In order to examine the mechanism of evolution, one must first investigate four main causes to microevolution; Genetic drift, Gene flow, Mutation, and Selection. Evolution is a change in a population's frequencies of alleles from generation to generation. Alleles are an alternative form a gene. Genetic drift occurs when chance events and accidents such as earthquakes, floods and fires remove alleles from a larger population, and leaving a much small population. This reduction in size is generally called the bottleneck effect, which reduces the overall genetic variability in a population. Gene flow, formerly known as migration, can bring new alleles into a population through immigrating organisms. A population may gain or lose alleles when individual move from one community to the next. Gene flow has become an important representative in evolution.
Mutations are changes made in an organisms DNA. Mutation allows for new alleles to be created from old ones. This gene duplication event provides the opportunity for genes to be repurposed. Mutation in itself serves a useful purpose and is essential to evolution because it is the original source of genetic variation for Natural Selection.