Children learn to swear before they have mastered the alphabet, according to research from scientists in California.
But they are only following the example of adults, said Dr Melissa Mohr of the University of Stanford.
English speakers use a swear word for every 140 words they speak, or 0.7 per cent of the time, her research found. And that's why most children know a profanity by the age of one or two — although, said Dr Mohr, the level of juvenile swearing really takes off at the age of three and four.
Her book, "Holy Sh*t: A Brief History of Swearing," says the upper classes are just as likely to swear as anyone else, although those identifying as middle class are less likely to.