"Life"
is very difficult to define.
Indeed, it is practically impossible to agree upon
a definition of life, even among biologists of the same
generation. Most prefer to use an operational
description of what living entities can do and perform
rather than use an definition. There are generally two
approaches that have used to describe life: 1) focuses upon a molecular
view, while 2) uses a cell-centered
point of view.
Below please find a table listing of some
Definitions and characterizations of life as published in Noam
Lahav's book,
Biogenesis -
Theories of Life's Origin, 1999, Oxford University Press, N.Y.
(isbn 0-19-511754-9)
"Spontaneous generation exists, and higher forms have gradually and slowly become developed from previously existing lower forms, always determined by the state of the earth, but without immediate influence of a higher power."
"Life will always remain something apart, even if we should find out that it is mechanically aroused and propagated down to the minutest detail."
"Any detailed hypothesis whatever concerning the origin of life must, as yet, be considered worthless, because, up till now, we have not satisfactory information concerning the extremely peculiar conditions which prevailed on the surface of the earth at the time when the first organisms developed."
"The vital forces are molecular forces."
"We may only assume that life is just as old and just as eternal as matter itself. ...Why should not organic life be thought of as present from the very beginning just as much as carbon and its compounds, or as the whole of un- creatable and indestructible matter in general."
"There is no boundary line between organic and inorganic substances. ...Reasoning by analogy, I believe that we shall before long find it an equally difficult task to draw a distinction between the lowest forms of living matter and dead matter. "
"Life is a power, force, or property of a special and peculiar kind, temporarily influencing matter and its ordinary force, but entirely different from, and in no way correlated with, any of these."
"Living things are peculiar aggregates of ordinary matter and of ordinary force which in their separate states do not possess the aggregates of qualities known as life."
"Life is neither a principle nor a resultant. It is not a principle because this principle, in some way dormant or expectant, would be incapable of acting by itself. Life is not a resultant either, because the physicochemical conditions that govern its manifestation can not give it any direction or any definite form...
None of these two factors, neither the directing principle of the phenomena nor the ensemble of the material conditions for its manifestation, can alone explain life. Their union is necessary. In consequence, life is to us a conflict."
"If I had to define life in a single phrase… I should say: Life is creation."
"No physiology is held to be scientific if it does not consider death an essential factor of life. ...Life means dying."
"The broadest and most complete definition of life will be 'the continuous adjustment of internal relations to external relations."
1897 W.
Pfeffer:
"Even the best chemical knowledge of the bodies
occurring in the protoplasm no more suffices for the explanation
and understanding of the vital processes, than the most complete
chemical knowledge of coal and iron suffices for the
understanding of a steam engine. "
"When we seek to explain the origin of life, we do not require to postulate a highly complex organism. ..as being the primal parent of all, but rather one which consists of a few molecules only and of such a size that it is be- yond the limit of vision with the highest powers of the microscope. "
"It is the particular manner of composition of the materials and processes, their spatial and temporal organization which constitute what we call life."
"Life may be recognized only in bodies which have particular special characteristics. These characteristics are peculiar to living things and are not seen in the world of the dead. What are these characteristics? In the first place there is a definite structure or organization. Then there is the ability of the organisms to metabolize, to reproduce other like themselves and also their response to stimulation."
"It does not seem necessary to stop at the word 'life' because this term can be eliminated from the scientific vocabulary since it is an indefinable abstraction and we can get along perfectly well with 'living organisms' which is an entity which can be speculatively demonstrated. "
"A living organism is a system organized in hierarchial order... of a great number of different parts, in which a great number of processes are so disposed that by means of their mutual relations within wide limits with constant change of the materials and energies constituting the system and also in spite of disturbances conditioned by external influences, the system is generated or remains in the state characteristic of it, or these processes lead to the production of similar systems. "
"The existence of life must be considered as an elementary fact that cannot be explained, but must be taken as a starting point in biology, in a similar way as the quantum of action, which appears as an irrational element from the point of view of classical mechanical physics, taken together with the existence of elementary particles, forms the foundation of atomic physics."
"Life seems to be orderly and lawful behavior of matter, not based exclusively on its tendency to go over from order to disorder, but based partly on existing order that is kept up. "
"The essential criteria of life are twofold: (1) the ability to direct chemical change by catalysis; (2) the ability to reproduce by autocatalysis. The ability to undergo heritable catalysis changes is general, and is essential where there is competition between different types of living things, as has been the case in the evolution of plants and animals."
"Life is potentially self-perpetuating open system of linked organic reactions, catalyzed stepwise and almost isothermally by complex and specific organic catalysts which are themselves produced by the system."
"Life is the repetitive production of ordered heterogeneity."
"I suggest that these three properties - mutability, self-duplication and heterocatalysis - comprise a necessary and sufficient definition of living matter."
"All biochemical and biophysical studies lead straight back to the general question of origins. Origin, structure, and function can no longer be separated."
"Life is a partial, continuous, progressive, multiform and conditionally interactive, self-realization of the potentialities of atomic electron state."
"Structural hierarchy of functioning units that has acquired through evolution the ability to store and process the information necessary for its own reproduction."
"Life is made of three basic elements: matter, energy and information. Any element in life that is not matter and energy can be reduced to information. "
"Life... seems to flout the second law of thermodynamics. Biological organisms seem to be something more than chemical systems, yet at the same time measurements on these systems reveal that natural laws are obeyed. The fact that information is at the same time a quantity which can be defined mathematically and operationally and yet exists in living matter, but not non-living matter, may perhaps contribute to a resolution of this paradox. "
"We regard as alive any population of entities which has the properties of multiplication, heredity and variation."
"Life on earth today is a highly degenerate process in that there are millions of different gene strings (species) that spell the one word 'life."
"Life is that property of matter that results in the coupled cycling of bioelements in aqueous solution, ultimately driven by radiant energy to attain maximum complexity."
"The sole distinguishing feature, and therefore the defining characteristic, of a living organism is that it is the transient material support of an organization with the property of survival."
"The most conspicuous attribute of biological organization is its complexity... The physical problem of the origin of life can be reduced to the question: 'Is there a mechanism of which complexity can be generated in a regular, reproducible way?"
"A living organism is defined as an open system which is able to fulfill the condition: it is able to maintain itself as an automaton. ...the long- term functioning of automata is possible only if there exists an organization building new automata. An automaton may serve as such an organization."
"The uniqueness of life seemingly cannot be traced down to a single feature which is missing in the non-living world. It is the simultaneous presence of all the characteristic properties... and eventually many more, what makes the essence of a biological system."
1985
V. Csanyi and G.
Kampis:
"It is suggested that replication -
a copying process achieved by a special network of
inter-relatedness of components and component-producing
processes that produces the same network as that which
produces them-characterizes the living organism."
"Life is synonymous with the possession of genetic properties. Any system with the capacity to mutate freely and to reproduce its mutation must almost inevitably evolve in directions that will ensure its preservation. Given sufficient time, the system will acquire the complexity, variety and purposefulness that we recognize as 'alive."
"Life is characterized by maximally-complex determinate patterns, patterns requiring maximal determinate for their assembly. ...Biological templets are determinant templets, and the uniquely biological temp lets have stability, coherence, and permanence. ...Stable templets-reproducibility was the great leap, for life is matter that learned to recreate faithfully what are in all other respects random patterns."
"Living system is an open system that is self-replicating, self-regulating, and feeds on energy from environment."
"Just as wave-particle duality signifies microscopic systems, irreversibility and trend toward equilibrium is characteristic of thermodynamic systems, space-symmetry groups are typical for crystals, so do organization and telemony signify animate matter. Animate, and only animate matter can be said to be organized, meaning that it is a system made of elements, each one having a function to fulfill as a necessary contribution to the functioning of the system as a whole."
"Life is an expected, collectively self-organized property of catalytic polymers."
"Life as the ability to communicate."
"Life is a self-sustained chemical system capable of undergoing Darwinian Evolution"
(Joyce, 1994, p. xi).
"An autopoietic system is organized (defined as unity) as a network of processes of production (synthesis and destruction) of components such that: i) continuously regenerate and realize the network that produces them, and ii) constitute the system as a distinguishable unity in the domain in which they exist."
"Signal transduction is as fundamental a feature of life as metabolism and self-replication."
"Life may well be described as 'a flow of energy, matter and information."
"We propose that living organisms are systems characterized by being highly integrated through the process of organization driven by molecular (and higher levels of) complementarity."