Design In Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology, and Social Organization by Adrian Bejan and J. Peder Zane. Doubleday. $27.95. 296 pages.

Raleigh News & Observer & The Charlotte Observer

January 22, 2012

A look at the science of going with the flow

BY PHILLIP MANNING
 
In this provocative, witty, well-written book, Adrian Bejan, a mechanical engineering professor at Duke University, pitches a theory he calls the constructal law. The idea came to him in 1995.

In his notebook, he wrote, "For a finite-size flow system to persist in time (to live), its configuration must evolve in such a way that provides easier access to the currents that flow through it."

The idea is a familiar, but slippery and confusing, concept, so Bejan and co-author J. Peder Zane, a former N&O book review editor, elaborate. "Everything that moves is a flow system that evolves over time ... The changes we witness in animals, plants, rivers, and steaming pots of rice represent a clear improvement over the configuration that had been flowing before.
"This," they add, "is the direction of evolution, creating flows that move more easily, better, farther, etc."

Improvement is not a word usually associated with evolution. Harvard professor (until his death in 2002) Stephen J. Gould summed up most biologists' view: "The basic theory of natural selection talks not about predictable universal progress, or any inherent direction of evolution."

How does one rebut the arguments of a distinguished academic? Bejan attempts to do so by applying constructal law to explain the physical world.

"I have shown," he proclaims, "how a single law of physics shapes the design of all around us."

He even uses constructal law to explain why sprinters run faster today than a few years ago. Athletes are getting bigger, which allows them to flow easier and faster.

In The Wall Street Journal, one writer extended Bejan's bigger-is-faster rule. "The human race," he wrote, "is figuring out what animals have long known, that bigger means faster. Whales swim faster than tuna, for instance, and horses run faster than mice." In the article's comment section, one reader pointed out the obvious flaw in this argument. "Yes, but greyhounds run faster than elephants and cows run slower than cheetahs."

The constructal law is easy to misinterpret because it cannot be summarized in a neat mathematical statement, as can Newton's laws of motion, for instance. Possibly for this reason, few scientists have actually used, tested, praised or critiqued the law. More than half of the 50 references in the book's bibliography are either authored or co-authored by Bejan or were published in books he edited.

One reason for the scientific community's oversight might be because the constructal law seems obvious. Of course, water and lightning follow the path of least resistance. A similar law was formulated long ago as the principle of least action.
Another problem with the constructal law as presented here is that the things it predicts are already known. The design of river basins, lightning strikes, and other examples are established facts.

If the constructal law predicted something new or at variance with the accepted laws of physics, it would attract more attention. Einstein's prediction that Mercury's orbit obeyed the laws of relativity, not Newton's law of gravity, quickly changed the face of science.

Despite these problems, the book makes a strong case for constructal theory. Perhaps it will stimulate more scientists to weigh in on its importance and validity.
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