For a long period of time, we believed in a natural ranking order in the world around us, also known as the great chain of being, or “Scala naturae” in Latin, a top-down structure that normally starts with God at the very top, followed by angels, noblemen, common people, animals, and so on. This idea was actually based on Aristotle's ontology, which classified all things known to man in a set of opposing categories, like the ones you see behind me. But over time, interestingly enough, this concept adopted the branching schema of a tree in what became known as the Porphyrian tree, also considered to be the oldest tree of knowledge.
The branching scheme of the tree was, in fact, such a powerful metaphor for conveying information that it became, over time, an important communication tool to map a variety of systems of knowledge. We can see trees being used to map morality, with the popular tree of virtues and tree of vices, … with these beautiful illustrations from medieval Europe. We can see trees being used to map consanguinity, the various blood ties between people. We can also see trees being used to map genealogy, perhaps the most famous archetype of the tree diagram. … We can see trees even mapping systems of law, the various decrees and rulings of kings and rulers. And finally, of course, also a very popular scientific metaphor, we can see trees being used to map all species known to man. And trees ultimately became such a powerful visual metaphor because in many ways, they really embody this human desire for order, for balance, for unity, for symmetry.
However, nowadays we are really facing new complex, intricate challenges that cannot be understood by simply employing a simple tree diagram. And a new metaphor is currently emerging, and it's currently replacing the tree in visualizing various systems of knowledge. It's really providing us with a new lens to understand the world around us. And this new metaphor is the metaphor of the network. And we can see this shift from trees into networks in many domains of knowledge.
We can see this shift in the way we try to understand the brain. While before, we used to think of the brain as a modular, centralized organ, where a given area was responsible for a set of actions and behaviors, the more we know about the brain, the more we think of it as a large music symphony, played by hundreds and thousands of instruments. This is a beautiful snapshot created by the Blue Brain Project, where you can see 10,000 neurons and 30 million connections. And this is only mapping 10 percent of a mammalian neocortex. We can also see this shift in the way we try to conceive of human knowledge.
These are some remarkable trees of knowledge, or trees of science, by Spanish scholar Ramon Llull. And Llull was actually the precursor, the very first one who created the metaphor of science as a tree, a metaphor we use every single day, when we say, “Biology is a branch of science,” when we say, “Genetics is a branch of science.” But perhaps the most beautiful of all trees of knowledge, at least for me, was created for the French encyclopedia by Diderot and d'Alembert in 1751. This was really the bastion of the French Enlightenment, and this gorgeous illustration was featured as a table of contents for the encyclopedia. And it actually maps out all domains of knowledge as separate branches of a tree.
But knowledge is much more intricate than this. These are two maps of Wikipedia showing the inter-linkage of articles — related to history on the left, and mathematics on the right. And I think by looking at these maps and other ones that have been created of Wikipedia — arguably one of the largest rhizomatic structures ever created by man — we can really understand how human knowledge is much more intricate and interdependent, just like a network.