Genetic factors relating to physical maturation and personality may influence the age at which people first have sex, a study has found.
Researchers at the University of Cambridge examined data from 125,000 people aged 40-69 acquired from the UK Biobank and identified 38 regions in the genome that correlated with age at first intercourse, most commonly found to be 18 years old. The findings were then compared with genetic data from 250,000 men and women from Iceland and the USA.
The areas of the genome identified by the researchers contained genes not only known to influence biological sexual maturity, such as the release of sex hormones and the onset of puberty, but also those linked to personality traits that could influence how likely people will engage in behaviours leading to earlier sexual intercourse.
In particular, the CADM2 gene, associated with risk-seeking behaviour was associated with people losing their virginity at a younger age, while the MSRA gene, relating to irritability, was linked to people having their first sexual intercourse later than average.
'We were able to calculate for the first time that there is a heritable component to age at first sex, and the heritability is about 25 percent, so one quarter nature, three quarters nurture,' said lead researcher on the study Dr John Perry, a geneticist from the University of Cambridge.
Upbringing, social factors, influence from peers and religious status are still therefore likely to remain the main contributing factors to the age at first intercourse.
Dr Alicia Smith, associate professor in psychiatry and behavioural sciences at Emory University in the USA called for caution when interpreting the results, particularly when drawing conclusions about age of puberty and age at first intercourse.
'Certainly, the age at which a person first has sex is based on a lot more than the age at which they are first biologically capable. It is also based on cultural and socioeconomic factors that are very difficult to account for in genetic studies,' said Dr Smith.
Speaking with Scientific American, Dr Perry added: 'If you look in [the scientific] literature, relatively early ages at first sex and first birth have been associated with lower educational achievement, poorer physical health, poorer mental health—a complex web of negative stuff'.
Dr Ewan Birney, co-director of the European Bioinformatics Institute, welcomed the contribution of the recent study to research on the relationship between early sexual activity and other life events.
He told the Guardian: 'This is an interesting study where using genetics one can better untangle cause and consequence of a complex human behaviour. Genetics only contributes a small part to age of first sexual intercourse, but the very random nature of each person's genome means it can be used to trace the impact of this behaviour into later life with less concern about complex correlations confusing cause and consequence.'
The study was published in Nature Genetics.