To the editors:
There is a saying in Latin: verba volant, scripta manent (words fly, writings remain). The evolution of science further sharpens the cutting edge of this truth: writings fly, laws remain.
Scott Turner’s essay illustrates this dictum with a captivating story about the evolution of the view of evolution in biology, from before Darwin to today. A big field ensued—if not the biggest, then certainly the most impactful for humankind. It is not about subparticles and entropy death of the universe. The story begins with the fittest, heritability, stasis, genes, and natural selection through random mutations. It highlights the dead end that arises from the argument of adaptation by natural selection. It then opens the view to the bigger picture, organisms that modify their environments, niche construction and the extended organism, all happening as if driven with purpose.
The conclusion of the story is that life does not evolve by chance. Instead, life evolves in a discernible direction. It is a great story for science students who graduate convinced that science is static, because the textbook says so. It is particularly useful to scientists who are not biologists, because they are in a good position to see beyond the forest.
My contribution to the readers and Turner’s conclusion is that “evolution in a particular way” is universally true, and not just in biology.1 It is true for any flow system that morphs in freedom, inanimate2 (geophysics), animate,3 and human-made (social organization, technology).4 This conclusion is the physics principle: the constructal law of 1996. The law states that for a finite size flow system to persist in time, it must evolve freely such that it provides easier access to what flows. This physics statement accounts for the concepts of evolution, life, efficiency, the more fit, and the evolution of animals, people and societies with power from food and fuels.
Turner was the first biologist to connect biological evolution to the constructal law.5 In his book The Tinkerer’s Accomplice, the accomplice is the purpose of evolutionary change. Viewed from the constructal law, the accomplice is the factory owner who by investing in science-based technology is putting the tinkerer out of business.
Evolution is a phenomenon of all physics. Evolving configurations are everywhere and macroscopic. If we see them, something is, or was, flowing. The physics can be summarized as follows.
Nothing moves unless it is driven by power. The power comes from engines, which are natural and everywhere, from the smallest animals and vehicles to the earth’s climate and the water cycle. The engines consume food or fuel: the thermodynamics name for that flow is useful energy, or exergy.6 The flows dissipate the power instantly into heat, which is rejected as heat transfer to the environment of the mover.
The live flow system is an engine and brake system that consumes useful energy, generates power, creates movement that reshapes the earth’s surface, and rejects as heat the dissipated power. The engine and brake system is free to morph, and it does so in the direction identified in the constructal law. The engine part—animal, earth, vehicle—evolves in its internal configuration toward flowing more easily, which means more power and movement per unit of useful energy input. The brake part—animal locomotion, winds, traffic—evolves toward providing easier and greater access to the mover, which means farther and longer lasting travel per unit of power dissipated. In sum, the engine and brake systems that fill nature evolve toward creating greater movement and mixing on earth.
Physicists, sociologists, philosophers and biologists are now coming up with writings that add further confirmation of the constructal law. These writings have become so voluminous that they could easily form the basis for another essay. The words are different, but the mental viewing is the same: antifragility, heterogeneity, complexity, dissipation-driven abiogenesis, dynamic kinetic stability, constructor theory, active matter, and intelligent behavior that maximizes future histories.7
The trend is to express the evolution-as-physics mental viewing in a language that sounds akin to mathematics and physics. The examples of overlap, good ideas and good hunches go on, especially if we look back to earlier concepts that have generated their own fields. Emergence is thought of as the phenomenon where the whole is greater than its parts. This thought is the same as design, or a construction with purpose and meaning. The word emergence has the direction of time printed on it, just like evolution, construction and constructal law. The snowflake, the termite mound and the lung are known as classical examples of emergence. Yet they are also predictable if one invokes the constructal law.8 Emergence after emergence after emergence is evolution everywhere, as physics.
Homeostasis is another way of describing evolutionary design, or construction with flow, freedom, morphing, function, and time direction. Homeostasis is the name for the stable being of a live system such that it has optimal functioning. Permaculture is a similar concept at the much larger scale of human settlement and society. Granularity and building blocks are concepts that account for how the continuous whole is constructed. These features and concepts have been present predictively in the constructal-law field since its inception two decades ago.
Contrary to the current doctrine in science, there is a time direction in nature.9 The time arrow is in plain view in all the macroscopic forms of changing continua—flows, shapes, structures, configurations, designs—which are all around us and inside of us. The time arrow is printed on the words that scientists are forced to use to describe the obvious.
Our nature is continuous and morphing, not infinitesimal, discrete and still. With the law of evolution in place, physics accounts for form and the time direction in evolving macroscopic structures everywhere. Turner’s essay and my letter show how science is spreading and leaving for us the laws that underpin it.10
Adrian Bejan
J. Scott Turner replies:
I thank both Adrian Bejan and Adam Scarfe for their thoughtful comments on my essay. I agree with much in both of their responses. However, both raised questions in my mind that I think warrant exploring further.
The first concerns the question of how we—students of life—should think about life as a phenomenon. Biology has always been split on this question. On the one hand, biologists seek to emulate modes of inquiry appropriate to the physical sciences, the exemplar of this being molecular biology. This mindset is widespread throughout the various physiological sciences: the sciences concerned with how life works, in short. On the other hand, there are concerns with notions of form, mentality, history, and contingency, which include most prominently the human sciences, but more broadly the ecological and evolutionary sciences as well. These differing concerns would seem to call for different modes of inquiry from those that prevail in the physical sciences. Nevertheless, there has been for many years a strong tendency for students of life to emulate physicists and chemists, a tendency long ago described by Ernst Mayr as “physics envy.” Modern Darwinism is the triumphant exemplar of this.
Nevertheless, undercurrents of discontent run through our modern scientific discourse which can only be described as crypto-vitalist. What I have tried to do is to bring up a question that needs asking. Do we believe that life is a phenomenon unlike any other in the universe? If we answer “yes,” we are vitalists. It then becomes incumbent upon us to answer just what it is that makes life unique. My claim is that the answer to this question will not be found through physics envy.
What makes Adrian Bejan’s constructal theory so interesting is that it contains within it both explicit and incipient truths. The explicit truth is that there is a formal and discernible logic of the forms necessary to facilitate flows of matter and energy through systems, whether they be natural, artificial, or biological. There is a compelling logic to the argument that optimum distribution of heat, matter, and information through networks will coalesce around certain forms. This can be seen in a variety of networks, ranging from heat transfer fins in an electrical circuit, municipal water systems, arterial vascular systems, electrical grids, information networks, brains, and nervous systems. I have not exhausted the list.
There is an incipient truth in constructal theory, however, and it revolves around the concept of agency. For example, both systems of watershed drainage and arterial vascular networks have similar form, a branching system of tributary channels that conforms to certain dimensional constraints. Here is the question: does similarity of form imply similarity of agency? The constructal theory opens the door to that question, but does not quite answer it. Watersheds are formed by purely physical agents—passive agency—whereas systems of arteries are constructed by active and intentional agents. The one is driven by physical law, the other is vital, driven by a form of mind, rife with uncomfortable intentionality and purposefulness. Which is correct? We have no good answer.
