Why Do Goat Eyes Rotate? | Explorer

To understand how some prey animals see differently than we do, let's play a game. Tilt your head and body to the side. What happens? Everything looks, uh, sideways. Kind of obvious.

Well, for one scientist, it turns out that this little problem of our eye not rotating very much in our head was the answer to an evolutionary puzzle no one had ever cracked. Dr. Marty Banks and Dr. William Sprig are taking us to the San Francisco Zoo. They are on the hunt to understand why some animals have different shaped pupils and how their pupil shape helps them survive.

The pupil is the actual hole in our eye that lets light bounce to receptors in the back of our eye. Those receptors then send signals to our brain to be processed. It's kind of like a camera that has an aperture where you can open and close it to let more or less light in while collecting pictures of different pupil shapes.

Marty noticed something that no one else had ever noticed before: the animals with horizontal elongated pupils. There were two things that they were exceedingly likely to have. One was eyes on the side of their head, and the other is that they were prey animals that graze. Typically, that is worried about other animals approaching on the ground to possibly attack them.

But what happens when the goats go to lower their heads to graze? Do these horizontal shaped pupils move? If they don't move, all the goat will see is the ground, and that wouldn't be very useful to see predators, would it? Our idea about the horizontal pupil is it should remain parallel to the ground. That way, they can see predators, and that way they can also see in front of them if they have to run from a predator.

Let's see what they do with the head up and the head down. If Marty's theory is correct, a goat's pupil will actually physically move when they put their head down like this. There we go; looks parallel to the ground. Yep, it's definitely horizontal. Looks like we see that movement in every one of these guys.

Mhm, and his colleagues discovered that goats do move their eyes to be parallel with the ground. These eyes are rotating through dozens of degrees. That's a big movement, bigger than we can do.

Oh yeah, rotating pupils in grazing animals seems obvious now, but actually, scientists had never really thought about it before. Marty and his colleagues started their research, and it was very surprising to me that had been part of the discussion sooner, even among ourselves. It's kind of embarrassing that we didn't think of it right off.