a scientist is studying trait variation in oldfield mice. mice that live on the beach are lighter colored than mice that live inland. she collects infant mice from populations in both regions and rears them under two conditions in her lab: on sand and on soil. reared on sand, the beach mice are just as light as their parents, while the inland mice are just as dark as their parents. reared on soil, both types of mice are dark. from this she concludes that: