History of The Rat... There are, in fact, over 80 different species of rats that live throughout the world. However when people use the name rat, they are usually referring to the ones that attach themselves to human civilization. These rats are referred to as commensal, which means they share our table. There are two kinds of commensal rats: the black rat also called the roof rat (Rattus rattus), and the brown rat also called the Norway rat (Rattus norvegicus). The black rat is smaller and more agile, it's origins evolving somewhere in India. Black rats were the first rats to reach Europe, as stowaways in ships carrying soldiers home from the Crusades. Once found all across North America, they are now found mainly in the southern states and California. The brown rat is larger and more aggressive, it's origins evolving somewhere in northeastern China. Brown rats prefer sewers and basements as opposed to the black rat who prefers attics and warmer climates. The brown rat is the dominant rat species of North America and is found in all 50 states. It was during the early 1800's that rats were first bred in captivity for a sport called "ratting". This was a sport were terrier dogs were released into pits filled with rats to see how many they could kill within an allotted time. In the later 1800's brown rats were domesticated on a large scale for use in the laboratory. It was through these laboratory animals that the first domesticated pet rats derived their origins, as scientists, seeing what good pets they made, would bring them home for their children to raise. The domestication process caused many changes to the brown rat. The most obvious one being color. Breeding for white was prevalent at first, but now you can find domesticated rats in all forms of colorations, not to mention mutations like the hairless rat and tailless rat. Domestic rats also have smaller brains, livers, kidneys, and hearts than those of their wild cousins, and are more tolerant of greater crowding, and are more receptive to breeding at a much earlier age. However, most importantly, the domestic rats' psychology has been changed from that of it's wild cousin. When seized or restrained, domestic rats rarely attack their owners, and the instinct to flee from human beings has been greatly reduced.