So I was gazing soulfully into my cat’s eyes last night (some people say I’m a bit too attatched, but I shoot these people, and bury them in shallow graves) and I noticed that you can’t see the whites of her eyes, no matter which way she looks. This is true of most animals, unless I’m forgetting some. IIRC, even most primates are pretty much the same–maybe great apes, less so?
Why do humans have such small pupils/irises (the pupil can, of course, dilate so that it the iris shrinks down to almost nothing) compared the size of our eye-opening? It seems like a great expanse of sensitive, delicate tissue that doesn’t do anything for us, but yet is exposed to air and dust and grit and pathogens. Does it have something to do with how we see, allowing us to redirect our gaze through a greater range without turning our heads? Or does it have a social function, allowing other humans to tell with greater ease where we are looking? And are there other animals that have very prominent sclera?
You’ve obviously never owned a dog – they have priminent sclera. So do apes, and cows. I think that Big Cats (lions, etc.) have prominent sclera, too.
If you look really closely at the eyes of many rodents the eyes don’t appear to have “white”, but you can see that the pupil is only a small portion of that dark eye (the reflection is different in the pupil than elsewhere). I think a lot of rodents have black “whites” – dark sclera.
How about bears?
I beliebve a lot of the purpose of white sclera is in sending signals (the pupil-iris-sclera forms a “bullseye” pattern that lets you extrapolate where the eye is looking – Hey, doesn’t that imply that you can see Bull sclera?). There was an interesting bit on this in some nature book or magazine.
There’s an old saying in dog training that if a dog shows you the whites of its eyes, it trusts you. This isn’t a conscious display on the dog’s part; it just means the dog is willing to look way from you which implies a large amount of trust. Obviously there’s some social context in whether you see the sclera or just the beady stare.
Well, I think there’s also a connection to the fact that our eyes move in the sockets, so that we can gaze to the sides without moving our heads. Many other animals do not have this facility, e.g. cats. Those animals lack obvious sclera. I presume the back of the eyeball even in those animals is coated with the hard, maybe white, surface. Now, that still begs the question as to why some animals have eyes which slide back and forth and up and down, while others do not. I’d like to know what evolutionary biologists have to say about this. But for now, I think I’ll go back to sleep. xo
Actually, yes, I have, but I wouldn’t call the sclera prominent, as you can’t see it unless the dog is straining somewhat looking off to the side and can’t (or is too lazy to) orient his head/body to look at it directly. You can’t see the sclera, for example, if you’re looking at the dog in profile and he is looking straight ahead. This is true of the dogs I’ve had, at least–YDEMV (your dog eyeballs may vary.)
And again, with the cows I’ve known, you can’t usually see the sclera unless they’re rolling their eyes in suprise or fear.
About dogs: Our dog had very visible whites, and he was a collie/retriever hybrid. My aunt had a pug, with equally visible whites. They didn’t have to strain to make the whites visible – they were especially visible if their eyes weren’t pointed straight ahead. (Dogs and cats can, in my experience, move their eyes pretty easily).
The rodent pictures I saw with “black” sclera were, I think, guinea pigs or something like that. In any event, the eye certainly wasn’t all pupil, and the black part wasn’t a colored iris.
It’s so that men can feign a lofty aesthetic appreciation of feminine pulchritude — ah, those flashing (azure / earthy brown) orbs (of verdant green) in a sea of milky white! — whereas they really have in mind lower things, um, so to speak…
slinks off shame-faced, clutching his Freudian slip tight about him