Scientists Think Our Eyes Began as a Single Eye on Top of The Head

Researchers suggest vertebrate eyes descended from a worm-like ancestor about 600 million years ago.

The study surveyed 36 major animal groups covering nearly all bilaterians.

Across species, light-sensing cells appear in two places: paired lateral sites and a midline atop the brain.

Paired-position cells steer movement; midline cells indicate day/night and up/down.

An ancestral worm became a stationary filter feeder and lost paired eyes while midline cells persisted and developed into a small midline eye; within a few million years it returned to swimming.