 <unk> , domesticated pet rats are tamer than those in the wild . They are more comfortable around humans and known to seek out their owners while roaming freely . They have decreased reactions to light and sound , have less cautions to new food , and have better tolerance to overcrowding . Domesticated rats are shown to mate earlier , more readily , and for a longer period of time over their lifespan . Also , domesticated rats exhibit different behaviors when fighting with each other ; while wild rats almost always flee a lost battle , caged rats spend protracted amounts of time in a belly @-@ up or boxing position . These behavioral traits are thought to be products of environment as opposed to genetics . However , it is also theorized that there are certain underlying biological reasons for why some members of a wild species are more receptive to domestication than others , and that these differences are then passed down to offspring ( compare Domesticated silver fox ) . 
