For more than a hundred years, scientists have puzzled over a simple question: why do natural networks—like blood vessels, neurons, tree branches, and plant roots—look the way they do?
These structures appear everywhere in living systems, yet they follow surprisingly similar patterns.
For a long time, researchers believed the answer was efficiency.
The idea was that nature builds networks using the least possible material, much like designing the shortest set of wires to connect points. But when scientists tested real biological networks against these mathematical models, the results didn’t quite match reality.
According to new research from Rensselaer Polytechnic Institute, the problem wasn’t nature—it was the math.
“We were thinking in one dimension,” explains physicist Xiangyi Meng. “We treated biological networks like thin wires. But in real life, these structures have thickness, surfaces, and volume. They live in three-dimensional space.”
In a study published in Nature, Meng and his colleagues show that natural networks follow rules borrowed from an unexpected place: string theory.
String theory is a complex and still unproven framework that physicists use to explore the deepest structure of the universe. Surprisingly, its mathematics turns out to be extremely useful for describing how living systems organize themselves.
In the 1980s, physicists working on string theory developed equations to describe “minimal surfaces”—the smoothest, most efficient way to connect objects in space.
Think of soap films stretching across wire frames. Meng’s team realized these same equations can explain how biological networks grow and branch.
Traditional models predict that networks mostly split in two, forming simple Y-shaped branches. But nature is far more diverse. Tree branches, blood vessels, and neurons often split into three, four, or even more directions at once. The surface-based rules from string theory naturally allow for these complex junctions.
The theory also explains something else scientists have long observed: thin, perpendicular offshoots that end abruptly.
These appear in plant roots, fungal networks, and especially in the brain. In fact, about 98% of these tiny perpendicular branches in human neurons end in synapses, where neurons communicate. These offshoots help cells reach nearby targets while using the least amount of biological material.
To test their idea, the researchers analyzed detailed 3D scans of six very different networks: human neurons, fruit fly neurons, human blood vessels, tropical trees, coral structures, and the plant Arabidopsis. Across all of them, the real-world patterns matched the surface-minimization predictions far better than older models.
Biology, of course, is not driven by physics alone. The team found that real networks can be up to 25% longer than the theoretical minimum, reflecting the many competing demands of growth, repair, and survival. Still, the consistency across species suggests that evolution repeatedly arrives at the same geometric solutions.
“This work shows how abstract physics can help us understand real biological systems,” says Gyorgy Korniss, head of physics at RPI. In the future, these insights could guide the design of artificial blood vessels, brain-inspired networks, or even more efficient transport systems.
At a deeper level, the study reveals something elegant: the same mathematical rules that help describe the universe may also shape the living world around us.
