Behaviorally, 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, are less cautious of 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).