Genetic diversity.

Genetic diversity is the most fundamental level of biological diversity because genetic material is responsible for the variety of life. For new species to form, genetic material must change. Changes in the inherited properties of populations occur deterministically through gene flow (mating between individual organisms representing formerly separated populations) and through natural or artificial selection (which occurs when some types of individuals breed more successfully than others). Change can also occur randomly through mutations or genetic drift (when the relative proportions of genes change by chance in small populations). Populations with higher levels of diversity tend to do better—to have more survival options—as surroundings change than do populations (particularly smaller ones) with lower levels of genetic diversity.