Yesterday's papers told us about a 17-year-old, who gave birth to her first child at the age of 15, who is now expecting triplets. The girl, Sian Robbins admits, 'I didn’t really want a baby so it was a shock but we weren’t using contraception.'

Today we learn that a 13-year-old boy, Alfie Patten, has become one of Britain's youngest fathers following a night of unprotected sex with his 15-year-old girlfriend. The free paper that was thrust into my hand as I was heading home from a day in London today asks, 'Why does UK have so many teenage mums?' By coincidence, that is a question I had been exploring during the day, in the context of Britain having the highest rate of teenage pregnancies in Europe - unofficial government figures apparently show that the rate among under-16s is now up to 8.3 per 1000 - and the failure of the government's ten-year campaign to reduce underage pregnancies.

Some authorities are considering giving sexually active children controversial contraceptive implants. Others respond that the problem is not just getting pregnant, but that there is also the issue of disease. While true (16 to 19-year-olds account for more than a third of some sexually transmitted infections, including chlamydia, which can result in infertility), this also misses the point.

To answer the paper's question, the biologist in me would point out that the UK has so many teenage mums because so many teenagers are having sex. The question then becomes, 'Why are so many teenagers in the UK having sex?' Part of the answer was offered last week by the person who said teenage pregnancies might not be all bad after all as it gives the girls some purpose in their lives. Not that every sexually active teenager is looking to have a baby to love them and be dependent on them. However, when almost every explicit and subliminal message that we and our children are exposed to tells us that our identity is defined by our sexuality, that we are to look inward to discover our true selves, and that the way to find our own Prince Charming is to kiss as many frogs as possible, it is little wonder that our young people behave in a way as though they believe that sexual intercourse has the capacity to create intimacy and reveal identity - rather than merely reinforcing these where they already exist.

In truth, sex is not about defining or discovering self. It is not even about just the two consenting adults - or, in the cases currenting causing our politicians to reflect on the broken state of Britain, the two underage teens. Rather, it's about how we fit in society and the contribution we make as individuals to the wider community. Which is why marriage is ultimately about the bringing together not just of two individuals but of two extended families.

Neither having sex nor having a baby is about finding a purpose in life. As my mother used to observe when recounting tales of pregnant teenagers in the classroom where she taught - in the same school where Sian Robbins attended until recently - babies soon grow up and cease to need their mothers in the same way, leaving the young mothers just as in need of a purpose in life. It is by being able to make a valuable contribution to society that any of us find our place in this world and, ultimately, there is only one person outside of ourselves in whom we can find life-long purpose - the One who died that we might 'have life, and have it to the full'!

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