Science, maths and computers.
Above is a resin cast of a lung. Notice its fractal nature - how it displays self similarity at smaller and smaller scales. You might also notice how this structure is quite ‘tree-like’. Why are they so similar?
Well actually, both lungs and trees want to maximise the surface area of their functional components while constrained to some maximum volume. For lungs this strict constraint is the size of the thorax, but for trees is more relaxed and is to do with the mass they can achieve through photosynthesis and mineral uptake and density of trees around them.
Interestingly, nature has solved both these mathematical problems of optimisation using the mathematical solution of fractals. This is a great example of complexity and universality. Complex structures such as trees and lungs emerge from very simple mathematical rules, laws and constraints. The result is some kind of universality to the structures that we humans see and assume to be very different, though they are fundamentally the same.
Check out this animation I made of a simple fractal construct being transformed into a ‘tree-like’ (or ‘lung-like’!) structure.