When discussing sheep, it's essential to distinguish between goats and sheep, specifically domesticated ones.

Our modern domestic sheep are descendants of wild sheep that humans have selectively bred over time.

Essentially, domesticated and wild sheep share a common distant ancestor. One of the most noticeable characteristics of both wild and domesticated sheep is their distinctively shaped horns. Similar to those of cows and antelopes, these horns are hollow inside, earning them the nickname "cave horns."

Cave-horned animals, including sheep, cattle, and antelopes, trace their origins back to the Miocene era and represent an evolutionary branch stemming from ancient deer. Eurasia served as the primary area for their early development.

Current wild sheep species encompass various taxa, including sheep, goats, rock sheep, brute sheep, half sheep, goat-antelope, and high-nosed antelope. Notable examples include the Asian pan sheep, Oriental pan sheep, and Vichy's pan sheep, as well as the European bighorn sheep, white bighorn sheep, and mouflon sheep.

For instance, the Vichy pan sheep, also known as the red pan sheep, found in northwestern India, is the wild ancestor of Asian livestock sheep. Conversely, the mouflon sheep, also known as the European wild sheep and the only sheep breed native to Europe, serves as the wild ancestor of European livestock sheep.

Mountain goats, inhabiting mountainous regions, are characterized by a beard on their lower jaw, earning them the moniker "goatee." Wild goat species include the wild goat of Asia, the northern goat, the twisted-horn goat, and the Spanish goat of Europe. The wild goat is believed to be the progenitor of the Central Asian wild goat.

Sitting between sheep and goats are rock goats, brute goats, and half-goats, which exhibit morphological features of both species. Among these, the rock sheep, widely distributed in western China, particularly in the Helan Mountains of Ningxia, resembles a sheep but lacks rounded horns and bears a striking resemblance to goats.

In contrast, the bonneted rock sheep, with a limited range along the banks of the Jinsha River and its tributaries in China, boasts a unique appearance distinct from other sheep and goats. Barbary sheep, also known as bearded sheep, represent the sole wild sheep species in Africa. Distinguished by long, coarse hairs on the throat, chest, and forelimbs of males, extending down to their knees, this species sets itself apart from other sheep.

There are three subspecies of half-sheep—Himalayan thar, Arabian thar, and South Indian thar—found across West and South Asia. The goat-antelope, goat-cow, and high-nosed antelope are considered "collateral" relatives of sheep. These groups include species like the Asian hyrax, iguana, gazelle, oryx, and European hyrax, exhibiting intermediate characteristics between goats and antelopes.

Notably, four antelope species residing in Asia are indigenous to China. Two species—antelope and musk ox—serve as transitional animals between sheep and cattle, belonging to the category of "oxen." The musk ox, inhabiting the Arctic tundra, resembles a cow but possesses horns growing from the sides of its head, unlike other sheep. Its molars resemble those of a goat, indicating its transitional nature between cattle and sheep. Despite its name, the musk ox does not possess musk glands, with only males emitting a fragrant odor from their genitals during the hot season.