64; poor households: hazard ratio male versus female 1.46, P = 0.01) and sons also had higher weights in rich households (P = 0.008).

Conclusions and implications: In rich households, men have higher reproductive prospects in this polygynous society and, in line with Trivers–Willard, we registered more sons in rich households, sons had lower mortality and higher weights, maximizing the reproductive output in this society.

Boy or girl: gender preferences from a Darwinian point of view

This article reviews evolutionary biological studies of sex-biased post-natal parental investment that may be relevant to the issue of preconception gender selection. The focus is on tests of the Trivers-Willard hypothesis, which predicts that natural selection has favoured parents that bias investment in favour of the sex with the best reproductive prospects. Because resource abundance and scarcity often have greater effects on male than on female reproductive success, the Trivers-Willard model predicts that natural selection will most often favour parents who favour males when conditions are good and females when conditions are poor. Empirical tests of this hypothesis are mixed in terms of the appropriateness of their methods and their relevance to the model. Tests with more appropriate measures of such key variables as parental investment tend more often to provide support for the hypothesis. The implications of these findings for the issue of preconception gender selection are briefly discussed.

Preference for sons and sex ratio in two non-western societies

Moroccan Berbers and the Bolivian Aymara are two unrelated peasant groups living in adverse environments with a still rather traditional agriculture. Precarious life conditions may be responsible for the importance given to male labor and hence for the cultural preference conferred on male descent. This preference, expressed in the social valorization of sons to the detriment of daughters, is more emphasized if the socioeconomic status of the family is lower. Interpreted according to the cost/benefit approach of Fisher (1958 Genetical Theory of Natural Selection, New York: Dover) of variations in the sex ratio and to its later developments (Trivers and Willard 1973 Science 179:90-91; Trivers 1985 Social Evolution, Menlo Park: Benjamin/Cummings; Hewlett 1991 J. Anthropol. Res. 47:1-37; Smith 1993 Ethol. Sociobiol. 14:39-44), these cultural characteristics could determine that parents bias the care allocated to their progeny in favor of sons, to the detriment of daughters. This could eventually affect their respective survival and finally modify the offspring tertiary sex ratio. This study compares differences in survival as indicators of parental care according to a child's sex and across three economic strata: poor, medium, and high. The Moroccan data express no other sex differences in survival than an advantage for daughters during the preweaning period in the medium and high strata. Within the same sex and across economic strata, a greater mortality between age 10-20 years is observed for boys of the poorest stratum. The Aymara data do not show sex differences by economic stratum, except for an advantage to daughters between birth and 5 years in the medium group, and no survival differences within the same sex across economic strata. These results suggest either that despite the social valorization of male progeny no differences in parental care according to sex occur, or that their magnitude is not great enough to contrast the survival of sons and daughters.

Food allocation in rural Peruvian households: concepts and behavior regarding children

Intrahousehold food allocation is an important determinant of child health and survival. In this paper I explore the ways in which food is distributed to young children in Ura Ayllu, a farming community located in the southern Peruvian highlands (Province of Sandia, Department of Puno, Peru). Quantitative data on energy intake and growth status are analyzed for two groups of children: toddlers (one through three years) and preschoolers (four through six years). The analyses indicate no gender differences in energy intake or growth among toddlers (one through three years) and preschoolers (four through six years) and that young children do not appear to be deprived of food relative to older household members, especially adults. Relative to standards specific to Andean populations, the mean caloric content of the toddler diet falls slightly below the estimated requirement for the age group while the preschooler diet is found to be calorically adequate. This paper also examines the ideological bases that shape food allocation within households. Regarding the local concepts and cultural rules that guide food allocation to children, Ura Ayllinos view young children as developmentally immature and believe their dietary and health needs are different from those of older children and adults. Infants and young children are considered weak (debil) and vulnerable to illness. Parents state that young children should not feel hunger which is thought to weaken a person and make him more susceptible to the natural and supernatural agents that cause illness. Certain dietary practices, such as on-demand breastfeeding and snacking between meals, suggest that parents try to avoid the experience of hunger and the potential for illness by making food available to their children. This study suggests that young Ura Ayllu children are viewed as having a right to food based on local concepts of child development, personhood, and general health maintenance.

Health care allocation and selective neglect in rural Peru

This study of health care allocation to children in northern Puno, Peru, utilizes quantitative and qualitative data to explore differential resource allocation to children in rural Andean households. As part of a broader ethnographic study of health in two communities, quantitative data on reported health status, symptoms, and treatments (both lay and specialist) were collected for 23 children under the age of 7 over a one year period. Additional data were collected from local health post records. Data were analyzed by gender, and by three age groups (birth to 1 year, 1-3 years, 4-6 years) to determine if differences existed in the allocation of health care. The data suggest a pattern of discrimination against females and younger children, especially infants under age one, despite the fact that these groups were reported to be sicker. Differences were especially significant in the allocation of biomedical treatments, the most costly in terms of parental time, effort, and money. Ethnographic data on child illness, gender, and developmental concepts help to explain why children of different genders and ages may be treated differently in the rural andes. They provide a context in which to interpret health care allocation data, and, in the absence of a population-based study, reinforce findings based on the limited study sample. Female children are valued less because of their future social and economic potential. Females are also regarded to be less vulnerable to illness than male children, meaning that less elaborate measures are necessary to protect their health. Young children are thought to have a loose body-soul connection, making them more vulnerable to illness, and are though to be less human than older individuals. The folk illnesses uraña (fright) and larpa explain child deaths in culturally acceptable ways, and the types of funerals given to children of different ages indicate that the death of young children is not considered unusual. Health care allocation and ethnographic data suggest that selective neglect (passive infanticide) may be occurring in rural Peru, possibly as a means of regulating family size and sex ratio. It is important to go beyond placing blame on individual parents or on culture, however, to address the underlying causes of differential health care allocation, such as poor socioeconomic conditions, lack of access to contraceptives, and female subordination.

Sex ratio at birth deviations in modern Venezuela: the Trivers-Willard effect

This study evaluates the impact of the Trivers-Willard (T-W) effect on human populations, using demographic data collected from vital registration data in Venezuela. The evaluation of the sex ratio at birth (SRB) and of fetal and infant deaths supports the existence of T-W effect in the Venezuelan population in extreme conditions. This T-W effect was observable in the SRB but not at later ages and is related to the marital status of the mother. The results indicate that the investment in females associated with environmental adversity is greater than the investment in males associated with good environmental conditions.