Theories of kin selection and parental investment predict stronger investment in children and grandchildren by women and maternal kin. Due to paternity uncertainty, parental and grandparental investments along paternal lineages are based on less certain genetic relatedness with the children and grandchildren. Additionally, the hypothesis of preferential investment (Laham, Gonsalkorale, and von Hippel, 2005) predicts investment to vary according to available investment options. Two previous studies have tested this hypothesis with small samples and conflicting results. Using the second wave of the large and multinational Survey of Health, Ageing and Retirement in Europe (SHARE), collected in 2006-07, we study the preferential investment hypothesis in contemporary Europe based on self-reported grandparental provision of child care. We predict that 1) maternal grandmothers provide most care for their grandchildren, followed by maternal grandfathers, paternal grandmothers and last by paternal grandfathers; 2) maternal grandfathers and paternal grandmothers provide equal amounts of care when the latter do not have grandchildren via a daughter; 3) women who have grandchildren via both a daughter and a son will look after the children of the daughter more; and 4) men who have grandchildren via both a daughter and a son will look after the children of the daughter more. Results support all four hypotheses and provide evidence for the continuing effects of paternity uncertainty in contemporary kin behavior.

Whether and how human populations exposed to the agricultural revolution are still affected by Darwinian selection remains controversial among social scientists, biologists, and the general public. Although methods of studying selection in natural populations are well established, our understanding of selection in humans has been limited by the availability of suitable datasets. Here, we present a study comparing the maximum strengths of natural and sexual selection in humans that includes the effects of sex and wealth on different episodes of selection. Our dataset was compiled from church records of preindustrial Finnish populations characterized by socially imposed monogamy, and it contains a complete distribution of survival, mating, and reproductive success for 5,923 individuals born 1760-1849. Individual differences in early survival and fertility (natural selection) were responsible for most variation in fitness, even among wealthier individuals. Variance in mating success explained most of the higher variance in reproductive success in males compared with females, but mating success also influenced reproductive success in females, allowing for sexual selection to operate in both sexes. The detected opportunity for selection is in line with measurements for other species but higher than most previous reports for human samples. This disparity results from biological, demographic, economic, and social differences across populations as well as from failures by most previous studies to account for variation in fitness introduced by nonreproductive individuals. Our results emphasize that the demographic, cultural, and technological changes of the last 10,000 y did not preclude the potential for natural and sexual selection in our species.Bateman gradient | Bateman principles | selection differential | human evolution | mating system D isagreement about the strength of selection affecting humans has influenced how the theory of natural and sexual selection has been perceived since Darwin (1). In particular, humans exhibit a pronounced ecological flexibility through social and cultural adaptations (2) that is often invoked to cast doubt on the continued relevance of Darwinian selection in our species. Even among those applying evolutionary theory in humans, some scientists consider recent selective pressures weak and therefore only study human adaptations in the demographic, social, and physical environments of the Pleistocene, whereas others view selection as an effective force also operating in societies affected by the agricultural revolution (3).Darwinian selection results from variation in fitness between individuals of the same population and the evolutionary response of traits to this selection depends on the genetic covariation between traits and fitness. Such evolutionary change is traditionally approximated by multiplying heritability (the proportion of phenotypic variance in the trait attributable to genetic differences among individuals) and phenotypic selection (the covariance between the trait and ...

The ability to create lasting, trust-based friendships makes it possible for humans to form large and coherent groups. The recent literature on the evolution of sociality and on the network dynamics of human societies suggests that large human groups have a layered structure generated by emotionally supported social relationships. There are also gender differences in adult social style which may involve different trade-offs between the quantity and quality of friendships. Although many have suggested that females tend to focus on intimate relations with a few other females, while males build larger, more hierarchical coalitions, the existence of such gender differences is disputed and data from adults is scarce. Here, we present cross-cultural evidence for gender differences in the preference for close friendships. We use a sample of ∼112,000 profile pictures from nine world regions posted on a popular social networking site to show that, in self-selected displays of social relationships, women favour dyadic relations, whereas men favour larger, all-male cliques. These apparently different solutions to quality-quantity trade-offs suggest a universal and fundamental difference in the function of close friendships for the two sexes.

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in Future Fertility in Low Fertility Countries AbstractThis paper discusses results of the global survey of experts on the future of low fertility in low-fertility countries. The survey was coordinated by the Wittgenstein Centre for Demography and Global Human Capital as a part of an effort to produce global argumentbased population projections by age, sex and level of education. First we give an overview of fertility changes in major low-fertility regions. Next we outline main theoretical arguments and review a wide range of factors contributing to fertility change and variation in contemporary low-fertility settings. Subsequently, we present survey results based on 184 assessments of over 170 experts analysing 41 countries with currently low or aroundreplacement fertility and Israel. These experts provided forecasts of period total fertility rate (TFR) in 2030 and 2050, estimated 80% confidence interval of their forecast and assessed the validity and potential impact on fertility of 46 factors. We also compare expert-derived projections of the TFR trends with the forecasts formulated by the UN World Population Prospects in 2010. The survey results in combination with the feedback provided by the invited experts then serve as a basis for formulating a set of projection scenarios for all low fertility countries up until 2050, which are additionally expanded (in a simpler form) through 2200. We present these scenarios and discuss past changes in fertility differences by level of education and their potential future trends in main regions. Presented analyses and projections indicate that a global convergence of fertility to around replacement level, envisioned in the UN projections, appears unlikely. Continuing differentiation combined with partial convergence in fertility towards lower levels is suggested as a more plausible scenario, with East Asia (including China) as well as Russia expected to have sustained very low fertility below 1.5 through 2050.

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