Gene Flow- A population of a certain species moves and begins to blend and interact with the local species. This blending of the foreign species and local special creates 'gene flow'. For Example- There are two populations of seal on an island, but one from one group gets split from its home group and joins the other group, creating Gene Flow for the next generation.
Genetic Drift- When a certain portion of a species is separated, and leaves a population to go to a geographically isolated area, they genetically change or drift... For Example- These Guinea Pigs were once the same species, but the lighted colored one left with a small "herd," and over generations they changed slightly to adapt better to their new environment.
Natural Selection- The idea of Natural Selection is basically survival of the fittest. Whatever trait an organism gains that the environment favors goes on to be passed to the next generation. For Example- These white geese adapted dark shapes around their eyes to help prevent blindness while in the desert, and their feet widened to get better balance on shifting desert sands...
Non-Random Mating- Organisms often prefer certain traits that help their offspring thrive, so they look for mates with those traits. For Example- A female falcon will pick the stronger of the two Male falcons to mate with, because he will be better able to help protect them, and they will be stronger when they are older too.