Human life courses are embedded within family networks. Although family structures and kin availability vary to a large extent around the globe and have changed considerably over the last centuries, in all human societies family members cooperate in raising children, and economic and productive activities are often organized in family networks. The consequences of the primary social constitution of humans has been in the focus of the social sciences for a long time. Family and life course sociology as well as demography, investigating historical as well as contemporary populations, have produced a broad spectrum of knowledge and theoretical frameworks. For future research in this field, evolutionary anthropology has at least two promising theoretical offers to make which could be fruitfully integrated into the social sciences. Independently from life course sociology, evolutionary anthropology has investigated human life courses in the framework of life history theory (LHT). The concepts are surprisingly similar and the integration of the two approaches is in progress. Another framework that evolutionary sciences have to offer has become known as cooperative breeding hypothesis (CBH) in the literature. Both evolutionary frameworks enable the investigation on how environmental factors such as mortality risk affect the life course and kin relationships in humans. Further, this interdisciplinary approach is crucial for the study of contemporary demographic developments, since these are the aggregation of individual life courses affected by kin networks.
In the planned research project, in collaboration with colleagues from Canada, The Netherlands, and Sweden, I will investigate the functioning of family networks by estimating their effect on adult mortality and fertility using five different historical populations from Europe and North America. The main aim hereby is to assess to what extent these effects may derive from evolved behavioral tendencies (or anthropological inclinations) and to what extent these are due to the socio- and economic-structural contexts. Including both the evolutionary and social science perspectives is essential because evolved anthropological inclinations might be hidden, moderated, and/or compensated by the population-specific context.
Costs and benefits of trade-off decisions might be associated with differential mortality and fertility patterns. For instance, reproduction in families who can provide less support because of increased spatial distance might be associated with lower fertility and higher maternal mortality than in families where support can be given in daily life. Such consequences of kin network compositions can be investigated with the demographic state of the art methodology which can take timing and spatial effects comprehensively into account. The project will therefore focus on family network influences on mortality and fertility of men and women. Women are vulnerable shortly after delivery and therefore kin support (or competition between kin) should have a significant impact on their health and therefore on their survival. Although the fertility consequences of CB have been investigated, we know little about whether kinship affect mortality of mothers in a similar fashion as it has been reported for fertility. Further, the effect of kinship during the reproductive period might be relevant for the trade-off between current and future survival. Survival at advanced ages may be affected beneficially, if reproduction effort was reduced by significant assistance of kin. It is therefore essential to strengthen the investigation of the effects of kin on the mortality of reproductive females based on different environmental contexts to assess the extent to which these effects are generalizable. Furthermore, to date, very little is known about whether kin networks affect male mortality. Therefore, fertility and mortality should be studied comprehensively, using a comparative perspective between populations and the sexes. Some earlier studies suggest that the presence of mothers-in-law promotes fertility through shorter interbirth intervals (also known as kin priming), but increased reproduction cannot solely explain increased maternal mortality among their daughters-in-law, indicating that other mechanisms, such as a genetic in-law-conflict, are relevant, too. Finally, we will evaluate to what extent the different interpretations are compatible, to what extent they contradict each other, and to what extent a fruitful synthesis is possible.