A one-eyed creature that lived 600 million years ago is among humanity's oldest ancestors and gave rise to our modern eyes, according to a study from Lund University. Researchers analyzed light-sensitive cells in various animal groups to explain why vertebrate eyes differ from those of others. The study was published in the journal Current Biology.
A study from Lund University reveals that a one-eyed, worm-like organism from 600 million years ago is a common ancestor to all vertebrates, including humans. This cyclops-like creature lived sedentary as a burrowing filterer, sifting plankton from seawater, which meant it had little need for paired eyes for movement and orientation.
"They were burrowing filterers, sat still and filtered plankton from seawater. Then the paired organs, which are really for steering when moving and knowing where you're going, weren't needed," says Dan-E Nilsson, professor emeritus in sensory biology at Lund University.
Through evolution, the organism lost its paired eyes but retained a group of light-sensitive cells in the middle of its head. These cells were used to monitor circadian rhythms and determine up from down.
Eyes in vertebrates, like humans, differ significantly from those in invertebrates such as insects, crustaceans, and octopuses. "The kind of light-sensitive cells that invertebrates have for their paired side eyes are not the kind we see with," explains Nilsson.
Through a comprehensive analysis of light-sensitive cells in all animal groups, researchers discovered that modern vertebrate eyes evolved from the single eye on the head when the ancestor began swimming and living an active life. The human retina developed from the brain, unlike insects' and octopuses' eyes which developed in the skin on the sides of the head.
"It has always been a small mystery why our eyes are different... We haven't understood why it was like that, but now we do. The pieces fell into place," says Dan-E Nilsson.
The study was published in the journal Current Biology.