Evolution is the process of biological change over time. Such changes, especially at the genetic level are accomplished by a complex set of evolutionary mechanisms that act to increase or decrease genetic variation.
Evolutionary theory is the cornerstone of modern biology, and unites all the fields of biology under one theoretical umbrella to explain the changes in any given gene pool of a population over time. Biological evolutionary theory is compatible with nucelosynthesis (the evolution of the elements) and current cosmological theories in physics regarding the origin and evolution of the universe.
There is no currently accepted scientific data that is incompatible with the general postulates of evolutionary theory, and the mechanisms of evolution. Moreover, there is an abundance of observational and experimental data to support the theory and its subtle variations…
Evolution requires genetic variation, and these variations or changes (mutations) can be beneficial, neutral or deleterious. In general, there are two major types of evolutionary mechanisms, those that act to increase genetic variation, and mechanisms that operate to decrease genetic variation.
Mechanisms that increase genetic variation include mutation, recombination and gene flow….
...In contrast to mechanisms that operate to increase genetic variation, there are fewer mechanisms that operate to decrease genetic variation. Mechanisms that decrease genetic variation include genetic drift and natural selection. (more).