The guinea pig was first domesticated as long ago as 2000BC in the Andes in South America, in the region now known as Peru and Bolivia. They were originally kept for food, but some may have become family pets for the children at that time. Guinea pigs were not often bought; rather they were given as presents, especially as wedding gifts, or as gifts to special guests or children! They would be kept in the household kitchen, where they would be allowed to run around freely.
At this time the guinea pig also played the role of the evil spirit collector in traditional healing rituals. In Andean medicine the guinea pig was rubbed over the body of a sick patient, and when it started squeaking they believed it had identified the affected area! Black guinea pigs were considered especially holy, as in the wild black is the rarest colour, most wild guinea pigs are brown or grey, similar to the agouti colour we see today.
In the 1700s Dutch and English traders brought guinea pigs over from South America to Europe, where they became popular pets for the aristocracy. It is possible that on the journey over to Europe that they did stop at Guinea, leading people to believe that was where they came from. Queen Elizabeth 1 owned a pet guinea pig, which probably accounted for their popularity as pets from that time.
Guinea pigs are now extremely popular pets. They are very friendly and have no tendency to bite or scratch (if you do get nipped by mistake it is probably because they mistook your finger for a carrot!). They are also very hardy, and if cared for properly they have very few health problems.