Richer women who face a shortage of men will delay having children and focus on their careers, according to new research.
However, poorer women will start having children younger if there are not enough men to go around, the study by the University of Portsmouth suggests.
Lead author Abby Chipman, of the department of psychology, said the results showed the ratio of males to females in small urban geographical areas of England had a direct effect on the age women start having children.
She said 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."
Ms Chipman said that in poor neighbourhoods there was less geographical movement, partly because fewer people own cars and and higher levels of unemployment.
She added that the results helped confirm that people's experiences of their local neighbourhoods are an important factor related to when they were most likely to give birth.
The research was funded by a bursary from the department of psychology and was published in the journal Biology Letters. It 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 for 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.