ratio of word probabilities predicted from brain for dog and horse

dog	horse
top 10 words in brain distribution (in article): animal horse wear species breed cat wolf hunt male human	top 10 words in brain distribution (in article): species animal horse wear male female time breed human food
top 10 words in brain distribution (not in article): woman century lion elephant cattle saddle deer forest cell dress	top 10 words in brain distribution (not in article): bird egg cat woman fish clothe card kill dress store
times more probable under dog 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under horse (words not in the model)
The dog'" ("Canis lupus familiaris",) is a domesticated subspecies of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history. The domestication of the gray wolf took place in a handful of events roughly 15,000 years ago in central Asia. The dog quickly became ubiquitous across culture in all parts of the world, and was extremely valuable to early human settlements. For instance, it is believed that the successful emigration across the Bering Strait might not have been possible without sled dogs. As a result of the domestication process, the dog developed a sophisticated intelligence that includes unparalleled social cognition and a simple theory of mind that is important to their interaction with humans. These social skills have helped the dog to perform in myriad roles, such as hunting, herding, protection, and, more recently, assisting handicapped individuals. Currently, there are estimated to be 400 million dogs in the world. Over the 15,000 year span that the dog had been domesticated, it diverged into only a handful of landraces, groups of similar animals whose morphology and behavior have been shaped by environmental factors and functional roles. Humans did not take an active, intentional role in this process until the last few hundred years. As the modern understanding of genetics developed, humans began to intentionally breed dogs for a wide range of specific traits. Through this process, the dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal. For example, height measured to the withers ranges from a few inches in the Chihuahua to a few feet in the Irish Wolfhound; color varies from white through grays (usually called "blue'") to black, and browns from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. It is common for most breeds to shed this coat, but non-shedding breeds are also popular. Etymology and related terminology. "Dog" is the common use term that refers to members of the subspecies "Canis lupus familiaris". The term is sometimes used to refer to a wider range of species: it can be used to refer to any mammal belonging to the family Canidae, which includes wolves, foxes, jackals, and coyotes; it can be used to refer to the subfamily of Caninae, or the genus Canis, also often called the "true dogs". Some members of the family have "dog" in their common names, such as the raccoon dog and the African wild dog. A few animals have "dog" in their common names but are not canids, such as the prairie dog and the dog fish. The English word "dog" can be traced back to the Old English "docga", a "powerful breed of canine". The term may derive from Proto-Germanic "*dukkōn", represented in Old English "finger-docce" ("finger-muscle"). Due to the linguistically archaic structure of the word, the term "dog" may ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliest domesticated animal. The English word "hound", which refers to a specific breed group in English, means "dog" in general in other Germanic languages; it is cognate to German "hund", Dutch "hond", common Scandinavian "hund", and Icelandic "hundur". "Hound" itself is derived from the Proto-Indo-European "*kwon-", which is also the direct root of the Greek κυων (kuōn) and the indirect root of the Latin "canis" through the variant form "*kani-". In breeding circles, a male canine is referred to as a "dog", while a female is called a "bitch". A group of offspring is a "litter". The father of a litter is called the "sire", and the mother is called the "dam". Offspring are generally called "pups" or "puppies" until they are about a year old. The process of birth is "whelping". Taxonomy and evolution. The domestic dog was originally classified as "Canis familiaris" and "Canis familiarus domesticus" by Linnaeus in 1758, and is currently classified as "Canis lupus familiaris", a subspecies of the gray wolf "Canis lupus", by the Smithsonian Institution and the American Society of Mammalogists. Overwhelming evidence from behavior, vocalizations, morphology, and molecular biology led to the contemporary scientific understanding that a single species, the gray wolf, is the common ancestor for all breeds of domestic dogs, however the timeframe and mechanisms by which dogs diverged are controversial. The current consensus among biologists and archaeologists is that no one can be sure when dogs were domesticated. There is conclusive evidence that dogs genetically diverged from their wolf ancestors at least 15,000 years ago but most believe domestication to have occurred much earlier. The evidence cited for an earlier divergence comes from archaeological findings and mitochondrial DNA studies, both of which are inconclusive. The archaeological evidence demonstrates that the domestication of dogs occurred prior to 15,000 years ago. Some genetic evidence indicates that the domestication of dogs from their wolf ancestors began in the late Upper Paleolithic close to the Pleistocene Holocene boundary, between 17,000 and 14,000 years ago. The earliest dog fossils, two large skulls from Russia and a mandible from Germany, date from roughly 14,000 years ago. Their likely ancestor is the large Eurasian wolf ("Canis lupus lupus"). Remains of smaller dogs from Natufian cave deposits in the Middle East have been dated to around 10,000 to 12,000 years ago. There is a great deal of archealogical evidence for dogs throughout Europe and Asia around this period and through the next two thousand years (roughly 8,000 to 10,000 years ago), with fossils uncovered in Germany, the French Alps, and Iraq, and cave paintings in Turkey. DNA studies have provided a wider range of possible divergence dates, from 15,000 to 40,000 years ago, to as much as 100,000 to 140,000 years ago. This evidence depends on a number of assumptions that others claim are violated. Genetic studies are based in comparisons of genetic diversity between species, and depend on a calibration date, such as the wolf-coyote divergence date, which is estimated to be roughly 1 million years ago. If this divergence date is closer to 750,000 or 2 million years ago, then genetic analyses would be interpreted very differently. Furthermore, it is believed that the genetic diversity of wolves has been in decline for the last 200 years, and that the genetic diversity of dogs has been reduced by selective breeding, which could bias DNA analyses to support an earlier divergence. The genetic evidence for the domestication event occurring in East Asia is also subject to violations of assumptions. These conclusions are based on the location of maximal genetic divergence, assumes that hybridization does not occur, and that breeds remain geographically localized. Although these assumptions hold for many species, there is good reason to believe that they do not hold for canines. Genetic analyses indicate all dogs are likely descended from a handful of domestication events with a small number of founding females, although there is evidence that domesticated dogs interbred with local populations of wild wolves on several occasions. Data suggests that dogs first diverged from wolves in East Asia, and that these domesticated dogs then quickly migrated throughout the world, reaching the North American continent around 8000 B.C. The oldest groups of dogs, which show the greatest genetic variability and are the most similar to their wolf ancestors, are primarily Asian and African breeds, including the Basenji, Saluki, Afghan Hound, Tibetan Terrier, Lhasa Apso, Chow Chow, Pekingese, Shar-Pei, Shi Tzu, Akita, Shiba Inu, Alaskan Malamute, Siberian Husky, and Samoyed. Some breeds that were thought to be very old, such as the Pharaoh Hound, Ibizan Hound, and Norwegian Elkhound, are now known to have been recreated more recently. There is a great deal of controversy surrounding the evolutionary framework for the domestication of dogs. At least three early species of the "Homo" genus began spreading out of Africa roughly 400,000 years ago, and thus lived for a considerable period in contact with canine species. Despite this, there is no evidence of any adaptation of these canine species to the presence of the close relatives of modern man. If dogs were domesticated, as believed, roughly 15,000 years ago, the event (or events) would have coincided with a large expansion in human territory and the development of agriculture. This has led some biologists to suggest that one of the forces that led to the domestication of dogs was a shift in human lifestyle in the form of established human settlements. Permanent settlements would have coincided with a greater amount of disposable food and would have created a barrier between wild and anthropogenic canine populations. Biology. Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes. Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Nevertheless, their morphology is based on that of their wild ancestors, gray wolves. Dogs are predators and scavengers, and like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Dogs are highly variable in height and weight. The smallest known dog was a Yorkshire Terrier, who stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.75 in) in length along the head-and-body, and weighed only 113 grams (4 ounces). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lbs) and was 250 cm (8.2 feet) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.2 in) at the shoulder. Sight. The dog's visual system is engineered to serve the purposes of a hunter. While a dog's visual acuity is poor (that of a poodle's has been estimated to translate to a Snellen rating of 20 75), their visual discrimination for moving objects is very high; dogs have been shown to be able to discriminate between humans (i.e., identifying their owner) from distances up to a mile. As crepuscular hunters, dogs often rely on their vision in low light situations: they have very large pupils, a high density of rods in the fovea, an increased flicker rate, and a tapetum lucidum. The tapetum is a reflective surface behind the retina that reflects light back to give the photoreceptors a second chance to catch the photons. Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans. The eyes of different breeds of dogs have different shapes, dimensions, and retina configurations. Many long-nosed breeds have a "visual streak" — a wide foveal region that runs across the width of the retina and gives them a very wide field of excellent vision. Some long-muzzled breeds, particularly the sighthounds, have a field of vision up to 270° (compared to 180° for humans). Short-nosed breeds, on the other hand, have an "area centralis": a central patch with up to three times the density of nerve endings as the visual streak, giving them detailed sight much more like a human's. Some broad-headed breeds with short noses have a field of vision similar to that of humans. Most breeds have good vision, but some show a genetic predisposition for myopia — such as Rottweilers, where one out of every two has been found to be myopic. Hearing. The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz, which means that dogs can detect sounds outside both ends of the human auditory spectrum. Additionally, dogs have ear mobility which allows them to rapidly pinpoint the exact location of a sound. Eighteen or more muscles can tilt, rotate, raise, or lower a dog's ear. A dog can identify a sound's location much faster than a human can, as well as hear sounds at four times the distance. Smell. While the human brain is dominated by a large visual cortex, the dog brain is largely dominated by an olfactory cortex. The olfactory bulb in dogs is roughly forty times bigger than the olfactory bulb in humans, relative to total brain size, with 125 to 220 million smell-sensitive receptors. The bloodhound exceeds this standard with nearly 300 million receptors. Dogs can discriminate odors at concentrations nearly 100 million times lower than humans can. Coat. The coats of domestic dogs are either "double", made up of a coarse topcoat and a soft undercoat, like a wolf, or "single", with the topcoat only. Dogs with double coats tend to originate in colder climates. Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. The general theory of countershading is that an animal that is lit from above will appear lighter on its upper half and darker on its lower half, where it will usually be in its own shade. This is a pattern that predators can learn to watch for. A countershaded animal will have dark coloring on its upper surfaces and light coloring below, which reduces its general visibility. Thus many breeds will have an occasional "blaze", stripe, or "star" of white fur on their chest or underside. Tail. There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. In some breeds, the tail is traditionally docked to avoid injuries (especially for hunting dogs). In some breeds, puppies can be born with a short tail or no tail at all. This occurs more frequently in those breeds that are frequently docked and thus have no breed standard regarding the tail. Types and breeds. While all dogs are genetically very similar, natural selection and selective breeding have reinforced certain characteristics in certain populations of dogs, giving rise to dog types and dog breeds. Dog types are broad categories based on function, genetics, or characteristics. Dog breeds are groups of animals that possess a set of inherited characteristics that distinguishes them from other animals within the same species. Modern dog breeds are non-scientific classifications of dogs kept by modern kennel clubs. Purebred dogs of one breed are genetically distinguishable from purebred dogs of other breeds, but the means by which kennel clubs classify dogs is unsystematic. Systematic analyses of the dog genome has revealed only four major types of dogs that can be said to be statistically distinct. These include the "old world dogs" (e.g., Malamute and Shar-Pei), "Mastiff"-type (e.g., Labrador Retriever), "herding"-type (e.g., St. Bernard), and "all others" (also called "modern"- or "hunting"-type). Health. Dogs are susceptible to various diseases, ailments, and poisons, some of which can affect humans. To defend against many common diseases, dogs are often vaccinated. Some breeds of dogs are prone to certain genetic ailments such as elbow or hip dysplasia, blindness, deafness, pulmonic stenosis, cleft palate, and trick knees. Two serious medical conditions particularly affecting dogs are pyometra, affecting unspayed females of all types and ages, and bloat, which affects the larger breeds or deep-chested dogs. Both of these are acute conditions, and can kill rapidly. Dogs are also susceptible to parasites such as fleas, ticks, and mites, as well as hookworms, tapeworms, roundworms, and heartworms. Dogs are also vulnerable to some of the same health conditions as humans, including diabetes, dental and heart disease, epilepsy, cancer, hypothyroidism, and arthritis. Mortality. The typical lifespan of dogs varies widely among breeds, but for most the median longevity, the age at which half the dogs in a population have died and half are still alive, ranges from 10 to 13 years. Individual dogs may live well beyond the median of their breed. The breed with the shortest lifespan (among breeds for which there is a questionnaire survey with a reasonable sample size) is the Dogue de Bordeaux, with a median longevity of about 5.2 years, but several breeds, including Miniature Bull Terriers, Bulldogs, Nova Scotia Duck-Tolling Retrievers, Bloodhounds, Irish Wolfhounds, Greater Swiss Mountain Dogs, Great Danes, and Mastiffs, are nearly as short-lived, with median longevities of 6 to 7 years. The longest-lived breeds, including Toy Poodles, Border Terriers, Miniature Dachshunds, Miniature Poodles, and Tibetan Spaniels, have median longevities of 14 to 15 years. The median longevity of mixed breed dogs, taken as an average of all sizes, is one or more years longer than that of purebred dogs when all breeds are averaged. The dog widely reported to be the longest-lived is "Bluey," who died in 1939 and was claimed to be 29.5 years old at the time of his death; however, the Bluey record is anecdotal and unverified. The longest verified records are of dogs living for 24 years. Predation. Although wild dogs, like wolves, are apex predators, they can be killed in territory disputes with wild animals. Furthermore, in areas where both dogs and other large predators live, dogs can be a major food source for big cats or canines. Reports from Croatia indicate that dogs are killed more frequently than sheep. Wolves in Russia apparently limit feral dog populations. In Wisconsin, more compensation has been paid for dog losses than livestock. Some wolf pairs have been reported to prey on dogs by having one wolf lure the dog out into heavy brush where the second animal waits in ambush. In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs, to the extent that they have to be beaten off or killed. Coyotes and big cats have also been known to attack dogs. Leopards in particular are known to have a predilection for dogs, and have been recorded to kill and consume them regardless of the dog's size or ferocity. Tigers in Manchuria, Indochina, Indonesia, and Malaysia, are reputed to kill dogs with the same vigor as leopards. Striped Hyenas are major predators of village dogs in Turkmenistan, India, and the Caucasus. Diet. Despite its descent from wolves, the domestic dog is an omnivore, though it is classified in the order Carnivora. Unlike an obligate carnivore, such as a member of the cat family with its shorter small intestine, a dog is neither dependent on meat-specific protein nor a very high level of protein in order to fulfill its basic dietary requirements. Dogs are able to healthily digest a variety of foods, including vegetables and grains, and can consume a large proportion of these in their diet. In the wild, canines often eat available plants and fruits. Reproduction. In domestic dogs, sexual maturity begins to happen around age six to twelve months for both males and females, although this can be delayed until up to two years old for some large breeds. This is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles biannually, during which the body prepares for pregnancy. At the peak of the cycle, females will come into estrus, being mentally and physically receptive to copulation. Because the ova survive and are capable of being fertilized for a week after ovulation, it is possible for a female to mate with more than one male. Adolescence for most domestic dogs is around 12 to 15 months, beyond which they are for the most part more adult than puppy. Domestication has selectively bred for higher libido and earlier and more frequent breeding cycles in dogs than in their wild ancestors, and dogs remain reproductively active until old age. Dogs bear their litters roughly 56 to 72 days after fertilization, with an average of 63 days, although the length of gestation can vary. An average litter consists of about six puppies, though this number may vary widely based on the breed of dog. Toy dogs generally produce from one to four puppies in each litter, while much larger breeds may average as many as twelve. Some dog breeds have acquired traits through selective breeding that interfere with reproduction. Male French Bulldogs, for instance, are incapable of mounting the female. For many dogs of this breed, the female must be artificially inseminated in order to reproduce. Spaying and neutering. Neutering refers to the sterilization of animals, usually by removal of the male's testicles or the female's ovaries and uterus, in order to eliminate the ability to procreate and reduce sex drive. Because of the overpopulation of dogs in some countries, animal control agencies, such as the American Society for the Prevention of Cruelty to Animals (ASPCA), advise that dogs not intended for further breeding should be neutered, so that they do not have undesired puppies that may have to be destroyed later. According to the Humane Society of the United States, 3–4 million dogs and cats are put down each year in the United States and many more are confined to cages in shelters because there are many more animals than there are homes. Spaying or castrating dogs helps keep overpopulation down. Local humane societies, SPCAs, and other animal protection organizations urge people to neuter their pets and to adopt animals from shelters instead of purchasing them. Several notable public figures have spoken out against animal overpopulation, including Bob Barker. On his game show, "The Price Is Right", Barker stressed the problem at the end of every episode, saying: "Help control the pet population. Have your pets spayed or neutered." The current host, Drew Carey, makes a similar plea at the conclusion of each episode. Neutering reduces problems caused by hypersexuality, especially in male dogs. Spayed female dogs are less likely to develop some forms of cancer, affecting mammary glands, ovaries, and other reproductive organs. However, neutering increases the risk of urinary incontinence in female dogs, and prostate cancer in males, as well as osteosarcoma, hemangiosarcoma, cruciate ligament rupture, obesity, and diabetes mellitus in either gender. The hormonal changes involved with sterilization can change the animal's personality and metabolism. Recent studies proved that spayed and neutered dogs in general are more aggressive towards people and other dogs, and more fearful and sensitive to touch than dogs than had not been sterilized. Spaying or neutering very young animals ("early-age spay"), can result in increased health concerns later on in life for both sexes. Incontinence in female dogs is made worse by spaying too early. In both males and females, alteration causes changes in hormones during development. This inhibits the natural signals needed for proper body development, leading to larger animals with greater risk for hip dysplasia, osteoporosis, and other joint disorders. Other studies have shown, however, that early-age neutering of male dogs is associated with no major risks compared to neutering at the more traditional age of six months. Behavior and intelligence. Although dogs have been the subject of a great deal of Behaviorist psychology (e.g.,Pavlov's Dog), they do not enter the world with a psychological "blank slate". Rather, dog behavior is affected by genetic factors as well as environmental factors. Domestic dogs exhibit a number of behaviors and predispositions that were inherited from wolves. The grey wolf is a social animal that has evolved a sophisticated means of communication and social structure. The domestic dog has inherited some of these predispositions, but many of the salient characteristics in dog behavior have been largely shaped by selective breeding by humans. Thus, some of these characteristics, such as the dog's highly developed social cognition, are found only in primitive forms in grey wolves. Intelligence. "Intelligence" is an umbrella term that encompasses the faculties involved in a wide range of mental tasks, such as learning, problem-solving, and communication. The domestic dog has a predisposition to exhibit a social intelligence that is uncommon in the animal world. Dogs are capable of learning in a number of ways, such as through simple reinforcement learning (e.g.,classical or operant conditioning) and by observation. Dogs go through a series of stages of cognitive development. They are not born with an understanding of object permanence; the understanding that objects which are not being actively perceived still remain in existence. The understanding of object permanence occurs during as the infant is learning the coordination of secondary circular reactions, as described by Jean Piaget. That is, as the infants learn to interact intentionally with objects around it. For dogs, this occurs at roughly 8 weeks of age. Handlers of working dogs such as herding dogs and sled dogs know that pups learn behaviors quickly by following examples set by experienced dogs. Many of these behaviors are allelomimetic in that they depend on a genetic predisposition to learn and imitate behaviors of other dogs. This form of intelligence is not peculiar to those tasks dogs have been bred to perform, but can be generalized to myriad abstract problems. Adler & Alder demonstrated this by giving Dachshund puppies the task of learning to pull a cart by tugging on an attached piece of ribbon in order to get a reward in the cart. Puppies that watched an experienced dog successfully retrieve the reward in this way learned the task fifteen times faster than those who were left to solve the problem on their own. In addition to learning by example from other dogs, dogs have also been shown to learn by mimicking human behaviors. In another study, puppies were presented with a box, and shown that when a handler pressed a lever, a ball would roll out of the box. The handler then allowed the puppy to play with the ball, making it an intrinsic reward. The pups were then allowed to interact with the box. Roughly three-quarters of the puppies subsequently touched the lever, and over half successfully released the ball, compared to only 6 percent in a control group that did not watch the human manipulate the lever. Furthermore, the ability for dogs to learn by example has been shown to be as effective as operant conditioning. McKinley and Young have demonstrated that dogs show equivalent accuracy and learning times when taught to identify an object by operant conditioning as they do when taught by human example. Their study found that handing an object between experimenters who then use its name in a sentence successfully taught an observing dog each object's name, allowing the dog to subsequently retrieve the item. Dogs also demonstrate sophisticated social cognition by associating behavioral cues with abstract meanings. One such class of social cognition involves the understanding that others are conscious agents. This is called a theory of mind, and is an area in which dogs excel. Research has shown that dogs are capable of interpreting subtle social cues, and appear to recognize when a human or dog's attention is focused on them. To test this, researchers devised a task in which a reward was hidden underneath one of two buckets. The experimenter then attempted to communicate with the dog to indicate the location of the reward by using a wide range of signals: tapping the bucket, pointing to the bucket, nodding to the bucket, or simply looking at the bucket. The results showed that domestic dogs were better than chimpanzees, wolves, and human infants at this task, and even young puppies with limited exposure to humans performed well. Dr. Stanley Coren, an expert on dog psychology, states that these results demonstrated the social cognition of dogs can exceed that of even our closest genetic relatives, and that this capacity is a recent genetic acquisition which distinguishes the dog from its ancestor, the wolf. Studies have also investigated whether dogs engaged in partnered play change their behavior depending on the attention-state of their partner. Those studies showed that play signals were only sent when the dog was holding the attention of its partner. If the partner was distracted, the dog instead engaged in attention-getting behavior before sending a play signal. Dr. Coren has also argued that dogs demonstrate a sophisticated theory of mind by engaging in deception, which he supports with a number of anecdotes, including one example where a dog hid a stolen treat by sitting on it until the rightful owner of the treat left the room. Although this could have been accidental, Coren suggests that the thief understood that the treat's owner would be unable to find the treat if it were out of view. Together, the empirical data and anecdotal evidence points to dogs possessing at least a limited form of theory of mind. Interactions with humans. Domestic dogs inherited a complex social hierarchy and behaviors from their ancestor, the wolf. Dogs are pack animals with a complex set of behaviors related to determining each dog's position in the social hierarchy, and they exhibit various postures and other means of nonverbal communication that reveal their states of mind. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations, and these attributes have earned dogs a unique relationship with humans despite being potentially dangerous apex predators. Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies. Shortly after domestication, dogs became ubiquitous in human populations, and spread throughout the world. Emigrants from Siberia likely crossed the Bering Strait with dogs in their company, and some experts suggest that use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago. Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs also carried much of the load in the migration of the Apache and Navajo tribes 1,400 years ago. Use of dogs as pack animals in these cultures often persisted after the introduction of the horse to North America. Work. Dogs have lived and worked with humans in so many roles that they have earned the unique nickname, "man's best friend", a phrase which is used in other languages as well. They have been bred for herding livestock, hunting (e.g.,pointers, hounds), keeping living spaces clear of rats, guarding, helping fishermen with nets, and pulling loads, in addition to their roles as companions. More recently, dogs have taken on a number of roles under the general classification of service dogs, which provide assistance to individuals with physical or mental disabilities. Service dogs include guide dogs, utility dogs, assistance dogs, hearing dogs, and psychological therapy dogs. Some dogs owned by epileptics have even been shown to alert their handler when the handler shows signs of an impending seizure, sometimes well in advance of onset, allowing the owner to seek safety, medication or medical care. Sports and shows. Owners of dogs often enter them in competitions, whether show (breed conformation shows) or sports, including dog racing and dog sledding. Conformation shows, also referred to as breed shows, are a type of dog show in which a judge familiar with a specific dog breed evaluates individual purebred dogs for how well the dogs conform to their established breed type as described in their breed standard. As the breed standard only deals with the externally observable qualities of the dog (such as appearance, movement, and temperament), separately tested-for qualities are not part of the judging in conformation shows (such as tests for ability, health, or any other specific tests for characteristics that cannot be directly observed). Physical characteristics. Compared to equally sized wolves, dogs tend to have 20% smaller skulls, 10% smaller brains, as well as proportionately smaller teeth than other canid species. Dogs require fewer calories to function than wolves. Their diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog's limp ears are a result of atrophy of the jaw muscles. The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favoring the former for use as clothing due to its greater resistance to wear and tear in harsh weather. The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves. Behavior. Dogs tend to be poorer than wolves at observational learning, being more responsive to instrumental conditioning. Feral dogs show little of the complex social structure or dominance hierarchy present in wolf packs. For dogs, other members of their kind are of no help in locating food items, and are more like competitors. Feral dogs are primarily scavengers, with studies showing that unlike their wild cousins, they are poor ungulate hunters, having little impact on wildlife populations where they are sympatric. However, feral dogs have been reported to be effective hunters of reptiles in the Galapagos islands, and free ranging pet dogs are more prone to predatory behavior toward wild animals. Despite common belief, domestic dogs can be monogamous. Breeding in feral packs can be, but does not have to be restricted to a dominant alpha pair (despite common belief, such things also occur in wolf packs). Male dogs are unusual among canids by the fact that they mostly seem to play no role in raising their puppies, and do not kill the young of other females to increase their own reproductive success. Some sources say that dogs differ from wolves and most other large canid species by the fact that they do not regurgitate food for their young, nor the young of other dogs in the same territory. However, this difference was not observed in all domestic dogs. Regurgitating of food by the females for the young as well as care for the young by the males has been observed in domestic dogs, dingos as well as in other feral or semi-feral dogs. Regurgitating of food by the females and direct choosing of only one mate has been observed even in those semi-feral dogs of direct domestic dog ancestry. Also regurgitating of food by males has been observed in free-ranging domestic dogs. Trainability. Dogs display much greater tractability than tame wolves, and are generally much more responsive to coercive techniques involving fear, aversive stimuli, and force than wolves, which are most responsive toward positive conditioning and rewards. Unlike tame wolves, dogs tend to respond more to voice than hand signals. Although they are less difficult to control than wolves, they can be comparatively more difficult to teach than a motivated wolf.	The horse'" ("Equus ferus caballus") is a hoofed (ungulate) mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today. Humans began to domesticate horses around 4000 BC, and their domestication is believed to have been widespread by 3000 BC; by 2000 BC the use of domesticated horses had spread throughout the Eurasian continent. Although most horses today are domesticated, there are still endangered populations of the Przewalski's Horse, the only remaining true wild horse, as well as more common feral horses which live in the wild but are descended from domesticated ancestors. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior. Horses are anatomically designed to use speed to escape predators, and have a well-developed sense of balance and a strong fight-or-flight instinct. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down. Female horses, called mares, carry their young for approximately 11 months, and a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training under saddle or in harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years. Horse breeds are loosely divided into three categories based on general temperament: spirited "hot bloods" with speed and endurance; "cold bloods," such as draft horses and some ponies, suitable for slow, heavy work; and "warmbloods," developed from crosses between hot bloods and cold bloods, often focusing on creating breeds for specific riding purposes, particularly in Europe. There are over 300 breeds of horses in the world today, developed for many different uses. Horses and humans interact in many ways, not only in a wide variety of sport competitions and non-competitive recreational pursuits, but also in working activities including police work, agriculture, entertainment, assisted learning and therapy. Horses were historically used in warfare. A wide variety of riding and driving techniques have been developed, using many different styles of equipment and methods of control. Many products are derived from horses, including meat, milk, hide, hair, bone, and pharmaceuticals extracted from the urine of pregnant mares. Humans provide domesticated horses with food, water and shelter, as well as attention from specialists such as veterinarians and farriers. Biology. Horse anatomy is described by a large number of specific terms, as illustrated by the chart to the right. Specific terms also describe various ages, colors and breeds. Age. Depending on breed, management and environment, the domestic horse today has a life expectancy of 25 to 30 years. It is uncommon, but a few animals live into their 40s and, occasionally, beyond. The oldest verifiable record was "Old Billy," a 19th-century horse that lived to the age of 62. In modern times, Sugar Puff, who had been listed in the Guinness Book of World Records as the world's oldest living pony, died in 2007, aged 56. Regardless of a horse's actual birth date, for most competition purposes an animal is considered a year older on January 1 of each year in the northern hemisphere and August 1 in the southern hemisphere. The exception is in endurance riding, where the minimum age to compete is based on the animal's calendar age. A very rough estimate of a horse's age can be made from looking at its teeth. The following terminology is used to describe horses of various ages: In horse racing, the definitions of colt, filly, mare, and stallion may differ from those given above. In the UK, Thoroughbred horse racing defines a colt as a male less than five years old, and a filly as a female less than five years old. In the USA, both Thoroughbred racing and harness racing defines colts and fillies as four years old and younger. Size. The English-speaking world measures the height of horses in hands, abbreviated "h" or "hh," for "hands high," measured at the highest point of an animal's withers, where the neck meets the back, chosen as a stable point of the anatomy, unlike the head or neck, which move up and down; one hand is. Intermediate heights are defined by hands and inches, rounding to the lower measurement in hands, followed by a decimal point and the number of additional inches between 1 and 3. Thus a horse described as "15.2 h," is 15 hands, 2 inches in height. The size of horses varies by breed, but can also be influenced by nutrition. The general rule for cutoff in height between what is considered a horse and a pony at maturity is 14.2 hands. An animal 14.2 h or over is usually considered to be a horse and one less than 14.2 h a pony. However, there are exceptions to the general rule. Some breeds which typically produce individuals both under and over 14.2 h are considered horses regardless of their height. Conversely, some pony breeds may have features in common with horses, and individual animals may occasionally mature at over 14.2 h, but are still considered to be ponies. The distinction between a horse and pony is not simply a difference in height, but takes account of other aspects of "phenotype" or appearance, such as conformation and temperament. Ponies often exhibit thicker manes, tails and overall coat. They also have proportionally shorter legs, wider barrels, heavier bone, shorter and thicker necks, and short heads with broad foreheads. They often have calmer temperaments than horses and also a high level of equine intelligence that may or may not be used to cooperate with human handlers. In fact, small size, by itself, is sometimes not a factor at all. While the Shetland pony stands on average 10 hands high, the Falabella and other miniature horses, which can be no taller than, the size of a medium-sized dog, are classified by their respective registries as very small horses rather than as ponies. Light riding horses such as Arabians, Morgans, or Quarter Horses usually range in height from 14 to 16 hands and can weigh from. Larger riding horses such as Thoroughbreds, American Saddlebreds or Warmbloods usually start at about 15.2 hands and often are as tall as 17 hands, weighing from. Heavy or draft horses such as the Clydesdale, Belgian, Percheron, and Shire are usually at least 16 to 18 hands high and can weigh from about. The largest horse in recorded history was probably a Shire horse named Sampson, who lived during the late 1800s. He stood 21.2½ hands high, and his peak weight was estimated at. The current record holder for the world's smallest horse is Thumbelina, a fully mature miniature horse affected by dwarfism. She is tall and weighs. Colors and markings. Horses exhibit a diverse array of coat colors and distinctive markings, described with a specialized vocabulary. Often, a horse is classified first by its coat color, before breed or sex. Flashy or unusual colors are sometimes very popular, as are horses with particularly attractive markings. Horses of the same color may be distinguished from one another by their markings. The genetics that create many horse coat colors have been identified, although research continues on specific genes and mutations that result in specific color traits. Essentially, all horse colors begin with a genetic base of "red" (chestnut) or "black," with the addition of alleles for spotting, graying, suppression or dilution of color, or other effects acting upon the base colors to create the dozens of possible coat colors found in horses. Horses which are light in color are often misnamed as being "white" horses. A horse that looks pure white is, in most cases, actually a middle-aged or older gray. Grays have black skin underneath their white hair coat (with the exception of small amounts of pink skin under white markings). The only horses properly called white are those with pink skin under a white hair coat, a fairly rare occurrence. There are no truly albino horses, with pink skin and red eyes, as albinism is a lethal condition in horses. Reproduction and development. Pregnancy lasts for approximately 335–340 days and usually results in one foal. Twins are very rare. Colts are carried on average about 4 days longer than fillies. Horses are a precocial species, and foals are capable of standing and running within a short time following birth. Horses, particularly colts, may sometimes be physically capable of reproduction at about 18 months. In practice, individuals are rarely allowed to breed before the age of three, especially females. Horses four years old are considered mature, although the skeleton normally continues to develop until the age of six; the precise time of completion of development also depends on the horse's size, breed, gender, and the quality of care provided by its owner. Also, if the horse is larger, its bones are larger; therefore, not only do the bones take longer to actually form bone tissue, but the epiphyseal plates are also larger and take longer to convert from cartilage to bone. These plates convert after the other parts of the bones, but are crucial to development. Depending on maturity, breed, and the tasks expected, young horses are usually put under saddle and trained to be ridden between the ages of two and four. Although Thoroughbred race horses are put on the track at as young as two years old in some countries, horses specifically bred for sports such as dressage are generally not entered into top-level competition until they are a minimum of four years old, because their bones and muscles are not solidly developed, nor is their advanced training complete. For endurance riding competition, horses are not deemed mature enough to compete until they are a full 60 calendar months (5 years) old. Skeletal system. Horses have a skeleton that averages 205 bones. A significant difference between the horse skeleton, compared to that of a human, is the lack of a collarbone—the horse's front limb system is attached to the spinal column by a powerful set of muscles, tendons and ligaments that attach the shoulder blade to the torso. The horse's legs and hooves are also unique structures. Their leg bones are proportioned differently from those of a human. For example, the body part that is called a horse's "knee" is actually made up of the carpal bones that correspond to the human wrist. Similarly, the hock, contains the bones equivalent to those in the human ankle and heel. The lower leg bones of a horse correspond to the bones of the human hand or foot, and the fetlock (incorrectly called the "ankle") is actually the proximal sesamoid bones between the cannon bones (a single equivalent to the human metacarpal or metatarsal bones) and the proximal phalanges, located where one finds the "knuckles" of a human. A horse also has no muscles in its legs below the knees and hocks, only skin, hair, bone, tendons, ligaments, cartilage, and the assorted specialized tissues that make up the hoof. Hooves. The critical importance of the feet and legs is summed up by the traditional adage, "no foot, no horse". The horse hoof begins with the distal phalanges, the equivalent of the human fingertip or tip of the toe, surrounded by cartilage and other specialized, blood-rich soft tissues such as the laminae. The exterior hoof wall and horn of the sole is made of essentially the same material as a human fingernail. The end result is that a horse, weighing on average, travels on the same bones as a human on tiptoe. For the protection of the hoof under certain conditions, some horses have horseshoes placed on their feet by a professional farrier. The hoof continually grows, and needs to be trimmed (and horseshoes reset, if used) every five to eight weeks. Teeth. Horses are adapted to grazing. In an adult horse, there are 12 incisors, adapted to biting off the grass or other vegetation, at the front of the mouth. There are 24 teeth adapted for chewing, the premolars and molars, at the back of the mouth. Stallions and geldings have four additional teeth just behind the incisors, a type of canine teeth that are called "tushes." Some horses, both male and female, will also develop one to four very small vestigial teeth in front of the molars, known as "wolf" teeth, which are generally removed because they can interfere with the bit. There is an empty interdental space between the incisors and the molars where the bit rests directly on the bars (gums) of the horse's mouth when the horse is bridled. The incisors show a distinct wear and growth pattern as the horse ages, as well as change in the angle at which the chewing surfaces meet. The teeth continue to erupt throughout life as they are worn down by grazing, so a very rough estimate of a horse's age can be made by an examination of its teeth, although diet and veterinary care can affect the rate of tooth wear. Digestion. Horses are herbivores with a digestive system adapted to a forage diet of grasses and other plant material, consumed steadily throughout the day. Therefore, compared to humans, they have a relatively small stomach but very long intestines to facilitate a steady flow of nutrients. A horse will eat of food per day and, under normal use, drink to of water. Horses are not ruminants, so they have only one stomach, like humans, but unlike humans, they can also digest cellulose from grasses due to the presence of a "hind gut" called the cecum, or "water gut," which food goes through before reaching the large intestine. Unlike humans, horses cannot vomit, so digestion problems can quickly cause colic, a leading cause of death. Senses. The horse's senses are generally superior to those of a human. As prey animals, they must be aware of their surroundings at all times. They have the largest eyes of any land mammal, and because their eyes are positioned on the sides of their heads, horses have a range of vision of more than 350°, with approximately 65° of this being binocular (seen with both eyes) and the remaining 285° monocular (seen with only one eye). Horses have excellent day and night vision, but studies indicate that they have two-color, or dichromatic vision; their color vision is somewhat like red-green color blindness in humans. This means that certain colors, especially red and related colors, appear more green. Their hearing is good, and the pinna of each ear can rotate up to 180°, giving the potential for 360° hearing without having to move the head. Their sense of smell, while much better than that of humans, is not their strongest asset; they rely to a greater extent on vision. Horses have a great sense of balance, due partly to their ability to feel their footing and partly to highly developed proprioceptive abilities (the unconscious sense of where the body and limbs are at all times). A horse's sense of touch is well developed. The most sensitive areas are around the eyes, ears and nose. Via touch, horses perceive and respond immediately to changes in their environment, sensing contact as subtle as an insect landing anywhere on the body. Horses have an advanced sense of taste that allows them to sort through grains and grasses to choose what they would most like to eat, and their prehensile lips can easily sort even the smallest grains. Horses generally will not eat poisonous plants. However, there are exceptions and horses will occasionally eat toxic amounts of poisonous plants even when there is adequate healthy food. Movement. All horses move naturally with four basic gaits: the four-beat walk, which averages four miles per hour; the two-beat trot or jog, which averages per hour (faster for harness racing horses); and the leaping gaits known as the canter or lope (a three-beat gait that is per hour), and the gallop. The gallop averages per hour. The world record for a horse galloping over a short, sprint distance is per hour. Besides these basic gaits, some horses perform a two-beat pace, instead of the trot. In addition, there are several four-beat "ambling" gaits that are approximately the speed of a trot or pace, though smoother to ride. These include the lateral slow gait, rack, running walk, and tölt as well as the diagonal fox trot. Ambling gaits are often genetic traits in specific breeds, known collectively as gaited horses. In most cases, gaited horses replace the standard trot with one of the ambling gaits. Behavior. Horses are prey animals with a well-developed fight-or-flight instinct. Their first response to threat is to startle and usually flee, although they are known to stand their ground and defend themselves or their offspring in cases where flight is not possible, or when their young are threatened. They also tend to be curious; when startled, they will often hesitate an instant to ascertain the cause of their fright, and may not always flee from something that they perceive as non-threatening. Through selective breeding, some breeds of horses are quite docile, particularly certain large draft horses. Most light horse riding breeds were developed for speed, agility, alertness and endurance; natural qualities that extend from their wild ancestors. Horses are herd animals, with a clear hierarchy of rank, led by a dominant animal (usually a mare). They are also social creatures who are able to form companionship attachments to their own species and to other animals, including humans. They communicate in various ways, including vocalizations such as nickering or whinnying, mutual grooming, and body language. Many horses will become difficult to manage if they are isolated. Through proper training, it is possible to teach any horse to accept a human as a type of companion, and thus be comfortable away from other horses. When confined with insufficient companionship, exercise or stimulation, individuals may develop stable vices, an assortment of bad habits, mostly psychological in origin, that include wood chewing, wall kicking, "weaving" (rocking back and forth) and other problems. Intelligence and learning. In the past, horses were considered unintelligent, with no abstract thinking ability, unable to generalize, and driven primarily by a herd mentality. However, recent studies show that they perform a number of cognitive tasks on a daily basis, and frequently engage in mental challenges that include food procurement and social system identification. They have also been shown to have good spatial discrimination abilities. Studies have assessed equine intelligence in the realms of problem solving, learning speed, and knowledge retention. Results show that horses excel at simple learning, but also are able to solve advanced cognitive challenges that involve categorization and concept learning. They have been shown to learn from habituation, desensitization, Pavlovian conditioning, and operant conditioning. They respond to and learn from both positive and negative reinforcement. Domesticated horses tend to face greater mental challenges than wild horses, due to living in artificial environments that stifle instinctual behavior while learning tasks that are not natural. Horses are creatures of habit that respond and adapt well to regimentation, and respond best when the same routines and techniques are used consistently. Some trainers believe that "intelligent" horses are reflections of intelligent trainers who effectively use response conditioning techniques and positive reinforcement to train in the style that fits best with an individual animal's natural inclinations. Others who handle horses regularly note that personality also may play a role separate from intelligence in determining how a given animal responds to various experiences. Temperament. Thoroughbred race horses are a "hot blooded" breed. Horses are mammals, and as such are "warm-blooded" creatures, as opposed to reptiles, which are cold-blooded. However, these words have developed a separate meaning in the context of equine terminology, used to describe temperament, not body temperature. For example, the "hot-bloods," such as many race horses, exhibit more sensitivity and energy, while the "cold-bloods," such as most draft breeds, are quieter and calmer. "Hot blooded" breeds include "oriental horses" such as the Akhal-Teke, Barb, Arabian horse and now-extinct Turkoman horse, as well as the Thoroughbred, a breed developed in England from the older oriental breeds. Hot bloods tend to be spirited, bold, and learn quickly. They are bred for agility and speed. They tend to be physically refined—thin-skinned, slim, and long-legged. The original oriental breeds were brought to Europe from the Middle East and North Africa when European breeders wished to infuse these traits into racing and light cavalry horses. The "cold blooded" draft breeds are powerful and heavily-muscled Muscular, heavy draft horses are known as "cold bloods," as they are bred not only for strength, but also to have the calm, patient temperament needed to pull a plow or a heavy carriage full of people. They are sometimes nicknamed "gentle giants." Well-known draft breeds include the Belgian and the Clydesdale. Some, like the Percheron are lighter and livelier, developed to pull carriages or to plow large fields in drier climates. Others, such as the Shire, are slower and more powerful, bred to plow fields with heavy, clay-based soils. The cold-blooded group also includes some pony breeds. "Warmblood" breeds, such as the Trakehner or Hanoverian, developed when European carriage and war horses were crossed with Arabians or Thoroughbreds, producing a riding horse with more refinement than a draft horse, but greater size and more phlegmatic temperament than a lighter breed. Certain pony breeds with warmblood characteristics have been developed for smaller riders. A modern "Warmblood" horse is large, but agile and athletic. Today, the term "Warmblood" refers to a specific subset of sport horse breeds that have dominated the Olympic Games and international FEI competition in dressage and show jumping since the 1970s. Prior to that time, the term "warm blood" often referred to any cross between cold-blooded and hot-blooded breeds. Examples included breeds such as the Irish Draught or the Cleveland Bay. Less often, the term was even used to refer to breeds of light riding horse other than Thoroughbreds or Arabians, such as the Morgan horse. Sleep patterns. Horses are able to sleep both standing up and lying down. In an adaptation from life in the wild, horses are able to enter light sleep by using a "stay apparatus" in their legs, allowing them to doze without collapsing. Horses sleep better when in groups because some animals will sleep while others stand guard to watch for predators. A horse kept alone will not sleep well because its instincts are to keep a constant eye out for danger. Unlike humans, horses do not sleep in a solid, unbroken period of time, but take many short periods of rest. Horses may spend anywhere from four to fifteen hours a day in standing rest, and from a few minutes to several hours lying down. Total sleep time in a day may range from several minutes to a couple of hours, mostly in short intervals of about 15 minutes each. Horses must lie down to reach REM sleep. They only have to lie down for an hour or two every few days to meet their minimum REM sleep requirements. However, if a horse is never allowed to lie down, after several days it will become sleep-deprived, and in rare cases may suddenly collapse as it involuntarily slips into REM sleep while still standing. This condition differs from narcolepsy, although horses may also suffer from that disorder. Taxonomy and evolution. The horse as it is known today adapted by evolution to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families and many species, but only three families—Equidae (the horse and related species), the tapir and the rhinoceros—containing 18 known species have survived to the present day. The earliest known member of the Equidae family was the "Hyracotherium", which lived between 45 and 55 million years ago, during the Eocene period and had 4 toes on each front foot, and 3 toes on each back foot. The extra toe on the front feet soon disappeared with the "Mesohippus", which lived 32 to 37 million years ago, and by about 5 million years ago, the modern Equus had developed. The extra side toes shrank in size until they have vanished in modern horses. All that remains is a set of small vestigial bones on the leg above the hoof, known informally as ergots, chestnuts, or splint bones. Their legs also lengthened as their toes disappeared and until they were a hoofed animal capable of running at great speed. Over millions of years, equid teeth also evolved from browsing on soft, tropical plants to adapt to browsing of drier plant material, and grazing of tougher plains grasses. Thus the proto-horses changed from leaf-eating forest-dwellers to grass-eating inhabitants of semi-arid regions worldwide, including the steppes of Eurasia and the Great Plains of North America. For reasons not fully understood, "Equus caballus" disappeared from North America around 10,000 years ago, at the end of the last ice age. The "Four Foundations" theory. Modern DNA evidence suggests that domesticated horses evolved from multiple wild populations. Specifically, the "Four Foundations" theory suggests that the modern horse evolved from multiple ancient wild prototypes, each adapted to a given habitat. However, an older theory holds that there was only one type of wild horse, the Tarpan subtype, and all other types diverged in form after domestication to meet human needs. Under the four foundations theory, all types and breeds of horses are thought to have developed from the following base prototypes: Domestication and surviving wild species. Competing theories exist as to the time and place of initial domestication. The earliest evidence for the domestication of the horse comes from Ukraine and dates to approximately 4,000 BC. It is thought that the horse was completely domesticated by 3000 BC, and by 2000 BC there was a sharp increase in the number of horse bones found in human settlements in northwestern Europe, indicating the spread of domesticated horses throughout the continent. Wild species surviving into modern times. A truly wild horse is a species or subspecies which has no ancestors that were ever domesticated. Therefore, most "wild" horses today are actually feral horses, animals that escaped or were turned loose from domestic herds and the descendants of those animals. Only two types of truly wild horses survived into recorded history. One, the Tarpan ("Equus ferus ferus") survived into the historical era, but became extinct in 1887. Its pure genetic line was lost, but three attempts have been made to re-create the Tarpan. In the early 1930s, Berlin Zoo Director Lutz Heck and Heinz Heck of the Munich Zoo began a program that by the 1960s produced the Heck horse. In 1936, Polish university professor Tadeusz Vetulani began a program using Konik horses, and in the mid-1960s Harry Hegard started a program in the United States using feral mustangs and local working ranch horses that has resulted in the Hegardt or Stroebel's Horse. None of the breeding programs were completely successful, although all three resulted in horses with many similarities to the Tarpan. There is only one true wild horse species alive today, the Przewalski's Horse ("Equus ferus przewalskii"). It is a rare Asian animal, also known as the Mongolian Wild Horse; Mongolian people know it as the "taki", and the Kyrgyz people call it a "kirtag". Small wild breeding populations of this animal, named after the Russian explorer Nikolai Przhevalsky, exist in Mongolia. There are also small populations maintained at zoos throughout the world. The species was considered extinct in the wild between 1969 and 1992, but a small breeding population was reestablished in the wild due to the conservation efforts of numerous zoos. Feral populations. Feral horses are born and live in the wild, but are descended from domesticated animals. Many populations of feral horses exist throughout the world. Studies of feral herds have provided useful insights into the behavior of prehistoric horses, as well as greater understanding of the instincts and behaviors that drive horses that live in domesticated conditions. Other modern equids. Besides the horse, there are seven other species of genus "equus" in the equidae family. These are the ass or donkey, "Equus asinus"; the Mountain Zebra, "Equus zebra"; Plains Zebra, "Equus burchelli"; Grévy's Zebra, "Equus grevyi"; the Kiang, "Equus kiang"; and the Kulan, "Equus hemionus", including its subspecies, the Onager, "Equus hemionus onager". Horses can crossbreed with other members of the "equus" genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse, a cross between a zebra and a horse that is bred in Africa and used for trekking on Mount Kenya. With rare exceptions, most hybrids are sterile and cannot reproduce. Breeds. Horse breeds are groups of horses with distinctive characteristics that are transmitted consistently to their offspring, such as conformation, color, performance ability, or disposition. These inherited traits are usually the result of a combination of natural crosses and artificial selection methods aimed at producing horses for specific tasks. Certain breeds are known for certain talents. For example, Standardbreds are known for their speed in harness racing. Some breeds have been developed through centuries of crossings with other breeds, while others, such as Tennessee Walking Horses and Morgans, developed from a single sire from which all current breed members descend. There are more than 300 horse breeds in the world today. Origin of breeds. Modern horse breeds developed in response to a need for "form to function", the necessity to develop certain physical characteristics in order to perform a certain type of work. Thus, powerful but refined breeds such as the Andalusian or the Lusitano developed in the Iberian peninsula as riding horses that also had a great aptitude for dressage, while heavy draft horses such as the Clydesdale and the Shire developed out of a need to perform demanding farm work and pull heavy wagons. Ponies of all breeds originally developed mainly from the need for a working animal that could fulfill specific local draft and transportation needs while surviving in harsh environments. However, by the 20th century, many pony breeds had Arabian and other blood added to make a more refined pony suitable for riding. Other horse breeds developed specifically for light agricultural work, heavy and light carriage and road work, various equestrian disciplines, or simply as pets. Purebreds and registries. Horses have been selectively bred since their domestication. Today, there are over 300 breeds of horses in the world. However, the concept of purebred bloodstock and a controlled, written breed registry only became of significant importance in modern times. Today, the standards for defining and registration of different breeds vary. Sometimes purebred horses are called Thoroughbreds, which is incorrect; "Thoroughbred" is a specific breed of horse, while a "purebred" is a horse (or any other animal) with a defined pedigree recognized by a breed registry. An early example of people who practiced selective horse breeding were the Bedouin, who had a reputation for careful breeding practices, keeping extensive pedigrees of their Arabian horses and placing great value upon pure bloodlines. Though these pedigrees were originally transmitted via an oral tradition, written pedigrees of Arabian horses can be found that date to the 14th century. In the same period of the early Renaissance, the Carthusian monks of southern Spain bred horses and kept meticulous pedigrees of the best bloodstock; the lineage survives to this day in the Andalusian horse. One of the earliest formal registries was General Stud Book for Thoroughbreds, which began in 1791 and traced back to the Arabian stallions imported to England from the Middle East that became the foundation stallions for the breed. Some breed registries have a closed stud book, where registration is based on pedigree, and no outside animals can gain admittance. For example, a registered Thoroughbred or Arabian must have two registered parents of the same breed. Other breeds have a partially closed stud book but still allow certain infusions from other breeds. For example, the modern Appaloosa must have at least one Appaloosa parent, but may also have a Quarter Horse, Thoroughbred, or Arabian parent so long as the offspring exhibits appropriate color characteristics. The Quarter Horse normally requires both parents to be registered Quarter Horses, but allows "Appendix" registration of horses with one Thoroughbred parent, and the horse may earn its way to full registration by completing certain performance requirements. Others, such as most of the warmblood breeds used in sport horse disciplines, have open stud books to varying degrees. While pedigree is considered, outside bloodlines are admitted to the registry if the horses meet the set standard for the registry. These registries usually require a studbook selection process involving judging of an individual animal's quality, performance, and conformation before registration is finalized. A few "registries," particularly some color breed registries, are very open and will allow membership of all horses that meet limited criteria, such as coat color and species, regardless of pedigree or conformation. Breed registries also differ as to their acceptance or rejection of breeding technology. For example, all Jockey Club Thoroughbred registries require that a registered Thoroughbred be a product of a natural mating, so called "live cover". A foal born of two Thoroughbred parents, but by means of artificial insemination or embryo transfer, cannot be registered in the Thoroughbred studbook. On the other hand, since the advent of DNA testing to verify parentage, most breed registries now allow artificial insemination (AI), embryo transfer (ET), or both. The high value of stallions has helped with the acceptance of these techniques because they allow a stallion to breed more mares with each "collection," and greatly reduce the risk of injury during mating. Cloning of horses is highly controversial, and at the present time most mainstream breed registries will not accept cloned horses, though several cloned horses and mules have been produced. Interaction with humans. Around the world, horses play a role within human cultures. Horses are used for leisure activities, sports, and working purposes. The Food and Agriculture Organization (FAO) reports that in 2003, China had the largest number of horses in the world with over 8 million, followed by Mexico (6,260,000), Brazil (5,900,500), the United States (5,300,000), and Argentina (3,655,000). The American Horse Council estimates that horse-related activities have a direct impact on the economy of the United States of over $39 billion, and when indirect spending is considered, the impact is over $102 billion. In a 2004 "poll" conducted by Animal Planet, more than 50,000 viewers from 73 countries voted for the horse as the world's 4th favorite animal. Sport. Historically, equestrians honed their skills through competitions, games and races. Equestrian sports have the dual purpose of providing entertainment for crowds and creating and preserving the excellent horsemanship that was needed in battle. Many sports, such as dressage, eventing and show jumping, had origins in military training, which were focused on control and balance in both the horse and the rider. Other sports, such as rodeo, developed from practical skills such as those needed on working ranches. Sport hunting from horseback evolved from earlier practical hunting techniques. Horse racing, whether the horse was ridden or driven, evolved out of impromptu competitions between riders or drivers. The evolving competitions, requiring ever more demanding and specialized skills from both horse and rider, resulted in the systematic development of specialized breeds and equipment for each sport. The popularity of equestrian sports through the centuries has resulted in the preservation of skills that would otherwise have rapidly disappeared after horses stopped being used in combat. Horses are trained to be ridden or driven in many different sporting events and competitions. Examples include show jumping, dressage, three-day eventing, competitive driving, endurance riding, gymkhana, rodeos and fox hunting. Horse shows, which have their origins in medieval European fairs, are held around the world as venues in which horses are competed, exhibited and sold. They host a huge range of classes, covering all of the mounted and harness disciplines, as well as "In-hand" classes where the horses are led, rather than ridden, to exhibit their conformation. The method of judging classes varies depending on the discipline, but winning awards usually depends on style and ability of both horse and rider. Sports such as polo do not judge the horse itself, but rather use the horse as a partner for human competitors as a necessary part of the game. Although the horse assists this process and requires specialized training to do so, the details of its performance are not judged, only the result of the rider's actions—be it getting a ball through a goal or some other achievement. Examples of these sports of partnership between human and animal also include jousting (reenacting the skills used by medieval knights), in which the main goal is for one rider to unseat the other, and buzkashi, a team game played throughout Central Asia, the aim being to capture a goat carcass while on horseback. Horse racing is an equestrian sport and also a huge international industry, watched in almost every nation of the world. There are three types: "flat" racing; steeplechasing, i.e. racing over jumps; and harness racing, where horses trot or pace while pulling a driver in a small, light cart known as a sulky. A major part of horse racing's economic importance lies in the gambling associated with it. Communication between human and horse is paramount in any equestrian activity; to aid this process horses are usually ridden with a saddle on their backs to assist the rider with balance and positioning, and a bridle or related headgear to assist the rider in maintaining control. Sometimes horses are ridden without a saddle, and occasionally, horses are trained to perform without a bridle or other headgear. Many horses are also driven, which requires a harness, bridle and some type of vehicle. Work. There are certain jobs that horses do very well, and no technology has yet developed that can fully replace them. For example, mounted police horses are still effective for certain types of patrol duties and crowd control. Cattle ranches still require riders on horseback to round up cattle that are scattered across remote, rugged terrain. Search and rescue organizations in some countries depend upon mounted teams to locate people, particularly hikers and children, and to provide disaster relief assistance. Horses can also be used in other areas where it is necessary to avoid vehicular disruption to delicate soil. Examples include areas such as nature reserves. They may also be the only form of transport allowed in wilderness areas. They are also quieter than motorized vehicles. Law enforcement officers such as park rangers or game wardens may use horses for patrols, and horses or mules may also be used for clearing trails or other work in areas of rough terrain where vehicles are less effective. Some land management practices such as cultivating and logging can be efficiently performed with horses. In agriculture, less use of fossil fuels and increased environmental conservation can be seen over time with the use of draft animals such as horses. In forestry, logging can be done with horses and can result in reduced damage to soil structure and less damage to trees due to more selective logging. Although machinery has replaced horses in many parts of the world, an estimated 100 million horses, donkeys and mules are still used for agriculture and transportation in less developed areas such as Morocco, Kenya and Guatemala. Entertainment and culture. Modern horses are often used to reenact many of their historical work purposes. Horses are used, complete with equipment that is authentic or a meticulously recreated replica, in various live action historical reenactments of specific periods of history, especially recreations of famous battles. Horses also are used to preserve cultural traditions and for ceremonial purposes. Countries such as the United Kingdom still use horse-drawn carriages to convey royalty and other VIPs to and from certain culturally significant events. Public exhibitions are another example, such as the Budweiser Clydesdales, seen in parades and other public settings, a team of draft horses that pull a beer wagon similar to that used before to the invention of the modern motorized truck. Horses are frequently used in television and films to add authenticity to historical dramas as well as adding charm to films set in modern-day, or even futuristic science fiction settings. Both live horses and iconic images of horses are used in advertising to promote a variety of products. The horse frequently appears in coats of arms in heraldry. The horse can be represented as standing, trotting, courant (running) or salient (rearing). The horse may be saddled and bridled, harnessed, or without any harness whatsoever. The horse appears in the 12-year cycle of animals in the Chinese zodiac related to the Chinese calendar. According to Chinese folklore, each animal is associated with certain personality traits, and those born in the year of the horse are intelligent, independent and free-spirited. Assisted learning and therapy. People of all ages with physical and mental disabilities obtain beneficial results from association with horses. Therapeutic riding is used to mentally and physically stimulate disabled persons and help them improve their lives through improved balance and coordination, increased self-confidence and a greater feeling of freedom and independence. The benefits of equestrian activity for people with disabilities has also been recognized with the addition of equestrian events to the Paralympic Games and recognition of para-equestrian events by the FEI. Hippotherapy and therapeutic horseback riding are names for different physical, occupational, and speech therapy treatment strategies that utilize equine movement. In hippotherapy, a therapist uses the horse's movement to provide improve their patient's cognitive, coordination, balance and fine motor skills, whereas therapeutic horseback riding uses specific riding skills. Horses also provide psychological benefits to people whether they actually ride or not. "Equine-assisted" or "equine-facilitated" psychotherapy is a form of experiential psychotherapy that uses horses as companion animals to assist people with psychological problems, including anxiety disorders, psychotic disorders, mood disorders, behavioral difficulties, mental illness and those who are going through major life changes. Equine Assisted Learning (EAL) (also known as equine guided education or equine assisted professional development) is a field of experiential learning for corporate, professional and personal development. There are also experimental programs using horses in prison settings. Exposure to horses appears to improve the behavior of inmates in a prison setting and help reduce recidivism when they leave. Warfare. Horses in warfare have been seen for most of recorded history. The first archaeological evidence of horses used in warfare dates to between 3000 to 4000 BC, and the use of horses in warfare was widespread by the end of the Bronze Age. Although mechanization has largely replaced the horse as a weapon of war, horses are still seen today in limited military uses, mostly for ceremonial purposes, or for reconnaissance and transport activities in areas of rough terrain where motorized vehicles are ineffective. Horses have been used in the 21st century by the Janjaweed militias in the War in Darfur. Products. Horses have been used as raw material for many products made by humans throughout history, including byproducts from the slaughter of horses as well as materials collected from living horses. Products collected from living horses include mare's milk, used by people with large horse herds, such as the Mongols, who let it ferment to produce kumis. Horse blood was once used as food by the Mongols and other nomadic tribes, who found it a convenient source of nutrition when traveling. Drinking their own horses' blood allowed the Mongols to ride for extended periods of time without stopping to eat. Today, the drug Premarin is a mixture of estrogens extracted from the urine of pregnant mares (pre'"gnant "'mar'"es' ur"'in'"e). It is a widely used drug for hormone replacement therapy. The tail hair of horses can be used for making bows for string instruments such as the violin, viola, cello, and double bass. Horse meat has been used as food for humans and carnivorous animals throughout the ages. It is eaten in many parts of the world, though consumption is taboo in some cultures. Horsemeat has been an export industry in the United States and other countries, though legislation has periodically been introduced in the United States Congress which would end export from the United States. Horsehide leather has been used for boots, gloves, jackets, baseballs, and baseball gloves. Horse hooves can also be used to produce animal glue. Horse bones can be used to make implements. Specifically, in Italian cuisine, the horse tibia is sharpened into a probe called a "spinto", which is used to test the readiness of a (pig) ham as it cures. In Asia, the saba is a horsehide vessel used in the production of kumis. Care. Horses are grazing animals, and their major source of nutrients is good-quality forage from hay or pasture. They can consume approximately 2% to 2.5% of their body weight in dry feed each day. Therefore, a adult horse could eat up to of food. Sometimes, concentrated feed such as grain is fed in addition to pasture or hay, especially when the animal is very active. When grain is fed, equine nutritionists recommend that 50% or more of the animal's diet by weight should still be forage. Horses require a plentiful supply of clean water, a minimum of to per day. Although horses are adapted to live outside, they require shelter from the wind and precipitation, which can range from a simple shed or shelter to an elaborate stable. Horses require routine hoof care from a farrier as well as regular vaccinations to protect against various diseases, and periodic dental examinations from a veterinarian or a specialized equine dentist. If horses are kept inside in a barn, they require regular daily exercise for their physical health and mental well-being. When turned outside, they require well-maintained, sturdy fences to be safely contained. Regular grooming is also helpful to help the horse maintain good health of the hair coat and underlying skin.