Chemistry matters. Join us to get the news you need.

If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.


Physical Chemistry

The Chemistry Of Life

Chemist argues that origin of life and Darwinian evolution are a continuum that can be linked by chemical principles

by Rudy M. Baum
June 17, 2013 | APPEARED IN VOLUME 91, ISSUE 24

What Is Life?: How Chemistry Becomes Biology, by Addy Pross, Oxford University Press, 2012, 224 pages, $29.95, hardcover, £16.99 (ISBN: 978-0-19-964101-7)
What Is Life?: How Chemistry Becomes Biology, by Addy Pross, Oxford University Press, 2012, 224 pages, $29.95, hardcover, £16.99 (ISBN: 978-0-19-964101-7)

What is life? And how did it get started here on Earth? These are two of the thorniest questions humans have been asking themselves through the ages. They are the basis of all religions, and even when a deity is not invoked to answer them, until fairly recently almost all answers to these questions involved some force outside the realm of the purely physical.

This was all well and good, because once you remove some sort of élan vital from the equation and insist on a purely physicochemical explanation for life’s origin, things get very tricky. It’s hard to get from an abiotic world governed by the laws of thermodynamics to a world teeming with living organisms, each of which is an entity of organized matter far from equilibrium that maintains its existence by constantly tapping external energy sources.

In “What Is Life?: How Chemistry Becomes Biology,” chemist Addy Pross attempts to answer these fundamental questions strictly within the framework of physics and, especially, chemistry. Pross believes that a relatively recent subdiscipline of chemistry—systems chemistry, which focuses on replicating systems—holds the answer to these age-old questions and provides a framework for unifying biology and chemistry as a single discipline.

Does Pross accomplish his ambitious goal in this book? I’m not sure. But he certainly leads his readers on an intellectually lively exploration of some fundamental issues in life’s origins and posits an intriguing theory about how inanimate matter can become animate within the constraints of thermodynamics.

Pross is an organic chemistry professor at Ben-Gurion University of the Negev, in Israel. The book “What Is Life?” grew out of a paper, “Toward a General Theory of Evolution: Extending Darwinian Theory to Inanimate Matter,” Pross published in the Journal of Systems Chemistry in 2011 (DOI: 10.1186/1759-2208-2-1).

Pross succinctly states the problem facing theories of the origin of life early in the book. “It is not just common sense that tells us that highly organized entities don’t just spontaneously come about,” he writes. “Certain basic laws of physics preach the same sermon—systems tend toward chaos and disorder, not toward order and function. No wonder several of the great physicists of the twentieth century, among them Eugene Wigner, Niels Bohr, and Erwin Schrödinger, found the issue highly troublesome. Biology and physics seem contradictory, quite incompatible.”

The title of Pross’s book is, in fact, a direct tribute to a book entitled “What Is Life” that Schrödinger wrote in 1944. In this book the great physicist admitted that, at that point in time, physics and chemistry could not account for the existence of life. Pross writes that the purpose of his book “is to reassess this enthralling subject and demonstrate that a general law that underlies the emergence, existence, and nature of all living things can now be outlined. I will argue that thanks to a newly defined area of chemistry … the existing chasm separating chemistry and biology can now be bridged, and that the central biological paradigm, Darwinism, is just the biological manifestation of a broader physicochemical description of natural forces.”

In the first three chapters of “What Is Life?” Pross explores the scientific and philosophic challenges of understanding life. “Living and non-living entities are strikingly different, yet somehow the precise manner in which these two material forms relate to one another has remained provocatively out of reach,” he writes. He points to the complexity of organisms: their purposeful character—dubbed teleonomy, as distinguishable from teleology—their dynamism, resilience, diversity, and other unique characteristics. He briefly discusses previous efforts to develop a “theory of life,” most of which he finds unsatisfactory. He probes what it means to “understand” a phenomenon, focusing especially on the distinction between reduction and holism.

Credit: Shutterstock
Credit: Shutterstock

These are deeply philosophical issues, and Pross is adept at exploring them in clear and concise prose. He has obviously read widely on these topics and given them deep thought. He usefully quotes other scientists and philosophers to explain how thinking on the topics has evolved over time.

Pross then engages in a discussion of chemical stability and instability and introduces a concept he calls “dynamic kinetic stability,” which applies to replicative systems. Dynamic kinetic stability, or DKS, is central to Pross’s attempt to develop a chemical explanation of life. “In the context of chemical systems,” he writes, “static and dynamic forms of stability are very different. In the ‘regular’ chemical world a system is stable if it does not react. … In the world of replicating systems, however, a system is stable (in the sense of being persistent and maintaining a presence) if it does react—to make more of itself, and those replicating entities that are more reactive, in that they are better at making more of themselves, are more stable (in the sense of being persistent) than those that aren’t. This is almost a paradox—greater stability is associated with greater reactivity.”

Throughout the remainder of “What Is Life?” Pross makes the case that DKS, although entirely consistent with the second law of thermodynamics, is sort of the dodge that allowed living systems to arise from inanimate matter. Replicating entities are, he maintains, a different sort of matter governed by a different sort of chemistry from nonreplicating entities. In the long, penultimate chapter of the book, entitled “Biology Is Chemistry,” Pross insists that “Darwinian theory can be integrated into a more general chemical theory of matter, and that biology is just chemistry, or to be more precise, a sub-branch of chemistry—replicative chemistry.”

Pross explicitly equates evolutionary concepts with concepts drawn from systems chemistry. Natural selection, for example, is “kinetic selection”; fitness is “dynamic kinetic stability”; and maximizing fitness is “maximizing DKS.” I’m not sure I buy all of these connections. Pross doesn’t provide a chemical mechanism that underpins natural selection, for example. His argument that natural selection equals kinetic selection seems to be based entirely on the fact that the two forms of selection lead to the same result, but that doesn’t make them equivalent.

Nevertheless, equating fitness and DKS is critical to Pross’s complex argument. “The immediate consequence of relating fitness and DKS is that it indicates more explicitly that fitness is best viewed as a population characteristic, not an individual one,” he writes. “The concept of DKS has no real meaning at the individual level. A stable population of some replicating system is the reality that comes about through individual replicators being formed and then decaying,” and “if you focus on the individual entity … you are missing the essence of what defines life—its dynamic nature, the continual turnover of the individual entities that make up a particular replicating population.” This line of argument even leads Pross to question whether individual living entities actually exist.

All of this leads Pross to conclude that “biology then is just a particularly complex kind of replicative chemistry and the living state can be thought of as a new state of matter, the replicative state of matter, whose properties derive from the special kind of stability that characterizes replicating entities—DKS. That leads to the following working definition of life: a self-sustaining kinetically stable dynamic reaction network derived from the replication reaction.” Complexity, he argues, is not the essence of life but a consequence of life—replication induces complexity. And the teleonomic, or purposeful, aspect of life can be accounted for by the energy-gathering capability of living organisms.

Does Pross’s argument hold water? I’m not entirely convinced. Pross attributes almost mystical power to the dynamic kinetic stability of replicating systems. He freely admits that his ideas get us no closer to knowing precisely what occurred chemically to produce the first living organisms and that they probably won’t help chemists synthesize artificial life. He devotes much of “What Is Life?” to developing the ideas behind DKS and replicating systems but only a couple of pages to the critical corollary of how those replicating systems latched onto energy-gathering systems to fuel their continued growth. Without access to a source of external energy, the replicators could never be viewed as “alive.”

But I’m also not sure that it matters all that much. “What Is Life?” is a lively, intellectually stimulating examination of profound scientific and philosophic questions. It provides an intriguing and possibly plausible way to think about life and its origins. It provides much food for constructive thought, and that’s probably enough.

Rudy Baum is C&EN editor-at-large.



This article has been sent to the following recipient:

Robert Buntrock (June 30, 2013 2:48 PM)
Thanks, Rudy. I'll definitely have to read this interesting book myself. I'm wondering if he accounts for one theory of the origin of life, that of a preliminary RNA world. For that matter, I wonder how he considers viruses in his scheme.
Bob Buntrock (August 17, 2013 4:01 PM)
I finally read Pross' book. Like Rudy Baum, I found it very interesting but I was distressed by several simplifications and misconceptions. Pross considers only entropy (second law) as influencing chemical reactivity, ignoring Gibbs Free Energy. He also fails to acknowledge chemical equilibria, change in kinetics by dwindling resources, especially for self catalyzed reactions, etc. Metabolism is discussed but not as a provider of stasis. His definition of life, by applying only to organisms that can replicate, causes mules and other non-fertile organisms to not be considered "living" although every growing cell in their bodies is replicating. Does he plan to extend this definition to non-fertile or non-breeding humans. Overall, very redundant. Although I haven't read it, the paper upon which this book is based would seem to be a better read (fortunately I bought this book at discount).
Georgi (November 1, 2013 11:53 AM)
Origin of life and its evolution are the result of action of laws of hierarchical thermodynamics.

Criterion of evolution
The approval about the reduction of the entropy of living systems as a result of biological evolution is incorrect. The criterion of evolution of living system is the change (during evolution) of the specific free energy (Gibbs function, G) of this living system. The evolution of living system takes place against the background of flows of energy (e.g., light, energy of physical fields) from the environment. It increases its specific free energy. At the same time, the specific free energy of this living system is decreased as a result of spontaneous processes in this system.
Thus, the total change in the specific free energy of a living system is composed of two parts: 1. The change of free energy due to the inflow of external energy (G1> 0) and 2. The change of free energy due to spontaneous transformations in the system (G2 < 0) . The evolving system constantly adapts to a changing environment. The principle of substance stability contributes to this adaptation.
Thermodynamics of evolution obeys the generalized equation of Gibbs (that is the generalized equation of the first and second laws of thermodynamics)*. Biological evolution and the processes of origin of life are well described by the hierarchical thermodynamics, established on the firm foundation of theory of JW Gibbs. Our theory created without the notion on dissipative structures of I. Prigogine and negentropy of L. Boltzmann and E. Schrodinger.
“Thermodynamics serves as a basis for optimal solutions of the tasks of physiology, which are solved by organisms in the characteristic process of life: evolution, development, homeostasis, and adaptation. It is stated that the quasi-equilibrium thermodynamics of quasi-closed complex systems serves as an impetus of evolution, functions, and activities of all levels of biological systems’ organization. This fact predetermines the use of Gibbs’ methods and leads to a hierarchical thermodynamics in all spheres of physiology. The interaction of structurally related levels and sub-levels of biological systems is determined by the thermodynamic principle of substance stability. Thus, life is accompanied by a thermodynamic optimization of physiological functions of biological systems. Living matter, while functioning and evolving, seeks the minimum of specific Gibbs free energy of structure formation at all levels. The spontaneous search of this minimum takes place with participation of not only spontaneous, but also non-spontaneous processes, initiated by the surrounding environment.”
Works of the author:

Georgi Gladyshev
Professor of Physical Chemistry

*) The generalized equation of Gibbs (See: )

P.S. Lastly, it is important to take into account, from the viewpoint of hierarchical thermodynamics, that anti-aging diets and many drugs can be used for the prophylaxis and treatment of cardiovascular diseases, cancer, and for numerous other illnesses.

Leave A Comment

*Required to comment