In a film that blends paleontological wonders with existential pondering, Cave of Forgotten Dreams asks the question, "What constitutes humanness?" German director Werner Herzog creeps deep into Chauvet Cave in southern France, where researchers say they have found the earliest known cave paintings. The charcoal paintings etched on the curved walls of the cave—some say from 32,000 B.C., others say 10,000 B.C.—look as though someone scratched them there last week. A landslide sealed the cave thousands of years ago, creating a perfectly preserved time capsule until explorers discovered it in 1994. Only a few scientists are allowed inside, and Herzog...