Genetic markers have been discovered that can help to predict the age at which people first become sexually active and have children, according to a new study published yesterday.
The genes point to particular personality traits that may make teenagers defy convention or experiment with sexual activity, researchers say.
A team from Oxford University, UK, working with researchers from Cambridge University, UK, and scientists from overseas, linked 371 genetic variants, 11 of which were sex-specific, helping to pinpoint the timing of first sex and birth.
They say these variants interact with environmental factors, such as socioeconomic status and are predictors of longevity and later life disease.
Writing in Nature Human Behaviour, the authors say their findings could help scientists to understand human behaviour more deeply.
In the largest genomic study conducted to date, they undertook a Genome-Wide Association Study (GWAS) to see if there is a relationship between reproductive behaviour and a particular genetic variant.
They combined multiple data sources to examine age at first sex and birth in men and women and went on to calculate a genetic score. All genetic loci combined to explain about 5-6% of the variability in the average age at sexual debut or having a first child.
First author Professor Melinda Mills, director of the Leverhulme Centre for Demographic Science at the University of Oxford and Nuffield College, said: “Our study has discovered hundreds additional genetic markers that shape this most fundamental part of our lives and have the potential for deeper understanding of infertility, later life disease and longevity.”
The genetic signals were not only driven by social factors and the environment; they were also driven by reproductive biology and the team discovered variants related to follicle-stimulating hormone, implantation, infertility, and spermatid differentiation.
Prof Mills said although it was known that childhood socioeconomic circumstances or level of education are important predictors of the timing of reproduction, they discovered a relationship with substance abuse, personality traits, attention deficit hyperactivity disorder (ADHD) and some that were predictive of some diseases and longevity.
Genetic factors driving reproductive behaviour were found to be strongly related to later-life diseases such as Type 2 diabetes and cardiovascular disease.
“We demonstrated that it is a combination of genetics, social predictors and the environment that drives early or late reproductive onset,” she said.
“It was incredible to see that the genetics underlying early sex and fertility were related to behavioural dis-inhibition, like ADHD, but also addiction and early smoking. Or those genetically prone to postpone sex or first birth had better later life health outcomes and longevity, related to a higher socioeconomic status in during childhood.
“It is exciting that the genetics underlying these reproductive behaviours may help us understand later life disease.”
The research team found particularly strong links between early sexual debut, ADHD and substance abuse, such as early age at smoking and say they hope their findings lead to better understanding of teenage mental and sexual health, infertility, later life disease and treatments to help.
Mills MC, Tropf FC, Brazel DM et al. Identification of 371 genetic variants for age at first sex and birth linked to externalising behaviour. Nature 1 July 2021
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