Genes play a significant role in determining when modern women have their first baby and how many children they have in their lifetime, a study has found.
The findings suggest that human fertility is still evolving despite the fact that most women in Britain and other developed countries override their genetic instincts by delaying the start of their family.
Oxford University researchers said their study, based on analysing the genomes of thousands of women, shows that about 15 per cent of the difference in modern women in the age of first birth, and 10 per cent of the difference in total number of children, is due to genes.