Effects of remarriage after widowhood on long-term fitness in a monogamous historical human population

Parental Investment by Birth Fathers and Stepfathers : Roles of Mating Effort and Childhood Co-residence Duration

This study investigates the determinants of paternal investment by birth fathers and stepfathers. Inclusive fitness theory predicts higher parental investment in birth children than stepchildren, and this has consistently been found in previous studies. Here we investigate whether paternal investment varies with childhood co-residence duration and differs between stepfathers and divorced birth fathers by comparing the investment of (1) stepfathers, (2) birth fathers who are separated from the child's mother, and (3) birth fathers who still are in a relationship with her. Path analysis was conducted using cross-sectional data from adolescents and younger adults (aged 17-19, 27-29, and 37-39 years) from the German Family Panel (pairfam), collected in 2010-2011 (n = 8326). As proxies of paternal investment, we used financial and practical help, emotional support, intimacy, and emotional closeness, as reported by the children. We found that birth fathers who were still in a relationship with the mother invested the most, and stepfathers invested the least. Furthermore, the investment of both separated fathers and stepfathers increased with the duration of co-residence with the child. However, in the case of financial help and intimacy, the effect of childhood co-residence duration was stronger in stepfathers than in separated fathers. Our findings support inclusive fitness theory and mating effort theory in explaining social behavior and family dynamics in this population. Furthermore, social environment, such as childhood co-residence was associated with paternal investment.

Religion and fertility patterns: comparison of life history traits in Catholics and Protestants, Hallstatt (Austria) 1733-1908

Catholicism and Protestantism have different ways of promoting the family unit that could influence survival and fertility at a population level. Parish records in the Austrian village of Hallstatt allowed the reconstruction of Catholic and Protestant genealogies over a period of 175 years (1733-1908) to evaluate how religion and social changes affected reproduction and survival. Life history traits such as lifespan beyond 15 years, number of offspring, reproductive span, children born out of wedlock and child mortality were estimated in 5678 Catholic and 3282 Protestant individuals. The interaction of sex, time and religion was checked through non-parametric factorial ANOVAs. Religion and time showed statistically significant interactions with lifespan >15 years, number of offspring and age at birth of first child. Protestants lived longer, had a larger reproductive span and an earlier age at birth of first child. Before the famine crisis of 1845-1850, Protestants showed lower values of childhood mortality than Catholics. Comparison of the number of children born out of wedlock revealed small differences between the two religions. Religion influenced reproduction and survival, as significant differences were found between Catholics and Protestants. This influence could be explained in part by differential socioeconomic characteristics, since Protestants may have enjoyed better living and sanitary conditions in Hallstatt.

What do men want? Re-examining whether men benefit from higher fertility than is optimal for women

Several empirical observations suggest that when women have more autonomy over their reproductive decisions, fertility is lower. Some evolutionary theorists have interpreted this as evidence for sexual conflicts of interest, arguing that higher fertility is more adaptive for men than women. We suggest the assumptions underlying these arguments are problematic: assuming that women suffer higher costs of reproduction than men neglects the (different) costs of reproduction for men; the assumption that men can repartner is often false. We use simple models to illustrate that (i) menorwomen can prefer longer interbirth intervals (IBIs), (ii) if men can only partner with wives sequentially they may favour shorter IBIs than women, but such a strategy would only be optimal for a few men who can repartner. This suggests that an evolved universal male preference for higher fertility than women prefer is implausible and is unlikely to fully account for the empirical data. This further implies that if women have more reproductive autonomy, populations should grow, not decline. More precise theoretical explanations with clearly stated assumptions, and data that better address both ultimate fitness consequences and proximate psychological motivations, are needed to understand under which conditions sexual conflict over reproductive timing should arise.

Genomic signatures of sex-biased demography: progress and prospects

Sex-biased demographic events have played a crucial role in shaping human history. Many of these processes affect genetic variation and can therefore leave detectable signatures in the genome because autosomal, X-linked, Y-linked, and mitochondrial DNA inheritance differ between sexes. Here, we discuss how sex-biased processes shape patterns of genetic diversity across the genome, review recent genomic evidence for sex-biased demography in modern human populations, and suggest directions for future research.

SIBLING CONFLICTS IN FULL- AND HALF-SIBLING HOUSEHOLDS IN THE UK

Sibling relations are by nature ambivalent with high levels of both altruistic helping and competition. Higher relatedness is often assumed to reduce the occurrence of conflicts between siblings, but evidence of this has been scarce and mixed. Siblings typically compete over resources and parental attention, and parental constellations vary with sibship types. Since full-siblings compete over the same two biological parents, while half-siblings have only one shared biological parent and often a higher number of parents overall, it is hypothesized that conflicts are more common between full- than half-siblings. This study tested this assumption using the British Millennium Cohort Study (n=7527 children at age 11). Conflicts were measured as children's reports of how much siblings picked on and hurt each other. Households with full-siblings only, maternal half-siblings only, and both full- and maternal half-siblings were compared. The results show that children who were living with only their full-siblings were more likely to experience sibling conflicts compared with children living with their maternal half-siblings only. This was the case also after controlling for several potentially confounding variables. The results suggest that differential access to parental resources of available biological and step-parents may explain the higher amount of sibling conflict between full- compared with maternal half-siblings.