A domesticated rodent occasionally used in research
Comment Whilst guinea pigs–e.g., Cavia cobaya–are cuddly and resemble humans hormonally and in reproductive physiology, they are poor experimental models, and comprise a mere 2% of the rodents in the research rat race: they’re slow learners, have simple immune systems, long gestation periods, produce small litters, are picky eaters, are susceptible to infections and are more expensive to maintain than small rodents. Most research is performed on rats or mice, the choice being based on the researcher’s needs–e.g., mice have an immune system similar to the human MHC. Guinea pigs are traditionally classified as a New World hystricomorph rodent, phylogenetic analysis of amino acid sequence data suggest that they diverged before the separation of the primates and artiodactyls from myomorph rodents.
Definition A popular term for a person used in any empirical situation, analogous to guinea pigs which, in fact, have a very limited role as experimental animals; the name stuck, use of guinea pigs as guinea pigs did not.