Whatever else your parents give you,it won't include a sense of humour

Teenagers, something to celebrate: scientists have discovered that your sense of humour is not inherited. Instead, they say it depends entirely on upbringing and culture, unlike almost every other personality trait such as how introverted or extroverted you are.

A team at St Thomas' Hospital in London began searching for a genetic link in humour by studying 71 pairs of identical and 56 pairs of non-identical twins, whom in all cases had been raised together. It might sound like something in a Gary Larson cartoon - and that is exactly what the team used as test material.

The researchers, led by Tim Spector and Lynn Cherkas, asked pairs of twins to go into separate rooms and rate five cartoons from Larson's Far Side series on a scale of 0 ("a waste of paper") to 10 ("one of the funniest cartoons you've ever seen").

The results showed that siblings tended to have a similar view of how funny a cartoon was. But identical twins - who share all the same genes - were no more likely to agree than non-identical twins, who normally share only half their genes.

The researchers told New Scientist magazine, which reports the story today, that this suggests it is a shared environment, rather than shared genes, that makes brothers and sisters laugh at the same things.

"It's a surprise, because most personality traits have genetic components," Dr Spector said. "This implies that there's a lot of cultural influence on humour." He thought that it might explain why popular jokes varied so much between nations.

The widely held British view that Germans lack a sense of humour may stem from such differences; Germans think the same about the Swiss.

Dr Spector acknowledged that his team had studied only one type of humour - so-called cognitive humour, which involves a blending of contradictory ideas, a commonplace in Larson cartoons, which tend to involve surreal juxtapositions of people or events.

The researchers now plan to investigate other kinds of humour, such as sexual innuendo, possibly by using saucy seaside postcards.