Domestic rats differ from wild rats in that they are calmer, less likely to bite, can tolerate greater crowding, breed earlier and are more prolific. Also, their brains, livers, kidneys, adrenal glands and hearts are smaller. | Domestic rats differ from wild rats in that they are calmer, less likely to bite, can tolerate greater crowding, breed earlier and are more prolific. Also, their brains, livers, kidneys, adrenal glands and hearts are smaller. |