People - Ruth Mace, David Lawson

Fertility in modern (post demographic transition) societies, such as the UK, is at its lowest level in recorded human history, and consequently children are now being raised with few or no siblings on a scale never before witnessed in our species. Most of the world is now moving in this direction, with even rural Africa now, finally, entering fertility decline. At the population level, modern societies are characterised by negative or null relationships between wealth and fertility, further suggesting that resources are not effectively channelled into reproduction.

Modelling the Trade-off between Offspring Quantity and Quality

In societies where wealth is needed to raise children, optimising wealth inheritance is one major reason why having a small family could lead to greater long-term fitness. Mace (1998) used stochastic dynamic models to identify the how wealth inheritance and fertility strategies co-evolve to maximise number of grandchildren under different ecological conditions. The model showed that when parental investment in each child has to be high (for example when the costs of marriage and setting up home are high) then smaller families have higher fitness over the long term, and, furthermore, the population average wealth is actually higher, possibly explaining the lack of correlation between wealth and reproductive success observed in large, heterogeneous populations.

Sibling Competition in Contemporary British Families

Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC) we are currently exploring the role of family size and configuration in determining a broad range of child development outcomes in a sample of over 11,000 British families tracked over a 10 year period. From a life history perspective, all else being equal, children with more siblings will suffer negative consequences necessitated by lower levels of parental investment per offspring. This project aims to explore identifiable costs of sibling competition which may be lead parents to evaluate low fertility as the best reproductive strategy. Furthermore, we are exploring how sibling competition effects may vary across the population due to factors such as parental social support or socioeconomic status.

Contraception Uptake in the Gambia

One explanation for low fertility is that the cultural diffusion of new strategies is leading to a maladaptive behaviour. We are testing various hypotheses relating to cultural transmission using long term data on contraceptive uptake in rural Gambia.

Publications:

Mace,R., Allal N., Sear,R., Prentice,A. (2006). The uptake of modern contraception in a Gambian community: the diffusion of an innovation over 25 years. in Wells,J.C.K., Strickland,S.S., Laland,K. (ed.) Social Information Transmission and Human Biology. Florida: Taylor and Francis, 191-205. ISBN: 0-8493-4047-0

Mace,R. (2002). Demographic Transition. in Pagel,M. (ed.) Encyclopedia of Evolution. New York: Open University Press, 235-238. ISBN: 0-19-512200-3

Mace,R. (2000). An adaptive model of human reproductive rate where wealth is inherited: why people have small families. in Cronk,L., Chagnon,N., Irons,W. (ed.) Adaptation and human behaviour. NY: Aldine de Gruyter, 261-282. ISBN: 0 202 02043 6

Mace R. (1998) The co-evolution of human fertility and wealth inheritance strategies. Philosophical Transactions of the Royal Society of London: Biological Sciences 353:389-397

Gurmu E. & R. Mace (in press) Fertility decline as a response to poverty: the case of Addis Ababa (Ethiopia)

Mace R (in press) The evolutionary ecology of human family size. In Dunbar & Barrett (eds) Oxford Handbook of Evolutionary Psychology. OUP.