Rattus sapiens, more commonly referred to as Rats are a fictional, sentient, humanoid species from the Red Dwarf television series.
The series generally refers to them simply as Rats. In one universe visited by Rimmer, whose history may mirror the prime universe, they are all originally descended from a single pregnant rat of Earth-origin, a pregnant pet rat of Dave Lister whom he bought on shore leave on Mimas for companionship after breaking up with Kristine Kochanski.
After the radiation leak which killed the crew of Red Dwarf, the rat's bred, safely sealed in the hold, and evolved to a humanoid form - much like humans did from apes - over three million years, sped up by traces of the radiation. However unlike the Felis sapiens they did not leave the ship they remained taking over much of the ship. Unlike their Cat counterparts, Rats looks like giant rats with the ability to walk and talk like humans. They seem to enjoy eating cheese. When Lister was brought out of Stasis he befriended one of them calling him the Rat.
Red Dwarf the Roleplaying Game
In the Red Dwarf the Roleplaying Game, Rattus sapiens (also known as Evolved Rats) are one of several known breeds of Evolved Animals that exist in the multiverse, and these are also playable races. See the Evolved Animals article for more.
Rats are the descendants of the ship's evolved lab rats, evolving into Rattus sapiens and have set up shops all along the Blue Dwarf's Promenade. The shops offer a variety of services such as dinning, pubs, game centres, clothing repair, trinket repair and resale shops. The rats didn't keep very good history on their race since survival was their first concern until they were able to get a strong hold on the ships trade center. Once the rats were established they had a strong period of growth before the crew began to awaken.