Into the Cool: Energy Flow, Thermodynamics and Life

  • Eric D. Schneider &
  • Dorion Sagan
University of Chicago Press: 2005. 362 pp. $30, £21 0226739368 | ISBN: 0-226-73936-8

The level of organization in even the simplest living systems is so remarkable that many, if not most, non-scientists believe that we need to go outside science to explain it. This belief is subtly reinforced by the fact that many scientists still think the emergence of life was a fortuitous accident that required a good roll of the molecular dice, in a place where the conditions are just so, in a Universe where the laws of physics are just right.

The opposing view is that matter tends to organize itself according to general principles, making the eventual emergence of life inevitable. Such principles would not require any modifications of the laws of physics, but would come from a better understanding of how complex behaviour arises from the interaction of simple components.

Complex organization is not unique to living systems: it can be generated by very simple mathematical models, and is observed in many non-living physical systems, ranging from fluid flows to chemistry. Self-organization in non-living systems must have played a key role in setting the stage for the emergence of life. Many scientists have argued that certain principles of complex systems could explain the emergence of life and the universal properties of form and function in biology, and perhaps even provide insights for social science. The problem is that these principles have so far remained undiscovered.

In their book Into the Cool, Eric Schneider and Dorion Sagan claim that non-equilibrium thermodynamics provides the key principle that has been lacking. They review its application to topics ranging from fluid dynamics and meteorology to the origin of life, ecology, plant physiology, and evolutionary biology, and even speculate about its relevance to health, economics and metaphysics. The book contains a wealth of good references and is worth buying for this reason alone.

A complex problem: can a need to reduce energy gradients help to drive the evolution of forests? Credit: G. JECAN/CORBIS

When the discussion sticks to applications where thermodynamics is the leading actor, such as the energy and entropy flows of the Earth, or the thermodynamics of ecological systems, it is informative and worthwhile, but it is repetitive and seems disorganized in places.

The book is less successful as an exposition of a grand theory. It gets off to a bad start on the dust-jacket, which says: “If Charles Darwin shook the world by showing the common ancestry of all life, so Into the Cool has a similar power to disturb — and delight.” While it may be wise to stand on the shoulders of giants, it is not advisable to stand back to back with one and call for a tape measure.

The authors' central thesis is that the broad principle needed to understand self-organization is already implicit in the second law of thermodynamics, and so has been right under our noses for a century and a half. Although the second law is a statement about increasing disorder, they argue that recent generalizations in non-equilibrium thermodynamics make it clear that it also plays a central role in creating order. The catchphrase they use to summarize this idea is “nature abhors a gradient”. Being out of equilibrium automatically implies a gradient in the flow of energy from free energy to heat. For example, an organism takes in food, which provides the free energy needed to do work to perform its activities, maintain its form and reproduce. The conversion of free energy to entropy goes hand in hand with the maintenance of organization in living systems.

The twist is to claim that the need to reduce energy gradients drives a tendency towards increasing complexity in both living and non-living systems. In their words: “Even before natural selection, the second law ‘selects’, from the kinetic, thermodynamic, and chemical options available, those systems best able to reduce gradients under given constraints.” For example, they argue that the reason a climax forest replaces an earlier transition forest is that it is more efficient at fixing energy from the Sun, which also reduces the temperature gradient. They claim that the competition to reduce gradients introduces a force for selection, in which less effective mechanisms to reduce gradients are replaced by more effective ones. They argue that this is the fundamental reason why both living and non-living systems tend to display higher levels of organization over time.

This is an intriguing idea but I am not convinced that it makes sense. The selection process that the authors posit is never clearly defined, and they never explain why, or in what sense, it necessarily leads to increasing complexity. No one would dispute that the second law of thermodynamics is important for understanding the functioning of complex systems. Being out of equilibrium is a necessary condition for a physical phenomenon to display interesting complex behaviour, even if ‘interesting’ remains difficult to define. But the authors' claim that non-equilibrium thermodynamics explains just about everything falls flat. For example, consider a computer. No one would dispute that a power supply is essential. Even for a perfectly efficient computer, thermodynamics tells us that it takes at least kT ln2 energy units to erase a bit, where T is the temperature and k is the Boltzmann constant. But the need for power tells us nothing about what makes a laptop different from a washing machine. To understand how a computer works, and what it can and cannot do, requires the theory of computation, which is a logical theory that is disconnected from thermodynamics. The power supply can be designed by the same person who designs them for washing machines.

The key point is that, although the second law is necessary for the emergence of complex order, it is far from sufficient. Life is inherently an out-of-equilibrium phenomenon, but then so is an explosion. Something other than nonequilibrium thermodynamics is needed to explain why these are fundamentally different. Life relies on the ability of matter to store information and to implement functional relationships, which allow organisms to maintain their form and execute purposeful behaviours that enhance their survival. Such complex order depends on the rules by which matter interacts. It may well be that many of the details are not important, and that there are general principles that might allow us to determine when the result will be organization and when it will be chaos. But this cannot be understood in terms of thermodynamics alone.

Understanding the logical and physical principles that provide sufficient conditions for life is a fascinating and difficult problem that should keep scientists busy for at least a millennium. Thermodynamics clearly plays an essential part, and it is appropriate that the authors stress this — many accounts of the origin of life are easily rebutted on this point. But it isn't the principal actor, just one of many. The others remain unknown.