PIXABAY, SABINCHEN

Slit-shaped pupils help animals adjust their eyes to see clearly day or night, but that attribute doesn’t explain why some animals have horizontal slit pupils and others have vertical ones. A study published last week (August 7) in Science Advances suggested that pupil orientation is related to an animal’s eating or hunting habits.

“People had been saying that the horizontal pupil helps expand the horizontal view of the ground, they just hadn’t shown that,” study coauthor Martin Banks of the University of California, Berkeley, told The New York Times. “Our contribution was to build a model and show that that happened.”

Banks and his colleagues analyzed the eyes of 214 land animal species and found that those with slit pupils roughly fell into two groups: vegetarian animals that tended to have horizontal pupils and ambush predators that hunt close to the ground, which tended to have vertical...