Genes make you laugh, say scientists.

I’m not surprised. I’ve been laughing at them for years. Particularly those that are worn by youths that are so low and saggy on the hips you can not only see their underpants, but they become a danger to their ability to walk.

I have often thought that magistrates should make young offenders wear them as part of a period of probation because it would hinder their escape if they ever attempted to run from another crime.

Whoops! He didn’t get far.

The police would find him laying face down with his trousers round his ankles.

But wait! What’s this? I’ve got it wrong. It’s not those kind of jeans. It’s genes within the human body.

Researchers at California-Berkeley University say a variant of the gene 5-HTTLPR (which is a very catchy name) affects the way serotonin works in the brain. It makes those people who have it smile, chuckle and laugh more than those who don’t.

So if you know someone who is likely to giggle at the drop of a quip or convulse at a joke they could well have special genes on a par with designer jeans.

It means their sense of humour is not, after all, due to the six vodka tonics or four pints of Stella they have just downed, but something in their brain.

Try these jokes to discover the Special Ones among your crowd ...

Did you hear about the girl who thought Benefits Street was a budget box of chocolates that you could buy at Lidl?

Then there was the chap who had a neck brace fitted: he never looked back.

Jim decided to sell his Hoover. “Well,” he said, “it was just collecting dust.”

Having the chuckle gene is good news because laughter is a health tonic that relaxes the body, boosts the immune system, releases feel-good endorphins and protects the heart.

Which makes me think that maybe youths in saggy jeans should get sponsorship from the National Health.

Well, they make me laugh.