The pupil is the opening in the eye’s iris that lets in light. It appears black because the
light is absorbed by the eye tissue. The dilation and contraction of the iris is a reflex action to adjust the amount of light entering the eye. If you were able to stare into the eyes of various animals, you’d notice that there’s no one-size-fits-all option.
Scientists have looked at the different pupils of animals and concluded that the different shapes perform different jobs to benefit the ecological niche of the animal. For example, the pupils of prey animals offer a wide field of view that helps them scan for predators as well as decide where to flee.
Conversely, the pupils of predators dilate much more, to better equip them for hunting in all light conditions and to allow them to gauge the distance of prey without moving their heads and giving up their position before it’s time to pounce.
One especially interesting trait is how the oblong, horizontal pupils of animals such as
sheep, goats and horses are able to rotate to stay parallel to the ground, even when the animal moves its head – a process called cyclovergence. This incredibly clever evolutionary adaptation helps the pupils to work best for the animal, and proves invaluable should the animal need to run.
Read on to find out about the other types of pupil shape, and how they link to the animal’s lifestyle.