The domesticated guinea pig (Cavia porcellus) does not live in the wild but is most likely derived from the Andean montane guinea pig (Cavia tschudii) found in Peru, highland Bolivia, northwestern Argentina and northeastern Chile. Guinea pigs were first domesticated in 5,000 B.C. and are now globally distributed as pets and for their meat.

Guinea pigs have no tails. The length, texture and color of their fur varies by breed. There are now 13 different breeds of domestic guinea pigs: American, American satin, Abyssinian, Abyssinian satin, Peruvian, Peruvian satin, silkie, silkie satin, teddy, teddy satin, Texel, coronet and white-crested. Through selective breeding, 20 different fur color phenotypes and 13 different coat length and texture phenotypes exist among these guinea pig breeds.

These rodents have two defensive responses: the immobility response and the scatter response. The immobility response occurs when a single guinea pig perceives danger. During this response, the guinea pig becomes completely immobile until the threat has passed. The scatter response involves a group of guinea pigs. When the group perceives a threat, they scatter and split up to confuse a predator.

Male guinea pigs tend to be larger than females. In general, these rodents range from 8-10 inches (20-25 centimeters) long and weigh between 25 and 39 ounces (700 and 1,100 grams).

Guinea pigs have spread across the globe as popular laboratory animals and pets but were first domesticated and used as a traditional food source in South America. Their wild ancestors (Cavia tschudii) are native to the Andes mountains, from Peru to Argentina, and live at altitudes of more than 14,000 feet.

Guinea pigs can live up to 14 years in human care but live an average of 8 years. Female guinea pigs that reproduce have shortened lifespans and tend to live approximately 3.5 years.

This shortened lifespan is caused by the stiffening of a joint called the symphysis, which is located between the guinea pig's two pelvic bones. Pregnancy causes this stiffening and results in an inability to birth young naturally, which usually results in death due to birthing complications.

Guinea pigs produce six main vocalizations: chutts, squeaks, whines, whistles, purrs and chirps. Each vocalization conveys a different meaning. A chutt is used during predatory pursuit and whines after predatory pursuit. Squeals, squeaks and tweets indicate the presence of danger or injury. And finally, whistles and chirps convey the presence of food and are used for long-distance communication.

Guinea pigs are adapted to a diet of the herbs and grasses of montane (or mountain) meadows. As pets, they are commonly fed lettuce, cabbage, grasses, barley and Timothy hay. They are also fed pellets that are made of compressed plant material (usually alfalfa or barley). These pellets are enhanced with different vitamins and minerals vital to guinea pig health.

At the Smithsonian's National Zoo, guinea pigs eat greens, carrots, peppers, oranges, kiwis and grains. 

These rodents are crepuscular, meaning they are active during dusk and dawn.

Guinea pigs are typically considered gregarious, or social, animals. They often huddle for warmth and protection, and prefer to be in close contact with other individuals.

They are polygynous. Males form social hierarchies over food and mates, typically resulting in an alpha male within the group. For this reason, females are not typically housed with more than one male.

Female guinea pigs are called "sows" and males are called "boars." Sows are typically in estrus three to four times per year, and estrus lasts 16 days. Boars become sexually mature between 56 and 70 days old, while sows are sexually mature around 67 days old. Guinea pigs give birth to three or four pups per litter and provide little care for their pups, which wean in approximately two to three weeks.

Guinea pigs are different than most of the Smithsonian's National Zoo's animals in that they are domesticated and are not threatened or endangered. The same is true of the animals at Kids' Farm.

Amazonia is home to six female guinea pigs. Peruvian guinea pig Masi's name is Aymaran and means "friend." The other guinea pigs have names of Quechan origin. Inti, Sinchi and Miski are Abyssinian guinea pigs. Inti's name means "sun." Her sister Sinchi's name means "brave," and their half-sister Miski's name means "sweet" or "good." Peruvian guinea pig Sani's name means "brown," and American guinea pig Tuta's name means "night."