Ever wondered what determines whether you have a high, low or medium drive to have sex? If you're female you might be surprised by what the studies show (causes are much less clear among men).
Consider two sisters whom I used to know in my teens. The oldest was demurely sexy, although she did not actually sleep with, or even get off with, many men. She did not come into puberty until aged 13 and although exceptionally attractive, did not make a big fuss of her looks.
By contrast, her equally desirable younger sister was a full-on wild child, coming into puberty two years younger. Her rather strait-laced parents would have been horrified to learn what she got up to with a wide variety of men.
The two sisters also reported very different satisfaction ratings with their menfolk's performance. The younger one was usually rather dismissive of her 'lays' as she called them. The elder, while demanding more involvement and commitment, tended to be more complimentary.
The remarkable fact is that such radical variations seem to be largely attributable to differences in a girl's relationship with her father. On average, a girl whose father divorced or separated from her mother before she was 10 comes into puberty fully six months before girls from intact homes. This pubertal precocity puts young girls at greater risk of a host of later problems, including rampant promiscuity and pregnancy. Fatherless girls are also more liable to have negative attitudes towards men and to declare themselves less interested in long-term, stable relationships.
But girls from intact families are also affected by Daddy. They come into puberty earlier if they have a negative relationship with him; the more he is involved in their care, the later is puberty. (Relationship with Mum does not predict pubertal age at all.) If the girl felt able to talk openly and congenially with her dad when small, she is also subsequently more likely to report a satisfying adult sex life.
Crucially, when it comes to explaining differences between siblings, a father may have been close to, and able to talk well with, one daughter, but unlike this with another. He may have been comfortable being nude in the presence of one, but made anxious about this, perhaps because of her beauty, in the case of another.
Outsiders observing these two daughters may say, 'They are completely different, yet they had the same parents and upbringing - even went to the same schools - so it must be nature, not nurture, that made them so.' Except that, in effect, they did not have the same father. And indeed, studies show sex drives are not genetically inherited.
With my demure and wild child sisters, for instance, the eldest had been very close to her dad when small. But a career change meant that he was much less around during the youth of the youngest and they never really connected. In fact, so different was he in his dealings with her that they might as well have had different fathers.
· Oliver James is unable to enter into any personal correspondence.