Maintenance of Deleterious Alleles

Deleterious alleles are, by definition, not beneficial and should be selected out. However, sometimes deleterious alleles are maintained in a population, despite their harmful effects. Scientists have proposed several explanations for this unintuitive quirk of biology. Overdominance, otherwise known as heterozygote advantage, and mutation-selection balance are two such explanations.

The Fitness Illusion

The problem here is three fold. One, the evolutionists are very inconsistent with their application of this definition. Second, measuring fitness in this way is, in a sense, the ultimate rescuing device. Third, fitness must be measured at the organismal level, not the genetic level, but evolutionists almost always appeal to genetic fitness.