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Domestication of the horse

How and when horses became domesticated has been disputed. Although horses appeared in Paleolithic cave art as early as 30,000 BC, these were wild horses and were probably hunted for meat. The clearest evidence of early use of the horse as a means of transport is from chariot burials dated c. 2000 BC. However, an increasing amount of evidence began to support the hypothesis that horses were domesticated in the Eurasian Steppes in approximately 3500 BC. Discoveries in the context of the Botai culture had suggested that Botai settlements in the Akmola Province of Kazakhstan are the location of the earliest domestication of the horse. Warmouth et al. (2012) pointed to horses having been domesticated around 3000 BC in what is now Ukraine and Western Kazakhstan.

Genetic evidence indicates that domestication of the modern horse's ancestors likely occurred in an area known as the Volga–Don, in the Pontic–Caspian steppe region of eastern Europe, around 2200 BC. From there, use of horses spread across Eurasia for transportation, agricultural work, and warfare. Scientists have linked the successful spread of domesticated horses to observed genetic changes. They speculate that stronger backs (GSDMC gene) and increased docility (ZFPM1 gene) may have made horses more suitable for riding.

Background

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; weapons, art, and spiritual artifacts; and lifestyle patterns of human cultures. There is evidence that horses were kept as a source of meat and milk before they were trained as working animals.

Attempts to date domestication by genetic study or analysis of physical remains rest 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 (which will occur naturally as long as the domesticated population is kept within the habitat of the wild population).

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 the 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, and the appearance of horse bones in human graves. On the other hand, measurable changes in size and increases in variability associated with domestication occurred later, 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 transportation, agricultural work and warfare. Horses and mules in agriculture used a breastplate type harness or a yoke more suitable for oxen, which was not as efficient at utilizing the full strength of the animals as the later-invented padded horse collar that arose several millennia later.

Predecessors to the domestic horse

A 2005 study analyzed the mitochondrial DNA (mtDNA) 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: the South American Hippidion, the North American New World stilt-legged horse, and Equus, the true horse. The true horse included prehistoric horses and the Przewalski's horse, as well as what is now the modern domestic horse, belonged to a single Holarctic species.

The true horse migrated from the Americas to Eurasia via Beringia, becoming broadly distributed from North America to central Europe, north and south of Pleistocene ice sheets. It became extinct in Beringia around 14,200 years ago, and in the rest of the Americas around 10,000 years ago. This clade survived in Eurasia, however, and it is from these horses which all domestic horses appear to have descended. These horses showed little phylogeographic structure, probably reflecting their high degree of mobility and adaptability.

Therefore, the domestic horse today is classified as Equus ferus caballus. No genetic originals of native wild horses currently exist. The Przewalski diverged from the modern horse before domestication. It has 66 chromosomes, as opposed to 64 among modern domesticated horses, and their Mitochondrial DNA (mtDNA) 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. Nevertheless, evidence such as the cave paintings of Lascaux suggests that the ancient wild horses that some researchers now label the "Tarpan subtype" probably resembled Przewalski horses in their general appearance: big heads, dun coloration, thick necks, stiff upright manes, and relatively 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, particularly in North America, where the horse became completely extinct.

Classification based on body types and conformation, before the availability of DNA for research, once suggested that there were roughly four basic wild prototypes, thought to have developed with adaptations to their environment before domestication. There were competing theories: some argued that the four prototypes were separate species or subspecies, while others suggested that the prototypes were physically different manifestations of the same species. However, more recent study indicates that there was only one wild species and all different body types were entirely a result of selective breeding or landrace adaptation after domestication. Either way, the most common theories of prototypes include four base prototypes:
 * The "Tarpan subtype"
 * The "Warmblood subspecies" or "Forest Horse" (once proposed as Equus ferus silvaticus, also known as the Diluvial Horse), which evolved into a later variety sometimes called Equus ferus germanicus. This prototype may have contributed to the development of the warmblood horses of northern Europe, as well as older "heavy horses" such as the Ardennais.
 * The "Draft" subspecies, a small, sturdy, heavyset animal with a heavy hair coat, arising in northern Europe, adapted to cold, damp climates, somewhat resembling today's draft horse and even the Shetland pony.
 * The "Oriental" subspecies (once proposed as Equus agilis), a taller, slim, refined and agile animal arising in Western Asia, adapted to hot, dry climates. It is thought to be the progenitor of the modern Arabian horse and Akhal-Teke.

Two "wild" groups, that were believed to be never-domesticated, survived into historic times: Przewalski's horse (Equus ferus przewalski), and the Tarpan (Equus ferus ferus). The Tarpan became extinct in the late 19th century and Przewalski's horse is endangered; it became extinct in the wild during the late 1960s, but was re-introduced in the early 1990s to two preserves in Mongolia. Although researchers such as Marija Gimbutas theorized that the horses of the Chalcolithic (Copper Age) were Przewalski's, more recent genetic studies indicate that Przewalski's horse is not an ancestor to modern domesticated horses.

Genetic evidence

A 2014 study compared DNA from ancient horse bones that predated domestication and compared them to DNA of modern horses, discovering 125 genes that correlated to domestication. Some were physical, affecting muscle and limb development, cardiac strength and balance. Others were linked to cognitive function and most likely were critical to the taming of the horse, including social behavior, learning capabilities, fear response, and agreeableness. The DNA used in this study came from horse bones 16,000 to 43,000 years ago, and therefore the precise changes that occurred at the time of domestication have yet to be sequenced.

The domestication of stallions and mares can be analyzed separately by looking at those portions of the DNA that are passed on exclusively along the maternal (mitochondrial DNA or mtDNA) or paternal line (Y-chromosome or Y-DNA). DNA studies indicate that there may have been multiple domestication events for mares, as the number of female lines required to account for the genetic diversity of the modern horse suggests a minimum of 77 different ancestral mares, divided into 17 distinct lineages. Studies of modern horses showed very little Y chromosome diversity, which was originally interpreted as evidence of a single domestication event for a limited number of stallions combined with repeated restocking of wild females into the domesticated herds. However, more recent studies of ancient DNA show that Y chromosome diversity was significantly higher a thousand years ago. The low present diversity may be partially explained by the popularity of Arabian and Turkoman studs, especially the three foundation stallions of the Thoroughbred breed.

A study published in 2012 that performed genomic sampling on 300 work horses from local areas as well as a review of previous studies of archaeology, mitochondrial DNA, and Y-DNA suggested that horses were originally domesticated in the western part of the Eurasian steppe. Both domesticated stallions and mares spread out from this area, and then additional wild mares were added from local herds; wild mares were easier to handle than wild stallions. Most other parts of the world were ruled out as sites for horse domestication, either due to climate unsuitable for an indigenous wild horse population or no evidence of domestication.

Genes located on the Y-chromosome are inherited only from sire to its male offspring and these lines show a very reduced degree of genetic variation (aka genetic homogeneity) in modern domestic horses, far less than expected based on the overall genetic variation in the remaining genetic material. This indicates that a relatively few stallions were domesticated and that it is unlikely that many male offspring originating from unions between wild stallions and domestic mares were included in early domesticated breeding stock.

Genes located in the mitochondrial DNA are passed on along the maternal line from the mother to her offspring. Multiple analyses of the mitochondrial DNA obtained from modern horses as well as from horse bones and teeth from archaeological and palaeological finds consistently shows an increased genetic diversity in the mitochondrial DNA compared to the remaining DNA, showing that a large number of mares has been included into the breeding stock of the originally domesticated horse.

Variation in the mitochondrial DNA is used to determine so-called haplogroups. A haplogroup is a group of closely related haplotypes that share the same common ancestor. In horses, eighteen main haplogroups are recognized (A-R). Several haplogroups are unequally distributed around the world, indicating the addition of local wild mares to the domesticated stock. In 2018, genomic comparison of 42 ancient-horse genomes, 20 of which were from Botai, with 46 published ancient and modern-horse genomes yielded surprising results. It was found that modern domestic horses are not closely related to the horses at Botai. Rather, Przewalski’s horses were identified as feral descendants of horses herded at Botai. Evidence suggested that "a massive genomic turnover" had occurred along with the domestication of horses and large-scale human population expansion in the Early Bronze Age. Subsequent research showed that horse lineages from Iberia and Siberia, also associated with early domestication, had little influence on the genetics of modern domestic horses.

More than 150 scientists collaborated in gathering 264 ancient horse genomes from across Eurasia, dating from 50,000 to 200 B.C.E. In October 2021, results of the analysis were published in Nature. They indicated that domestication of the modern horse's ancestors likely occurred in the Volga-Don region of the Pontic–Caspian steppe grasslands of Western Eurasia. Both Tarpan and Przewalski’s horse were related to different ancestral populations than those underlying the modern domestic horses (DOM2).

In addition, researchers were able to map population changes over time as modern domestic horses expanded rapidly across Eurasia and displaced other local populations, from about 2000 BCE onwards. The genetic profile for DOM2 horses is associated with horses buried in Sintashta kurgans with early spoke-wheeled chariots, and with horses in Central Anatolia where two-wheeled vehicles were depicted. DOM2 horses also occur in some areas prior to the earliest evidence for chariots, suggesting that both horseback riding and chariot use were factors in expansion.

Genetic data may also provide clues as to why this particular domestication event had far more widespread impact than other domestication events in Botai, Iberia, SIberia and Anatolia. The genetic lineage that leads to modern domestic horses shows evidence of strong selection for locomotor and behavioural adaptations. Changes relate to the GSDMC gene and the ZFPM1 gene. The GSDMC gene is linked to back problems in people, and scientists speculate that changes may have made horses' backs stronger. The ZFPM1 gene is related to mood regulation, and scientists speculate that this may have made horses more docile and easier to tame and manage. Strength and docility would have made horses more suitable for riding and other uses.

Archaeological evidence
Archaeological evidence for the domestication of the horse comes from three kinds of sources: 1) changes in the skeletons and teeth of ancient horses; 2) changes in the geographic distribution of ancient horses, particularly the introduction of horses into regions where no wild horses had existed; and 3) archaeological sites containing artifacts, images, or evidence of changes in human behavior connected with horses.

Examples include horse remains interred in human graves; changes in the ages and sexes of the horses killed by humans; the appearance of horse corrals; equipment such as bits or other types of horse tack; horses interred with equipment intended for use by horses, such as chariots; and depictions of horses used for riding, driving, draught work, or symbols of human power.

Few of these categories, taken alone, provide irrefutable evidence of domestication, but the cumulative evidence becomes increasingly more persuasive.

Horses interred with chariots
The least ancient, but most persuasive, evidence of domestication comes from sites where horse leg bones and skulls, probably originally attached to hides, were interred with the remains of chariots in at least 16 graves of the Sintashta and Petrovka cultures. These were located in the steppes southeast of the Ural Mountains, between the upper Ural and upper Tobol Rivers, a region today divided between southern Russia and northern Kazakhstan. Petrovka was a little later than and probably grew out of Sintashta, and the two complexes together spanned about 2100–1700 BCE. A few of these graves contained the remains of as many as eight sacrificed horses placed in, above, and beside the grave.

In all of the dated chariot graves, the heads and hooves of a pair of horses were placed in a grave that once contained a chariot. Evidence of chariots in these graves was inferred from the impressions of two spoked wheels set in grave floors 1.2–1.6m apart; in most cases the rest of the vehicle left no trace. In addition, a pair of disk-shaped antler "cheekpieces," an ancient predecessor to a modern bit shank or bit ring, were placed in pairs beside each horse head-and-hoof sacrifice. The inner faces of the disks had protruding prongs or studs that would have pressed against the horse's lips when the reins were pulled on the opposite side. Studded cheekpieces were a new and fairly severe kind of control device that appeared simultaneously with chariots.

All of the dated chariot graves contained wheel impressions, horse bones, weapons (arrow and javelin points, axes, daggers, or stone mace-heads), human skeletal remains, and cheekpieces. Because they were buried in teams of two with chariots and studded cheekpieces, the evidence is extremely persuasive that these steppe horses of 2100–1700 BCE were domesticated. Shortly after the period of these burials, the expansion of the domestic horse throughout Europe was little short of explosive. In the space of possibly 500 years, there is evidence of horse-drawn chariots in Greece, Egypt, and Mesopotamia. By another 500 years, the horse-drawn chariot had spread to China.

Skeletal indicators of domestication
Some researchers do not consider an animal to be "domesticated" until it exhibits physical changes consistent with selective breeding, or at least having been born and raised entirely in captivity. Until that point, they classify captive animals as merely "tamed". Those who hold to this theory of domestication point to a change in skeletal measurements detected among horse bones recovered from middens dated about 2500 BCE in eastern Hungary in Bell-Beaker sites, and in later Bronze Age sites in the Russian steppes, Spain, and Eastern Europe. Horse bones from these contexts exhibited an increase in variability, thought to reflect the survival under human care of both larger and smaller individuals than appeared in the wild; and a decrease in average size, thought to reflect penning and restriction in diet. Horse populations that showed this combination of skeletal changes probably were domesticated. Most evidence suggests that horses were increasingly controlled by humans after about 2500 BCE. However, more recently there have been skeletal remains found at a site in Kazakhstan which display the smaller, more slender limbs characteristic of corralled animals, dated to 3500 BCE.

Botai culture
Some of the most intriguing evidence of early domestication comes from the Botai culture, found in northern Kazakhstan. The Botai culture was a culture of foragers who seem to have adopted horseback riding in order to hunt the abundant wild horses of northern Kazakhstan between 3500 and 3000 BCE. Botai sites had no cattle or sheep bones; the only domesticated animals, in addition to horses, were dogs. Botai settlements in this period contained between 50 and 150 pit houses. Garbage deposits contained tens to hundreds of thousands of discarded animal bones, 65% to 99% of which had come from horses. Also, there has been evidence found of horse milking at these sites, with horse milk fats soaked into pottery shards dating to 3500 BCE. Earlier hunter-gatherers who lived in the same region had not hunted wild horses with such success, and lived for millennia in smaller, more shifting settlements, often containing less than 200 wild animal bones.

Entire herds of horses were slaughtered by the Botai hunters, apparently in hunting drives. The adoption of horseback riding might explain the emergence of specialized horse-hunting techniques and larger, more permanent settlements. Domesticated horses could have been adopted from neighboring herding societies in the steppes west of the Ural Mountains, where the Khvalynsk culture had herds of cattle and sheep, and perhaps had domesticated horses, as early as 4800 BCE.

Other researchers have argued that all of the Botai horses were wild, and that the horse-hunters of Botai hunted wild horses on foot. As evidence, they note that zoologists have found no skeletal changes in the Botai horses that indicate domestication. Moreover, because they were hunted for food, the majority of the horse remains found in Botai-culture settlements indeed probably were wild. On the other hand, any domesticated riding horses were probably the same size as their wild cousins and cannot now be distinguished by bone measurements. They also note that the age structure of the horses slaughtered at Botai represents a natural demographic profile for hunted animals, not the pattern expected if they were domesticated and selected for slaughter. However, these arguments were published before a Copper Age corral was discovered at Krasnyi Yar in 2006 and mats of horse-dung at two other Botai sites. Current findings continue to support the Botai as having domesticated horses.

A study in 2018 revealed that the Botai horses did not contribute significantly to the genetics of modern domesticated horses, and that therefore a subsequent and separate domestication event must have been responsible for the modern domestic horse. Genetic evidence also connects Botai horses with Przewalski's horse in Mongolia, which has led to debates over whether Przewalski's horses should be considered a never-domesticated population or feral descendants of domesticated Botai horses.

Bit wear

The presence of bit wear is an indicator that a horse was ridden or driven, and the earliest of such evidence from a site in Kazakhstan dates to 3500 BCE. The absence of bit wear on horse teeth is not conclusive evidence against domestication because horses can be ridden and controlled without bits by using a noseband or a hackamore, but such materials do not produce significant physiological changes nor are they apt to be preserved for millennia.

The regular use of a bit to control a horse can create wear facets or bevels on the anterior corners of the lower second premolars. The corners of the horse's mouth normally keep the bit on the "bars" of the mouth, an interdental space where there are no teeth, forward of the premolars. The bit must be manipulated by a human or the horse must move it with its tongue for it to touch the teeth. Wear can be caused by the bit abrading the front corners of the premolars if the horse grasps and releases the bit between its teeth; other wear can be created by the bit striking the vertical front edge of the lower premolars, due to very strong pressure from a human handler.

Modern experiments showed that even organic bits of rope or leather can create significant wear facets, and also showed that facets 3mm (.118 in) deep or more do not appear on the premolars of wild horses. However, other researchers disputed both conclusions.

Wear facets of 3 mm or more were found on seven horse premolars in two sites of the Botai culture, Botai and Kozhai 1, dated about 3500–3000 BCE. The Botai culture premolars are the earliest reported multiple examples of this dental pathology in any archaeological site, and preceded any skeletal change indicators by 1,000 years. While wear facets more than 3 mm deep were discovered on the lower second premolars of a single stallion from Dereivka in Ukraine, an Eneolithic settlement dated about 4000 BCE, dental material from one of the worn teeth later produced a radiocarbon date of 700–200 BCE, indicating that this stallion was actually deposited in a pit dug into the older Eneolithic site during the Iron Age.

Dung and corrals
Soil scientists working with Sandra Olsen of the Carnegie Museum of Natural History at the Chalcolithic settlements of Botai and Krasnyi Yar in northern Kazakhstan found layers of horse dung, discarded in unused house pits in both settlements. The collection and disposal of horse dung suggests that horses were confined in corrals or stables. An actual corral, dated to 3500–3000 BCE was identified at Krasnyi Yar by a pattern of post holes for a circular fence, with the soils inside the fence yielding ten times more phosphorus than the soils outside. The phosphorus could represent the remains of manure.

Geographic expansion
The appearance of horse remains in human settlements in regions where they had not previously been present is another indicator of domestication. Although images of horses appear as early as the Upper Paleolithic period in places such as the caves of Lascaux, France, suggesting that wild horses lived in regions outside of the Eurasian steppes before domestication and may have even been hunted by early humans, concentration of remains suggests animals being deliberately captured and contained, an indicator of domestication, at least for food, if not necessarily use as a working animal.

Around 3500–3000 BCE, horse bones began to appear more frequently in archaeological sites beyond their center of distribution in the Eurasian steppes and were seen in central Europe, the middle and lower Danube valley, and the North Caucasus and Transcaucasia. Evidence of horses in these areas had been rare before, and as numbers increased, larger animals also began to appear in horse remains. This expansion in range was contemporary with the Botai culture, where there are indications that horses were corralled and ridden. This does not necessarily mean that horses were first domesticated in the steppes, but the horse-hunters of the steppes certainly pursued wild horses more than in any other region.

European wild horses were hunted for up to 10% of the animal bones in a handful of Mesolithic and Neolithic settlements scattered across Spain, France, and the marshlands of northern Germany, but in many other parts of Europe, including Greece, the Balkans, the British Isles, and much of central Europe, horse bones do not occur or occur very rarely in Mesolithic, Neolithic or Chalcolithic sites. In contrast, wild horse bones regularly exceeded 40% of the identified animal bones in Mesolithic and Neolithic camps in the Eurasian steppes, west of the Ural Mountains.

Horse bones were rare or absent in Neolithic and Chalcolithic kitchen garbage in western Turkey, Mesopotamia, most of Iran, South and Central Asia, and much of Europe. While horse bones have been identified in Neolithic sites in central Turkey, all equids together totaled less than 3% of the animal bones. Within this three percent, horses were less than 10%, with 90% or more of the equids represented by onagers (Equus hemionus) or another ass-like equid that later became extinct, the hydruntine or European wild ass (Equus hydruntinus). Onagers were the most common native wild equids of the Near East. They were hunted in Syria, Anatolia, Mesopotamia, Iran, and Central Asia; and domesticated asses (Equus asinus) were imported into Mesopotamia, probably from Egypt, but wild horses apparently did not live there.

Other evidence of geographic expansion
In Northern Caucasus, the Maikop culture settlements and burials of c. 3300 BC contain both horse bones and images of horses. A frieze of nineteen horses painted in black and red colors is found in one of the Maikop graves. The widespread appearance of horse bones and images in Maikop sites suggest to some observers that horseback riding began in the Maikop period.

Later, images of horses, identified by their short ears, flowing manes, and tails that bushed out at the dock, began to appear in artistic media in Mesopotamia during the Akkadian period, 2300–2100 BCE. The word for "horse", literally translated as ass of the mountains, first appeared in Sumerian documents during the Third dynasty of Ur, about 2100–2000 BCE. The kings of the Third Dynasty of Ur apparently fed horses to lions for royal entertainment, perhaps indicating that horses were still regarded as more exotic than useful, but King Shulgi, about 2050 BCE, compared himself to "a horse of the highway that swishes its tail", and one image from his reign showed a man apparently riding a horse at full gallop. Horses were imported into Mesopotamia and the lowland Near East in larger numbers after 2000 BCE in connection with the beginning of chariot warfare, replacing the long-established kunga (a hybrid between the now-extinct Syrian wild ass and a domestic donkey) as the main equid for warfare.

A further expansion, into the lowland Near East and northwestern China, also happened around 2000 BCE. Although Equus bones of uncertain species are found in some Late Neolithic sites in China dated before 2000 BCE, Equus caballus or Equus ferus bones first appeared in multiple sites and in significant numbers in sites of the Qijia and Siba cultures, 2000–1600 BCE, in Gansu and the northwestern provinces of China. Skeletal evidence from sites in Shirenzigou and Xigou in eastern Xinjiang indicate that by the fourth century BCE both horseback riding and mounted archery were practiced along China’s northwest frontier.

In 2008, archaeologists announced the discovery of rock art in Somalia's northern Dhambalin region, which the researchers suggest is one of the earliest known depictions of a hunter on horseback. The rock art is in the Ethiopian-Arabian style, dated to 1000 to 3000 BCE.

Horse images as symbols of power
About 4200-4000 BCE, more than 500 years before the geographic expansion evidenced by the presence of horse bones, new kinds of graves, named after a grave at Suvorovo, appeared north of the Danube delta in the coastal steppes of Ukraine near Izmail. Suvorovo graves were similar to and probably derived from earlier funeral traditions in the steppes around the Dnieper River. Some Suvorovo graves contained polished stone mace-heads shaped like horse heads and horse tooth beads. Earlier steppe graves also had contained polished stone mace-heads, some of them carved in the shape of animal heads. Settlements in the steppes contemporary with Suvorovo, such as Sredni Stog II and Dereivka on the Dnieper River, contained 12–52% horse bones.

When Suvorovo graves appeared in the Danube delta grasslands, horse-head maces also appeared in some of the indigenous farming towns of the Trypillia and Gumelnitsa cultures in present-day Romania and Moldova, near the Suvorovo graves. These agricultural cultures had not previously used polished-stone maces, and horse bones were rare or absent in their settlement sites. Probably their horse-head maces came from the Suvorovo immigrants. The Suvorovo people in turn acquired many copper ornaments from the Trypillia and Gumelnitsa towns. After this episode of contact and trade, but still during the period 4200–4000 BCE, about 600 agricultural towns in the Balkans and the lower Danube valley, some of which had been occupied for 2000 years, were abandoned. Copper mining ceased in the Balkan copper mines, and the cultural traditions associated with the agricultural towns were terminated in the Balkans and the lower Danube valley. This collapse of "Old Europe" has been attributed to the immigration of mounted Indo-European warriors. The collapse could have been caused by intensified warfare, for which there is some evidence; and warfare could have been worsened by mounted raiding; and the horse-head maces have been interpreted as indicating the introduction of domesticated horses and riding just before the collapse.

However, mounted raiding is just one possible explanation for this complex event. Environmental deterioration, ecological degradation from millennia of farming, and the exhaustion of easily mined oxide copper ores also are cited as causal factors.

Artifacts
Perforated antler objects discovered at Derievka (mistakenly, Dereivka) and other sites contemporary with Suvorovo have been identified as cheekpieces or psalia for horse bits. This identification is no longer widely accepted, as the objects in question have not been found associated with horse bones, and could have had a variety of other functions. However, through studies of microscopic wear, it has been established that many of the bone tools at Botai were used to smooth rawhide thongs, and rawhide thongs might have been used to manufacture of rawhide cords and ropes, useful for horse tack. Similar bone thong-smoothers are known from many other steppe settlements, but it cannot be known how the thongs were used. The oldest artifacts clearly identified as horse tack—bits, bridles, cheekpieces, or any other kind of horse gear—are the antler disk-shaped cheekpieces associated with the invention of the chariot, at the Sintashta-Petrovka sites.

Horses interred in human graves
The oldest possible archaeological indicator of a changed relationship between horses and humans is the appearance about 4800–4400 BCE of horse bones and carved images of horses in Chalcolithic graves of the early Khvalynsk culture and the Samara culture in the middle Volga region of Russia. At the Khvalynsk cemetery near the town of Khvalynsk, 158 graves of this period were excavated. Of these, 26 graves contained parts of sacrificed domestic animals, and additional sacrifices occurred in ritual deposits on the original ground surface above the graves. Ten graves contained parts of lower horse legs; two of these also contained the bones of domesticated cattle and sheep. At least 52 domesticated sheep or goats, 23 domesticated cattle, and 11 horses were sacrificed at Khvalynsk. The inclusion of horses with cattle and sheep and the exclusion of obviously wild animals together suggest that horses were categorized symbolically with domesticated animals.

At S'yezzhe, a contemporary cemetery of the Samara culture, parts of two horses were placed above a group of human graves. The pair of horses here was represented by the head and hooves, probably originally attached to hides. The same ritual—using the hide with the head and lower leg bones as a symbol for the whole animal—was used for many domesticated cattle and sheep sacrifices at Khvalynsk. Horse images carved from bone were placed in the above-ground ochre deposit at S’yezzhe and occurred at several other sites of the same period in the middle and lower Volga region. Together these archaeological clues suggest that horses had a symbolic importance in the Khvalynsk and Samara cultures that they had lacked earlier, and that they were associated with humans, domesticated cattle, and domesticated sheep. Thus, the earliest phase in the domestication of the horse might have begun during the period 4800-4400 BCE.

Methods of domestication
Equidae died out in the Western Hemisphere at the end of the last glacial period. A question raised is why and how horses avoided this fate on the Eurasian continent. It has been theorized that domestication saved the species. While the environmental conditions for equine survival were somewhat more favorable in Eurasia than in the Americas, the same stressors that led to extinction for the mammoth had an effect upon horse populations. Thus, some time after 8000 BCE, the approximate date of extinction in the Americas, humans in Eurasia may have begun to keep horses as a livestock food source, and by keeping them in captivity, may have helped to preserve the species. Horses also fit the six core criteria for livestock domestication, and thus, it could be argued, "chose" to live in close proximity to humans.

One model of horse domestication starts with individual foals being kept as pets while the adult horses were slaughtered for meat. Foals are relatively small and easy to handle. Horses behave as herd animals and need companionship to thrive. Both historic and modern data shows that foals can and will bond to humans and other domestic animals to meet their social needs. Thus domestication may have started with young horses being repeatedly made into pets over time, preceding the great discovery that these pets could be ridden or otherwise put to work.

However, there is disagreement over the definition of the term domestication. One interpretation of domestication is that it must include physiological changes associated with being selectively bred in captivity, and not merely "tamed." It has been noted that traditional peoples worldwide (both hunter-gatherers and horticulturists) routinely tame individuals from wild species, typically by hand-rearing infants whose parents have been killed, and these animals are not necessarily "domesticated."

On the other hand, some researchers look to examples from historical times to hypothesize how domestication occurred. For example, while Native American cultures captured and rode horses from the 16th century onwards, most tribes did not exert significant control over their breeding, thus their horses developed a genotype and phenotype adapted to the uses and climatological conditions in which they were kept, making them more of a landrace than a planned breed as defined by modern standards, but nonetheless "domesticated".

Driving versus riding
A difficult question is if domesticated horses were first ridden or driven. While the most unequivocal evidence shows horses first being used to pull chariots in warfare, there is strong, though indirect, evidence for riding occurring first, particularly by the Botai. Bit wear may correlate to riding, though, as the modern hackamore demonstrates, horses can be ridden without a bit by using rope and other evanescent materials to make equipment that fastens around the nose. So the absence of unequivocal evidence of early riding in the record does not settle the question.

Thus, on one hand, logic suggests that horses would have been ridden long before they were driven. But it is also far more difficult to gather evidence of this, as the materials required for riding—simple hackamores or blankets—would not survive as artifacts, and other than tooth wear from a bit, the skeletal changes in an animal that was ridden would not necessarily be particularly noticeable. Direct evidence of horses being driven is much stronger.

Horses in historic warfare
While riding may have been practiced during the 4th and 3rd millennia BCE, and the disappearance of "Old European" settlements may be related to attacks by horseback-mounted warriors, the clearest influence by horses on ancient warfare was by pulling chariots, introduced around 2000 BCE.

Horses in the Bronze Age were relatively small by modern standards, which led some theorists to believe the ancient horses were too small to be ridden and so must have been used for driving. Herodotus' description of the Sigynnae, a steppe people who bred horses too small to ride but extremely efficient at drawing chariots, illustrates this stage. However, as horses remained generally smaller than modern equines well into the Middle Ages, this theory is highly questionable.

The Iron Age in Mesopotamia saw the rise of mounted cavalry as a tool of war, as evidenced by the notable successes of mounted archer tactics used by various invading eurasian nomads such as the Parthians. Over time, the chariot gradually became obsolete.

The horse of the Iron Age was still relatively small, perhaps high (measured at the withers.) This was shorter overall than the average height of modern riding horses, which range from about. However, small horses were used successfully as light cavalry for many centuries. For example, Fell ponies, believed to be descended from Roman cavalry horses, are comfortably able to carry fully grown adults (although with rather limited ground clearance) at an average height of Likewise, the Arabian horse is noted for a short back and dense bone, and the successes of the Muslims against the heavy mounted knights of Europe demonstrated that a horse standing  can easily carry a full-grown human adult into battle.

Mounted warriors such as the Scythians, Huns and Vandals of late Roman antiquity, the Turks and Mongols who invaded eastern Europe in the 7th century through 14th centuries CE, the Arab warriors of the 7th through 14th centuries CE, and the Native Americans in the 16th through 19th centuries each demonstrated effective forms of light cavalry.

title: Domestication of the horse


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Crab canon

A crab canon (also known by the Latin form of the name, canon cancrizans; as well as retrograde canon, canon per recte et retro or canon per rectus et inversus) is an arrangement of two musical lines that are complementary and backward. If the two lines were placed next to each other (as opposed to stacked), the lines would form something conceptually similar to a palindrome. The name 'crab' refers to the fact that crabs are known to walk backward (although they can also walk forward and sideways). It originally referred to a kind of canon in which one line is played backward (e.g. FABACEAE played simultaneously with EAECABAF). An example is found in J. S. Bach's The Musical Offering, which also contains a table canon ("Quaerendo invenietis"), which combines retrogression with inversion by having one player turn the music upside down.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Crab canon


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University of Idaho

The University of Idaho (U of I, or UIdaho) is a public land-grant research university in Moscow, Idaho. It is the state's land-grant and primary research university, and the lead university in the Idaho Space Grant Consortium. The University of Idaho was the state's sole university for 71 years, until 1963. Its College of Law, established in 1909, was first accredited by the American Bar Association in 1925.

It has an enrollment exceeding 12,000, with over 11,000 on the Moscow campus. The university offers 142 degree programs, from accountancy to wildlife resources, including bachelor's, master's, doctoral, and specialists' degrees, and accompanying honors programs. Certificates of completion are offered in 30 areas of study. At 25% and 53%, its 4 and 6 year graduation rates are the highest of any public university in Idaho, and it generates 74 percent of all research money in the state, with research expenditures of $100 million in 2010 alone. It is classified among "R2: Doctoral Universities – High research activity".

As a land-grant university and the primary research university in the state, U of I has the largest campus in the state at 1585 acre, in the rolling hills of the Palouse region at an elevation of 2600 ft above sea level. The school is home to the Idaho Vandals, who compete in NCAA Division I athletics. In addition to the main campus in Moscow, the U of I has branch campuses in Coeur d'Alene, Boise, and Idaho Falls. It also operates a research park in Post Falls, and dozens of extension offices statewide.

History
On January 30, 1889, Governor Edward Stevenson of the Idaho Territory signed the territorial legislature's Council Bill No. 20, which officially established the UI as the upcoming state's land-grant institution. Nearly four years later, the university opened for classes on October 3, 1892. The choice of location for the University of Idaho was an "Olive Branch of Peace" by Gov. Stevenson for his actions in styming the nearly successful effort to detach the north Idaho Panhandle and join the state of Washington.

Formed by the Idaho Territory legislature in 1889, the university opened its doors in 1892 with a class of 40 students. The first graduating class in 1896 consisted of two men and two women.

In 2023 the University of Idaho established a non-profit organization, Four Three Education, which would acquire the University of Phoenix by issuing $550 million in bonds (creating an estimated $685 million in debt). Idaho spent approximately $7 million on consultants prior to the deal. Three University of Idaho administrators sit on the Four Three board, including UI attorney Kent Nelson. The slate of directors of Four Three Education will be selected by the Regents of the University of Idaho. However, President Green and University of Phoenix President Chris Lynne will be "ex-officio members with full voting rights."

Campus

According to the U of I Facts Books, the Moscow campus, abutting the Washington state line, is 1585 acre, including 253 buildings with a replacement value of $812 million. It has 49 acre of parking lots, 1.2 mi of bike paths, 22 computer labs, an 18-hole golf course on 150 acre, 80 acre of arboreta, and 860 acre of farms.

Administration Building
The Administration Building, with its 80 ft clock tower and Collegiate Gothic-style structure, was built from 1907 to 1909 and has become an icon of the university. The building holds classrooms, an auditorium, and administrative offices, including the offices of the President and Provost. Multiple expansions were made, with the north wing added in 1912, the eastern portion of the south wing in 1916 (extended west in 1936 for the library), and the functional annex in 1950, incorporated into the Albertson addition of 2002. The U of I library was housed in the Administration building until 1957, when the Library building opened, constructed on the former site of tennis courts. The College of Law occupied the south wing until its building (Menard) opened in 1973.

The original Administration building, with a single tall spire reaching to 163 ft, was constructed through the decade of the 1890s and ultimately finished in 1899. It burned in 1906. In the meantime, classes were held at various sites in Moscow. The new Administration building was designed by John E. Tourtellotte, who modeled the new structure after Hampton Court Palace in England.

The 1909 Administration building was added to the National Register of Historic Places in 1978. Two years out of office, former U.S. president Theodore Roosevelt spoke outside the main east entrance of the new building on April 9, 1911, on a platform built of Palouse wheat.

Hello Walk

"Hello Walk" is one of the best-known and traveled pathways on the Idaho campus. It includes monuments such as Presidential Grove, where historical figures, such as Teddy Roosevelt, planted trees; the Spanish–American War memorial statue who had his hands cut off but was reconstructed by the handless sculptor Bud Washburn; and Administration Lawn that was designed by the Olmsted Brothers.

Idaho Student Union Building
The Idaho Student Union Building, (ISUB) completed in 2000 as the Commons, is the heart of campus and contains a food court, copy center, bagel and coffee shop (Einstein's Bagels), Credit Union, and convenience store. Additionally, there is study space, wireless internet, laptop checkout, and many student services such as the offices of the Associated Students of the University of Idaho (ASUI), Academics Assistance, the University of Idaho Writing Center, and Student Support.

With the completion of the Teaching and Learning Center (TLC) at the beginning of the fall semester of 2005, the second phase, the Idaho Student Union Building gained classrooms and completed the vision of a common area where students could learn, study, relax, and get university services all in one place.

Bruce M. Pitman Center
The Bruce M. Pitman Center is located on the east end of campus on Deakin Street. The building houses the university's financial aid, admissions, new student services, registrar and Graduate & Professional Student Association (GPSA) offices. For students, the Pitman Center also features meeting rooms, a computer lab, wireless access, borrowable laptops and a movie theater. The building began as a motel, the Blue Bucket Inn, which UI purchased in 1936 and later expanded. The VandalStore, built in 1989 on a former parking lot, is located directly across the street to the east; it was previously adjacent to the south.

UI student-run media offices are also present on the third floor of the Pitman Center: The Argonaut, a newspaper; KUOI-FM, a radio station; student media advertising; and Blot, a magazine.

In October 2014, the University of Idaho announced the renaming of the Student Union Building as Bruce M. Pitman Center in honor of the retiring dean of students and vice provost for student affairs, who had served the campus community for more than 41 years. The name change took effect on January 1, 2015.

ASUI-Kibbie Activity Center

UI's multi-purpose "Kibbie Dome" is the primary home to Vandal athletics; it is the venue for football, soccer, tennis, and indoor track & field. Its Trus-Dek roof system, constructed in 1975, uses natural wood arches to span 400 ft at a height of 150 ft over the field's hashmarks. Previously on this site was Neale Stadium, which opened in 1937 as an earthen horseshoe with wooden sideline grandstands.

Tartan Turf, similar to AstroTurf, was installed in 1972 with the roll-up mechanism; the arched roof and vertical end walls were completed in time for the 1975 home opener on September 27, enclosing the stadium to become the Kibbie Dome. The seating capacity is 16,000 for football games, 7,000 for basketball games (in a configuration known as the "Cowan Spectrum" since 2001), and 7,500 for concerts.

Idaho Central Credit Union Arena
Idaho Central Credit Union Arena (ICCU Arena), located immediately to the north of the Kibbie Dome, became the new home of Vandals men's and women's basketball for the 2021–22 season. The university had attempted to build a new arena to replace Memorial Gym for over 50 years, but nothing came of the plans until 2018, when a $10 million naming gift from Idaho Central Credit Union encouraged the administration to go forward with construction. Ground was broken the following year. The 4,200-seat facility, costing about $51 million, is primarily made from engineered wood, with the superstructure consisting mainly of over 850 Douglas fir beams prepared from trees logged at the university's experimental forest. Several major forest products companies assisted in the construction process. The arena opened for a media tour on September 29, 2021, with the basketball teams using the main arena and an included practice court during preseason practice. The first event in the new arena was a men's basketball exhibition against NAIA member Evergreen State on October 29. The first regular-season game was a men's game against Long Beach State on November 10. This game served as a homecoming for Beach head coach Dan Monson, son of former longtime Vandals head coach Don Monson and himself a former Vandals football player.

Golf course
The UI Golf Course was established in 1933 on the southwest edge of campus and opened as nine holes in 1937. It was expanded to 18 holes in 1970 and its current clubhouse was built in 1969. Due to its demanding rolling terrain and southwesterly summer winds, the par-72 course's moderate length of 6637 yd from the back tees yields a challenging slope of 135 with a scratch rating of 72.4.

Arboretum and botanical garden

Referred to as "Tree City" or "The Arb" by U of I students, the Arboretum is a 65 acre site adjacent to the golf course which features display gardens, ponds, and a variety of trees and plants from Asia, Europe, and North America.

The original Shattuck Arboretum was conceived in 1910 by Charles H. Shattuck, the head of the forestry department. His efforts gradually turned a treeless slope southwest of the Administration Building into a dense forest grove. The arboretum was named for Shattuck in 1933, two years after his death. Until the late 1960s, this area provided the background for left & center field of the MacLean baseball field, whose infield was displaced by the construction of the new College of Education buildings, which were completed in 1968.

The newer portion of the arboretum complex is south of the Shattuck area, in the valley below the president's residence (1967), along the eastern edge of the campus' 18-hole golf course.

Library
The U of I Library is the state's largest library, with more than 1.4 million books, periodicals, government documents, maps, videorecordings, and special collections. The Library's Special Collections and Archives houses a collection of first edition works by Sir Walter Scott, as well as more than 1200 texts by and about the author. The Library also has materials by many famous Idahoans, including Ezra Pound, Vardis Fisher, Frank Bruce Robinson, and Carol Ryrie Brink of Moscow. Digitized historic photographs from the University of Idaho campus and the state of Idaho, yearbooks, and the student newspaper the Argonaut, can be found on the Library's Digital Initiatives website.

Directly north of the Memorial Gymnasium and built on the former site of tennis courts, the library opened in 1957, relocating from the south wing of the Administration Building. The U of I post office station was formerly housed in its lower northwest corner; it was moved to the new U of I bookstore in 1990. The U of I Library was expanded by 50% in 1993 and rededicated in 1994. The first floor underwent major renovation during the 2016 academic year to up-date collaborative spaces and technology.

Memorial Gymnasium

The Tudor Gothic-style Memorial Gymnasium is another U of I icon, known for its whimsical athletic gargoyles perched along the brick building's ledges. The multi-purpose "Mem Gym" has a modest seating capacity of only 1,500. Opened in 1928 to honor the Idaho citizens who died in World War I (1917–18) and Spanish–American War (1898), the heavily buttressed structure was designed by the chairman of the university's architecture department, David C. Lang.

Memorial Gym was the primary venue for men's basketball until January 1976, following the enclosure of the Kibbie Dome the previous fall. The women's team hosted its home games in the gym until 2001, when the Cowan Spectrum (inside the Kibbie Dome) was completed. The gym is still in active use today as the home court for the women's volleyball team, and was also used for early-season basketball games before the opening of ICCU Arena. It is also used extensively for intramurals and open recreation, as well as for ROTC.

The MacLean baseball field was located directly south of the Memorial Gym, until its infield was displaced by the construction of the College of Education building in 1967. The catcher and batter faced southwest (towards the pitcher's mound); the right field line was just south of the gym, running east–west. The background of left and center field was the Shattuck Arboretum. The new baseball field (Guy Wicks Field) was relocated northwest, to the vast intramural fields near the Moscow-Pullman Highway, northwest of the Wallace Complex dormitories. The batter and catcher now faced southeast, toward campus, an unorthodox configuration resulting in a difficult sun field for the left side of the defense (the recommended alignment is east-northeast). Due to budget constraints, varsity baseball was dropped following the 1980 season, but continued for a while as a club sport. MacLean was also the venue for football until the opening of Neale Stadium in 1937.

The swim center and physical education building (formerly known as the "Women's Gym"), which both opened in 1970, are adjacent to the south side of the gym. Before the swim center was opened, the Mem Gym had a narrow swimming pool in its basement.

In 1977, the Memorial Gymnasium was added to the National Register of Historic Places after only 49 years.

Under the elms
Rare Camperdown elms line the walkway between the Music building, Nichols Building (home to Family and Consumer Sciences) and Administration Building. These "upside-down" trees have been on campus for over 80 years and are among few of their kind in the Northwest. The weeping branches and knotty trunk are formed by being grafted upwards.

Steam plant
Built in 1926, the steam plant provides heat to U of I buildings from a single location. Originally designed to burn coal, then oil, then natural gas, the plant was modified in 1986 to burn waste wood chips left over from local sawmills. The use of wood has significantly reduced the emissions of the plant, as well as cut costs to heat the campus. The plant is shut down twice a year for cleaning and maintenance. As a side benefit of the heat generation, the steam pipes are routed underneath campus walkways and provide clean (and ice free) walkways throughout the north Idaho winter.

University housing
The University of Idaho offers various options for on-campus housing, including five residence halls (Wallace Residence Center, Theophilus Tower, McConnell Hall, Living Learning Communities, and North Campus Communities) for students and Apartments (South Hill Apartments, South Hill Vista Apartments, and Elmwood Apartments) for non-traditional students or those who need special accommodations.

Usually apartments are only available to single parents, married couples (with or without children), law students, and students over 21 years old. Theophilus Tower, 3 of the 4 Wallace Residence wings, and one LLC building is only available for first-year students. Students can also live in a Fraternity or Sorority chapter on campus. Summer housing is available but choices are limited.

Ridenbaugh Hall
The Board of Regents authorized the construction of Ridenbaugh Hall as the first women's dormitory on campus. Completed in 1901 at a cost of $17,000, it is the oldest extant building on campus. It was designed by architect Willis A. Ritchie of Spokane, who also designed the Spokane County Courthouse. The building used stone quarried in Latah County for the exterior walls. It was also used as a space for domestic science classes until 1927 when it became a men's dormitory. The building was later used for music practice rooms and currently houses the Art and Architecture gallery.

Ridenbaugh Hall was the first U of I campus structure to be named after a person. The hall was dedicated to "the young women of Idaho" in honor of Mary E. Ridenbaugh (1857–1926) of Boise, who was vice president of the U of I Board of Regents, and served as regent from 1901 to 1907. The building was placed on the National Register of Historic Places in 1977.

Student life
U of I is a rural, residential campus, with four residence hall communities to choose from on campus, as well as 27 housed fraternities and sororities. On-campus residence is currently required for freshmen, and many other upperclassmen choose to live on campus in the Greek system or the residence halls.

Apartments on campus are available for families, married couples, graduate students, law students, and non-traditional students. The "Law Cluster" is a group of apartments reserved for law students, allowing for a community close to campus for law students, facilitating study groups.

Student organizations
Many students participate in a wide variety of over 200 clubs and organizations. Clubs range from sports to faith based, and everything in between. Palousafest is a fair that brings clubs and students together, and is a way for students to find out more about how to get involved with extracurricular activities. The fair is usually the weekend just before the fall semester starts. The literary journal Fugue is published at the university.

Greek life
The University of Idaho is home to more than two dozen (multicultural) Greek organizations that make up more than 20% of the student population. Over 44% of the students who live on campus are involved in Greek life. Greeks claimed to have the highest GPA for 9 consecutive semesters as of Spring 2011.

Academics
From 1896 through May 2011, the University of Idaho granted 80,233 bachelor's degrees, 21,734 master's degrees, 2,694 doctoral degrees, 240 honorary degrees, 1,164 specialist degrees, and 3,654 law degrees.

The university is organized into ten colleges; two are exclusively for graduate students (Law & Graduate Studies).

In July 2002, the College of Letters & Science was split into two separate colleges: the College of Science and the College of Letters, Arts, and Social Sciences (CLASS). Concurrently, the College of Mines and Earth Resources was discontinued; its programs were split between the College of Engineering and the new College of Science.

The College of Law opened a second campus in Boise in 2010. Initially, the Boise campus only offered third-year classes. It expanded to offer second-year classes in 2014, and as of 2017–18, law students can take their entire three-year curriculum at either location.

 * College of Agricultural and Life Sciences - (renamed 2001, formerly Agriculture (1901))
 * College of Art and Architecture - (1981)
 * College of Business and Economics - (1925)
 * College of Education, Health and Human Sciences - (1920)
 * College of Engineering - (1911)
 * College of Graduate Studies
 * College of Law - (1909)
 * College of Letters, Arts, and Social Sciences - (2002, formed after split of Letters and Science (1900))
 * College of Natural Resources - (renamed 2000, formerly Forestry, Wildlife, & Range Sciences, originally Forestry (1917))
 * College of Science - (2002, formed after split of Letters and Science, and dissolution of Mines and Earth Resources)

Rankings and recognition

 * U.S. News & World Report ranks U of I tied for 89th among the nation's best public universities and tied for 179th among the best national universities in its 2020 report.
 * A Top 50 America's Best Value College - U.S. News & World Report
 * One of America's Top 100 Best Public Colleges - U.S. News & World Report
 * The University of Idaho is included in the 2021 edition of Princeton Review's "Best 386 Colleges." The Princeton Review also ranks U-Idaho as one of the nation's top 286 environmentally responsible colleges.
 * Named by the Corporation for National and Community Service to the 2010 President's Higher Education Community Service Honor Roll for exemplary service efforts—more than 3,800 students volunteered more than 150,000 hours to community and service-learning. This was the fifth consecutive year Idaho has earned this highest federal recognition for its commitment to service-learning and civic engagement.

Certification programs

 * Data Analytics (open exclusively to graduate students)
 * Geographic Information Systems/Sciences.

title: University of Idaho


text:
Mnemonic link system

A mnemonic link system, sometimes also known as a chain method, is a method of remembering lists that is based on creating an association between the elements of that list. For example, when memorizing the list (dog, envelope, thirteen, yarn, window), one could create a story about a "dog stuck in an envelope, mailed to an unlucky thirteen black cat playing with yarn by the window". It is argued that the story would be easier to remember than the list itself.

Another method is to actually link each element of the list with a mental picture of an image that includes two elements in the list that are next to each other. This would form an open doubly linked list which could be traversed at will, backwards or forwards. For example, in the last list one could imagine their dog inside of a giant envelope, then a black cat eating an envelope. The same logic would be used with the rest of the items. The observation that absurd images are easier to remember is known as the Von Restorff effect, although the success of this effect was refuted by several studies (Hock et al. 1978; Einstein 1987), which found that the established connection between the two words is more important than the image's absurdity.

In order to access a certain element of the list, one needs to recite the list step by step, much in the same vein as a linked list, in order to get the element from the system.

There are three limitations to the link system. The first is that there is no numerical order imposed when memorizing, hence the practitioner cannot immediately determine the numerical position of an item; this can be solved by bundling numerical markers at set points in the chain or using the peg system instead. The second is that if any of the items is forgotten, the entire list may be in jeopardy. The third is the potential for confusing repeated segments of the list, a common problem when memorizing binary digits. This limitation can be resolved either through bundling or by using either the peg system or the method of loci.

title: Mnemonic link system


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Charadriiformes

Charadriiformes (, from Charadrius, the type genus of family Charadriidae) is a diverse order of small to medium-large birds. It includes about 390 species and has members in all parts of the world. Most charadriiform birds live near water and eat invertebrates or other small animals; however, some are pelagic (seabirds), others frequent deserts, and a few are found in dense forest. Members of this group can also collectively be referred to as shorebirds.

Taxonomy, systematics and evolution
The order was formerly divided into three suborders:

 * The waders (or "Charadrii"): typical shorebirds, most of which feed by probing in the mud or picking items off the surface in both coastal and freshwater environments.
 * The gulls and their allies (or "Lari"): these are generally larger species which take fish from the sea. Several gulls and skuas will also take food items from beaches, or rob smaller species, and some have become adapted to inland environments.
 * The auks (or "Alcae") are coastal species which nest on sea cliffs and "fly" underwater to catch fish.

The Sibley-Ahlquist taxonomy lumps all the Charadriiformes together with other seabirds and birds of prey into a greatly enlarged order Ciconiiformes. However, the resolution of the DNA-DNA hybridization technique used by Sibley & Ahlquist was not sufficient to properly resolve the relationships in this group, and indeed it appears as if the Charadriiformes constitute a single large and very distinctive lineage of modern birds of their own.

The auks, usually considered distinct because of their peculiar morphology, are more likely related to gulls, the "distinctness" being a result of adaptation for diving.

Families
The order Charadriiformes contains 3 suborders, 19 families and 391 species.
 * Suborder Charadrii
 * Family Burhinidae – stone-curlews, thick-knees (10 species)
 * Family Pluvianellidae – Magellanic plover
 * Family Chionidae – sheathbills (2 species)
 * Family Pluvianidae – Egyptian plover
 * Family Charadriidae – plovers (69 species)
 * Family Recurvirostridae – stilts, avocets (10 species)
 * Family Ibidorhynchidae – ibisbill
 * Family Haematopodidae – oystercatchers (12 species)
 * Suborder Scolopaci
 * Family Rostratulidae – painted-snipes (3 species)
 * Family Jacanidae – jacanas (8 species)
 * Family Pedionomidae – plains-wanderer
 * Family Thinocoridae – seedsnipes (4 species)
 * Family Scolopacidae – sandpipers, snipes (98 species)
 * Suborder Lari
 * Family Turnicidae – buttonquails (18 species)
 * Family Dromadidae – crab-plover
 * Family Glareolidae – coursers, pratincoles (17 species)
 * Family Laridae – gulls, terns, skimmers (103 species)
 * Family Stercorariidae – skuas (7 species)
 * Family Alcidae – auks (25 species)

Evolutionary history
That the Charadriiformes are an ancient group is also borne out by the fossil record. Alongside the Anseriformes, the Charadriiformes are the only other order of modern bird to have an established fossil record within the late Cretaceous, alongside the other dinosaurs. Much of the Neornithes' fossil record around the Cretaceous–Paleogene extinction event is made up of bits and pieces of birds which resemble this order. In many, this is probably due to convergent evolution brought about by semiaquatic habits. Specimen VI 9901 (López de Bertodano Formation, Late Cretaceous of Vega Island, Antarctica) is probably a basal charadriiform somewhat reminiscent of a thick-knee. However, more complete remains of undisputed charadriiforms are known only from the mid-Paleogene onwards. Present-day orders emerged around the Eocene-Oligocene boundary, roughly 35-30 mya. Basal or unresolved charadriiforms are:
 * "Morsoravis" (Late Paleocene/Early Eocene of Jutland, Denmark) - a nomen nudum?
 * Jiliniornis (Huadian Middle Eocene of Huadian, China) - charadriid?
 * Boutersemia (Early Oligocene of Boutersem, Belgium) - glareolid?
 * Turnipax (Early Oligocene) - turnicid?
 * Elorius (Early Miocene Saint-Gérand-le-Puy, France)
 * "Larus" desnoyersii (Early Miocene of SE France) - larid? stercorarid?
 * "Larus" pristinus (John Day Early Miocene of Willow Creek, US) - larid?
 * Charadriiformes gen. et sp. indet. (Bathans Early/Middle Miocene of Otago, New Zealand) - charadriid? scolopacid?
 * Charadriiformes gen. et sp. indet. (Bathans Early/Middle Miocene of Otago, New Zealand) - charadriid? scolopacid?
 * Charadriiformes gen. et sp. indet. (Bathans Early/Middle Miocene of Otago, New Zealand) - larid?
 * Charadriiformes gen. et sp. indet. (Sajóvölgyi Middle Miocene of Mátraszõlõs, Hungary
 * "Totanus" teruelensis (Late Miocene of Los Mansuetos, Spain) - scolopacid? larid?

The "transitional shorebirds" ("Graculavidae") are a generally Mesozoic form taxon formerly believed to constitute the common ancestors of charadriiforms, waterfowl and flamingos. They are now assumed to be mostly basal taxa of the charadriiforms and/or "higher waterbirds", which probably were two distinct lineages 65 mya already, and few if any are still believed to be related to the well-distinct waterfowl. Taxa formerly considered graculavids are:
 * Laornithidae - charadriiform? gruiform?
 * Laornis (Late Cretaceous?)
 * "Graculavidae"
 * Graculavus (Lance Creek Late Cretaceous - Hornerstown Late Cretaceous/Early Palaeocene) - charadriiform?
 * Palaeotringa (Hornerstown Late Cretaceous?) - charadriiform?
 * Telmatornis (Navesink Late Cretaceous?) - charadriiform? gruiform?
 * Scaniornis - phoenicopteriform?
 * Zhylgaia - presbyornithid?
 * Dakotornis
 * "Graculavidae" gen. et sp. indet. (Gloucester County, US)

Other wader- or gull-like birds incertae sedis, which may or may not be Charadriiformes, are:
 * Ceramornis (Lance Creek Late Cretaceous)
 * "Cimolopteryx" (Lance Creek Late Cretaceous)
 * Palintropus (Lance Creek Late Cretaceous)
 * Torotix (Late Cretaceous)
 * Volgavis (Early Paleocene of Volgograd, Russia)
 * Eupterornis (Paleocene of France)
 * Neornithes incerta sedis (Late Paleocene/Early Eocene of Ouled Abdoun Basin, Morocco)
 * Fluviatitavis (Early Eocene of Silveirinha, Portugal)

Evolution of parental care in Charadriiformes
Shorebirds pursue a larger diversity of parental care strategies than do most other avian orders. They therefore present an attractive set of examples to support the understanding of the evolution of parental care in avians generally. The ancestral avian most likely had a female parental care system. The shorebird ancestor specifically evolved from a bi-parental care system, yet the species within the clade Scolopacidae evolved from a male parental care system. These transitions might have occurred for several reasons. Brooding density is correlated with male parental care. Male care systems in birds are shown to have a very low breeding density while female care systems in birds have a high breeding density. (Owens 2005). Certain rates of male and female mortality, male and female egg maturation rate, and egg death rate have been associated with particular systems as well. It has also been shown that sex role reversal is motivated by the male-biased adult sex ratio. The reason for such diversity in shorebirds, compared to other birds, has yet to be understood.

title: Charadriiformes


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