According to US researchers, some children have their first sexual intercourse at an early age not because they were raised without a father at home, but because it is in their genes.
In the study, the researchers at the University of Oregon tested for genetic influences as well as factors like poverty, educational opportunities, and religion.
They found that the more genes the children shared, the more similar their ages of first intercourse were, irrespective of whether they had an absent father or not.
A spokesman for the charity, Brook, said that children needed early education to help them make informed choices.
While several theories have been advanced about the environmental factors, which influence this association between absent fathers and early sex, the current study has shown that these factors are not as important as genes in determining early sexual behavior.
The researchers compared the average age of first intercourse among children whose fathers were always absent, partially absent or always present throughout childhood.
They looked at more than 1,000 cousins aged 14 and older from the American National Longitudinal Survey of Youth.
It was found that the children whose fathers were always absent, 63.2 percent reported having had sex, as compared to 52.5 percent of children whose fathers were sometimes absent and only 21 percent of children whose fathers were always present.
The average age of first intercourse for children whose fathers were always absent was 15.28, compared to partially fathered children at 15.36 and 16.11 for children whose fathers were present for all of their childhood.
The researchers compared children who were related in different ways to each other, and who differed in whether they had lived with their fathers.
Surprisingly, they found that the more genes the children shared, the more similar their ages of first intercourse, regardless of whether they had an absent father or not.
"The association between father's absence and children's sexuality is best explained by genetic influences, rather than by environmental theories alone," the BBC quoted Jane Mendle, professor of psychology at the University of Oregon, who led the study, as saying.
"While there is clearly no such thing as a 'father absence gene', there are genetic contributions to traits in both mums and dads that increase the likelihood of earlier sexual behavior in their children," she added.
But she said that her study did not have the power to discriminate conclusively between genetic and environmental factors and further research with a larger number of children would be necessary.
Simon Blake, from the sexual health charity, Brook Advisory Center, said: "All young people need access to confidential sexual health services as well as high quality education about sex and relationships from a young age."
The study has been published in the journal Child Development.