A link between the animate and inanimate.

• Position: Nature

Living beings and inanimate phenomena may have more in common than previously thought. At least that is the view of Adrian Bejan of Duke University, Durham, N.C., and biologist James Marden of Pennsylvania State University, College Park. What they believe connects the two worlds is a theory that flow systems--from animal locomotion to the formation of river deltas--evolve in time to balance and minimize imperfections. Flows evolve to reduce friction or other forms of resistance, so that they flow more easily with time. This view has been termed the constructal law, which Bejan first stated 13 years ago.

With the help of Marden, Bejan believes that he now has unified the biological and geophysical principles of nature's design through the constructal law, which also can be viewed as the physics of evolution. "This is an exciting development for physicists, but it should also resonate with biologists,' Bejan relates. "The idea that organic evolution is analogous to the way form evolves in inanimate flow systems is a novel concept that has the potential to unite perspectives and approaches across disparate disciplines. We suggest that the constructal law provides a powerful tool for examining and understanding variation in both the animate and inanimate compartments of nature."

The story began with the two scientists trying to determine if the same laws applied to two very different forms of locomotion--the swimming of fish and running or flying of animals. The commonly held belief among biologists was that fish locomotion was different than other animal locomotion. Since they live in water, the conventional wisdom...