This selection and variation happens more gradually. It is hard to notice over a short period of time. The change is slow, constant and consistent. In punctuated equilibrium, the changes come in spurts. There are periods wherein a huge change occurs and there are also periods with very little change. The mutation is at random. Genetic drift is the change in the frequency of a gene variant due to a random sampling of organisms.
It is a group designed to not be affected by any variables and to be used as a comparison to the other groups. It helps increase the reliability of your results, as it shows your independent variable is what made something happen in your experiment.
