But if we only have strangers' names and can't see their faces, how do we begin to encompass who they might be and where they belong? Human beings are terrible at remembering multitudinous connections between abstract things like names or ideas. Without a visible presence, these are hard to grasp.
Oddly enough, storing and retrieving data about connections is a ridiculously simple task to design into a computer program. But for most people, it can take hours of reciting and revision to learn by heart how a hundred facts or words or values are interconnected. We are not built to do that well.
About 2,000 years ago, some very clever people invented a method to get around this issue. They looked for a mechanism in the human brain which operates in some other context to solve similar problems. To understand what they discovered, let's imagine we go to some beach resort for the first time.
In the first hour, you figure out the path down to the beach, recognizing some landmark you need to pass on the way, like a restaurant. You immediately note a couple of other landmarks like an especially ugly hotel and an ice-cream booth. As you walk around the village, you discover a caravan park behind the ice-cream joint and a bus-stop past the hotel. In time, you realize that the bus-stop is in a street which leads to a boat-hire place and out to the main highway.
What's developing in your head is a mental map full of branching connections. Now strangely enough, most of us can remember hundreds of landmarks and waypoints when we are out and about. We retain them much more easily than we remember interconnections between abstract facts.
So the solution devised back in the Roman Empire was a hack. If you pretend to yourself that abstractions are landmarks along forking paths, your innate guidance system will do the heavy computing work for you, and aid you to grasp the interconnections among the concepts.
All you have to do is draw a branching path, plant the facts along it, and then walk this path with your eyes. This is a drawing of the descendants of Leah, a biblical woman, as it was devised around the year 400. The manuscript you are looking at (Florence, Plutei 20.54) was accurately copied from it about 600 years after that.
You might look at this and think: OK, that's just a family tree. For us in the 21st century, diagrams where you walk paths with your eyes are common and unremarkable. But back then the invention was very new. It had not previously been realized that abstractions like a genealogy of three generations could be visualized in this way.
Because this hack was very new, the design had to respect where its readers were at. Nobody was yet educated in how to read these abstract diagrams. Readers only had their instinctive human ability to walk branching paths and find their way by landmarks back to where they started.
In our mental maps of the world, almost anything can serve as a landmark. Every waypoint has a unique appearance, but is similar in its function. So in the Roman abstract diagram, every node had unique content, but was standardized in its circular shape.
In our mental maps, it's easy to learn waypoints, but hard to learn bearings. We imagine the waypoints of every path as one behind another and we ignore slight changes of direction. So in a Roman abstract diagram, the nodes are arranged in straight lines with as few turns as possible.
This Roman diagram was only recently re-discovered. It's the only chart of its type to have been copied in the Middle Ages. It's now the only one surviving from antiquity. Because the Roman diagram is stripped down to the bare essentials, it shows the essence of how we learned to harness the brain to do something new: grasp abstract facts by treating them as if they were landmarks on paths.
This may be the greatest brain hack of all time, a kludge that's so good that we no longer even realize we are harnessing our guidance systems to do something they were not designed to do.
And because it was devised for a world that did not yet use visualizations, it provides valuable clues to how all mental maps work in humans, and indeed in most animals, and even in many insects.
We humans are not as good at thinking about abstractions as we pretend to be. But if we had not adapted our mental navigation machinery to help in the task, we would be far worse at it.
