How do rats reproduce?

Being mammals, rats use a very similar method to humans when it comes to reproduction. Unlike humans, however, rats can breed much quicker because the gestation period of a female is roughly 21 days.

When in heat, a female rat can mate as many as 500 times during a period of 6 hours or so. Females go through this state six times a year, so although the average lifespan is only 2 or 3 years, it isn't unreasonable to expect a pair of rats to create several thousand descendants before passing on.