When exactly you lose your virginity has been thought of as a fairly random event, dictated by chance and circumstance.
But now an international team of scientists, led by the University of Oxford, reveal the milestone is more controlled by our genetics than we may realise.
They say they've identified 371 regions of our genetic code that appear to influence not only when exactly we first have sex, but also when we have our first child.
Their analysis of Brits' data revealed genetics can explain between five and 17 per cent of when individuals achieve these two milestones.
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An Oxford-led team discovered hundreds of genetic markers driving two of life’s most momentous milestones - the age at which people first have sex and become parents
The study has been led by Professor Melinda Mills at the Leverhulme Centre for Demographic Science, the University of Oxford.
'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,' she said.
'Age at first sexual intercourse and age at first birth have implications for health and evolutionary fitness.
'We anticipate that our results will address important interventions in infertility, teenage sexual and mental health.'
The study, published in Nature Human Behaviour, used data on age at first sexual intercourse (AFS) and age at first birth (AFB) – how old a woman is when they have their first baby.
For AFS, the team included 397,338 pooled individuals from the UK Biobank – a database containing in-depth genetic and health information from half a million UK participants.
For AFB, researchers included 542,901 individuals from 36 previous studies.
The team linked 371 specific areas of our DNA, called 'genetic variants' (known locations on chromosomes, in other words) to the timing of first sex and birth.
In all, there were 282 genetic variants linked to AFS and 89 linked to AFB.
This is hundreds more than the previous studies that found 38 for AFS and just 10 for AFB.
Professor Mills told MailOnline that is is not genetics or social environment alone that dictate AFS and AFB, but rather an 'interaction of both nature and nurture'.
'We knew that the timing of what we call "reproductive onset" – age at first sexual intercourse and child – is largely related to and predicted by social and environmental factors, like obtaining higher education and availability of contraception,' she said.
'What this study does is extend what we know about the social and genetic predictors to find not only the proportion explained by genetics, but isolate actually the genetic variants (location on your DNA) and examine their biological function.'
Surprisingly, the influence of genes on when women have their first child appears to have increased over the years, the study
