Genetic variation is important because a population has a better chance of surviving and flourishing than a population with limited genetic variation. Genetic diversity also decreases the occurrence of unfavorable inherited traits.
Genetic variation comes from mutations within DNA; the movement of genes from one population to another, or gene flow; and new genetic combinations resulting from sex. When a population contains genetics of individuals who vary significantly, some of the individuals in the group can possess traits that make them resistant to disease or cold, increasing the group's chance for survival when these individuals breed with the others. A small, isolated population's individuals may be forced to breed with close relatives, increasing the occurrence of genetic flaws. When inbreeding occurs, any genetic weaknesses found in the parents can be multiplied in future generations.
Genetic variation also helps organisms survive in different climates and environments. If the environment is unpredictable over time and includes a variety of diseases and predators, some differences among individuals increase the chances of some individuals surviving to reproduce, while others do not. In disease resistance, genetic diversity is important because a disease can decimate a homogeneous population in which all the individuals are equally susceptible to the disease.