Pig | The pig was among the first animals to be domesticated.

Among the first animals to be domesticated by humans, the pig is found everywhere in the world except in Antarctica, North Africa, and far-northern Eurasia. These highly social and intelligent creatures are among the most populous large mammals in the world and are very biologically similar to humans.
The domestic pig, scientific name Sus scrofa, is a major food source for humans; approximately 60 million are found on farms in the U.S. alone, and more than 1 billion are slaughtered annually. Some pig species are classified at various levels of endangerment, however; examples of many of these species can be found in zoos around the world.
Mud Wallowers: These animals lack sufficient sweat glands to effectively regulate their body temperatures, so they often wallow in mud to cool down on hot days. The mud is also used as a sunscreen and as a way to protect their skin from parasites.
Highly Intelligent: The pig is among the most intelligent animals on the planet. It can perceive time, remember objects, use learned information to navigate environments, and engage in a range of playful behaviors.
Unique Among Hooved Animals: Unlike most hooved mammals, they do not have multichambered ruminating stomachs, so they can’t subsist off of grass and leaves alone. Also, unlike most hooved creatures, pigs build nests for their young.
It’s in the Tail: The easiest way to tell if the animal is domesticated or wild is by looking at its tail. Domestic pigs have curly tails while wild pigs have straight tails.
Hundreds of Breeds: In 2007, the Food and Agricultural Organization of the UN reported that there were more than 740 classifications, or breeds, of the domesticated pig; 137 are listed as extinct, and 130 are classified as endangered.