Balancing Fertility and Child Survival in the Developing World
Limiting fertility as a strategy in poor countries, so that mothers can invest more time caring for each child only modestly improves the prospects of child survival
Children in smaller families are only a little more likely to survive childhood in high mortality environments, according to a new study of mothers and children in sub-Saharan Africa. Researchers are seeking to understand why women, even in the highest fertility populations in the world, rarely give birth to more than eight children.
The study by Dr David Lawson and Dr Alex Alvergne from UCL Anthropology, and Dr Mhairi Gibson from the University of Bristol, challenges the popular theory proposed by evolutionary anthropologists that natural selection sets the upper limit of high fertility to balance a 'life history trade-off'' between fertility and child survival.
Too many births are believed to dangerously
compromise a mother's ability to provide
sufficient care for each child.
The study also considered why fertility rates drop
when societies become richer, a trend referred to
as the demographic transition.
The research, published today in the journal Proceedings of the Royal Society B: Biological Sciences, compiled information on more than 150,000 mothers and their children from 27 sub-Saharan African countries using the Demographic and Health Surveys national household surveys that record information on births, deaths and measures of health and socioeconomic status throughout the developing world.
This enabled Lawson and colleagues to statistically test, with much more data than ever before, when and where high fertility places children at risk.
Overall, the results confirm that mothers with many
children are more likely to experience the death of a child.
Younger mothers, and particularly those having had
many children early in life, were also more likely
to see a child die.
Furthermore, being a twin, or being born
relatively soon after an older sibling,
also decreased the likelihood of early survival.
However, while important from a public health
perspective, these relationships were much weaker
than predicted, as women with the most births always
produce more surviving offspring in total.
Lead author Dr David Lawson says: "In the poorest countries, as many as 1 in 4 children may die before they reach five years of age, but the number of births a woman has is only weakly predictive of whether or not her children will live.
Instead, parents in these countries, particularly when poor and unhealthy themselves, often have very little ability to protect their children from the common causes of death, such as malaria, diarrhoea and respiratory infections. Our results imply that for these parents, limiting fertility as a strategy to invest more time caring for each one only modestly improves the prospects of child survival.
It seems more likely that natural selection favours fertility limitation because of the the costs of offspring production. Pregnancy and lactation are hugely energy expensive in humans and few women's bodies can cope with more than eight pregnancies in a lifetime.
This fits well with the observation that in many traditional societies, women rarely appear to consciously limit the number of births, instead their bodies do this for them, automatically suppressing ovulation while they breastfeed and aborting conceptions when mothers' are in poor physical condition."
The results of the study also improve our understanding of why fertility rates fall when populations undergo socioeconomic development.
"We find that when mortality is lower and maternal education and health improved, fertility limitation is more likely to reduce remaining child mortality risk. Also according to our previous studies, the chance that surviving offspring will grow up to be successful adults improves as well.
This suggests fertility drops as societies become richer and more stable, because such wealth and stability now enables parents to invest more effectively in the wellbeing of their children, provided they keep family size small."
Original article: http://www.eurekalert.org/pub_releases/2012-10/ucl-bfa100112.php