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No life on earth has eyes anywhere else but on their head, why is this?

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posted on Jul, 9 2009 @ 09:52 AM
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only Spiders on earth has more than two eyes. Now some people might say flys but these animals dont have those eyes separated. The many so called eyes on a fly for instance are all part of the same eye. It would be more accurate to say that a fly has two eyes made of many pupils.

So ok spiders the one creature on earth with more than two eyes and we are not even sure if all of them are functional as complete eyes. So it is possible that no creature on earth does in fact have more than two eyes.

But what is certain is that no animal has eyes on its back or other body part seperate from the skull area. This might be because the signals that eyes send to the brain need to be within close reach of it. Or that all brains of creatures on earth are limited in their processing power of dealing with more than two eyes.

But would it not make evolutionary sense for a creature to have more eyes, perhaps on its back or tail end?

So this to me seems almost like either there is some MAJOR barrier to having more than two eyes in earth creatures or that life was engineered and the idea of having more than two eyes or eyes else where besides the skull is important.

Either way it seems like its a major engineering problem, because when it really comes down to it having eyes else where on the
body especially in the back side would be a big benefit.

Special Note--- I do not consider antennae or fine hairs eyes though they have some similar functions still they are not eyes and does not answer why it seems to be limit to the number of eyes on creatures.




posted on Jul, 9 2009 @ 09:59 AM
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Good question!

I think bats deserve some type of attention in this thread. And do creatures like jelly fish have eyes?



posted on Jul, 9 2009 @ 10:17 AM
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In the case of vertebrates (especially large ones) locating the major sensory organs in close proximity to the brain makes good sense in terms of speed getting info to the brain for processing. The skull also provides bony protection for the delicate eyeballs as well as the inner ear plus the ability to quickly turn the head in 3 dimensions to focus on something of interest. A bipedal stance also gives the eyes the highest possible vantage point for scanning the surroundings.

I always found it fascinating how the actual 'mounting' of the eyes varies between predators and prey. Predators like dogs, cats, bears, man etc have 2 forward facing eyes while prey like horses, antelopes, fish, birds etc have eyes on the side of their head allowing them to actually see behind them with little movement of the head (hardly any blind spots in their field of view). Horses and donkeys and probably all herd type vegetarians can actually see all 4 feet as they move which allows them to avoid holes and obstacles like rocks.

2 eyes is the minimum for depth perception and distance gauging (stereo vison), more than that seems a bit redundant.



posted on Jul, 9 2009 @ 10:23 AM
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reply to post by Desolate Cancer
 


The best explanation is a combination of several factors.

For starters, two eyes are better than one because you get depth perception. One eye can be handy over no eyes, but without at least two you can not judge depth very well.

More than than two eyes then starts to stress out the brain. All the information coming in form eyes has to be processed and interpreted by the brain. If you add more eyes, that is more processing.

As for them being on the head, this makes them very close to the brain for faster transmission. For tall humans, it can take up to a tenth of a second for nerve signals to get there. Well when something is lunging at you with the desire to eat you, you can as much reaction time as possible.

So in terms of evolution, two eyes would be the ideal. Things with many eyes all over the body would struggle to sync up the information in their head. It would mean the brain requires much more energy and thus food, oxygen, and other nutrients.

Flounder, which over the last few million years saw the lopsided group win out and become the norm with both eyes on one side of the head, show that even when the eyes are better off some where else, it is still two near the brain that win the game of natural selection.

I hope this helps.

BTW, you can find mutants in most animals species that have more or less than two eyes. They don't survive well, even the ones with more.



posted on Jul, 9 2009 @ 10:29 AM
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The eys are always evolved in front of the organism because creatures move forward. Thus being able to see or sense whats in front of them whether it be food or danger. This is a definite plus in terms of evolution. If an animal moved in reverse then the eyes would most likely eventually move toward the rear over thousands of years in an attempt to keep the species alive. The organisms which move around and hunt or must survive by eluding predators must have a sense of the direction in front of them where they are moving or the species wouldnt stand a chance of surviving. Everything is the way it is because it works and is efficient. The eyes in the back simply wouldnt be efficient for survival so therefore it doesnt exist. If an animal had a mutation with eyes in the back alone it wouldnt survive to procreate and spread the gene. Now I suppose if a human developed a mutation which consisted of an extra set of eyes in the rear along with ther regular eyes that it would be a definita advantage, but Im willing to bet that they'd have trouble getting a date. lol



posted on Jul, 9 2009 @ 12:39 PM
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I agree that having eyes in the back of the head, or for an animal at the back of the body would seem to make a lot of sense.
Most animals are able to twist their outer ears around to hear what is behind them. It is amazing how much information there is in sound. Its the kind of information that keeps one safe.
I suspect that with excellent forward vision and and excellent capacity for hearing whats behind you; then you really have a very efficient system for personal safety.

I think that as we humans have much less sensitivity for sound than most animals, we really could use an extra eye facing backwards. Wouldn't that just help enormously in a party situation (to see who's talking behind your back, or on a jungle trek to see who is stalking you.



posted on Jul, 9 2009 @ 12:59 PM
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Very simple: where there are eyes - that is head



posted on Jul, 9 2009 @ 01:44 PM
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reply to post by DangerDeath
 


Hey Cancer I really liked your question. I have never thought of it before or heard anyone ask it in my life.

I have asked why "two separate sexes" instead of "one that can procreate with itself" or "one that can procreate with any other member of its species" would not beat out genetically having two separate sexes.

Your idea about having , as my Mom used to tell me when I was a kid whenever she caught me doing something wrong, "Eyes in the back of her head" is a GREAT question!

It must have something to do with optic nerve length between eyeballs and the brain?

Would not having a set of eyes to cover your 6 be FAR more beneficial to a species?

Evolutionarily speaking you would think being able to maybe not fight from your 6 but at least use vision to detect incoming threats from your backside to be 100% more likely to go on to breed and reproduce?

Maybe that mutation never occurred when eyes were first forming and adapting to the environment?

Maybe that mutation DID occur but got wiped out not from not being superior but a natural accident killed off multi-eye life?

Like I said GREAT question.



posted on Jul, 9 2009 @ 01:49 PM
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closer to the brain, you'd lose vision if they were in your feet, with all the work the body does, the signals would glitch



posted on Jul, 9 2009 @ 02:08 PM
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Just a thought...one post stated that the eyes are close to the brain for speed of nerve transfer...surely if the optic nerve where 30ft long the time lag would be imperceptible.

Another...the eyes are at the front because creatures move in that direction...what about species of crabs they move sideways, don`t they.?
On crab anatomy it shows eye stalks and says that they are useful for directing food into the mouth...but creatures that have two articulations, shoulder and elbow, cannot help but hit the mouth...try it yourself, raise your arms to a crucified position then bend at the elbow towards the face, slap in the mouth.



posted on Jul, 9 2009 @ 02:24 PM
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I think that quest had the right answer. I did some quick searches and found that eyes take up a HUGE amount of brain power.

In squids and octopus it can be HALF of the entire brains capacity used for the eyes.

In some birds the eyes weigh more than the entire brain.

Things like eagles who have very powerful eyes that see a great distance have eyes that cannot adjust for refraction like when you put a rose stem in a glass vase with water the stem will appear crooked?

Well when eagles hunt fish the eagles eyes do not adjust for it and scientists have watched a great deal of young eagles hunting fish for the first time completely missing the fish they are diving for because of refraction. They use a large chunk of the small bird brain to do adjustments for the refraction.

If we factor in that eyes evolved from simple light receptors that allowed the first life on Earth to use light sensors to move towards light for heat or whatever purpose maybe there were a great many light receptors to detect light.

But if the species had not developed a brain to process the extra information from extra eyes it would not be able to process the information.

I also found out from searching that Humans have the largest Brain to Body ratio of any living thing on earth.

So bigger brain equals more processing power to handle the massively brain intensive eyeball.

I think the best bet for a species to develop additional eyes that could be used and have the information processable would be humans.



posted on Jul, 9 2009 @ 04:29 PM
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You wouldn't get a very good view out of your arse, would you.




posted on Jul, 9 2009 @ 04:41 PM
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What about the creatures that have very large eyes in comparison to the skull and brain cavity.? ..this would leave very little brain power left for anything else.

[edit on 9/7/09 by ironbutterflyrusted]



posted on Jul, 9 2009 @ 04:53 PM
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The speed of impulse transmission in the optic nerve is 423 miles/second, this does not fit well with the idea of needing the eye close to the brain.


on the crab articulations...I think that this could even apply to the four legged creatures, like a giraffe, maybe it too could reach its mouth with a toe if it was anatomically possible to do so, a question of proportion.



posted on Jul, 9 2009 @ 05:03 PM
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Originally posted by ironbutterflyrusted
What about the creatures that have very large eyes in comparison to the skull and brain cavity.? ..this would leave very little brain power left for anything else.

[edit on 9/7/09 by ironbutterflyrusted]


I do not think it has to do with eye to brain size ratio more of the capabilities of that type of eye with that type of brain.

We as humans can distinguish between something like 256 different colors I think?

There are some types of desert ant that can see differences between colors that the human eye cannot.

I also understand that bees can very clearly focus on things less than an inch from their eye. For a human we need equipment aid to focus on things that close to our eyes.



posted on Jul, 9 2009 @ 05:47 PM
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Guess what a giraffe could bite its toenails.






posted on Jul, 9 2009 @ 06:10 PM
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I was thinking along the lines of- Loris, Tarsier, Bushbaby etc...I take your point on what type of eye the creature has.



posted on Jul, 9 2009 @ 06:11 PM
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reply to post by ironbutterflyrusted
 


Wait there is something strange about the number of legs that giraffe has....I will continue to analyze the drawing to determine what it is.



posted on Jul, 9 2009 @ 06:25 PM
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If the leg was able to more across a greater circumference, it to could slap itself in the face...just like us and the crab that uses its eyes to see where the food is in comparison to the mouth...my point being that many creatures are proportioned to reach the mouth with a limb, but not mechanically able to.

good eh.?



posted on Jul, 9 2009 @ 07:16 PM
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Eyes have to be in your head. If they were anywhere else you would not get a field of vision in relation to your height. If they were half way down your body your upper body would be out your field of observation. The higher the better!

[edit on 9-7-2009 by purplemer]



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