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Study investigates how Mongolian fertility is linked to wealth

16 October 2014

Title: Ecological variation in wealth–fertility relationships in Mongolia: the ‘central theoretical problem of sociobiology’ not a problem after all?

Authors: Alexandra Alvergne and Virpi Lummaa

Journal: Proceedings of the Royal Society B

In Proceedings of the Royal Society B today a study of fertility in Mongolia suggests that women are more driven to seek wealth and status than they are to reproduce.

Classical ideas of evolution suggest fertility should increase as limitations enforced by scarce resources are removed allowing genes to be passed on through reproduction. These ideas seem to suggest that as wealth and status increase fertility should increase. However, recent patterns show that there is a negative relationship between access to resources and fertility. Researchers behind this study say wealthier and socially successful women are choosing to have smaller families, showing a drive for ‘status enhancement rather than fertility maximisation’.

The researchers analysed survey data collected in Mongolia from 9,000 women, aged from 15 to 49 years old, and over 4,000 husbands. Mongolia underwent a sudden transition from a Soviet-style state to mass privatisation over the past decades and the scientists wanted to see how the relationship between fertility and wealth changed when these systems switched over.

The surveyed women were asked about income, household amenities, educational level, the total number of children born, and how many children they already had when they first used contraceptive methods. The survey also collected data about whether the women lived in cities, in rural environments or in remote regions; this enabled the researchers to compare results across different areas.

The team compared the fertility of older women who started reproducing before the socialist system was replaced in the early 1990s, with younger women who started reproducing after the change in government. In the older cohort, and in all regions, the wealthier women had larger families as predicted by classic evolutionary models. The opposite relationships applied to the younger women for whom wealth was linked with small family sizes.

The researchers argue that this pattern of behaviour has emerged because the transition to a market economy since the early 1990s has created more economic opportunities for educated women, driving them to take these opportunities and delay reproduction. The team found that this effect was three times stronger in urban as compared with remote, rural areas where education creates fewer opportunities. The team say this might explain why those in the wealthy cities tend to delay reproduction while those in the countryside were more likely to have children at the time of the survey.

 ‘For a long time scholars have associated later child bearing with the length of time a mother has spent in education,’ said Dr Alexandra Alvergne, one of the authors behind the paper. ‘However, we find that education on its own does not drive the decision on when to start a family. Rather, how much education translates into future wealth best explains fertility patterns across regions. It seems that women’s prime objective is to accrue wealth and status. This might be securing a well-paid job or finding a partner who has relatively high social standing.’