Of the various examples, rivers are especially revealing, I think, since they arise from neither biological evolution nor urban planning, but rather chaotic Earth processes. A discovery about river networks in 2026 reignited my curiosity about their universal form and mathematical nature. These were hot topics in the 1980s and ’90s, when rivers were studied as natural examples of “fractals”: mathematical objects whose features repeat in roughly similar forms at many different scales. In 1957, a U.S. Geological Survey scientist named John Hack discovered the most important law of river networks. “Stream lengths tend to increase proportionally to the 0.6 power of the drainage area, regardless of the geological or structural characteristics of the area.”