Improved healthcare and nutrition is causing taller and slimmer women to have more babies, scientists have claimed.
The study, carried out by Durham University, followed two communities of women in Gambia, but researchers said the trend could also be observed in the wider world.
The research also challenges the idea that low death rates in the West had hindered natural selection, and that the evolution of the human race had, in effect, stopped.
Data collected by the UK Medical Research Council between 1956 and 2010 was used to provide information concerning the inhabitants of two Gambian villages
The researchers had thorough data on the height and weight of the women.
Over this period, both communities experienced significant demographic shifts - from high mortality and fertility rates to rapidly declining ones.
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This change was down to improved nutrition and medical care.
The researchers found that as birth rates declined, the women's weight and height changed too.
The analysis showed that selection initially favoured short and heavier women but this shifted over time to favour tall women with a lower body weight.
By the end of the period, this preference had reversed, with taller, thin women having more children than average .
Dr Ian Rickard, lecturer in the Department of Anthropology, said: ‘This is a reminder that declines in mortality rates do not necessarily mean that evolution stops, but that it changes.
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‘Our results are important because the majority of human populations have either recently undergone, or are currently undergoing, a demographic transition from high to low fertility and mortality rates.
‘Therefore the temporal dynamics of the evolutionary processes revealed here may reflect the shifts in evolutionary pressures being experienced by human societies generally.’
The study, published in the journal Current Biology were unable to determine precisely why this was however.
It is thought that better healthcare determined which women were more likely to reproduce.
There is evidence that a similar trend is being seen in Britain, although for different reasons.
A study found that taller men tended to have more children and another found that women with with lower than average weights also tended to have more children.