The Mongolian gerbil or Mongolian jird is a small rodent belonging to the subfamily Gerbillinae. Body size is 110-135mm, with a 95-120mm tail, body weight 60-130g, with adult males larger than females; the animal is kept as a small house pet. Their use in science dates back to the latter half of the 19th century, but they only started to be kept as pets after 1954, when they were brought to the United States. However, their use in scientific research has fallen out of favor. Mongolian gerbils inhabit grassland and desert, including semidesert and steppes in China and the Russian Federation. Soil on the steppes is sandy and is covered with grasses and shrubs; the steppes have dry winters and hot summers. The temperature can get up to 50 °C, but the average temperature for most of the year is around 20 °C. In the wild, these gerbils live in groups consisting of one parental pair, the most recent litter, a few older pups. Only the dominant female will produce pups. One group of gerbils ranges over 325–1,550 square metres.
A group lives in a central burrow with 10–20 exits. Some deeper burrows with only one to three exits in their territory may exist; these deeper burrows are used to escape from predators when they are too far from the central burrow. A group's burrows interconnect with other groups; the first known mention of gerbils came in 1866, by Father Armand David, who sent "yellow rats" to the French National Museum of Natural History in Paris, from northern China. They were named Meriones unguiculatus by the scientist Henri Milne-Edwards in 1867. There's a popular misconception about the meaning of this scientific name, appearing both in printed works and in websites, due to the genus Meriones sharing the name with Greek warrior Meriones in Homer's Iliad; the genus was named by Johann Karl Wilhelm Illiger in 1811, deriving from the Greek word μηρος. Combined with'unguiculate', meaning to have claws or nails in Latin, the name can be loosely translated as'clawed femur'. Gerbils only became popular pets after 1954, when 20 breeding pairs were brought to the United States from eastern Mongolia for scientific testing.
All pet gerbils today are descended from these 40. Gerbils were brought to the United Kingdom in 1964 from the United States. Gerbils have a long history of use in scientific research, although nowadays they are used. For example, in the United Kingdom in 2017, only around 300 Mongolian gerbils were used in experimental procedures, compared to over 2 million mice. Most gerbils used in scientific research are derived from the Tumblebrook Farm strain, which has its origins in 20 pairs of wild-caught Mongolian gerbils sent to Japan in 1935. 11 of these animals were subsequently sent to Tumblebrook Farm in the USA, with additional animals sent to Charles River Ltd in Italy in 1996. Gerbils have a wide hearing range, from detection of low frequency foot drumming to higher frequency chirps and therefore may be a more suitable model of human hearing loss than mice and rats, which are high-frequency specialists. 10-20% of gerbils exhibit spontaneous epileptiform seizures in response to a stressor such as handling or cage cleaning.
Epilepsy in gerbils has a genetic basis, seizure-prone and seizure-resistant lines have been bred. Like other desert rodents such as fat sandrats, Mongolian gerbils are susceptible to diet-induced diabetes, although incidence is low. A diabetes-prone line has been generated, showing that gerbil diabetes has at least some genetic basis. Laboratory gerbils are derived from a small number of founders, so genetic diversity was assumed to be low. Initial genetic studies based on small numbers of genetic markers appeared to support this, but more recent genome-wide Genotyping-by-Sequencing data has shown that genetic diversity is quite high, it has been suggested that laboratory gerbils should be considered domesticated, designated "M. unguiculatus forma domestica" to differentiate them from wild animals. A Mongolian gerbil genome sequence was published in 2018 and a genetic map comprising 22 linkage groups in 2019; the Mongolian gerbil, a gentle and hardy animal, has become a popular small house pet.
It was first brought from China to Paris in the 19th century, became a popular house pet. It was brought to the United States in 1954 by Dr. Victor Schwentker for use in research. Selective breeding for the pet trade has resulted in a wide range of different color and pattern varieties. Mongolian gerbils prefer to live in groups rather than alone, they are social and gentle, do not bite readily. As diggers and tunnel-makers they are better suited to a tank with a deep substrate or bedding rather than a hamster cage, since the absorbent substrate is liable to be kicked up and out of a cage pretty quickly. Mongolian gerbils are chewers and need plenty of cardboard items and chew toys, they do not need fresh food like vegetables and it can give them diarrhea. Water should be provided with a drip-feed system to prevent an accidental build-up of harmful molds in the tank environment. Although gerbils are adapted to the desert, they require water to be supplied at all times to be safe and healthy. Care should be taken not to introduce new smells into the tank, because the tank is considered by the gerbils to be their territory.
Gerbils appreciate a running or exercise wheel. Repe
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
Libya the State of Libya, is a country in the Maghreb region in North Africa, bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad to the south, Niger to the southwest, Algeria to the west, Tunisia to the northwest. The sovereign state is made of three historical regions: Tripolitania and Cyrenaica. With an area of 1.8 million square kilometres, Libya is the fourth largest country in Africa, is the 16th largest country in the world. Libya has the 10th-largest proven oil reserves of any country in the world; the largest city and capital, Tripoli, is located in western Libya and contains over one million of Libya's six million people. The second-largest city is Benghazi, located in eastern Libya. Libya has been inhabited by Berbers since the late Bronze Age; the Phoenicians established trading posts in western Libya, ancient Greek colonists established city-states in eastern Libya. Libya was variously ruled by Carthaginians, Persians and Greeks before becoming a part of the Roman Empire.
Libya was an early centre of Christianity. After the fall of the Western Roman Empire, the area of Libya was occupied by the Vandals until the 7th century, when invasions brought Islam to the region. In the 16th century, the Spanish Empire and the Knights of St John occupied Tripoli, until Ottoman rule began in 1551. Libya was involved in the Barbary Wars of the 19th centuries. Ottoman rule continued until the Italian occupation of Libya resulted in the temporary Italian Libya colony from 1911 to 1947. During the Second World War, Libya was an important area of warfare in the North African Campaign; the Italian population went into decline. Libya became independent as a kingdom in 1951. A military coup in 1969 overthrew King Idris I; the "bloodless" coup leader Muammar Gaddafi ruled the country from 1969 and the Libyan Cultural Revolution in 1973 until he was overthrown and killed in the 2011 Libyan Civil War. Two authorities claimed to govern Libya: the Council of Deputies in Tobruk and the 2014 General National Congress in Tripoli, which considered itself the continuation of the General National Congress, elected in 2012.
After UN-led peace talks between the Tobruk and Tripoli governments, a unified interim UN-backed Government of National Accord was established in 2015, the GNC disbanded to support it. Parts of Libya remain outside either government's control, with various Islamist and tribal militias administering some areas; as of July 2017, talks are still ongoing between the GNA and the Tobruk-based authorities to end the strife and unify the divided establishments of the state, including the Libyan National Army and the Central Bank of Libya. Libya is a member of the United Nations, the Non-Aligned Movement, the Arab League, the OIC and OPEC; the country's official religion is Islam, with 96.6% of the Libyan population being Sunni Muslims. The Latin name Libya referred to the region west of the Nile corresponding to its central location in North Africa visited by many Mediterranean cultures which referred to its original inhabitants as the "Libúē." The name Libya was introduced in 1934 for Italian Libya, reviving the historical name for Northwest Africa, from the ancient Greek Λιβύη.
It was intended to supplant terms applied to Ottoman Tripolitania, the coastal region of what is today Libya having been ruled by the Ottoman Empire from 1551 to 1911, as the Eyalet of Tripolitania. The name "Libya" was brought back into use in 1903 by Italian geographer Federico Minutilli. Libya gained independence in 1951 as the United Libyan Kingdom, changing its name to the Kingdom of Libya in 1963. Following a coup d'état led by Muammar Gaddafi in 1969, the name of the state was changed to the Libyan Arab Republic; the official name was "Socialist People's Libyan Arab Jamahiriya" from 1977 to 1986, "Great Socialist People's Libyan Arab Jamahiriya" from 1986 to 2011. The National Transitional Council, established in 2011, referred to the state as "Libya"; the UN formally recognized the country as "Libya" in September 2011, based on a request from the Permanent Mission of Libya citing the Libyan interim Constitutional Declaration of 3 August 2011. In November 2011, the ISO 3166-1 was altered to reflect the new country name "Libya" in English, "Libye" in French.
In December 2017 the Permanent Mission of Libya to the United Nations informed the United Nations that the country's official name was henceforth the "State of Libya". The coastal plain of Libya was inhabited by Neolithic peoples from as early as 8000 BC; the Afroasiatic ancestors of the Berber people are assumed to have spread into the area by the Late Bronze Age. The earliest known name of such a tribe was the Garamantes, based in Germa; the Phoenicians were the first to establish trading posts in Libya. By the 5th century BC, the greatest of the Phoenician colonies, had extended its hegemony across much of North Africa, where a distinctive civilization, known as Punic, came into being. In 630 BC, the ancient Greeks colonized the area around Barca in Eastern Libya and founded the city of Cyrene. Within 200 years, four more important Greek cities were established in the area that became known as
In botany, a fruit is the seed-bearing structure in flowering plants formed from the ovary after flowering. Fruits are the means. Edible fruits, in particular, have propagated with the movements of humans and animals in a symbiotic relationship as a means for seed dispersal and nutrition. Accordingly, fruits account for a substantial fraction of the world's agricultural output, some have acquired extensive cultural and symbolic meanings. In common language usage, "fruit" means the fleshy seed-associated structures of a plant that are sweet or sour, edible in the raw state, such as apples, grapes, lemons and strawberries. On the other hand, in botanical usage, "fruit" includes many structures that are not called "fruits", such as bean pods, corn kernels and wheat grains; the section of a fungus that produces spores is called a fruiting body. Many common terms for seeds and fruit do not correspond to the botanical classifications. In culinary terminology, a fruit is any sweet-tasting plant part a botanical fruit.
However, in botany, a fruit is the ripened ovary or carpel that contains seeds, a nut is a type of fruit and not a seed, a seed is a ripened ovule. Examples of culinary "vegetables" and nuts that are botanically fruit include corn, eggplant, sweet pepper, tomato. In addition, some spices, such as allspice and chili pepper, are fruits. In contrast, rhubarb is referred to as a fruit, because it is used to make sweet desserts such as pies, though only the petiole of the rhubarb plant is edible, edible gymnosperm seeds are given fruit names, e.g. ginkgo nuts and pine nuts. Botanically, a cereal grain, such as corn, rice, or wheat, is a kind of fruit, termed a caryopsis. However, the fruit wall is thin and is fused to the seed coat, so all of the edible grain is a seed; the outer edible layer, is the pericarp, formed from the ovary and surrounding the seeds, although in some species other tissues contribute to or form the edible portion. The pericarp may be described in three layers from outer to inner, the epicarp and endocarp.
Fruit that bears a prominent pointed terminal projection is said to be beaked. A fruit results from maturation of one or more flowers, the gynoecium of the flower forms all or part of the fruit. Inside the ovary/ovaries are one or more ovules where the megagametophyte contains the egg cell. After double fertilization, these ovules will become seeds; the ovules are fertilized in a process that starts with pollination, which involves the movement of pollen from the stamens to the stigma of flowers. After pollination, a tube grows from the pollen through the stigma into the ovary to the ovule and two sperm are transferred from the pollen to the megagametophyte. Within the megagametophyte one of the two sperm unites with the egg, forming a zygote, the second sperm enters the central cell forming the endosperm mother cell, which completes the double fertilization process; the zygote will give rise to the embryo of the seed, the endosperm mother cell will give rise to endosperm, a nutritive tissue used by the embryo.
As the ovules develop into seeds, the ovary begins to ripen and the ovary wall, the pericarp, may become fleshy, or form a hard outer covering. In some multiseeded fruits, the extent to which the flesh develops is proportional to the number of fertilized ovules; the pericarp is differentiated into two or three distinct layers called the exocarp and endocarp. In some fruits simple fruits derived from an inferior ovary, other parts of the flower, fuse with the ovary and ripen with it. In other cases, the sepals, petals and/or stamens and style of the flower fall off; when such other floral parts are a significant part of the fruit, it is called an accessory fruit. Since other parts of the flower may contribute to the structure of the fruit, it is important to study flower structure to understand how a particular fruit forms. There are three general modes of fruit development: Apocarpous fruits develop from a single flower having one or more separate carpels, they are the simplest fruits. Syncarpous fruits develop from a single gynoecium having two or more carpels fused together.
Multiple fruits form from many different flowers. Plant scientists have grouped fruits into three main groups, simple fruits, aggregate fruits, composite or multiple fruits; the groupings are not evolutionarily relevant, since many diverse plant taxa may be in the same group, but reflect how the flower organs are arranged and how the fruits develop. Simple fruits can be either dry or fleshy, result from the ripening of a simple or compound ovary in a flower with only one pistil. Dry fruits may be either dehiscent, or indehiscent. Types of dry, simple fruits, examples of each, include: achene – most seen in aggregate fruits capsule – caryopsis – cypsela – an achene-like fruit derived from the individual florets in a capitulum. Fibrous drupe – follicle – is formed from a single carpel, opens by one suture
Fiber or fibre is a natural or synthetic substance, longer than it is wide. Fibers are used in the manufacture of other materials; the strongest engineering materials incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene. Synthetic fibers can be produced cheaply and in large amounts compared to natural fibers, but for clothing natural fibers can give some benefits, such as comfort, over their synthetic counterparts. Natural fibers develop or occur in the fiber shape, include those produced by plants and geological processes, they can be classified according to their origin: Vegetable fibers are based on arrangements of cellulose with lignin: examples include cotton, jute, ramie, sisal and banana. Plant fibers are employed in the manufacture of paper and textile, dietary fiber is an important component of human nutrition. Wood fiber, distinguished from vegetable fiber, is from tree sources. Forms include groundwood, thermomechanical pulp, bleached or unbleached kraft or sulfite pulps.
Kraft and sulfite refer to the type of pulping process used to remove the lignin bonding the original wood structure, thus freeing the fibers for use in paper and engineered wood products such as fiberboard. Animal fibers consist of particular proteins. Instances are silkworm silk, spider silk, catgut, sea silk and hair such as cashmere wool and angora, fur such as sheepskin, mink, beaver, etc. Mineral fibers include the asbestos group. Asbestos is the only occurring long mineral fiber. Six minerals have been classified as "asbestos" including chrysotile of the serpentine class and those belonging to the amphibole class: amosite, tremolite and actinolite. Short, fiber-like minerals include palygorskite. Biological fibers known as fibrous proteins or protein filaments consist of biologically relevant and biologically important proteins, mutations or other genetic defects can lead to severe diseases. Instances are collagen family of proteins, muscle proteins like actin, cell proteins like microtubules and many others, spider silk and hair etc.
Human-made or chemical fibers are fibers whose chemical composition and properties are modified during the manufacturing process. Man-made fibers consist of synthetic fibers. Semi-synthetic fibers are made from raw materials with long-chain polymer structure and are only modified and degraded by chemical processes, in contrast to synthetic fibers such as nylon or dacron, which the chemist synthesizes from low-molecular weight compounds by polymerization reactions; the earliest semi-synthetic fiber is rayon. Most semi-synthetic fibers are cellulose regenerated fibers. Cellulose fibers are a subset of man-made fibers, regenerated from natural cellulose; the cellulose comes from various sources: rayon from tree wood fiber, Modal from beech trees, bamboo fiber from bamboo, seacell from seaweed, etc. In the production of these fibers, the cellulose is reduced to a pure form as a viscous mass and formed into fibers by extrusion through spinnerets. Therefore, the manufacturing process leaves few characteristics distinctive of the natural source material in the finished products.
Some examples of this fiber type are: rayon bamboo fiber Lyocell, a brand of rayon Modal, using beech trees as input diacetate fiber triacetate fiber. Cellulose diacetate and -triacetate were classified under the term rayon, but are now considered distinct materials. Synthetic come from synthetic materials such as petrochemicals, unlike those man-made fibers derived from such natural substances as cellulose or protein. Fiber classification in reinforced plastics falls into two classes: short fibers known as discontinuous fibers, with a general aspect ratio between 20 and 60, long fibers known as continuous fibers, the general aspect ratio is between 200 and 500. Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones, such as nickel, aluminum or iron. See Stainless steel fibers. Carbon fibers are based on oxidized and via pyrolysis carbonized polymers like PAN, but the end product is pure carbon. Silicon carbide fibers, where the basic polymers are not hydrocarbons but polymers, where about 50% of the carbon atoms are replaced by silicon atoms, so-called poly-carbo-silanes.
The pyrolysis yields an amorphous silicon carbide, including other elements like oxygen, titanium, or aluminium, but with mechanical properties similar to those of carbon fibers. Fiberglass, made from specific glass, optical fiber, made from purified natural quartz, are man-made fibers that come from natural raw materials, silica fiber, made from sodium silicate and basalt fiber made from melted basalt. Mineral fibers can be strong because they are formed with a low number of surface defects, asbestos is a common one. Polymer fibers are a subset of man-made fibers, which are based on synthetic chemicals rather than arising from natural materials by a purely physical process; these fibers are made from: polyamide nylon PET or PBT polyester phenol-formaldehyde polyvinyl chloride fiber vinyon polyolefins olefin fiber acrylic polyesters, pure polyester PAN fibers are used to make carbon fiber by roasting them in a low oxygen enviro
Zoology is the branch of biology that studies the animal kingdom, including the structure, evolution, classification and distribution of all animals, both living and extinct, how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōion, i.e. "animal" and λόγος, logos, i.e. "knowledge, study". The history of zoology traces the study of the animal kingdom from ancient to modern times. Although the concept of zoology as a single coherent field arose much the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world; this ancient work was further developed in the Middle Ages by Muslim physicians and scholars such as Albertus Magnus. During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Vesalius and William Harvey, who used experimentation and careful observation in physiology, naturalists such as Carl Linnaeus, Jean-Baptiste Lamarck, Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms.
Microscopy revealed the unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology a response to the rise of mechanical philosophy, encouraged the growth of natural history. Over the 18th, 19th, 20th centuries, zoology became an professional scientific discipline. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, the ways this relationship depends on geography, laying the foundations for biogeography and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life; these developments, as well as the results from embryology and paleontology, were synthesized in Charles Darwin's theory of evolution by natural selection. In 1859, Darwin placed the theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, provided observational evidence that it had done so.
Darwin gave a new direction to morphology and physiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, early attempts to determine their genetic relationships; the end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics, by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology. Cell biology studies the structural and physiological properties of cells, including their behavior and environment; this is done on both the microscopic and molecular levels, for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans.
Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are relevant to molecular biology. Anatomy considers the forms of macroscopic structures such as organs and organ systems, it focuses on how organs and organ systems work together in the bodies of humans and animals, in addition to how they work independently. Anatomy and cell biology are two studies that are related, can be categorized under "structural" studies. Physiology studies the mechanical and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole; the theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can apply to human cells.
The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how for example nervous, endocrine and circulatory systems and interact. Evolutionary research is concerned with the origin and descent of species, as well as their change over time, includes scientists from many taxonomically oriented disciplines. For example, it involves scientists who have special training in particular organisms such as mammalogy, herpetology, or entomology, but use those organisms as systems to answer general questions about evolution. Evolutionary biology is based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution, on the developments in areas such as population genetics and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology.
Related fields considered part of evolutionary biology are phylogenetics and taxonomy. Scientific classification in zoology, is a method by which
A pet or companion animal is an animal kept for a person's company, entertainment, or as an act of compassion such as taking in and protecting a hungry stray cat, rather than as a working animal, livestock, or laboratory animal. Popular pets are noted for their attractive appearances and relatable personalities, or may just be accepted as they are because they need a home. Two of the most popular pets are cats; the technical term for a cat lover is an ailurophile, for a dog lover, a cynophile. Other animals kept include rabbits. Small pets may be grouped together as pocket pets, while the equine and bovine group include the largest companion animals. Pets provide their owners both emotional benefits. Walking a dog can provide both the human and the dog with exercise, fresh air, social interaction. Pets can give companionship to people who are living alone or elderly adults who do not have adequate social interaction with other people. There is a medically approved class of therapy animals dogs or cats, that are brought to visit confined humans, such as children in hospitals or elders in nursing homes.
Pet therapy utilizes trained animals and handlers to achieve specific physical, cognitive or emotional goals with patients. Some scholars and animal rights organizations have raised concerns over keeping pets because of the lack of autonomy and objectification of nonhuman animals. There are 86.4 million pet cats and 78.2 million pet dogs in the United States, a United States 2007–2008 survey showed that dog-owning households outnumbered those owning cats, but that the total number of pet cats was higher than that of dogs. The same was true for 2011. In 2013, pets outnumbered children four to one in the United States. For a small to medium-size dog, the total cost over a dog's lifetime is about $7,240 to $12,700. For an indoor cat, the total cost over a cat's lifetime is about $8,620 to $11,275. People most get pets for companionship, to protect a home or property, or because of the beauty or attractiveness of the animals; the most common reasons for not owning a pet are lack of time, lack of suitable housing, lack of ability to care for the pet when traveling.
According to the 2007-2008 Pet Owners survey: The latest survey done by Colin Siren of Ipsos Reid estimates that there are 7.9 million cats and 5.9 million dogs in Canada. The survey shows that 35% of Canadian households have a dog, while 38% have a cat, consistent with other surveys conducted around the world. In China, spending on domestic animals has grown from and estimated $3.12 billion in 2010 to $25 billion in 2018. The Chinese people own 51 million dogs and 41 million cats, with pet owners preferring to source pet food internationally. A 2007 survey by the University of Bristol found that 26% of UK households owned cats and 31% owned dogs, estimating total domestic populations of 10.3 million cats and 10.5 million dogs in 2006. The survey found that 47.2% of households with a cat had at least one person educated to degree level, compared with 38.4% of homes with dogs. According to a survey promoted by Italian family associations in 2009, it is estimated that there are 45 million pets in Italy.
This includes 7 million dogs, 7.5 million cats, 16 million fish, 12 million birds, 10 million snakes. Keeping animals as pets may be detrimental to their health if certain requirements are not met. An important issue is inappropriate feeding; the consumption of chocolate or grapes by dogs, for example, may prove fatal. Certain species of houseplants can prove toxic if consumed by pets. Examples include philodendrons and Easter lilies and poinsettias and aloe vera. Housepets dogs and cats in industrialized societies, are highly susceptible to obesity. Overweight pets have been shown to be at a higher risk of developing diabetes, liver problems, joint pain, kidney failure, cancer. Lack of exercise and high-caloric diets are considered to be the primary contributors to pet obesity, it is believed among the public, among many scientists, that pets bring mental and physical health benefits to their owners. A recent dissent comes from a 2017 RAND study, which found that at least in the case of children, having a pet per se failed to improve physical or mental health by a statistically significant amount.
Conducting long-term randomized trials to settle the issue would be costly or infeasible. Pets might have the ability to stimulate their caregivers, in particular the elderly, giving people someone to take care of, someone to exercise with, someone to help them heal from a physically or psychologically troubled past. Animal company can help people to preserve acceptable levels of happiness despite the presence of mood symptoms like anxiety or depression. Having a pet may help people achieve health goals, such as lowered blood pressure, or mental goals, such as decreased stress. Ther