Pig

• 1. Introduction

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  A pig called Big Bill weighed 1157 kg and stood 1.5 metres at the shoulder, a creature far beyond the 140 to 300 kg of an ordinary adult. The pig, known as Sus domesticus, also goes by swine or hog, an omnivorous, even-toed, hoofed mammal that humans have lived alongside since Neolithic times. Around 1.5 billion of them are raised each year, yet the animal resists easy classification. Some authorities call it a subspecies of the wild boar, others a distinct species in its own right. How did an animal domesticated twice, on two separate continents, become one of the most numerous large mammals on Earth? And what hides behind that long snout, sharp enough to find a truffle and strong enough to dig through soil?

• 2. Two Domestications

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  Around the Tigris Basin in the Near East, wild boar were first brought under human management, kept in a semi-wild state much as some modern New Guineans keep pigs today. The evidence runs deep. Pigs lived in Cyprus more than 11,400 years ago, carried there from the mainland, which means domestication on the adjacent mainland had already happened by then. In China, the process began again and independently, starting some 8,000 years ago. These were two separate beginnings during the Neolithic. When Western Asian pigs reached Europe at least 8,500 years ago, they crossed with European wild boar. Over the next 3,000 years they interbred until their genome carried less than 5% Near Eastern ancestry, yet they held onto their domesticated traits. DNA from the teeth and jawbones of Neolithic pigs shows the first European domestic pigs came from the Near East, stimulating a third domestication event from local wild boar. The Near Eastern genes eventually died out in European stock. Later, Asian pig breeds were reintroduced to Europe during the 18th and early 19th centuries.

• 3. A Body Built To Dig

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  The snout is the pig's masterpiece, strengthened by a special prenasal bone and capped with a disk of cartilage. It digs into soil to find food and serves as an acute sense organ. Adult pigs carry 44 teeth, with rear teeth shaped for crushing, and in males the canine teeth can grow into tusks that lengthen continuously and sharpen against each other. Each foot ends in four hoofed toes, the two central ones bearing most of the weight while the outer pair helps on soft ground. The pig's relationship with heat is unusual. It possesses both apocrine and eccrine sweat glands, but the eccrine ones sit only on the snout, so pigs do not sweat to cool down. Like elephants and other hairless mammals, they lose heat instead by wallowing in mud or water. Pigs also carry a rare biochemical defense. They are among four mammalian species with mutations in the nicotinic acetylcholine receptor that protect against snake venom, sharing this trait with mongooses, honey badgers, and hedgehogs. Their lungs, though, are small for their body size, leaving them more prone than other domesticated animals to fatal bronchitis and pneumonia.

• 4. The Sow And Her Nest

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  A sow roots in the ground to carve a depression the size of her body, then builds a mound of twigs and leaves, softer in the middle. When the mound reaches the height she wants, she lays large branches up to 2 metres long across the surface, then roots out a hollow within. Unlike other artiodactyls that stand to give birth, she lies down. Nest-building begins in the last 24 hours before farrowing and grows most intense 12 to 6 hours before. She separates from the group to find well-drained soil sheltered from rain and wind, a refuge that keeps her piglets warm and safe from being trampled. The behaviour is chemically timed, triggered by a rise in prolactin caused by falling progesterone and rising prostaglandin. Female pigs reach sexual maturity between 3 and 12 months and come into estrus every 18 to 24 days if not bred. Their gestation averages 112 to 120 days. A shift in their breeding history is recorded in the bones. Medieval European pigs farrowed once a year, but by the nineteenth century European piglets routinely double-farrowed, bearing two litters annually, though exactly when the change occurred remains unclear.

• 5. The Language Of Suckling

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  Nursing in pigs unfolds in measured phases, occurring every 50 to 60 minutes, and the sow requires stimulation from her piglets before milk lets down. The piglets first compete for position, then massage around their teats with their snouts while the sow grunts at slow, regular intervals. As milk begins to flow, the piglets hold the teats and suck with slow mouth movements, one per second, and the sow's grunting quickens for about 20 seconds. The grunt peak does not match the milk ejection itself but the release of oxytocin from the pituitary into the blood. When the main flow arrives, lasting 10 to 20 seconds, the piglets pull back slightly and suck rapidly, about three movements per second, while the sow grunts low and fast in runs of three or four. Afterward, piglets keep massaging the teats to signal their nutritional status, and the more intense the massaging, the more milk that teat releases next time. Order rules the udder. Piglets are born with sharp teeth and fight for the anterior teats, which produce more milk, and once that teat order is set it stays stable, each piglet returning to its own teat.

• 6. Smarter Than Expected

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  Pigs are roughly on par with dogs in intelligence, able to recognise each other as individuals, play, and form structured communities. They hold good long-term memory and experience emotions, even changing their behaviour in response to the emotional states of other pigs. In experiments they locate objects, solve mazes, work with a simple language of symbols, and recognise themselves in a mirror. Trained pigs have learned to associate Bach with food and a military march with social isolation, then communicate the resulting positive or negative emotion to untrained pigs. Some have been taught to move a joystick with their snout to hit a target on screen. Their senses are tuned for a different world than ours. Pigs have panoramic vision of about 310° and binocular vision of 35° to 50°, though they appear to have no eye accommodation. Smell carries far more weight. Pigs have 1,113 genes for smell receptors, compared with 1,094 in dogs, and in Europe trained pigs use that nose to find underground truffles. They identify other pigs by smell rather than sight, and a sow knows her piglets by olfactory and vocal cues.

• 7. Pork And The Marketplace

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  China produced 55 million tonnes of pork in 2023, more than any other country, followed by the European Union with 22.8 million tonnes and the United States with 12.5 million tonnes. Global production that year reached 120 million tonnes. India, despite its enormous population, consumed under 0.3 million tonnes. The meat takes countless forms, from pork chops and loin roasts to ham, bacon from the back and belly, and sausages. Charcuterie extends the range into terrines, galantines, pâtés, and confits, while fermented and air-dried salami includes Italian varieties such as Genovese, Milanese, and Cacciatorino, with spicier southern kinds like Calabrese, Napoletano, and Peperone. The animal even shaped financial markets. The pork belly futures contract became an icon of commodities trading, appearing in the arena of popular entertainment such as the 1983 film Trading Places, before trade declined and the contract was delisted from the Chicago Mercantile Exchange in 2011. Beyond the plate, pig hide becomes soft, durable pigskin leather, used for gloves, wallets, and jackets, and in 16th-century Germany it was the most popular book-binding material.

• 8. Cost And Consequence

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  In 2021 a pig became the first animal to successfully donate an organ to a human body, using a donor genetically engineered to lack a carbohydrate the human body treats as a threat, Galactose-alpha-1,3-galactose. Pigs make strong medical candidates because their biology, physiology, and anatomy resemble ours, and human skin is very similar to pigskin, which has served in many preclinical studies. Their long, close contact with humans lowers the danger of creating new diseases. That same closeness carries risk. The 2009 swine flu pandemic came from an influenza A variant that first emerged in pigs, and pigs were essential to the first Nipah virus outbreak in 1999, when 93% of infected humans had contact with them. Intensive production leaves marks on land and animal alike. Swine waste is stored above ground in lagoons holding high levels of nitrogen and phosphorus, and by 2015 manure leakage was estimated to have contaminated 35,000 mi of river across more than 20 states in the United States. Inside the barns, sows often begin life's cycle in farrowing crates too small to turn around in, and as many as 25% to 50% of sows can die of prolapse. Around 600 breeds exist worldwide, yet three of them, the Choctaw hog, the Mulefoot, and the Ossabaw Island hog, were critically rare as of 2016, each with fewer than 2000 animals left.