In science, life principle is a supposed or hypothetical scientific principle, theory, hypothesis, or argument that attempts to quantify or justify the existence of “living things” as opposed to something “dead” or non-living things.

Overview
The first to label or group the ubiquity of notions of “life principles” employed in debates on life or the origin of life, in the context of a universe governed by physical science, in terms of one of three “categories” of argument style, was French-born American physicist Léon Brillouin. Specifically, in followup to a 1938 debate at the College of France, wherein physicists, chemists, and biologists met to address the Swiss physicist Charles Guye's 1920 query: “How is it possible to understand life, when the whole world is ruled by the second law of thermodynamics, which points towards death and annihilation?”; during which no consensus was reached.

In 1949, in followup to a Harvard University debate (1946) on the subject of what exactly is or constitutes life in the context of a universe governed by the second law, Brillouin, in his “Life, Thermodynamics, and Cybernetics”, stated that in "what is life?" debates one of three points of view tend to be employed: [1]

(a) Physics and chemistry will soon be able to explain life, without any special “life principle”.
(b) Something more is needed before we understand life.
(c) Life cannot be understood without reference to a special “life principle”; that thermodynamics only applies to dead and inert matter; that life is an exception to the second law.

Brillouin, in this article, argues for the latter opinion. Brillouin’s basic argument, which is rather nonsensical, is that a living organism has special properties, namely: resist destruction and healing ability, which do not appear in inert matter, hence we must accept a life principle that allows for such exceptions to the second law. He states:

“When life ceases and death occurs, the ‘life principle’ stops working, and the second principle regains its full power, implying demolition of the living structure.”

To exemplify the contrived nature of this statement, we point out that nowhere in German physicist Rudolf Clausius’ 1865 mechanical theory of heat (thermodynamics) is there any supposition that the second law implies demolition of living structure; nor, for that matter, does the thermodynamics explicitly differentiate as to two types of bodies (living or dead; life or non-life), there is only the hot body, the cold body, and the working body.

Brillouin followed this publication by “Thermodynamics and Information Theory” (1950), “Negentropy Principle of Information” (1953), and Science and Information Theory (1956) all of which use a hodgepodge of mathematical derivation to make connections between thermodynamics, information, and cybernetics so to attempt to substantiate what seem to be his effort to position his "living principle" argument.

Life principle theorists
A few recent examples of "life principles" include:

Principle
Date
Author
Description

Negative entropy 1943 Erwin Schrodinger Argues that life is something that feeds on negative entropy.
Principle of substance stability 1978 Georgi Gladyshev Used with his "law of temporal hierarchies" to explain the origin of living beings, thermodynamically, as some type of gradual or emergent phenomenon.
Thermosynthesis 1983 Anthonie Muller Argues that the first form of life was some type of pre-respiratory, pre-photosynthesis, version of a molecular heat engine; motto “from negative entropy—by evolution—to intelligence”.
Auto-catalytic closure 1993 Stuart Kauffman Argues that "dead" individual molecular species A, B, and C, become "alive" once catalytic closure among them is achieved and they are able to complete one thermodynamic cycle.
Thermodynamic Dissipation Theory Origin of Life 2009 Karo Michaelian Argues that the thermodynamic function of life today is to produce entropy through the dissipation into heat of high energy photons from the sun. This foments the water cycle as well as ocean and wind currents, increasing the entropy production. This probably was life's function at its very beginnings.
Autogen theory 2011 Terrence Deacon Life originated from a self-generating system—termed an “autogen”—of the form or neighborhood of stable but active inanimate systems, like whirlpools, tornadoes, and “autocatalytic molecules”, systems that maintain their existence notwithstanding material interaction and change. [2]

Principle	Date	Author	Description

Negative entropy	1943	Erwin Schrodinger	Argues that life is something that feeds on negative entropy.
Principle of substance stability	1978	Georgi Gladyshev	Used with his "law of temporal hierarchies" to explain the origin of living beings, thermodynamically, as some type of gradual or emergent phenomenon.
Thermosynthesis	1983	Anthonie Muller	Argues that the first form of life was some type of pre-respiratory, pre-photosynthesis, version of a molecular heat engine; motto “from negative entropy—by evolution—to intelligence”.
Auto-catalytic closure	1993	Stuart Kauffman	Argues that "dead" individual molecular species A, B, and C, become "alive" once catalytic closure among them is achieved and they are able to complete one thermodynamic cycle.
Thermodynamic Dissipation Theory Origin of Life	2009	Karo Michaelian	Argues that the thermodynamic function of life today is to produce entropy through the dissipation into heat of high energy photons from the sun. This foments the water cycle as well as ocean and wind currents, increasing the entropy production. This probably was life's function at its very beginnings.
Autogen theory	2011	Terrence Deacon	Life originated from a self-generating system—termed an “autogen”—of the form or neighborhood of stable but active inanimate systems, like whirlpools, tornadoes, and “autocatalytic molecules”, systems that maintain their existence notwithstanding material interaction and change. [2]

See also
● Defunct theory of life

References
1. Brillouin, Leon. (1949). “Life, Thermodynamics, and Cybernetics”, American Scientist, Vol. 37, pgs. 554-68; In: Biology and Computation: a Physicist’s Choice (pgs. 37-51), by H. Gutfreudn and G. Toulouse. World Scientific, 1994; In: Maxwell’s Demon 2: Entropy, Classical and Quantum Information, Computing (pgs. 73-87), Harvey S. Leff, Andrew F. Rex. CRC Press, 2003.
2. McGinn, Colin. (2012). “Can Anything Emerge from Nothing?; Review: Incomplete Nature: How Mind Emerged from Matter by Terrence Deacon”, The New Yorker Review (pgs. 65-66), Jun. 7.

External links
● Life principle – TheFreeDictionary.com.