Guinea pigs and hamsters differ in size, life expectancy, sleep schedule, native range, sociability and biological grouping. Although they are both kinds of rodents, hamsters are from the family Cricetidae and are actually more closely related to mice or voles than to guinea pigs. Guinea pigs belong to the family Caviidae, a group of rodents unique to South America.
Guinea pigs sold in the pet trade no longer exist in the wild. They have been developed as domestic animals over thousands of years, initially as a food source for native people in South America. They are still eaten in certain countries, whereas domestic hamsters were never bred as food animals. Domestic hamsters make up several different species; there is only one species of domestic guinea pig. The native distribution of hamsters is Europe, Asia and Africa, very far from the native distribution of guinea pigs.
Guinea pigs are larger, and in some cases much larger, than hamsters, particularly the dwarf varieties. Guinea pigs grow to be between 8 and 12 inches long; dwarf hamsters can be as small as 2 inches. Guinea pigs also live much longer than hamsters. The oldest guinea pigs can live for 14 years. The longest-lived captive hamster on record lived for 10 years, but most only live from two to four years.
Hamsters are mostly active at night and sleep during the day. Guinea pigs are mostly active during dawn and dusk. Guinea pigs have a larger repertoire of vocalizations than hamsters, including squeaks and screams. Guinea pigs are sociable animals and more amiable to human handling, while most hamster species are solitary and may slowly warm to handling by their owners.