Sheep

• 1. Introduction

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  Sheep recognize and remember the faces of fifty other sheep for over two years. That finding, reported in 2001 by Kenneth M. Kendrick and colleagues in the journal Nature, sits oddly against the animal's reputation. Across the English language, to call a person a sheep is to call them timid and easily led. Yet this is a creature that can learn its own name, respond to clicker training, and read emotion in another sheep's face. There are roughly 1.2 billion domestic sheep alive as of 2019, which makes Ovis aries the most common sheep on Earth by a wide margin. They were among the very first animals humans ever domesticated. So how did a wild mountain animal become wool, mutton, milk, and myth all at once? What does an animal raised for fleece actually see, taste, and fear? And why does a single black lamb born into a white flock carry so much meaning that its name became an insult?

• 2. From Mouflon To Mesopotamia

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  Iran sits at the heart of the story of where sheep began, a geographic envelope of the domestication center. Domestic sheep most likely descend from the wild mouflon of Europe and Asia, with the common hypothesis tracing Ovis aries back to the Asiatic mouflon. The domestication date is estimated between 11,000 and 9000 BC in Mesopotamia. From there the practice reached Mehrgarh in the Indus Valley loosely around 7000 BC.

  Wool, surprisingly, came later. Initially sheep were kept for meat, milk, and skins, not their fleece. Archaeological evidence from statuary found at sites in Iran suggests selection for woolly sheep may have begun around 6000 BC. The earliest woven wool garments have been dated to around 4000 BC, roughly two thousand years after that.

  The Castelnovien people, living around Châteauneuf-les-Martigues near present-day Marseille, were among the first in Europe to keep domestic sheep, in about 6000 BC during the Neolithic period. Ancient Greek civilization relied on sheep almost from its inception, and were even said to name individual animals. Pliny the Elder, in his Natural History, speaks at length about sheep and wool. European colonists carried the practice to the New World from 1493 onwards.

• 3. The Neotenic Animal

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  Wild sheep come in largely variations of brown hues, with extremely limited variation within a species. Domestic sheep break that rule completely. Their colors range from pure white to dark chocolate brown, and even spotted or piebald. Selection for easily dyeable white fleeces began early, and because white wool is a dominant trait, it spread quickly. Domestic sheep have become uniquely neotenic through selective breeding, retaining juvenile traits, though a few primitive breeds keep wild characteristics like short tails.

  Horns tell another story of human shaping. Depending on breed, sheep may be polled with no horns at all, or carry horns in both sexes, or in males only. Most horned breeds have a single pair, but Jacob sheep may have several. Ewes typically weigh between 45 and 100 kg, and rams between 45 and 160 kg.

  The full set of eight adult front teeth is complete at about four years of age. In a ruminant's lower jaw, the front teeth bite against a hard, toothless dental pad in the upper jaw to pick off vegetation. As sheep age, these teeth grind down on pasture, which is why domestic sheep on normal pasture begin to slowly decline from four years on. A sheep's life expectancy is 10 to 12 years, though some may live as long as 20.

• 4. A Stomach In Four Chambers

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  The rumen is a 19 to 38 liter organ where feed is fermented by bacteria, fungi, and protozoa. Some of the organisms living there are archaea, which produce methane from carbon dioxide. When sheep graze, vegetation is chewed into a mass called a bolus, then periodically regurgitated back to the mouth as cud for more chewing. After fermentation, feed passes through the reticulum and omasum into the abomasum, the chamber most like a human stomach and sometimes called the true stomach.

  Copper is the hidden danger in this system. Sheep are substantially more vulnerable to copper toxicity than other livestock, because copper becomes a cumulative poison that they excrete very slowly. Sheep feeding on plants such as heliotropes can release stored copper from the liver en masse, resulting in sudden death. Careless farmers using mineral supplements designed for cattle, pigs, or horses can sicken or kill a flock.

  Sheep crop plants very close to the ground and can overgraze a pasture much faster than cattle. That close grazing has a modern use. Sheep prefer to eat invasives such as cheatgrass, leafy spurge, kudzu and spotted knapweed over native sagebrush. Trials in Imperial County, California found grazing lambs just as effective as herbicides at controlling winter weeds in seedling alfalfa, and as effective as insecticides at insect control. In the 21st century, sheep have grazed plants near solar power arrays in a practice called agrivoltaics.

• 5. The Logic Of The Flock

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  Four is the threshold. Flock behavior in sheep is generally only exhibited in groups of four or more; fewer sheep may not react as expected. The dominance hierarchy of sheep and their inclination to follow a leader to new pastures were pivotal factors in making them one of the first domesticated livestock. A leader may simply be the first individual to move. Sheep can become hefted to one particular local pasture, learning the heft from ewes, so that if a whole flock is culled, the replacements must be taught it again.

  Being a prey species, the primary defense of a sheep is to flee when its flight zone is entered. Cornered sheep may stamp a hoof, jump, or adopt an aggressive posture, and will charge and butt if they decide to fight. The English verb to ram comes directly from male sheep charging at the targets of their ire. Among rams, horn size shapes the hierarchy; rams with similarly sized horns are more inclined to fight, while those with mismatched horns fight less.

  Sheep navigate by sight in ways suited to a hunted animal. With horizontal slit-shaped pupils, they have visual fields of about 270 to 320 degrees and can see behind themselves without turning their heads. They have poor depth perception, so shadows and dips in the ground may cause them to baulk, and they tend to move out of the dark into well-lit areas and uphill when disturbed. An isolated sheep grows stressed, and that stress is reduced if it is given a mirror.

• 6. Megan, Morag, And Dolly

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  The Roslin Institute of Edinburgh, Scotland produced groundbreaking results using sheep in genetics research. In 1995, two ewes named Megan and Morag became the first mammals cloned from differentiated cells. A year later, a Finnish Dorset sheep named Dolly became the first mammal cloned from an adult somatic cell, dubbed the world's most famous sheep in Scientific American. Polly and Molly followed as the first mammals to be simultaneously cloned and transgenic.

  Sheep are generally too large and reproduce too slowly to make ideal research subjects, so they are not a common model organism. Yet their value persists in specific fields. The sheep genome was sequenced in 2014. In 2012, Chinese scientists cloned a transgenic sheep named Peng Peng, splicing in genes from the roundworm C. elegans to increase production of fats healthier for human consumption.

  On the island of Hirta, a feral population of Soay sheep has helped explain natural selection. Soay sheep come in several colors, and researchers investigated why the larger, darker sheep were in decline, an outcome that contradicted the rule that larger members of a population tend to reproduce more successfully. Pregnant sheep also serve as a useful model for human pregnancy, used to study the effects of malnutrition and hypoxia on fetal development.

• 7. Mutton, Milk, And Meaning

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  Mutton comes from the Old French moton, the word for sheep used by the Anglo-Norman rulers of the British Isles in the Middle Ages. It became the English name for the meat, while the Old English sceap stayed with the live animal. Today mutton means the meat of mature sheep at least two years old, and lamb the meat of immature sheep under a year. Approximately 540 million sheep are slaughtered each year for meat worldwide.

  Sheep's milk is rarely drunk fresh and goes mostly into cheese and yogurt. A ewe has only two teats and gives far less milk than a cow, but its milk carries far more fat, solids, and minerals, and higher calcium that helps it resist contamination during cooling. The feta of Bulgaria and Greece, Roquefort of France, Manchego from Spain, and Italy's pecorino romano all come from sheep milk. The Italian word for sheep is pecore. Sheep milk contains 4.8% lactose.

  A black lamb carries a weight beyond its wool. To call someone a black sheep implies they are an odd or disreputable member of a group, a usage drawn from the recessive trait that produces an occasional black lamb in a white flock. Shepherds considered these lambs undesirable because black wool is less commercially viable. The same animal becomes a symbol of power elsewhere: the logos of the Los Angeles Rams and the Dodge Ram pickup truck allude to the bighorn sheep, Ovis canadensis.

• 8. The Sacrificial Animal

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  Skulls of rams, along with bulls, held central placement in shrines at the Çatalhöyük settlement around 6,000 BCE. In Ancient Egyptian religion, the ram symbolized Khnum, Heryshaf, and Amun in his incarnation as a god of fertility. Ram features also appeared on the goddess Ishtar, the Phoenician god Baal-Hamon, and the Babylonian god Ea-Oannes. In Madagascar, sheep were not eaten because they were believed to be incarnations of the souls of ancestors.

  Abraham, Isaac, Jacob, Moses, and King David were all shepherds, and sheep run through all the Abrahamic faiths. In the Binding of Isaac, a ram is sacrificed in place of Isaac after an angel stays Abraham's hand; in the Islamic tradition, the son is Ishmael. Eid al-Adha is a major annual festival in Islam in which sheep or other animals are sacrificed in remembrance of this act. Judaism once offered sheep as a Korban, such as the Passover lamb, and the shofar still sounds in modern Judaic tradition.

  Followers of Christianity are often called a flock, with Christ as the Good Shepherd. Christ is also portrayed as the Sacrificial lamb of God, the Agnus Dei, and Easter meals in Greece and Romania traditionally feature Paschal lamb. The word pastor derives from the Latin for shepherd. A bishop's crosier, the staff that symbolizes the episcopal office, is modeled on the shepherd's crook that once guided real flocks across the hills.