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Monday, November 01, 2004

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 Mystery of evolution of human eye solved

When Darwin's skeptics attack his theory of evolution, they often focus on the eye. Scientists at the European Molecular Biology Laboratory (EMBL) have now tackled Darwin's major challenge in an evolutionary study published this week in the journal Science. They have elucidated the evolutionary origin of the human eye.

Researchers in the laboratories of Detlev Arendt and Jochen Wittbrodt have discovered that the lightsensitive cells of our eyes, the rods and cones, are of unexpected evolutionary origin ­ they come from an ancient population of light-sensitive cells that were initially located in the brain.

"It is not surprising that cells of human eyes come from the brain. We still have light-sensitive cells in our brains today which detect light and influence our daily rhythms of activity," explains Wittbrodt. "Quite possibly, the human eye has originated from light-sensitive cells in the brain. Only later in evolution would such brain cells have relocated into an eye and gained the potential to confer vision."

The scientists discovered that two types of lightsensitive cells existed in our early animal ancestors: rhabdomeric and ciliary. In most animals, rhabdomeric cells became part of the eyes, and ciliary cells remained embedded in the brain. But the evolution of the human eye is peculiar ­ it is the ciliary cells that were recruited for vision which eventually gave rise to the rods and cones of the retina.

So how did EMBL researchers finally trace the evolution of the eye?

By studying a "living fossil," Platynereis dumerilii, a marine worm that still resembles early ancestors that lived up to 600 million years ago. Arendt had seen pictures of this worm's brain taken by researcher Adriaan Dorresteijn. "When I saw these pictures, I noticed that the shape of the cells in the worm’s brain resembled the rods and cones in the human eye. I was immediately intrigued by the idea that both of these light-sensitive cells may have the same evolutionary origin."

To test this hypothesis, Arendt and Wittbrodt used a new tool for today’s evolutionary biologists – "molecular fingerprints." Such a fingerprint is a unique combination of molecules that is found in a specific cell. He explains that if cells between species have matching molecular fingerprints, then the cells are very likely to share a common ancestor cell.

Creationists, including so-called "intelligent design" folk, shroud their Christian faith with pseudoscience. I am not optimistic that this practice will change, so I therefore remain doubtful that this new discovery will be addressed seriously by the ID fundamentalists.

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