As in any pet care, the wild origins dictate a lot of what is important in Guinea Pig care. The guinea pig is a type of rodent that is also known as the Cacy. They are not in fact pigs, as their name would have suggested.  They come from the moutains of South America, and research has shown Guinea Pigs are descendants of closely related species such as Cavia aperea, C. fulgida, or C. tschudii, so therefore do not exist as a wild species.
The guinea pig plays an important role as both a food source and the culture of many South Americans. Guinea Pigs were domesticated 5000 years ago for nourishment and have appeared in the history and culture and are frequently used in metaphors.
They came to Europe in the 16th century by European traders and has since enjoyed widespread fame as a family pet.  In the early days they were seen as an mysterious pet and even Queen Elisabeth I had one. They were widely used for biological experimentation since the 17th century, giving way to the metaphor “guinea pig” for a test subject, though more recently they have been replaced by mice and rats.
They are very docile easy to look after and are easy to handle and feed and are therefore popular with pet sitters. They hate exploring and will not try to escape, even if the cage door is left open (no promises!). Guinea pigs will often whistle when interested, for example when they hear food being prepared or the owner comes near.
There are lots types of domesticated guinea pigs, which vary in color and hair differences. The most normal varieties are the shorthair (or American shorthair), the Abyssinian with a ruffled coat. More specialist long hair types include the Peruvian and the Sheltie (or Silkie) and the curly long hair Texel.

So should I choose a Guinea Pig?

Guinea Pigs are very friendly animals – so you need to be able to dedicate enough time for them, or else they will feel lonely and this might lead to stress and sickness. This is especially important if you are buying one for the kids, on the understanding that the kids will look after the guinea pig. Consider carefully that they typically live for about five, but may live for 8 years and the Guinness Book of Records has the record age for a guinea pig at 14 years.
Guinea pigs are particularly large for rodents, weighing between 700 and 1200g (1.5-2.5 pounds), and measuring between 20 and 25 cm (8–10 inches) in length. Which means that you need to have more space for the cage. Though as a tough animal, this could be located in an outbuilding or a protected corner outside. They put up with cold better than excessive heat. Avoid wire mesh floored cages, as this can hurt their feet and lead to infection.
As for many pets you do not want to put two males together as they will fight  together when they become mature at about 6 months for leadership. Females can however be grouped together. Obviously you do not want to add a male to the group as they breed very easily.

They are grass eaters, which they digest with the help of their long colon. Hay is an alternative to the grass in a domestic situation. Like us they cannot synthesise vitamin C and will need to attain this through their diet, otherwise scurvy will kill them. Scurvy shows itself through sluggishness.  So feed them often fresh, raw fruits and vegetables (such as broccoli, apple, cabbage, carrot, spinach and celery). Another option is through dietary supplements. They are fussy eaters when mature, so with a young guinea pig give a varied foods. They feed continuously, so ensure there is hay available for them to eat.
They, as well as scurvy, may also suffer from respiratory tract infections, diarrhea,  abscesses due to infection (often in the neck, due to hay embedded in the throat, or from external scratches), and infections by mites, lice or fungus.

They are active throughout the day, with periods of sleep inter dispersed with activity. They often groom themselves and will groom others.