In the history of thermodynamics, the question of what is life? and a debate on thermodynamic theories of existence arose following the publication of English naturalist Charles Darwin’s 1859 On the Origin of Species, and has been ongoing; generally viewed to have started with Austrian physicists Ludwig Boltzmann’s 1886 postulate that: [1]


Struggle for existence
In 1798, English demographer and political economist Thomas Malthus published his ‘Essay on Population’, arguing that existence of life is a perpetual struggle for room and food. [2] In short, Malthus outlined the view that population, when unchecked, increases in a geometrical [exponential] rate, but that subsistence increases only in an arithmetic [linear] ratio. Subsequently, according to Malthus, ‘as more individuals of each species are born that can possibly survive … it follows that any being, if it vary ever so slightly in a manner profitable to itself … will have a better chance of survival, and thus be naturally selected.” This meant that, in accordance with Earth’s limited resources, that a ‘struggle for existence’ would emerge. [3]

In opposition to the utopian thinkers of the day, Malthus believed that unless people exercised restraint in the number of children they had, the inevitable shortfall of food in the face of spiraling population growth would doom mankind to a ceaseless struggle for existence. Out of that unforgiving battle, some would survive and many would not, as famine, disease, and war put a ceiling on the growth in population. [4]

In 1938, Darwin, newly back from his voyage on the Beagle and trying to understand the forces that drove the origin of new species, began reading the works of Malthus. [4] Reading Malthus's book (presumably its 6th edition, 1826) triggered in Darwin's mind the idea for a causal mechanism of natural selection. Darwin wrote in his Autobiography (nearly 40 years later), "… [the question] how selection could be applied to organisms living in a state of nature [as opposed to artificial selection, that is] remained for some time a mystery to me. In October, 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population…." [5]

These ideas galvanized Darwin's thinking about the struggles for survival in the wild, where restraint is unknown. Before reading Malthus, Darwin had thought that living things reproduced just enough individuals to keep populations stable. But now he came to realize that, as in human society, populations bred beyond their means, leaving survivors and losers in the effort to exist. [4]

On the logic of Malthus, the general theory that life is a ‘struggle for existence’ is found in the subtitle of Darwin’s Origin of Species , namely that natural selection equates to ‘the preservation of favored races in the struggle for life’, as well as the title of chapter three: ‘Struggle For Existence’. In short, Darwin theorized that: "in the struggle for survival, the fittest win out at the expense of their rivals because they succeed in adapting themselves best to their environment." Moreover, as Darwin stated: "I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection".

In sum, Darwin tended to see species being engaged in a competitive Struggle for Existence. Under the influence of Malthus, Darwin saw this as primarily a struggle for food to support growth, life, and the generation of young individuals to continue the species in question.

Thermodynamics
The collision between Darwin’s 1859 theory of natural selection as a struggle for existence and newly forming 1850 science of energetics, the study of the production of motion by heat, was inevitable. In other words, how can life as a struggle be explained by life as a production of motion by heat? Said another way, how does one energetically-explain a “struggle” of animate beings. The first to take a crack at this was Austrian physicist Ludwig von Boltzmann, who in 1886 stated that: [1]

“The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, all abundantly available – nor for energy, which exists in plenty in any body in the form of heat Q, but of a struggle for entropy S, which becomes available through the transition of energy from the hot sun to the cold earth.”

In 1920, American 200+ IQ prodigy William James Sidis, in his book The Animate and the Inanimate, outlined the view that life is a "reversal of the second law of thermodynamics". [12]

In 1944, Austrian physicist Erwin Schrödinger, in his popular book What is Life?, outlined the view, using crude probability arguments, that “life feeds on negative entropy.” [6] The basic difficulty in Schrödinger’s negative entropy theory is that he equates sustenance (metabolism) with measures of entropy; whereas in the correct sense, sustenance is a function of substrate interactions, as studied in the field of surface chemistry. In an appended note to his thermodynamics-life chapter, however, Schrödinger states that:

“The remarks on negative entropy have met with doubt and opposition from physicist colleagues. Let me say first, that if I had been law catering for them alone I should have let the discussion turn on free energy instead. It is the more familiar notion in this context. But this highly technical term seemed linguistically too near to energy for making the average reader alive to the contrast between the two things.”

In 1978, writer Peter Molton defined life as "regions of order which use energy to maintain their organization against the disruptive force of entropy.” [13]

In 1987 commentary on Schrödinger’s What is Life?, American chemical engineer Linus Pauling noted that Schrödinger was discussing a change in the entropy of the "system", he never defined the system. In other words, one must first define both the system and the boundary, before speaking about either the entropy or the free energy of the system, living or not. Pauling wrote, "Sometimes he seems to consider that the system is a living organism with no interaction whatever with the environment; sometimes it is a living organism in thermal equilibrium with the environment; and sometimes it is the living organism plus the environment, that is, the universe as a whole." Pauling wrote that Schrödinger failed to recognize the most important question: "How biological specificity is achieved; that is, how the amino-acid residues are ordered into the well-defined sequence characteristic of the specific organism." [7]

Another to have commentary on Schrödinger’s negative entropy postulate, was Austrian-born English molecular biologist Max Perutz who stated that: [8]

“We live on free energy and there [is] no [need] to postulate negative entropy.”

Similar to this, in 2003 Danish theoretical chemist John Avery argued, using a bit of information theory, mixed with thermodynamics, and statistical mechanics, that: [9]

“The phenomenon of life, including its origin and evolution (including cultural evolution) … has its resolution in the information content of the Gibbs free energy that enters the biosphere from outside sources”

Difficulties on theory
The general difficulty in each of these entropy/negative-entropy/free energy theories, as stated above, is that the thermodynamic terms used are defined for systems of reactive molecules subjected to a heat gradient. Said another way, the term "free energy", for instance, is the measure of the reactive "affinity" felt between the atoms and molecules of the system and "entropy" is the amount of system energy consumed when the molecules of the system do work on each other irreversibly.

As such, one must firstly define humans as “molecules”, i.e. human molecules, then define “boundaries” to the thermodynamic systems of study, on the surface of the earth, such as an ecosystem, a type of species, a small town, a group of friends, etc., and then define the factors of the "surroundings" that will affect the internal energy of the system. The difficulties involved in making these assignments are enormous. [10] When this is done, the illogic in all of the suggested what is life statements becomes apparent:

Boltzmann - a system of molecules in a flask on a hot-plate (for instance) do not: ‘struggle for entropy’.
Schrödinger - a system of molecules in a flask on a hot-plate (for instance) do not: ‘feed on negative entropy’.
Perutz - a system of molecules in a flask on a hot-plate (for instance) do not: ‘live on free energy’.
Avery - ‘free energy’ is not something that comes from outside the system.

In other words, to define life thermodynamically, one must use a statement that holds for the human molecule as well as for the hydrogen molecule. An example of such a molecular-based (as well as particle physics based) definition, according to the 2007 views of American chemical engineer Libb Thims, is that: [10]

“Life is a chemical or subatomic species in a state of evolution reactivity”

As such, evolution can be further broken down, via standard chemical analysis, into its component chemical reactions, which are coupled, due to the continuous driving force of heat from the sun, and the spontaneity criterion of standard chemical thermodynamics for isothermal-isobaric systems, such as energy, enthalpy, entropy, free energy, chemical potential, external forces, etc., can then be applied in great detail, leaving the long-sought single-statement thermodynamic description of existence to rigorous analysis. In unison with this modern logic, in 2001 American biophysicist Donald Haynie clearly stated that: [11]

“Any theory claiming to describe how organisms originate and continue to exist by natural causes must be compatible with the first and second laws of thermodynamics.”

References
1. Boltzmann, Ludwig. (1886). The Second Law of Thermodynamics. In B. McGinness, ed., Ludwig Boltzmann: Theoretical physics and philosophical problems: Seelct writings. Dordrecht, Netherlands: D. Reidel, 1974.
2. Malthus, Thomas. (1798). On Population, (quote: "the perpetual struggle for room and food", chapter iii. p. 48). Augustus M Kelley Publishers.
3. Moore, Janice and Moore, Randy. (2006). Evolution 101, (pgs. 20-21). Greenwood Publishing Co.
4. Evolution Library: Darwin and Malthus – PBS.
5. Thomson, Keith S. (1998). “1798: Darwin and Malthus”, American Scientist Online, May-June.
6. (a) Schrödinger, Erwin. (1944). What is Life? (ch. 6 “Order, Disorder, and Entropy). pgs. 67-75 Cambridge: Cambridge University Press.
(b) What is Life? (1944 book in word doc download).
7. Pauling, Linus. (1987). "Schrödinger's contribution to chemistry and biology", pp. 225–233 in Schrödinger: Centenary Celebration of a Polymath, edited by C. W. Kilmister. Cambridge University Press, Cambridge.
8. Perutz, Max. (1987). “Erwin Schrödinger's What Is Life? and molecular biology”, pp. 234–251 in Schrödinger: Centenary Celebration of a Polymath, edited by C. W. Kilmister. Cambridge University Press, Cambridge.
9. Avery, John (2003). Information Theory and Evolution. New Jersey: World Scientific.
10. (a) Thims, Libb. (2007). Human Chemistry (Volume One), (preview). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (preview). Morrisville, NC: LuLu.
11. Haynie, Donald. (2001). Biological Thermodynamics. Cambridge: Cambridge University Press.
12. Sidis, William J. (1920). The Animate and the Inanimate, 131-pgs, (published in 1925, R.G. Badger).
13. Peter M. Molton, 1978. J. Brit. Interplanet. Soc. 31, 147.