If you have ever had an up-close look at a goat on a farm, you have probably noticed the strange rectangular pupils in their eyes. Researchers have discovered the reason why these strangely-shaped pupils devloped in some animals like goat and horses, while humans have smaller circular pupils, and cats and some other animals have vertical slits.
A new study by researchers analyzing how light enters the eye has revealed that goats and horses can see in nearly 360° degrees area. It all depends on their uniquely elongated pupils on the sides of their head. The shape of the pupil allows a wide range of vision, as well as the ability to rotate the eye to stay level with the ground when the head is raised and lowered.
The study was led by scientist Martin Banks, UC Berkeley professor of optometry, in collaboration with Durham University. The results present a new hypothesis as to why pupils are shaped and oriented the way they are.
They analyzed 214 species of land animals, and found that the pupil shape is strongly correlated with a species’ ecological niche. Species with pupils that are vertical slits “are more likely to be ambush predators that are active both day and night”. In contrast, those with horizontally elongated pupils are “extremely likely to be plant-eating prey species” with eyes on the sides of their heads.
Animals like horses, goats, and impala spend most of their time grazing, and need to be able to be aware of the presence of predators all around them, especially while their head is down near the ground during grazing.
So if you ever wondered why your cat has vertical pupils, or why goats have those bizarre rectangular pupils, you can now rest assured that it is an evolutionary development!
Read the full report here.