Check Out: The Evolution of an Eye by Jess Shillaw

The Evolution of an Eye

Jess Shillaw March 9, 2020

Have you ever watched an action-packed scene unfold around you and you try your best to focus on a certain object moving? Or have you ever watched your house cat hunt and noticed that they don’t lose focus of what they are chasing in front of them?
I asked the question whether this it discipline or is it a predatory adaptation that happens automatically? After mulling over it for a while, I did some research. 

Hosana Male Chasing Leopard - His eyes were locked on one individual as he hurtled towards it.
A male leopard chasing a herd of an impala, as you can see here he has locked on his target while an explosion of animals happens around him.
Photo by: Alex Jordan

I found an article on the research on the pupils of land animals by researchers at the University of California in Berkeley and how they have adapted this eyes due to their niches. They tested the pupils of 214 species of land animals, both predator and prey. 

Predators on land have eyes facing forward, giving them the ability to judge distance and focus on the prey in front of them that they are chasing. Prey species on the other hand – but more specifically many herbivores – have eyes facing to the side, giving them great peripheral vision. INterstingly enough, it is ther pupils that can differ the most between species, conferring different advantage upon them. 

Lion Cub Eye - A close up shot of a young lions eye as he glances into the treetops where a vulture lands.
Photo by: Nick Kleer

Some animals have a round pupil, like us, some have a vertical slit-shaped pupil and some have a horizontal slit-shaped pupil.

Predators that ambush their prey and hunt both day and night tend to have vertical slit- shaped pupils – like a house cat. The researchers then concluded that the shape of the pupils depend on how the animal hunts. However, lions and leopards are also ambush prey, yet their pupils are round. Researchers then concluded that predators that have round pupils are more “active foragers” since they chase down their prey.  This confused them too so they furthered their research. They found out that pupil shapes are not only dependent on their hunting techniques but also their size

Being closer to the ground, making it difficult to focus on the object in front of them (difficult to focus on prey when you much shorter than the grass/logs), smaller predators need to use “focus blur” which will help the predator judge the distance more accurately than taller predators. That I found incredible! We, like taller predators, don’t have that much worry of tall grass getting in our way so we don’t need to use focus blur as much to judge distance, hence our circular pupils.  

Ac2a1382 - African wild cat - GB - 2019
An African Wildcat which has vertical slit-shaped pupils, notice how small it is compared to a leopard (with circular pupils)
Photo by: Guy Brunskill

But what about the prey species’ pupils? Most prey animals, like antelope and especially especially grazers, have horizontal slit-shapes pupils. The researchers used technology to see exactly how these animals see. They saw that the horizontal slit-shaped eyes allowed them to see in perfect alignment with the ground as they feed and more light is let in from the front, the sides and behind them. Not only does this help them spot predators in their preiphary, but if/when chased, it allows them to have superior collision avoidance, detecting obstacles that might cause them to stumble while running.

They say the devil’s in the details, but when it comes to the different pupil types in the wild, it’s more like life and death that you can find in the details!

Jess Shillaw

Author and Contributor

Jess was born in Kwazulu/Natal but grew up in Cape Town. Having an innate love for all things wild but getting to spent little time in the bush while growing up, she headed straight for the Lowveld after school. She completed a guiding course and spent a year guiding in the Sabi Sand Reserve. It was during this time that she realised that Londolozi was the place she really wanted to be, and in 2018 she successfully completed the Londolozi Guide Selection Course.

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