Gene differences may influence age of first sex

19th April 2016 - The age at which we first have sex, enter puberty or start a family may be more heavily influenced by our genes than we thought, say scientists.

The timing of when an individual loses his or her virginity is known to be influenced by social circumstances and upbringing. Peer pressure, for instance, often plays a part.

However, a study in the journal Nature Genetics casts insight on how genetic differences can influence the timing of sexual behaviour.

UK Biobank

To identify these gene differences, researchers led by a team at the University of Cambridge analysed genetic data of 59,357 men and 66,310 women aged 40 to 69 which are held by UK Biobank, a national study for health research.

This analysis identified 38 gene variants that had been associated with the age at which people first have sexual intercourse in 2 studies conducted in Iceland and the US.

They also found that several of these gene variants were located in or near genes previously implicated in brain development and neural connections.

The analysis further uncovered associations with a range of reproductive behaviours, such as a person's age when they first give birth and even the number of children they have.

Physical maturity

Explaining the findings in a statement, lead author Dr John Perry from the Medical Research Council Epidemiology Unit at the University of Cambridge, says: "While social and cultural factors are clearly relevant, we show that age at first sexual intercourse is also influenced by genes which act on the timing of childhood physical maturity and by genes which contribute to our natural differences in personality types.

"One example is a genetic variant in CADM2, a gene that controls brain cell connections and brain activity, which we found was associated with a greater likelihood of having a risk-taking personality, and with an earlier age at first sexual intercourse and higher lifetime number of children."

Disease risk link to puberty

Previous studies by the team have found that an earlier age at puberty is linked to having a higher risk of diseases such as diabetes, heart disease and some cancers.

Paediatrician Dr Ken Ong, a lead author on the paper, adds: "We have already shown that early puberty and rapid childhood growth adversely affect disease risks in later life, but we have now shown that the same factors can have a negative effect at a much younger age, including earlier sexual intercourse and poorer education attainment."

The researchers say that having a greater understanding of when puberty is likely to take place could lead to improvements in promoting healthy behaviour among young people.

Difficult to evaluate

Commenting on the study in a statement, Dr Alicia Smith, associate professor of psychiatry and behavioural sciences at Emory University, Atlanta, US, says: "This is a hard paper to evaluate. The methods are not the traditional ones used. Their results suggest that a much larger proportion of the genome is associated with age at first sexual intercourse than one typically sees in genome-wide association studies. In many cases, this indicates that the statistical model used to test the association doesn’t fit the data and that there are false positives in the results.

"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.

"While this study does find an association with genetic factors, it nonetheless supports the idea that the age at which a man or woman first has sex is overwhelmingly due to non-genetic factors, such as social or environmental context.

"Among 40-69 year old adults in the United Kingdom that report their age at first sexual intercourse between 18 and 21 years, the study estimates that genetic factors can account for 1 year, but environmental factors account for the other 3 years."