An investigation into French children's names by two sociologists at the Centre National de la Recherche Scientifique leaves one outstanding mystery. Why Kevin? An extraordinary one-in-ten boys born in France in the early 1990s is called by that very un-French name (pronounced Kiveene).

Cyril Grange and Philippe Besnard studied French parents' choice of first names since the start of the century, comparing upper-crust names in Bottin Mondain with those in the population at large.

Bottin Mondain, first published in 1903, is an annual listing of the genuine aristocracy, of the far less (who often adopted their name by deed polls) and of members of the bourgeoisie. Families apply to be included and 200,000 people feature in the 1995 edition.

Mr Besnard has written La Cote des Prenoms, an in-depth study on choice of first names throughout the population, with Guy Desplangues of INSEE, the national statistics office. Their research dovetailed perfectly with Mr Grange's own study of the Bottin.

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Comparisons were made in two ways: by measuring the speed at which names filtered down from the Bottin to the general public and by comparing the Bottin's "top ten" with the general public's in different years.

Enduringly popular names, such as Paulette, Josianne and Liliane do not move up the social ladder, nor do newer popular names like Christelle.

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But there was a "considerable acceleration in the taking up of Bottin names," explained Mr Grange.

From an average of 25 years for Marguerite and Yvonne to reach the humble homes of ordinary families at the start of the century, the time-lag dropped to three years for Stephanie, between 1972 and 1975.

Although the rate of transfer speeded up by a factor of five, the two "hit parades" show greater divergency.

Bottin families still chose traditional names - Pierre and Edouard are back again - or little-used names, like Ombeline, Isaure or Sixtine for the l990s upper class baby girl. Genuine aristocrats still go for Amaury, Arnaud and Bernadette, while the bourgeoisie have an enduring weakness for Charles-Edouard, Anne-Sophie and similar composite names.

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In working-class families, "there is a complete change of decor", say the sociologists. The all-time number one is the inexplicable Kevin, while other "Anglo-saxon" names - Christopher, Anthony and Jordan - are also hugely popular.

The role of American soaps on French TV appears to explain some of those choices, but trawl through the series as they may, the researchers could find no soap hero called Kevin.

"Dylan, Cassandra and Brandon seem to be linked to TV series, but apart from those names, the others do not appear to be taken directly from television", said Besnard.