Brandon Keim, writing for Wired:
On the surface, these core-and-branch systems — evident in New York City, Tokyo, London or most any large metropolitan subway — may seem intuitively optimal. But in the absence of top-down central planning, their movement over decades toward a common mathematical space may hint at universal principles of human self-organization.
I love—just love—studies like this. The peculiarities of the human brain pop up all over the place, from reading comprehension to place name density to, now, subway systems.