Principle #1 - Genetic Variation Variation exists, some deer have long legs and some deer have shorter legs
Principle #2 - Overproduction and the Struggle to Survive Deer will always produce more offspring than the environment can survive, however, not all will live and survive.
Principle #3 - Survival and Reproduction of the Fittest Deer with longer legs can run faster away from predators like coyotes while deer with shorter legs can't.
Principle #3 - Survival and Reproduction of the Fittest Because deer with longer legs survive longer, they are able to reproduce more offspring that has the same genes as them, such as long legs.
Principle #4 - Changes in the Gene Pool Since deer with longer legs survive longer and are able to reproduce more offspring, there is a change in frequency over time in populating. Deer with long legs increased and deer with shorter legs decreased.