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  • ["The beauty of the universe consists not only of unity in variety, but also of variety in unity." - Umberto Eco, The Name of the Rose ]

  • Peering into the eyes of different animals, you'll see some extraordinarily shaped pupils.

  • But why?

  • It turns out that pupil shape is a powerful indicator of what role an animal plays in its ecosystem.

  • Pupils mark the hollow opening in the iris, the eye's band of pigmented muscle.

  • They're the portholes through which light enters the eye, where it then strikes the retina and activates light-sensitive cells, setting the process of vision in motion.

  • Pupils are black because most of the light that enters them is absorbed.

  • Their size changes in response to brightness, as well as certain drugs and emotional and mental statesbut their basic form varies greatly among species.

  • House cats, for one, are twilight hunters with vertically elongated pupils.

  • In the dark, these structures expand dramatically, taking in the available light.

  • When it's bright, they shrink into slits.

  • In fact, cat pupils are so flexible that their maximum area is 135 times greater than their minimum areawhereas our pupils only shrink and expand 15-fold.

  • And because of how the slit pupil takes in light, it creates sharp, vertical contours.

  • When the cat's brain processes the visuals from each eye, the small but sharp differences between them help the cat judge the precise distance of its target.

  • In fact, many other ambush hunters also have vertically elongated pupilsbut mainly those whose eyes are located closer to the ground.

  • This may be because these pupils are especially useful in perceiving objects at the relative short distances these animals tend to hunt.

  • The world looks very different from behind the horizontally elongated pupils of many grazing and browsing animals, like goats.

  • These pupils, situated on either side of the head, let horizontal bands of light in that give the goat a near-360-degree view and provide it with sharp, horizontal images.

  • This helps goats detect any disruption to the horizonalerting them to potential predatorswhile still enabling them to see ahead and detect obstacles as they make their escape.

  • In fact, goats always keep their pupils aligned with the horizon, rotating their eyeballs in their sockets as they move their heads up and down.

  • Meanwhile, nocturnal geckos have pupils that shrink into slits studded with pinholes in higher light conditions.

  • Each pinhole projects a separate, sharp image onto the geckos retina.

  • Scientists think that comparing these different inputs might help the gecko judge distance without having to move.

  • And while they might have fooled you, mantises and other insects and crustaceans have "pseudopupils."

  • These aren't optical structures; they're optical illusions experienced by the observer.

  • Mantises have compound eyes composed of thousands of light-sensing units.

  • When some are aimed at you, they appear black because they're absorbing most wavelengths of incoming lightbut there's no actual opening.

  • So, why do we have round pupils?

  • Elongated pupils help sharpen certain dimensions of an animal's vision.

  • But scientists think that, for animals like us with circular pupils, this is a lower priority.

  • Instead of seeing some elements of a scene in extreme focus, we see a larger picture in relative detail, which enables more general skills of observation.

  • This may be especially helpful for foragers looking for food, hunters eyeballing and chasing their prey, and social animals recognizing other faces.

  • As we peer at different pupils, patterns emerge.

  • And yet there are exceptions.

  • For example, Pallas's cats and mongooses are both small ambush predators, but the Pallas's cat has round pupils and mongooses have goat-like pupils.

  • And we've only explored a few pupil shapes.

  • Other animals have crescent- or heart-shaped pupils.

  • And the cuttlefish has perhaps some of the most bizarre: their pupils are circular in the dark, but W-shaped in the light.

  • So, what's going on here?

  • Well, wouldn't we all like to know?

  • But are some adaptations just cooler than others? Allow us to introduce you to the aphid: a bug that poops candy.

  • Or, if you think the variety of pupils in the animal kingdom is impressive, wait until you see the variety of genitalia.

  • Keep exploring with these videos.

["The beauty of the universe consists not only of unity in variety, but also of variety in unity." - Umberto Eco, The Name of the Rose ]

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B2 US TED-Ed pupil sharp shrink shaped retina

Why do cats have vertical pupils? - Emma Bryce

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    Jeff Chiao posted on 2022/03/30
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