A. Individuals migrate between 2 populations that have the same gene pool. b. The thickness in fur coat for particular small mammal is determined by the average temperature in its environment. Over time, the environment gets warmer. c. A mutation introduces a new wing color in a group of butterflies. d. A flood washes away 3/4 of a population of ground squirrels. e. Within a lizard population, there is genetic variation in the length of the tail. The neighborhood cats chase the lizards, and have an easier time catching the ones with long tails.