In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic or adaptive trait, with a functional role in each individual organism, maintained and has evolved through natural selection. Organisms face a succession of environmental challenges as they grow, show adaptive plasticity as traits develop in response to the imposed conditions; this gives them resilience to varying environments. Adaptation is an observable fact of life accepted by philosophers and natural historians from ancient times, independently of their views on evolution, but their explanations differed. Empedocles did not believe that adaptation required a final cause, but thought that it "came about since such things survived." Aristotle assumed that species were fixed. In natural theology, adaptation was interpreted as the work of a deity and as evidence for the existence of God.
William Paley believed that organisms were adapted to the lives they led, an argument that shadowed Gottfried Wilhelm Leibniz, who had argued that God had brought about "the best of all possible worlds." Voltaire's Dr. Pangloss is a parody of this optimistic idea, David Hume argued against design; the Bridgewater Treatises are a product of natural theology, though some of the authors managed to present their work in a neutral manner. The series was lampooned by Robert Knox, who held quasi-evolutionary views, as the Bilgewater Treatises. Charles Darwin broke with the tradition by emphasising the flaws and limitations which occurred in the animal and plant worlds. Jean-Baptiste Lamarck proposed a tendency for organisms to become more complex, moving up a ladder of progress, plus "the influence of circumstances," expressed as use and disuse; this second, subsidiary element of his theory is what is now called Lamarckism, a proto-evolutionary hypothesis of the inheritance of acquired characteristics, intended to explain adaptations by natural means.
Other natural historians, such as Buffon, accepted adaptation, some accepted evolution, without voicing their opinions as to the mechanism. This illustrates the real merit of Darwin and Alfred Russel Wallace, secondary figures such as Henry Walter Bates, for putting forward a mechanism whose significance had only been glimpsed previously. A century experimental field studies and breeding experiments by people such as E. B. Ford and Theodosius Dobzhansky produced evidence that natural selection was not only the'engine' behind adaptation, but was a much stronger force than had been thought; the significance of an adaptation can only be understood in relation to the total biology of the species. Adaptation is a process rather than a physical form or part of a body. An internal parasite can illustrate the distinction: such a parasite may have a simple bodily structure, but the organism is adapted to its specific environment. From this we see that adaptation is not just a matter of visible traits: in such parasites critical adaptations take place in the life cycle, quite complex.
However, as a practical term, "adaptation" refers to a product: those features of a species which result from the process. Many aspects of an animal or plant can be called adaptations, though there are always some features whose function remains in doubt. By using the term adaptation for the evolutionary process, adaptive trait for the bodily part or function, one may distinguish the two different senses of the word. Adaptation is one of the two main processes that explain the observed diversity of species, such as the different species of Darwin's finches; the other process is speciation, in which new species arise through reproductive isolation. A favourite example used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes, where the question of reproductive isolation is complex. Adaptation is not always a simple matter where the ideal phenotype evolves for a given external environment. An organism must be viable at all stages of its development and at all stages of its evolution.
This places constraints on the evolution of development and structure of organisms. The main constraint, over which there has been much debate, is the requirement that each genetic and phenotypic change during evolution should be small, because developmental systems are so complex and interlinked. However, it is not clear what "relatively small" should mean, for example polyploidy in plants is a reasonably common large genetic change; the origin of eukaryotic endosymbiosis is a more dramatic example. All adaptations help; the adaptive traits may be behavioural or physiological. Structural adaptations are physical features of an organism, such as shape, body covering and internal organization. Behavioural adaptations are inherited systems of behaviour, whether inherited in detail as instincts, or as a neuropsychological capacity for learning. Examples include searching for food and vocalizations. Physiological adaptations permit the organism to perform special functions such as making venom, secreting slime, phototropism), but involve more general functions such as growth and development, temperature regulation, ionic balance and other aspects of homeostasis.
Adaptation affects all aspects of the life of an organism. The following definitions are given by the evolutionary biologist Theodosius Dobzhansky: 1. Adaptation is the evolutionary pr
An omnivore is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein and fiber, metabolize the nutrients and energy of the sources absorbed, they have the ability to incorporate food sources such as algae and bacteria into their diet. Omnivores come from diverse backgrounds that independently evolved sophisticated consumption capabilities. For instance, dogs evolved from carnivorous organisms while pigs evolved from herbivorous organisms. What this means is that physical characteristics are not reliable indicators of whether an animal has the ability to obtain energy and nutrients from both plant and animal matter. Owing to the wide range of unrelated organisms independently evolving the capability to obtain energy and nutrients from both plant and animal materials, no generalizations about the anatomical features of all omnivores can realistically be made; the variety of different animals that are classified as omnivores can be placed into further categories depending on their feeding behaviors.
Frugivores include maned orangutans. All of these animals are omnivores, yet still fall into special niches in terms of feeding behavior and preferred foods. Being omnivores gives these animals more food security in stressful times or makes possible living in less consistent environments; the word omnivore derives from the Latin omnis, vora, from vorare, having been coined by the French and adopted by the English in the 1800s. Traditionally the definition for omnivory was behavioral by means of "including both animal and vegetable tissue in the diet." In more recent times, with the advent of advanced technological capabilities in fields like gastroenterology, biologists have formulated a standardized variation of omnivore used for labeling a species' actual ability to obtain energy and nutrients from materials. This has subsequently conditioned two context specific definitions. Behavioral: This definition is used to specify if a species or individual is consuming both plant and animal materials.
Physiological: This definition is used in academia to specify species that have the capability to obtain energy and nutrients from both plant and animal matter. The taxonomic utility of omnivore's traditional and behavioral definition is limited, since the diet and phylogeny of one omnivorous species might be different from that of another: for instance, an omnivorous pig digging for roots and scavenging for fruit and carrion is taxonomically and ecologically quite distinct from an omnivorous chameleon that eats leaves and insects; the term "omnivory" is not always comprehensive because it does not deal with mineral foods such as salt licks and the consumption of plant and animal material for medical purposes which would not otherwise be consumed within non-omnivores. Though Carnivora is a taxon for species classification, no such equivalent exists for omnivores, as omnivores are widespread across multiple taxonomic clades; the Carnivora order does not include all carnivorous species, not all species within the Carnivora taxon are carnivorous.
It is common to find physiological carnivores consuming materials from plants or physiological herbivores consuming material from animals, e.g. felines eating grass and deer eating birds. From a behavioral aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy. Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous. Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not complement their classification. For instance, it is well documented that animals such as giraffes and cattle will gnaw on bones, preferably dry bones, for particular minerals and nutrients. Felines, which are regarded as obligate carnivores eat grass to regurgitate indigestibles, aid with hemoglobin production, as a laxative, it is found that animals classified as carnivorous may deliberately eat plant material.
For example, in 2013, it was considered that American alligators may be physiologically omnivorous once investigations had been conducted on why they eat fruits. It was suggested that alligators ate fruits both accidentally but deliberately."Life-history omnivores" is a specialized classification given to organisms that change their eating habits during their life cycle. Some species, such as grazing waterfowl like geese, are known to eat animal tissue at one stage of their lives, but plant matter at another; the same is true for many insects, such as beetles in the family Meloidae, which begin by eating animal tissue as larvae, but change to eating plant matter after they mature. Many mosquito species in early life eat plants or assorted detritus, but as they mature, males continue to eat plant matter and nectar whereas the females eat blood to reproduce effectively. Although cases exist of herbivores eating meat and carnivores eating plant matter, the classification "omnivore" re
The brown rat known as the common rat, street rat, sewer rat, Hanover rat, Norway rat, Norwegian rat, Parisian rat, water rat, or wharf rat, is one of the best known and most common rats. One of the largest muroids, it is a brown or grey rodent with a head and body length of up to 28 cm long, a tail shorter than that, it weighs between 500 g. Thought to have originated in northern China, this rodent has now spread to all continents except Antarctica, is the dominant rat in Europe and much of North America, making it, by at least this particular definition, the most successful mammal on the planet alongside humans. With rare exceptions, the brown rat lives wherever humans live in urban areas. Selective breeding of the brown rat has produced the fancy rat as a pet, as well as the laboratory rat – the white rats used as model organisms in biological research. Called the "Hanover rat" by people wishing to link problems in 18th century England with the House of Hanover, it is not known for certain why the brown rat is named Rattus norvegicus, as it did not originate from Norway.
However, the English naturalist John Berkenhout, author of the 1769 book Outlines of the Natural History of Great Britain, is most responsible for popularizing the misnomer. Berkenhout gave the brown rat the binomial name Rattus norvegicus, believing it had migrated to England from Norwegian ships in 1728. By the early to middle part of the 19th century, British academics believed that the brown rat was not native to Norway, hypothesizing that it may have come from Ireland, Gibraltar or across the English Channel with William the Conqueror; as early as 1850, however, a new hypothesis of the rat's origins was beginning to develop. The British novelist Charles Dickens acknowledged this in his weekly journal, All the Year Round, writing: Now there is a mystery about the native country of the best known species of rat, the common brown rat, it is called, in books and otherwise, the'Norway rat', it is said to have been imported into this country in a ship-load of timber from Norway. Against this hypothesis stands the fact that when the brown rat had become common in this country, it was unknown in Norway, although there was a small animal like a rat, but a lemming, which made its home there.
Academics began to prefer this etymology of the brown rat towards the end of the 19th century, as seen in the 1895 text Natural History by American scholar Alfred Henry Miles: The brown rat is the species common in England, best known throughout the world. It is said to have travelled from Persia to England less than two hundred years ago and to have spread from thence to other countries visited by English ships. Though the assumptions surrounding this species' origins were not yet the same as modern ones, by the 20th century, it was believed among naturalists that the brown rat did not originate in Norway, rather the species came from central Asia and China; the fur is coarse and brown or dark grey, while the underparts are lighter grey or brown. The brown rat is a rather large murid and can weigh twice as much as a black rat and many times more than a house mouse; the head and body length ranges from 15 to 28 cm while the tail ranges in length from 10.5 to 24 cm, therefore being shorter than the head and body.
Adult weight ranges from 140 to 500 g. Exceptionally large individuals can reach 900 to 1,000 g but are not expected outside of domestic specimens. Stories of rats attaining sizes as big as cats are exaggerations, or misidentifications of larger rodents, such as the coypu and muskrat. In fact, it is common for breeding wild brown rats to weigh less than 300 g. Brown rats have acute hearing, are sensitive to ultrasound, possess a highly developed olfactory sense, their average heart rate is 300 to 400 beats per minute, with a respiratory rate of around 100 per minute. The vision of a pigmented rat is poor, around 20/600, while a non-pigmented with no melanin in its eyes has both around 20/1200 vision and a terrible scattering of light within its vision. Brown rats are dichromates which perceive colors rather like a human with red-green colorblindness, their colour saturation may be quite faint, their blue perception, however has UV receptors, allowing them to see ultraviolet lights that some species cannot.
The brown rat is nocturnal and is a good swimmer, both on the surface and underwater, has been observed climbing slim round metal poles several feet in order to reach garden bird feeders. Brown rats dig well, excavate extensive burrow systems. A 2007 study found brown rats to possess metacognition, a mental ability only found in humans and some primates, but further analysis suggested they may have been following simple operant conditioning principles. Brown rats are capable of producing ultrasonic vocalizations; as pups, young rats use different types of ultrasonic cries to elicit and direct maternal search behavior, as well as to regulate their mother's movements in the nest. Although pups will produce ultrasounds around any other rats at 7 days old, by 14 days old they reduce ultrasound production around male rats as a defensive response. Adult rats will emit ultrasonic vocalizations in response to perceived danger; the female rat will emit ultrasonic vocalizations during mating. Rats may emit short, high frequency, ultrasonic induced vocalization during rough and tumble play, before receiving morphine, or mating
IUCN Red List
The IUCN Red List of Threatened Species, founded in 1965, has evolved to become the world's most comprehensive inventory of the global conservation status of biological species. It uses a set of criteria to evaluate the extinction risk of thousands of subspecies; these criteria are relevant to all species and all regions of the world, With its strong scientific base, the IUCN Red List is recognized as the most authoritative guide to the status of biological diversity. A series of Regional Red List are produced by countries or organizations, which assess the risk of extinction to species within a political management unit; the IUCN Red List is set upon precise criteria to evaluate the extinction risk of thousands of species and subspecies. These criteria are relevant to all regions of the world; the aim is to convey the urgency of conservation issues to the public and policy makers, as well as help the international community to try to reduce species extinction. According to the International Union for Conservation of Nature, the formally stated goals of the Red List are to provide scientifically based information on the status of species and subspecies at a global level, to draw attention to the magnitude and importance of threatened biodiversity, to influence national and international policy and decision-making, to provide information to guide actions to conserve biological diversity.
Major species assessors include BirdLife International, the Institute of Zoology, the World Conservation Monitoring Centre, many Specialist Groups within the IUCN Species Survival Commission. Collectively, assessments by these organizations and groups account for nearly half the species on the Red List; the IUCN aims to have the category of every species re-evaluated every five years if possible, or at least every ten years. This is done in a peer reviewed manner through IUCN Species Survival Commission Specialist Groups, which are Red List Authorities responsible for a species, group of species or specific geographic area, or in the case of BirdLife International, an entire class; as of 2018, 26,197 species are now classified critical or endangered. The 1964 IUCN Red List of Threatened Plants used the older pre-criteria Red List assessment system. Plants listed may not, appear in the current Red List. IUCN advise that it is best to check both the online Red List and the 1997 plants Red List publication.
The 2006 Red List, released on 4 May 2006 evaluated 40,168 species as a whole, plus an additional 2,160 subspecies, aquatic stocks, subpopulations. On 12 September 2007, the World Conservation Union released the 2007 IUCN Red List of Threatened Species. In this release, they have raised their classification of both the western lowland gorilla and the Cross River gorilla from endangered to critically endangered, the last category before extinct in the wild, due to Ebola virus and poaching, along with other factors. Russ Mittermeier, chief of Swiss-based IUCN's Primate Specialist Group, stated that 16,306 species are endangered with extinction, 188 more than in 2006; the Red List includes the Sumatran orangutan in the Critically Endangered category and the Bornean orangutan in the Endangered category. The 2008 Red List was released on 6 October 2008, at the IUCN World Conservation Congress in Barcelona, "has confirmed an extinction crisis, with one in four at risk of disappearing forever"; the study shows at least 1,141 of the 5,487 mammals on Earth are known to be threatened with extinction, 836 are listed as Data Deficient.
The Red List of 2012 was released 19 July 2012 at Rio+20 Earth Summit. The IUCN assessed a total of 63,837 species. 3,947 were described as "critically endangered" and 5,766 as "endangered," while more than 10,000 species are listed as "vulnerable." At threat are 41% of amphibian species, 33% of reef-building corals, 30% of conifers, 25% of mammals, 13% of birds. The IUCN Red List has listed 132 species of plants and animals from India as "Critically Endangered." Species are classified by the IUCN Red List into nine groups, specified through criteria such as rate of decline, population size, area of geographic distribution, degree of population and distribution fragmentation. There is an emphasis on the acceptability of applying any criteria in the absence of high quality data including suspicion and potential future threats, "so long as these can reasonably be supported." Extinct – beyond reasonable doubt that the species is no longer extant. Extinct in the wild – survives only in captivity, cultivation and/or outside native range, as presumed after exhaustive surveys.
Critically endangered – in a and critical state. Endangered – high risk of extinction in the wild, meets any of criteria A to E for Endangered. Vulnerable – meets one of the 5 red list criteria and thus considered to be at high risk of unnatural extinction without further human intervention. Near threatened – close to being at high risk of extinction in the near future. Least concern – unlikely to become extinct in the near future. Data deficient Not evaluated In the IUCN Red List, "threatened" embraces the categories of Critically Endangered and Vulnerable; the older 1994 list has only a single "Lower Risk" category which contained three subcategories: Conservation Depe
A lemming is a small rodent found in or near the Arctic in tundra biomes. Lemmings make up the subfamily Arvicolinae together with voles and muskrats, which form part of the superfamily Muroidea, which includes rats, mice and gerbils. Lemmings measure around 13–18 cm in length and weigh around 23–34 g. Lemmings are quite rounded in shape, with brown and black, soft fur, they have a short tail, a stubby, hairy snout, short legs, small ears. They have a flattened claw on the first digit of their front feet, which helps them to dig in the snow, they are herbivorous, feeding on mosses and grasses. They forage through the snow surface to find berries, shoots, roots and lichens. Lemmings choose their preferred dietary vegetation disproportionately to its occurrence in their habitat, they digest grasses and sedges less than related voles. Like other rodents, their incisors grow continuously, allowing them to feed on much tougher forage. Lemmings do not hibernate through the harsh northern winter, they remain active.
These rodents live in large tunnel systems beneath the snow in winter, which protect them from predators. Their underground burrows have rest areas, toilet areas, nesting rooms, they make nests out of grasses and muskox wool. In the spring, they move to higher ground, where they live on mountain heaths or in forests, continuously breeding before returning in autumn to the tundra. Like many other rodents, lemmings have periodic population booms and disperse in all directions, seeking the food and shelter their natural habitats cannot provide; the Norway lemming and brown lemming are two of the few vertebrates which reproduce so that their population fluctuations are chaotic, rather than following linear growth to a carrying capacity or regular oscillations. Why lemming populations fluctuate with such great variance every four years, before numbers drop to near extinction, is not known. Lemming behaviour and appearance are markedly different from those of other rodents, which are inconspicuously coloured and try to conceal themselves from their predators.
Lemmings, by contrast, are conspicuously coloured and behave aggressively towards predators and human observers. The lemming defence system is thought to be based on aposematism. Fluctuations in the lemming population affect the behaviour of predators, may fuel irruptions of birds of prey such as snowy owls to areas further south. For many years, the population of lemmings was believed to change with the population cycle, but now some evidence suggests their predators' populations those of the stoat, may be more involved in changing the lemming population. Misconceptions about lemmings go back many centuries. In the 1530s, geographer Zeigler of Strasbourg proposed the theory that the creatures fell out of the sky during stormy weather and died when the grass grew in spring; this description was contradicted by natural historian Ole Worm, who accepted that lemmings could fall out of the sky, but claimed that they had been brought over by the wind rather than created by spontaneous generation.
Worm first published dissections of a lemming, which showed that they are anatomically similar to most other rodents such as voles and hamsters, the work of Carl Linnaeus proved that they had a natural origin. Lemmings have become the subject of a popular misconception that they are driven to commit mass suicide when they migrate by jumping off cliffs, it is not a deliberate mass suicide where the animal voluntarily chooses to die, but rather a result of their migratory behavior. Driven by strong biological urges, some species of lemmings may migrate in large groups when population density becomes too great, they may choose to cross a body of water in search of a new habitat. In such cases, many drown if the chosen body of water happens to be the Atlantic Ocean, or is in any case so wide as to exceed their physical capabilities. This, the unexplained fluctuations in the population of Norwegian lemmings, a small amount of semantic confusion, gave rise to the myth; the misconception of lemming "mass suicide" is long-standing and has been popularized by a number of factors.
It was well enough known to be mentioned in "The Marching Morons", a 1951 short story by Cyril M. Kornbluth. In 1955, Disney Studio illustrator Carl Barks drew an Uncle Scrooge adventure comic with the title "The Lemming with the Locket"; this comic, inspired by a 1953 American Mercury article, showed massive numbers of lemmings jumping over Norwegian cliffs. The most influential and, for the lemmings involved, tragic presentation of the myth was the 1958 Disney film White Wilderness which won an Academy Award for Documentary Feature and in which staged footage was shown of lemmings jumping to certain death after faked scenes of mass migration. A Canadian Broadcasting Corporation documentary, Cruel Camera, found the lemmings used for White Wilderness were flown from Hudson Bay to Calgary, Canada, where far from "casting themselves bodily out into space", they were, in fact, dumped off the cliff by the camera crew from a truck; because of the limited number of lemmings at their disposal, which in any case were the wrong sub-species, the migration scenes were simulated using tight camera angles and a large, snow-covered turntable.
Lemmings appear in Arthur C. Clarke's 1953 short story The Possessed, where their suicidal urges are attributed to the lingering consciousness of an alien group mind, which had inhabited the speci
A civet is a small, lithe-bodied nocturnal mammal native to tropical Asia and Africa the tropical forests. The term civet applies to over a dozen different mammal species. Most of the species diversity is found in southeast Asia; the best-known civet species is the African civet, Civettictis civetta, the main species from, obtained a musky scent used in perfumery. The word civet may refer to the distinctive musky scent produced by the animals. A minority of writers use "civet" to refer only to Civettictis and Viverricula civets, but in more common usage in English, the name covers Chrotogale, Diplogale, Arctogalidia, Macrogalidia and Paradoxurus civets. The common name is used for a variety of carnivorous mammalian species of the family Viverridae; the African palm civet belongs in its own monotypic family, Nandiniidae. Civets are called "toddycats" in English, "Luwak" in Bahasa Indonesian "musang" in Malay and urulǣvā in Sinhala; the latter may lead to some confusion among Malay speakers and non-speakers alike as the indigenous word "musang" has been mistakenly appropriated to foxes by certain printed media over the years instead of "rubah", the correct but lesser known term.
Foxes are not native to Malaysia or Southeast Asia, are never encountered in that geographical region, although they exist in popular culture imported from the West, where the animal's habitat exists. Civets have a broadly cat-like general appearance, though the muzzle is extended and pointed, rather like that of an otter or a mongoose, they range in length in weight from about 1.4 to 4.5 kg. The civet produces a musk valued as a fragrance and stabilizing agent for perfume. Both male and female civets produce the strong-smelling secretion, produced by the civet's perineal glands, it is harvested by either killing the animal and removing the glands, or by scraping the secretions from the glands of a live animal. The latter is the preferred method today. Animal rights groups, such as World Animal Protection, express concern that harvesting musk is cruel to animals. Between these ethical concerns and the availability of synthetic substitutes, the practice of raising civets for musk is dying out. Chanel, maker of the popular perfume Chanel No.
5, claims that natural civet has been replaced with a synthetic substitute since 1998. Viverrids are native to sub-Saharan Africa, the Iberian Peninsula, southern China and Southeast Asia. Favoured habitats include woodland and mountain biome. In consequence, many are faced with severe loss of habitat; some species of civet are rare and elusive and hardly anything is known about them, e.g. the Hose's civet, endemic to the montane forests of northern Borneo, is one of the world's least known carnivores. In Sri Lanka, the Asian palm civet species is known as "uguduwa" by the Sinhala speaking community; the terms uguduwa and kalawedda are used interchangeably by the Sri Lankan community to refer to the same animal. However, the term kalawedda is used to refer to another species in the civet family, the small Indian civet. Sri Lanka has an endemic civet species called golden palm civet; this species was split into 3 separate endemic species as Paradoxurus montanus, P. aureus, P. stenocephalus. In Bangladesh and Bengali-speaking areas of India, civets are known as "khatash" for the smaller species and "bagdash" for the larger ones and is now rare in Bangladesh.
In Assamese this animal is known as "zohamola" which means "to have zoha aromatic feces". Civets are unusual among feliforms, carnivora in general, in that they are omnivores or herbivores. Many species eat fruit; some use flower nectar as a major source of energy. Kopi Luwak is called caphe cut chon, in Vietnam, kape alamid, in the Philippines, it is coffee, prepared using coffee cherries that have been eaten and digested by the Asian palm civet harvested from its fecal matter. The civets digest the flesh of the coffee cherries but pass the pits inside, where stomach enzymes affect the beans, which adds to the coffee's prized aroma and flavor. 0.5 kg can cost up to $600 in about $100 a cup in others. The Malay civet is found in many habitats, including forests, secondary habitats, cultivated land, the outskirts of villages, is adaptable to human disturbances, including "selecting logging". African civets are listed as Least Concern, but in certain regions of Africa the population is declining due to hunting, both direct and indirect poisoning, an increase in large scale farm fences that limit population flow.
They are seen as comparatively abundant options in the bushmeat trade. Palm civets venture into cities and suburbs, with people complaining about civet feces and the noise of the animals' climbing on roofs; some studies have been undertaken to mitigate such human -- animal conflict. Raising Small Indian civet archive.org copy from website www.vietlinh.vn
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m