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Visualizing the Evolution of Vision and the Eye

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Infographic illustrating the development of the eye

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Roadmapping the Evolution of the Eye

Throughout history, numerous creatures have evolved increasingly complex eyes in response to different selective pressures.

Not all organisms, however, experience the same pressures. It’s why some creatures today still have eyes that are quite simple, or why some have no eyes at all. These organisms exemplify eyes that are “frozen” in time. They provide snapshots of the past, or “checkpoints” of how the eye has transformed throughout its evolutionary journey.

Scientists study the genes, anatomy, and vision of these creatures to figure out a roadmap of how the eye came to be. And so, we put together an evolutionary graphic timeline of the eye’s different stages using several candidate species.

Let’s take a look at how the eye has formed throughout time.

Where Vision Comes From

The retina is a layer of nerve tissue, often at the back of the eye, that is sensitive to light.

When light hits it, specialized cells called photoreceptors transform light energy into electrical signals and send them to the brain. Then the brain processes these electrical signals into images, creating vision.

The earliest form of vision arose in unicellular organisms. Containing simple nerve cells that can only distinguish light from dark, they are the most common eye in existence today.

The ability to detect shapes, direction, and color comes from all of the add-ons evolution introduces to these cells.

Two Major Types of Eyes

Two major eye types are dominant across species. Despite having different shapes or specialized parts, improved vision in both eye types is a product of small, gradual changes that optimize the physics of light.

Simple Eyes

Simple eyes are actually quite complex, but get their name because they consist of one individual unit.

Some mollusks and all of the higher vertebrates, like birds, reptiles, or humans, have simple eyes.

Grid of photos showing examples of simple eyes in the animal kingdom

Simple eyes evolved from a pigment cup, slowly folding inwards with time into the shape we recognize today. Specialized structures like the lens, cornea, and pupil arose to help improve the focus of light on the retina. This helps create sharper, clearer images for the brain to process.

Simple eye evolution

Compound Eyes

Compound eyes are formed by repeating the same basic units of photoreceptors called ommatidia. Each ommatidium is similar to a simple eye, composed of lenses and photoreceptors.

Grouped together, ommatidia form a geodesic pattern that is commonly seen in insects and crustaceans.

Grid of photos showing examples of compound eyes in the animal kingdom

Our understanding of the evolution of the compound eye is a bit murky, but we know that rudimentary ommatidia evolved into larger, grouped structures that maximize light capture.

compound eye evolution

In environments like caves, the deep subsurface, or the ocean floor where little to no light exists, compound eyes are useful for producing vision that gives even the slightest advantage over other species.

How Will Vision Evolve?

Our increasing dependency on technology and digital devices may be ushering in the advent of a new eye shape.

The muscles around the eye stretch to shift the lens when staring at something close by. The eye’s round shape elongates in response to this muscle strain.

Screen time with cellphones, tablets, and computers has risen dramatically over the years, especially during the COVID-19 pandemic. Recent studies are already reporting rises in childhood myopia, the inability to see far away. Since the pandemic, cases have increased by 17%, affecting almost 37% of schoolchildren.

Other evolutionary opportunities for our eyes are currently less obvious. It remains to be seen whether advanced corrective therapies, like corneal transplants or visual prosthetics, will have any long-term evolutionary impact on the eye.

For now, colored contacts and wearable tech may be our peek into the future of vision.

Complete Sources

Fernald, Russell D. “Casting a Genetic Light on the Evolution of Eyes.” Science, vol. 313, no. 5795, 29 Sept. 2006, pp. 1914–1918

Gehring, W. J. “New Perspectives on Eye Development and the Evolution of Eyes and Photoreceptors.” Journal of Heredity, vol. 96, no. 3, 13 Jan. 2005, pp. 171–184. Accessed 18 Dec. 2019.

The Evolution of Sight | PHOS.”

Land, Michael F, and Dan-Eric Nilsson. Animal Eyes. Oxford ; New York, Oxford University Press, 2002.

“The Major Topics of the Research Work of Prof. Dan-E. Nilsson: Vision-Research.eu – the Gateway to European Vision Research.” Accessed 3 Oct. 2022.

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Misc

Ranked: The Top 10 U.S. Pizza Chains by Market Share

Domino’s is the biggest pizza chain in the U.S. by sales.

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Graphic showing America’s biggest pizza chains by 2022 revenue.

Ranked: Top 10 U.S. Pizza Chains by Market Share

This was originally posted on our Voronoi app. Download the app for free on iOS or Android and discover incredible data-driven charts from a variety of trusted sources.

About 3 billion pizzas are sold annually in the United States. In 2022, pizza restaurant sales in the U.S. reached an all-time high of $46.9 billion, an increase of roughly $10 billion compared to just a decade prior.

This graphic lists the top 10 U.S. pizza chains based on 2022 sales figures. This data was accessed via Statista (published June 2023).

Domino’s Domination

Domino’s is the biggest pizza chain in the U.S. by sales, reaching $8.6 billion in revenue in 2022. The brand is also found in 90 other countries around the globe, including stores on every continent except Antarctica.

According to Domino’s main website, there are over 20,500 locations worldwide, which collectively serve over 1 million customers per day.

Domino’s is followed by Pizza Hut with $5.3 billion in revenue. Little Caesars, with $4.7 billion, completes the top three.

Company2022 Revenue (USD)
Domino's Pizza8,572,000,000
Pizza Hut5,270,000,000
Little Caesars4,724,000,000
Papa Johns3,712,000,000
Marco's Pizza1,063,000,000
Papa Murphy's753,000,000
MOD Pizza662,000,000
Hungry Howie's534,000,000
Round Table463,000,000
Jet's Pizza441,000,000

The top end of this ranking contains household names, but regional pizza chains also make the cut. Jet’s Pizza is popular in the Great Lakes region, and most Hungry Howie’s locations can be found in Michigan and Florida.

The overall number of pizza restaurants in the U.S. has been on the rise, reaching more than 80,000 units in 2022.

If you enjoyed this post, be sure to check out this graphic, which visualizes the change in market share of U.S. carbonated soft drinks between 1995 and 2023.

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