55

Picture of a goat (?) eye with a horizontal slit and cat (?) eye with a vertical slit

The picture above is taken from a Telegram channel and the text in Russian goes as follows.

Prey has got a horizontally shaped pupil to better scan the horizon and a predator's pupil has a vertical shape to better focus on a prey.

Is this true?

90

Generally true. Some nuance applies, plus exceptions.

It is generally true that eyes of predators are different than eyes of prey. Not only are the pupils sometimes different in the way suggested in the claim, but eye placement and some other factors are different as well. The general theory accepted by biologists is that predators tend to fixate on their prey targets, so they evolve eyes that suit looking forward and intently fixating on single points. Prey, on the other hand, is suited well by having a broader periphery that helps them spot approaching predators, even if at the expense of the ability to converge the eyes and look straight forward.

Scientists have now done the first comprehensive study of these three kinds of pupils [horizontal slits, vertical slits, and round]. The shape of the animal's pupil, it turns out, is closely related to the animal's size and whether it's a predator or prey.
Eye Shapes Of The Animal World Hint At Differences In Our Lifestyles - NPR

The nuance and exceptions is that slits are by no means the only pupil shape. Round, as in humans, is common. There's also some crazy shapes like 'W', crescent, heart, and pinholes. The generally true part is that horizontal slits are typically only on prey while vertical slits are typically only on predators. I don't know of any exceptions to this specific point.

The researchers gathered information on 214 species. They noted the pupil shape and the location of the eyes on the head, plus the animal's lifestyle. ...

When they pulled everything together, a clear pattern emerged. In the journal Science Advances, the scientists report that there's a strong link between the shape of an animal's pupil and its way of life.

"If you have a vertical slit, you're very likely to be an ambush predator," says Banks. That's the kind of animal who lies in wait and then leaps out to kill. He says these predators need to accurately judge the distance to their prey, and the vertical slit has optical features that make it ideal for that.

But that rule only holds if the animal is short, so its eyes aren't too high off the ground, Sprague says.

"So for example foxes, in the dog lineage, have vertical pupils, but wolves have round pupils," he says.

And while a small pet cat has vertical slits, Sprague says, "the larger predators, like lions and tigers, have round pupils."

In general, round pupils seem to be common in taller hunters that actively chase down their prey, says Banks.

Meanwhile, he says, if you're the kind of animal that gets hunted, "you're very likely to have a horizontal pupil" and to have your eyes on the side of your head. That makes sense, he says, because it gives prey animals a panoramic view, so they can best scan all directions for danger.
ibid

There's a lot more going on with evolved eye structure, some of which you can learn about in the linked NPR article.

The NPR article is based off

  • 8
    I skimmed the paper. It puts forward a hypothesis of why it helps, optically. (I think it would take me an hour or two to understand it though.) – Oddthinking Aug 17 at 0:23
  • 6
    Further generality is that pupil shapes do correlate strongly to predator/prey behaviors. – fredsbend Aug 17 at 22:01
  • 4
    @Nyos Did you read through in the link? Some prey eyes actually rotate with the head to maintain horizontal orientation. – fredsbend Aug 19 at 2:26
  • 8
    Note that most of these biases (eye placement, pupil, ...) tend to focus on land-based animals. These generally don't apply to marine or flying animals, who have a higher need for peripheral view (including the predators) due to navigating a 3D space as opposed to the predominantly 2D space land animals navigate. – Flater Aug 19 at 11:31
  • 6
    @DarrelHoffman Their eyes may be on the sides of their heads, but clearly raptors' eyes point forward. images.unsplash.com/… – nasch Aug 19 at 15:16
13

Some University of California scientists suspect the eye shape to be highly related with the animal's lifestyle.

When they pulled everything together, a clear pattern emerged. In the journal Science Advances, the scientists report that there's a strong link between the shape of an animal's pupil and its way of life.

"If you have a vertical slit, you're very likely to be an ambush predator," says Banks. That's the kind of animal who lies in wait and then leaps out to kill. He says these predators need to accurately judge the distance to their prey, and the vertical slit has optical features that make it ideal for that.

But that rule only holds if the animal is short, so its eyes aren't too high off the ground, Sprague says.

A vertical eye is seen on ambush predators as they need to judge distance, but only when their eyes aren't high off the ground. Examples, a house cat has vertical eye slits but a tiger has round eyes, a fox has vertical eye slits but a wolf has round eyes.

A round eye was mostly seen on taller animals that chase down their prey.

A horizontal eye slit is indeed mostly found on prey animals as it gives them a wider field of view. Interestingly, since many of these animals (horses, sheep, goats, etc) lower their head to graze their eyes also have the ability to rotate so that the slit stays horizontal.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .