The fact that children raised in homes without a dad have sex earlier is down to their genes², say US researchers.

美国研究人员称，没有父亲的家庭中长大的孩子过早接触到性是由于他们的基因问题。

Early education about sex and relationships is key, say campaigners

The study tested for genetic³ influences as well as factors such as poverty, educational opportunities and religion.

The more genes the children shared, the more similar their ages of first intercourse⁴（交流，交往） regardless of whether they had an absent father or not.

A spokesman for the charity, Brook⁵, said children needed early education to help them make informed choices.

Competing theories

The study published in the journal, Child Development, says several theories have been advanced about the environmental factors which influence this association between absent fathers and early sex.

One suggests that because these children observe（观察，遵守） unstable⁶ or stressed parental⁷ relationships, they learn that resources are scarce, and people untrustworthy.

This leads them to mature in such a way that they are geared towards mating rather than parenting.

Another states that because adolescents reared in single-parent households may have parents engaging in sexual behaviour with partners to whom they are not married, the children may be more likely to view non-marital（婚姻的） sex as the norm.

And a third theory states that a single-parent family structure may encourage adolescent sexuality by reduced parental control.

In other words two parents can much more closely monitor their offspring's activities and social networks, reducing the opportunities for sex.

But this study shows these factors are not as important as genes in determining early sexual behaviour.

Results

The researchers at the University of Oregon compared the average age of first intercourse among children whose fathers were always absent, partially⁸ absent or always present throughout childhood.

They looked at more than 1,000 cousins aged⁹ 14 and older from the American National Longitudinal Survey of Youth.

For the children whose fathers were always absent, 63.2% reported having had sex.

This compared to 52.5% of children whose fathers were sometimes absent.

And only 21% 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.

It compared children who were related in different ways to each other, and who differed in whether they had lived with their fathers.

The more genes the children shared, the more similar their ages of first intercourse, regardless of whether or not the children had an absent father.

Genetic risk factor

Jane Mendle, professor of psychology¹⁰ at the University of Oregon, who led the study said: "The association between father's absence and children's sexuality is best explained by genetic influences, rather than by environmental theories alone.

"While there is clearly no such thing as a 'father absence gene¹', there are genetic contributions to traits（特征，性格） in both mums and dads that increase the likelihood of earlier sexual behaviour in their children.

"These include impulsivity¹¹, substance use and abuse, argumentativeness（激辩） and sensation（情感） seeking."

But Professor Mendle said her study did not have the power to discriminate¹² conclusively¹³ 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 Advisory¹⁴ Centre, took issue with the idea that genes were the overriding¹⁵（最主要的） factor in early sex.

He said: "We know from research that factors associated with young people having first intercourse at a younger age are: lower educational achievements; friends and the media being the main source of information about sex education; socio-economic status; early sexual experience and the earlier age at which girls start their periods.

"All young people need access to confidential¹⁶ sexual health services as well as high quality education about sex and relationships from a young age.

"This gives them the skills and information to make informed choices, and the self-esteem and aspirations¹⁷（愿望） for themselves for the future.

"Targeted outreach work is also an effective way of reaching those more vulnerable groups."