Some caves have pictures painted on their walls. Scientists went into 11 of these caves in Spain and Portugal. They looked for tiny traces of people from long ago.
The traces are called DNA. DNA is like a tiny set of instructions inside every living thing. The scientists took more than 100 samples. Half came from painted spots. Half came from bare rock nearby.
Five samples had human DNA. Only one came from a painting, in Escoural Cave in Portugal. The DNA is at least 2,000 years old, and probably much older.
The scientists cannot say who painted the pictures. Rock art expert Benjamin Smith said the DNA could come from anyone near the rock, maybe long after the art was made.