fitnesses

Fitness, in evolutionary biology, refers to the genetic contribution of an individual or genotype to future generations. It captures reproductive success and the likelihood that an individual's genes will be represented in the population. Fitness is not synonymous with health or vigor; it is a relative measure of genetic propagation within a given environment and population.

Fitness can be described as absolute fitness or relative fitness. Absolute fitness (W) is the ratio of the number of offspring an individual leaves to the average number of offspring in the population. Relative fitness scales absolute fitness so that the most successful genotype has fitness 1; the mean fitness W_bar serves as a baseline.

Fitness typically comprises components such as viability (survival to reproductive age), fecundity (offspring production), and mating success. The environment, social structure, and interactions among genes shape these components, making fitness context-dependent. Fitness values, or fitnesses, are used in population-genetic models to predict changes in genotype frequencies; fitness landscapes map genotypes to reproductive success.

The plural fitnesses is used when comparing multiple genotypes, populations, or environments; in many texts, fitness or fitness values are preferred. In everyday language, fitness can also mean physical fitness or health, a distinct concept from evolutionary fitness.