Why?
I have no cites, but it’s my understanding that cat pupils are vertical as a hunting adaptation. The theory is, IIRC, that cats evolved hunting in areas where the vegetation was just thick enough to block the view. Vegetation growing vertical as it normally does is easier to see through, or spot movement, with vertical slits than with normal round pupils. I suppose if this is the case, that goats, being prey animals, would have the same advantage in seeing predators.
Why not?
Seriously, this is my answer to most “why” questions about physical structures. There is no innate reason for pupils to be round, so there probably is some advantage to round pupils, but all we can say about cats and goats is that said advantage was not determinative for them.
Goat eyes are predominately horizontal, not vertical. Also, they have a square end instead of coming to a point like a cat’s does.
IIRC and goggle images show that too.
Well, there you go…everytime I look a goat in the eye it freaks the hell out of me. No wonder I didn’t notice! I used to win the occasional staring contest with my cat Zero (r.i.p.) though, so I had cats figured out.
Vertical pupils will have the effect that a cat’s eyes will have better horizontal resolution though the range of distances viewed than in the vertical direction.
This seems to be a trait across many hunting animals. When the animal’s irises are wide open they get maximum light, but the depth of field is worse, and for many animals - including cats - they won’t get a focussed image of distant objects. But if the iris is a vertical slit, they will retain a lot of the light input (relative to a small circle - such as we have) whilst improving resolution in the horizontal direction. This may improve their ability to sight prey as it moves across the ground, at the expense of not having nearly as good resolution of its vertical extent. Indeed a cat’s eyes can close to a very small slit, and they may obtain very good horizontal resolution through a very deep range of distances. We have equal resolution (or lack thereof) in both directions. This is probably much more important for more general application of sight - hunting, being hunted.
I’m delighted – I’ve been pushing this concept for years now, and it has finally taken root somewhere.
“Big” cats, like Lions and Tigers, very noticeably do NOT have vertical slit pupils – their pupils are round. But snakes do have vertical slit pupils, as do night-hunting geckos.
Goats, by the way, don’t – they have roughly rectangular pupils that are wider than they arte high – almost as opposite to vertical slit pupils as you can get. I’m still not sure why, although I have some ideas.
This is not in any way a useful answer. There is always a reason for physical structures. It may be due to physical or developmental constraints, or it may be adaptive. But simply saying “Why not?” doesn’t provide any insight.
You want to see freaky eyes, check out the cuttlefish.
There are a variety of hypotheses for the evolution of slit pupils, and the issue has not been completely resolved.
A horizontal slit will provide better spatial resolution and thus detection of something coming at you - which is possibly a better compromise for prey - as they may get better warning of an impending attack.
Only venomous snakes have vertical slit pupils. Non-venomous snakes and even young venomous snakes have round pupils.
Maybe goats USED to be venomous, hunting predators…
Baaaaahh.
I’ve read the theories such as what **Colibri **and Francis V. posted and I would dearly love to know how that quite logical hypothesis applies to that squiggly nonsensical eye!
Dang! The illustrator of the copy of “The Three Billy Goats Gruff” that I’ve been reading to the Cub has grievously misled me!
Thanks for the correction. Those rectangular pupils are also weird. Learn something new everyday!
He was probably illustrating those Satanic Billy Goats Gruff.
**Not just venomous predatory goats !
Humans can be born with vertical pupils.
A long time ago I worked with a gentleman with vertical pupils. He was a dishwasher in a restaurant I worked at. I asked him about it. He knew it was a genetic mistake, but as he was mildly cognitively impaired, (part of the syndrome),
that was all he could tell me.
Haven’t seen it since.
http://www.socialstyrelsen.se/rarediseases/cateyesyndrome
Very interesting. From the description on your linked page, it appears as if the pupils don’t really resemble cat’s pupils, except in being elongated vertically. Nothing indicates that they function as cat’s eyes do (closing to a vertical slit in bright light, opening to a circle in dim light).
I knew a kid with one eye like this when I was young. I just thought it was some sort of damage – I never thought it could be a genetic mutation. His pupil was larger vertically than horizontally, but wasn’t symmetric, and didn’t really resemble a cat’s vertical pupil.
Indeed, the photo on the Wikipedia page illustrates that the pupil doesn’t closely resemble that of a real cat:
see here, too:
And this guy only has it in one eye, like the fellow I knew:
