105-460: An animal is a multicellular, eukaryotic organism of the kingdom Animalia or Metazoa. Animal , Animals , or The Animal may also refer to: Animal Animals are multicellular , eukaryotic organisms in the biological kingdom Animalia ( / ˌ æ n ɪ ˈ m eɪ l i ə / ). With few exceptions, animals consume organic material , breathe oxygen , have myocytes and are able to move , can reproduce sexually , and grow from
210-399: A gastrula with a digestive chamber and two separate germ layers , an external ectoderm and an internal endoderm . In most cases, a third germ layer, the mesoderm , also develops between them. These germ layers then differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within
315-527: A will in which he asked to be buried next to his wife. Aristotle left his works to Theophrastus, his successor as the head of the Lyceum, who in turn passed them down to Neleus of Scepsis in Asia Minor. There, the papers remained hidden for protection until they were purchased by the collector Apellicon . In the meantime, many copies of Aristotle's major works had already begun to circulate and be used in
420-541: A "survival of the fittest" origin of living things and their organs, and ridiculed the idea that accidents could lead to orderly results. To put his views into modern terms, he nowhere says that different species can have a common ancestor , or that one kind can change into another , or that kinds can become extinct . Aristotle did not do experiments in the modern sense. He used the ancient Greek term pepeiramenoi to mean observations, or at most investigative procedures like dissection. In Generation of Animals , he finds
525-573: A broad range of subjects spanning the natural sciences , philosophy , linguistics , economics , politics , psychology , and the arts . As the founder of the Peripatetic school of philosophy in the Lyceum in Athens , he began the wider Aristotelian tradition that followed, which set the groundwork for the development of modern science . Little is known about Aristotle's life. He was born in
630-495: A building known as the Lyceum (named after the sacred grove of Apollo Lykeios ), in which he established his own school. The building included a gymnasium and a colonnade ( peripatos ), from which the school acquired the name Peripatetic . Aristotle conducted courses and research at the school for the next twelve years. He often lectured small groups of distinguished students and, along with some of them, such as Theophrastus , Eudemus , and Aristoxenus , Aristotle built
735-561: A clade Xenambulacraria for the Xenacoelamorpha + Ambulacraria; this is either within Deuterostomia, as sister to Chordata, or the Deuterostomia are recovered as paraphyletic, and Xenambulacraria is sister to the proposed clade Centroneuralia , consisting of Chordata + Protostomia. Eumetazoa , a clade which contains Ctenophora and ParaHoxozoa , has been proposed as a sister group to Porifera . A competing hypothesis
840-438: A fertilized hen's egg of a suitable stage and opens it to see the embryo's heart beating inside. Instead, he practiced a different style of science: systematically gathering data, discovering patterns common to whole groups of animals, and inferring possible causal explanations from these. This style is common in modern biology when large amounts of data become available in a new field, such as genomics . It does not result in
945-574: A few salient points. Aristotle was born in 384 BC in Stagira , Chalcidice , about 55 km (34 miles) east of modern-day Thessaloniki . He was the son of Nicomachus , the personal physician of King Amyntas of Macedon , and Phaestis, a woman with origins from Chalcis , Euboea . Nicomachus was said to have belonged to the medical guild of Asclepiadae and was likely responsible for Aristotle's early interest in biology and medicine. Ancient tradition held that Aristotle's family descended from
1050-497: A fluid such as air. In this system, heavy bodies in steady fall indeed travel faster than light ones (whether friction is ignored, or not ), and they do fall more slowly in a denser medium. Newton's "forced" motion corresponds to Aristotle's "violent" motion with its external agent, but Aristotle's assumption that the agent's effect stops immediately it stops acting (e.g., the ball leaves the thrower's hand) has awkward consequences: he has to suppose that surrounding fluid helps to push
1155-406: A form of an apple. In this distinction, there is a particular apple and a universal form of an apple. Moreover, one can place an apple next to a book, so that one can speak of both the book and apple as being next to each other. Plato argued that there are some universal forms that are not a part of particular things. For example, it is possible that there is no particular good in existence, but "good"
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#17328017571391260-658: A hollow sphere of cells, the blastula , during embryonic development . Animals form a clade , meaning that they arose from a single common ancestor . Over 1.5 million living animal species have been described , of which around 1.05 million are insects , over 85,000 are molluscs , and around 65,000 are vertebrates . It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs . The scientific study of animals
1365-554: A large library which included manuscripts, maps, and museum objects. While in Athens, his wife Pythias died and Aristotle became involved with Herpyllis of Stagira. They had a son whom Aristotle named after his father, Nicomachus . This period in Athens, between 335 and 323 BC, is when Aristotle is believed to have composed many of his philosophical works. He wrote many dialogues, of which only fragments have survived. Those works that have survived are in treatise form and were not, for
1470-597: A linear scale, and noted various exceptions, such as that sharks had a placenta like the tetrapods. To a modern biologist, the explanation, not available to Aristotle, is convergent evolution . Philosophers of science have generally concluded that Aristotle was not interested in taxonomy, but zoologists who studied this question in the early 21st century think otherwise. He believed that purposive final causes guided all natural processes; this teleological view justified his observed data as an expression of formal design. Aristotle's psychology , given in his treatise On
1575-427: A plant in the soil is potentially ( dynamei ) a plant, and if it is not prevented by something, it will become a plant. Potentially, beings can either 'act' ( poiein ) or 'be acted upon' ( paschein ), which can be either innate or learned. For example, the eyes possess the potentiality of sight (innate – being acted upon), while the capability of playing the flute can be possessed by learning (exercise – acting). Actuality
1680-1109: A population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding . Some animals are capable of asexual reproduction , which often results in a genetic clone of the parent. This may take place through fragmentation ; budding , such as in Hydra and other cnidarians ; or parthenogenesis , where fertile eggs are produced without mating , such as in aphids . Animals are categorised into ecological groups depending on their trophic levels and how they consume organic material . Such groupings include carnivores (further divided into subcategories such as piscivores , insectivores , ovivores , etc.), herbivores (subcategorized into folivores , graminivores , frugivores , granivores , nectarivores , algivores , etc.), omnivores , fungivores , scavengers / detritivores , and parasites . Interactions between animals of each biome form complex food webs within that ecosystem . In carnivorous or omnivorous species, predation
1785-498: A priori principles. Aristotle's "natural philosophy" spans a wide range of natural phenomena including those now covered by physics, biology and other natural sciences. In Aristotle's terminology, "natural philosophy" is a branch of philosophy examining the phenomena of the natural world, and includes fields that would be regarded today as physics, biology and other natural sciences. Aristotle's work encompassed virtually all facets of intellectual inquiry. Aristotle makes philosophy in
1890-576: A researcher and lecturer, earning for himself the nickname "mind of the school" by his tutor Plato . In Athens, he probably experienced the Eleusinian Mysteries as he wrote when describing the sights one viewed at the Mysteries, "to experience is to learn" ( παθεĩν μαθεĩν ). Aristotle remained in Athens for nearly twenty years before leaving in 348/47 BC after Plato's death. The traditional story about his departure records that he
1995-646: A significant impact across the world, and remain a subject of contemporary philosophical discussion. Aristotle's views profoundly shaped medieval scholarship . The influence of his physical science extended from late antiquity and the Early Middle Ages into the Renaissance , and was not replaced systematically until the Enlightenment and theories such as classical mechanics were developed. He influenced Judeo-Islamic philosophies during
2100-427: A single opening, which serves as both mouth and anus. Animals in both phyla have distinct tissues, but these are not organised into discrete organs . They are diploblastic , having only two main germ layers, ectoderm and endoderm. Aristotle Aristotle ( Attic Greek : Ἀριστοτέλης , romanized: Aristotélēs ; 384–322 BC) was an Ancient Greek philosopher and polymath . His writings cover
2205-562: A thrown stone, in the Physics (254b10), and "natural motion", such as of a falling object, in On the Heavens (300a20). In violent motion, as soon as the agent stops causing it, the motion stops also: in other words, the natural state of an object is to be at rest, since Aristotle does not address friction . With this understanding, it can be observed that, as Aristotle stated, heavy objects (on
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#17328017571392310-464: Is a consumer–resource interaction where the predator feeds on another organism, its prey , who often evolves anti-predator adaptations to avoid being fed upon. Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various antagonistic/ competitive coevolutions . Almost all multicellular predators are animals. Some consumers use multiple methods; for example, in parasitoid wasps ,
2415-454: Is a historical accident: his works on botany have been lost, but two books on plants by his pupil Theophrastus have survived. Aristotle reports on the sea-life visible from observation on Lesbos and the catches of fishermen. He describes the catfish , electric ray , and frogfish in detail, as well as cephalopods such as the octopus and paper nautilus . His description of the hectocotyl arm of cephalopods, used in sexual reproduction,
2520-433: Is a stage in embryonic development that is unique to animals, allowing cells to be differentiated into specialised tissues and organs. All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins . During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised, making
2625-419: Is also a final cause or end. Then Aristotle proceeds and concludes that the actuality is prior to potentiality in formula, in time and in substantiality. With this definition of the particular substance (i.e., matter and form), Aristotle tries to solve the problem of the unity of the beings, for example, "what is it that makes a man one"? Since, according to Plato there are two Ideas: animal and biped, how then
2730-463: Is disputed, as they might be water-escape or other structures. Animals are monophyletic , meaning they are derived from a common ancestor. Animals are the sister group to the choanoflagellates , with which they form the Choanozoa . The dates on the phylogenetic tree indicate approximately how many millions of years ago ( mya ) the lineages split. Ros-Rocher and colleagues (2021) trace
2835-450: Is known as zoology , and the study of animal behaviour is known as ethology . The animal kingdom is divided into five infrakingdoms / superphyla , namely Porifera , Ctenophora , Placozoa , Cnidaria and Bilateria . Most living animal species belong to the infrakingdom Bilateria, a highly proliferative clade whose members have a bilaterally symmetric body plan , and the vast majority of bilaterians belong to two large superphyla :
2940-541: Is man a unity? However, according to Aristotle, the potential being (matter) and the actual one (form) are one and the same. Aristotle's immanent realism means his epistemology is based on the study of things that exist or happen in the world, and rises to knowledge of the universal, whereas for Plato epistemology begins with knowledge of universal Forms (or ideas) and descends to knowledge of particular imitations of these. Aristotle uses induction from examples alongside deduction , whereas Plato relies on deduction from
3045-808: Is often used to refer only to nonhuman animals. The term metazoa is derived from Ancient Greek μετα ( meta ) 'after' (in biology, the prefix meta- stands for 'later') and ζῷᾰ ( zōia ) 'animals', plural of ζῷον zōion 'animal'. Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular . Unlike plants and algae , which produce their own nutrients , animals are heterotrophic , feeding on organic material and digesting it internally. With very few exceptions, animals respire aerobically . All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle , but some animals, such as sponges , corals , mussels , and barnacles , later become sessile . The blastula
3150-422: Is only produced by sponges and pelagophyte algae. Its likely origin is from sponges based on molecular clock estimates for the origin of 24-ipc production in both groups. Analyses of pelagophyte algae consistently recover a Phanerozoic origin, while analyses of sponges recover a Neoproterozoic origin, consistent with the appearance of 24-ipc in the fossil record. The first body fossils of animals appear in
3255-406: Is predicated. So, according to Aristotle, the form of apple exists within each apple, rather than in the world of the forms. Concerning the nature of change ( kinesis ) and its causes, as he outlines in his Physics and On Generation and Corruption ( 319b–320a), he distinguishes coming-to-be ( genesis , also translated as 'generation') from: Coming-to-be is a change where the substrate of
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3360-502: Is probably not in its original form, because it was most likely edited by students and later lecturers. The logical works of Aristotle were compiled into a set of six books called the Organon around 40 BC by Andronicus of Rhodes or others among his followers. The books are: The order of the books (or the teachings from which they are composed) is not certain, but this list was derived from analysis of Aristotle's writings. It goes from
3465-480: Is still a proper universal form. Aristotle disagreed with Plato on this point, arguing that all universals are instantiated at some period of time, and that there are no universals that are unattached to existing things. In addition, Aristotle disagreed with Plato about the location of universals. Where Plato spoke of the forms as existing separately from the things that participate in them, Aristotle maintained that universals exist within each thing on which each universal
3570-547: Is the Benthozoa clade, which would consist of Porifera and ParaHoxozoa as a sister group of Ctenophora . Several animal phyla lack bilateral symmetry. These are the Porifera (sea sponges), Placozoa , Cnidaria (which includes jellyfish , sea anemones , and corals), and Ctenophora (comb jellies). Sponges are physically very distinct from other animals, and were long thought to have diverged first, representing
3675-413: Is the fulfilment of the end of the potentiality. Because the end ( telos ) is the principle of every change, and potentiality exists for the sake of the end, actuality, accordingly, is the end. Referring then to the previous example, it can be said that an actuality is when a plant does one of the activities that plants do. For that for the sake of which ( to hou heneka ) a thing is, is its principle, and
3780-548: The Iliad , which reportedly became one of Alexander's most prized possessions. Scholars speculate that two of Aristotle's now lost works, On kingship and On behalf of the Colonies , were composed by the philosopher for the young prince. After Philip II's assassination in 336 BC, Aristotle returned to Athens for the second and final time a year later. As a metic , Aristotle could not own property in Athens and thus rented
3885-622: The Cambrian explosion , which began around 539 million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived about 650 Mya during the Cryogenian period. Historically, Aristotle divided animals into those with blood and those without . Carl Linnaeus created
3990-652: The Early Modern period. John Philoponus (in Late antiquity ) and Galileo (in Early modern period ) are said to have shown by experiment that Aristotle's claim that a heavier object falls faster than a lighter object is incorrect. A contrary opinion is given by Carlo Rovelli , who argues that Aristotle's physics of motion is correct within its domain of validity, that of objects in the Earth 's gravitational field immersed in
4095-619: The Ediacaran , represented by forms such as Charnia and Spriggina . It had long been doubted whether these fossils truly represented animals, but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes their nature. Animals are thought to have originated under low-oxygen conditions, suggesting that they were capable of living entirely by anaerobic respiration , but as they became specialized for aerobic metabolism they became fully dependent on oxygen in their environments. Many animal phyla first appear in
4200-525: The Great Comet of 371 BC . Aristotle was one of the first people to record any geological observations. He stated that geological change was too slow to be observed in one person's lifetime. The geologist Charles Lyell noted that Aristotle described such change, including "lakes that had dried up" and "deserts that had become watered by rivers", giving as examples the growth of the Nile delta since
4305-476: The History of Animals in a graded scale of perfection, a nonreligious version of the scala naturae , with man at the top. His system had eleven grades of animal, from highest potential to lowest, expressed in their form at birth: the highest gave live birth to hot and wet creatures, the lowest laid cold, dry mineral-like eggs. Animals came above plants , and these in turn were above minerals. He grouped what
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4410-456: The Milky Way was made up of "those stars which are shaded by the earth from the sun's rays," pointing out partly correctly that if "the size of the sun is greater than that of the earth and the distance of the stars from the earth many times greater than that of the sun, then... the sun shines on all the stars and the earth screens none of them." He also wrote descriptions of comets, including
4515-508: The Physics (215a25), Aristotle effectively states a quantitative law, that the speed, v, of a falling body is proportional (say, with constant c) to its weight, W, and inversely proportional to the density, ρ, of the fluid in which it is falling:; Aristotle implies that in a vacuum the speed of fall would become infinite, and concludes from this apparent absurdity that a vacuum is not possible. Opinions have varied on whether Aristotle intended to state quantitative laws. Henri Carteron held
4620-485: The Wnt and TGF-beta signalling pathways which may have enabled animals to become multicellular by providing a pattern for the body's system of axes (in three dimensions), and another 7 are for transcription factors including homeodomain proteins involved in the control of development . Giribet and Edgecombe (2020) provide what they consider to be a consensus internal phylogeny of the animals, embodying uncertainty about
4725-665: The evolutionary relationships between taxa . Humans make use of many other animal species for food (including meat , eggs , and dairy products ), for materials (such as leather , fur , and wool ), as pets and as working animals for transportation , and services . Dogs , the first domesticated animal, have been used in hunting , in security and in warfare , as have horses , pigeons and birds of prey ; while other terrestrial and aquatic animals are hunted for sports, trophies or profits. Non-human animals are also an important cultural element of human evolution , having appeared in cave arts and totems since
4830-473: The fossil record during the Cambrian explosion , starting about 539 million years ago, in beds such as the Burgess shale . Extant phyla in these rocks include molluscs , brachiopods , onychophorans , tardigrades , arthropods , echinoderms and hemichordates , along with numerous now-extinct forms such as the predatory Anomalocaris . The apparent suddenness of the event may however be an artifact of
4935-497: The lobe-finned fish Tiktaalik started to move on to land in the late Devonian , about 375 million years ago. Animals occupy virtually all of earth's habitats and microhabitats, with faunas adapted to salt water, hydrothermal vents, fresh water, hot springs, swamps, forests, pastures, deserts, air, and the interiors of other organisms. Animals are however not particularly heat tolerant ; very few of them can survive at constant temperatures above 50 °C (122 °F) or in
5040-500: The protostomes , which includes organisms such as arthropods , molluscs , flatworms , annelids and nematodes ; and the deuterostomes , which include echinoderms , hemichordates and chordates , the latter of which contains the vertebrates . The much smaller basal phylum Xenacoelomorpha have an uncertain position within Bilateria. Animals first appear in the fossil record in the late Cryogenian period and diversified in
5145-519: The "extreme view" that Aristotle's concept of force was basically qualitative, but other authors reject this. Archimedes corrected Aristotle's theory that bodies move towards their natural resting places; metal boats can float if they displace enough water ; floating depends in Archimedes' scheme on the mass and volume of the object, not, as Aristotle thought, its elementary composition. Aristotle's writings on motion remained influential until
5250-715: The Cambrian explosion, possibly as early as 1 billion years ago. Early fossils that might represent animals appear for example in the 665-million-year-old rocks of the Trezona Formation of South Australia . These fossils are interpreted as most probably being early sponges . Trace fossils such as tracks and burrows found in the Tonian period (from 1 gya) may indicate the presence of triploblastic worm-like animals, roughly as large (about 5 mm wide) and complex as earthworms. However, similar tracks are produced by
5355-717: The Cnidaria) never grow larger than 20 μm , and one of the smallest species ( Myxobolus shekel ) is no more than 8.5 μm when fully grown. The following table lists estimated numbers of described extant species for the major animal phyla, along with their principal habitats (terrestrial, fresh water, and marine), and free-living or parasitic ways of life. Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of
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#17328017571395460-508: The Great beginning in 343 BC. He established a library in the Lyceum, which helped him to produce many of his hundreds of books on papyrus scrolls . Though Aristotle wrote many treatises and dialogues for publication, only around a third of his original output has survived , none of it intended for publication. Aristotle provided a complex synthesis of the various philosophies existing prior to him. His teachings and methods of inquiry have had
5565-566: The Lyceum of Athens, Alexandria , and later in Rome . With the Prior Analytics , Aristotle is credited with the earliest study of formal logic, and his conception of it was the dominant form of Western logic until 19th-century advances in mathematical logic . Kant stated in the Critique of Pure Reason that with Aristotle, logic reached its completion. Most of Aristotle's work
5670-646: The Middle Ages, as well as Christian theology , especially the Neoplatonism of the Early Church and the scholastic tradition of the Catholic Church . Aristotle was revered among medieval Muslim scholars as "The First Teacher", and among medieval Christians like Thomas Aquinas as simply "The Philosopher", while the poet Dante called him "the master of those who know". His works contain
5775-494: The ball along to make it continue to rise even though the hand is no longer acting on it, resulting in the Medieval theory of impetus . Aristotle suggested that the reason for anything coming about can be attributed to four different types of simultaneously active factors. His term aitia is traditionally translated as "cause", but it does not always refer to temporal sequence; it might be better translated as "explanation", but
5880-640: The basics, the analysis of simple terms in the Categories, the analysis of propositions and their elementary relations in On Interpretation , to the study of more complex forms, namely, syllogisms (in the Analytics ) and dialectics (in the Topics and Sophistical Refutations ). The first three treatises form the core of the logical theory stricto sensu : the grammar of the language of logic and
5985-399: The becoming is for the sake of the end; and the actuality is the end, and it is for the sake of this that the potentiality is acquired. For animals do not see in order that they may have sight, but they have sight that they may see. In summary, the matter used to make a house has potentiality to be a house and both the activity of building and the form of the final house are actualities, which
6090-574: The broad sense coextensive with reasoning, which he also would describe as "science". However, his use of the term science carries a different meaning than that covered by the term "scientific method". For Aristotle, "all science ( dianoia ) is either practical, poetical or theoretical" ( Metaphysics 1025b25). His practical science includes ethics and politics; his poetical science means the study of fine arts including poetry; his theoretical science covers physics, mathematics and metaphysics. In his On Generation and Corruption , Aristotle related each of
6195-433: The cause of earthquakes was a gas or vapor ( anathymiaseis ) that was trapped inside the earth and trying to escape, following other Greek authors Anaxagoras , Empedocles and Democritus . Aristotle also made many observations about the hydrologic cycle. For example, he made some of the earliest observations about desalination: he observed early – and correctly – that when seawater is heated, freshwater evaporates and that
6300-491: The city of Stagira in northern Greece during the Classical period . His father, Nicomachus , died when Aristotle was a child, and he was brought up by a guardian. At around eighteen years old, he joined Plato 's Academy in Athens and remained there until the age of thirty seven ( c. 347 BC ). Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon , tutored his son Alexander
6405-487: The correct rules of reasoning. The Rhetoric is not conventionally included, but it states that it relies on the Topics . What is today called Aristotelian logic with its types of syllogism (methods of logical argument), Aristotle himself would have labelled "analytics". The term "logic" he reserved to mean dialectics . The word "metaphysics" appears to have been coined by the first century AD editor who assembled various small selections of Aristotle's works to create
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#17328017571396510-463: The dark sea floor consume organic matter produced through chemosynthesis (via oxidizing inorganic compounds such as hydrogen sulfide ) by archaea and bacteria . Animals evolved in the sea. Lineages of arthropods colonised land around the same time as land plants , probably between 510 and 471 million years ago during the Late Cambrian or Early Ordovician . Vertebrates such as
6615-399: The data to come to the theory of evolution . Aristotle's writings can seem to modern readers close to implying evolution, but while Aristotle was aware that new mutations or hybridizations could occur, he saw these as rare accidents. For Aristotle, accidents, like heat waves in winter, must be considered distinct from natural causes. He was thus critical of Empedocles's materialist theory of
6720-808: The death. Following Alexander's death, anti-Macedonian sentiment in Athens was rekindled. In 322 BC, Demophilus and Eurymedon the Hierophant reportedly denounced Aristotle for impiety, prompting him to flee to his mother's family estate in Chalcis, Euboea , at which occasion he was said to have stated "I will not allow the Athenians to sin twice against philosophy" – a reference to Athens's trial and execution of Socrates . He died in Chalcis, Euboea of natural causes later that same year, having named his student Antipater as his chief executor and leaving
6825-479: The earliest known formal study of logic, and were studied by medieval scholars such as Peter Abelard and Jean Buridan . Aristotle's influence on logic continued well into the 19th century. In addition, his ethics , although always influential, gained renewed interest with the modern advent of virtue ethics . In general, the details of Aristotle's life are not well-established. The biographies written in ancient times are often speculative and historians only agree on
6930-454: The earliest times, and are frequently featured in mythology , religion , arts , literature , heraldry , politics , and sports . The word animal comes from the Latin noun animal of the same meaning, which is itself derived from Latin animalis 'having breath or soul'. The biological definition includes all members of the kingdom Animalia. In colloquial usage, the term animal
7035-553: The end of his life, the two men became estranged having diverging opinions over issues, like the optimal administration of city-states, the treatment of conquered populations, such as the Persians, and philosophical questions, like the definition of braveness. A widespread speculation in antiquity suggested that Aristotle played a role in Alexander's death, but the only evidence of this is an unlikely claim made some six years after
7140-570: The first hierarchical biological classification for animals in 1758 with his Systema Naturae , which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa , single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics , which are effective at demonstrating
7245-533: The following. Brood size decreases with (adult) body mass, so that an elephant has fewer young (usually just one) per brood than a mouse. Lifespan increases with gestation period , and also with body mass, so that elephants live longer than mice, have a longer period of gestation, and are heavier. As a final example, fecundity decreases with lifespan, so long-lived kinds like elephants have fewer young in total than short-lived kinds like mice. Aristotle distinguished about 500 species of animals , arranging these in
7350-403: The form of the substance is the actual house, namely 'covering for bodies and chattels' or any other differentia that let us define something as a house. The formula that gives the components is the account of the matter, and the formula that gives the differentia is the account of the form. Like his teacher Plato, Aristotle's philosophy aims at the universal . Aristotle's ontology places
7455-448: The formation of complex structures possible. This may be calcified, forming structures such as shells , bones , and spicules . In contrast, the cells of other multicellular organisms (primarily algae, plants, and fungi ) are held in place by cell walls, and so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions , gap junctions , and desmosomes . With few exceptions—in particular,
7560-520: The fossil record, rather than showing that all these animals appeared simultaneously. That view is supported by the discovery of Auroralumina attenboroughii , the earliest known Ediacaran crown-group cnidarian (557–562 mya, some 20 million years before the Cambrian explosion) from Charnwood Forest , England. It is thought to be one of the earliest predators , catching small prey with its nematocysts as modern cnidarians do. Some palaeontologists have suggested that animals appeared much earlier than
7665-515: The four elements proposed earlier by Empedocles , earth , water , air , and fire , to two of the four sensible qualities, hot, cold, wet, and dry. In the Empedoclean scheme, all matter was made of the four elements, in differing proportions. Aristotle's scheme added the heavenly aether , the divine substance of the heavenly spheres , stars and planets. Aristotle describes two kinds of motion: "violent" or "unnatural motion", such as that of
7770-737: The giant single-celled protist Gromia sphaerica , so the Tonian trace fossils may not indicate early animal evolution. Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals. Objects such as sediment-filled tubes that resemble trace fossils of the burrows of wormlike animals have been found in 1.2 gya rocks in North America, in 1.5 gya rocks in Australia and North America, and in 1.7 gya rocks in Australia. Their interpretation as having an animal origin
7875-428: The ground, say) require more force to make them move; and objects pushed with greater force move faster. This would imply the equation incorrect in modern physics. Natural motion depends on the element concerned: the aether naturally moves in a circle around the heavens, while the 4 Empedoclean elements move vertically up (like fire, as is observed) or down (like earth) towards their natural resting places. In
7980-440: The image. According to Aristotle, spontaneity and chance are causes of some things, distinguishable from other types of cause such as simple necessity. Chance as an incidental cause lies in the realm of accidental things , "from what is spontaneous". There is also more a specific kind of chance, which Aristotle names "luck", that only applies to people's moral choices. In astronomy , Aristotle refuted Democritus 's claim that
8085-441: The larvae feed on the hosts' living tissues, killing them in the process, but the adults primarily consume nectar from flowers. Other animals may have very specific feeding behaviours , such as hawksbill sea turtles which mainly eat sponges . Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers ) through photosynthesis . Herbivores, as primary consumers , eat
8190-564: The legendary physician Asclepius and his son Machaon . Both of Aristotle's parents died when he was still at a young age and Proxenus of Atarneus became his guardian. Although little information about Aristotle's childhood has survived, he probably spent some time in the Macedonian capital, making his first connections with the Macedonian monarchy . At the age of seventeen or eighteen, Aristotle moved to Athens to continue his education at Plato's Academy . He became distinguished as
8295-468: The modern zoologist would call vertebrates as the hotter "animals with blood", and below them the colder invertebrates as "animals without blood". Those with blood were divided into the live-bearing ( mammals ), and the egg-laying ( birds , reptiles , fish ). Those without blood were insects, crustacea (non-shelled – cephalopods, and shelled ) and the hard-shelled molluscs ( bivalves and gastropods ). He recognised that animals did not exactly fit into
8400-753: The most extreme cold deserts of continental Antarctica . The blue whale ( Balaenoptera musculus ) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long. The largest extant terrestrial animal is the African bush elephant ( Loxodonta africana ), weighing up to 12.25 tonnes and measuring up to 10.67 metres (35.0 ft) long. The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus , which may have weighed as much as 73 tonnes, and Supersaurus which may have reached 39 meters. Several animals are microscopic; some Myxozoa ( obligate parasites within
8505-532: The most part, intended for widespread publication; they are generally thought to be lecture aids for his students. His most important treatises include Physics , Metaphysics , Nicomachean Ethics , Politics , On the Soul and Poetics . Aristotle studied and made significant contributions to "logic, metaphysics, mathematics, physics, biology, botany, ethics, politics, agriculture, medicine, dance, and theatre." While Alexander deeply admired Aristotle, near
8610-504: The near-by island of Lesbos . During this time, Aristotle married Pythias , Hermias's adoptive daughter and niece, and had a daughter whom they also named Pythias. In 343/42 BC, Aristotle was invited to Pella by Philip II of Macedon in order to become the tutor to his thirteen-year-old son Alexander ; a choice perhaps influenced by the relationship of Aristotle's family with the Macedonian dynasty. Aristotle taught Alexander at
8715-404: The oceans are then replenished by the cycle of rainfall and river runoff ("I have proved by experiment that salt water evaporated forms fresh and the vapor does not when it condenses condense into sea water again.") Aristotle was the first person to study biology systematically, and biology forms a large part of his writings. He spent two years observing and describing the zoology of Lesbos and
8820-620: The oldest animal phylum and forming a sister clade to all other animals. Despite their morphological dissimilarity with all other animals, genetic evidence suggests sponges may be more closely related to other animals than the comb jellies are. Sponges lack the complex organization found in most other animal phyla; their cells are differentiated, but in most cases not organised into distinct tissues, unlike all other animals. They typically feed by drawing in water through pores, filtering out small particles of food. The comb jellies and Cnidaria are radially symmetric and have digestive chambers with
8925-525: The origins of animals to unicellular ancestors, providing the external phylogeny shown in the cladogram. Uncertainty of relationships is indicated with dashed lines. Holomycota (inc. fungi) [REDACTED] Ichthyosporea [REDACTED] Pluriformea [REDACTED] Filasterea [REDACTED] [REDACTED] [REDACTED] The most basal animals, the Porifera , Ctenophora , Cnidaria , and Placozoa , have body plans that lack bilateral symmetry . Their relationships are still disputed;
9030-519: The plant material directly to digest and absorb the nutrients, while carnivores and other animals on higher trophic levels indirectly acquire the nutrients by eating the herbivores or other animals that have eaten the herbivores. Animals oxidize carbohydrates , lipids , proteins and other biomolecules, which allows the animal to grow and to sustain basal metabolism and fuel other biological processes such as locomotion . Some benthic animals living close to hydrothermal vents and cold seeps on
9135-437: The primary kind of knowledge; but if there is some motionless independent thing, the knowledge of this precedes it and is first philosophy, and it is universal in just this way , because it is first. And it belongs to this sort of philosophy to study being as being, both what it is and what belongs to it just by virtue of being. Aristotle examines the concepts of substance ( ousia ) and essence ( to ti ên einai , "the what it
9240-571: The private school of Mieza , in the gardens of the Nymphs , the royal estate near Pella. Alexander's education probably included a number of subjects, such as ethics and politics , as well as standard literary texts, like Euripides and Homer . It is likely that during Aristotle's time in the Macedonian court, other prominent nobles, like Ptolemy and Cassander , would have occasionally attended his lectures. Aristotle encouraged Alexander toward eastern conquest, and his own attitude towards Persia
9345-433: The same certainty as experimental science, but it sets out testable hypotheses and constructs a narrative explanation of what is observed. In this sense, Aristotle's biology is scientific. From the data he collected and documented, Aristotle inferred quite a number of rules relating the life-history features of the live-bearing tetrapods (terrestrial placental mammals) that he studied. Among these correct predictions are
9450-753: The sister group to all other animals could be the Porifera or the Ctenophora, both of which lack hox genes , which are important for body plan development . Hox genes are found in the Placozoa, Cnidaria, and Bilateria. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian . 25 of these are novel core gene groups, found only in animals; of those, 8 are for essential components of
9555-407: The smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova . These fuse to form zygotes , which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form
9660-474: The sponges and placozoans —animal bodies are differentiated into tissues . These include muscles , which enable locomotion, and nerve tissues , which transmit signals and coordinate the body. Typically, there is also an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians). Nearly all animals make use of some form of sexual reproduction. They produce haploid gametes by meiosis ;
9765-411: The structure at the base of the tree (dashed lines). Porifera [REDACTED] Ctenophora [REDACTED] Placozoa [REDACTED] Cnidaria [REDACTED] Xenacoelomorpha [REDACTED] Ambulacraria [REDACTED] Chordata [REDACTED] Ecdysozoa [REDACTED] Spiralia [REDACTED] An alternative phylogeny, from Kapli and colleagues (2021), proposes
9870-522: The subsequent Ediacaran period in what is known as the Avalon explosion . Earlier evidence of animals is still controversial; the sponge -like organism Otavia has been dated back to the Tonian period at the start of the Neoproterozoic , but its identity as an animal is heavily contested. Nearly all modern animal phyla became clearly established in the fossil record as marine species during
9975-558: The surrounding seas, including in particular the Pyrrha lagoon in the centre of Lesbos. His data in History of Animals , Generation of Animals , Movement of Animals , and Parts of Animals are assembled from his own observations, statements given by people with specialized knowledge, such as beekeepers and fishermen, and less accurate accounts provided by travellers from overseas. His apparent emphasis on animals rather than plants
10080-402: The thing that has undergone the change has itself changed. In that particular change he introduces the concept of potentiality ( dynamis ) and actuality ( entelecheia ) in association with the matter and the form. Referring to potentiality, this is what a thing is capable of doing or being acted upon if the conditions are right and it is not prevented by something else. For example, the seed of
10185-475: The time of Homer , and "the upheaving of one of the Aeolian islands , previous to a volcanic eruption ."' Meteorologica lends its name to the modern study of meteorology, but its modern usage diverges from the content of Aristotle's ancient treatise on meteors . The ancient Greeks did use the term for a range of atmospheric phenomena, but also for earthquakes and volcanic eruptions. Aristotle proposed that
10290-467: The total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011. 3,000–6,500 4,000–25,000 Evidence of animals is found as long ago as the Cryogenian period. 24-Isopropylcholestane (24-ipc) has been found in rocks from roughly 650 million years ago; it
10395-478: The traditional rendering will be employed here. Aristotle describes experiments in optics using a camera obscura in Problems , book 15. The apparatus consisted of a dark chamber with a small aperture that let light in. With it, he saw that whatever shape he made the hole, the sun's image always remained circular. He also noted that increasing the distance between the aperture and the image surface magnified
10500-401: The treatise we know by the name Metaphysics . Aristotle called it "first philosophy", and distinguished it from mathematics and natural science (physics) as the contemplative ( theoretikē ) philosophy which is "theological" and studies the divine. He wrote in his Metaphysics (1026a16): If there were no other independent things besides the composite natural ones, the study of nature would be
10605-492: The universal ( katholou ) in particulars ( kath' hekaston ), things in the world, whereas for Plato the universal is a separately existing form which actual things imitate. For Aristotle, "form" is still what phenomena are based on, but is "instantiated" in a particular substance. Plato argued that all things have a universal form , which could be either a property or a relation to other things. When one looks at an apple, for example, one sees an apple, and one can also analyse
10710-681: Was disappointed with the Academy's direction after control passed to Plato's nephew Speusippus , although it is possible that the anti-Macedonian sentiments in Athens could have also influenced his decision. Aristotle left with Xenocrates to Assos in Asia Minor , where he was invited by his former fellow student Hermias of Atarneus ; he stayed there for a few years and left around the time of Hermias' death. While at Assos, Aristotle and his colleague Theophrastus did extensive research in botany and marine biology , which they later continued at
10815-478: Was strongly ethnocentric . In one famous example, he counsels Alexander to be "a leader to the Greeks and a despot to the barbarians". Alexander's education under the guardianship of Aristotle likely lasted for only a few years, as at around the age of sixteen he returned to Pella and was appointed regent of Macedon by his father Philip. During this time, Aristotle is said to have gifted Alexander an annotated copy of
10920-421: Was to be") in his Metaphysics (Book VII), and he concludes that a particular substance is a combination of both matter and form, a philosophical theory called hylomorphism . In Book VIII, he distinguishes the matter of the substance as the substratum , or the stuff of which it is composed. For example, the matter of a house is the bricks, stones, timbers, etc., or whatever constitutes the potential house, while
11025-588: Was widely disbelieved until the 19th century. He gives accurate descriptions of the four-chambered fore-stomachs of ruminants , and of the ovoviviparous embryological development of the hound shark . He notes that an animal's structure is well matched to function so birds like the heron (which live in marshes with soft mud and live by catching fish) have a long neck, long legs, and a sharp spear-like beak, whereas ducks that swim have short legs and webbed feet. Darwin , too, noted these sorts of differences between similar kinds of animal, but unlike Aristotle used
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