Why didn't mammals evolve eyes in the back of the head?

Question

I'm serious, why would a mammal, especially a herbivore, not evolve eyes on the back of its head. Surely it would have been very useful.

I understand it would have been hard but if initial eyes were evolved, then surely eyes in the back of the head should also be possible.

And would the brain be able to analyse the information from all four eyes and create the picture?

Answer 1

Because the eye is so complex it could take millions of years. Many animals have no need for eyes in the back of there head because they have wonderful hearing, helping them sense moement behind them.

Answer 2

all predators have eyes located in the front, like humans. Humans are predators because we like all predators have the ability to judge distance to prey. all herbivores have eyes on the side of their head which gives them the unique ability to see on the side AND behind them for protection against predators. Animals do not evolve because of need but through genetic mutations, and selective breeding, and genetic drift.

Answer 3

Evolution only moves forward.

A lot of herbivores do have their eyes mounted further from the front of their faces, which gives them a wider peripheral vision.

Answer 4

Because they didn't evolve, they were created to be a certain way. If they had just, evolved without something with intelligence causing it to happen, the thoughtless matters that makes them up would have gotten all screwy and there'd be eyeballs who knows where, humans would have tree branches and fish would be flying dead.

Answer 5

They already have, in effect.

Many herbivores and prey animals do have 360-degree vision. Many others have nearly that range. Their eyes are located far to the side of their heads to facilitate this. Predators on the other hand, usually have forward vision, many times to the point of binocular vision for judging distance to their prey.

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Answer 6

The natural selection process says that if an attribute or feature caused a species to survive better than that feature would continue.  My guess is that if there ever were animals that had this feature, it just wasn't enough to keep them alive.  The predator was probably faster, better at fighting, smarter, etc. and eyes in the back of the head just wasn't good enough.

The other option is that this is probably a pretty big jump from where many species are at and they may or may not be smart enough, as you mentioned, to put the picture together in their mind.  Insects do this though as flies and other bugs have hundreds of lenses or "eyes".

Lastly, it just may not be long enough.  Natural selection and evolution take millions of years.  Just think about how much time it took human's to evolve from single celled organisms.  Maybe eyes in the back of the head are still a feature that's coming in the next several million years!

Answer 7

If you'll note the type and positioning of the eyes on many species, you'll be able to tell whether it's typically a predator or prey animal. Prey animals tend to have eyes situated on the sides of their heads, and the eyes tend to be bulbous. This gives them a nearly spherical field of view, so they can see behind them to a certain extent - certainly they can pick up motion in their peripheral vision (you do this as well) and then they'll turn to look with the center of their vision.

Predators' eyes tend to be on the front of their head. This allows more overlap in the eyes' fields of view, allowing for a greater field of depth perception. It's more important for predators to have depth perception than field of view, which is why they evolved this way.

An interesting combination of this is chameleons. Their eyes are independantly moving and focusing, allowing them to look all around them. They tend to move around with their eyes looking in various directions, but whenever they spot an insect, they bring both eyes onto the target, allowing for depth perception so that they can aim their sticky tongue accurately. It's really neat to watch, actually.

I'm 100% certain that any animal that evolved with eyes on the back of its head would also have the visual cortex in its brain capable of decoding the information. Otherwise, the eyes would be useless and it would likely not succeed, thus ending that genetic trait's bloodline. Spiders have many eyes, and their brains can interpret the signals quite well.

Answer 8

This is a very good question, but I don't believe anyone can give you a "true" answer because no one can know why mammals are the way they are.

But you get a star from me, because I have no idea how to answer it without making something up!

EDIT: haha, now everyone else said smart stuff.....ah well

Answer 9

I would have to answer simply, it wasn't a genetic mutation that made it to the next step. Perhaps if it had, it would have survived. All a matter of chance, I believe...

The brain could handle it and would have been a useful tool for survival. Not everything is as perfect as it seems. Yes everything seems to work, but if a species out-evolved others and was vastly superior (ie 4 eyes) it would survive and possible overpopulate.

Answer 10

Because it is not necessary as all species have developed other senses like smell,hearing,etc. Like cats: their whiskers detect vibrations all around them and their brain processes each different vibration to alert them as a threat or just lunch.

Answer 11

they didn't need to. a lot of animals, horses for instance can see in a full circle around (when there head is down) them with just 2 eyes, One one each side of the head. just try to sneak up on them while there eating, but be careful, you may get kicked.

Answer 12

Many animals have a wide field of vision already.  Also they can move the head and neck easily.  They also have great hearing and smell.

It is pretty simple.  If the characteristic did not evolve and is not present in today's animals, then the conditions that exist now have been successful, therefore no need for improvement.  Obviously eyes in the back of a head is not possible, because if it was, it would have happened.