Skip to comments.Darwin's greatest challenge tackled
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 worms 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 todays 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."
Ciliary photoreceptors with vertebrate-type opsins in an invertebrate brain.
D. Arendt, K. Tessmar-Raible, Snyman, Dorresteijn, J. Wittbrodt
Science. October 29, 2004.
Man! God's going to be pissed that you found out his secret!
The eye cells have it!
Salamanders don't get glaucoma because they can readily regenerate retinal cells. The same is true of newts, frogs, and some types of fish. "We're trying to understand the remarkable regenerative powers of these lower vertebrates, and through this understanding, develop strategies to stimulate regeneration in the human retina," Reh said.
While salamanders can regenerate retinal cells through their life, many other species lose this ability as they age. "At some point in each species life cycle, the stem cells in the retina make a transition from a regenerative cell to a cell that will make a scar in response to injury, like the cells that cause scars in the spinal cord," Reh said. "Chickens make the transition a few weeks after hatching in most of their retina, though they retain some limited capacity to regenerate retinal cells throughout life. In rats, it's only a matter of a few days after the cells are generated that they lose their ability to regenerate other retinal cells."
Human retinas seemingly can't repair themselves, yet in recent studies human retinal cells have grown new neurons when cultured in the laboratory. "The hope is that many of the molecular and cellular mechanisms necessary for regeneration, that serve amphibians so well, are still in place in humans," Reh said. "Future studies from the nervous system, as well as other organ systems, should enable us to define the roadblocks in the regenerative process, and develop strategies to go around them."
Now that's real interesting, a light sensitive cell "evolving" in a dark area. It couldn't be that God was getting it ready, oh perish the thought /sarcasm
Could be. Perhaps our knowledge of how He did it is evolving as well ;)
"They have elucidated..."
Well, he just lost half the Creationists by using that big word.
I see. ;)
Well, he just lost half the Creationists by using that big word.
He sure lost the dyslexics--they think he's discussing plane geometry...
No, "Eye" see.
For a well-thought out explanation go here -- and then read the book.
How long until a Christian brings in John 9:41 out of context?
Jesus said, "If you were blind, you would not be guilty of sin; but now that you claim you can see, your guilt remains."
Didn't Hume base an early version of argument-from-design upon the eye?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.