Goats belong to the order Artiodactyla (genus Capra), which is made up of a number of hoofed mammals having an even number of toes. Goats have existed on Earth for at least 35 million years and, during the course of evolution, have undergone an incredibly wide radiation, both in distribution and ecology. Although the taxonomy of this group is still unclear, eight species are generally recognized as being true goats, with representatives found from the barren plains of central Asia to an altitude of 22,000 ft (6,700 m) on snow-clad peaks.
Despite such divergence, all goats have a similar design and frequently display similar behaviors. The majority are stocky, gregarious animals that live in barren habitats, often under inhospitable weather conditions. All goats are adapted to living in steep and often unstable terrain, and their physical appearance demonstrates several features that have evolved to cope with these conditions. The main toes of the hoof are often concave on the underside, are hard as steel, and can be widely splayed to spread the animal's body weight over a large area. The legs are usually short and highly muscular.
The ancestor of all domestic breeds of goats is thought to have been the wild goat of western Asia (Capra aegagrus). This species, which occupies a wide range of habitats at altitudes up to 13,800 ft (4,200 m), was formerly widespread throughout much of Eurasia. The wild goat reaches a height of 28-39 in (70-100 cm) at the shoulder and weighs from 55-200 lb (25-90 kg). The coat is usually a silver-white color, with a gray facial pattern and black or brown undersides. There is usually a distinct line of longer, darker hairs extending from the neck down along the spine. Females are usually a yellowish brown or reddish gray color. The males, which are larger than females, bear a pair of arched, scimitar-shaped horns that extend far along the back and may reach 47 in (120 cm) in length. The horns of a female are much thinner and may measure just 8-12 in (20-30 cm) in length.
Goats living at higher altitudes or under colder conditions always have a much thicker coat that is made up of several layers. More primitive forms tend to have small, pointed horns and a patterned coast, while more evolved forms have larger and more curved horns. The horns themselves are often used to classify different species and vary considerably in this group: the horns of the East Caucasian tur (Capra cylindricornis), for example, are curved directly back and down towards the shoulders, while those of the ibex (Capra ibex) are upright, curved, and heavily ridged, and those of the Kashmir markhor (C. falconeri) are upright and spiralled like a corkscrew. The horns, which are not shed each year, display growth patterns which enable biologists to determine the age of the animals—an important feature when management of certain threatened species are involved.
Goats are highly sociable animals that live in herds whose size and composition varies according to the species and time of year. Herds of up to 500 goats have at times been recorded but, in general, groups tend to be much smaller, often around 20-30 animals. In some species, the adult males (or billies) may either follow a solitary existence or form small groups of 3-5 animals for much of the year, while the females (or nannies) and offspring (kids) form larger, more cohesive groups. The two come together prior to the breeding season—period known as the rutting season—when males compete against one another in an attempt to mate with as many females as possible. In some herds, there will be just one dominant male, but even he will have to defend the herd of females from potential competitors from outside the herd. Within the herd, there is also a distinct hierarchy, with older animals almost always being dominant over younger ones. Females are responsible for bringing up the kids and a mother will only suckle its own kids, those of another goat being gently rebuffed.
Wild goats vary considerably in their activity patterns. Most species are active in the early morning and late afternoon, resting during the hottest part of the day to digest their food. Many species display distinctive seasonal and even daily patterns of migration, coming down to the lower parts of their ranges to feed and then returning to their scaly heights to rest.
All goats are herbivorous animals that feed on a vast range of plants. They are not grazing animals like the majority of herbivores, but prefer to browse on the leaves and twigs of shrubs and coarse weeds. Goats will go to any lengths to obtain a meal, and in some parts of North Africa, feral domestic goats are commonly seen browsing in Acacia trees some 23 ft (7 m) off the ground, their cleft hooves and powerful legs enabling them to jump and climb into trees. Herds of feral goats, which are widespread throughout the world, are known to cause considerable environmental destruction as they destroy natural vegetation and contribute to erosion and, in some drier regions, desertification. In some countries, feral goats have had to be exterminated because of the damage they cause to native, and often endangered, vegetation.
Goats are well-known for their aggressive behavior when settling territorial or reproductive disputes. The
most common means of settling such issues is in head-to-head combat, with both animals using their skulls and horns as offensive weapons. Among the most dramatic of these encounters are the clashes of adult male ibex: standing 10 ft (3m) apart, often on a steep precipice, the males rear up on their hind legs and charge one another, bringing their large curved horns down at the last moment to crash against its opponents. Scientists have estimated that the force of these blows may be as much as 60 times greater than that needed to fracture a human skull. Goats, however, have highly efficient shock absorbers built into their skulls and are able to withstand such attacks without too great an injury to their heads. In this obvious show of physical strength, the weaker animal usually recognizes its shortcomings at an early stage of the encounter and tries to escape before too much damage is caused to other parts of the body.
Goats have long been domesticated, and in many parts of the world these herds may constitute an important source of food and revenue for people. A great many domestic breeds have been developed, some of which have been either deliberately released, or escaped and later bred in the wild. Some of these feral domestic goats breed with wild populations—a point of concern for some threatened wild species, as the genetic component of the original true stock might be diluted by such breeding activities.
Although goats live in almost inaccessible regions, their populations have been seriously affected by hunting and human encroachment to the foothills, where many species feed during the summer months. Wild goats have long been sought after as trophy specimens. The magnificent ibex was exterminated in the Alps during the nineteenth century, but has since been reestablished in many of its former habitats as a result of a concentrated breeding and reintroduction programme. The West Caucasian tur (C. caucasica) is now confined to a narrow strip of montane habitat in the western Caucasus, where its existence is threatened by hunters and human encroachment. Natural predators, too, take their toll on wild goat populations, and it is because of this pressure that goats have developed many of their behavioral patterns, such as living in small groups, and their ability to rapidly flee over rough terrain. Wolves and big cats such as snow leopards are among the main predators of goats, while bears, wild dogs, and foxes may prey on kids. Aerial predators such as golden eagles are also a threat to kids. Despite the vigilance of the adults, kids are also highly susceptible to natural causes of death as a result of their playful behavior; many engagements and mock fights can result in an inexperienced animal slipping from a rock or precipice to its death.
See also Ungulates.