Thursday 11 September 2003, 4pm, Quiet Room
Evolution, direct childcare constraints and fertility
David Waynforth and Schuyler Waynforth, University of Durham
Evolutionary theorists have struggled to make sense of the fertility reduction that accompanies the demographic transition. This fertility reduction appears to be evolutionarily maladaptive, especially since wealthy individuals in industrialised economies could almost certainly have many more children than they do without substantially compromising their children's survival to adulthood.
Attempts at reconciliation with evolutionary theory have largely focused on wealth, and how resources and modern economies may reduce the optimal number of children to produce, or how we could have evolved in ways that would not yield the optimum under highly novel industrialised contexts.
In this talk, arguments based on evolutionary life-history theory are applied to the comparatively ignored topic of direct, non-economic forms of parental care and fertility. We address the idea that direct parental care constraints affect women's fertility decisions in industrialised nations, and may play a role in demographic transition. Data are presented showing that when women leave their kin-support networks their attitudes towards birth control and views on abortion are rapidly adjusted to avoid childbearing. The results are consistent with the proposed idea of evolved mechanisms matching reproduction to available direct childcare.
Department of Psychology
University of Durham
Queen's Campus
Stockton
Thornaby
Stockton-on-Tees TS17 6BH
Tel: +44 (0)191 334 0118
Email: David.waynforth@durham.ac.uk
Family connections and demand for children
Lesley Newson, University of Exeter
If human reproductive behaviour is a product of evolution, how can the demographic transition have occurred? The answer may lie in the change that occurred in the composition of social networks.
Like many social primates, humans enhance their inclusive fitness by contributing to the reproductive success of their kin - providing practical help and social support. In humans, social support might include encouraging behaviour likely to lead to reproductive success.
In traditional human societies and the social groups in which humans evolved, contact between kin made up a high proportion of the social contact that group members experienced. This could have resulted in the development of social norms that encouraged large families. Improved transportation and communication allowed humans to leave their kinship network and have increased contact with non-relatives who have no interest in promoting their reproductive success. This change in social networks appears to coincide with the change in fertility norms.
An analysis of the 1995 British Social Attitudes Survey, which included a questionnaire assessing the strength of participants' social network, revealed positive correlation between strength of kinship ties and fertility. Participants with stronger kinship ties were also more likely to have a partner and children at a younger age. The same questions about kinship ties administered in 2001-02 to a group of 100 women (aged 18-37) expecting their first child revealed stronger kinship ties to be linked to beginning childbearing at a younger age.
Lesley Newson
School of Psychology
University of Exeter
Exeter EX4 4QG
Email: l.newson@exeter.ac.uk
Kin and child survival in a matrilineal population in Malawi
Rebecca Sear, London School of Economics
Raising children is a cooperative effort in human societies. Evidence is accumulating across diverse cultures that mothers are not solely responsible for bringing up children but receive help from other family members. But which family members are most important seems to differ between populations.
Evolutionary approaches to demography involve explaining variation in demographic patterns in their ecological and social context. A topic of interest is therefore how and why help from relatives varies by social and ecological conditions.
I have previously investigated the effects of kin on reproductive success in a patrilineal, agricultural society in the Gambia. This study demonstrated that child survival rates and nutritional status were higher in the presence of maternal grandmothers. Other relatives, including fathers and paternal grandmothers, had no effect on child outcomes. Here, I present an analysis investigating the effects of kin on child survival in a matrilineal, agricultural population in Malawi, in order to determine whether patterns of helping by relatives differ across societies with different inheritance systems.
Department of Social Policy
London School of Economics
Houghton St
London WC2A 2AE
Tel: +44 (0)20 7955 7348
Email: r.sear@lse.ac.uk