A Brief History:
Rats started becoming domesticated around the 1800's. They were originally used for "ratting", a sport in which hundreds of rats were put into a pit. A dog (trained specifically for this sport) was then let into the pit, and had to kill as many as possible.
Wild rats were the first to be caught and put into the pit, until someone thought to breed them specifically for the sport. A rat catcher, named Jack Black, was supposedly the first to breed and sell Pet Rats. Over the years the idea for rats as childrens' pets has caught on, and only in recent years has it evolved to a pet for children and adults alike. Rats were officially seen as pets in the 1900's.
Rats Around the World:
There are many references to rats all over the world. China has their Year of the Rat in their Chinese Zodiac, and a rat is considered a sign of prosperity. Japan see rats as a sign of wealth and white rats are considered a messenger of one of the seven gods of luck, Daikoku, and were not killed due to this connection. They believed if the rats left your house, it was a bad omen.
There's a story about a rat couple who wanted the strongest husband in the world for their rat-daughter. They asked the Sun who declined saying that clouds had more power because they could cover him up. When they asked a cloud, he responded, "The wind is stronger than I because it can blow me away." The wind could not make the grade either. "The wall stops me cold," he said. And the wall, though honored by the offer wailed, "The rat is stronger. He can bore a hole right through me." So the couple wisely gave their daughter in marriage to another rat who was indeed the strongest creature of them all.
In Deshnoke, India, there is a temple dedicated to rats, and within it they are protected. The rats in the temple are fed the same milk shared by humans, and only ever bite when cornered. There is also a park in Calcutta, India where the rats are fed.
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