The reason for this is their extreme hardiness. Adapted to living in habitats even more marginal than those of sheep - which, at least in their wild form, are themselves more resilient than, say, cows or pigs - they're ideal for raising in the sort of scrubby environments that you get in much of Africa and the Middle East. Even so, after approximately twelve thousand of years of selective breeding, the domestic goat has come a long way from its wild ancestors. They're often larger, with smaller horns, or none at all, and some have long, floppy ears. There are a number of different breeds, from milk-producers like Saanens and Toggenburgs, to the muscular Boer goats, bred for their meat, to the long-haired angora and cashmere goats that produce fine wool and mohair.
Because of these differences, like sheep, the domestic goat is often considered a separate species (Capra hircus) from its wild progenitor. Today, goats can be found living wild on Crete and parts of the Greek mainland, but it turns out that these aren't really "wild goats" at all. Instead, genetic evidence shows that they are actually feral. That is, they are descended from domestic goats brought to Crete in the distant past, and subsequently abandoned - they're really no more "wild goats" than a feral dogs are wolves. This is, perhaps, especially true on the mainland, where they have bred with fully domesticated animals in the relatively recent past.
To find the true wild ancestor, we have to travel further east. Wild goats (Capra aegagrus) inhabit the Middle East, from southern Turkey, through the Caucasus, Iraq, and Iran, and into Pakistan and Afghanistan. They are sometimes also called bezoars, a term that's slightly confusing, since it also has a medical meaning. Another possible name is "Persian ibex", which is arguably even worse, unless you happen to think that "ibex" and "goat" mean the same thing.
There is some dispute as to how many different subspecies there are - anything from one to four have been suggested. If there are multiple subspecies, it's unlikely that any one is the sole ancestor of the domesticated animal, which was probably bred over thousands of years from whatever happened to be available. Indeed, there's a reasonable chance that some of the earliest domestic goats were cross-bred with local ibex or markhors, making the modern form a hybrid. If so, these other species haven't contributed much to modern goat DNA, and there certainly isn't any doubt that the wild goat is, by far and away, the main ancestor of the farm animal.
Considering the range of appearances among domesticated goats, the wild species is remarkably uniform - indeed, this is why there is debate over the number of subspecies. They have a distinctive black-and-brown pattern to their hair, with black shoulders and stripes running along the flanks and the centre of the back, as well as black markings on the face and limbs and a pale belly. Males have long beards and large curving horns up to 125 cm (about four feet) in length. It's possible to age a male wild goat by examining those horns, since they develop a slight knob on the front once every year, as they continue to grow. Like other caprines, the females have horns too, but these are much smaller, no more than 30 cm in length, and they're too slow-growing to develop the annual knobs that would enable you to age them.
Wild sheep live in hilly terrain, often at the foot of steep rocky slopes up which they can clamber at the first sign of predators. Goats, however, take the different approach of living at the top of those slopes. This has both pros and cons. On the plus side, there are less predators in such difficult terrain, and it's often easier to spot them coming when they do venture that high. On the negative, aside from the need to be very sure-footed (which, of course, goats are), there's usually not a lot to eat on a rocky cliff face. As a result, goats are fairly indiscriminate feeders, eating whatever they happen to come across. That's mainly grass, and goats are considered grazing animals, as sheep are, but they'll certainly tuck into any bushes or shrubs that they find, even if they're so thorny that other animals wouldn't make the effort.
Herds of wild goats can be large, with over a hundred members, although they're usually rather smaller than that. They're biggest through the winter and spring, when mating occurs. Males establish dominance by rearing up on their hind legs then dropping down suddenly to head butt one another. Older males are not only physically stronger than their younger kin, but have larger horns, too, and this counts for a lot when they're whacking each other about the head. As a result, younger males, while they'll certainly join the mixed sex mating herds in the hope of some action, rarely get much of a look-in, and the older males will mate with several females each during the course of the rut.
Once it's over, and all the available females are pregnant, the males leave the females to their own devices, forming small bachelor herds through the summer and autumn. These herds tend to be comprised of goats of similar age and social status; it's apparently still a good idea for the younger animals to stay away from their larger relatives even when there aren't any females to compete for. The females, however, all stay together, relying on safety in numbers to help protect their kids.
Unlike sheep, goats normally give birth to twins, not singletons. Something like two-thirds of all births are twins, with a little under 5% being triplets. They're evidently able to control either mating or pregnancy, with births being noticeably less common in years with poor rainfall, and the exact timing of the rut may also depend on the weather and the amount of fresh greenery available.
Living in places like Chechnya, Iraq, and Afghanistan, wild goats aren't exactly found in the most politically stable parts of the world. Their need for mountainous terrain means that individual populations are, of necessity, somewhat isolated from one another even before the advance of things like roads are taken into account. All of this does put them under some pressure from illegal hunting, attacks by feral dogs, and the like. Nonetheless, there are some areas where their populations are being successfully protected, and, in 1970, some were even introduced to Luna County, New Mexico. Overall, therefore, we can't say that they're an endangered species.
[Update: Since this post was written, the markhor was removed from the endangered species list in 2015.]
Yet markhor are, perhaps, the most visually distinctive of all goats. Nonetheless, mitochondrial DNA, which traces the female ancestry of animals, shows that, despite their appearance, they unquestionably are goats, in the sense of belonging to the genus Capra. Analysis of the Y chromosome, which traces ancestry through the male line, shows a slightly different pattern, but ultimately concludes that markhor are, in fact, the closest living relatives of wild goats. Which is surprising, because they look rather less like wild goats than ibex do.
Perhaps, despite their different appearance, markhors and wild goats have interbred in the past, muddling their genetic ancestry. Certainly, they can interbreed, and one supposed subspecies, the "Chiltan goat" of Pakistan, is, most likely a marhkor-goat hybrid.
Markhors are a yellowish-grey colour with only a few markings, and with more yellow in the summer coat, and more grey in winter. They're also slightly larger than wild goats, although no more so than some ibex. The males have a huge ruff of long hair over the chest and shoulders, as well as a mane running down the spine, and both males and females have beards. These are all features that are rare or unknown in other wild species of goat, but it's the markhor's horns that are truly distinctive.
The horns are large, up to 165 cm (5' 5") in length and wound in a corkscrew spiral. The exact shape of the spiral varies considerably, especially between different subspecies, but it's always completely unlike anything found in any other caprine. In the so-called "straight-horned" subspecies, the corkscrew is tightly wound, with the horn otherwise sharp and conical, sticking straight out of the head. In others, the spiral can be looser, curling around and upwards, often with a flared and flattened tip. The horns of females are much shorter, no more than 35 cm (13 inches), with the corkscrew only turning once or twice, but still quite unmistakable in the adults.
Like other goats, markhors live in steep and mountainous terrain. They apparently prefer forested slopes, spending more time under cover of trees than wild goats do, but they are also at home in relatively barren and arid wasteland. They live at anything up to 3600 metres (12,000 feet) elevation, and try to stick to south-facing slopes when they can. In at least some areas, outside the mating season, males live higher up the slopes than females do, with the latter inhabiting rocky canyons surrounded by precipitous cliffs.
Markhors are said to be more agile than either wild goats or ibexes, which is no mean feat. In fact, they are so agile that, quite remarkably for anything with hooves, they regularly climb trees. Females and immature males can apparently be found five metres (15 feet) or more above the ground, leaping from branch to branch just as they normally would between rocky ledges. They do this, of course, to munch on the leaves, and presumably the only reason that older males don't join in is that they're too heavy and, besides, those five-foot horns would rather get in the way.
In other respects, markhor are much like other goats. They breed at around the same time, often give birth to twins, and eat much the same kinds of food. They do live in smaller herds, of typically no more than a dozen individuals, although that's as likely due to their current rarity as anything else. Quite how rare that is is hard to say, given the difficulty of conducting studies over much of their range. For example, for fairly obvious reasons, there haven't been any population surveys of the animals in Afghanistan since the 1970s. The situation wasn't great then, and it's hardly likely to have improved. Pakistan is at least making some effort to protect the animals - the markhor is the country's national mammal - but the mountainous north of the country where they live is hardly the easiest place to patrol, and has plenty of other concerns to worry about.
It's a familiar story of encroaching agriculture and illegal hunting threatening a creature that lives in marginal and isolated habitats. But markhors are not the only endangered species of goat, and while some of those we're going to see next time are much better off, others are certainly not.
[Pictures by F Spangenberg and "Thomas", from Wikimedia Commons. Cladogram adapted from Lalueza-Fox et al 2005]