Genetic Drift

 What genetic drift IS:

Genetic Drift is RANDOM. In the case shown above there is a population of pink, blue, and purple bugs. A portion of that population got squashed by a shoe. That portion happened to be 2 purple bugs and a blue bug. There was only 2 purple bugs in the population to begin with so now there is not any more purple bugs in the population at all because these bugs randomly died. 

What Genetic Drift is NOT: 

Genetic Drift is not when a species has a phenotype that will allow them to better survive their environment. The green bugs above all get eaten by the lizard because their color stands out to the lizard against the dark bark of the tree. The brown bugs are not seen by the lizard so they are not eaten. This is not Genetic Drift, this is Natural Selection.