Pig Facts: What the Sources Actually Say

• A wild boar in a farmyard. The domestic pig is a subspecies of the wild boar, and pigs were domesticated at least 9,000 years ago.
• One sow stands behind most pig science. The pig reference genome — the DNA blueprint behind most modern pig research — was assembled from a single Duroc sow catalogued as "Duroc 2-14", published in Nature in 2012.
• The lineages split long before farming. European and Asian wild boars split from one another roughly 1 million years ago — long before humans had anything to do with pigs.
• A smell record that no longer stands. When the pig genome was published in Nature in 2012, pigs had the largest repertoire of functional olfactory receptor genes then known — 1,301 of them. That record has since been broken: a 2014 survey of 13 placental mammals found African elephants carry about 2,000 functional olfactory receptor genes. The pig figure still shows how much of its genome the animal devotes to smell; it is no longer a record.
• Very little of that machinery is broken. Across the pig's olfactory receptor sequences — 1,301 genes plus 343 partial sequences — only 14% are pseudogenes, the lowest fraction observed in any species so far.
• Bitterness barely registers. Pigs are less sensitive to bitter tastes than humans and tolerate higher concentrations of bitter compounds. This gets repeated as "pigs will eat literally anything", which overshoots: the genome shows 17 intact bitter-taste receptor genes in the pig against 25 in humans, 18 in cattle, 19 in horses and 15 in dogs, so pigs are not even the least bitter-sensitive animal on that list. Reduced bitter sensitivity explains why pigs can eat things we find foul; it does not mean they lack food preferences.
• The joystick study, minus the headlines. In a 2021 study, four pigs — two Yorkshire barrows and two Panepinto micro pigs — learned to move an on-screen cursor with a joystick and hit targets at rates better than chance. It was one cursor-to-target exercise originally designed for primates, the pigs pushed the joystick with their snouts, and the authors present the result as evidence of conceptual understanding rather than gaming skill. All four pigs beat chance on the easiest one-walled targets; three of four also beat chance on two-walled targets, and both micro pigs beat chance on three-walled targets. Performance was uneven across difficulty levels rather than limited to the easiest one.
• Every pig tested was far-sighted. Each subject in that study measured between +1 and +2 diopters of hyperopia.
• Grunts carry the mood. An algorithm trained on more than 7,000 recordings — 7,414 sounds from 411 pigs, captured from birth to death — sorted 92% of pig calls into the correct emotional context.
• A happy pig sounds different from a frightened one. In positive situations calls are far shorter, and grunts begin high and gradually go lower in frequency; screams and squeals cluster in negative situations.
• Heat leaves through the breath. Above its upper critical temperature, a pig relies mainly on evaporative heat loss by increasing its respiratory rate — shedding heat as moisture from the respiratory tract.
• The gestation rhyme is out of date. "Three months, three weeks and three days" gives 114 days and is quoted almost everywhere. Average gestation is 115–116 ± 1 days from first service, and Merck notes it has been increasing over time — while also noting it runs slightly shorter in sows with larger litters. The source gives no cause for the upward drift.
• Piglets arrive one at a time. Delivery intervals average 10–15 minutes, though the gap between siblings can range from 5 to 45 minutes.
• Kunekunes are an import with an unclear past. Kunekune sows — a relatively small breed whose origin is unknown, sharing traits with domestic pigs from Asia, South America and the Polynesian Islands, and whose ancestors were likely brought to New Zealand in the 1800s by whalers and then traded with Māori communities — carry for about 116 days and give birth to litters of 6–12 piglets.
• One island breed stores fat like no other hog. Ossabaw Island hogs, feral descendants of Spanish pigs marooned on a Georgia island, developed a unique biochemical system of fat metabolism that lets them store a larger proportion of fat than any other hog.
• Feral swine hold a third of the United States. They have been reported in at least 35 states, the population is estimated at over 6 million and rapidly expanding, and the first animals arrived in the 1500s.
• Half the world's pigs live in one country. China is home to almost half of all the pigs on Earth.
• Babirusa tusks grow through the face. Male babirusas — a wild pig of Sulawesi and neighbouring Indonesian islands — grow upper canines that first point downward, then curve back up and through the skin of the snout toward the forehead, reaching up to 12 inches if they are not first worn down or snapped off in fights. Females have only the lower tusks.

"Sweating like a pig — pigs must be famously sweaty animals." Pigs barely sweat at all. The phrase has nothing to do with the animal: it comes from iron smelting, where molten iron poured into sand cooled into linked ingots that looked like a sow with suckling piglets, and "sweated" condensation as they cooled.

"Pigs wallow in mud because they are dirty animals that enjoy filth." What is documented is the physiology. Pigs have only a limited number of functional sweat glands, so they cannot cool by sweating the way we do, and above their upper critical temperature they rely mainly on evaporative heat loss through increased respiratory rate. The usual follow-on — that a coating of mud supplies the evaporative cooling the skin cannot manage — is not supported by the thermoregulation review cited here, which never mentions mud or wallowing, so treat that half as unverified rather than established.

"A teacup or micro pig will stay small enough to sit on your lap for life." There is no such thing as a defined teacup pig. Veterinary reference data puts typical adult weight for miniature pet pigs at 45.5–68.2 kg (100–150 lb) and notes they can be heavier — and that they keep growing until they are two to three years old, long after the cute piglet phase is over.

"Javelinas (peccaries) are American wild pigs." Peccaries are Tayassuidae, not Suidae. San Diego Zoo says the most reliable tell is the mouth — the number and arrangement of teeth. Internally, a peccary's complex, three-chambered stomach houses microflora for digesting cellulose, which no pig has, and it carries a pungent dorsal scent gland near the rump.

"Warthogs are called warthogs because they are covered in warts." The "warts" are not warts and not a disease — they are thickened pads of skin on the face that help cushion blows during fights between males.

Pigs get cast as either tyrants or innocents, rarely anything in between. George Orwell made them the ruling class in Animal Farm, first published in 1945, where Napoleon and Snowball turn a farmyard revolution into a police state. E. B. White inverted the arrangement in Charlotte's Web (1952): Wilbur is the runt everyone intends to eat, rescued by a spider who writes advertising copy in her web.

Television softened the image considerably. Miss Piggy arrived with The Muppet Show, which began broadcasting on 5 September 1976, and quickly outgrew the ensemble to become its diva. Peppa Pig premiered on 31 May 2004 and became one of the most widely exported British preschool series ever made.

On film, Chris Noonan's Babe (1995) played the talking-animal premise straight enough to win over adult critics, and its sheep-herding pig remains the reference point for anthropomorphic livestock. Warner Bros.' Porky Pig, meanwhile, has spent decades as the stuttering everyman who closes out the cartoon.

The most consequential pig in modern science has a catalogue number rather than a name. Duroc 2-14 was the sow whose DNA was used to assemble the pig reference genome published in Nature in 2012 — the sequence underpinning most pig research since.

In medicine, the landmark animal was an unnamed genetically modified donor pig whose heart went to David Bennett, Sr., 57, at the University of Maryland Medical Center in January 2022, the first such transplant into a living person. Bennett's new heart worked with no obvious sign of acute rejection for nearly seven weeks; sudden heart failure killed him two months after surgery.

Wild pigs have their own entries in the record. The pygmy hog was feared extinct after two decades without a sighting, then rediscovered.