Scientists propose that a tiny one-eyed creature that lived nearly 600 million years ago shaped the evolution of eyes in all vertebrates, including humans. The study also links the modern pineal gland to that ancient median eye.
Researchers from Lund University and the University of Sussex examined light-detecting cells across animal groups. They concluded that an early vertebrate ancestor lost its paired eyes after adopting a stationary lifestyle filtering plankton in the ocean.
The creature retained a central cluster of light-sensitive cells that formed a simple median eye. This structure later contributed to the development of image-forming paired eyes when descendants became mobile again.
Dan-E Nilsson, professor emeritus at Lund University, said the results turn understanding of eye and brain evolution upside down. He noted that the vertebrate retina developed from brain tissue, unlike eyes in insects and squid.
The researchers argue that the pineal gland, which regulates sleep through light response, is the surviving remnant of the ancient median eye.
