Pig

The pig, scientifically known as Sus domesticus, is an omnivorous, even-toed, hoofed mammal. It is commonly called swine or a hog. This animal is a vital part of human civilization and global agriculture. Pigs are raised primarily for meat, which is known as pork. Their skin, or hide, is also harvested to produce leather.

Because they are so useful, pigs are raised in massive numbers globally. Approximately 1.5 billion pigs are raised every year. This production results in about 120 million tonnes of meat. China is the world's largest producer, followed by the European Union and the United States.

A pig's physical anatomy is specialized for its lifestyle. They possess a large head with a long snout. This snout is strengthened by a unique prenasal bone and a disk of cartilage at the tip. The snout serves as an acute sense organ and a tool for digging in soil to find food.

An adult pig has a dental formula that results in 44 total teeth. The rear teeth are specifically adapted for crushing food. In males, the canine teeth can develop into tusks. These tusks grow continuously and are kept sharp by grinding against one another.

Pigs have unique biological mechanisms for regulating their body temperature. They possess both apocrine and eccrine sweat glands. However, their eccrine glands, which are used for cooling, are limited to the snout. Unlike many other mammals, pigs cannot rely on thermal sweat glands to cool down. They are also less efficient than many mammals at dissipating heat through panting.

Their thermoneutral zone, the temperature range where they are most comfortable, is 15 to 25 degrees Celsius. To manage heat, pigs use evaporative cooling. They do this by wallowing in mud or water. This behavior may also provide protection from sunburn, control ecto-parasites, or assist in scent-marking.

The reproductive cycle of a pig involves complex hormonal signaling. Female pigs, called sows, reach sexual maturity between 3 and 12 months of age. They enter estrus, or a period of sexual receptivity, every 18 to 24 days. This receptivity is often triggered by pheromones like androstenol, which is produced in the saliva of male boars.

The gestation period, or the time a mother is pregnant, averages 112 to 120 days. During pregnancy, the mother's body recognizes the embryo through hormones like progesterone and estradiol. Sows also exhibit unique nest-building behaviors before giving birth, a process called farrowing. They gather twigs and leaves to create a mound. This nest provides thermoregulation and protection for the piglets from predators and weather.

The history of pig domestication is a subject of scientific study. Evidence shows pigs were domesticated independently twice during the Neolithic period. One event occurred in the Near East around the Tigris Basin. A second event happened in China about 8,000 years ago.

When domestic pigs were introduced to Europe from the Near East, they interbred with local wild boar. Despite this interbreeding, they retained many of their domesticated features. Some taxonomists classify the pig as a subspecies of the wild boar, Sus scrofa. Others, including the American Society of Mammalogists, consider it a distinct species, Sus domesticus.

Pigs also possess remarkable evolutionary adaptations. They are one of only four mammalian species with specific mutations in the nicotinic acetylcholine receptor. This mutation protects them against certain snake venoms. Specifically, it prevents α-neurotoxin from binding to the receptor. This trait is also found in mongooses, honey badgers, and hedgehogs.

However, pigs do have some biological vulnerabilities. They have relatively small lungs for their body size. This makes them more susceptible to fatal illnesses like pneumonia and bronchitis compared to other domesticated animals.

In the modern world, pigs have a significant impact on various ecosystems. While many are farmed, some have escaped and become feral. Feral pigs can cause substantial environmental damage. In places like New Zealand and parts of South America, they destroy crops and consume wildlife, such as young tortoises and seabirds.

They can also spread animal diseases, including foot-and-mouth disease. Despite these challenges, pigs remain deeply connected to human culture. They appear frequently in art and literature and are celebrated in many cities for their meat products.