Though Living Matter is occasionally technical, physicist Alex Levine elucidates complex concepts in simple and direct prose. Helpfully, the text is bountifully illustrated with many color plates, graphs, and charts. Guided by mechanics and atomic structures, Levine comes to grips with the biological world on a molecular level. He brings alive challenging ideas and concepts by employing clever analogies, and his easy prose is often tinged with humor. As a bonus, the book includes much historical information about scientific discoveries and particular scientists. Living Matter is an impressive book that tackles important scientific principles about the material world and philosophical questions about the origins of life. As an insightful and wondrous narrative about biophysics, this book would be useful for inquisitive, advanced students in biology, physics, chemistry, and philosophy.

Physics, Levine says, attempts to address the long chain of inquiry about a so-called theory of everything. But, he wonders, can such materialistic reductionism really answer questions about living nature. Indeed, an implied question of the book is why we think we can understand the complexities of nature. The biological world is an unusual “transient organization” of atomic particles eating and feeding into entropy (energy dispersal and random disorder). His claim is that physics is a necessary tool for understanding biology. For instance, every particle in the natural world acts in such a way as to build complex organizations. The simple part becomes a complex whole, but there’s no real property of the whole in the part. It’s less to the individual actor but rather, on scale, the combined properties of many pieces forming a dynamic new entity. Levine seems sure that all of this activity can be governed by rules and principles of physics. The problem is that complex systems are not completely knowable. For example, weather is unpredictable and chaotic. He continues by saying that whatever the rules, they differ from any complex system where outcomes could become unpredictable. Take one bacterium, which is complex and consists of billions of atoms because it is alive and moves and morphs. Now, consider many bacteria teaming up as a biofilm.

Organic matter is not in a state of equilibrium but is always changing in terms of energy. Levine suggests that living substances through evolution maintain a quasi-balance of nonequilibrium: controlled inputs and outputs of energy and matter. Moreover, the second law of thermodynamics (concerning force and motion) runs throughout the book. Per the second law, the much larger the system, the less likely are improbabilities since there are more probabilities. His example is how over time the casino wins with lots of gamblers. Levine says the laws of probability in distributions are central to biophysics even though nature seems ordered. Material in a state of equilibrium is actually at odds with internal and surrounding bits. Does this mean that Newtonian mechanics is disorderly deterministic? Not really since these mathematical laws provide only partial and not complete answers. Complex systems appear in the organic realm in spite of entropy, where energy is consumed and then repurposed (e.g., plants in sunlight become food). He calls this process “active matter” that results in material changes essentially diminishing the second law and entropy. Levine’s best example of active matter is a cell’s cytoskeleton.

To use his analogy, physical organisms cannot be divided, as with a computer, into hardware/software. Levine believes DNA is central to organisms and must be viewed not in isolation but through a matrix of interdisciplinary sciences, as he does in his book. The information (programming) of DNA is built into the organism, not added later. DNA molecules affect all the atoms of a being, selecting and moving information from cells and their functions. Over time, some favored traits remain while others are selected out. We can find our history in DNA, as we can find evolutionary narratives in the DNA of other animals and plants. The key question is how so much information in DNA is used, when, and under what circumstances. For example, humans share DNA with other forms of life from great apes to cats, dogs, and chickens. In evolution, there’s an emerging process of stability and mutation. Thus, DNA’s genes don’t work in a straight line, as we learned after Gregor Mendel, and now realize there are other, shifting scripts created through stress and diet by an interpretive epigenome (switches outside of the genetic sequence).

As a physicist, Levine shows on the molecular level how physical forces underlie biological life, what he calls “condensed matter physics” responsible for chemical cell growth and lively interaction. While there is still an abundance of single-celled organisms on earth, billions of years ago some of these cells began communicating with each other and organizing, so movement, energy, and force on the microscopic level is not new but evolutionarily old. Levine offers a version of popular mechanics, if you will, for cells as living engines, not metal machines. He suggests that cells know where they belong and, like genes, react to environment, as in blood cell flow. In this way, cells are active matter that shift and change shape and are not necessarily in equilibrium. Moreover, there’s action with cells among the many moving components called organelles in a minuscular, fluid world. He offers, as illustration of cell force and movement, white blood cells that aggressively attack bacterial invaders. This activity also demonstrates how cells respond to and affect their environment. Recalling his earlier chapters, cells operate in a state of nonequilibrium since they trade off energy for mass. Here’s a non-static, dynamic world where entropy means that the probable outweighs the improbable while many possibilities are in play. Nonequilibrium could simply mean tensions within a cell regarding structure, mass, and energy as it seeks control in any given environment, an adaptive mechanism.

These reflections give rise to a discussion of viruses, which, unlike other cells, cannot metabolize, feed, or reproduce without a host. These tiny parasites are alive but by some definitions not quite living matter. That said, they can reproduce rapidly with a simple equilibrium, though there’s a high rate of mutation. Viruses are Darwinian replicators, and we are surrounded by so many that scores have yet to be identified. The good news is that lots of viruses are not interested in humans. Viruses more commonly attack bacteria, which can facilitate gene transfer: evolution in action. Entropy can assemble growth, as he notes with some viruses that evolve and mutate quickly enough via laws of probability to overcome a host’s immune system.

There’s much active matter (energy transmission seeking to avoid disorder) involved in our abilities to see and hear. Levine spends much time discussing the evolution and physics of perception across animal species. We also share with many animals highlyconserved genes that dictate a body plan, more evidence of how physics on the molecular level is worth studying. Even closer to what physicists examine, consider the canals, nerves, membranes, tubes, cavities, bones, and hairs of mammalian ears mechanically responding to sound waves. Much molecular energy goes into the ability to amplify sounds into comprehensible units. Animal bodies are not just machines powered by molecules, proteins, and cells; there’s also electricity. This discovery in 1786 by Luigi Galvani, notes Levine, was a major breakthrough in the study of medicine. Information directing neuronal-muscular movement is essentially electrical, driven by brain neurons in an evolutionary marvel. More interesting, how does all of this bodily wiring work? How is it related to consciousness and behavior? Part but certainly not all of the answer has to do initially with survival and reproduction and then with species socialization.

Are complex systems evolutionary necessary? Why did they evolve cells and ecosystems? What happens if one component of any complex system breaks or dies; does the system then collapse? How strong does a system need to be? Levine asks these questions and suggests that some protein hubs in a network are not random, perhaps programmed by evolution. Random variation follows probability rules. This statement might not be surprising since species in an ecosystem are characteristically more connected through processes like hydration, feeding, and symbiotic behaviors than not. Beyond eating, species engage in mutualistic enterprises maintaining different aspects of a shared environment as with fungi connecting tree roots, water, nutrients, and bacteria. The big question in physics is how biological webs evolve, what’s the structural difference between an organism’s cell network and an ecosystem, and what can we learn?

The puzzle of how living forms generated seems appropriate in a discussion about the second law and entropy. In fact, Levine goes on to explain how the earth of 4 billion years ago would be unrecognizable to us. Yet life arose on this dead planet or came from meteorites elsewhere. Nonequilibrium is important since it’s part of metabolism in biomolecular compartmentalization and replication, all of the ingredients dependent on each other for life at the simplest level. How did these molecular dependencies arise to produce cellular complexities? The answer might not (via biology) reside in a swampy surface but (via physics) exist in the dark depths of oceans heated by underwater volcanic eruptions stewing elements like iron and sulfur. There are questions surrounding the last common universal ancestor, for example life forms prior to bacteria. What Levine knows is that there was likely gene transfer afterwards that might have facilitated early life.

In sum, Levine sees biological physics as charting the way forward not only in theoretical thinking about evolution but also in practical areas like medicine. Biophysics could help explain the outer limits of possible structures in nature, how equilibrium does/not work, and the dynamic spark that brings vitality to molecules and chemical compounds. Living Matter is a book worthy of consideration by anyone interested in life’s big questions.