Genetic variation is caused by mutations in the gametes and meiosis.
The large ears of the rabbits may help them hear when predators are coming. If they hear them coming, then they may be able to escape.
A polar bear with dark fur would be more obvious to its prey, who would more easily avoid him. The other white ones can blend in better and have a less chance of being detected by prey.
Organisms have genetic variation The conditions change The ones better at coping... survive Survivors breed and pass on their variation natural selection occurs
Some bacteria are more resistant Antibiotic is added Some bacteria survive The survivors reproduce Low levels of antibiotic remain