For example, rodents, like people, have different temperaments: some are timid, others are social; some are intrepid explorers, others stick close to home. And some rat mothers—even genetically identical animals—are better than others at nurturing their offspring. A nurturing rat mom pampers her pups. She hovers over them with her back conspicuously arched and legs splayed outward, allowing them to switch nipples, and she spends a lot of time licking and grooming them. A more negligent rat mom lazes on her side or lies on top of her pups as they struggle to nurse.
