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Genes influence timing of motherhood

08 June 2015

By Ceri Durham

Appeared in BioNews 805

Analysis of the genomes of thousands of women suggests that a woman's genes influence the age at which she first becomes a mother and the number of children she will have.

In a new study published in PLOS One, researchers found that genes account for about 15 percent of the differences between women when they have their first baby, and 10 percent of the differences in the number of children they have.

'Social and environmental factors mean women in modern societies are delaying starting families. This research tells us there are genetic differences between women which could be significant for women making decisions about when to have their first baby,' said project leader Professor Melinda Mills of the Department of Sociology at the University of Oxford, UK.

While previous studies considering women's fertility have been based primarily on twins, this study used molecular and quantitative genetics to examine the genomes of 7,700 unrelated women. It was part of the Sociogenome project, a collaboration between sociologists and geneticists in the UK and the Netherlands.

Social and environmental factors, such as use of contraception, were much more important than genetic factors in determining when women had their first babies and the number of children they had overall. The study also found, in keeping with previous studies, a negative correlation between these two - the later a woman has her first child the fewer children she is likely to have. The study found that genetics account for 20 percent of this correlation.

The researchers say that this shows that natural selection is still at play when it comes to human fertility patterns, and early fertility is an inherited reproductive advantage.

'In evolutionary and genetic terms, this suggests that younger generations today should be inclined to have children at an earlier age than women in the past,' said Professor Mills. 'However, what we actually observe is that the reverse is happening. Social and environmental factors mean women in modern societies are delaying starting families.'

The study's authors describe this as an 'evolutionary override', and they call for 'an integrative approach between the social and biological sciences... to better understand the changing patterns in, or even predict, future levels of human fertility'.


07 November 2016 - by Dr James Heather 
Twelve locations in the human genome have been linked with differences in reproductive behaviour...
03 May 2016 - by Anneesa Amjad 
A study has identified two gene variants that increase the likelihood of a woman having twins and could explain why twins appears to run in families...
10 August 2015 - by Kirsty Oswald 
All this talk of the age a woman's fertility 'drops off a cliff' is just a distractor from the truth – this phenomenon of women finding themselves 'up against' the biological clock is a cultural one, not a biological one....
03 August 2015 - by Ruth Retassie 
Researchers have developed a mathematical model for determining what age women should start trying to conceive...

30 June 2014 - by David O'Rourke 
A recent study has shown that mothers who have children at the age of 33 or after are twice as likely to live longer than women who stop childbearing by the age of 29....
10 February 2014 - by Patricia Cassidy 
A recent poll conducted ahead of a television documentary has shown that one quarter of respondents believed women should stop trying to 'trying to bring babies into the world' past the age of 40...
25 November 2013 - by Ari Haque 
A report from the Office for National Statistics (ONS) shows that the number of multiple births among women over 45 has increased by 23 percent in the past year. The increase is thought to be in part due to more older women using IVF treatment to conceive...
15 July 2013 - by Dr Irenee Daly 
Who could blame women for hoping that they are more reproductively robust than is actually the case?....
31 January 2011 - by Dr Tamara Hirsch 
A recent review paper has emphasised the need for improved provision of fertility information, especially regarding age-associated risks, as the trend for women having children later in life continues....

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