Pig

**Physical Characteristics:**
– Large head with a long snout and a disk of cartilage at the tip.
– Dental formula of adult pigs is 3.1.4.33.1.4.3, totaling 44 teeth.
– Four hoofed toes on each foot, with two larger central toes bearing most weight.
– Most pigs have sparsely bristled hair on their skin.
– Adult pigs weigh between 140-300kg, with exceptions like Big Bill weighing 1,157kg.

**Evolution and Domestication:**
– Domestic pigs are related to other pig species based on mitochondrial DNA analysis.
– Pigs were domesticated from wild boar in the Near East and China.
– Domestication did not involve reproductive isolation with population bottlenecks.
– Pigs arrived in Europe from the Near East at least 8,500 years ago.
– DNA evidence shows complex exchanges of domesticated pig lines between regions.

**Historical Impact and Environmental Issues:**
– Spanish introduced pigs to the Chiloé Archipelago in the 16th century Columbian Exchange.
– Escaped pigs became feral in southeastern North America.
– Feral pigs have caused substantial environmental damage in various regions.
– Feral hybrids of European wild boar and domestic pig are disruptive to the environment and agriculture.
– Feral pig damage is a significant issue in southeastern South America.

**Reproduction and Lifespan:**
– Female pigs reach sexual maturity at 3-12 months of age.
– Estrus lasts 2-3 days, with females displaying receptiveness known as standing heat.
– Female cervix contains interdigitating pads to hold boar’s penis during copulation.
– Females have bicornuate uteruses for pregnancy.
– Pigs have a maximum lifespan of about 27 years.

**Nesting Behavior and Care:**
– Pigs share nest-building characteristics with carnivores.
– Nest-building behavior is innate and observed in wild and domesticated pigs.
– Nest-building intensifies 12 to 6 hours before farrowing.
– Nest sites are sought with well-drained soil and shelter from rain and wind.
– Nests provide shelter, comfort, and thermoregulation for offspring.