Genetic diversity is so important because it helps organisms to cope with current environmental variability, as well as reduces potentially deleterious effects of close relative breeding. Genetic diversity is also the primary basis for adaption in the face of future environmental uncertainty.
Organisms exist in varying environments. These environments change through conditions such as resource availability, weather, disturbance events and the population sizes of competitor organism societies. If organisms lived in a stable environment without much variation, then a standard phenotype might be ideal because the phenotype would be optimally adapted to the stable environment's conditions. However, because the world is naturally full of unstable environments, multiple phenotypes are necessary, particularly in preventing disease through genetic disease resistance. Populations that are genetically identical are especially vulnerable to pathogens and diseases.
Close relatives that breed and have offspring create offspring that lack genetic variation. This lack of genetic variation often leads to the expression of genes and traits that are less beneficial to reproduction or survival in the world. It can also create physiological or behavioral problems that stem from the lack of genetic variation including poor biochemical balance, malformed physical structure, improper organ formation and function and disease susceptibility. Inbreeding is therefore a serious problem for organisms and organism populations.