The Trade-Off between Female Fertility and Longevity during the Epidemiological Transition in the Netherlands.

Several hypotheses have been put forward to explain the relationship between women's fertility and their post-reproductive longevity. In this study, we focus on the disposable soma theory, which posits that a negative relationship between women's fertility and longevity can be understood as an evolutionary trade-off between reproduction and survival. We examine the relationship between fertility and longevity during the epidemiological transition in the Netherlands. This period of rapid decline in mortality from infectious diseases offers a good opportunity to study the relationship between fertility and longevity, using registry data from 6,359 women born in The Netherlands between 1850 and 1910. We hypothesize that an initially negative relationship between women's fertility and their longevity gradually turns less negative during the epidemiological transition, because of decreasing costs of higher parities. An initially inversed U-shaped association between fertility and longevity changes to zero during the epidemiological transition. This does suggest a diminishing environmental pressure on fertility. However, we find no evidence of an initial linear trade-off between fertility and post-reproductive survival.

Testing evolutionary theories of discriminative grandparental investment.

This study tests two evolutionary hypotheses on grandparental investments differentiated by the child's sex: the paternity uncertainty hypothesis and the Trivers-Willard hypothesis. Data are from two culturally different countries: the Dutch Longitudinal Aging Study Amsterdam (n=2375) and the Chinese Anhui Survey (n=4026). In the Netherlands, grandparental investments are biased towards daughters' children, which is in accordance with the paternity uncertainty hypothesis. But in China, grandparental investments are biased towards sons' children, which is in conflict with the paternity uncertainty hypothesis. This study found no support for the Trivers-Willard hypothesis. These results raise doubts over the relevance of paternity uncertainty as an explanation of a grandparental investment bias towards daughters' children that is often found in Western populations. The results suggest that discriminative grandparental investments are better understood as the outcome of cultural prescriptions and economic motives.

How Grandparents Matter: Support for the Cooperative Breeding Hypothesis in a Contemporary Dutch Population.

Low birth rates in developed societies reflect women's difficulties in combining work and motherhood. While demographic research has focused on the role of formal childcare in easing this dilemma, evolutionary theory points to the importance of kin. The cooperative breeding hypothesis states that the wider kin group has facilitated women's reproduction during our evolutionary history. This mechanism has been demonstrated in pre-industrial societies, but there is no direct evidence of beneficial effects of kin's support on parents' reproduction in modern societies. Using three-generation longitudinal data anchored in a sample of grandparents aged 55 and over in 1992 in the Netherlands, we show that childcare support from grandparents increases the probability that parents have additional children in the next 8 to 10 years. Grandparental childcare provided to a nephew or niece of childless children did not significantly increase the probability that those children started a family. These results suggest that childcare support by grandparents can enhance their children's reproductive success in modern societies and is an important factor in people's fertility decisions, along with the availability of formal childcare.

Socio-economic status by rapid appraisal is highly correlated with mortality risks in rural Africa.

Socio-economic status is an important determinant of health and survival in rural Africa and necessitates a practical and valid instrument to implement in health studies. Our objective was to investigate the validity of the rapid appraisal method to assess socio-economic status and its ability to identify individuals at risk. Among 1573 households in rural northern Ghana, we calculated the Demographic Health Survey (DHS) wealth index and conducted two rapid appraisal methods: self-reported wealth and interviewer-reported wealth. In addition we followed the 25,184 participants from these households for survival with a mean follow-up of 3.9 years, during which 885 participants died. The DHS wealth index was moderately correlated to self-reported wealth (Spearman's rho 0.59, P<0.001) and interviewer-reported wealth (Spearman's rho 0.75, P<0.001). Mortality risks were significantly higher for people with lower than average self-reported wealth [hazard ratio (HR) 1.30 (95% CI 1.11-1.51)] and lower interviewer-reported wealth [HR 1.40 (95% CI 1.21-1.62)]. Mortality risks were lower for people with higher self-reported wealth [HR 0.81 (95% CI 0.32-2.03)] and higher interviewer-reported wealth [HR 0.84 (95% CI 0.58-1.21)]. Similar discriminative mortality risks were assessed when using tertiles of the DHS wealth index (Ptrend<0.001).