See also: Life (homonymy)

The life is the name given:

  1. with a particularly important phenomenon empirical for the human ones (which is themselves alive and for which the other living beings have an essential place), but which is not easily let define (cf will infra). This phenomenon is opposed to the concept of inert matter, and is articulated with the concept of Mort;
  2. with a temporal extent, between the Birth and the Dead;
  3. with the contents in events or actions of this temporal extent, for human;
  4. with the harmonious approach of the human relations (see “ social question”).

One of the marks of the hominisation is the existence of funerary rites, and thus of a conscience of a transition between the life and death. The life is a paramount concept which gave place since unmemorable times to many empirical reflections, philosophical, scientific, etc It is also a subject of political debate, which it is about the treatment granted to the living beings compared to the human ones and the inert things (cf écologisme) or of the considerations on the beginning and the end of the human life (cf Avortement, Euthanasie, “eternal life”).

These reflections concern:

  • the static category (in opposition to the “inert” matter or with the state of dead)   ;
  • the concept of evolution (passage of the inert matter to the life, development and dissolution of the alive forms, died, creation, etc).

They are always related to the concepts of Esprit and Intelligence. They also lead to reflections on the temporal and space extent of the life (including in the universe: “extraterrestrial life”). They wonder at the same time on the conditions of appearance of the life (single phenomenon or on the contrary very banal) and about the possibility of an advanced life (by comparison with the humanity, implicitly considered as the completion of the evolution of the terrestrial life) within the universe.

In science, the study of the life was called Biologie. It proved to be a development of the Chimie, more specifically from the Organic chemistry (containing Carbone), but the theorists do not exclude to adopt definitions being able to include mechanical or electromechanical forms, and even of the forms created by the man out of any natural reproductive process (“artificial life” or artificial Cellule).

Scientific definitions

Any definition must take account of the concept of structural levels of organization, emergence, homeostasis, Entropie and metabolism to avoid finding itself in a “grey area”, as for the example of the viruses (they are alive or not-alive?). The following definitions seem to limit the number of grey areas:

According to NASA, is living any system delimited on the space level by a membrane semipermeable of its own manufacture and able car-to discuss, like reproducing by manufacturing its own components starting from energy and/or external elements.

the life is a state organized and homeostatic of the matter .

Generating mode of organization of the matter of the various forms, of variable complexities, in interaction and having like principal property to almost reproduce with identical the by using materials and L `energy available in the their environment to which they can adapt. The expression almost with identical the refers to the changes which appear at the time of the replication of the organization and which can confer a adaptif advantage on this one.

Life like property of a living organism

The period extending from the design with died of a singular and individual organization.

The organization is the object of a development process, the life, which in general leads it by stages of an embryonic state to the adult and death.

The Seed, the Spore, the Spermatozoon or the Ovule are also forms of the alive one, although they have in themselves neither the form nor the characteristics of the living beings which they will become. It is thus difficult to completely isolate the life from an individual of the Lignée to which it belongs. The alive one is born from the alive one: we do not know the alive one emerging from the inert one, which makes difficult the reconstitution of the stages prebiotic.

Biological characteristics of an living being

Or how can one affirm that an entity is “alive”?

Characteristics on the level of the activities
In Biology, a Entité is traditionally regarded as alive if it presents the following activities, at least once during its Existence:

  1. Development or growth: the entity grows or matures until the moment when it becomes able to reproduce;

  2. Metabolism: consumption, transformation and storage of energy or Mass; growth by absorbing energy or nutrients present in its environment or by reorganizing its mass, by energy production, work and rejection of waste;
  3. external Motricity (locomotion) or intern (circulation);
  4. Reproduction: to be able to create in an autonomous way of other entities similar to oneself.
  5. Answer to stimuli: to be able to detect properties of sound Environnement and to act in an adapted way.

Discussion on these criteria:

  • They all are not at the same time satisfied for a particular individual: sometimes it is necessary to consider the line or the species so that they coexist (the Hybride S deads are living beings);
  • to isolate one or two From it can lead to erroneous conclusions: the Fire (combustion) comparable to a Digestion, because they are two processes of Oxydation, does not transform fire into living being;
  • Sometimes, a criterion misses: the Virus do not grow, but some regard them as alive since they can contain DNA and be provided with mechanisms (transcription of DNA in ARN) causing their reproduction in the host cells;
  • Of other times still, it is only one property which is present and which is transmitted to other entities, as a MIME of the function of reproduction (the prion is a protein, formed out of mirror compared to normal protein, which transmits its pathogenic property to other proteins), etc

Characteristics on the level of the structures and compounds chemical
From where the need, tested by the biologists, to supplement these characteristics to reduce these ambiguities:
  1. the living organisms are made up at least of a cell, i.e. of a closed membrane, separating an external medium and an intracellular medium, which contains genetic material;
  2. the living organisms contain Molécule S such as: carbohydrates, Lipid S, nucleic acid and Protein S, all containing carbon; but one can see there a skewed vision because carbocentric of the life. Forms of life could in theory being based on the Silicium, but this one does not present the astonishing variety of forms and properties of the Carbone;

Other definitions

For Francisco Varela and Humberto Maturana, an entity is alive if:
  • it can reproduce itself;
  • it is based on water;
  • it produces lipids and proteins (?) ;
  • its metabolism is based on carbon;
  • it is retorted thanks to nucleic acids;
  • it has a system making it possible “to read” proteins.
This definition was largely used by Lynn Margulis.

“A system of rétrocontrôles negative inferiors subordinates with a Rétrocontrôle positive superior” (J. theor Biol. 2001)

Tom Kinch defines the life as a system Autophage, highly organized, emerging naturally from the ordinary conditions on the planetary bodies and which consists of a population of replicator S able to transfer.

In the adventure of alive the , the biologist Joel de Rosnay enumerates three fundamental properties:

  • the autoconservation, which is the capacity of the organizations to be maintained in life by the assimilation, the nutrition, the energy reactions of fermentation and breathing;
  • the autoreproduction, their possibility of propagating the life;
  • the Self-regulation: functions of coordination, synchronization and control of the overall reactions.
It is necessary to add to these three properties the capacity of the living beings to evolve/move.

Philosophical definitions

Idealism and materialism

Two great groups of definitions are discussed since the beginnings of the Philosophie: the idealistic designs which are based on a more or less clear separation between the matter and the life (cf the phenomenologic definition, hereafter) and the designs materialists which suppose the life like one of the emergent demonstrations of the matter.

Historically, one can distinguish two theses, without it being possible to determine if one is former to the different one, the more so as they can be the subject of varied syntheses (two theses cohabiting to differing degree within more sophisticated theories). One finds them in the ancient Greek thought.

According to the theses known as dualistic, the life is conceived like basically different from the matter: there is the alive one (spiritual) and the inert one (material and energy) as there is iron and water. The only difficulty, it is “to purify” and “to isolate” (with the almost chemical direction) living it from inert, all the more difficult separation as it is, by definition, inaccessible to the exclusively material methods. These theses call upon various concepts: the heart, the vital breath, the vital dash, etc This separation gave place to various theories, like that of the spontaneous Generation, still long-lived at the time of Louis Pasteur.

According to the theses monists, on the contrary, the life is a manifestation of the matter, a emergent property which appears spontaneously under certain conditions. It is then possible to vary the definition of the life according to the conditions which one regards as characteristics, which introduces of the margins of false debates (contradictors believing to discuss on the concept of life whereas, by adopting different criteria, they prohibit a priori any agreement) even if in practice only the objects in margin are prone to discussion (the microbes, the viruses, let us request them, fire, etc). The modern scientific thought concerns this type of thesis, in particular following the experiments of Pasteur on sterilization: as long as one did not show the need for postulating a duality, it is advisable to stick to the assumption monist. Even if the stages of the appearance of the life, or the organization of the living beings, remain to be explained, the known chemical laws are for the moment sufficient.

Perhaps research on the original material conditions of our planet, with the hope to manage to cross this information with those existing on another planets, will give us a day convincing scenarios of the passage of the inert matter to the life.

A phenomenologic definition

See also: Phenomenology of the life

The philosopher Michel Henry defines the life from a phenomenologic point of view as what has faculty and the capacity “to feel and to test oneself in any point of its being”. For him, the life is primarily subjective force and affectivity, it consists of a pure subjective experiment of oneself which oscillates permanently between the suffering and the joy. A “subjective force” is not a force impersonal, blind and insensitive like are the objective forces which one meets in nature, but a tested force alive and significant interior and resulting from a subjective desire and a subjective effort of the will to satisfy it. It also establishes a radical opposition between the alive flesh endowed with sensitivity and the material body, which is by insensitive principle, in its book Incarnation, a philosophy of the flesh .

Religion

The religion insists on the inalienable character of the life as a fruit of divine creation. The book of the Genèse contains the account of creation.

In the Ten commands, it is written that it is interdict to kill. The Decalog is to some extent a Code of life for the Jews and the Church.

In the New Testament, Jesus known as I am the way, the truth and the life . (Jn 14,6). The the Holy Spirit is called breath of life . The supernatural life finds its source in the hypostatic Union of God.

Magistère addressed the encyclicals Evangelium vitae and Humanae Vitae on the Droit to the life and the fundamental respect that it is owe him.

See too

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