101-666: [REDACTED] Look up lives in Wiktionary, the free dictionary. Lives may refer to: The plural form of a life Lives, Iran , a village in Khuzestan Province, Iran The number of lives in a video game Parallel Lives , aka Lives of the Noble Greeks and Romans , a series of biographies of famous men, written by Plutarch and thus often called Plutarch's Lives or The Lives of Plutarch LiVES ,
202-420: A double helix . The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides . Each nucleotide is composed of a nitrogen-containing nucleobase —either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a sugar called deoxyribose and a phosphate group . The nucleotides are joined to one another in a chain by covalent bonds between
303-420: A living systems theory viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this include Stuart Kauffman 's definition as an autonomous agent or a multi-agent system capable of reproducing itself, and of completing at least one thermodynamic work cycle . This definition
404-428: A nucleus and other membrane-bound organelles , although they have circular DNA and ribosomes . Bacteria and Archaea are two domains of prokaryotes. The other primary type is the eukaryote cell, which has a distinct nucleus bound by a nuclear membrane and membrane-bound organelles, including mitochondria , chloroplasts , lysosomes , rough and smooth endoplasmic reticulum , and vacuoles . In addition, their DNA
505-407: A common origin. All life forms require certain core chemical elements for their biochemical functioning. These include carbon , hydrogen , nitrogen , oxygen , phosphorus , and sulfur —the elemental macronutrients for all organisms. Together these make up nucleic acids , proteins and lipids , the bulk of living matter. Five of these six elements comprise the chemical components of DNA,
606-528: A consequence of these microbial activities, the physical-chemical environment on Earth has been changing on a geologic time scale , thereby affecting the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this posed novel evolutionary challenges, and ultimately resulted in
707-442: A host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life , as it may support the hypothesis that life could have started as self-assembling organic molecules . Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles (430 BC) argued that everything in
808-472: A matter of debate; viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses have been classed into "species" based on their genetics , but many aspects of such a classification remain controversial. The original Linnaean system has been modified many times, for example as follows: The attempt to organise the Eukaryotes into
909-535: A month in a simulated Martian environment . Beyond the Solar System, the region around another main-sequence star that could support Earth-like life on an Earth-like planet is known as the habitable zone . The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on
1010-452: A resurgence of interest in the work of Russell, Barge and colleagues. Hylomorphism is a theory first expressed by the Greek philosopher Aristotle (322 BC). The application of hylomorphism to biology was important to Aristotle, and biology is extensively covered in his extant writings . In this view, everything in the material universe has both matter and form, and the form of a living thing
1111-465: A selected few among them, were originally long-lived daimons who dwelt in a state of bliss until committing an unspecified crime, possibly bloodshed or perjury. As a consequence, they fell to Earth, where they would be forced to spend 30,000 cycles of metempsychosis through different bodies before being able to return to the sphere of divinity . One's behavior during his lifetime would also determine his next incarnation. Wise people, who have learned
SECTION 10
#17327660803561212-809: A set of 355 genes from the last universal common ancestor was tentatively identified. The biosphere is postulated to have developed, from the origin of life onwards, at least some 3.5 billion years ago. The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia . More recently, in 2015, "remains of biotic life " were found in 4.1 billion-year-old rocks in Western Australia. In 2017, putative fossilised microorganisms (or microfossils ) were announced to have been discovered in hydrothermal vent precipitates in
1313-619: A short period Linnaeus had classified them in the taxon Vermes in Animalia, but later placed them back in Plantae. Herbert Copeland classified the Fungi in his Protoctista , including them with single-celled organisms and thus partially avoiding the problem but acknowledging their special status. The problem was eventually solved by Whittaker , when he gave them their own kingdom in his five-kingdom system . Evolutionary history shows that
1414-467: A small number of kingdoms has been challenged. The Protozoa do not form a clade or natural grouping, and nor do the Chromista (Chromalveolata). The ability to sequence large numbers of complete genomes has allowed biologists to take a metagenomic view of the phylogeny of the whole tree of life . This has led to the realisation that the majority of living things are bacteria, and that all have
1515-530: A state of death , and none is immortal . Many philosophical definitions of living systems have been proposed, such as self-organizing systems. Viruses in particular make definition difficult as they replicate only in host cells. Life exists all over the Earth in air, water, and soil , with many ecosystems forming the biosphere . Some of these are harsh environments occupied only by extremophiles . Life has been studied since ancient times, with theories such as Empedocles 's materialism asserting that it
1616-408: A thousand years. In the late 1740s, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning. The fungi were originally treated as plants. For
1717-501: A victory in the horse race at Olympia in the 71st Olympiad (496–495 BC). Little else can be determined with accuracy. Primary sources of information on the life of Empedocles come from the Hellenistic period , several centuries after his own death and long after any reliable evidence about his life would have perished. Modern scholarship generally believes that these biographical details, including Aristotle 's assertion that he
1818-719: A video editing program and VJ tool "Lives", a song by Daron Malakian and Scars on Broadway from the album Dictator "Lives", a song by Modest Mouse from the album The Moon & Antarctica A short form of Lives of the Most Excellent Painters, Sculptors, and Architects , a 16th-century book by Giorgio Vasari 'LIVES' - Lincolnshire Integrated Voluntary Emergency Service , Prehospital care provider in Lincolnshire, UK See also [ edit ] Live (disambiguation) Life (disambiguation) Living (disambiguation) Topics referred to by
1919-473: Is a mechanistic explanation for the origin of species by means of natural selection . At the beginning of the 20th century Stéphane Leduc (1853–1939) promoted the idea that biological processes could be understood in terms of physics and chemistry, and that their growth resembled that of inorganic crystals immersed in solutions of sodium silicate. His ideas, set out in his book La biologie synthétique , were widely dismissed during his lifetime, but has incurred
2020-561: Is about 4.54 billion years . Life on Earth has existed for at least 3.5 billion years, with the oldest physical traces of life dating back 3.7 billion years. Estimates from molecular clocks, as summarised in the TimeTree public database, place the origin of life around 4.0 billion years ago. Hypotheses on the origin of life attempt to explain the formation of a universal common ancestor from simple organic molecules via pre-cellular life to protocells and metabolism. In 2016,
2121-479: Is being simulated and explored by scientists and engineers. The definition of life has long been a challenge for scientists and philosophers. This is partially because life is a process, not a substance. This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth. Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from
SECTION 20
#17327660803562222-558: Is capable of forming the various specialised cells that form the adult organism. This specialisation allows multicellular organisms to exploit resources more efficiently than single cells. About 800 million years ago, a minor genetic change in a single molecule, the enzyme GK-PID , may have allowed organisms to go from a single cell organism to one of many cells. Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability. Cell signalling coordinates cellular activities, and hence governs
2323-422: Is considered the starting point of modern organic chemistry . It is of historical significance because for the first time an organic compound was produced in inorganic reactions. During the 1850s Hermann von Helmholtz , anticipated by Julius Robert von Mayer , demonstrated that no energy is lost in muscle movement, suggesting that there were no "vital forces" necessary to move a muscle. These results led to
2424-489: Is different from Wikidata All article disambiguation pages All disambiguation pages Life Life on Earth: Life is a quality that distinguishes matter that has biological processes , such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis , organisation , metabolism , growth , adaptation , response to stimuli , and reproduction . All life over time eventually reaches
2525-421: Is extended by the evolution of novel functions over time. Death is the termination of all vital functions or life processes in an organism or cell. One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins. However, determining when death has occurred is difficult, as cessation of life functions
2626-425: Is its soul (Greek psyche , Latin anima ). There are three kinds of souls: the vegetative soul of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the animal soul , which causes animals to move and feel; and the rational soul , which is the source of consciousness and reasoning, which (Aristotle believed) is found only in man. Each higher soul has all of
2727-407: Is most likely to exist, within wide bounds of uncertainty. A "Confidence of Life Detection" scale (CoLD) for reporting evidence of life beyond Earth has been proposed. Artificial life is the simulation of any aspect of life, as through computers, robotics , or biochemistry . Synthetic biology is a new area of biotechnology that combines science and biological engineering . The common goal
2828-476: Is not only plausible, but probable or inevitable, possibly resulting in a biophysical cosmology instead of a mere physical cosmology . Other planets and moons in the Solar System and other planetary systems are being examined for evidence of having once supported simple life, and projects such as SETI are trying to detect radio transmissions from possible alien civilisations. Other locations within
2929-428: Is often not simultaneous across organ systems. Such determination, therefore, requires drawing conceptual lines between life and death. This is problematic because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for
3030-485: Is organised into chromosomes . All species of large complex organisms are eukaryotes, including animals, plants and fungi, though with a wide diversity of protist microorganisms . The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through endosymbiosis between bacteria and the progenitor eukaryotic cell. The molecular mechanisms of cell biology are based on proteins . Most of these are synthesised by
3131-423: Is produced. It is in the aggregation and segregation of elements thus arising, that Empedocles, like the atomists, found the real process which corresponds to what is popularly termed growth, increase or decrease. One interpreter describes his philosophy as asserting that "Nothing new comes or can come into being; the only change that can occur is a change in the juxtaposition of element with element." This theory of
Lives - Misplaced Pages Continue
3232-473: Is responsible for the attraction of different forms of what we now call matter , and Strife ( νεῖκος ) is the cause of their separation. If the four elements make up the universe, then Love and Strife explain their variation and harmony. Love and Strife are attractive and repulsive forces, respectively, which are plainly observable in human behavior, but also pervade the universe. The two forces wax and wane in their dominance, but neither force ever wholly escapes
3333-417: Is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of biotechnology, with the ultimate goals of being able to design and build engineered biological systems that process information, manipulate chemicals, fabricate materials and structures, produce energy, provide food, and maintain and enhance human health and
3434-434: Is to define life as "a self-sustained chemical system capable of undergoing Darwinian evolution ", a definition adopted by a NASA committee attempting to define life for the purposes of exobiology , based on a suggestion by Carl Sagan . This definition, however, has been widely criticised because according to it, a single sexually reproducing individual is not alive as it is incapable of evolving on its own. Others take
3535-509: Is unlikely or impossible. Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance. To survive, some microorganisms have evolved to withstand freezing , complete desiccation , starvation , high levels of radiation exposure , and other physical or chemical challenges. These extremophile microorganisms may survive exposure to such conditions for long periods. They excel at exploiting uncommon sources of energy. Characterization of
3636-714: The International Ocean Discovery Program found unicellular life in 120 °C sediment 1.2 km below seafloor in the Nankai Trough subduction zone. According to one researcher, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or chemical energy ), water, heat, atmosphere , gravity , nutrients , and ultraviolet solar radiation protection . In most ecosystems,
3737-504: The Nuvvuagittuq Belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on Earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago , and not long after the formation of the Earth 4.54 billion years ago. Evolution is the change in heritable characteristics of biological populations over successive generations. It results in
3838-458: The Solar System that may host microbial life include the subsurface of Mars , the upper atmosphere of Venus , and subsurface oceans on some of the moons of the giant planets . Investigation of the tenacity and versatility of life on Earth, as well as an understanding of the molecular systems that some organisms utilise to survive such extremes, is important for the search for extraterrestrial life. For example, lichen could survive for
3939-530: The corporeality of air, but he says nothing whatever about the void, and there is no evidence that Empedocles performed any experiment with clepsydras. According to Diogenes Laertius, Empedocles wrote two poems, "On Nature" and "On Purifications", which together comprised 5000 lines. However, only some 550 lines of his poetry survive, quoted in fragments by later ancient sources. In old editions of Empedocles, about 450 lines were ascribed to "On Nature" which outlined his philosophical system, and explains not only
4040-609: The right to destroy themselves . In Icaro-Menippus [ it ] , a comedic dialogue written by the second-century satirist Lucian of Samosata , Empedocles' final fate is re-evaluated. Rather than being incinerated in the fires of Mount Etna, he was carried up into the heavens by a volcanic eruption. Although singed by the ordeal, Empedocles survives and continues his life on the Moon, surviving by feeding on dew. Burnet states that Empedocles likely did not die in Sicily, that both
4141-480: The soul , or resurrection of the body at a later date. Whether or not viruses should be considered as alive is controversial. They are most often considered as just gene coding replicators rather than forms of life. They have been described as "organisms at the edge of life" because they possess genes , evolve by natural selection, and replicate by making multiple copies of themselves through self-assembly. However, viruses do not metabolise and they require
Lives - Misplaced Pages Continue
4242-467: The structure and metabolic diversity of microbial communities in such extreme environments is ongoing. The first classification of organisms was made by the Greek philosopher Aristotle (384–322 BC), who grouped living things as either plants or animals, based mainly on their ability to move. He distinguished animals with blood from animals without blood, which can be compared with the concepts of vertebrates and invertebrates respectively, and divided
4343-419: The 1740s. Living things are composed of biochemical molecules , formed mainly from a few core chemical elements . All living things contain two types of large molecule, proteins and nucleic acids , the latter usually both DNA and RNA : these carry the information needed by each species, including the instructions to make each type of protein. The proteins, in turn, serve as the machinery which carries out
4444-459: The Sun-like "main sequence" of stellar evolution for a shorter time interval. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits. Hence, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop. The location of
4545-403: The abandonment of scientific interest in vitalistic theories, especially after Eduard Buchner 's demonstration that alcoholic fermentation could occur in cell-free extracts of yeast. Nonetheless, belief still exists in pseudoscientific theories such as homoeopathy , which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force. The age of Earth
4646-441: The age of 109. Likewise, there are myths concerning his death: a tradition, which is traced to Heraclides Ponticus , represented him as having been removed from the Earth; whereas others had him perishing in the flames of Mount Etna . Diogenes Laërtius records the legend that Empedocles died by throwing himself into Mount Etna in Sicily, so that the people would believe his body had vanished and he had turned into an immortal god;
4747-466: The appearance of new species and often the disappearance of old ones. Evolution occurs when evolutionary processes such as natural selection (including sexual selection ) and genetic drift act on genetic variation, resulting in certain characteristics increasing or decreasing in frequency within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation . Fossils are
4848-450: The attributes of the lower ones. Aristotle believed that while matter can exist without form, form cannot exist without matter, and that therefore the soul cannot exist without the body. This account is consistent with teleological explanations of life , which account for phenomena in terms of purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality (from
4949-399: The basic functions of multicellular organisms. Signaling between cells can occur through direct cell contact using juxtacrine signalling , or indirectly through the exchange of agents as in the endocrine system . In more complex organisms, coordination of activities can occur through a dedicated nervous system . Though life is confirmed only on Earth, many think that extraterrestrial life
5050-502: The basis of his doctrine of reincarnation, although he may have instead learned this from a local tradition rather than directly from the Pythagoreans . Empedocles established four ultimate elements which make all the structures in the world— fire , air , water , earth . Empedocles called these four elements "roots", which he also identified with the mythical names of Zeus , Hera , Nestis , and Aidoneus (e.g., "Now hear
5151-436: The biosphere, including soil , hot springs , inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere. For example, spores of Aspergillus niger have been detected in the mesosphere at an altitude of 48 to 77 km. Under test conditions, life forms have been observed to survive in the vacuum of space. Life forms thrive in
SECTION 50
#17327660803565252-457: The blooded animals into five groups: viviparous quadrupeds ( mammals ), oviparous quadrupeds (reptiles and amphibians ), birds, fishes and whales . The bloodless animals were divided into five groups: cephalopods , crustaceans , insects (which included the spiders, scorpions , and centipedes ), shelled animals (such as most molluscs and echinoderms ), and " zoophytes " (animals that resemble plants). This theory remained dominant for more than
5353-426: The bond which kept the pure elementary substances together in the sphere was dissolved. The elements became the world of phenomena we see today, full of contrasts and oppositions, operated on by both Love and Strife. Empedocles assumed a cyclical universe whereby the elements return and prepare the formation of the sphere for the next period of the universe. Empedocles attempted to explain the separation of elements,
5454-412: The conditions vary during the day and from one season to the next. To live in most ecosystems, then, organisms must be able to survive a range of conditions, called the "range of tolerance". Outside that are the "zones of physiological stress", where the survival and reproduction are possible but not optimal. Beyond these zones are the "zones of intolerance", where survival and reproduction of that organism
5555-422: The deep Mariana Trench , and inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of the northwestern United States, and 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. In 2014, life forms were found living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. Expeditions of
5656-418: The elements, respectively. Empedocles challenged the practice of animal sacrifice and killing animals for food. He developed a distinctive doctrine of reincarnation . He is generally considered the last Greek philosopher to have recorded his ideas in verse. Some of his work survives, more than is the case for any other pre-Socratic philosopher. Empedocles' death was mythologized by ancient writers, and has been
5757-551: The environment. Empedocles Empedocles ( / ɛ m ˈ p ɛ d ə k l iː z / ; ‹See Tfd› Greek : Ἐμπεδοκλῆς ; c. 494 – c. 434 BC , fl. 444–443 BC) was a Greek pre-Socratic philosopher and a native citizen of Akragas , a Greek city in Sicily . Empedocles' philosophy is known best for originating the cosmogonic theory of the four classical elements . He also proposed forces he called Love and Strife which would mix and separate
5858-523: The exception being sulfur. The latter is a component of the amino acids cysteine and methionine . The most abundant of these elements in organisms is carbon, which has the desirable attribute of forming multiple, stable covalent bonds . This allows carbon-based (organic) molecules to form the immense variety of chemical arrangements described in organic chemistry . Alternative hypothetical types of biochemistry have been proposed that eliminate one or more of these elements, swap out an element for one not on
5959-409: The formation of colonies of identical cells. These cells can form group organisms through cell adhesion . The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specialisations, making them dependent on the remainder of the organism for survival. Such organisms are formed clonally or from a single germ cell that
6060-474: The formation of Earth's major animal and plant species. This interplay between organisms and their environment is an inherent feature of living systems. The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. Organisms exist in every part of
6161-549: The formation of earth and sea, of Sun and Moon, of atmosphere. He also dealt with the first origin of plants and animals, and with the physiology of humans. As the elements entered into combinations, there appeared strange results—heads without necks, arms without shoulders. Then as these fragmentary structures met, there were seen horned heads on human bodies, bodies of oxen with human heads, and figures of double sex . But most of these products of natural forces disappeared as suddenly as they arose; only in those rare cases where
SECTION 60
#17327660803566262-493: The four elements became the standard dogma for the next two thousand years. The four elements, however, are simple, eternal, and unalterable, and as change is the consequence of their mixture and separation, it was also necessary to suppose the existence of moving powers that bring about mixture and separation. The four elements are both eternally brought into union and parted from one another by two divine powers, Love and Strife ( Philotes and Neikos ). Love ( φιλότης )
6363-406: The fourfold roots of everything: enlivening Hera, Hades, shining Zeus. And Nestis, moistening mortal springs with tears"). Empedocles never used the term "element" ( στοιχεῖον , stoicheion ), which seems to have been first used by Plato . According to the different proportions in which these four indestructible and unchangeable elements are combined with each other the difference of the structure
6464-410: The fundamental basis on which later Greek philosophers and mathematicians like Euclid would construct some of the most important theories of light, vision, and optics. Knowledge is explained by the principle that elements in the things outside us are perceived by the corresponding elements in ourselves. Like is known by like. The whole body is full of pores and hence respiration takes place over
6565-406: The fungi are more closely related to animals than to plants. As advances in microscopy enabled detailed study of cells and microorganisms, new groups of life were revealed, and the fields of cell biology and microbiology were created. These new organisms were originally described separately in protozoa as animals and protophyta/thallophyta as plants, but were united by Ernst Haeckel in
6666-480: The future to the past) is in contradiction with the scientific evidence for natural selection, which explains the consequence in terms of a prior cause. Biological features are explained not by looking at future optimal results, but by looking at the past evolutionary history of a species, which led to the natural selection of the features in question. Spontaneous generation was the belief that living organisms can form without descent from similar organisms. Typically,
6767-426: The given environment. This implies all or most of the following traits: From a physics perspective, an organism is a thermodynamic system with an organised molecular structure that can reproduce itself and evolve as survival dictates. Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. Another way of putting this
6868-434: The idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from mud or garbage. The theory of spontaneous generation was proposed by Aristotle , who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it was considered the best explanation for two millennia. It
6969-451: The imposition of the other. As the best and original state, there was a time when the pure elements and the two powers co-existed in a condition of rest and inertness in the form of a sphere. The elements existed together in their purity, without mixture and separation, and the uniting power of Love predominated in the sphere: the separating power of Strife guarded the extreme edges of the sphere. Since that time, strife gained more sway and
7070-496: The information to be preserved during reproduction and cell division. Within cells, DNA is organised into long structures called chromosomes . During cell division these chromosomes are duplicated in the process of DNA replication , providing each cell its own complete set of chromosomes. Eukaryotes store most of their DNA inside the cell nucleus . Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by division . Cell theory
7171-642: The kingdom Protista ; later, the prokaryotes were split off in the kingdom Monera , which would eventually be divided into two separate groups, the Bacteria and the Archaea . This led to the six-kingdom system and eventually to the current three-domain system , which is based on evolutionary relationships. However, the classification of eukaryotes, especially of protists, is still controversial. As microbiology developed, viruses, which are non-cellular, were discovered. Whether these are considered alive has been
7272-563: The list, or change required chiralities or other chemical properties. Deoxyribonucleic acid or DNA is a molecule that carries most of the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids ; alongside proteins and complex carbohydrates , they are one of the three major types of macromolecule that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form
7373-423: The many chemical processes of life. The cell is the structural and functional unit of life. Smaller organisms, including prokaryotes (bacteria and archaea ), consist of small single cells. Larger organisms , mainly eukaryotes , can consist of single cells or may be multicellular with more complex structure. Life is only known to exist on Earth but extraterrestrial life is thought probable . Artificial life
7474-508: The middle of the 19th century. It appealed to philosophers such as Henri Bergson , Friedrich Nietzsche , and Wilhelm Dilthey , anatomists like Xavier Bichat , and chemists like Justus von Liebig . Vitalism included the idea that there was a fundamental difference between organic and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828, when Friedrich Wöhler prepared urea from inorganic materials. This Wöhler synthesis
7575-453: The nature and history of the universe, including his theory of the four classical elements , but also theories on causation, perception, and thought, as well as explanations of terrestrial phenomena and biological processes. The other 100 lines were typically ascribed to his "Purifications", which was taken to be a poem about ritual purification, or the poem that contained all his religious and ethical thought, which early editors supposed that it
7676-448: The non-living. Legal definitions of life have been debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision. At least 123 definitions of life have been compiled. Since there is no consensus for a definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in
7777-566: The oldest from the Archaean Eon, up to 3.4 billion years old. Extinction is the process by which a species dies out. The moment of extinction is the death of the last individual of that species. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in changing habitat or against superior competition. Over 99% of all
7878-609: The parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of fission in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In eukaryotes , a more complex process of mitosis is followed. However, the result is the same; the resulting cell copies are identical to each other and to the original cell (except for mutations ), and both are capable of further division following an interphase period. Multicellular organisms may have first evolved through
7979-544: The parts were found to be adapted to each other did the complex structures last. Thus the organic universe sprang from spontaneous aggregations that suited each other as if this had been intended. Soon various influences reduced creatures of double sex to a male and a female, and the world was replenished with organic life. Like Pythagoras , Empedocles believed in the transmigration of the soul or metempsychosis , that souls can be reincarnated between humans, animals and even plants. According to him, all humans, or maybe only
8080-485: The phenomenon of respiration by means of an elaborate analogy with the clepsydra , an ancient device for conveying liquids from one vessel to another. This fragment has sometimes been connected to a passage in Aristotle 's Physics where Aristotle refers to people who twisted wineskins and captured air in clepsydras to demonstrate that void does not exist. The fragment certainly implies that Empedocles knew about
8181-406: The positive story of Empedocles being taken up to heaven and the negative one about him throwing himself into a volcano could be easily accepted by ancient writers, as there was no local tradition to contradict them. Empedocles' death is the subject of Friedrich Hölderlin 's play Tod des Empedokles ( The Death of Empedocles ) as well as Matthew Arnold 's poem Empedocles on Etna . Based on
8282-473: The preserved remains or traces of organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in layers ( strata ) of sedimentary rock is known as the fossil record . A preserved specimen is called a fossil if it is older than the arbitrary date of 10,000 years ago. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to
8383-460: The ribosomes through an enzyme-catalyzed process called protein biosynthesis . A sequence of amino acids is assembled and joined based upon gene expression of the cell's nucleic acid. In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination. Cells reproduce through a process of cell division in which
8484-420: The same spiritual plane; plants and animals are links in a chain where humans are a link too. Empedocles is credited with the first comprehensive theory of light and vision. Historian Will Durant noted that "Empedocles suggested that light takes time to pass from one point to another." He put forward the idea that we see objects because light streams out of our eyes and touches them. While flawed, this became
8585-407: The same term [REDACTED] This disambiguation page lists articles associated with the title Lives . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Lives&oldid=1113992101 " Category : Disambiguation pages Hidden categories: Short description
8686-497: The secret of life, are closer to the divine, while their souls similarly are closer to the freedom from the cycle of reincarnations, after which they are able to rest in happiness for eternity. This cycle of mortal incarnation seems to have been inspired by the god Apollo 's punishment as a servant to Admetus . Empedocles was a vegetarian and advocated vegetarianism, since the bodies of animals are also dwelling places of punished souls. For Empedocles, all living things were on
8787-435: The soul, like everything else, was composed of fiery atoms. He elaborated on fire because of the apparent connection between life and heat, and because fire moves. Plato , in contrast, held that the world was organised by permanent forms , reflected imperfectly in matter; forms provided direction or intelligence, explaining the regularities observed in the world. The mechanistic materialism that originated in ancient Greece
8888-493: The species that have ever lived are now extinct. Mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. The diversity of life on Earth is a result of the dynamic interplay between genetic opportunity , metabolic capability, environmental challenges, and symbiosis . For most of its existence, Earth's habitable environment has been dominated by microorganisms and subjected to their metabolism and evolution. As
8989-488: The star within a galaxy may also affect the likelihood of life forming. Stars in regions with a greater abundance of heavier elements that can form planets, in combination with a low rate of potentially habitat -damaging supernova events, are predicted to have a higher probability of hosting planets with complex life. The variables of the Drake equation are used to discuss the conditions in planetary systems where civilisation
9090-526: The subject of a number of literary treatments. The exact dates of Empedocles' birth and death are unknown, and ancient accounts of his life conflict on the exact details. However, they agree that he was born in the early 5th century BC in the Greek city of Akragas in Magna Graecia , present-day Sicily . Modern scholars believe the accuracy of the accounts that he came from a rich and noble family and that his grandfather, also named Empedocles, had won
9191-408: The sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone . According to base pairing rules (A with T, and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. This has the key property that each strand contains all the information needed to recreate the other strand, enabling
9292-454: The surviving fragments of his work, modern scholars generally believe that Empedocles was directly responding to Parmenides ' doctrine of monism and was likely acquainted with the work of Anaxagoras , although it is unlikely he was aware of either the later Eleatics or the doctrines of the Atomists . Many later accounts of his life claim that Empedocles studied with the Pythagoreans on
9393-413: The universe is made up of a combination of four eternal "elements" or "roots of all": earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. Democritus (460 BC) was an atomist ; he thought that the essential characteristic of life was having a soul ( psyche ), and that
9494-443: The volcano, however, threw back one of his bronze sandals, revealing the deceit. Another legend maintains that he threw himself into the volcano to prove to his disciples that he was immortal; he believed he would come back as a god after being consumed by the fire. Lucretius speaks of him with enthusiasm, and evidently viewed him as his model. Horace also refers to the death of Empedocles in his work Ars Poetica and admits poets
9595-439: The whole frame. In the organs of sense these pores are specially adapted to receive the effluences which are continually rising from bodies around us; thus perception occurs. In vision, certain particles go forth from the eye to meet similar particles given forth from the object, and the resultant contact constitutes vision. Perception is not merely a passive reflection of external objects. Empedocles also attempted to explain
9696-589: Was a poem that offered a mythical account of the world which may, nevertheless, have been part of Empedocles' philosophical system. A late 20th century discovery has changed this situation. The Strasbourg papyrus contains a large section of "On Nature", including many lines formerly attributed to "On Purifications". This has raised considerable debate about whether the surviving fragments of his teaching should be attributed to two separate poems, with different subject matter; whether they may all derive from one poem with two titles; or whether one title refers to part of
9797-535: Was composed of four eternal elements , and Aristotle 's hylomorphism asserting that living things have souls and embody both form and matter. Life originated at least 3.5 billion years ago, resulting in a universal common ancestor . This evolved into all the species that exist now, by way of many extinct species, some of which have left traces as fossils . Attempts to classify living things, too, began with Aristotle . Modern classification began with Carl Linnaeus 's system of binomial nomenclature in
9898-414: Was decisively dispelled by the experiments of Louis Pasteur in 1859, who expanded upon the investigations of predecessors such as Francesco Redi . Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists. Vitalism is the belief that there is a non-material life-principle. This originated with Georg Ernst Stahl (17th century), and remained popular until
9999-495: Was formulated by Henri Dutrochet , Theodor Schwann , Rudolf Virchow and others during the early nineteenth century, and subsequently became widely accepted. The activity of an organism depends on the total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information that is carried forward as a genetic code during cell division. There are two primary types of cells, reflecting their evolutionary origins. Prokaryote cells lack
10100-486: Was revived and revised by the French philosopher René Descartes (1596–1650), who held that animals and humans were assemblages of parts that together functioned as a machine. This idea was developed further by Julien Offray de La Mettrie (1709–1750) in his book L'Homme Machine . In the 19th century the advances in cell theory in biological science encouraged this view. The evolutionary theory of Charles Darwin (1859)
10201-410: Was the "father of rhetoric ", his chronologically impossible tutelage under Pythagoras , and his employment as a doctor and miracle worker, were fabricated from interpretations of Empedocles' poetry, as was common practice for the biographies written during this time. According to Aristotle , Empedocles died at the age of 60 ( c. 430 BC ), even though other writers have him living up to
#355644