Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that second group. Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors, he was the first to recognize the difference between conscious selective breeding in which humans directly select for desirable traits, unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits. There is a genetic difference between wild populations. There is such a difference between the domestication traits that researchers believe to have been essential at the early stages of domestication, the improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are fixed within all domesticates, were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations.
The dog was the first domesticated vertebrate, was established across Eurasia before the end of the Late Pleistocene era, well before cultivation and before the domestication of other animals. The archaeological and genetic data suggest that long-term bidirectional gene flow between wild and domestic stocks – including donkeys, horses and Old World camelids, goats and pigs – was common. Given its importance to humans and its value as a model of evolutionary and demographic change, domestication has attracted scientists from archaeology, anthropology, zoology and the environmental sciences. Among birds, the major domestic species today is the chicken, important for meat and eggs, though economically valuable poultry include the turkey and numerous other species. Birds are widely kept as cagebirds, from songbirds to parrots; the longest established invertebrate domesticates are the silkworm. Terrestrial snails are raised for food, while species from several phyla are kept for research, others are bred for biological control.
The domestication of plants began at least 12,000 years ago with cereals in the Middle East, the bottle gourd in Asia. Agriculture developed in at least 11 different centres around the world, domesticating different crops and animals. Domestication, from the Latin domesticus,'belonging to the house', is "a sustained multi-generational, mutualistic relationship in which one organism assumes a significant degree of influence over the reproduction and care of another organism in order to secure a more predictable supply of a resource of interest, through which the partner organism gains advantage over individuals that remain outside this relationship, thereby benefitting and increasing the fitness of both the domesticator and the target domesticate." This definition recognizes both the biological and the cultural components of the domestication process and the impacts on both humans and the domesticated animals and plants. All past definitions of domestication have included a relationship between humans with plants and animals, but their differences lay in, considered as the lead partner in the relationship.
This new definition recognizes a mutualistic relationship. Domestication has vastly enhanced the reproductive output of crop plants and pets far beyond that of their wild progenitors. Domesticates have provided humans with resources that they could more predictably and securely control and redistribute, the advantage that had fueled a population explosion of the agro-pastoralists and their spread to all corners of the planet. Houseplants and ornamentals are plants domesticated for aesthetic enjoyment in and around the home, while those domesticated for large-scale food production are called crops. Domesticated plants deliberately altered or selected for special desirable characteristics are cultigens. Animals domesticated for home companionship are called pets, while those domesticated for food or work are known as livestock; this biological mutualism is not restricted to humans with domestic crops and livestock but is well-documented in nonhuman species among a number of social insect domesticators and their plant and animal domesticates, for example the ant–fungus mutualism that exists between leafcutter ants and certain fungi.
Domestication syndrome is the suite of phenotypic traits arising during domestication that distinguish crops from their wild ancestors. The term is applied to vertebrate animals, includes increased docility and tameness, coat color changes, reductions in tooth size, changes in craniofacial morphology, alterations in ear and tail form, more frequent and nonseasonal estrus cycles, alterations in adrenocorticotropic hormone levels, changed concentrations of several neurotransmitters, prolongations in juvenile behavior, reductions in both total brain size and of particular brain regions; the domestication of animals and plants began with the wolf at least 15,000 years before present, which led to a rapid shift in the evolution and demography of both humans and numerous species of animals and plants. The sudden appearance of the domestic dog in the archaeological record was followed by livestock and crop domestication, the transition of humans from foraging to farming in different places and times across the planet.
Around 10,000 YBP, a new way of life emerged for humans through the management and exploitation of plant and an
Domestication of the horse
A number of hypotheses exist on many of the key issues regarding the domestication of the horse. Although horses appeared in Paleolithic cave art as early as 30,000 BCE, these were wild horses and were hunted for meat. How and when horses became domesticated is disputed; the clearest evidence of early use of the horse as a means of transport is from chariot burials dated c. 2000 BCE. However, an increasing amount of evidence supports the hypothesis that horses were domesticated in the Eurasian Steppes 3500 BCE. Use of horses spread across Eurasia for agricultural work and warfare; the date of the domestication of the horse depends to some degree upon the definition of "domestication". Some zoologists define "domestication" as human control over breeding, which can be detected in ancient skeletal samples by changes in the size and variability of ancient horse populations. Other researchers look at the broader evidence, including skeletal and dental evidence of working activity. There is evidence that horses were kept as meat animals prior to being trained as working animals.
Attempts to date domestication by genetic study or analysis of physical remains rests on the assumption that there was a separation of the genotypes of domesticated and wild populations. Such a separation appears to have taken place, but dates based on such methods can only produce an estimate of the latest possible date for domestication without excluding the possibility of an unknown period of earlier gene-flow between wild and domestic populations. Further, all modern horse populations retain the ability to revert to a feral state, all feral horses are of domestic types. Whether one adopts the narrower zoological definition of domestication or the broader cultural definition that rests on an array of zoological and archaeological evidence affects the time frame chosen for domestication of the horse; the date of 4000 BCE is based on evidence that includes the appearance of dental pathologies associated with bitting, changes in butchering practices, changes in human economies and settlement patterns, the depiction of horses as symbols of power in artifacts, the appearance of horse bones in human graves.
On the other hand, measurable changes in size and increases in variability associated with domestication occurred about 2500–2000 BCE, as seen in horse remains found at the site of Csepel-Haros in Hungary, a settlement of the Bell Beaker culture. Use of horses spread across Eurasia for agricultural work and warfare. Horses and mules in agriculture used a breastplate type harness or a yoke more suitable for oxen, not as efficient at utilizing the full strength of the animals as the later-invented padded horse collar that arose several millennia later. A 2005 study analyzed the mitochondrial DNA of a worldwide range of equids, from 53,000-year-old fossils to contemporary horses, their analysis placed all equids into a single clade, or group with a single common ancestor, consisting of three genetically divergent species: Hippidion, the New World stilt-legged horse, the true horse. The true horse, which ranged from western Europe to eastern Beringia, included prehistoric horses and the Przewalski's Horse, as well as what is now the modern domestic horse, belonged to a single Holarctic species.
A more detailed analysis of the true horses grouped them into two major clades. One of these clades, which seemed to have been restricted to North America, is now extinct; the other clade was broadly distributed from North America to central Europe and south of Pleistocene ice sheets. It became extinct in Beringia around 14,200 years ago, in the rest of the Americas around 10,000 years ago; this clade survived in Eurasia, it is from these horses which all domestic horses appear to have descended. These horses showed little phylogeographic structure reflecting their high degree of mobility and adaptability. Therefore, the domestic horse today is classified. No genetic originals of native wild horses exist the Przewalski's Horse; the Przewalski has 66 chromosomes, however, as opposed to 64 among modern domesticated horses, their Mitochondrial DNA forms a distinct cluster. Genetic evidence suggests that modern Przewalski's horses are descended from a distinct regional gene pool in the eastern part of the Eurasian steppes, not from the same genetic group that gave rise to modern domesticated horses.
Evidence such as the cave paintings of Lascaux suggests that the ancient wild horses that some researchers now label the "Tarpan subtype" resembled Przewalski horses in their general appearance: big heads, dun coloration, thick necks, stiff upright manes, short, stout legs. The horses of the Ice Age were hunted for meat in Europe and across the Eurasian steppes and in North America by early modern humans. Numerous kill sites exist and many cave paintings in Europe indicate what they looked like. Many of these Ice Age subspecies died out during the rapid climate changes associated with the end of the last Ice Age or were hunted out by humans in North America, where the horse became extinct. Classification based on body types and conformation, absent the availability of DNA for research, once suggested that there were four basic wild prototypes, thought t
Free-roaming horse management in North America
Management of free-roaming feral and semi-feral horses, on various public or tribal lands in North America is accomplished under the authority of law, either by the government of jurisdiction or efforts of private groups. In western Canada, management is a provincial matter, with several associations and societies helping to manage wild horses in British Columbia and Alberta. In Nova Scotia and various locations in the United States, management is under the jurisdiction of various federal agencies; the largest population of free-roaming horses are found in the Western United States, where most of them are protected under the Wild and Free-Roaming Horses and Burros Act of 1971, their management is undertaken by the Bureau of Land Management, but by the U. S. Forest Service Because free-roaming horses multiply able to increase their numbers by up to 20% per year, all North American herds are managed in some fashion in an attempt to keep the population size at a level deemed appropriate. In the western United States, implementation of the WFRH&BA has been controversial.
The law requires that "appropriate management levels" be set and maintained on public rangelands and that excess horses be removed and offered for adoption. If no adoption demand exists, animals are to be humanely destroyed or sold "without limitation" which allows the horses to be sent to slaughter. Since continuous Congressional fiscal mandates have prevented euthanizing healthy animals or allowing sales that result in slaughter, more animals are removed from the range than can be adopted or sold, excess horses are sent to short- and long-term holding facilities, which are at capacity; the population of free-roaming horses has increased since 2005, triple the AML and at the numbers estimated to be on the range in 1930. While the horse evolved in North America, it became extinct between 10,000 years ago. There are multiple theories for this extinction, ranging from climate change to the arrival of humans. Horses returned to the Americas beginning with Christopher Columbus in 1493, arriving on the mainland with Cortés in 1519.
These were Iberian horses now described as "Spanish type." The horse became an important part of Native American culture. The horse population expanded rapidly. Additional European settlers brought a variety of horse types to the Americas, from all sources, some animals escaped human control and became feral. Modern studies have identified a few modern herds, the Sulphur Springs herd, the Cerbat herd, the Pryor Mountains herd, the Kiger herd as retaining the original phenotype of horses brought to New World by the Spanish. Since 1960, the horses of Sable Island, unlike those in the rest of Canada, were protected under the Sable Island Regulations section of the Canadian Shipping Act. Following the designation of Sable Island as a National Park Reserve in December 2013, the horses are now protected by Parks Canada as wildlife under the Canada National Parks Act and the National Parks Wildlife Regulations. Parks Canada considers the Sable Island horses as'naturalized wildlife’ and, as such, they are being managed as a taxon equal to other species living on the island.
In the U. S. there are free-roaming herds on some of the barrier islands along the East Coast, notably Chincoteague Ponies, Banker horses and Cumberland Island horses. Most of these herds are managed by the National Park Service with assistance from various organizations, their populations are held stable through use of removal and adoption. The population of free-roaming horses in historic times and today it is estimated to be less than 2,000 horses. Herds are found on the Chilcotin Plateau of British Columbia, the Eastern Slopes of the Rocky Mountains in Alberta, in Saskatchewan's Bronson Forest. There are 800-1000 free-roaming horses in British Columbia. In 2014 the Alberta Government provided an official count of 880 for the horses of the Eastern Slopes of the Rockies and there are thought to be less than 100 horses in the Bronson Forest of Saskatchewan; the free-roaming horses of Western Canada have been subjected to repeated attempts to reduce or eradicate the population. As early as 1896 the Government of British Columbia passed the Wild Horse Extermination Act that made it lawful for anyone licensed by the Government to shoot or otherwise destroy an unbranded stallion over the age of twenty months east of the Cascade Mountains.
In the 40 years following implementation of the bounty system in B. C. in 1924, it is estimated. In a 1925 roundup in British Columbia horses were driven into corrals and offered for sale at $5 a head. At the same time the Government offered a bounty of $2.50 for a pair of a scalp. In 1943 an export market developed in Europe and the United States and thousands of free-roaming horses were rounded up in Western Canada and shipped for both food consumption and domestic use. In Alberta some roundups were done as far back as the 1950s and a horse permit system was in effect from 1962 to 1972 when about 2000 horses were removed over the span of the ten years. In 1994 the entire herd of over 1,200 horses, which at the time was the largest population of free-roaming horses in Canada, were removed from the Suffield military base on the Alberta-Saskatchewan border. In 1993, Alberta introduced the Horse Capture Regulation under the Stray Animals Act which regulates the capture of wild horses, with between 25 and 35 horses being captured each year.
However, during the 2011-12 capture season a record 216 horses were captured in Alberta. The Horse Capture Regulation expires on June 30, 2017. In Canada, except for Sable Island
The donkey or ass is a domesticated member of the horse family, Equidae. The wild ancestor of the donkey is the African wild ass, E. africanus. The donkey has been used as a working animal for at least 5000 years. There are more than 40 million donkeys in the world in underdeveloped countries, where they are used principally as draught or pack animals. Working donkeys are associated with those living at or below subsistence levels. Small numbers of donkeys are kept for breeding or as pets in developed countries. A male donkey or ass is called a female a jenny or jennet. Jack donkeys are used to mate with female horses to produce mules. Asses were first domesticated around 3000 BC in Egypt or Mesopotamia, have spread around the world, they continue to fill important roles in many places today. While domesticated species are increasing in numbers, the African wild ass is an endangered species; as beasts of burden and companions and donkeys have worked together with humans for millennia. Traditionally, the scientific name for the donkey is Equus asinus asinus based on the principle of priority used for scientific names of animals.
However, the International Commission on Zoological Nomenclature ruled in 2003 that if the domestic species and the wild species are considered subspecies of one another, the scientific name of the wild species has priority when that subspecies was described after the domestic subspecies. This means that the proper scientific name for the donkey is Equus africanus asinus when it is considered a subspecies, Equus asinus when it is considered a species. At one time, the synonym ass was the more common term for the donkey; the first recorded use of donkey was in either 1784 or 1785. While the word ass has cognates in most other Indo-European languages, donkey is an etymologically obscure word for which no credible cognate has been identified. Hypotheses on its derivation include the following: for its don-like gravity. From the name Duncan. Of imitative origin. From the 18th century, donkey replaced ass, jenny replaced she-ass, now considered archaic; the change may have come about through a tendency to avoid pejorative terms in speech, be comparable to the substitution in North American English of rooster for cock, or that of rabbit for coney, homophonic with cunny.
By the end of the 17th century, changes in pronunciation of both ass and arse had caused them to become homophones. Other words used for the ass in English from this time include cuddy in Scotland, neddy in southwest England and dicky in the southeast. Donkeys vary in size, depending on breed and management; the height at the withers ranges from 7.3 to 15.3 hands, the weight from 80 to 480 kg. Working donkeys in the poorest countries have a life expectancy of 12 to 15 years. Donkeys are adapted to marginal desert lands. Unlike wild and feral horses, wild donkeys in dry areas do not form harems; each adult donkey establishes a home range. The loud call or bray of the donkey, which lasts for twenty seconds and can be heard for over three kilometres, may help keep in contact with other donkeys over the wide spaces of the desert. Donkeys have large ears, which may pick up more distant sounds, may help cool the donkey's blood. Donkeys can defend themselves by biting, striking with the front hooves or kicking with the hind legs.
A jenny is pregnant for about 12 months, though the gestation period varies from 11 to 14 months, gives birth to a single foal. Births of twins are rare, though less so than in horses. About 1.7 percent of donkey pregnancies result in twins. In general jennies have a conception rate, lower than that of horses. Although jennies come into heat within 9 or 10 days of giving birth, their fertility remains low, it is the reproductive tract has not returned to normal, thus it is usual to wait one or two further oestrous cycles before rebreeding, unlike the practice with mares. Jennies are very protective of their foals, some will not come into estrus while they have a foal at side; the time lapse involved in rebreeding, the length of a jenny's gestation, means that a jenny will have fewer than one foal per year. Because of this and the longer gestation period, donkey breeders do not expect to obtain a foal every year, as horse breeders do, but may plan for three foals in four years. Donkeys can interbreed with other members of the family Equidae, are interbred with horses.
The hybrid between a jack and a mare is a mule, valued as a working and riding animal in many countries. Some large donkey breeds such as the Asino di Martina Franca, the Baudet de Poitou and the Mammoth Jack are raised only for mule production; the hybrid between a stallion and a jenny is a hinny, is less common. Like other inter-species hybrids and hinnies are sterile. Donkeys can breed with zebras in which the offspring is called a zonkey. Donkeys have a notorious reputation for stubbornness, but this has been attributed to a much stronger sense of self-preservation than exhibited by
Alberta is a western province of Canada. With an estimated population of 4,067,175 as of 2016 census, it is Canada's fourth most populous province and the most populous of Canada's three prairie provinces, its area is about 660,000 square kilometres. Alberta and its neighbour Saskatchewan were districts of the Northwest Territories until they were established as provinces on September 1, 1905; the premier has been Rachel Notley since May 2015. Alberta is bounded by the provinces of British Columbia to the west and Saskatchewan to the east, the Northwest Territories to the north, the U. S. state of Montana to the south. Alberta is one of three Canadian provinces and territories to border only a single U. S. state and one of only two landlocked provinces. It has a predominantly humid continental climate, with stark contrasts over a year. Alberta's capital, Edmonton, is near the geographic centre of the province and is the primary supply and service hub for Canada's crude oil, the Athabasca oil sands and other northern resource industries.
About 290 km south of the capital is the largest city in Alberta. Calgary and Edmonton centre Alberta's two census metropolitan areas, both of which have populations exceeding one million, while the province has 16 census agglomerations. Tourist destinations in the province include Banff, Drumheller, Sylvan Lake and Lake Louise. Alberta is named after the fourth daughter of Queen Victoria. Princess Louise was the wife of Marquess of Lorne, Governor General of Canada. Lake Louise and Mount Alberta were named in her honour. Alberta, with an area of 661,848 km2, is the fourth-largest province after Quebec and British Columbia. To the south, the province borders on the 49th parallel north, separating it from the U. S. state of Montana, while to the north the 60th parallel north divides it from the Northwest Territories. To the east, the 110th meridian west separates it from the province of Saskatchewan, while on the west its boundary with British Columbia follows the 120th meridian west south from the Northwest Territories at 60°N until it reaches the Continental Divide at the Rocky Mountains, from that point follows the line of peaks marking the Continental Divide in a southeasterly direction until it reaches the Montana border at 49°N.
The province extends 660 km east to west at its maximum width. Its highest point is 3,747 m at the summit of Mount Columbia in the Rocky Mountains along the southwest border while its lowest point is 152 m on the Slave River in Wood Buffalo National Park in the northeast. With the exception of the semi-arid steppe of the south-eastern section, the province has adequate water resources. There are numerous lakes used for swimming, fishing and a range of water sports. There are three large lakes, Lake Claire in Wood Buffalo National Park, Lesser Slave Lake, Lake Athabasca which lies in both Alberta and Saskatchewan; the longest river in the province is the Athabasca River which travels 1,538 km from the Columbia Icefield in the Rocky Mountains to Lake Athabasca. The largest river is the Peace River with an average flow of 2161 m3/s; the Peace River originates in the Rocky Mountains of northern British Columbia and flows through northern Alberta and into the Slave River, a tributary of the Mackenzie River.
Alberta's capital city, Edmonton, is located at about the geographic centre of the province. It is the most northerly major city in Canada, serves as a gateway and hub for resource development in northern Canada; the region, with its proximity to Canada's largest oil fields, has most of western Canada's oil refinery capacity. Calgary is about 280 km south of Edmonton and 240 km north of Montana, surrounded by extensive ranching country. 75% of the province's population lives in the Calgary–Edmonton Corridor. The land grant policy to the railroads served as a means to populate the province in its early years. Most of the northern half of the province is boreal forest, while the Rocky Mountains along the southwestern boundary are forested; the southern quarter of the province is prairie, ranging from shortgrass prairie in the southeastern corner to mixed grass prairie in an arc to the west and north of it. The central aspen parkland region extending in a broad arc between the prairies and the forests, from Calgary, north to Edmonton, east to Lloydminster, contains the most fertile soil in the province and most of the population.
Much of the unforested part of Alberta is given over either to grain or to dairy farming, with mixed farming more common in the north and centre, while ranching and irrigated agriculture predominate in the south. The Alberta badlands are located in southeastern Alberta, where the Red Deer River crosses the flat prairie and farmland, features deep canyons and striking landforms. Dinosaur Provincial Park, near Brooks, showcases the badlands terrain, desert flora, remnants from Alberta's past when dinosaurs roamed the lush landscape. Alberta has a humid continental climate with cold winters; the province is open to cold arctic weather systems from the north, which produce cold conditions in winter. As the fronts between the air masses shift north and south across Alberta, the temperature can change rapidly. Arctic
The Chincoteague Pony known as the Assateague horse, is a breed of horse that developed and lives in a feral condition on Assateague Island in the United States states of Virginia and Maryland. The breed was made famous by the Misty of Chincoteague series of novels written by Marguerite Henry starting in 1947. While phenotypically horse-like, they are called "ponies"; this is due in part to their smaller stature, created by the poor habitat on Assateague Island. Variation is found in their physical characteristics due to blood from different breeds being introduced at various points in their history, they can be any solid color, are found in pinto patterns, which are a favorite with breed enthusiasts. Island Chincoteagues live on a diet of brush; this poor-quality and scarce food combined with uncontrolled inbreeding created a propensity for conformation faults in the Chincoteague before outside blood was added beginning in the early 20th century. Several legends are told regarding the origins of the Chincoteague ponies, the most popular holds that they descend from survivors of wrecked Spanish galleons off the Virginia coast.
It is more that they descend from stock released on the island by 17th-century colonists looking to escape livestock laws and taxes on the mainland. In 1835, the practice of pony penning began, with local residents rounding up ponies and removing some of them to the mainland. In 1924 the first official "Pony Penning Day" was held by the Chincoteague Volunteer Fire Company, where ponies were auctioned as a way to raise money for fire equipment; the annual event has continued in the same fashion uninterrupted to the present day. Although popularly known as Chincoteague ponies, the feral ponies live on Assateague Island; the entire Island is owned by the federal government and is split by a fence at the Maryland/Virginia state line, with a herd of around 150 ponies living on each side of the fence. The herds live on land managed by two different federal agencies with different management strategies. Ponies from the Maryland herd, referred to in literature of the National Park Service as Assateague horses, live within Assateague Island National Seashore.
They are treated as wild animals, given no more or less assistance than other species on the island, other than to be treated with contraceptives to prevent overpopulation. Conversely, the Virginia herd, referred to as Chincoteague ponies, lives within the Chincoteague National Wildlife Refuge but is owned by the Chincoteague Volunteer Fire Company; the Virginia ponies are treated to twice yearly veterinary inspections, which prepare them for life among the general equine population, if they are sold at auction. While only around 300 ponies live on Assateague Island, around 1,000 more live off-island, having been purchased or bred by private breeders. While phenotypically horses, the Chincoteague is most referred to as a pony breed. Chincoteagues average around 13.2 hands in their feral state, but grow to at least 14.2 hands when domesticated and provided better nutrition. They weigh around 850 pounds. All solid colors are found in the breed. Horses with pinto coloration tend to sell for the most money at the annual auction.
Due to outside bloodlines being added to the Chincoteague herd, there is some variation in physical characteristics. In general, the breed tends to have a straight or concave facial profile with a broad forehead and refined throatlatch and neck; the shoulders are well angled, the ribs well sprung, the chest broad and the back short with broad loins. The croup is rounded, with a low-set tail; the breed's legs tend to be straight, with dense bone that makes them sound and sturdy. Domesticated Chincoteagues are considered willing to please, they are viewed as easy to train, are used as hunter and trail ponies. In terms of health, they are hardy and easy keepers. In the late 19th century, one author praised their "good manners and gentle disposition" while reporting the story of one pony, ridden a distance of around 1,000 miles in 34 days by a man with equipment, a load that weighed around 160 pounds —the pony weighed 500 pounds. Legend states that Chincoteague ponies descend from Spanish horses shipwrecked off the Virginia coast on their way to Peru in the 16th century.
Another story holds. Both of these theories are unlikely, as no documentation has been found to show horses inhabiting the island this early, no mention of horses existing on the island was made by colonists on either the mainland or the island in the mid-to-late 1600s. Evidence points, however, to their ancestors being horses brought to the islands in the 17th century by mainland farmers. Livestock on the islands were not subject to taxes or fencing laws, so many animals, including hogs, sheep and horses, were brought to the islands. While the National Park Service holds to the theory that the horses were brought to the island in the 17th century, the Chincoteague Volunteer Fire Company, which owns the ponies on the Virginia side of Assateague, argues that the Spanish shipwreck theory is correct, they argue that horses were too valuable in the 17th century to have been left to run wild on the island, claim that there are two sunken Spanish galleons off the Virginia coast in support of their theory.
The National Chincoteague Pony Association promotes the shipwreck theory. In the early 1900s, they were described as having been on the islands since well before the American Revolution, were described at that time as "v
A stallion is a male horse that has not been gelded. Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, "cresty" neck, as well as a somewhat more muscular physique as compared to female horses, known as mares, castrated males, called geldings. Temperament varies based on genetics, training, but because of their instincts as herd animals, they may be prone to aggressive behavior toward other stallions, thus require careful management by knowledgeable handlers. However, with proper training and management, stallions are effective equine athletes at the highest levels of many disciplines, including horse racing, horse shows, international Olympic competition; the term "stallion" dates from the era of Henry VII, who passed a number of laws relating to the breeding and export of horses in an attempt to improve the British stock, under which it was forbidden to allow uncastrated male horses to be turned out in fields or on the commons.
"Stallion" is used to refer to males of other equids, including zebras and donkeys. Contrary to popular myths, many stallions do not live with a harem of mares. Nor, in natural settings, do they fight each other to the death in competition for mares. Being social animals, stallions who are not able to find or win a harem of mares band together in stallions-only "bachelor" groups which are composed of stallions of all ages. With a band of mares, the stallion is not the leader of a herd but defends and protects the herd from predators and other stallions; the leadership role in a herd is held by a mare, known colloquially as the "lead mare" or "boss mare." The mare determines the movement of the herd as it travels to obtain food and shelter. She determines the route the herd takes when fleeing from danger; when the herd is in motion, the dominant stallion herds the straggling members closer to the group and acts as a "rear guard" between the herd and a potential source of danger. When the herd is at rest, all members share the responsibility of keeping watch for danger.
The stallion is on the edge of the group, to defend the herd if needed. There is one dominant mature stallion for every mixed-sex herd of horses; the dominant stallion in the herd will tolerate both sexes of horses while young, but once they become sexually mature as yearlings or two-year-olds, the stallion will drive both colts and fillies from the herd. Colts may present competition for the stallion, but studies suggest that driving off young horses of both sexes may be an instinctive behavior that minimizes the risk of inbreeding within the herd, as most young are the offspring of the dominant stallion in the group. In some cases, a single younger mature male may be tolerated on the fringes of the herd. One theory is that this young male is considered a potential successor, as in time the younger stallion will drive out the older herd stallion. Fillies soon join a different band with a dominant stallion different from the one that sired them. Colts or young stallions without mares of their own form small, all-male, "bachelor bands" in the wild.
Living in a group gives these stallions the protective benefits of living in a herd. A bachelor herd may contain older stallions who have lost their herd in a challenge. Other stallions may directly challenge a herd stallion, or may attempt to "steal" mares and form a new, smaller herd. In either case, if the two stallions meet, there is a true fight. If a fight for dominance occurs do opponents hurt each other in the wild because the weaker combatant has a chance to flee. Fights between stallions in captivity may result in serious injuries. In the wild, feral stallions have been known to mate with domesticated mares; the stallion's reproductive system is responsible for his sexual behavior and secondary sex characteristics. The external genitalia comprise: the testes; the testes of an average stallion are ovoids 8 to 12 cm long, 6 to 7 cm high by 5 cm wide. Stallions have a vascular penis; when non-erect, it is quite flaccid and contained within the prepuce. The retractor penis muscle is underdeveloped.
Erection and protrusion take place by the increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis. When not erect, the penis is housed within the prepuce, 50 cm long and 2.5 to 6 cm in diameter with the distal end 15 to 20 cm. The retractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath; when erect, the penis doubles in length and thickness and the glans increases by 3 to 4 times. The urethra opens within a small pouch at the distal end of the glans. A structure called the urethral process projects beyond the glans; the internal genitalia comprise the accessory sex glands, which include the vesicular glands, the prostate gland and the bulbourethral glands. These contribute fluid to the semen at ejaculation, but are not necessary for fertility. Domesticated stallions are trained and managed in a variety of ways, depending on the region of the w