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The Influence of Health in Early Adulthood on Male Fertility


Despite the large literature examining predictors of fertility, previous research has not offered a population-level perspective on how health in early adulthood is related to male fertility. Using Swedish population and military conscription registers, we study how body mass index (BMI), physical fitness, and height are associated with total fertility and parity transitions by 2012 among 405,427 Swedish men born 1965-1972, meaning we observe fertility up to age 40 or older. Applying linear regression and sibling fixed effects, we find that these anthropometric measures are strong predictors of fertility, even after accounting for education and cumulative income. Men with a normal BMI and in the highest decile of physical fitness have the most children. Men who were obese at ages 17-20 had a relative probability of childlessness almost twice as high as men who had a normal BMI, and men in the bottom decile of physical fitness had a relatively probability of childlessness more than 50 percent higher than men in the top decile. In sibling comparison models the tallest men have the most children and men in the lowest two deciles of height have significantly lower fertility. Further analyses show that the strong associations persist even among men who married.

Segregation within school classes : Detecting social clustering in choice data


We suggest a new method for detecting patterns of social clustering based on choice data. The method compares similar subjects within and between cohorts and thereby allows us to isolate the effect of peer influence from that of exogenous factors. Using this method on Norwegian register data, we address the question of whether students tend to cluster socially based on similar background. We find that common background correlates with making the same choices of curricular tracks, and that both exogenous preferences and peer influence matter. This applies to immigrant students from the same country, and, to some extent, to descendants of immigrants, but not to students from culturally similar countries. There are also small effects related to parents' education and income.

Two Decades of Same-Sex Marriage in Sweden : A Demographic Account of Developments in Marriage, Childbearing, and Divorce


In this study, we provide demographic insight into the still relatively new family form of same-sex marriage. We focus on period trends in same-sex marriage formation and divorce during 1995-2012 in Sweden and the role of childbearing in same-sex unions. The period begins with the introduction of registered partnership for same-sex couples and also covers the introduction of formal same-sex marriage in 2009. We use register data for the complete population of Sweden to contrast patterns in male and female same-sex marriage formation and divorce. We show that female same-sex union formation increased rapidly over the period, while trends for male same-sex unions increased less. The introduction of same-sex marriage legislation in 2009 appears to have had little effect on the pace of formation of same-sex unions. In contrast, legal changes supporting parental rights in same-sex unions may have fueled the formation of female same-sex marriages as well as parenthood in such unions. Further, we show that divorce risks in the marital unions of two women are much higher than in other types of marriages. We find some convergence of divorce risks across union types at the end of our study period: male same-sex unions have the same divorce risk levels as opposite-sex marriages, and the elevated risks of divorce in female same-sex unions appear to have stabilized at somewhat lower levels than those observed in the late 1990s.

A systems approach to cultural evolution


A widely accepted view in the cultural evolutionary literature is that culture forms a dynamic system of elements (or 'traits') linked together by a variety of relationships. Despite this, large families of models within the cultural evolutionary literature tend to represent only a small number of traits, or traits without interrelationships. As such, these models may be unable to capture complex dynamics resulting from multiple interrelated traits. Here we put forward a systems approach to cultural evolutionary research-one that explicitly represents numerous cultural traits and their relationships to one another. Basing our discussion on simple graph-based models, we examine the implications of the systems approach in four domains: (i) the cultural evolution of decision rules ('filters') and their influence on the distribution of cultural traits in a population; (ii) the contingency and stochasticity of system trajectories through a structured state space; (iii) how trait interrelationships can modulate rates of cultural change; and (iv) how trait interrelationships can contribute to understandings of inter-group differences in realised traits. We suggest that the preliminary results presented here should inspire greater attention to the role of multiple interrelated traits on cultural evolution, and should motivate attempts to formalise the rich body of analyses and hypotheses within the humanities and social science literatures.

Generosity Pays : Selfish People Have Fewer Children and Earn Less Money


Does selfishness pay in the long term? Previous research has indicated that being prosocial (or otherish) rather than selfish has positive consequences for psychological well-being, physical health, and relationships. Here we instead examine the consequences for individuals' incomes and number of children, as these are the currencies that matter most in theories that emphasize the power of self-interest, namely economics and evolutionary thinking. Drawing on both cross-sectional (Studies 1 and 2) and panel data (Studies 3 and 4), we find that prosocial individuals tend to have more children and higher income than selfish individuals. An additional survey (Study 5) of lay beliefs about how self-interest impacts income and fertility suggests one reason selfish people may persist in their behavior even though it leads to poorer outcomes: people generally expect selfish individuals to have higher incomes. Our findings have implications for lay decisions about the allocation of scarce resources, as well as for economic and evolutionary theories of human behavior.

On revolutions


Sometimes the normal course of events is disrupted by a particularly swift and profound change. Historians have often referred to such changes as revolutions, and, though they have identified many of them, they have rarely supported their claims with statistical evidence. Here, we present a method to identify revolutions based on a measure of multivariate rate of change called Foote novelty. We define revolutions as those periods of time when the value of this measure is, by a non-parametric test, shown to significantly exceed the background rate. Our method also identifies conservative periods when the rate of change is unusually low. We apply it to several quantitative data sets that capture long-term political, social and cultural changes and, in some of them, identify revolutions - both well known and not. Our method is general and can be applied to any phenomenon captured by multivariate time series data of sufficient quality.

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