Robert J. Quinlan

Human parental effort and environmental risk

Parental investment decisions depend on multiple factors, including the extent that parental care benefits offspring. Humans should show reduced parental effort in environments where parenting cannot improve offspring survival. Data from the standard cross-cultural sample are used to test this prediction. The results show that maternal care was inversely associated with famine and warfare, and also showed a quadratic association with pathogen stress, increasing as pathogen stress increased to moderate levels, but decreasing at higher levels. Age at weaning showed a similar quadratic relation with pathogens. The curvilinear associations between parental effort and pathogen stress may reflect that the saturation point of parental care is a function of environmental hazards. Paternal involvement was also inversely related to pathogen stress. The association between pathogens and paternal involvement was partially mediated by polygyny. In sum, maternal and paternal care appears to have somewhat different relations with environmental hazards, presumably owing to sex-specific tradeoffs in reproductive effort.

Intergenerational Wealth Transmission and the Dynamics of Inequality in Small-Scale Societies

Origins of Egalitarianism Wealthy contemporary societies exhibit varying extents of economic inequality, with the Nordic countries being relatively egalitarian, whereas there is a much larger gap between top and bottom in the United States. Borgerhoff Mulder et al. (p. 682; see the Perspective by Acemoglu and Robinson) build a bare-bones model describing the intergenerational transmission of three different types of wealth—based on social networks, land and livestock, and physical and cognitive capacity—in four types of small-scale societies in which livelihoods depended primarily on hunting, herding, farming, or horticulture. Parameter estimates from a large-scale analysis of historical and ethnographic data were added to the model to reveal that the four types of societies display distinctive patterns of wealth transmission and that these patterns are associated with different extents of inequality. Some types of wealth are strongly inherited and, hence, contribute to long-term economic inequality. Small-scale human societies range from foraging bands with a strong egalitarian ethos to more economically stratified agrarian and pastoral societies. We explain this variation in inequality using a dynamic model in which a population’s long-run steady-state level of inequality depends on the extent to which its most important forms of wealth are transmitted within families across generations. We estimate the degree of intergenerational transmission of three different types of wealth (material, embodied, and relational), as well as the extent of wealth inequality in 21 historical and contemporary populations. We show that intergenerational transmission of wealth and wealth inequality are substantial among pastoral and small-scale agricultural societies (on a par with or even exceeding the most unequal modern industrial economies) but are limited among horticultural and foraging peoples (equivalent to the most egalitarian of modern industrial populations). Differences in the technology by which a people derive their livelihood and in the institutions and norms making up the economic system jointly contribute to this pattern.

Male-female differences in effects of parental absence on glucocorticoid stress response.

This study examines the family environments and hormone profiles of 316 individuals aged 2 months-58 years residing in a rural village on the east coast of Dominica, a former British colony in the West Indies. Fieldwork was conducted over an eight-year period (1988–1995). Research methods and techniques include radioimmunoassay of cortisol and testosterone from saliva samples (N=22,340), residence histories, behavioral observations of family interactions, extensive ethnographic interview and participant observation, psychological questionnaires, and medical examinations.Analyses of data indicate complex, sex-specific effects of family environment on endocrine function. Male endocrine profiles exhibit greater sensitivity to presence of father than do female endocrine profiles. Father-absent males tend to have (a) low cortisol levels during infancy, (b) high or abnormal cortisol profiles during childhood and adolescence, and (c) high cortisol and low testosterone levels during adulthood compared with those of males raised with a resident father. These results indicate that early family environment has significant effects on endocrine response throughout male life histories.

Parental investment and age at weaning in a Caribbean village

Abstract Predicting the timing of weaning in diverse environments is important because breast-feeding significantly contributes to child survival and overall health, especially in developing countries. This study examines associations between weaning and household demographic variables that test predictions derived from parental investment (PI) theory. Data were collected for 101 children (49 males and 52 females) in a rural community in Dominica. Analyses indicate that father absence is associated with early weaning. This was the only prediction from PI theory that was supported. The following results were contrary to expectations: (1) Availability of female alloparents and household wealth were negatively associated with age at weaning. (2) Number of dependent children in the household was positively associated with age at weaning. (3) Mothers age at birth was not correlated with the timing of weaning. Lastly, (4) interaction terms for childs sex by wealth and sex by maternal social support were not associated with age at weaning, indicating the lack of a Trivers–Willard effect on weaning in this population. We suggest that explanations of weaning from PI theory will benefit from including high opportunity costs of prolonged nursing, demands for reciprocal female labor, and the importance of investment in “embodied capital.”

Human Lactation, Pair-bonds, and Alloparents A Cross-Cultural Analysis

The evolutionary origin of human pair-bonds is uncertain. One hypothesis, supported by data from forgers, suggests that pair-bonds function to provision mothers and dependent offspring during lactation. Similarly, public health data from large-scale industrial societies indicate that single mothers tend to wean their children earlier than do women living with a mate. Here we examine relations between pair-bond stability, alloparenting, and cross-cultural trends in breastfeeding using data from 58 “traditional” societies in the Standard Cross-Cultural Sample (SCCS). Analyses show that stable conjugal relationships were associated with significantly later weaning among the societies in the SCCS. The relationship between pair-bond stability and age at weaning was not mediated by women’s ability to provision themselves or women’s kin support. Availability of alloparental care was also inversely related to age at weaning, and the association was not significantly reduced after controlling for frequency of divorce. This study indicates that among a woman’s kin relationships, a pair-bond with a child’s father is especially supportive of breastfeeding. These cross-cultural findings are further evidence that human pair-bonds may have evolved to support lactation.

Evolutionary ecology of human pair-bonds : Cross-cultural tests of alternative hypotheses

Human pair-bonds may have multiple evolved functions. One long-standing hypothesis suggests that pair-bonds evolved for male provisioning. Alternatively pair-bonds may occur as a response to male mating competition when benefits of staying with a current mate outweigh costs of seeking new mates. A third hypothesis suggests that pair-bonds function to protect against infanticide by aggressive males. Tests of these hypotheses used data from the Standard Cross-Cultural Sample on divorce, alloparenting, polygyny, male contribution to subsistence, and male aggression. Results were not consistent with the infanticide and/or male aggression hypothesis; however, parental investment and male mating competition accounted for significant cross-cultural variance in conjugal stability, suggesting that human pairing has multiple functions. Pair-bonds tended to be stable when men and women contributed equally to subsistence, and unstable when either sex contributed the majority to subsistence. The authors use the ethnographic record to explore relations among pair-bonds, mating competition, showing off, and conjugal complementarity.

Domestication Alone Does Not Lead to Inequality: Intergenerational Wealth Transmission among Horticulturalists

We present empirical measures of wealth inequality and its intergenerational transmission among four horticulturalist populations. Wealth is construed broadly as embodied somatic and neural capital, including body size, fertility and cultural knowledge, material capital such as land and household wealth, and relational capital in the form of coalitional support and field labor. Wealth inequality is moderate for most forms of wealth, and intergenerational wealth transmission is low for material resources and moderate for embodied and relational wealth. Our analysis suggests that domestication alone does not transform social structure; rather, the presence of scarce, defensible resources may be required before inequality and wealth transmission patterns resemble the familiar pattern in more complex societies. Land ownership based on usufruct and low‐intensity cultivation, especially in the context of other economic activities such as hunting and fishing, is associated with more egalitarian wealth distributions as found among hunter‐gatherers.

Local Resource Enhancement and Sex-biased Breastfeeding in a Caribbean Community

Quinlan, Robert J., Marsha B. Quinlan, and Mark V. Flinn. (2005) Local Resource Enhancement and Sex-biased Breastfeeding in a Caribbean Community. Current Anthropology, 46(3):471-480.

Growth and Fluctuating Asymmetry of Stepchildren

Abstract Parental caretaking is critical for child health and psychological development. Evolutionary logic and empirical studies suggest that stepchildren sometimes may receive less care and experience more traumas than genetic offspring. In this article, we investigate the effects of stepfamily environment on childrens physical growth as part of a 12-year (1988–1999) project investigating child health in a rural village on the east coast of Dominica. Participants were 238 children aged 0–20 (X = 10.53) residing in the village of Bwa Mawego. Information on family environments was collected continuously since 1988. Here we analyze data from a longitudinal series of anthropometric measures collected in 1997, 1998, and 1999. To assess general growth, we measured height, weight, head circumference, triceps skinfold, subscapular skinfold, and peri-umbilical skinfold. We also collected medical records of weight from birth through 3 years of age. To assess fluctuating asymmetry (FA), we measured bilateral (right and left side) arm circumference, calf circumference, wrist breadth, ankle breadth, ear breadth, ear height, and length of digits 2–5. Coresidence with stepfather was associated with suboptimal growth. Female stepchildren aged 0–10 and male stepchildren aged 10–20 had lower body weight for age than other children, including their coresident half-siblings. Stepchildren and nonstepchildren had similar weights at birth, and similar muscle and fat cross-sections. Contrary to expectations, FA of stepchildren was lower than in other children. Recognition of the high risk of poor growth for stepchildren is important because of subsequent associations with morbidity, psychological problems, and educational performance. Why stepchildren had significantly lower FA than others warrants further investigation.

Kinship, family, and gender effects in the ultimatum game

Kinship and reciprocity are two main predictors of altruism. The ultimatum game has been used to study altruism in many small-scale societies. We used the ultimatum game to examine effects of individuals’ family and kin relations on altruistic behavior in a kin-based horticultural community in rural Dominica. Results show sex-specific effects of kin on ultimatum game play. Average coefficient of relatedness to the village was negatively associated with women’s ultimatum game proposals and had little effect on men’s proposals. Number of brothers in the village was positively associated with men’s ultimatum game proposals and negatively associated with women’s proposals. Similarly, presence of father in the village was associated with higher proposals by men and lower proposals by women. We interpret the effect of brothers on men’s proposals as a consequence of local competition among brothers. We speculate that daughter-biased parental care in this community creates a sense of entitlement among women with brothers, which may explain the inverse relation between number of brothers and women’s ultimatum game proposals. The pattern of results may be consistent with how matrifocality affects cultural models of fairness differently along gender and family lines.