Generally speaking, rats are quite sociable and function best with at least one cage mate. It is generally ill-advised to keep a single rat unless there are severe behavioral problems. The earlier rats are introduced to one another, the better. Often, rat breeders will encourage new owners to take two or more rats of the same sex from the same litter for starters. Particularly with males, there can be some fighting in the beginning, but once an alpha rat has been determined, the rats should get along well. Within two weeks to a month, the rats will most likely have adjusted and become friendlier with each other. Rats are generally very friendly to other cage mates. They will even sometimes help or take care of other sick rats.