Why Your Brain Loves Sorting Things Into Boxes

The mind's favorite shortcut for a hard problem is to break it into smaller, labeled pieces. In 1740, Spain and Britain went to war after Spanish coast guards cut off the ear of a British captain named Jenkins.

Ask what caused the war, and every kind of expert hands back a different answer.

• Politics: a geopolitical explanation, about power between two empires.
• Money: an economic explanation, about trade and profit.
• Religion: Catholic Spain against Protestant England.

Each piece gets handed to a different expert, and that is exactly what we do to problems that are really one connected story with no natural breaks in it at all.

Why Boxes Feel Useful

The rainbow is the clearest example. Light color changes smoothly from one end to the other, with no real lines anywhere in it. Yet every language draws its own lines across it anyway: this part is "yellow," that part is "orange."

We invent the line, then act like it was always there. We do this because it helps us remember things. English has one main word for blue. Russian splits that same range into two separate words, one for light blue and one for dark blue, with a line in between that English does not have.

Tested on whether they have seen a certain shade of blue before, Russian speakers remember better than English speakers do. They are sorting the same color into two labeled boxes instead of one big vague one. Thinking in boxes really does help memory. That is the good side. The bad side is what it costs us.

The Cost of Boxes

Drawing a line between two things creates two opposite mistakes:

• Same box, looks more alike. English hears "B" and "P" as two clearly different sounds, but many other languages do not hear a difference at all. A story is told of a Finnish doctor teaching someone how to take a small tissue sample from an animal, who said, with a completely straight face, to go practice on a "bear" first. He meant "pear." In Finnish, B and P sound the same, so two sounds that feel completely different to an English speaker land in the very same box for him.
• Split by a line, looks more different. In the last U.S. presidential election, Biden was in his early 80s and Trump was in his mid to late 70s, a gap of only a few years. Trump's campaign kept calling Biden "old" next to a "younger" opponent, and polls showed his supporters guessed the real age gap to be much bigger than it actually was.

Once people draw a line, old versus not old, the gap on either side of that line grows bigger in their minds, even when the real numbers barely move.

Even Your Brain Cells Do This

The pull toward sorting things into boxes is not just something we learn from language. It is built into single brain cells. Scientists at MIT found brain cells in monkeys that fire every time the monkey sees a picture of a cat, and different brain cells that fire for a picture of a dog.

Using computer graphics, the scientists then built a smooth blend between a cat picture and a dog picture: all cat, then mostly cat, then half and half, and on down to all dog. A "cat cell" that was tracking the picture honestly should fire a little less at each step as the picture looks less like a cat. Instead, its firing barely changes at all while the picture is still mostly cat, then drops off sharply the moment the picture becomes mostly dog.

The brain cell treats one small step across its own invisible line as a huge change, even though it is the exact same size step as all the others. A single brain cell is drawing its own arbitrary line and reacting as if that line were real. If sorting into boxes runs this deep, fighting the habit in something as complicated as human behavior takes real, deliberate effort.

Why Did the Rooster Cross the Road?

Here is what box-thinking does to explanations of behavior. A hen is ready to mate, makes a certain wing movement, and walks in front of a rooster. He runs over to her. Why did the rooster cross the road?

• Body expert: the shape of a chicken's hip and leg bones is what makes that run possible.
• Hormone expert: roosters with enough of a certain hormone respond to that exact wing movement.
• Evolution expert: over many generations, roosters that responded to that movement had more babies, so the response itself was passed down and grew stronger over time.

None of these three answers is wrong. The mistake is deciding that any one of them is the whole answer. That is the second cost of box-thinking. It is not just misjudging how alike or different two things are, it is believing that one field, one gene, one hormone, one brain part, can explain all of behavior by itself.

Further Reading

• Book: Behave: The Biology of Humans at Our Best and Worst by Robert Sapolsky, the source for the categorical thinking framework used across this series.
• Wikipedia: Categorical perception · War of Jenkins' Ear · Linguistic relativity