All networks form nodes; it’s in their nature, whether we’re talking about Facebook or an airline. As flying became more popular, nodes formed organically, connecting points for flights going to many different cities. As certain nodes started getting more traffic, like Denver, they became hubs. In the nervous system, the process is called encephalization, the evolutionary brain growth that marks a shift from non-centralized neural networks to the formation of the cerebral cortex. These centralized hubs with many incoming and outgoing circuits
