2007-10-08 07:54:03 · 12 answers · asked by Anonymous in Science & Mathematics ➔ Zoology
Of course not.
Many invertebrates have none, some single celled animals have one, lots of animals have two - basic stereoscopic vision, its evolved independently many times - and some animals have 8, or even 10.
Also the eyes themselves vary greatly in complexity and quality. Our eyes, though badly 'designed' are pretty good comparing to the pin hole camera a Nautilus sees out of.
2007-10-08 08:11:16 · answer #1 · answered by Leviathan 6 · 1⤊ 0⤋
Basically all animals with a backbone have two eyes. 4 eyed fish have an adaptation to their eyes that get 2 types of vision per eye and blind, cave fish and salamanders have eyes that don't develope. With invertebrates some have many eyes, as your other respondents have said, but then you have to ask "What is an eye"? They have light and motion detectors but not the huge image-processing centre in a brain. No brain as such either.
2007-10-08 21:14:30 · answer #2 · answered by Anonymous · 0⤊ 0⤋
Nope. Some have none (like earthworms), and some, like insects and spiders, have more than 2. I can't think of any animal that has only 1 eye, though....maybe somebody else can.
2007-10-08 07:58:30 · answer #3 · answered by Lucas C 7 · 0⤊ 0⤋
Mammals, birds, reptiles, amphibians, fish have two, except for:
Blind cavedwellers may have none
Four-eyed fish have two eyes with a division between underwater part and air part, so could be considered to actually have four.
Lampreys, hag fish, tuataras have three (a pineal eye).
Insects have compound eyes, either two sets or none.
Spiders have eight simple eyes on the head.
Some mollusks have rows of eyes (scallop), squid and octopus have two excellent eyes.
And so on.
2007-10-08 12:02:01 · answer #4 · answered by Howard H 7 · 1⤊ 0⤋
No, starfish had eyes on the tops of their "stars". Insects often have none or several more (like spiders - who sometimes have 8 eyes).
Mammal-wise. Yes, most mammals have two eyes. Although the golden mole has evolved not to need eyes, and therefore doesn't even have them. It's not just blind, it doesn't even have the ability to be blind!!
2007-10-09 09:36:25 · answer #5 · answered by Gnotknormal 3 · 0⤊ 0⤋
No spiders have 8 (1 on each leg I presume) I think I've heard butterflies have 12000 but I am not sure where. I think all mammals have 2 eyes.
2007-10-08 07:59:35 · answer #6 · answered by Grinning Football plinny younger 7 · 0⤊ 1⤋
Most animals have two eyes but Black Shuck has only one red eye that glares.
2007-10-08 09:04:58 · answer #7 · answered by ? 7 · 0⤊ 0⤋
If you are talking about mammals then yes, but never forget that spider's have 8, earthworms have none and many insects have a much greater number.
2007-10-09 16:37:47 · answer #8 · answered by arachnid-man 2 · 0⤊ 0⤋
There is the four eyed fish. It swims on the surface, one pair for seeing above the surface, two for under.
2007-10-08 11:56:34 · answer #9 · answered by Lee H 3 · 1⤊ 0⤋
No, some craetures have more. For example, spiders apparently have 4 pairs! Weird, hey? x
2007-10-10 02:33:45 · answer #10 · answered by Anonymous · 0⤊ 0⤋