Twelve locations in the human genome have been linked with differences in reproductive behaviour.
'Our genes do not determine our behaviour but, for the first time, we have identified parts of the DNA code that influence it. This is another small piece to understanding this very large jigsaw puzzle,' said first author Dr Nicola Barban, from the University of Oxford, UK.
Researchers analysed data from 238,064 men and women for the age of first birth (AFB), and almost 330,000 men and women for number of children ever born (NEB).
The data was taken from 62 previous studies involving over 250 sociologists, biologists and geneticists, and 175 research institutions worldwide, making this the largest genome-wide association study to date.
The analysis found ten regions of DNA that have never before been implicated in reproduction, as well as confirming two previously identified in smaller studies.
Childlessness, infertility and increased average AFB are often presumed to be entirely due to changing cultural or socioeconomic norms, rather than genetics, and are characteristic of many countries.
The 12 regions could explain up to the one percent of the variance in AFB, and 0.2 percent in NEB. Across the global population, this could be relevant to tens of millions of people.
Researchers suggest such information could be used in future medical assessments and interventions. DNA variants linked with AFB were associated with characteristics for sexual development, including age of first menstruation, or voice breaking in boys. Women with DNA variants for postponing parenthood also had variants associated with later menopause.
'One day it may be possible to use this information so doctors can answer the important question: "How late can you wait?" based on the DNA variants,' said Professor Melinda Mills from the University of Oxford, lead author of this paper and head of the Sociogenome Project that oversaw the study. However, she emphasised that social and environmental factors would always play a bigger role in whether or when to have babies.
In addition, many of the regions have little if any known function that could obviously relate to having children. The participants of this study were also largely of European descent, and the findings may not translate directly to other populations.
'Genetics is not about fortune telling,' cautions Darren Griffin, professor of genetics from the University of Kent, UK, who was not involved in this study. 'Rather, the paper is an important one in helping us to understand all the factors that have come together to understand a very complex and socially relevant phenomenon. The discovery that there are genetic as well as psycho-social factors at play is absolutely fascinating.'