One misconception regarding evolution is that it is only the result of natural selection. What many people don't realize, is that there are actually five contributing factors that result in the evolution of a species: mutations, gene flow, sex, small population size, and natural selection. .
Genetic variation is very important because it provides new genes for natural selection to act on. It basically provides the basic raw material for evolution. Without genetic variation evolution cannot occur, it is a prerequisite. There are three main sources of genetic variability: Mutations, Gene Flow and Sex. Mutations are changes in the DNA. Gene flow is the movement of different genes from one population to another. Sex introduces new combination of genes to the gene pool. .
Mutations are the one of the main sources of genetic variability. Mutations are any changes in the DNA sequence. Mutations mainly arise when DNA is not properly copied during mitosis and meiosis. Mitosis and meiosis are mechanical process with millions of operations that must be accurately alone for duplicated DNA molecules to be made. Environmental factors also contribute to the cause mutations are known as mutagens. Mutagens that affect human DNA are ultraviolet light, x rays, and various chemicals. .
Cells have mechanism that constantly scan the DNA and correct flaws caused by radiation, chemical damage, or any flaws in copying. But some changes in the DNA sequence slip past these near perfect mechanisms. Mutations are rare, once in 100,000 in 100,000,000 genes per individual. So mutations alone don't drive evolution but they are the source of all the new alleles. .
When these changes occur the cell that produces gametes, these mutations can be passed onto the organism's offspring, and enters the gene pool. Without mutations there wouldn't be diversity among organisms and therefore evolution would not occur. Mutations do not happen because of environmental needs and causes.