An embryologist examines human embryos at an IVF clinic / Getty Images

Julian Baggini ponders how the reality of childbirth is often messier than the natural ideal

IVF treatment is no picnic. The emotional turmoil it entails is so intense that a recent Danish study showed that couples who tried it and ended up childless were three times more likely to separate than those who were successful. To go though all this you have to really want not just children, but your children, the bearers of you and your partner's DNA. So imagine what it must feel like to be the Italian woman who discovered that someone else's fertilised eggs had been implanted in her womb.

It's difficult even to know how even to describe these unborn children. Is she carrying another couple's twins? Not in Italian law at least, which states the children are nobody's but hers. This state of affairs is disorientating because both our words and ways of thinking are tailored towards the one natural mode of reproduction that has been the same ever since we evolved into mammals.

In our confusion it is tempting to look for security in what is natural, which is often assumed to be what is good and real. But our general preference for the natural is not always just due to its familiarity. Some desires are inexplicable but for the assumption that deep-rooted instincts are driving them. Nowhere is this clearer than in the desire to have your own biological offspring. For almost all would-be parents, this is the number one choice, preferably by the time-honoured method. Artificial methods are second best, using a donor's egg or sperm as a last resort. Very few prefer adoption, even though objectively it involves much less risk and discomfort.

These preferences seem perfectly reasonable, which is why most people support more help for couples seeking fertility treatment. But at the same time, no one would be so crass as to say that non-biological parents aren't real parents, and many adopted children are offended when people talk about their adoptive parents as not being their “real” ones.

Nor is it historically unusual for children to be less than the full genetic progeny of their parents. Half-brothers and sisters were extremely common when death in childbirth was an occupational hazard for mothers. Infidelity is another hidden factor, with best estimates suggesting that one on ten people do not have the biological father they believe they have.

What all this shows is that there is often a tension between the natural ideal and the messy reality that we find ourselves in. With biotechnology promising even more dramatic departures from the natural in the future, this tension is only going to get greater.

The way to resolve it cannot be simply to retreat back to the natural, decrying the synthetic as inferior. Artificial technologies can give very real health and life, and only a fool would prefer that to all-too natural infertility, death and illness.

Nonetheless, we can't just expect instinctive preferences for the natural to disappear. The best we can do is gently keep push at the limits of the natural and see how far we are willing to go. We just don't know in advance what our limits will be. No matter how much we might instinctively recoil at unexpected, unnatural situations, where, on balance, they provide more good than harm, we tend to end up embracing them. The Italian woman, for instance, has embraced her situation and the odds are she will love her children as much as she would have loved those carrying her own genes. Our preference for the natural might well be natural, but what is most natural is not always best, for our own welfare or for that of others.