Principle #1 Genetic Variation: This is an example of genetic variation because there are different kinds of snakes. The ones with the right genetic variation can survive and reproduce but, the ones who don't have less chances of surviving.
Principle #2 Overproduction & the Struggle for Existence: This is example because the red and yellow snakes are going to die out because they can be easily seen and the green have an advantage because they can't be easily seen.
Principle #3 Differential Survival & Reproduction: The green snakes are reproducing more because they can't be easily seen unlike, the other snakes.
Principle #4 Changes in the Gene Pool: The change is, more of the snakes are now green in order to be able to blend in better with there surroundings.