Researchers have been long intrigued about what is the different between some animals having horizontal-shaped pupils and other having vertical shaped pupils. Last Friday a new study was published that studied 214 animal species and suggested the answers might be linked strongly to giving an edge in survival to animals.
In other words, circular and vertical pupils could help certain types of predators in their hunting, while the horizontal pupils likely help the other species to spot their predators from afar.
Not al vision specialists accept the hypothesis of the researchers however, as they cite examples of animals that do not fit the classifications.
A team of researchers from Britian’s Durham University and the University of California Berkeley conducted the study. The teams used a set of computer models that were based upon a sheep’s eye as support of the theories of why circular, vertical and horizontal shaped pupils benefit the different animals.
When the animal’s pupil was horizontal in the model, more light could be captured from the right and left of the eye, which is not surprising and a less amount of light from above and below the eye.
This gives animals who are grazers the ability to detect predators better when they approached from any direction except from behind, said the researchers.
A caveat to the conclusion was obvious. What happens when a sheep with vertical slits bends its head to eat. Logic says the horizontal pupil would then be perpendicular to the ground. However, researchers discovered that the eye of the sheep actually rotates up to 50 degrees when its head is turned downward and the pupils remain parallel to the ground. Other grazing animals such as antelopes and horses were studied and they too can rotate their eyes.
The vertical slit eyes give advantage to predators when ambushing prey as they make it easier to determine distance through better depth perception.
However, an exception to that are large predators such as lions and tigers have pupils that are circular and not vertical.
Researchers said that was due to them being taller.
Critics say there are many animals that do not fit into the different groupings due to the shapes of their pupils.