Our eyes developed from a cyclopean worm 600 million years ago and its lone eye is now our pineal gland. 'Remnants of the ancient parietal median eye from our distant ancestor actually remain in our heads today, transformed into the pineal gland. The pineal gland is a light‑sensitive organ in the vertebrate brain. It produces the hormone melatonin, which helps regulate the body’s circadian rhythm. “It’s mind‑boggling that our pineal gland’s ability to regulate our sleep according to light stems from the cyclopean median eye of a distant ancestor 600 million years ago,” concludes Dan‑E Nilsson.'