Humanity’s great fortune is that nature has shape, structure, configuration, pattern, rhythm, and similarity. It has rules and order: It is knowable, reliable, and, on the whole, predictable. From this stroke of luck, science was born and developed to the present day, where it is responsible for our well-being. If, for example, we couldn’t count on the fact that water should boil at a certain temperature, that seeds should sprout into fruits and vegetables, that flow systems should evolve to move more easily—we’d live in a Twilight Zone world that is, quite frankly, unimaginable.
Just as we found different centers of mass for humans based on their areas of origin, trees have certain idiosyncratic variation encoded in their genes, so that a pine tree always looks like a pine tree and will never be confused with a weeping willow or a palm tree.
Since the dawn of science, we have worked to improve our understanding of the natural laws that govern our world. The foundational idea of the modern scientific method is that our findings must be verifiable and reproducible, which means that anyone anywhere should get the same result from the same experiment. Nowadays, even schoolchildren recognize the power of these principles when studying the mindless forces of nature. Less clear is the question of whether the intricate sets of laws and relationships that govern the natural world also shape the human-built landscape. The regulations established by various governments, much less the peculiar set of assumptions and expectations each of us holds as we engage all around us, often seem so capricious and contradictory that the idea of pattern and predictable evolution in human affairs can seem as hard to imagine as a physical world without them.
That, of course, hasn’t stopped people from trying. A holy grail of Western thought has been to find principles as solid as those we find in science to explain complex social systems. Many of these efforts have involved the abuse, rather than use, of science. Karl Marx offered a “scientific” view of history that brought misery and death to the masses before it was discredited by experience. In the late nineteenth and early twentieth centuries, social Darwinists argued that the wealthier and more powerful people and races deserved to be on top because they were more fit than others. More recently, literary authors and social scientists have misused the concept of entropy (suggesting that all systems will tend toward disorder) and Heisenberg’s uncertainty principle (popularized as the notion that ultimate knowledge is unknowable) to advance pessimistic and relativistic arguments about society.
In hindsight, we can see these for what they were: the misapplication of science to further ideology. Name-dropping is not science. And yet, like the mystics who had nothing more than intuition to support their sense of the oneness of nature, these efforts reflected a correct hunch. This is often how knowledge proceeds: Thinkers consider mountains of observations and piles of data, then try to find the pattern that links and explains them. At bottom people say, “I know something’s going on here,” but until now they haven’t quite been able to put their finger on exactly what.
These efforts also reflect dissatisfaction with another wide current of thought, one that has separated people from the physical world and cast scientific knowledge as a tool we use to manipulate the world around us. This pragmatic “us” and “it” approach has paid huge dividends; the flourishing of civilization and technology has depended on our increasing understanding and control of nature, knowledge we use to create comforts and achieve progress. But it has left little room for the ancient inkling that we are, in fact, subject to these laws in profound ways. It cannot account for that sense that these laws push, prod, and shape us, guiding the choices we make about how we live, love, work, and play.
Now we can.
One of the most powerful insights born from the constructal law is that social systems are natural designs that emerge and evolve to facilitate the flow of the currents they represent on the landscape. This evolution has a direction in time, toward greater and greater access to move more mass (for example, people, goods, information) per unit of useful energy. The architecture and history of society, in fact, are not much different from the evolution of other complex (but simpler) flow architectures in the natural world: river basins and deltas, turbulence, blood vascularization, animal movement, respiration, dendritic solidification, and so on. All are throbbing, pulsing designs that evolve in time, that persist or perish based on their ability to facilitate flow access. Using the constructal law, we can, for the first time, predict the broad array of “pattern generation” phenomena that arises in geography, demography, communications, government, and economics.
This is a sharp break from conventional wisdom. It is also wholly unsurprising when we appreciate the fact that we sprang up from the world, were created by the same flows that generated all around us. The rise of humanity is not a radical break from the past but a chapter in the larger story of the Earth’s long history of flow design and evolution. We are a part of nature; its oneness includes everything, even us. Our special gift is not the ability to act apart from nature but the ability to generate complex and evolving natural designs that allow us to move more mass faster, farther, with longer lifetimes, and more cheaply than other animal-mass flows.
As my Duke University colleague the sociologist Gilbert W. Merkx has written, this constructal perspective differs significantly from dominant approaches in the social sciences, which assume that structure is a given that sets the context for social action or transaction. Structures are seen as static and transactions as dynamic. To be fair, there is a literature about transitions between structures, but these transitions are anomalies, periods of structural breakdowns or “revolutions” leading to new periods of stable structure.
Constructal theory sees social structures (economies, governments, educational institutions, etc.) as flow systems that are dynamic, not static. Structure is not viewed as stable. Rather than being taken as given, the living flow structure is always in flux, ever evolving to provide better and better flow access. The evolution of flow structures reflects the interaction between time and the environment. The environment is important because it also evolves, altering the parameters within which flow occurs. Thus the environment is an essential dimension of any given flow structure. The environment, in turn, can be defined as a series of overlapping and interwoven flows that interact in space and time.
I call these environments of multiple, interwoven flows “tapestries.” In nature, tapestries might be given labels such as “ecosystem” or “geomorphology,” and in the human environment they might be called an economy or society. But they share the similarity that any single flow system within the tapestry is morphing its configuration to seek better paths in the context of other flows doing the same.
By proclaiming that societal flows emerge and evolve according to the same principle as all other natural flows, the constructal law challenges a long tradition dating back to Immanuel Kant. The tradition holds that there are two different realms of human knowledge, the natural and the human. Perhaps the most famous expression of this perspective is found in Max Weber’s concept of Verstehen, or “sympathetic understanding.” This idea states that the behavior of social actors is motivated by thought and culture, allowing an understanding of the reasons for behavior that is very different in character from explanations that describe behavior without reference to motivation.
If we grant that people, unlike drops of water, can think, then why should social flows come to resemble river networks? There are several reasons. The first is that social flows, too, are constrained by the physical world through which they move. So the movement of people will tend to be along paths of less and less resistance. Over time, transportation systems, like highway and railroad networks, develop treelike patterns much like river basins, responding to similar geographic challenges.
Another explanation of the similarity between natural and social flow systems is that the unique characteristics of each of the individuals that compose a system are irrelevant to the character of the flow architecture. No two leaves on an oak tree are identical, but they perform similar functions as members of the same tree system. Weber’s concept of bureaucracy is premised on a similar assumption: that the rules of bureaucratic organization determine outcomes, not the unique characteristics of the individuals in a bureaucracy.
A third explanation is that individual motivations are canceled out in situations involving large numbers of people, a topic studied by the field of collective behavior. A final explanation is that while people’s motivations may vary to some extent, most people, most of the time, are rational actors who aspire to decrease the costs and increase the benefits of their behavior. This is the basis of rational choice theory, which underlies modern economics. To the extent that people behave to maximize their benefits, they will construct and gravitate toward social networks that exhibit, or are believed to exhibit, efficiency.
The constructal law captures the broad tendency of social organizations to construct evolving flow systems that enable people and their goods to move more easily, more cheaply. This is not human desire. It is physics.
In previous chapters we have observed that almost all flow systems carry a current from a point to an area or from an area to a point. Although they are far more complex, human organizations are also area-to-point or point-to-area flow systems. Governments, corporations, religious groups, universities, sports teams, communication and transportation networks, cities, nations, etc., produce and transmit currents (goods, services, people, information, etc.) to an area through actual channels. Science, for example, generates actual channels—including scientific laws, schools, disciples, libraries, journals, and books—for the organization and spread of its current: knowledge. Religions create actual channels—including houses of worship, clergy, sacred books, etc.—for the flow of the doctrine to the faithful. Militaries also carve actual channels for the flow of strategies, materiel, soldiers, vehicles, etc.
Consider this streamlined description of the Ford Motor Company. Sedans and SUVs don’t grow on trees. To create them, Ford needs raw materials to flow to its factory (a point) from the surrounding area. This involves multiple channels, including the lines of communication between the factory and suppliers—“Send us ten tons of steel and a million tires”—and the various transport routes (roads, train tracks, air transport routes) generated to ferry those materials to its factories, channels that are now strategically placed around the world to allow the company to increase efficiency. At the factory, supervisors use channels of communication to direct workers and machines on the assembly lines. Once the vehicles are manufactured, they are sent out into the world (an area) through actual channels that bring them to the dealerships that use their own channels of communication (advertising, word of mouth, etc.) to reach customers. All these channels evolve in time. Some become larger, others smaller. But the changes that stick are those that allow the flow system to persist in time.
This is the basic design of many businesses. By design, we mean something very specific—the actual drawing that flow systems create over time. We are not talking symbolically here, using analogy or metaphor. The constructal law is not an abstract theory but pure physics, observable nature, and unifying principle. It predicts the movement of physical entities over the globe, the flow of things we can see, hear, feel, taste, and touch. It is the black line on the white paper, the road on the map. The drawing is not a visual suggestion, but the design itself. A lightning bolt is the tree-shaped architecture that evolves in a flash to move electricity from a cloud to the ground. A river basin is the collection of waterways whose treelike structure moves water from the area to the river’s mouth. Ford is the vast global structure of channels and interstices through which currents of materials, products, and information flow. If these currents were to stop flowing, the factories would be dead buildings.
To appreciate this point, we need to clarify our language. So far we have used the phrase “treelike structure” to describe the, well, treelike structures that abound in nature. It is a vivid image that paints a pretty accurate picture. And yet, as my work on the constructal law evolved through the years, I found that this verbal symbol—this flow system for conveying information about the law to others—does not provide access to all the meanings running through it. I have resisted until now using the better word in this book because it is a mouthful—“vascularization.”
This word is an improvement, a better channel for communication, because it captures the central idea of the interdependency of life. Where a tree suggests the connection between point and area or volume, “vascularization” also contains the pivotal idea of life-giving flow and of a body (volume, area) filled with life. It reminds us that design arises in order to spread often-nourishing currents across an area or throughout a volume. The most familiar template for this is the vascular structure of our circulatory system, which delivers life-giving blood to all the cells in our bodies. Similarly, for a business to persist in time it must deliver life-giving ideas, materials, and goods to all its workers and customers.
This active, throbbing sense of design was contained in my original formulation of the constructal law sixteen years ago: “For a finite-size flow system to persist in time (to live), its configuration must evolve in such a way that it provides easier access to the currents that flow through it.” It also harkens back to the seemingly radical definition I offered in the introduction for what it means to be alive. There I said that everything that moves and morphs in order to flow and persist is alive. We can refine this now to say that everything evolves in order to provide greater access to the life-sustaining currents that run through its vasculature. When nothing flows through our bodies, we are dead. When the water stops moving through the river basin, it too is dead; when material and information stop flying to and from a business, the business withers and dies. And so it goes, with everything.
To show that human organizations are governed by this principle of physics, we should find two features: The patterns of their channels should have a vascular shape and structure as we observe in other point-to-area flow systems, and those patterns should evolve in time to provide greater flow access.
This is what we find. To see how, we have to introduce a cornerstone characteristic of natural design—hierarchy. Although it has received a bad rap as a symbol of inequality, hierarchy is essential to good design. Instead of providing advantages to one entity to the detriment of another, it arises naturally because it benefits the entire flow system, whether it is all the water in a river basin or all the people in a society.
Hierarchy evolves because good flow often involves multiscale architectures—that is, channels of varying sizes. On our commute we travel through many channels: highways, avenues, boulevards, side streets, and the path from our front door to the garage or curb. Even though highways handle many more cars and allow higher speeds, they are not more important than smaller avenues or even cul-de-sacs. All are necessary to spread the current that runs through it (us) to every destination, which means to provide access to the whole area. The few large feed the many small, and vice versa. An efficient transportation system strikes the right balance among all these components, just as other flow systems—including the distribution of people, wealth, knowledge, and education in society—should among their multiscale channels. The fact that hierarchy arises across the board offers further proof that the constructal law is a universal principle of physics.
As we have seen time and again, the constructal law was just waiting to be discovered. Its manifestations are so obvious and ubiquitous that we have danced around it for centuries—the hunches of scientists, the metaphors of poets and mystics, and everyday language (for example, “the tree of life,” “go with the flow,” “the path of least resistance,” “if you can’t beat ’em, join ’em,” “all roads lead to Rome”) suggested a phenomenon they could not quite capture. So it is with hierarchy. About twenty-four hundred years ago, Aristotle coined a famous phrase that also hinted at it—the one, the few, and the many. While the Greek philosopher was defining distinct political systems, he also suggested the hierarchical structure of design in nature. In our research group, this most essential feature is conveyed and taught by Lorente’s vision of few large and many small. Lorente’s insight is much closer to the truth than Aristotle’s because hierarchy means not only numbers but also sizes. “Few large and many small” is the concise name for what others describe as the emergence of “complex” design and “hierarchy.”
Start with the river basin. There is always one main channel—the Mississippi, the Danube, the Seine. It is the widest, fastest-moving component of the flow system. It is fed chiefly by a few large streams. These, in turn, are sustained by many small tributaries and rivulets in an immense system that moves water from the entire plain to the river mouth. Or consider the tree. It has one main channel, the trunk, a few main branches, and many roots, stems, and leaves. All are necessary for the efficient flow of water from the ground to the air.
This same hierarchical structure occurs in our bodies. As oxygenated blood leaves the heart it enters the one large main channel—the Danube of the circulatory system—the aorta, which continuously branches into a few arteries and many capillaries. Now take a deep breath. Feel the air whoosh down the respiratory system’s single main channel, the trachea. From there it enters the lungs, where it fills a few air passages before saturating the many tiny alveoli. The structure of lightning bolts, snowflakes, and lava flows, of forests, coral colonies, anthills, even clumps of dust—every multiscale flow system exhibits a hierarchical structure composed of a few large channels and many smaller ones.
And so we find the same design in human organizations. Almost every government has one leader—the chieftain, king, sultan, president, prime minister, governor, or mayor—who, like the main river channel, must handle the most important flow of information and authority. He or she is assisted by a few streams of top advisers, who themselves work with and oversee the many individuals who form the bureaucracy. This same hierarchy, which is often described as “vertical integration” in the business world, defines the structure of most corporations (one CEO, a few top managers, many workers), universities (one rector or president, a few provosts and vice presidents, more deans, even more department heads, and many more professors, teaching assistants, and students) and sports teams (one head coach, a few assistant coaches, many players).
The military, of course, is the classic example and main laboratory of this hierarchical chain of command. The Romans, for example, were able to expand their empire in no small part because of the hierarchical design of their military. Today, the United States of America has the most powerful military in the world, with a complex hierarchy spread across its major branches. People have written entire books analyzing this structure. Using the constructal law, we can predict that its structure should have a few large channels and many smaller ones, a fact confirmed by this very broad overview of the chain of command of the U.S. Army.
The president is the single commander in chief, responsible for all major decisions. Below him is the secretary of defense, who instructs the United States Central Command, which develops and implements strategy with commanders from each of the four branches.
Lieutenant Colonel Brian De Toy, director of the Defense & Strategic Studies Program at the U.S. Military Academy, told me that while there is plenty of variation in military formations, there are also clear patterns. By and large, the largest group is the army, which is commanded by a lieutenant general. The maneuver/fighting elements of the army are usually composed of two or more corps that are also typically commanded by lieutenant generals. Each corps is composed of two to five divisions, each commanded by a major general. This pattern continues as we proceed down the chain of command. Each division has three or four brigades; each brigade has three or more battalions; each battalion has three to five companies; each company has three to four platoons; each platoon usually has three to four squads; and each squad is divided into two teams.
What jumps out at us is that the hierarchical design has a predictable construction pattern very similar to what we find in the evolution of the river basin—essentially a rule of quadrupling, with each group composed of about four subunits.
Social systems generate hierarchical structure for the same basic reasons that other flow systems do: because point-to-area and area-to-point move their currents more efficiently with it than without it. Note that the constructal law makes no value judgments. Enlightened democracies and rigid dictatorships both display hierarchy, as do well and poorly run companies. What the constructal law predicts is that hierarchy should emerge naturally as a result of the tendency of moving things to generate designs that facilitate flow access. The constructal law also predicts that the rigid hierarchy will give way in time to a freely morphing hierarchy. This is why dictatorships are relatively short-lived and democracies have staying power.
Until now we’ve been looking at one snapshot—an entire river basin, the circulatory system, a tree, university, or corporation. As predicted, we found a hierarchical structure of multiscale channels defined by the few large and the many small. When we narrow our focus, we make the same observation. In the circulatory system, for example, small arteries are main channels for the network of even smaller arteries and capillaries they nourish.
Naturally, we find the same phenomenon in human organizations. As we saw in our sketch of the U.S. Army, the president is the main channel. He works with the secretary of defense, generals, and others to transmit orders to a hierarchically designed network of subordinates of various ranks. Except for the lowest soldiers, all of them have superiors, yet all have their own turf. Captains, for example, are the main channels of authority for each company; lieutenants serve the same function for members of their platoons. The Catholic Church also has an immense, complex hierarchy, from the pope to cardinals, archbishops, and on down. But at the parish level, the local priest is the main channel at the top of the hierarchy that includes monks, nuns, altar boys, and worshippers. When we look at an entire business, the CEO is the main channel. But as we go down the level of authority, from senior and middle managers to the foreman on the factory floor, these tributaries serve as main channels for the streams they feed.
We find hierarchy at almost every scale because flow architectures evolve in accordance with the constructal law. They do not generate hierarchy at the end of the day but at every step along the way. As soon as the seeping water starts coalescing to form rivulets, a hierarchical structure of a few large and many small channels emerges, which has evolved into the massive river basins that cover the globe. Similarly, the internal structure of multicellular organisms has a hierarchical structure, albeit one that is far less complex than that found in animals such as humans.
Flow systems continuously generate design for easier flow with hierarchy. This can be hard to see sometimes, in part because flow systems are always evolving, ever morphing toward better hierarchical configurations. I remember hearing an author on the radio claim that the early Catholic Church was not hierarchical. This statement appeared true to him because he was comparing the primitive group of churches to the highly organized structure that emerged, especially after Emperor Constantine embraced Christianity and advanced it throughout the Western Roman Empire during the fourth century. The early church had a more localized, less elaborate hierarchy, but in each community of Christians there were leaders, and certainly, very early on, St. Paul was the main channel for the dissemination of the doctrine.
This highlights the false assumption that because one flow system is younger and less evolved than another, it lacks hierarchy. As we have seen, the river basin is a more complex flow system than the one created by tiny rivulets, but both exhibit hierarchical design. Similarly, the government of the United States has a much more intricate hierarchical design than the network of tribal chiefs and warlords who hold sway over large swaths of Afghanistan or Pakistan. But even there, hierarchy rules.
This underscores a key point, and the fresh perspective, provided by the constructal law. The vascular design of the evolving architectures depends on the size of the flow system. Large structures have more levels of branching, that is, designs that are more complex, than smaller ones. In the opposite direction, smaller flow systems generate simpler tree shapes with fewer levels of branching.
While all multiscale, point-to-area flow systems generate easier flowing configurations that have hierarchy, they do not simply reiterate the simplest design into ever more complex patterns; the smallest detail is not simply a miniature version of the largest drawing. Just as one size never fits all, neither does one design. Flow systems generate just enough complexity for the size of the territory they bathe with current. They create architectures that work for them. The complexity of each architecture is modest, finite. The phenomenon of design in nature is not one where complexity increases in time. Each flow system evolves to acquire the right level (kind) of complexity to flow, to live. This is one reason why “simple” life-forms have persisted for billions of years even as other, more complex organisms have emerged. The phenomenon of design in nature also covers the rare cases of some fleas and tapeworms that have become simpler over time. The tendency in nature is not toward greater complexity but better flow access globally. This direction often gets lost because many natural flow systems become larger in time, and their finite complexity increases.
If we zero in on the subvolume between two alveoli in the lung, we do not rediscover the structure that resembles the human lung with its twenty-three levels of branching. Instead, we find the soft and wet tissue with diffusion, that is, with no distinct currents. Similarly, a local parish may have a hierarchical structure, but it is not a miniature version of the hierarchy we find in the entire Catholic Church. What we find is an evolving architecture of channels that handles its flows efficiently.
Let’s take a closer look at the evolutionary emergence of hierarchy in social systems by examining a flow system that is particularly close to my heart—scientific knowledge. Science is what we can say about nature; it is our knowledge of how things are in nature (around us and in us) and how they work. In its rawest form, science is a collection of many observations. The sun is in the sky. It feels warm. It disappears at night. The moon appears. The temperature drops. If science were only a collection of such statements, it would not be very useful. In time, scientists have organized and improved this deluge of information in the same way that a river basin has evolved: toward configurations (links, connections) that coalesce (condense) the flows and provide faster access for the flow of information.
For example, prehistoric humans knew very little about how things fall. They had no concept of gravity. Through experience, hunters learned to throw a rock or a spear so that it would strike their prey. Each generation transmitted this knowledge to the next, a flow of information that was effective but relatively inefficient as it required face-to-face training and firsthand experience as individuals developed a feel for the work. Over time, science progressed as people accumulated bulky measurements. Greek and Roman soldiers developed basic formulas for determining how far away they should stand from their adversaries to hit them with their arrows or the payloads of their catapults. This represented an advance in knowledge. The early sense of intuition possessed by hunters (the rivulets and first main channel) was replaced by these calculations (the new main channel for the flow of information of how things fall). The armies that possessed this knowledge and that had created channels so that it could flow to their soldiers in the field had an advantage over opponents who lacked it.
Then, Galileo stated the principle that rendered all those measurements unnecessary: Objects fall faster and faster downward at a predictable rate. He gave the world a single formula that allowed us to replace that collection of discrete calculations. Thanks to him, we could predict the speed at which any object falls. His discovery spread through various channels—books, disciples, etc. Unlike many other scientific breakthroughs, including his defense of Copernicus, Galileo’s discovery did not meet much resistance from competing ideas or entrenched dogma. Because it enhanced the flow of knowledge, it became a new main channel in the hierarchy of science. Indeed, all the great discoveries, from Newton’s laws of motion to the laws of thermodynamics, didn’t just tell us something new, they also organized and streamlined our knowledge. They replaced bulky measurement with principles that serve as new main channels in the hierarchical flow of knowledge about how things should be in nature. They didn’t just rewrite our science books, they made them thinner, easier to teach and to learn from, enhancing the flow of information from those who possessed it to those who wanted to have it. Today, the constructal law is uniting a host of seemingly far-flung phenomena—design and evolution of the inanimate and the animate—through a single principle of physics.
We “know more” because of this evolution of flow design in time, not because our brains are getting bigger. We keep up with the steady flow of new information through a process of simplification by replacement: In time, and stepwise, empirical information (such as measurements, data, and complex empirical models) are replaced by much smaller summarizing statements (such as concepts, formulas, constitutive relations, principles, and laws). Empirical facts (observations) are extremely numerous, like the hill slopes of a river basin. The laws are the extremely few big rivers. A hierarchy of statements emerges naturally because it facilitates the flow of information. It is an expression of the never-ending struggle of all flow systems to design and redesign themselves. As the constructal law predicts, better-flowing configurations continually replace existing configurations.
In a river basin, the marsh and the incipient rivulets that form after rain are akin to the relatively unorganized, raw volume of scientific data. Over time, they continuously generate ever more complex—and better—flow channels of rivulets, streams, and tributaries. In science, the evolving channels are language, subjects, laws, schools, disciples, libraries, journals, and books. The same thing happens in all social systems. Civilization is the story of better and better flow access. The evolving design of politics, economics, technology, and all the rest have created channels that improve the movement of people, goods, and ideas. It’s true that every change has not enhanced flow access; bad ideas are inevitable, and entrenched powers often try their best to defend their limited interests. In the short term, evolution looks like a jagged line. But in the long run, there is a clear direction in time: The currents that persist are those that facilitate movement. This is progress.
Scientists are constantly making new observations, just as the skies regularly pour rain on the ground. Both flow systems are preexisting and evolving. The first part of this statement is easier to appreciate than the second when we are looking at a river basin, because its design has emerged over millions of years. During that long period of time, each of its channels has constantly configured and reconfigured itself, finding better and better ways to move the water within its specific geographic area.
This time element explains why we don’t see new large rivers on the landscape. The river basin is still evolving but it is also entrenched. Now, if the worst fears about global warming were to come true or some other cataclysm were to dramatically alter the current system—if the middle of America turned into a desert and the Sahara became a floodplain—two things would happen. In the worst-case scenario (for America, anyway), the Mississippi would dry up and a new, hierarchal flow design would arise in what had been the African desert.
Science is a much younger and far more complex flow system than the river basin. So our drawing of scientific knowledge is changing far more quickly. The falling raindrops of this field (raw data, observations, creative minds) spark the visible creation of better channels (new laws) to handle the current (knowledge and ultimately the movement of humanity). To the extent that these new channels are able to handle the flow of all the observations that have come before and those still to be made, they will become deeper, more entrenched.
As an aside, I’ll add that this is one reason that scientific ideas appear to take a long time to take hold. As Max Planck observed, “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.” For lack of better laws, researchers try to squeeze new data into the old channels. They try because they depend on and benefit from the existing design, which is called the establishment. The establishment fights back, but after enough funerals it becomes a new structure, a new establishment. Truly original ideas break this mode and replace the existing structure with one that flows better. This is what the constructal law predicts for the evolution of science.
This view underscores another seminal aspect of hierarchy: the interconnectedness and interdependence of every component of the flow system. In the bigger picture, the river basin uses its rivulets, streams, and main channels to move water from the plain to the river mouth just as surely as our respiratory system uses tiny alveoli, bronchial tubes, and the trachea to bathe our lungs with oxygen. CEOs use managers and workers to create their company’s products and spread them to their distributors and customers, just as presidents, prime ministers, and dictators use advisers and countless bureaucrats to develop and spread their policies across the land. The main channels may facilitate wider, faster flows than the smaller ones, but all are necessary to bathe the entire area with the current. Hierarchy emerges because all flow systems use the right combination of components of varying sizes to efficiently move the currents that flow on the same, finite territory.
This finding leads to another insight that debunks conventional wisdom: Hierarchy arises because it is good for every component of the global flow system. The big need the small just as surely as the small need the big. The individual sustains the crowd—and vice versa. The big river sustains the many tiny streams of the river basin, just as those tiny streams feed the river basin. Citizens (the rivulets of politics) sustain the governments that serve them; workers (the rivulets of business) sustain the companies that employ and, in turn, sustain them. The urge to organize is selfish.
It is the integrative aspect of design—the balance that naturally emerges among all its flow components—that is one of the most revolutionary insights offered by the constructal law. While the prevailing Darwinian model of evolution makes some room for the idea of cooperation, it is based chiefly on the idea of struggle among individuals—the “good me” against my bad neighbors and society. Organisms compete with one another for scarce resources; we compete with the environment, etc. It is, largely, a tale of winners and losers.
The constructal law, however, reveals that the movement toward harmony, toward flowing together and in balance, is the central tendency of design in nature. Recall our discussion in chapter 2 about the predictable ratio between the number of daughter and mother streams in a river basin and the ratio between the mother and daughter air tubes in the lung. We showed that these relationships and the many scaling laws in nature have emerged because they are efficient designs for global flow access. Nobody is commanding these various waterways or blood vessels to act in concert, but they do, each part serving the flow performance of the whole. Similarly, human organizations thrive when they find the right balance of flows. Employees can strive to earn a particular position, and their success or failure at this can have personal results. But for the outfit to run efficiently, it must find a combination of workers at every level for its size at a given time that changes during periods of boom or bust. This is why hardworking, talented people often lose their jobs. Their best efforts no longer match the changing needs of the bigger system.
In a larger context we see that black markets and smuggling emerge where the official channels do not facilitate everything that flows. Under communism, for example, there were thriving black markets for almost every commodity because governments imposed artificial designs and constraints. In the United States of America today there are few black markets, but those that have emerged (for example, for illegal immigrants or illegal drugs) are in response to laws that hinder flow access.
So far we have seen how this works in relatively self-contained flow systems such as trees and river basins. In both cases it was easy to see that the flow system tends to strike the right balance among its multiscale channels and their interstices. Now we will widen our field of view to see how this predictable harmony of hierarchy occurs in even larger flow systems. The constructal law allows us to discover that the same design governs the relationship among all the seemingly independent flow systems that form various flow networks. I recognize that this is a fairly radical point—but it is also an obvious one when we take a holistic view.
To achieve this perspective, let’s pretend we’re on a space station orbiting the Earth. We see below a vast map covered with innumerable flow systems, each of which is evolving in time to provide easier access for its currents. Everything is connected to everything else as part of a global system that changes in order to flow better and better. Every river basin is part of the global system that includes ocean currents and global weather patterns and that tends to move toward equilibrium of all the heat and moisture on the planet. Every business is a component of local, national, and world economies. These larger systems are, of course, evolving. Because the global system to which the river basin belongs is less complex and far older, it displays a higher level of integration than the economy. Its channels have had more time to find the right places and combinations and so they are more entrenched. In time, we should also expect the channels of the economy to become more integrated, to provide easier and easier flow. They are, and we call this globalization.
Globalization is as old as civilization itself. It is an evolving design that began when the first people migrated and when the first individuals and tribes began trading with one another (both goods and ideas). Today’s world is just the latest chapter in this long story as technology has made it cheaper and easier for the entire globe to put the right channels (people, goods, ideas) in the right places.
I explored this phenomenon—the fact that seemingly independent flow systems are connected to larger systems that also display hierarchy—when our research group applied the constructal law to the design of vegetation (see chapter 5). After using it to predict the design of trees, plants, and roots, we figured: Since the forest is a giant pumping station for the movement of water from the ground to the air, it should also manifest a hierarchical design that maximizes the ground-to-air fluid flow access. We should find a few big trees and larger numbers of trees, grass, moss, etc., at progressively smaller scales. We then confirmed our theoretical findings in the real world.
This dovetailed with the findings of an earlier book in which my colleagues and I had used the constructal law to predict the same striking pattern in a far more complex flow system: the size and distribution of human settlements. We began again with pure theory—the idea that the flow system of demography must bathe the area (the continent) with people, goods, and services. To do this efficiently, it should have settlements of varying sizes that are proportional to one another and to the entire area.
Human settlements are a flow system for the movement of people and their goods, ideas, and so on. Like other natural flow phenomena, their evolution hinges on finding less travel time and cost for all these things. In the simplest description, civilization is the name for the coexistence of farmland with the market. Those who live on the area exchange farm products (and other goods, services, and information) with those who manufacture products and deliver services in compact places—first hamlets, then villages, then small towns, and finally cities.
Evolution depends on technology—significantly larger settlements can emerge only as technology allows people to minimize the travel time over greater distances. The allocation of land to human concentration also predicts that there should be proportionality between the number of people in the larger settlements and the surrounding areas. This balanced design should emerge at every step of the evolution of human settlements.
With this idea in mind, we created a series of ever larger constructs over an area with populations that remained proportional. As we added more settlements, hierarchy developed in two ways: Areas coalesced, from the smallest element to the first construct, and the population developed concentrations from farmers on several plots to traders at several points and finally to one trading point, which was, perhaps, a small town. The end of this sequence occurred when the constructal area matched the size of the available area. At this uppermost level of assembly, the number of large cities was one or two.
When plotted logarithmically, the size-versus-rank distribution of all the settlements formed the same pattern—a straight line with a descending slope—that we predicted for trees in the forest. This theory also predicted that this line should shift upward while remaining parallel to its previous position because of technology evolution: In time, each unit area sustains the living (the movement) of more and more inhabitants.
Next, we tested our finding in the real world by plotting the size and distribution of cities in Europe since 1600. The data confirmed our prediction: The populations of the various cities were always proportional, and they always generated a straight line with a descending slope on our graph. Other researchers who have recorded the size and distribution of human settlements around the world have reinforced this finding (Figure 41).
Figure 41. The sizes of cities line up against their rank, from the largest (1 on the abscissa) to the smallest. They form a straight line, which slides upward in time as technology, standard of living, and GNP rise. The curves show the city sizes versus city rank in Europe from 1600 to 1980. The stepped line shows the distribution predicted with the constructal law. The detail in the upper-right corner shows that the size of every city matches the size of the area on which the city participates in area-to-point flows. The detail in the lower-left corner shows the predicted distribution of multiscale human settlements on the map (few large and many small). This pattern is obtained after deleting the construction lines from the upper-right detail.
Nevertheless, it is important to note that this construction of compounding areas is not how human settlements form, grow, and get connected on the landscape in time. The compounding of areas (Figure 41, upper-right corner) is about how the tapestry takes concrete shape and structure in the mind, once we discover that those who live on the area must be proportional to the number of those who live in the settlement (because both numbers must be proportional to the same area).
On the ground, and in history, settlements become denser and each settlement grows in time. But they do not grow at the same rate. Some grow faster, and when they become large enough, they incorporate their small neighbors. And, from among those that are becoming larger, an even smaller number—a special very few—will grow even faster, in proportion with the growth of the population on the larger and larger areas that appear to be allocated to the special few. And so on, all the way to the single megacity on the map.
Because the emerging map of demography varies from country to country, the evolution to multiscale design can seem random. Luckily for the theoretician, this is not the puzzle. The real issue is the pattern, the broad features, performance, and evolution of the whole. This issue unifies all the seemingly unrelated counties, countries, and continents and it is predicted fully with the pattern shown in Figure 41. This is the power of the purely mental viewing and the constructal law.
I wasn’t aware of the breadth of this discovery until 2005, when I was presenting this theory at the Sun Valley Writers’ Conference. After my presentation, J. S. Adams, an engineer who worked in the city planning department, came up to me and said that I had predicted something called Zipf’s law. This was news to me. Zipf what? Who?
I learned that George Kingsley Zipf was a Harvard linguist whose studies included how often particular words appear in the English language. In a paper published in 1935, Zipf reported that the occurrence of any word is inversely proportional to its rank in the frequency table. That is, the most common word appears twice as frequently as the second two most common words, which appear twice as frequently as the next four most common words. When plotted on a log-log graph, this alignment of rank versus frequency creates a descending line.
Zipf’s work was refined by two scholars from Brown University, Henry Kucˇera and W. Nelson Francis, who performed an extensive computational study of English usage. They found that the most common word, “the,” accounted for 7 percent of all the words in the wide array of texts they studied. The next two most common words, “to” and “of,” each represented about 3 percent of the words used. As they continued their rank-versus-frequency study, they found that the third most frequent group of words was larger than the second group. Examining the ever-expanding groups of the fourth, fifth, sixth, etc., most common words, they corroborated Zipf’s line. They found that about 135 words account for half of all the words used in English. Think about it: We don’t say “ameliorate” or “egregious” very often.
No one would argue that “to” and “of” have outcompeted “ameliorate” and “egregious.” They have not emerged victorious in a Darwinian struggle, a dictionary war. The truth is that a hierarchy of words has emerged naturally. This becomes clear when we recognize that in written and spoken communication, words and sentences are the channels that carry the currents that represent the thoughts and feelings we wish to express. In order to spread this current efficiently, a hierarchy of channels has evolved of large channels (“to,” “of”) and small channels (“egregious,” “ameliorate”), all of which are necessary for the flow of information, and for our own flow (movement) on the globe.
Zipf titled his final book Human Behavior and the Principle of Least Effort: An Introduction to Human Ecology, and so we find yet another correct hunch. Other researchers have developed ad hoc principles to describe naturally emerging hierarchy in a variety of areas, including the distribution of wealth in society (Pareto’s principle), the frequency with which digits occur (Benford’s law), and the flow of scholarly publications (Lotka’s law). I have not confirmed their results, but I might have predicted them.
To take a more recent example, in a July 8, 2010, column in the New York Times, “The Medium Is the Medium,” David Brooks echoed the conventional wisdom that the Internet “smashes” hierarchy. At first glance, this insight seems obvious. Everyone who has watched the nation’s mighty (and not-so-mighty) newspapers suffer a million blog bytes knows the mainstream media is getting pummeled, beaten, and smashed by the World Wide Web. Innumerable folks with laptops and videocams are supplanting the towering edifices of modern journalism.
The hierarchy cannot hold; mere anarchy is loosed upon the world.
This view casts new media and traditional media as opposing forces, two fighters battling over the same piece of turf. In fact, the constructal law reveals that they are actually complementary channels in the global flow system spreading information over an area (populated by people who receive and use that information to move more easily across the landscape). Just as the river basin carries water from the ground to the river mouth, the Internet, newspapers, and other forms of media are channels for information.
The Internet is swelling as traditional channels shrink because it can facilitate heavier flows (more efficiently, to boot) than the structure generated by traditional media. One view of this intricate design shows us that the Internet is the new big river basin—the Mississippi of the Information Age—fed by a few large streams (such as YouTube, Facebook, and Brooks’s New York Times) and many smaller ones, including the millions of blogs and personal Web sites and billions of e-mails and instant messages sent each day. Like the design of science, the design of the Internet is evolving before our eyes to facilitate the flow of information. Tracking studies by Complete, a web analytics firm, show that the top ten Web sites accounted for 31 percent of U.S. page views in 2001, 40 percent in 2006, and about 75 percent in 2010.
All make up the evolving design of the global flow system for information. The rise of the Internet does not reflect the demise of hierarchy but its evolution and constructal design. It is larger and mightier (better flowing) than what came before. This is the same reason horse-drawn carriages were supplanted by automobiles but not replaced. Both could get you where you wanted to go, but one was much better than the other, and the two together are even better. That transition was not a radical break but a continuum in the evolution of better and better flow for the movement of people and goods predicted by the constructal law. This hierarchical structure emerges naturally because it facilitates the flow of information. And, in turn, the flow of information facilitates our own movement on the globe. This design change is analogous to the emergence of vision (the eye), which stepped up animal movement from groping in the dark to “guided” locomotion (see chapter 9).
Using the constructal law we say: The old hierarchy cannot hold; a better hierarchy is loosed upon the world.
Finally, the discovery that social systems emerge and evolve just like other natural phenomena raises what we might call the constructal paradox. Because human beings have consciousness, it is relatively easy to understand how we can organize ourselves into efficient flow systems. Unlike river basins and lightning bolts, we are smart and capable, and we can learn from the past in order to exert control over the future. When we look at the evolution of governments, corporations, religious organizations, etc., we see mankind’s intelligence at work—willful, calculated, purposeful.
This can make it hard to appreciate the fact that our actions are guided by a natural tendency. For all our thinking and debating, our long record of achievement, our torturous history of conflict, we have generated natural designs. And our legacy for having done this is the same as the legacy of the river basins: We moved more mass than we would have without such designs.
In chapter 3 we showed that if we reran Stephen Jay Gould’s tape of life and started it all over again, many things would change but not the constructal design of animal movement. Similarly, if we rewound the tape of human history and hit the record button anew, the movie would likely have different scenes and players than the ones we know, but the hierarchical design of our social systems would remain.
Here’s one way to think about it. People have created innumerable currents through time: transcendent ideas and can openers; miraculous medicines and Frisbees; cinema and basketball; air-conditioning, indoor plumbing, and pool tables. As useful as they all may be, none was inevitable. If history had taken a different turn, we might find other currents. But those currents would facilitate our flow through multiscale channels in order to reach all the people they serve, which means to enable all the people to move more easily on the globe.
That our social systems have the same evolving design as other natural phenomena alerts us to the fact that forces far larger than ourselves are in play. It shows that our movement on the landscape is governed by the same principle as movement all around us.
What our history makes clear is that human organizations are evolving like other flow designs because they are not separate from nature but a part of it. A government must bathe a nation with rules and policies; the Internet must spread knowledge around the world; and a corporation must deliver goods and services to its customers. All generate vascular designs with hierarchy, all go with the flow.