Evolutionary theory predicts that social status and fertility will be positively related. It also predicts that the relationship between status and fertility will differ for men and women. This is particularly likely in modern societies given evidence that females face greater trade-offs between status and resource acquisition and fertility than males. This paper tests these hypotheses using newly released data from the 2014 wave of the Survey of Income and Program Participation by the US Census, which has the first complete (...) measures of fertility and number of childbearing partners for a large, representative, national probability sample of men and women and also contains comprehensive measures of economic status as measured by personal and family resources, including income from all sources and all assets. Multivariate analyses show that personal income is positively associated with total fertility and number of childbearing unions for men only. For men, personal net worth is positively associated with number of childbearing unions; it is also positively associated with fertility for married men with a spouse present. These findings support evolutionary predictions of a positive relationship between status, access to mates, and reproductive success for males. Whereas personal income and personal net worth are negatively associated with total fertility and number of childbearing unions for women, family income is positively associated with total fertility for women. For married men living with a spouse, family income is negatively associated with total fertility. These findings are consistent with evolutionary theory given the existence of greater trade-offs between production and reproduction for women in an advanced industrial society. For women and men, family net worth is negatively associated with number of childbearing unions and fertility. Implications are discussed. (shrink)

Globally, mortality and fertility rates generally fall as resource abundance increases. This pattern represents an evolutionary paradox insofar as resource-rich ecological contexts can support higher numbers of offspring, a component of biological fitness. This paradox has not been resolved, in part because the relationships between fertility, life history strategies, reproductive behavior, and socioeconomic conditions are complex and cultural-historically contingent. We aim to understand how we might make sense of this paradox in the specific context of late-twentieth-century, mid–demographic transition Chile. We (...) use distribution-specific generalized linear models to analyze associations between fertility-related life-history traits—number of offspring, ages at first and last reproduction, average interbirth interval, and average number of live births per reproductive span year—and socioeconomic position (SEP) using data from a cohort of 6,802 Chilean women born between 1961 and 1970. We show that Chilean women of higher SEP have shorter average interbirth intervals, more births per reproductive span year, later age at first reproduction, earlier ages at last reproduction, and, ultimately, fewer children than women of lower SEP. Chilean women of higher SEP consolidate childbearing over a relatively short time span in the middle of their reproductive careers, whereas women of lower SEP tend to reproduce over the entirety of their reproductive lifespans. These patterns may indicate that different SEP groups follow different pathways toward declining fertility during the demographic transition, reflecting different life-history trade-offs in the process. (shrink)

Evolutionary anthropology has traditionally focused on the study of small-scale, largely self-sufficient societies. The increasing rarity of these societies underscores the importance of such research yet also suggests the need to understand the processes by which such societies are being lost—what we call “modernization”—and the effects of these processes on human behavior and biology. In this article, we discuss recent efforts by evolutionary anthropologists to incorporate modernization into their research and the challenges and rewards that follow. Advantages include that these (...) studies allow for explicit testing of hypotheses that explore how behavior and biology change in conjunction with changes in social, economic, and ecological factors. In addition, modernization often provides a source of “natural experiments” since it may proceed in a piecemeal fashion through a population. Challenges arise, however, in association with reduced variability in fitness proxies such as fertility, and with the increasing use of relatively novel methodologies in evolutionary anthropology, such as the analysis of secondary data. Confronting these challenges will require careful consideration but will lead to an improved understanding of humanity. We conclude that the study of modernization offers the prospect of developing a richer evolutionary anthropology, by encompassing ultimate and proximate explanations for behavior expressed across the full range of human societies. (shrink)