Wide-Eyed | Why Goats & Cuttlefish Have Weird Shaped Pupils

Summer is coming to an end and with it the time of state and county fairs. My family and I just went to the MN state fair this past weekend, the so-called Great Minnesota Get Together. It’s one of the few things that brings so many of us together at once, a shared experience of stuffing ourselves on various fried foods and foods on a stick. It also happens to be one of the few times many of us get up close and personal with a range of farm animals—like goats!

Who doesn’t love goats? Especially baby ones. Their gait, their bleat, their tiny horns. But there comes a time in any goat interaction I’ve had where we lock eyes and I’m struck with a mixture of curiosity and unease. 

I know, I know. Snakes and cats have vertical, diamond-like pupils. What’s the big deal? I couldn’t tell you. I know it’s irrational, but something about a goat’s horizontal rectangular pupils is just strangely disconcerting to me. Yet, at the same time, behind that immediate unease is actually a fascinating peek into the science of vision itself.

The first thing to consider is this: in nature, there’s always a reason.

The second is a matter of perspective. I’ve often found that the answers to some of the universe’s strangest questions suddenly become much more apparent when you stop thinking about why things are different and start thinking about why things are the same. Roots and veins, atoms and galaxies, or, for example, the commonality of round pupils.

Our pupils are round. In fact, they are round for most animals. Why?

Imagine yourself surrounded by complete darkness. You reach out in front of yourself and feel a heavy curtain. You reach into your pocket to retrieve a small metal pin and poke a hole in the barrier before you. Suddenly, a beam pierces through the darkness forming a spotlight. The round hole creates a round beam, and in the wall behind you—an inverted projection of the outside world. 

That is how your pupils function. Allowing in light in the form of inverted pictures which are translated into electrical signals to be received and interpreted by your brain. The larger the hole, the more light can enter. It’s the same way cameras work. The benefit here is this: having round pupils with round irises changing their size is the optimal shape for animals most active during the day who need to decipher detail from a bright world. 

Lizards and cats have vertical slits—perfect for seeing in the night and ambushing prey. 

So what then could possibly be the reason you and I have round pupils but a goat’s looks like a Daft Punk emoji?

Well, what else do we know about them? They’re hooved, they’re horned, they’re herbivores!

By the way, if you’ve ever wondered what the difference between horns and antlers is, horns are a boney part of the skull covered in a keratin sheet (you know, the stuff your fingernails are made of). Antlers are also bone, just without the keratin, and they’re temporary since they grow out of a boney stump in the skull during specific portions of the year.

In a way, horns are like conifer trees while antlers are deciduous.

Anyway, hooves, horns, herbs. Goats eat plants, and they’re good at it too! Some companies even train goats to eat specific plants and use them as invasive species controls for hire.

While goats may be veracious predators to plants, they aren’t for anything else

As a plant-eater, they spend much of their time with their heads down to the earth. Sure, horns come in handy for fighting off potential predators, as well as potential competition, but resorting to cranial fisticuffs is sort of a last resort. Instead, they rely on their vision as the first line of defense.

Combine the fact that their eyes are placed on the sides of their head, a common trait in prey animals, and their wide-screen pupils, and you get a broad line of sight with unparalleled peripheral vision.

Speaking of parallel, their eyes auto-level in their sockets. What does that mean? Well, when they lower and raise their heads, their eyes remain level and parallel with the horizon. Their eyes are like the ultimate camera stabilizer and it’s what makes them excellent survivors.

As strange as their pupils may appear, it’s fascinating to think about the why behind their wide eyes.

You know who’s got even weirder pupils, though? Cuttlefish!

Why Cuttlefish Have W-Shaped Pupils

Firstly, cuttlefish pupils are typically more round in lower lighting. Bring them into the light, and a shift occurs. What once was round takes on a squiggly, w-esque shape. Like with goats, a wider horizontal opening helps let in more light from more directions, but cuttlefish must strike a balance with the chaotic lighting of their environments. Living in shallow waters means lots of light coming in from above with a lot less light from below. The amount of light and intensities are vastly uneven. Adding these squiggles helps to find that balance between light entering from above and below.

If you think that’s cool, just wait.

If you listened to the last episode, Polar Bears and the Illusion of Color, you might remember learning about color receptors called cones. We have three, Red, Green, and Blue. Cuttlefish have one.

For a long time, we assumed that meant they must be colorblind, but varying experiments have suggested otherwise. Confusing, right? It’s thought that the W-shape of their pupil helps to create a sort of makeshift color vision.

Like I mentioned before, the wider the pupil, the more light is let in from more directions. This si great and all, but it comes with a downside–chromatic abberation. You know how sometimes when your vision gets blurry, you see these sort of colorful auras around lights and things? That’s what we’re talking about. Same thing happens when using a wide-angle lens.

The theory essentially goes that cuttlefish and other similar creatures are able to use the curved shape of their pupils to distinguish between different colors by the relative amounts and focus of the different wavelenghts of light on their retina.

If this theory turns out to be true, it might explain how these seemingly colorblind creatures are masterminds of color changing camoflaugue.

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The Wild Life was created in January of 2017 by, me, Devon Bowker (He/They) after finishing my degree in wildlife biology. It’s been amazing to see how things have changed over the past 5 years, both personally and here. I have tons of ideas and projects in the works and cannot wait to share them with you. Whether you’re a long-time follower or new to The Wild Life, thank you for being here.

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