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ON THE SHELF - Reviewed by Robin Tatu

the Flow

An engineer explores nature’s model for efficient systems.

Design in Nature: How the Constructal Law Governs Evolution in Biology, Physics, Technology, and Social Organization.

By Adrian Bejan and J. Peder Zane. Doubleday, 2012. 304 pages.

It was in 1995 at a conference in France that Adrian Bejan had his eureka moment. As he listened to Belgian Nobel Prize winner Ilya Prigogine describe the inexplicable presence of myriad tree-shaped structures in nature – trees, rivers, lightning bolts – Bejan realized that what was being labeled a random phenomenon was in fact a naturally occurring design in nature. Perhaps it took an engineer to make the connection; and for Bejan, a Duke University thermodynamics specialist who had long grappled with issues of flow, a pattern suddenly became clear: Everything that moves is a flow system, and over time, each system develops a structure that supports the best movement. Moreover, Bejan realized, this principle applies to both animate and inanimate systems. Riverbeds, bolts of lightning, and human lungs all share a similar branching shape because each seeks out the greatest efficiency in moving a current – whether water, electricity, or oxygen. “This treelike pattern emerges throughout nature because it is an effective design for facilitating point-to-area and area-to-point flow.”

Fired by his thoughts, Bejan scribbled down what he would come to call the constructal law: “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.” Sixteen years later, Bejan and his colleagues continue to expound upon constructal law through hundreds of publications, lectures, and conferences devoted to what he argues is a core principle of physics, one that accounts for all natural design and evolution.

In this new book, coauthored with journalist J. Peder Zane, Bejan provides a thorough exploration of constructal law in areas as diverse as natural phenomena, human and animal biology, and man-made, engineered structures such as roadways, communications, and even the university ranking system. Constructal law governs each of these systems, he argues, and provides new understanding of what it means to be alive: “(L)ife is movement and the constant morphing of the design of this movement.”

From the outset, Bejan distinguishes himself from proponents of so-called intelligent design, ensuring that readers understand that physical science, not God, is at work. Indeed, while many have identified enduring patterns in nature, mathematics, and physics – such as those found in fractals or evolutionary change – “what has been missing is a single principle of physics that unites these phenomena and allows us to predict how they should evolve in the future.”

Early chapters take us through the basic tenets of constructal law, replicating basic experimentation Bejan undertook in observing flow systems in drying mud puddles, crystallizing snowflakes, boiling rice, and elements of heat transfer in the field of thermodynamics. Subsequent chapters are more ambitious, challenging, for example, Darwin’s belief that the evolution of species is both unpredictable and based on a competition for survival. Fish, land animals, and birds are governed by the same, not different, principles of movement, Bejan argues. Despite their seeming differences, each evolves with a tendency toward more fluid movement. Moreover, life-forms evolve not as competitors but together, jointly responding to interlocking environments of a global flow system. People, too, are integral to this system, not apart from nature, evolving into a “human and machine” species that uses technology extensions to overcome natural limitations – and facilitate easier flow.

The pronouncement of an overarching global design and the evolutionary tendency of all life-forms working together “to make the whole Earth flow more easily” may not resonate with all readers. Nonetheless, Bejan’s constructal law is a provocative formulation that can inform design work in engineering fields ranging from the mechanical to the biomedical. As Bejan notes when discussing why Atlanta’s Hartsfield-Jackson International airport stands out as a masterpiece of design, understanding constructal law can avoid ad hoc approaches that rely upon slicing and dicing the variables. In short, for engineers, and for the evolving human-machine species in general, “it is a principle we can use to build better things.”


Robin Tatu is Prism’s senior editorial consultant.


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