Monday, November 01, 2004

The evolution of the vertebrate (human) eye

Science -- EMBL About Us - News and Communication - Press - Press Release 28 October 2004 - Darwin's greatest challenge tackled: the mystery of eye evolution
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 [University of Mainz, Germany]. "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.

Scientist Kristin Tessmar-Raible provided the crucial evidence to support Arendt's hypothesis. With the help of EMBL researcher Heidi Snyman, she determined the molecular fingerprint of the cells in the worm's brain. She found an opsin, a light-sensitive molecule, in the worm that strikingly resembled the opsin in the vertebrate rods and cones. "When I saw this vertebrate-type molecule active in the cells of the Playtnereis brain – it was clear that these cells and the vertebrate rods and cones shared a molecular fingerprint. This was concrete evidence of common evolutionary origin. We had finally solved one of the big mysteries in human eye evolution.

There was a Wired magazine article recently in which a fairly bright geek celebrity argued for intelligent design based on the computational impossibility of evolving anything like a human cell.

That article, as well as most of the "intelligent design" literatrure, perpetuates a deep and common misunderstanding about what Darwin said and about natural selection. Let me correct that misunderstanding in five words. We are not the point.

Or, in other words ...

This discovery demonstrated a starting point, from which it is possible to imagine a series of steps, each of manageable probability, that would lead to the design of the verterbrate eye.

But wait, say creationists -- what are the chances that all those steps would occur? Aren't the odds a bazillion to one?

Well, say the evolutionists, yes they are. A bazillion to one.

That's the point.

Start the game over again, role the 200 sided dice 10,000 times -- you'll get a different sequence of numbers. A very different light sensor. But, that light sensor will also have a plausible path of descent from the same worm brain.

Start over from those early terrestrial cells. Run the simulation forwards. Maybe you'll end up with sentience. Maybe you'll end up with a bacterial soup. Maybe you'll end up with something else. You will never, however, end up with anything that looks anything like us.

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