extracted from my biology book:
(it's German, so be aware of weird translations
)
There are 4 kinds of "eyes":
1) light sense cell
An earthworm has some of these in his skin. So, he can "see", if it is dark or bright.
If it's bright, he searches earth to get into the dark
2) dump eye
Same as earthwors "eyes", but reduced to a special part of the body, already.
Limpets have this kind of eyes.
The light sense cells are placed in a dump. This way, you're possible, to also "see" from where the light comes.
3) pinhole camera eye
This is already very close to our eye: it's spherical and the closing layer has a pinhole (pupil
) on it. This way, you can see
1)strength of light
2)direction of light
and, which is new,
3) Shapes
nautilus have this kind of eyes.
What's missing to our eye?
The lens!
Why do we need a lens?
To answer this, let's look at the disadvantage of this system:
1) and 3) are contingent on themselves.
If your pupils are wide opened, you can see in the dark quite well, but, since more light comes from more directions, the shape, you want to see gets blurry. So, the darker it is, the blurrier you can see.
The solution?
A lens, which bundles the light, to get it sharp.
For some reason, the sight of colour is the very last step of evolution.
Only a few of the animals, who have got lens eyes, can see colours.
Any type of eyes, that was there before, wasn't able to see colours at all.
Insects have done a quite different kind of development:
Faceted eyes, which are able to see very special parts of light:
They can see more pics/sec (if they wont, they would crash together much more often
)
They can see polarized light. (Don't know why this is important)
They can see more pixels (Your computer monitor would look quite "pixely" for them)
Very often, they can see a part of UV and IR-light.
I.e. Many flowers would be even more colourful, if you'd see UVlight. So bees can see much of this light...
But every facet is a lens, so it's just even more complex than ours.
Although we can't see very much of the spectrum of light, the part we CAN see, we can see most detailed in animality
