Women's subsistence strategies predict fertility across cultures, but context matters.

While it is commonly assumed that farmers have higher, and foragers lower, fertility compared to populations practicing other forms of subsistence, robust supportive evidence is lacking. We tested whether subsistence activities-incorporating market integration-are associated with fertility in 10,250 women from 27 small-scale societies and found considerable variation in fertility. This variation did not align with group-level subsistence typologies. Societies labeled as "farmers" did not have higher fertility than others, while "foragers" did not have lower fertility. However, at the individual level, we found strong evidence that fertility was positively associated with farming and moderate evidence of a negative relationship between foraging and fertility. Markers of market integration were strongly negatively correlated with fertility. Despite strong cross-cultural evidence, these relationships were not consistent in all populations, highlighting the importance of the socioecological context, which likely influences the diverse mechanisms driving the relationship between fertility and subsistence.

Extensive pedigrees reveal the social organization of a Neolithic community.

Social anthropology and ethnographic studies have described kinship systems and networks of contact and exchange in extant populations1-4. However, for prehistoric societies, these systems can be studied only indirectly from biological and cultural remains. Stable isotope data, sex and age at death can provide insights into the demographic structure of a burial community and identify local versus non-local childhood signatures, archaeogenetic data can reconstruct the biological relationships between individuals, which enables the reconstruction of pedigrees, and combined evidence informs on kinship practices and residence patterns in prehistoric societies. Here we report ancient DNA, strontium isotope and contextual data from more than 100 individuals from the site Gurgy 'les Noisats' (France), dated to the western European Neolithic around 4850-4500 BC. We find that this burial community was genetically connected by two main pedigrees, spanning seven generations, that were patrilocal and patrilineal, with evidence for female exogamy and exchange with genetically close neighbouring groups. The microdemographic structure of individuals linked and unlinked to the pedigrees reveals additional information about the social structure, living conditions and site occupation. The absence of half-siblings and the high number of adult full siblings suggest that there were stable health conditions and a supportive social network, facilitating high fertility and low mortality5. Age-structure differences and strontium isotope results by generation indicate that the site was used for just a few decades, providing new insights into shifting sedentary farming practices during the European Neolithic.

Differences between sons and daughters in the intergenerational transmission of wealth.

Persistent interest lies in gender inequality, especially with regard to the favouring of sons over daughters. Economists are concerned with how privilege is transmitted across generations, and anthropologists have long studied sex-biased inheritance norms. There has, however, been no focused cross-cultural investigation of how parent-offspring correlations in wealth vary by offspring sex. We estimate these correlations for 38 wealth measures, including somatic and relational wealth, from 15 populations ranging from hunter-gatherers to small-scale farmers. Although small sample sizes limit our statistical power, we find no evidence of ubiquitous male bias, at least as inferred from comparing parent-son and parent-daughter correlations. Rather we find wide variation in signatures of sex bias, with evidence of both son and daughter-biased transmission. Further, we introduce a model that helps pinpoint the conditions under which simple mid-point parent-offspring wealth correlations can reveal information about sex-biased parental investment. Our findings are relevant to the study of female-biased kinship by revealing just how little normative descriptors of kinship systems, such as patrilineal inheritance, capture intergenerational correlations in wealth, and how variable parent-son and parent-daughter correlations can be. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.

Greater wealth inequality, less polygyny: rethinking the polygyny threshold model.

Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

Pathways from education to fertility decline: a multi-site comparative study.

Women's education has emerged as a central predictor of fertility decline, but the many ways that education affects fertility have not been subject to detailed comparative investigation. Taking an evolutionary biosocial approach, we use structural equation modelling to examine potential pathways between education and fertility including: infant/child mortality, women's participation in the labour market, husband's education, social network influences, and contraceptive use or knowledge across three very different contexts: Matlab, Bangladesh; San Borja, Bolivia; and rural Poland. Using a comparable set of variables, we show that the pathways by which education affects fertility differ in important ways, yet also show key similarities. For example, we find that across all three contexts, education is associated with delayed age at first birth via increasing women's labour-force participation, but this pathway only influences fertility in rural Poland. In Matlab and San Borja, education is associated with lower local childhood mortality, which influences fertility, but this pathway is not important in rural Poland. Similarities across sites suggest that there are common elements in how education drives demographic transitions cross-culturally, but the differences suggest that local socioecologies also play an important role in the relationship between education and fertility decline.

Fertility decline and the changing dynamics of wealth, status and inequality.

In the course of demographic transitions (DTs), two large-scale trends become apparent: (i) the broadly positive association between wealth, status and fertility tends to reverse, and (ii) wealth inequalities increase and then temporarily decrease. We argue that these two broad patterns are linked, through a diversification of reproductive strategies that subsequently converge as populations consume more, become less self-sufficient and increasingly depend on education as a route to socio-economic status. We examine these links using data from 22 mid-transition communities in rural Poland. We identify changing relationships between fertility and multiple measures of wealth, status and inequality. Wealth and status generally have opposing effects on fertility, but these associations vary by community. Where farming remains a viable livelihood, reproductive strategies typical of both pre- and post-DT populations coexist. Fertility is lower and less variable in communities with lower wealth inequality, and macro-level patterns in inequality are generally reproduced at the community level. Our results provide a detailed insight into the changing dynamics of wealth, status and inequality that accompany DTs at the community level where peoples' social and economic interactions typically take place. We find no evidence to suggest that women with the most educational capital gain wealth advantages from reducing fertility, nor that higher educational capital delays the onset of childbearing in this population. Rather, these patterns reflect changing reproductive preferences during a period of profound economic and social change, with implications for our understanding of reproductive and socio-economic inequalities in transitioning populations.

Social network- and community-level influences on contraceptive use: evidence from rural Poland.

The diffusion of 'modern' contraceptives-as a proxy for the spread of low-fertility norms-has long interested researchers wishing to understand global fertility decline. A fundamental question is how local cultural norms and other people's behaviour influence the probability of contraceptive use, independent of women's socioeconomic and life-history characteristics. However, few studies have combined data at individual, social network and community levels to simultaneously capture multiple levels of influence. Fewer still have tested if the same predictors matter for different contraceptive types. Here, we use new data from 22 high-fertility communities in Poland to compare predictors of the use of (i) any contraceptives-a proxy for the decision to control fertility-with those of (ii) 'artificial' contraceptives-a subset of more culturally taboo methods. We find that the contraceptive behaviour of friends and family is more influential than are women's own characteristics and that community level characteristics additionally influence contraceptive use. Highly educated neighbours accelerate women's contraceptive use overall, but not their artificial method use. Highly religious neighbours slow women's artificial method use, but not their contraceptive use overall. Our results highlight different dimensions of sociocultural influence on contraceptive diffusion and suggest that these may be more influential than are individual characteristics. A comparative multilevel framework is needed to understand these dynamics.