The spread of names can be explained without recourse to the "celebrity effect", the research concludes. To those who fear a future populated by Brads and Britneys, Alexander Bentley of University College London says: "In many cases, names become popular by dumb luck."

Most parents copy existing names for their babies, say Bentley and Matthew Hahn of Duke University, North Carolina. The overall distrib ution looks like a product of random copying, they report in Proceedings of the Royal Society of London.

Bentley and Hahn modelled the allotment of names in the US in the 20th century, using the idea of "random drift" from population genetics. Genetic variants are inherited at random, and can become more or less widespread even in the absence of selection. New mutations stand a chance of making it big in future generations.

In a computer simulation, they assumed most babies are given existing names, with a few parents inventing original ones. The results closely matched the actual distribution of names.

"Some baby somewhere is being given an original name that will one day become highly popular," says Bentley. But he adds it's impossible to predict which ones will become common.

The pair found that the "mutation rate" - the likelihood that a baby will be given an original name - is higher for girls. Bentley speculates this might reflect the patriarchal nature of US society, where male names are often passed on to the next generation.

And celebrities seem not to influence the masses much as we might think. "I'd say it's a pretty small effect," says Hahn. A quick look at last year's top 10 reveals that Jacob headed the list for boys and Emily was the favourite for girls. Not a Keanu or a Kelly in sight.