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The research was carried out by an international team working on the Sociogenome project, led by the University of Oxford and funded by the European Research Council. Significantly, they have found that some women are genetically predisposed to have children earlier than others, and conclude that they have passed down their reproductive advantage to the next generation. They also find, however, that while modern women who were born in the 20th century might be expected to have babies even earlier than previous generations did, they are delaying motherhood. Their study, published in the latest issue of the journal, PLOS ONE, says women in modern societies are ‘over-riding’ natural selection because of the stronger effect of lifestyle choices and social factors.
The researchers exploited the latest advances in molecular and quantitative genetics taking existing datasets of 4,300 unrelated women in the Netherlands from the Lifelines Cohort Study. They combined these results with data relating to 2,400 women from TwinsUK, the country’s largest adult twin registry (from which they randomly selected only one twin for analysis).
The researchers found that genes account for about 15 per cent of the differences between modern women when they have their first baby, and 10 per cent in the differences in the number of children they have. They also discovered an overlap between these genetic effects that the study says partly explains why women who have children earlier also have a higher number of children.