Micro-evolution is evolution within a species. So organisms in a species change, but those organisms stay within that same species. There are five ways to change the gene pool of a population, which causes micro-evolution. Natural selection, mutations, genetic drift, gene flow, and non-random mating. Natural selection is the theory proposed by Charles Darwin. The theory is that only the organisms that are best suited to their environment survive, and pass their genes onto their offspring. Ex. A white mouse in the snow will blend in and therefore survive better than a black mouse, who is easily seen by predators. Mutations are changes in the DNA of an organism. A mutation can either be helpful, harmful, or have no effect on the organism, and this mutation can be passed on to future generations. Ex. A green frog has a mutation to become blue. This could be helpful, harmful, or have no effect, based on its environment. Genetic drift is the change in a gene pool due to a random event. Ex. There are four purple beetles and four yellow beetles in a population but only the yellow beetles reproduce, so now, due to a random event, the whole population is yellow. Gene flow is the movement of genes from one population to another. The introduction of a new organism, or the departure of an organism can cause changes to the gene pool, and therefore, evolution. Ex. The introduction of a red snake to a population of black snakes would introduce new genes from the red snake. Lastly, non-random mating is when organisms find a mate based on its characteristics. Organisms may choose their mate based on their size. territory, song, colour, display and so on. Therefore the organisms with the best characteristics are able to pass their genes on to future generations, because they could attract a mate the best. Ex. A peacock with the most spots on its tail will attract the most females, and pass its many spots genes onto its offspring. There are also three types of micro-evolution. Stabilizing selection, which favours the most common variation, and makes the most common, even more common. Directional selection is when a variation at one end of the curve is favoured over the middle and other end of the curve. Disruptive selection is when the variations at both ends of the curve are favoured over the average.