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."
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.
Dark is just the absence of light. Wouldn't the sensor just be responding to lowered light levels?
Respectfully,
O.C.
This is extremely cool. The sensor fires when it gets dark. The other light sensors respond to light. If you want to catch a frog, you must not block its light or it will be [kersplush] gone.
Funny how these anti-science buffoons cannot properly construct even a single coherent question.
I would be happy to discuss Krsna and his teachings. Suffice it to say his teachings are a parenthetical cult of Hinduism. Not a great deal of difference. Budhism is also a cult of Hinduism. We have plowed that ground and it only leads to the void. I ask one question only. I am not trying to be tricky. Will you tell me role of the 1st and 2nd law of thermodynamics as it relates to Origins.
Jesus Christ said:
Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
- Revelation 3:20
Jesus Christ is standing at the door of your heart right now. Imagine! The architect of the universe, the One who made you and I, wants to call us friend! It is too great to fathom and I am filled with joy!
Funny that! All your cults look the same to us too.
Budhism is also a cult of Hinduism. We have plowed that ground and it only leads to the void.
If you say so...
I ask one question only. I am not trying to be tricky. Will you tell me role of the 1st and 2nd law of thermodynamics as it relates to Origins.
Perhaps you could try to undumb-it-down a bit and be a bit more specific. And spurious capital letters are not needed.
If you would know of Him, you must consider His teachings and open the door of your heart. Make yourself available to Him and He will do as he promises in Revelation 3:20. The alternative is to spend an eternity separated from the One who made you. What profit is there in that?
Fool! Zeus is king of the gods. But don't take my word for it. Read the Iliad. The truth is there.
Only after he killed Uranus!
Nothing to see here - move along, little doggy!
Or something like that.
Secret message received.
All the best, O.C.
That makes for a really short biology textbook. A lot of us prefer to know more details about "how things work".
Okay, that just sounds painful...
Are so, actually, but I won't confuse you with the evidence.
What "dark area" are you talking about? The article mentioned no such thing, so you might want to explain your non sequitur.
It couldn't be that God was getting it ready, oh perish the thought /sarcasm
If you have evidence for such a hypothesis, feel free to present it. In the meantime, sarcasm is a poor substitute.
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