Absolute Fitness

∞ generated and posted on 2016.12.04 ∞

Number of successful offspring produced by a given entity, with entities often differentiated in terms of their genotypes.

Absolute Fitness is a measure of the ability of an organism, or genotype, to replace itself, with replacement representing an absolute fitness of 1.0 (one surviving and then successfully reproducing offspring per parent), greater than 1.0 meaning increasing representation in the environment (in absolute terms), and less than one meaning decreasing representation.

Genotype may be defined fairly narrowly, particularly to consider the fitness impact of different alleles found at a single locus. That fitness impact, though, can vary as a function of environment, the rest of an organism's genotype, and even the frequency of other genotypes within a population.

Offspring success is often defined in terms of further offspring production. Absolute fitness thus is the number of offspring produced that go on to produce offspring of their own, and as may vary depending upon what alleles an organism carries. See, by contrast, relative fitness and average fitness.

Figure legend: Reproduction of blue-eyed cats (hypothetically) is three per generation versus two per generation for green-eyed cats. The absolute fitness therefore is 3 versus 2, respectively. The relative fitness, in turn, is 50% higher for the blue-eyed cats versus the green-eyed cats.

For genotypes that are neither growing nor declining in absolute numbers, within specific environments, then the absolute fitness is 1.0. If the genotype is increasing in numbers then the absolute fitness is greater than one, or less than one if the genotype is decreasing in numbers.

Note in particular that this value is at least potentially independent of the absolute fitness of other members of the same population.