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Scripts for written languages tend to feature more horizontal and vertical lines than oblique ones—but they didn’t evolve that way, a new study says.

Why written languages look alike the world over

What do Cyrillic, Arabic, Sanskrit, and 113 other writing systems have in common? Different as they appear at first glance, they share basic structural features, according to a new study: characters with vertical symmetry (like the Roman letters A and T) and a preference for vertical and horizontal lines over oblique lines (like those in the letters X and W). The explanation appears to be rooted in the wiring of our brain.

“People appear to have an aesthetic preference for certain kinds of shapes and designs, and that preference seems to explain the writing systems we see,” says Julie Fiez, a psychologist at the University of Pittsburgh in Pennsylvania who was not involved in the study. Fiez, who studies the neuroscience of reading, says those features may tap into how our eyes and brains process images: Neurons fire faster at the sight of objects that display vertical symmetry—like human faces—and horizontal and vertical lines, which are common in natural landscapes.

Olivier Morin, a cognitive anthropologist at the Max Planck Institute for the Science of Human History in Jena, Germany, analyzed the features of 116 writing systems across 3000 years of history. He and a pair of independent coders looked only at languages that consisted of alphabets or syllabaries—in which characters represent syllables, as in Korean—or some combination of the two. They left out so-called logographic writing systems like Chinese and Sumerian cuneiform, which they say have too many characters and are too visually complex to easily analyze.

Together, the researchers sorted through more than 5500 characters and tallied the number of vertical, horizontal, and oblique lines. They ignored curves—a decision Morin says was necessary to compare standardized orientations across all the scripts—and only looked at both uppercase and lowercase letters in languages that have a case system. They also measured how many characters formed mirror images if split in half vertically or horizontally, properties known as vertical and horizontal symmetry.

Morin found, on average, that about 61% of lines across all scripts were either horizontal or vertical, higher than chance would predict. (That number rises to 70% for the Latin alphabet, in which English is written.) And vertically symmetrical characters accounted for 70% of all the symmetrical characters. Together, the findings suggest that humans are drawn to these characteristics in writing, Morin says.

But did written scripts evolve to have more of these features over time, as language users selected for certain shapes and orientations of a script? To find out, Morin looked at a subset of 93 scripts that descended from—or gave birth to—another script in the study. Morin found no evidence that scripts tend to become more horizontal or vertical over time, suggesting that the scribes who created them baked human preferences into the written word from the beginning, he reported last month in Cognitive Science.

That contrasts with claims that human preferences act as a kind of selective pressure on writing, forcing it to evolve to become more legible or die, Morin says. “We have an evolutionary view of writing, and in many ways, I’m frustrated with that.” 

Fiez adds that future studies should explore whether logographic writing systems follow a similarly static pattern. Because they are so much more visually complex than alphabetic or syllabic systems, logographic systems might indeed follow different rules, she said.

Florian Coulmas, a linguist at the University of Duisburg-Essen in Germany, agrees that an evolutionary framework doesn’t work well for written language, but says there’s another, simpler explanation: Once a script is introduced, people tend to follow it diligently to avoid confusion—a concept known as path dependence. “Historically speaking, in writing … once you set down a path, you go down that path without much change,” Coulmas says.