In France's Gargas cave, a late Paleolithic left-hand stencil glows green from a night vision camera. Archaeologist Dean Snow concluded the hand was female.

"We don't know what the roles of artists were in Upper Paleolithic society [roughly 40,000 to 20,000 years ago] generally," he said. "But it's a step forward to be able to say that a strong majority of them were women."

Snow's research was limited to Europe, but he hopes others will do similar studies at prehistoric sites elsewhere.

(Also see: pictures of hand stencils through time.)