The four main driving forces of evolution are natural selection, mutation, genetic drift and gene flow. The process of natural selection involves organisms possessing certain physical characteristics that can be deemed "advantageous" to the survival in their environment. This, in effect, allows them to reproduce and pass on those same genes at a higher rate than the same organisms that do not have that same competitive advantage. Mutation is the random of an organism's gene or chromosome that are the result of an addition, removal, or substitution of certain parts of the DNA sequence. Genetic drift is the alteration of allele regularity found in one generation as compared to the next generation. Gene flow is the exchange of genetic material between two populations of organisms. This process can work to reduce the amount of variation between the two populations. …show more content…
In the case of sickle-cell anemia, "individuals who have two copies of the β-globin sickle-cell allele develop sickle-cell disease and generally do not survive into adulthood without intensive medical care. Individuals with one copy of the β-globin sickle-cell allele and one β-globin wild-type allele have red blood cells that are functional and resistant to the organism that causes malaria. Because individuals with this combination of alleles tend to survive malaria better than those who carry only the wild-type allele, the combination is advantageous to those who live in areas where malaria is present. This is called "heterozygote advantage." As a result, the beta-globin sickle-cell allele will be maintained along with the wild-type allele in populations exposed to malaria—an example of balancing