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Author Topic: Are all mammal eyes basically the same?  (Read 7141 times)

Offline DoctorBeaver

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Are all mammal eyes basically the same?
« on: 04/10/2009 14:25:24 »
If you take an eye from a human, a mouse, and a cat they look different but, as far as I am aware, they work in basically the same way. Insects, on the other hand, have very different eyes. Are all mammal eyes basically the same or are there any mammals whose eyes differ in form or functionality? Also, are there any animals from different kingdoms (if that's the correct taxonomical word) whose eyes are similar? I.e., are there are types of, say, fish whose eyes are the same as that of an insect?


 

Offline RD

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Are all mammal eyes basically the same?
« Reply #1 on: 04/10/2009 18:48:49 »
Are all mammal eyes basically the same or are there any mammals whose eyes differ in form or functionality?

http://www.thenakedscientists.com/forum/index.php?topic=25487.0

 
 

Offline DoctorBeaver

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Are all mammal eyes basically the same?
« Reply #2 on: 04/10/2009 23:55:44 »
That doesn't answer the question at all. I looked at that thread before I posted this.
 

Offline RD

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Are all mammal eyes basically the same?
« Reply #3 on: 05/10/2009 00:05:58 »
You did ask about weird fish eyes ...


http://www.ryanphotographic.com/anablepidae.htm

Quote
The four-eyed fishes only have two eyes each, but the eyes are specially adapted for their surface-dwelling lifestyle. The eyes are positioned on the top of the head, and the fish floats at the water surface with only the lower half of each eye underwater. The two halves are divided by a band of tissue and the eye has two pupils, connected by part of the iris. The upper half of the eye is adapted for vision in air, the lower half for vision in water.[1] The lens of the eye also changes in thickness top to bottom to account for the difference in the refractive indices of air versus water.
http://en.wikipedia.org/wiki/Anableps_anableps
« Last Edit: 05/10/2009 00:12:26 by RD »
 

Offline JimBob

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Are all mammal eyes basically the same?
« Reply #4 on: 05/10/2009 02:45:41 »
Basically all vertebrate eyes are similar, having evolved from the same template. However, other types of animals - insects as you have said - have different types. Also, different eye types are found in octopus and squid, crabs, and, surprisingly enough - a very old arthropod, the horseshoe crab. Other arthropods have different eye types. 

Too add to the confusion - there are all sorts of other types of animal eyes as well.


And yes, - all mammalian eyes are basically the same.
« Last Edit: 05/10/2009 02:49:57 by JimBob »
 

Offline DoctorBeaver

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Are all mammal eyes basically the same?
« Reply #5 on: 06/10/2009 01:22:58 »
Thank you, Jim, and, of course, everyone else who has answered.
 

Offline LeeE

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Are all mammal eyes basically the same?
« Reply #6 on: 06/10/2009 16:38:59 »
Interestingly, all the different types of eye are directly related and their development via evolution is pretty well understood.  What is also interesting is that all of the different stages of development are still found in different types of organism today.

The 'first' eye was simply a small patch of light sensitive cells, and all it could do was register different levels of light intensity.  It gave a survival advantage to  an animal possessing them though, because if it detected a rapid change in the amount of light falling on it, it could possibly be the shadow of a potential predator.

The simple light sensitive patch 'eye' then developed into a pit, with the light sensitive patch at the bottom, or floor, of the pit.  This gave a degree of directionality to the source of light; if the light is falling from one side then part of the floor of the pit will be in light and part will be shaded by the pit walls.

The next stage of development was for the pit to deepen and enlarge into a cavity behind a reduced size pit opening, resulting in a pin-hole type camera.

The problem with the pin-hole type eye though, is that the cavity can fill with dirt etc. so the next stage was for the cavity to be filled with transparent mucus, allowing the dirt to be flushed out.

Eventually, the stage was reached where the mucus at the opening would harden, so the dirt would stay on the surface where it could be wiped off by eyelids.  Finally, the hardened surface evolved into a focusable lens and the iris developed to allow the regulation of the amount of light entering the eye.

I believe compound eyes are a trade-off between having a movable eye and one that is fixed; while insects do have movable parts in their exoskeletons, such as their mouths and limbs, at some point they ended up with fixed eyes (with the advantage that all the controlling muscles etc. could be omitted).  Although I think it would have been possible for a fixed non-compound eye to evolve that would have had similar capabilities, it would have been pushing the limits of optics a bit, and would have been very susceptible to damage.  Compound eyes, on the other hand, can use relatively simple optics to give the same field of view whilst also being more resilient to damage.
 

Offline JimBob

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Are all mammal eyes basically the same?
« Reply #7 on: 06/10/2009 17:04:05 »
I believe to the best of my recollection that the evolution of mollusk eyes, arachnid eyes and insect eyes and  the other types of eyes arose from parallel evolution, not the same root organism. This comes from the study of the way pectin "eyes" have evolved late in the development of these mollusks.   
 

Offline DoctorBeaver

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Are all mammal eyes basically the same?
« Reply #8 on: 06/10/2009 23:20:24 »
I also seem to remember reading that some creatures' eyes had evolved independently along totally different principles.
 

Offline JimBob

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Are all mammal eyes basically the same?
« Reply #9 on: 07/10/2009 00:16:59 »
Yep,

Parallel evolution is a process in which organism form the same design for the same function. For living in water, fish, Mosasaurs and Plesiosaur (reptiles), and cetaceans and seals (mammals) all have the same streamlined shape. Yet the reptiles and mammals developed on land and went back to the water, developing the same shape for the same environment.

Eyes seem to have done the same. All vertebrates came from the same protochordate lineage. But the other types of organisms have a different evolutionarily lineage. This is true of molluskan eyes which have developed at least twice. The eyes of Cephalopods are similar - but not identical - in design to mammalian eyes. But the pectin "eye" is vastly different. I can only have been developed independently.
 

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Are all mammal eyes basically the same?
« Reply #9 on: 07/10/2009 00:16:59 »

 

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