Eye of a sheep
If you look deep into a sheep’s eyes, you might notice something strange: instead of a round pupil like ours, sheep have a rectangular black spot in the middle of their eyes. So what’s going on?
Sheep are ruminant mammals, close to deer and antelopes — a group that is characterized by liking to ruminate — basically, repeatedly chewing partially digested food before finally swallowing it.
Another thing that sheep, deer and antelope can be said to have in common is the fact that occasionally have to flee when a predator invades your surroundings, and this is where having horizontal pupils is useful.
“The horizontal pupil, with a single exception that we found, is associated with prey animals“, explains the teacher Marty Banksprincipal investigator at Banks’ Lab, a visual space perception laboratory at the University of California at Berkeley,.
“It was very clear that these animals tend to almost always have their eyes on the side of their head. instead of frontal eyes like us“, adds the researcher. “The fact that their eyes are on the side of their head allows them to see almost 360 degrees around you. Something we can’t do, obviously.”
“The elongated pupil benefits this panoramic vision by letting in more light, so the left eye can see behind the animal on the left, and the longer pupil allows more light comes in that directionso they can see better”, details Banks.
“Interestingly, the fact that the pupil is vertically narrow has the effect of making sharper horizontal contours that the animal can see. And they may very well need it to put their feet on the ground while trying to escape a predator,” he adds.
In fact, there is a great diversity of pupil shapes in the animal kingdom. Os cats have vertical slits that are great for being ambush predators, while taller predators, like humanstend to have circular pupils.
The exception found by Banks is the to like. While most animals seem to adhere to this “vertical for predator and horizontal for prey” rule, this mammal, terrible predator always thirsty for bloodhas larger pupils sheep-like.
“This animal does not fit our description at all,” says Banks.
Certain species of mongoose, such as the Indian mongoose (or Herpestes javanicus), are famous for their ability to attack and kill snakes, including venomous ones, thanks to their agility and partial immunity to the venom of some species.
So, maybe for hunting snakes it would actually be more useful to have horizontal pupils…
