Genetic resistance (or genetic tolerance) refers to the ability of certain organisms to endure environmental conditions that are extremely stressful or lethal to non-adapted individuals of the same species. Such tolerance has a genetic basis, and it evolves at the population level in response to intense selection pressures.

Genetic resistance occurs when genetically variable populations contain some individuals that are relatively tolerant of an exposure to some environmental factor, such as the presence of a high concentration of a specific chemical. If the tolerance is genetically based (i.e., due to specific information embodied in the DNA of the organism's chromosomes), some or all of the offspring of these individuals will also be tolerant. Under conditions in which the chemical occurs in concentrations high enough to cause toxicity to non-tolerant individuals, the resistant ones will be relatively successful. As time...