News

Male-female ratio predicts age women have babies

Wed, 13 Feb 2013 15:43:00 GMT

Poor women will start having children younger if there aren’t enough men to go around, according to new research.

Rich women will respond to the problem of fewer men by delaying having children, potentially focusing on their education or career, and being prepared to travel further afield to find a mate.

The study by researchers at the University of Portsmouth is the first to show that, in England, the ratio of males to females in small urban geographical areas has a direct effect on the age women start having children.

Lead author Abby Chipman, of the Department of Psychology, said the results suggest rich and poor women adopt different strategies if women outnumber men and adjust their reproductive timing based on the number of available men.

She said: “The patterns we found suggest female-to-female competition is associated with poorer women adopting a ‘live fast, die young’ strategy.

“If there are more women than men, studies have shown that women have lower expectations of men. We found poor women are more likely to rush to start their ‘reproductive careers’ while rich women are more likely to delay having children. We speculate that instead they begin to accumulate resources and education that will be of benefit to their future offspring.”

In poor neighbourhoods there can be less geographical movement. In part this is due to fewer people owning cars and higher levels of unemployment, meaning people from poor areas are less likely to travel beyond their neighbourhoods. This may make the male-to-female ratio of their local environment more important than for people who are able to move to a new area.

The results help confirm that people’s experiences of their local neighbourhoods are an important factor related to when they are most likely to give birth.

The research is published in the journal Biology Letters. The research was funded by bursary from the Department of Psychology.

The study compared birth rates with data on neighbourhood deprivation for more than 2,500 urban neighbourhoods, each with about 8,000 residents, using data from the Office of National Statistics.

It examined women aged 15 to 50 and compared birth rates, deprivation and the male-to-female sex ratio in each area.

The results showed that every step change in the male-to-female ratio had an effect on the local birth rate. For example, for every ten per cent shift in the sex ratio towards an over-supply of women, 7.5 more babies will be born to women in the 25-29 year age group in an average urban neighbourhood.

Scientists have known for some time that women are more likely to give birth when young if they are faced with tough living conditions, and that the sex ratio can influence behaviour with the scarcer sex being most “in demand”.  For example, when men outnumber women, women become more selective resulting in poor men being less likely to marry.

The factors used to determine neighbourhood deprivation include income, employment, health, education, housing and access to services.

Previous studies have shown that in areas with more men than women, the crime rate tends to be higher, suggesting competition between men.

In England, about 105 boys are born to every 100 girls, but the distribution of males and females in any given area varies substantially.

The findings of this research could be of use to various agencies including social policy think tanks, educators and government officials to get a head start on problems in localised areas including teenage pregnancy, low educational achievement and joblessness.