Posted on 11/03/2004 5:11:47 PM PST by general_re
Darwin's greatest challenge tackled
The mystery of eye evolution
Researchers provide concrete evidence about how the human eye evolved
When Darwin's skeptics attack his theory of evolution, they often focus on the eye. Darwin himself confessed that it was 'absurd' to propose that the human eye, an 'organ of extreme perfection and complication' evolved through spontaneous mutation and natural selection. But he also reasoned that "if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist" then this difficulty should be overcome. 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 light-sensitive 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 light-sensitive 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 [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."
Source Article
Ciliary photoreceptors with vertebrate-type opsins in an invertebrate brain.
D. Arendt, K. Tessmar-Raible, Snyman, Dorresteijn, J. Wittbrodt
Science. October 29, 2004.
Read "Darwin's Black Box" by Michael Behe.
We are the product of intelligent design.
I find it amazing that the evolutionists can believe that all of the universe can spring from a “Big Bang” (the size of the head of a pin) but do not believe that all was created from nothing.
First tell me where the brain cells came from?
And, oh by the way, what went BANG! in the first place?
Election's over, now we can go back to arguing about evolution and whether predestination is true.
The Big Bang is not a biological theory.
I know, but if you believe evolution was the origin of life, you would believe the Big Bang theory too.
The theory of evolution is not involved with the origin of life, but rather with the proliferation of species, after life has begun.
As for the Big Bang, it's a theory that is only about 50 or 60 years old, and there were loads of biologists who accepted the theory of evolution before the Big Bang theory was ever dreamed of. They're quite unrelated.
It's true, however, that a science-minded person, who is impressed by evidence and rational thought, is likely to be favorably impressed by both theories; but that doesn't mean that they're related topics.
As I said, those who are impressed by evidence and rational thought will be impressed by well-supported scientific theories. The evidence supports evolution, and the Big Bang too. What's a rational person supposed to do?
The article mentions "the perfection of the human eye. The human eye is far from perfect. Eagles and falcons have much better eyes than we do.
Think. Answer the question in my first post. What went bang?
I donno. What's your point?
The big bang may well have happened, but it was not the origin of the universe. Something had to have been there to go bang, or it couldn't have happened.
Evolution happens, we know that. It could not have been the origin of life, however, or there would have been nothing to evolve.
The "scientific" explainations don't explain the origins of either. God is the origin.
Now I know we are getting back to normal, more threads exposing the crevos as cranks.
Thank God!
it seems to me, that God could have created a universe with or without evolution operating, and with or without a big bang. If He chose to create a universe in which evolution operates, why do people want to challenge that?
So many fresh, new faces. So many tired, old posts ;)
Giant squids seem to have better eyes too. The evolutionary path is somewhat different though.
I'll jump in here, since this is one of my favorite issues.
Same answer as where God came from . . .
I've argued this design issue extensively on another thread. The eye isn't particularly well designed. That is an opinion. Go out on a clear day, look up at the blue sky and notice all those little black things racing across the sky. Those are the red blood cells feeding the rods and cones that you see with, racing about feeding those same rods and cones. Disturbing your vision.
Because our eyes evolved from light sensitive patches under the skin, they are fed from above. As the eyes deepened for more efficiency, they kept the same configuration.
Squids, however, evolved in the cold water of oceans and their eyes are fed from beneath rather than from above, because it was more efficient to provide nutrients not being exposed to the cold water, from the beginning.
"Intelligent Design" is in the eye of the beholder.
Election's over, out to play placemarker.
Did Einstein wrap his mind around the concept of God always was?
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