Written on the body

The team linked 12 specific areas of DNA sequence with reproductive behaviour and identified a further 24 genes likely to drive these variations. Their paper, published today in Nature Genetics, is co-authored by 250 scientists from institutions worldwide, including Qatar and Saudi Arabia. 

The discovery deepens our understanding of the role of biology in falling birth rates and delayed parenting in industrialised societies today, until now ascribed mainly to sociological factors.

It is the largest genetic study of human reproductive behaviour to date, undertaken in partnership with the Universities of Groningen, The Netherlands, and Uppsala, Sweden. It combines 62 data sets with information from nearly 240,000 men and women for age at first birth and 330,000 for number of children ever born. 

All 12 DNA areas together predict around 1% of the variation in reproductive behaviour ­— large enough to be useful in many research avenues. As more genetic data become available this could rise to as much as 20%. 

The work provides fresh insights for future fertility treatments. Some lead DNA variants identified are for critical fertility processes, including follicle stimulating hormone, oestrogen, ovary growth, spermatid differentiation, and male germ cell development.

Ultimately, the authors hope their findings could someday help us understand our own personal biological clock.

“We found that women with DNA variants for postponing parenthood also have bits of DNA code associated with later onset of menstruation and menopause. One day it may be possible to use this information so doctors can answer the important question: “How late can you wait?” said lead author Melinda Mills, Oxford University. However, she cautioned, having a child depends on many social and environmental factors.

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