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The ability of an organism to exist and move

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Definition of life on earth: with energy metabolism Capable of responding to stimulation and reproduction open system 。

Life comes from energy: energy → plants microorganism , animals, etc. Life individual All have to experience birth, growth and death. In the replacement of individuals from generation to generation, the life population is constantly making progress towards reality depending on the random variation of genes Convergent evolution 。 Cosmopolitan philosophy believes that life is spontaneously replayed in accordance with the law Cosmic spirit 。^[1]

But in order to include the ones that cannot be excluded, the unknown ones Life forms The definition of life must be universal or even vague enough to cover as wide a range of life forms as possible. Life itself is a process, Life form This is the process carrier , which makes the definition of life and life body very difficult. There is no unified and widely accepted definition of life. Here is an attempt:

Life is aimed at reproduction and spontaneous Entropy change Evolution and Adaptive process 。 (Of course, life should lower itself Entropy , but this is not always successful: sometimes because their homeostasis is destroyed, such as aging; Sometimes, it is unable to completely resist the external high entropy pressure. Entropy change should mainly be a process facing metabolism and regulating metabolism: material, energy and information)

Chinese name: life
Foreign name: life，жизнь
Alias: Pulse of life, miracle

General: Stable material and energy metabolism phenomenon
Experience: birth 、 grow up and death
words whose meaning is similar: life

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Life definition

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Essence of life

Process. From a macro perspective: everything is life, that is, process. The process basically has three stages: occurrence, survival and extinction. Its basic characteristics are: Material indestructibility （ nuclear reaction Except that, in fact, this also conforms to Godel incompleteness theorem ）However, the structure of matter has changed (no matter at which stage), so the so-called life (what we care about) is logically the structure of matter, which is called information in terms.

The three stages of life are actually the process in which matter changes from disorder to order and finally returns to disorder.

The participants are matter and energy (actually energy), and what changes is the structure of matter (because matter is moving).

life

The life we talk about in daily life actually refers to organic life, but it still conforms to the basic definition of life. The difference (class expansion) is that this kind of life has the ability to respond to the outside world dynamically.

Life is the material system of growth and change. Organic life is a unique material system in a planetary environment such as the Earth, which is composed of water as a carrier, and has the ability to spit out old things, reproduce accurately, and divide gently. It is irreversible but always repeats or continues these abilities. An organic life such as cells, animals, plants, etc.

According to human convention, organic life is called life for short. It is not difficult for ordinary people to distinguish between what is alive and what is inanimate. But a scientific definition of life has been given for thousands of years Difficult problems , not completely resolved. This issue is directly related to human understanding of themselves.

Biological definition

Life is made up of nucleic acid and protein The molecular system composed of substances such as reproduction The ability of future generations and to respond to the outside world.

The general scientific definition given by modern biology is roughly as follows: life is the self reproduction Growth and development , metabolism genetic variation And the complex phenomenon of response to stimuli. Here, any single phenomenon is not unique to biology. Flame can also metabolize and reproduce, but most people do not think it is life. Many plant seeds can be preserved for a long time and do not appear Vital characteristics , such as Ancient lotus seed 、 Tardigrade It may not be metabolized for a long time, and when the conditions are appropriate, it will have vitality. The compound phenomenon of self reproduction, growth and development, metabolism, genetic variation, and response to stimulation shown by organisms is called "life".

There are some biological individuals critical period It will not reflect Life phenomenon , such as fertilized eggs, bacteria in the air Viruses , various seeds, even hibernating snakes, etc. They have no metabolism, growth and development and other life characteristics, but they are also the category of life. We cannot call them "non life". Every kind of life has its own way of survival. They are part of life. Without them, life will end. Such as eating, such as human communication, such as some behaviors of animals before copulation.

Let's recognize life by listing some changes and characteristics of living things.

identity

life

In terms of element composition, more than 110 species have been found chemical element The elements necessary for all kinds of organisms are almost specific, including C H、O、N、P、S、 Ca , Mg, K account for absolute majority 。

From the perspective of molecular composition, the important feature of organisms is that they basically contain Biomolecule Protein, nucleic acid lipid , sugar, vitamins and other organic substances, these organic molecules have the same Structure mode And features. Like all living things genetic material Both DNA and RNA , in the body Catalysis Enzymes are all kinds of proteins, which are used by all kinds of organisms High-energy compound （ ATP 、 NADH ...), etc Biosphere stay chemical composition There is a high degree of identity on.

structure

The various chemical components of organisms are not stacked together randomly in the body, but orderly (orderly structure). Vital Basic unit It is a cell (virus Viroid 、 Prion There is a dispute whether or not they belong to the category of life, but they all need to Cellular structure Can be completed normally within Life activities ）。 Intracellular Structural unit Both have specific structures and functions. Biomacromolecule No matter how complicated, it is not life, only when macromolecule Form a structure, or Only by forming such an orderly system as cells can life phenomenon be displayed 。 Loss of order, such as beating cells into homogenate Life is over.

The biological world is multi-level Ordered structure 。 There are tissues, organs, systems individual , population community 、 ecosystem Etc. Each structural unit in each hierarchy, such as Nine systems of human body Each organ in the has its own specific structure and function, and their coordination activities constitute a complex Life system 。

the new supersedes the old

Organisms are open system , organisms and surrounding environment Continuously Substance exchange and energy flow 。 After some substances are absorbed by organisms, a series of changes take place in them and become the final products and are discharged from the body, which is called metabolism. Metabolism is an orderly process, which is a series of enzymes chemical reaction Reaction network. If the order of the metabolic process is destroyed, for example, some links are blocked, the whole metabolic process may be disrupted, and life will be threatened, even leading to the disappearance of vital signs.

Irritability

life

Bioenergy React to external stimuli. It includes two processes: perception of stimulus and response. The result of the reaction is that the organism "tends to benefit and avoids harm". In a drop paramecium A small drop of acetic acid in the suspension will cause paramecium to swim away; a block Carrion Can be recruited fly ； Botany Stem apex Growing towards the light, these are Irritability 。

Stress is a universal characteristic of biology. However, the stress of animals is more obvious and diversified. Animalistic sense organ and Motor organ It is the product of highly developed stress.

steady-state

No matter how the environment changes, organisms must keep Internal environment The activity of stabilizing to maintain normal life. More than 100 years ago, Bernard (C. Bernard) found that although the external environment fluctuated greatly mammal There is always some mechanism to keep its internal environment unchanged. Later, W. B. Cannon developed this concept and called it steady state. Later, it was found that not only mammals, but also all organisms, cells, communities and even ecosystems are stable without the influence of intense external factors. Each of them has its own specific mechanism to ensure its own dynamic stability.

Growth and development

All living things can grow and develop through metabolism. A seed can become a tree, and a tadpole can become a frog. although environment condition It can affect the growth and development of organisms, but the growth and development of each kind of organism are carried out according to a certain size range, a certain model and a stable procedure.

Genetics and evolution

No individual organism can exist for a long time. They can reproduce to produce offspring so that life can continue. Offspring and Parental generation The similarity in morphological structure and physiological function between them is the result of heredity. The difference between parents and children is caused by variation. The evolution process of organisms from simple to complex and from low to high is the result of evolution from about 3.8 billion years ago.

adapt

Every creature has its own unique environment The specific structure and function are always suitable for survival and continuity under such environmental conditions. For example, the structure of fish gills is suitable for fish to breathe in water vertebrate The lung structure of Respiration 。 Adaptation is a special phenomenon of life.

The adaptation of any organism to its environment is always relative. Due to genetic and phenotypic differences, the adaptation of the same individuals to the environment is always different in degree. As long as there is such a difference, even if it is slight, natural selection It will take effect and promote the group to evolve in the direction of more adapting to the environment.

Other definitions

Life consists of nucleic acid, protein, etc Biomacromolecule The organism is constantly carrying out material, information and energy exchange A synthesis of Sports form 。 Human life is based on certain social environment The in the relationship has self-consciousness The biological entity of. Human life is a combination of biological attributes and Social attribute Human Social It is the most essential feature that distinguishes human beings from other animals, and it should be emphasized in human survival Material value 、 Spiritual value And the unity of human values.

Because of the complexity of life, there is no accurate definition of life, so we can only grasp Essence of life To define life.

Some people define life as "life has Autocatalysis Characteristic cyclic reaction molecular system, which can recycle with the environment; adopt Synergy 、 Integration ； It is a functionally coupled hypercycle organization ". According to this definition, the cyclic reactions of a large number of molecular systems can evolve coherently through synergy, thus maintaining stable state 。 Life information can be stored on macromolecular DNA, and can also be copied, transcribed and translated biochemistry loop Reaction structure And magnify, form individual, this is life. According to the traditional definition, virus is not a complete life; According to this definition, a virus is a complete "life". Viruses must rely on cells to survive; For a virus, cell is its living "environment", which can circulate together with the environment.

Common cycle The concept of“ Irritability ”The concept of homeostasis and evolution is fundamental, but heredity is not necessary (common cycle can be understood as Coevolution ）。

(1) [life]: the ability of living things to exist and move

(2) [vitality]: refers to the nature of things that can exist

(3) [condition]: refers to the qualification and ability to participate in certain activities

Basic Attributes

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Self-regulation

Self regulation is a part of life Essential attribute 。 Any life in every moment of its existence ， They are constantly adjusting their internal functions and the relationship between themselves and the external environment. Higher biological Self-regulation It is multi-level , including molecular, cellular and overall regulation. even if it is prokaryote There is also self-regulation, and it is also achieved through a variety of ways. For example, bacteria have the ability to synthesize many molecules they need. Whether or not a molecule is synthesized, and how fast it is synthesized, depends on their internal state and environment. The molecules needed by bacteria are neither produced too much nor lacked. They depend on themselves Regulatory mechanism Completed. Of the first enzyme in a molecular synthesis pathway Structural gene It also has the function of regulation, that is, the first enzyme has the function of both enzyme and Repressor protein The role of quality.

In genetics and biochemistry, this function is called Self regulating system 。 This kind of regulation system was initially Salmonella histidine biosynthesis Found in, and later in phage 、 mould It is also found in mammals. actually, Feedback suppression And the regulation of induction system and repression system can also be regarded as the way of biological self-regulation. Because in feedback suppression, Biosynthetic pathway The first enzyme in occurs by combining with metabolic end products reversibility Inactivation So that the synthesis rate of many compounds can be adjusted. In induction system and repression system, even the production of enzyme itself is regulated. The difference between them is that in the induction system, the enzyme needed for the substrate can be produced only when the substrate exists, in the way that the substrate and Repressor Combine and inactivate the repressor to open the structural gene to induce gene activity; In the suppression system, End product inhibition The enzyme is produced by combining the repressor with the end product to be activated, and then Manipulating gene To turn off structural genes to Repressase Generation of. Many biological regulatory systems are complex, and they often have both positive and negative regulatory effects. The regulating mechanism of the body is a self completing process, and the regulating program or command is inherited and inherent, so this kind of self regulating system is unique to life.

Self replication

It is the characteristic of life system different from chemical system. In a narrow sense, Self replication Means DNA molecule Of Unrotation , two chains separated and synthesized separately Complementary chain To form two new but identical molecules. Broadly speaking, it includes cell division , reproduction included. As far as the basis is concerned, division and reproduction are also carried out on the basis of molecular replication; As a result, two identical individuals are formed. Due to the periodicity of biological reproduction, as well as diseases, hybridization and other reasons, some organisms will lose Fecundity Therefore, reproduction is difficult to be the basic attribute of life. But self replication is different. As long as life is not in a state of disintegration, there is always self replication. Therefore, it is an attribute throughout the life process. stay In vitro experiment The lysis products of cells can still maintain the synthesis of DNA under certain conditions, and some single strand DNA can also be transformed into Double chain Form. However, nonliving systems cannot be realized by themselves DNA replication , although necessary nucleotide And helicase polymerase 、 Ligase DNA can also replicate, but the process of its formation is short-lived. Self replication is an inherent feature of life system 。

Selective reaction

Bacterial fossil

In vivo External environment The selective reaction is another important feature of life system. Reaction is an attribute of both nonliving matter and living matter. The difference is that physical and chemical reactions occurring in nonliving substances are not self completing processes. Only biological organisms can react independently, and this independent reaction is selective. It is controlled by the organism itself and varies with the internal and external environmental conditions. When cells exchange substances with the outside world, diffusion and Infiltration , but cell membrane What is absorbed and what is excluded is highly selective. An obvious example is the Active transportation Medium, material inverse concentration gradient And running. Another example is:, Escherichia coli Available glucose , also available lactose As carbon source 。 When there is both glucose and lactose in the environment Metabolic reaction First, glucose is used instead of lactose. At this time, only the enzyme system plays a role Inducible enzyme The system is irrelevant.

Biological selective reaction is also the result of coordinated activities of several systems. simple prokaryote This is the case for the reactions of higher organisms, especially for the selective reactions of higher organisms. Because there are different enzyme systems in higher organisms, these enzymes are not only incomparable to inorganic catalysts for their efficient catalysis, but also have strict selectivity. At the same time, organisms Endoenzyme The activity of the enzyme is regulated and controlled by many factors. The interactions between enzymes and between enzymes and other proteins will affect the activity of the enzyme, and the products of one enzyme will also have positive or negative effects on the activity of another enzyme.

In external behavior, biological selective reaction is more obvious. For example, animals in the satiety state do not respond to food; The novel motivation can initially attract the attention of animals, but over time, its response becomes very weak, and so on. In fact, all living things react to the environment in a certain way, but not in a certain way, or the same agent sometimes appears in this form of reaction, and sometimes in another form of reaction.

Purposiveness

Schopenhauer (1996), a 19th century German philosopher, once enumerated the three instincts of life: survival, reproduction and maternal love^[2] 。 Xie Ping (2014)^[3] It is pointed out that maternal love is meaningless in the lower life, like many Unicellular organism Their life behavior is to constantly split in two and repeat Cell growth A simple process of division and growth. Maternal love should be Higher animal A common one in Instinctive behavior In some species, it can even surpass itself.

mono (1977) believed that animals and plants have such nature and Purposiveness ：“ plant growth Seeking sunshine and death; Animals spy on hunting targets, attack enemies, feed and protect young, and males fight to occupy females These creatures all have one goal: to live and make their descendants live, even at the cost of death "^[4] 。

Others believe that "the purpose of a creature is Survival, competition and reproduction ', development, evolution and transformation of the universe and energy' ”Competition can be seen as a way of survival. Of course, Cooperative phenomenon It can also be seen as a kind of generalized competition, and this cooperation can occur between species (such as reciprocal symbiosis Phenomenon), can also occur within species (such as group hunting or Defensive behavior ）^[3] 。 As Williams (2001) said, a group composed of interacting individuals may be organized adaptively in such a way that individual interests are realized through a functional Subordination Submit to group interest^[5] 。

Therefore, Xie Ping (2014)^[3] It is believed that all life (belonging to specific species) must have three intrinsic original purposes, which are related to food, survival and reproduction. They are:

① It is the intrinsic purpose of all plants to enjoy the sunshine (of course, under the premise of the existence of appropriate nutrients and water), and to obtain the organics synthesized by plants ( Carnivore This is all animals and many Heterotrophic microorganism Intrinsic purpose.

② Survival (at least until successful reproduction) is all Life individual The second intrinsic purpose of the male of many species is to die immediately after mating (what a cruel life process it is). Survival is also an individual Survival competition And adaptation.

③ Reproduction or mating is the third intrinsic purpose of all life, whether through asexual or sexual means. Without it, there might not be the brilliance of flowers and butterflies in nature, and there would be no charming Birdsong Chirp, there is no male fight for love. Of course, no species will exist without reproduction.

just as Ancient Rome poet Lucretio Said, "The sacred joy, the things that life's guide seduces people to approach. She serves as a guide to people, with the purpose of making people reproduce new generations forever to avoid extinction through her treacherous seduction of love" (Lucretius 1981)^[6] 。

Self regulation, self replication, selective response and purposefulness are the important characteristics that distinguish life from non life.^[7] These characteristics of the life system, as far as its basis is concerned, are undoubtedly physical and chemical processes and obey the laws of physical and chemical. But these Physicochemical changes However, the result of is transformed into something of life and becomes a unique attribute of life. Although one of the four basic attributes, or some aspects of one attribute, may also exist in the inorganic world, only in life can these four attributes be linked and combined in a system.

Ancient view of life

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life

ancient Greek Philosophers of 20% tend to call all unknown causes of movement "force". Later scholars borrowed the concept of "force" and studied various movements, such as "gravity" and "electromagnetic force" in physics, and "affinity" in chemistry. The research has made many achievements, but it is not clear Ancient Greek philosopher What is the so-called "vitality" or "vitality".

Ancient Chinese philosophers tended to attribute the unknown causes of movement to "qi", and life was regarded as an activity of "qi". For example, "people's life is also the gathering of qi. Gathering means living, while dispersing means death... Therefore, it is said that all the people in the world have one breath ear". "Qi" is also an ambiguous concept, and different scholars have different interpretations. For example, "when people are born, they are like ice, and water condenses into ice, Gas accumulation But a man. " Here, the formation of life is compared to the process of freezing, and there is also a comparison of life to fire. For example, "people are born with gas, and die with all their essence. Death is still torn and extinguished. For example, if there is no light, and the fire is extinguished when the salary is exhausted, there is no light. Therefore, after putting out the fire, there is no inflammation left; after death, there is no soul left." This view emphasizes that life is an ignorant metabolic process. Ancient Chinese philosophers regarded life as one Material movement In the process, life and death are often discussed together, which is also Chinese philosophy The integrated thinking features, such as "there are blood lines, all things are born, all things are born, and all things are dead. Because they are born, they know that they are dead", and regard life as the opposite of death.

Special creation theory

Think that life is made up of Material power It is created by God or God or something beyond the material decision. This is an idea that came into being when human beings had a low ability to understand nature, and was later socialized ideology It is used occasionally or unintentionally, which makes people who advocate the absolute supremacy of spirit believe that Special creation theory 。

Autogenesis

Ancient times People have a low understanding of nature, but they have been able to carry out abstract thinking activities, and have concluded that life is a natural occurrence according to the phenomenon. The representative ideas are "meat rots and maggots, fish withers and fishes grow" in ancient China, Greece Aristotle "Some fish are developed from silt and gravel", etc.

Otherism

As people deepen their understanding, they realize that maggots come from the eggs laid by flies, louis pasteur Later, people believed that life was produced by parents and spores, that is, life could not be produced naturally. however Origin theory There is no answer to how the initial life was formed.

Buddhist life theory

The sun, the moon, the stars and the dust. Wind, fire, thunder, electricity, magnetism. Gold, wood, water, fire and earth are the lower embodiment of the energy flow of the universe's yin and yang, and have a basic Natural elements Conditions can breed life.

Sakyamuni Buddha said, "All living beings are equal." Here, life generally refers to those who have the ability to breathe and continue. Breathing is an advanced way for life to express yin and yang.

psychic determinism

All things in the universe are composed of "spirit", all things are constructed by the will of God, and man is Cosmic spirit Individualization of, the secret of the universe is in human itself, to be understood. Man himself is a single universe, temple It corresponds to the position of the sun, and the heart corresponds to the position of the earth. The ancients' "harmony of heaven and man" means that all changes in the universe will have a corresponding inevitable internal connection. In a sense, the "three flowers gather together and five qi move towards the yuan" of traditional Chinese medicine is the relationship between human beings and the universe Movement change development Relationship. The whole universe and the world are a harmonious unity. Nothing can escape from this harmonious law and can not exist in isolation. Life is "qi" in the sky, "qi+type" on the ground, "qi+type+emotion" on the objects, and "qi+type+emotion+righteousness" on the people. The difference between human existence in heaven and earth and other things lies in friendship. "People are different from animals. The common people will leave and the gentleman will keep". This is Mencius The famous saying of "love" should not be attributed to those who are righteous or to all things.

Cosmic spirit

One Life carrier The birth of is not simply a single cell, it is the external reflection of the inner spiritual individual. This spiritual individual is against other things, and is born with individual differences. Life is not a process from scratch, but a process that unfolds gradually. Every step is thrilling and painful. whatever Vital signs In the existence and individual composition of, only the spirit is an indispensable and important part. The spirit can endow all things with continuous upward momentum and dominate the whole Cosmic space The change and evolution of. A seed, a grass, a tree, everything on the ground that has life should be explained by the definition of spirit. Without spirit, the world would be doomed.

According to the complete closure theory of the universe, "now" corresponds to the future Or It is a point in the past. The future is not impossible to pass through, and the history is not impossible to change, but it lacks necessary conditions. along with Future mankind With the deepening of cognition, the interpretation of life and death and the understanding of human self will tend to be true and perfect.

Modern outlook on life

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According to the characteristics of life forms, life is defined in modern science After the emergence, people natural phenomena Study by category. Different sciences study life from different perspectives, so they have different views on life. Before the 1950s, people from all life forms Surface characteristics To sum up a definition of "life": Life is a material system with the characteristics of material and energy exchange with the environment, growth and reproduction, genetic variation and response to stimuli 。 This definition describes the general characteristics of life activities and has certain Scientific knowledge Value. But with the development of science, people increasingly feel that this definition has great limitations. Because all of these features can have some exceptions.^[8]

Chemical evolutionism

earth

It advocates to study the origin of life from the movement and change law of matter. It is believed that Primitive Earth , Inorganic It can be transformed into organic matter, and organic matter can be developed into biological macromolecules and Multimolecular system Until the original Life form 。 1924 Soviet Union Scholar A N. Opalin first put forward this view. In 1929, the British scholar J B. S. Haldane also made a similar point. They all believe that life on the earth is evolved from nonliving matter over a long period of time. This process is called Chemical evolution , as distinct from those after the emergence of organisms Biological evolution 。

Opalin's Origin of Life on Earth, published in 1936, is the first comprehensive exposition in the world Origin of life Monograph on problems. He believed that there was no free oxygen reducing atmosphere on the original earth Short wave ultraviolet Under the action of other energy sources, simple organic matter (biology Small molecule ）, simple organics can generate complex organics（ Biomacromolecule ）, and on Primitive ocean Polymolecular aggregate After a long period of evolution and "natural selection", the latter finally appeared Primitive life That is, primary body. Chemical evolutionism There are more and more experimental evidences, which have been accepted by most scientists.

Hegel's view of life

The concept of "life" Hegel It is a core concept. In the early stage Human alienation Hegel put forward the concept of "life", the unity of soul and body, subjective and objective, to make life free. In the later period, Hegel took life logically as Directness At the same time, it puts forward three kinds of life: logical life, natural life and spiritual life Outlook on life To generalize the concept of life ideological system They are regarded as an organic organism. Marx believes that Hegelian Reasonable kernel Just because of his dialectic thought, Hegel discussed dialectics and ideas together, so the discussion of dialectic thought does not occupy much space in Hegel's works. But there's no denying it Dialectics It plays an important role in Hegel's thought. Dialectics is the soul and core of Hegel's thought. Dialectics is inherent in the idea and the most intrinsic link of life and spirit. The idea of directness, that is, the movement of Hegel's so-called "life", makes dialectics become speculative dialectics and the internal root of dialectics that can carry out self reflection, self sublation, and return to self free movement. In Hegel's view, life or concept is a spiritual thing, hegelian dialectics The soul of is the self movement of life and spirit, that is, the dynamic and negative movement of the conceptual self, Negativity Make the dialectical movement of concept or possible.^[9]

Engels' view of life

Engels《 Anti Durin theory 》Life is Proteosome The existing form of. this Existing form Of Basic factors The reason lies in the continuous metabolism with the external nature around it, and once this metabolism stops, life will stop, and the result is the decomposition of protein.^[10]

Engels' definition was put forward on the basis of criticizing Durin's definition of life. Durin once defined life as "the metabolic activity of cells". Engels believed that advanced organisms are indeed composed of simple types of "cells", but there are lower than cells, which are similar to advanced Biofacies Because their basic component is protein, they perform the function of protein - life and death.

plant cell

Engels' definition of life is consistent with his thoughts on the form of motion of matter. Engels believed that there are five forms of movement in nature: mechanical movement 、 Physical motion , chemical movement Life movement and social movement 。 From a historical perspective, these five forms of motion reflect the order of evolution and development of nature. Each of the following forms of motion is evolved from the previous form of motion. Different forms of movement have different material undertakers and different laws of movement. Higher forms of movement include lower forms of movement. Life movement is an advanced movement, which is developed from chemical movement. Its material undertaker and its movement law are different from chemical movement, but life movement includes chemical movement. Engels emphasized the natural Continuity 。 If life is defined as Cellular structure It is difficult to explain the origin of life. Engels paid special attention to the dialectical development process from the inorganic world to the organic world, so Engels chose Proteosome Matter as life activity.

vitality

"Here, proteome is understood in the sense of modern chemistry, which includes everything similar to ordinary protein or protein in structure. The name of proteome is not appropriate, because ordinary protein is the most lifeless and passive among all the similar substances. It, together with eggs, is embryonic development But when the chemical structure of the protein body is still unclear, this name is better than all other names because it is more general. " It can be seen that the protein body referred to by Engels is in a broad sense. It is not even a polymer in the modern sense, but a material system. Engels used the word in different fields, and sometimes he even called cells "small pieces of protein". For example, he said, "Everything Organism Except for the lowest level, they are all composed of cells, which are very small and can only be seen after high magnification nucleus It's made of small pieces of protein. " In short, Engels equated life with proteome. Life is "inherent in protein, born with, without this process, protein cannot exist."

In the first half of the 20th century, with the progress of biochemical research, people have more and more clear understanding of the structure and function of proteins. Proteins are complex in shape and different in function, and play an extremely important role in the process of life activities. All these make many people more convinced that the molecular basis of life is protein.

Engels' "proteome" refers to nucleic acids and proteins. That is to say, there is no life without protein. Therefore, it fundamentally negates the creation theory that God created man. Engels' definition of life, to a certain extent, reveals the material basis of life, that is, the protein body with metabolic function. For 100 years, this definition has been guiding people to understand the idea of life.

Engels also boldly proposed that since life is Material movement As long as the conditions are suitable, the flower of life can also open on other planets. modern astronomer This statement is affirmed.^[11]

Cosmic germ theory

With the great development of astronomy, people proposed that life on the earth came from the "embryo" of other planets or the universe, which was popular in the 19th century.

All creatures have the same Genetic code , and rare element Molybdenum in Enzyme system The fact that it plays a particularly important role in provides some support for this argument.

molecular biology

Abundant and colorful biology

The definition of life is summarized from the commonness of the microscopic composition of life materials. according to molecular biology People have a more detailed understanding of the basic substances that constitute life activities. The shape, size and structure of life can vary greatly, but they are all determined by Deoxyribonucleic acid （DNA）、 Ribonucleic acid (RNA) and proteins as skeletons.

DNA is composed of four different types called Deoxynucleotide A very long molecular chain composed of small molecules (monomers) in a certain order. Listed as Escherichia coli DNA is composed of about 20000 deoxynucleotides Long chain 。 In various forms of life, DNA is equivalent to a book with the same letters written in different lengths, in different order, and therefore with different meanings. RNA It is also called Deoxyribonucleotide A molecular chain formed by the connection of monomers. The condition is similar to DNA, but the chain is short. In various forms Life form There are various molecular chains of different lengths. RNA proteins are composed of 20 different amino acid Monomers are linked to long chain molecules in a certain order. There are various protein chains with different lengths and monomer arrangements in different life forms, and the folding and curling shapes of the chains are also different. In short, DNA, RNA and protein of various organisms are respectively composed of four deoxynucleotides, four deoxyribonucleotides and 20 amino acid monomers, which means that they are all composed of universal "elements". These nucleic acids and proteins play basically the same role in the life activities of various organisms.

Because DNA can replicate itself, life materials have the ability to reproduce and inherit. Because DNA can determine the structure of RNA and protein through transcription and translation, it controls the morphological structure and physiological function The process of replication, transcription and translation requires the participation of protein enzymes and RNA. In this way, there is a molecular biology Definition of life: life is produced by the interaction of nucleic acid and protein, especially enzyme, which can continuously reproduce material feedback circulatory system 。^[11]

This statement is about life material Of Microstructure And the description of its movement process. It summarizes some important theoretical breakthroughs in molecular biology, but there are still some unclear boundaries. There is a kind of thing called "virus" in nature. Viruses are only naked annular Nucleic acid is composed of nucleic acid chain and protein shell. When it exists alone, it looks like a pure chemical substance and can be crystallized host cell In this way, we can use the "machine" of monomer energy supply, replication, transcription and translation in host cells to self reproduce. In addition, viroids have a similar situation. Do these substances have life? Some people believe that life should be called as long as it can control its own reproduction and genetic variation and respond independently to evolutionary forces. If so, then the virus phage , plasmids and other objects can be classified as life bodies. Others believe that life must be able to replicate, transcribe and translate independently. Viral viruses and plasmids are incomplete life forms. They are parasitic and cannot exist independently. The latter view cannot be the dividing line of a clear definition of life. Because life has never been an isolated existence, life and the surrounding environment are inextricably linked with other life. This makes what is independent life and what is parasitic life lose clear meaning. Therefore, it is also necessary to take a macro perspective, that is ecology To study Outlook on life 。

Biophysics

Biophysics Focus on Material movement Of general rule Indicate on Vital characteristics 。

solar system

Order and entropy. Matter and energy are conserved. The earth has nothing to do with the outside world Substance exchange , only from solar radiation The energy obtained is reflected and radiated into space. The energy radiated from the sun to the earth is equal to the energy reflected and radiated into space by the earth. Although there is no significant change in the material and energy of the earth, various elements on the earth have different reactions due to solar radiation, resulting in different movements of the earth's material uniform distribution 。 The impact of energy flow caused by solar radiation on the earth is stable, rhythmic and regular for a long time, so the uneven distribution of earth material is rhythmic and regular. This creates an orderly state of distribution and movement of the earth's material.

The second law of thermodynamics A function called "entropy" is used to measure the uniformity of a system. One Isolated system That is, the system without exchange of matter and energy with the outside world, and the motion always increases the entropy (disorder value). When entropy reaches maximum value The macro material movement will stop when thermodynamic equilibrium 。 At this time, the system is in a uniform and disordered state. The earth is not an isolated system, but a closed system, that is, a system with only energy exchange but no material exchange with the outside world. It receives the energy of solar radiation, and at the same time reflects and Radiant energy 。 The energy radiated by the sun makes the solar surface in a high temperature state (about 5800 ℃). According to the definition of entropy, the sun is relative Low entropy Region, due to the Earth surface temperature Far below the sun, the energy reflected and radiated by the earth to the sun is in a relatively high entropy area, which can be described by such a formula:

Energy state

Here S represents entropy, and dS/dt represents the rate of change of entropy with time. Q stands for energy, dQ/dt is the rate of change of energy with time. T Sun and T Earth represent the surface temperature of the sun and the surface temperature of the earth. If this formula is less than 0, it means that the entropy of the earth is falling during the transformation of the sun. Therefore, the material and energy on the earth are in an uneven and orderly state.

Life is an open system, which has not only energy transformation but also material exchange with the outside world. Life form In fact, it is to obtain the high entropy matter and energy in the form of food from the environment and transform them into Low entropy State and expel the waste out of the body, so as to keep its entropy at a lower level than the environment, that is, maintain its orderly state. The order of life is obvious at the molecular level. Macromolecules such as nucleic acids and proteins have a certain order in various cells, even one ecosystem There are certain space structure 。 Orderliness is not only shown in space distribution On the other hand, it is also reflected in the activity rules of life: growth, development, reproduction, aging, death, and regular response to external stimuli. from thermodynamics From the point of view of, these phenomena are all caused by solar radiation, but only life activities exist on the earth, and the emergence of life must have its own internal factors.^[12]

Mechanistic theory And Vitalism 。 On the origin of life Essence of life There has been a dispute for a long time. Mechanism is sometimes called Reductionism It believes that life phenomena can be explained by the laws of physical science, and the advanced and complex laws can be reduced to simpler and more basic laws. The theory of life regards life as a machine and takes different forms of expression in different periods. 16. Clockwork machinery was very fashionable in the 17th century. Some people thought that microorganisms were nothing more than machines like clocks, which were invented in the 19th century steam engine Others think that creatures are just“ heat engine ”。

ecology

biosphere

From the known facts, solar system Life activities are only found in the biosphere of the earth - atmosphere , up to a depth of more than ten kilometers on the surface, which is relatively not thick Spatial composition 。

In the biosphere, some life has chlorophyll , available photosynthesis , most plants blue-green algae And some bacteria belong to this kind of life. There are also some organisms that do not have chlorophyll and do not carry out photosynthesis and must rely on ingestion Autotroph Or other creatures live for food, called Heterotroph 。 Fungi, animals (including humans), and most bacteria belong to this kind of life. Inorganic substances in the biosphere enter the organism through the photosynthesis of autotrophs. Some of them return to the inorganic world through their own metabolic activities, and some of them are ingested by heterotrophs. Through their metabolic activities, they return to the inorganic world. Most plant straws and animal carcasses are Saprophyte (also heterotrophs) and finally return to the inorganic world. In this way, the material movement cycle in the biosphere is formed. This kind of circular movement is carried out unilaterally and irreversibly. Any missing link or blocked link in this circular movement will affect the whole Biosphere 。 If there is no autotroph or autotroph is insufficient, heterotroph is certainly difficult to survive; But only autotrophs, no heterotrophs, a large number of Organic matter It cannot be degraded after accumulation, and will also block the way for autotrophs to continue to survive.

In terms of the simple form of substances, such as those in the atmosphere carbon dioxide Formal carbon Elements enter into life through photosynthesis of autotrophs and hydration and synthesis of sugars. Some of them return to the atmosphere as carbon dioxide through their own respiration, while the rest are used by various heterotrophs to return to the inorganic world through their respiration. In this way, a cycle of carbon element is formed. This cycle must be coupled with the cycle of many other elements (such as hydrogen, oxygen, nitrogen, phosphorus, sulfur, etc.) in life through chemical reaction, and at the same time, these elements are promoted to circulate in space. Such a cycle exists not only in the macro biosphere, but also in the micro movement of organisms. Ecology life regard as It is the central link of various irreversible material circulation processes in the biosphere 。 However, it only describes the external conditions of life and its location, and does not specify the qualitative characteristics of life itself.

Contradiction theory

Every time the string vibrates Elementary particle and natural force , the combination of the two will further generate all things in the universe. And the effect produced by the inertia of basic particles and the role of natural forces is just a pair of contradictions - inertia maintains balance and changes the role. Therefore, the balance of inertia maintenance and the change caused by action are the most basic attribute contradictions of matter, which promote the evolution of matter from inorganic matter to organic matter to primitive life to animals and plants to human beings.

Inertial maintenance balance Externalization Out of the metabolism of life, internalized the heredity of life; The changes caused by the action externalize the birth, aging, disease and death of life, and internalize the variation of life. The changes caused by inertia maintenance balance and function externalize the metabolism, birth, aging, disease and death, and internalize the heredity and variation in life Multiply On. In this way, survival and reproduction become the two attributes of life, and death and variation become the two necessities of life. It is the pleasure of demand struggle and the desire for reproduction of the inertia maintenance balance push performance, which causes the pain of life, old age, sickness and death, and the short-lived alienation of the change push performance, supports the survival and reproduction of life, and further derives the natural quality And social attributes at the level of population continuity.^[13]

Life Quote

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1. Life is carved by nature for human beings gemstone 。—— Nobel

2. Life is a difficult and dangerous valley. Only brave people can pass through—— Michelpan

3. A great soul will strengthen thought and life—— Emerson

4. There is only one kind in the world heroism That is, people who understand life and love life—— Roman Roland

5. Only by giving our lives can we get life—— Tagore

6. A life full of content is a long life. We should measure life by action, not by time—— Seneca Minor

7. If we can make good use of it, life will be long—— Seneca

8. Life is brilliant in shining and real in ordinary—— Burke

9. The shortening of life is directly proportional to the waste of thought—— Darwin

10. To cherish life is to cherish today—— proverb

11. Who can enrich every moment with profound content is infinitely extending his life—— Kurtz

12. Our life is only once, but if we can use it correctly, once is enough—— english proverb

13. It is impossible to have two lives, but many people are not good at spending even one—— Lukate

14. Life is like flowing water. It is beautiful and meaningful only when it rushes forward—— Zhang Wentian

15. Respect for life, respect for others and respect for one's own life are companions in the process of life mental health A condition of.

——Fromm

16. There are two tragedies in life: one is disillusionment, the other is complacency—— Bernard Shaw

17. People who understand the true meaning of life can prolong the short life—— Cicero

18. It makes a person's limited life more effective, that is, it prolongs a person's life—— Lu Xun

19. You should face life with a smile, no matter what—— Fucik

20. A good year never comes again—— another name of Tao Yuanming

21. Life is long as you make full use of it—— Seneca

22. Before we know what life is, we have spent half of it—— Herbert

23. There is no round trip ticket in life. Once you leave, you can never return—— Roman Roland

24. Life is the existing form of protein body—— Engels

25. Life is the most precious thing. Everyone has only one life. A man's life should be spent like this: when he recalls the past, he will not regret for wasting his time, nor be ashamed of being mean and vulgar; On his deathbed, he was able to say: "My whole life and all my energy were dedicated to the most magnificent cause in the world - fighting for the liberation of all mankind." - Ostrovsky《 How is steel made 》

The chapters praising life include Wang Guozhen Of《 Love life 》Love of Life by Montaigne, a French thinker, and the United States Jack London Love Life.

Love Life Wang Guozhen

I don't care if I can succeed

Now that we have chosen the distance

They just go through the storm

I don't want to win love

Since I love rose

To be brave and honest

I don't want to think about whether there will be cold wind and cold rain behind me

Since the target is the horizon

The only thing left to the world is the back

I don't care if the future is flat or muddy

Just love life

Everything is expected

26. Health, also What I want , righteousness, also what I want, both You can't have both He who gives up his life and takes righteousness. Life is what I want, what I want To have It is better than living people, so they don't want to get anything. Death is also my evil, worse than the dead, so suffering will not be avoided. If people want nothing more than to live, then anyone who can live will need nothing. It makes people worse than the dead, so why not avoid the patient! If you are right, you will be born without use; Therefore, we can avoid problems and do nothing. So What you want is more than the living, and what you hate is more than the dead. Not only the virtuous have their own hearts, but all people have them. The virtuous can not lose their ears-- Ancient Chinese thinkers Mencius

scientific research

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September 2022, according to the UK《 New scientist 》According to the magazine website Aerospace Bureau（ NASA ）"Perseverance" Mars probe stay A large number of Organic molecule ——The discovery of carbon containing molecules that are considered to be part of life may make the dried up river delta area of Mars an ideal place to look for life , which is helpful to reveal the core question of whether there is life on Mars.^[14]

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