Researchers have traced the origins of vertebrate vision to a tiny cyclops-like ancestor that lived nearly 600 million years ago, long before humans walked the earth.
The study, conducted by Lund University and the University of Sussex and published in Current Biology, found that this distant ancestor had a single eye located on the top of its head.
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Scientists say the primitive “median eye” eventually evolved into the pineal gland in the human brain, reshaping long-held ideas about eye and brain development.
Lund University (Sensory Biology) Professor Emeritus Dan-E Nilsson described the findings as a surprising shift in understanding vertebrate evolution.
The cyclops-like ancestor was a small, worm-like organism that led a sedentary life, filtering plankton from seawater.
Although it once had some form of paired eyes, researchers say it is unclear whether these were simple light-sensitive cells or basic image-forming organs, and the creature later lost them.
A cluster of light-sensitive cells remained at the centre of its head, developing into a simple median eye that could sense light, track day and night, and determine orientation.
Millions of years later, as descendants returned to a more active, swimming lifestyle, new paired eyes formed from parts of the same median eye to meet renewed demands, helping explain why vertebrate eyes differ from those of insects and squid.
