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Author Topic:   Evolution of the Eye - Nerves in the air?
Equinox
Member (Idle past 5141 days)
Posts: 329
From: Michigan
Joined: 08-18-2006


Message 1 of 11 (441982)
12-19-2007 1:28 PM


Eye question:
A discussion with my son made me wonder about the course of eye evolution. I’m pretty familiar with the easy and sensible step by step evolution of the eye from a patch of light sensitive cells, to a cupped patch, to a nautilus like eye, then with the addition of a cornea, and so on up to what we have today. What we have today includes the fact that the rod and cone cells are upside down, forcing the nerves to come off them into the eye, and so the nerves then bundle up and leave the eye through a hole in the back of the eye, resulting in our “blind spot”. A really stupid “design”.
Now, that suggests to me that the earlier stages also had this “nerves out the front” setup, so back to the cup stage, the nerves would have been inside the cup. Farther back, the nerves would have been sticking up in the air from the patch of light sensitive cells. I would have imagined that the light sensitive cells might have evolved from skin cells with the enervation from the bottom, but if that were the case, then wouldn’t the whole bad design have been avoided?
So - I know we have examples of the intermediate stages, both light sensitive cells as well as cups, and so on. Do some of them have the nerves sticking up? Or, are there other ideas about how this arrangement evolved, and from what precursors on the skin?
-Equinox
"Biological Evolution", I would think.

Replies to this message:
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AdminWounded
Inactive Member


Message 2 of 11 (441986)
12-19-2007 1:40 PM


Thread moved here from the Proposed New Topics forum.

  
Taz
Member (Idle past 3291 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 3 of 11 (442000)
12-19-2007 3:30 PM
Reply to: Message 1 by Equinox
12-19-2007 1:28 PM


Equinox writes:
A really stupid “design”.
I wouldn't say stupid, but it is a design that could have been avoided if the designer was indeed intelligent.
For example, the designer seemed to have favored the octopus a lot more than us. From an evolutionary perspective, the octopus took a completely different path of eye evolution. The nerves are in the back rather than the front. The advantage of this is that the light doesn't have to go through blood vessels and nerves to get to the sensitive rods and cones, like what happens in our case.

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MartinV 
Suspended Member (Idle past 5828 days)
Posts: 502
From: Slovakia, Bratislava
Joined: 08-28-2006


Message 4 of 11 (442001)
12-19-2007 3:45 PM
Reply to: Message 3 by Taz
12-19-2007 3:30 PM


We know little about the reason of nerves to be in front of retina.
During ontogenesis when brain develops there are processes which establish connection between eye-nerves and brain cells responsible for vision. These connections are established during so called test vision, whene there are not present light signals entering the eye. Yet those signals are simulated in dry run in eye nerves.
The vision of octopus should be reconsidered if such precise connections are possible to be made during ontogenesis as for example in eagles.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 5 of 11 (442003)
12-19-2007 4:11 PM
Reply to: Message 1 by Equinox
12-19-2007 1:28 PM


So - I know we have examples of the intermediate stages, both light sensitive cells as well as cups, and so on. Do some of them have the nerves sticking up? Or, are there other ideas about how this arrangement evolved, and from what precursors on the skin?
Either way up the eye develops the top layer(s) need to be transluscent, and thus it is possible to have skin cells, nerves, retina cells for the initial light sensitive spot.
As taz pointed out the octopuses, squids, nautilus all have the retina light cells on the light side and the nerves behind.
It could be a flip of the coin for one or the other, or there could be some slight protection from UV for those venturing on land (or near the surface of the water).
Enjoy.

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This message is a reply to:
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EighteenDelta
Inactive Member


Message 6 of 11 (442010)
12-19-2007 4:35 PM
Reply to: Message 1 by Equinox
12-19-2007 1:28 PM


One shouldn't assume that the body of the first creature to start developing a light sensitive cluster of cells had an opaque body. An animal with a transparent body could have light sensitive cells as part of their nervous system, they would only need to migrate near the surface when the body becomes opaque.
-x

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RickJB
Member (Idle past 4990 days)
Posts: 917
From: London, UK
Joined: 04-14-2006


Message 7 of 11 (442130)
12-20-2007 9:50 AM
Reply to: Message 1 by Equinox
12-19-2007 1:28 PM


There is an artcle here that explains one theory as to why the nerves are reversed. It centres on embryonic development. This article is over twenty years old, however, so things may have moved on.
Link here

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 8 of 11 (442293)
12-20-2007 5:43 PM
Reply to: Message 7 by RickJB
12-20-2007 9:50 AM


I don't quite get that from the article
quote:
Fortunately, we have evidence far better than fossils to show us how eyes may have developed. Not only can we learn a lot about the stages of ocular evolution from the study of how eyes develop in the vertebrate embryo, organisms still living exhibit photoreceptor organs smoothly spanning the structural spectrum from the "eye-spots" of single-celled organisms to eyes even more complex than the human eye.
Rather they are using the evidence from stages recorded by embryonic development for how the eye evolved.
Thanks

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Equinox
Member (Idle past 5141 days)
Posts: 329
From: Michigan
Joined: 08-18-2006


Message 9 of 11 (442942)
12-23-2007 6:48 AM
Reply to: Message 6 by EighteenDelta
12-19-2007 4:35 PM


Thanks. Between posts 6 and 7 I see now how this evolved. Easy.
Happy Solstice-
-Equinox

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tymygy
Junior Member (Idle past 5927 days)
Posts: 8
Joined: 01-04-2008


Message 10 of 11 (445990)
01-04-2008 4:09 PM


has anybody ever stopped to think... maybe that is how the eye evolved.. but what about the organs the brains the nerves the veins... what about feelings..
and light sensitive opague couldnt have made eyes.. becuase we are not only sensitive to light.. otherwise we couldnt see in the dark after 30 minutes... plus if those light sensitive opaque migrated to were our eyes are now.. how could they have known to attach to the brain? and how did they know to evolve colors.. or why did our skull have bones that grew right around them.. without the brain thinking that the eyes can be removed in place of the bone...

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 11 of 11 (446363)
01-05-2008 9:49 PM
Reply to: Message 10 by tymygy
01-04-2008 4:09 PM


and light sensitive opague couldnt have made eyes..
Ever felt the sun on your arm?
Enjoy

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we are limited in our ability to understand
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RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
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