Colourful scenes of woolly mammoths and deer have been highlighted from the legendary Lascaux caves in France's Dordogne to Britain's Cresswell Crags. But the vast majority of prehistoric work shows little more than human genitalia and naked women crudely scratched into stone.

"In schools all over the world, you go to the toilets and you'll start seeing these same sexual images, " said the leader of the international research team that's work is set to revolutionise accepted views of early man's artistic urges.

In his new book The Nature of Palaeolithic Art, Prof Dale Guthrie, a US-based expert in the field, argues that most ancient artists were motivated by the most powerful force known to early man . . . sex.

The claims, based on the examination of 3,000 ancient images and hundreds of handprints, challenge the traditional view that the paintings were the work of senior religious figures.

Guthrie came to the conclusion that teenagers were the most prolific ancient artists by using forensic techniques to study one of the most common shapes represented: human hand prints.

By taking measurements of cave prints and comparing them to the hands of nearly 1,000 modern people, he found that they were mostly made by adolescent boys. But, in contrast to the traditional view that the caves were the preserves of senior men, he also found prints from all age groups and both sexes.