Eyes are about 700-Million-Years Old, Researcher Says

Eyes are about half-a-billion year old and are certainly older than the brain, according to Professor Trevor Lamb of The Vision Centre and Australian National University.

Lamb recently published his work detailing the origins of the vertebrate eyes.

"There are profound questions about the eye which are still not easy to answer because it appeared so very long ago," he said in a news release. "Why did the eye develop? Why are there many different kinds of eye, including one for insects and crustaceans - and one for vertebrates like us? "What kinds of animals needed these incredible seeing machines and how did they use them? How deep into time do the roots of vision go? How has the eye influenced our subsequent development?"

The research found that eyes appeared about 700 million years back when primitive organisms such as algae and corals used light-sensitive chemicals called opsins to detect day from night. These primitive animals had no brains to sense the information from these light sensors.

Genome research on sea-urchins has shown that they have opsin genes, but never went-on to develop eyes like the vertebrates because they lacked a specific pigment. Also, other studies have shown that many organisms didn't really need "eyes" to make use of opsins.

It took another 200 million years for the opsins to clump together and form a primitive type of eye. The opsins not only became more sensitive to detecting light, but also became faster and more reliable. About 500 million years ago, they started looking like the present-day cone cells.

"The first true eyes, consisting of clumps of light-sensing cells, only start to show up in the Cambrian, about 500 million years ago - and represent a huge leap in the evolutionary arms race," Prof. Lamb said. "Creatures that could see clearly had the jump on those that couldn't."

The research shows that as creatures began "seeing things", they required an organ that could process all this visual information, which led to the rapid development of the central nervous system that had to cope with all the data sent by optical sensors.

There are many creatures, some about 500-million-years old, which have the same kind of eye structure as the human, although in a rudimentary form. Our eye is basically a globe-like structure that's packed with billions of photoreceptors. Lamb said that baby squirts, hagfish and lampreys all have basic eye structures. Of course, baby squirts lose their "eyes" once they become adults because they no longer need them.

Lampreys' eyes closely resemble our camera-like eyes and according to Lamb, we might have inherited eyes from our fish ancestors.

The next advancement is the "paired eyes," which have been found by Chinese researchers in crest animals that are thought be about 500-million-years old. Paired eyes helped advanced creatures develop spatial vision- the ability to resolve spatially defined features.

"The advent of spatial vision provided immense survival value to the creature that had it - but the process occurred slowly, over countless steps, with the transition from a simple eye spot to the vertebrate-style camera eye possibly taking as long as 100 million years," he concluded.

The study is published in the journal Progress in Retinal and Eye Research.