Living ‘fast’ and dying young in Africa: Reproductive strategies when infection risk varies

Infection risk interview. Image credit Lucie Clech. Part of the Living Fast Dying Young research project

Conducting the infection risk interviewLucie Clech

3 February 2016

In this research project, funded by Cabot Institute Innovation Funds, researchers have been looking at how human infection risk – and perception of that risk – influences human reproductive behaviour.

Evolutionary life-history theory predicts that under conditions of high mortality, evolutionary fitness is maximised by accelerated reproductive behaviour (e.g. earlier age at first reproduction, short birth-spacing, reduced parental investment per offspring). This prediction is empirically supported in animals; cross-cultural studies in humans are consistent too. However, the extent to which human reproductive strategies respond to individual variation in infectious disease risk – a key driver of human evolution – and how such responses are influenced by perceptions, attitudes and social norms regulating reproduction has not been addressed.

During a pilot study in Spring 2015 we used of combination of methods from anthropology, psychology, demography, and infection biology in the context of West African communities where infection with malaria and parasitic worms is common. We studied individuals’ reproductive behaviour, attitudes to reproduction and to risk, and test how this is affected by their infections, as well as their perceived risk of infection. The aim was to provide proof-of –concept data which could be used to support a major funding bid, quantifying how reproduction – a key aspect of human life-history – is affected by infection.

The work has broad implications for evolutionary anthropology, population studies and public health interventions.

Pilot results

In March 2015 we surveyed 194 adult women and 37 men in rural Cameroon (funded by the Cabot Institute and ESRC- Transformative Social Science pump-priming funds) for measures of their reproduction as well as their malaria status and infection with the tissue worm parasite Onchocerca.

We found that women infected with Onchocerca had a statistically significant earlier menarche and age at first birth, compared with uninfected women (controlling for age and wealth) [Table 1]. This is consistent with infection risk driving faster life-history strategies. We also found that malaria infection co-varied with reproductive behaviour and attitudes of both sexes. Among adults with malaria (28%), those with higher parasitaemias showed a trend towards having more sexual unions and preferring earlier age at marriage. Also, those infected with malaria had a trend towards lower life expectancy than uninfected individuals [Table 1]. Together this is suggestive that perceived risk of mortality, putatively linked with infection, is underpinning faster life-history strategies.

Table 1. The impact of infection on reproduction and life expectancy (controlling for age).

ONCHOCERCA	Infected (n=64)	Uninfected (n=130)
Menarche (years)	14.36 ±2.07	15.17 ±2.07	t=1.92, p<0.05
Age at first birth	17.96 ±5.0	19.74 ±4.9	t=1.65, p<0.05

MALARIA	Infected (n=49)	Uninfected (n=168)
Life expectancy (years)	51.05 ±2.8	54.95 ±1.8	t=1.73, p<0.1

Further information

This research was carried out by Cabot Institute academics Dr Mhairi Gibson (School of Arts), Professor Mark Viney (Biological Sciences), and Samuel Wanji (University of Buea, Cameroon).