Principle #1 Genetic Variation: There are these rabbits that lived happily in the Sahara desert, there happened to be a variation in the population consisting of dark fur rabbits and the light fur rabbits.
Principle #2 Overproduction & the Struggle for Existence: One day, this hawk roamed the Sahara desert searching for food and came across this dark fur rabbit, not noticing the camouflaging light fur rabbit.
Principle#3 Differential Survival and Reproduction: The Sahara desert has light colored dirt which makes it easier for the light fur rabbits to blend in. Which makes it easier to spot the dark fur rabbits.
Principle #4 Changes in Gene Pool: Over the course of time the population of rabbits has changed , the population of the dark fur rabbit has decreased an increasingly large amount and the light fur rabbits has increased a generous amount. Thus, the light fur rabbit is the fittest and favorable trait in the environment.