Leading article: Grin and bear it

Say hello to 5-HTT. Scientists have identified this strip of DNA as the "happiness gene". If you've got it, you're likely to adopt a glass half full attitude to life. If you don't, your cup of sorrow will run over. But this leads us back to that old philosophical debate about nature versus nurture.

For what good is the happiness gene if life keeps delivering lemons? We can be biologically predisposed to happiness, but that does not mean we will attain it. A selection of love letters by the great French singer Edith Piaf, written in the 1950s, were published yesterday. Unhappiness defined Piaf's life. She was born into poverty and abandoned by her parents as a child. She temporarily lost her sight while young. An early boyfriend attempted to shoot her. The first love of her life, Marcel Cerdan, was killed in a plane crash on his way to meet her. She herself was later seriously injured in a car crash. Her only child died of meningitis aged two.

So even if Piaf was born with 5-HTT, it is difficult to see what good it would have done her. But then again, she channelled all the pain and anguish of her life into her music, making it transcendent. So if you're worried about lacking the happiness gene, take a leaf from Piaf's book: regret nothing.