Mary K. Shenk

A model comparison approach shows stronger support for economic models of fertility decline

The demographic transition is an ongoing global phenomenon in which high fertility and mortality rates are replaced by low fertility and mortality. Despite intense interest in the causes of the transition, especially with respect to decreasing fertility rates, the underlying mechanisms motivating it are still subject to much debate. The literature is crowded with competing theories, including causal models that emphasize (i) mortality and extrinsic risk, (ii) the economic costs and benefits of investing in self and children, and (iii) the cultural transmission of low-fertility social norms. Distinguishing between models, however, requires more comprehensive, better-controlled studies than have been published to date. We use detailed demographic data from recent fieldwork to determine which models produce the most robust explanation of the rapid, recent demographic transition in rural Bangladesh. To rigorously compare models, we use an evidence-based statistical approach using model selection techniques derived from likelihood theory. This approach allows us to quantify the relative evidence the data give to alternative models, even when model predictions are not mutually exclusive. Results indicate that fertility, measured as either total fertility or surviving children, is best explained by models emphasizing economic factors and related motivations for parental investment. Our results also suggest important synergies between models, implicating multiple causal pathways in the rapidity and degree of recent demographic transitions.

Production Systems, Inheritance, and Inequality in Premodern Societies

Premodern human societies differ greatly in socioeconomic inequality. Despite much useful theorizing on the causes of these differences, individual‐level quantitative data on wealth inequality is lacking. The papers in this special section provide the first comparable estimates of intergenerational wealth transmission and inequality in premodern societies, with data on more than 40 measures of embodied, material, and relational wealth from 21 premodern societies representing four production systems (hunter‐gatherers, horticulturalists, pastoralists, and agriculturalists). Key findings include (1) the importance of material, embodied, and relational wealth differs significantly across production systems, with material wealth more important in pastoral and agricultural systems; (2) the degree of wealth transmission from parent to offspring is markedly higher for material wealth than embodied and relational wealth; (3) aggregate wealth is transmitted to a higher degree among pastoralists and agriculturalists; (4) the degree of inequality is greater for material wealth; and (5) the degree of intergenerational transmission of wealth is correlated with wealth inequality. Surprisingly, horticulturalists exhibit no greater wealth inequality or intergenerational wealth transmission than do hunter‐gatherers, while pastoralists are very similar to agriculturalists. We discuss how these trends may have favored the emergence of institutionalized inequality, as intensified forms of production made material wealth transmission increasingly important.

Intergenerational Wealth Transmission among Agriculturalists: Foundations of Agrarian Inequality

This paper uses data from eight past and present societies practicing intensive agriculture to measure the transmission of wealth across generations in preindustrial agricultural societies. Focusing on embodied, material, and relational forms of wealth, we compare levels of wealth between parents and children to estimate how effectively wealth is transmitted from one generation to the next and how inequality in one generation impacts inequality in the next generation. We find that material wealth is by far the most important, unequally distributed, and highly transmitted form of wealth in these societies, while embodied and relational forms of wealth show much weaker importance and transmission. We conclude that the unique characteristics of material wealth, and especially wealth in land, are key to the high and persistent levels of inequality seen in societies practicing intensive agriculture. We explore the implications of our findings for the evolution of inequality in the course of human history and suggest that it is the intensification of agriculture and the accompanying transformation of land into a form of heritable wealth that may allow for the social complexity long associated with agricultural societies.

The evolution of inequality

Understanding how systems of political and economic inequality evolved from relatively egalitarian origins has long been a focus of anthropological inquiry. Many hypotheses have been suggested to link socio‐ecological features with the rise and spread of inequality, and empirical tests of these hypotheses in prehistoric and extant societies are increasing. In this review, we synthesize several streams of theory relevant to understanding the evolutionary origins, spread, and adaptive significance of inequality. We argue that while inequality may be produced by a variety of localized processes, its evolution is fundamentally dependent on the economic defensibility and transmissibility of wealth. Furthermore, these properties of wealth could become persistent drivers of inequality only following a shift to a more stable climate in the Holocene. We conclude by noting several key areas for future empirical research, emphasizing the need for more analyses of contemporary shifts toward institutionalized inequality as well as prehistoric cases.

Testing three evolutionary models of the demographic transition: Patterns of fertility and age at marriage in urban South India.

Over the last three decades many authors have addressed the demographic transition from the perspective of evolutionary theory. Some authors have emphasized parental investment factors such as the costs of raising children, others have emphasized the effects of mortality and other forms of risk, and others have emphasized the biased transmission of cultural norms from people of high status. Yet the literature says little about the relative strengths of each of these types of motivations or about which ones are more likely to serve as the primary impetus for large‐scale demographic change. In this paper, I examine how each of these factors has influenced the demographic transition in urban South India during the course of the 20th century using two measures of fertility transition: number of surviving children and age at marriage. I find that investment‐related, risk‐related, and cultural transmission predictors all have significant individual effects on the outcome variables, which persist when they are entered in combination. When the three types of predictors are compared, however, investment‐related models appear to provide more robust explanations for patterns in both fertility and age of marriage. Am. J. Hum. Biol., 2009.

Dowry and Public Policy in Contemporary India The Behavioral Ecology of a "Social Evil"

In modern Indian political discourse the custom of dowry is often represented as the cause of serious social problems, including the neglect of daughters, sex-selective abortion, female infanticide, and the harassment, abuse, and murder of brides. Attempts to deal with these problems through legislative prohibition of dowry, however, have resulted in virtually no diminution of either dowry or violence against women. In contrast, radically different interpretations of dowry can be found in the literatures of structural-functionalist anthropology, economics, and human behavioral ecology which muster wide-ranging forms of qualitative and quantitative evidence to support functional models of dowry as a form of inheritance or investment in daughters and/or their children. This paper argues that a functionalist perspective on dowry could lead to improved dowry policy, and that an approach based in human behavioral ecology (HBE) is uniquely suited to this task. After reviewing the relevant literature on dowry in South Asia, I discuss current dowry legislation and its limitations. I then develop a behavioral ecology model of Indian dowry and test it with quantitative and qualitative data. I conclude that if dowry legislation is to achieve broad support or bring about effective social change, it must address and support the positive motivations for and effects of dowry and take a targeted approach to dowry violence, which is not uniformly distributed across regions, castes, or social classes.

The rebirth of kinship: evolutionary and quantitative approaches in the revitalization of a dying field.

Kinship was one of the key areas of research interest among anthropologists in the nineteenth century, one of the most hotly debated areas of theory in the early and mid-twentieth century, and yet an area of waning interest by the end of the twentieth century. Since then, the study of kinship has experienced a revitalization, with concomitant disputes over how best to proceed. This special issue brings together recent studies of kinship by scientific anthropologists employing evolutionary theory and quantitative methods. We argue that the melding of the evolutionary theoretical perspective with quantitative and ethnographic methodologies has strengthened and reinvigorated the study of kinship by synthesizing and extending existing research via rigorous analyses of evidence.

Does Absence Matter

This paper examines the effects of three different types of father absence on the timing of life history events among women in rural Bangladesh. Age at marriage and age at first birth are compared across women who experienced different father presence/absence conditions as children. Survival analyses show that daughters of fathers who divorced their mothers or deserted their families have consistently younger ages at marriage and first birth than other women. In contrast, daughters whose fathers were labor migrants have consistently older ages at marriage and first birth. Daughters whose fathers died when they were children show older ages at marriage and first birth than women with divorced/deserted fathers and women with fathers present. These effects may be mediated by high socioeconomic status and high levels of parental investment among the children of labor migrants, and a combination of low investment, high psychosocial stress, and low alloparental investment among women with divorced/deserted fathers. Our findings are most consistent with the Child Development Theory model of female life history strategies, though the Paternal Investment and Psychosocial Acceleration models also help explain differences between women in low paternal investment situations (e.g., father divorced/abandoned vs. father dead). Father absence in and of itself seems to have little effect on the life history strategies of Bangladeshi women once key reasons for or correlates of absence are controlled, and none of the models is a good predictor of why women with deceased fathers have delayed life histories compared with women whose fathers are present.

PATERNAL INVESTMENT AND STATUS-RELATED CHILD OUTCOMES: TIMING OF FATHER'S DEATH AFFECTS OFFSPRING SUCCESS

Recent work in human behavioural ecology has suggested that analyses focusing on early childhood may underestimate the importance of paternal investment to child outcomes since such investment may not become crucial until adolescence or beyond. This may be especially important in societies with a heritable component to status, as later investment by fathers may be more strongly related to a childs adult status than early forms of parental investment that affect child survival and child health. In such circumstances, the death or absence of a father may have profoundly negative effects on the adult outcomes of his children that cannot be easily compensated for by the investment of mothers or other relatives. This proposition is tested using a multigenerational dataset from Bangalore, India, containing information on paternal mortality as well as several child outcomes dependent on parental investment during adolescence and young adulthood. The paper examines the effects of paternal death, and the timing of paternal death, on a childs education, adult income, age at marriage and the amount spent on his or her marriage, along with similar characteristics of spouses. Results indicate that a fathers death has a negative impact on child outcomes, and that, in contrast to some findings in the literature on father absence, the effects of paternal death are strongest for children who lose their father in late childhood or adolescence.

Understanding variation in human fertility: what can we learn from evolutionary demography?

Decades of research on human fertility has presented a clear picture of how fertility varies, including its dramatic decline over the last two centuries in most parts of the world. Why fertility varies, both between and within populations, is not nearly so well understood. Fertility is a complex phenomenon, partly physiologically and partly behaviourally determined, thus an interdisciplinary approach is required to understand it. Evolutionary demographers have focused on human fertility since the 1980s. The first wave of evolutionary demographic research made major theoretical and empirical advances, investigating variation in fertility primarily in terms of fitness maximization. Research focused particularly on variation within high-fertility populations and small-scale subsistence societies and also yielded a number of hypotheses for why fitness maximization seems to break down as fertility declines during the demographic transition. A second wave of evolutionary demography research on fertility is now underway, paying much more attention to the cultural and psychological mechanisms underpinning fertility. It is also engaging with the complex, multi-causal nature of fertility variation, and with understanding fertility in complex modern and transitioning societies. Here, we summarize the history of evolutionary demographic work on human fertility, describe the current state of the field, and suggest future directions.