Principle #1 Genetic Variation Gray rats dont blend in so they start to die
Principle #2 Overproduction and struggle for Existence Since the brown rats can blend into there environment they can survive and reproduce and more brown rats appear than the gray rats. The gray rats struggle to survive since the brown rats are the domninates.
Principle #3 Differential Survival & Reproduction The gray rat cant survive so they all die out and the brown rats keep reproducing.
Principle #4 Changes in Gene Pool Do to changes in the gene pool the rats turn different shades of brown.