19 kya. Lascaux cave paintings, Southwest France, discovered in 1940.
below, from Consciousness and the Brain: Deciphering how the Brain Codes Our Thoughts (an excellent book, not mainly about cave paintings)
Deep inside the Lascaux cave, past the world-renowned Great Hall of the Bulls, where Paleolithic artists painted a colorful menagerie of horses, deer, and bulls, starts a lesser-known corridor known as the Apse. There, at the bottom of a sixteen-foot pit, next to fine drawings of a wounded bison and a rhinoceros, lies one of the rare depictions of a human being in prehistoric art. The man is lying flat on his back, palms up and arms extended. Next to him stands a bird perched on a stick. Nearby lies a broken spear that was probably used to disembowel the bison, whose intestines are hanging out.
The person is clearly a man, for his penis is fully erect. And this, according to the sleep researcher Michel Jouvet, illuminates the drawing’s meaning: it depicts a dreamer and his dream. As Jouvet and his team discovered, dreaming occurs primarily during a specific phase of sleep, which they dubbed “paradoxical” because it does not look like sleep; during this period, the brain is almost as active as it is in wakefulness, and the eyes ceaselessly move around. In males, this phase is invariably accompanied by a strong erection (even when the dream is devoid of sexual content). Although this weird physiological fact became known to science only in the twentieth century, Jouvet wittily remarks that our ancestors could easily have noticed it. And the bird seems the most natural metaphor for the dreamer’s soul: during dreams, the mind flies to distant places and ancient times, free as a sparrow.
This idea might seem fanciful were it not for the remarkable recurrence of imagery of sleep birds, souls, and erections in the art and symbolism of all sorts of cultures. …