Women are evolving to become taller and slimmer as they live longer and have fewer children, a study has shown.

Data collected on people living in rural Gambia has provided evidence of a modern-day demographic transition with a direct influence on women's physiques.

Researchers from Durham University and the Leibniz Institute for Zoo and Wildlife Research in Germany used 55 years of data on thousands of women from two villages in the West Kiang district.

Over the five decades, mortality rates have improved and fertility rates have dropped - largely down to improvements in medical care after a clinic opened there in 1974.

The data included information on women's height and weight and analysis revealed a demographic shift towards taller women with lower body mass index (BMI).

Evolution does not stop

Researchers said it was unclear why such a change occurred but said it could be because natural selection began acting less on mortality and more on fertility. They also argued that environmental changes played a role.

Alexandre Courtiol, from the Leibniz institute, said: "Although we cannot tell directly, it may be due to healthcare improvements changing which women were more or less likely to reproduce."

The team believed the findings from Gambia might have global relevance as most populations around the world are living longer and having fewer children.

In the study, they wrote: "Our results are important because the majority of human populations have either recently undergone, or are undergoing, a demographic transition from high to low fertility and mortality rates.

"Thus the temporal dynamics of the evolutionary processes revealed here may reflect the shifts in evolutionary pressures being experienced by human societies generally."

Ian Rickard, of Durham University, added: "This is a reminder that declines in mortality rates do not necessarily mean that evolution stops, but that it changes."