Fitness is a term used in genetics and evolutionary biology, to indicate the contribution of the genotype (i.e., the specific genetic information encoded in the DNA of an organism) of a particular individual to the next generation of its population, in comparison to the contribution of other genotypes. (The term fitness is also sometimes used in reference to a particular allele, i.e., to one of two or more possible combinations of DNA comprising the information of a specific gene.)

All individual organisms eventually die. However, according to evolutionary theory, individuals can continue to influence the evolution of their population and species, if they have passed as much as possible of their genetic information on to succeeding generations, that is, by having a high fitness.

The fitness of an organism is related to the degree to which it is adapted to its environmental and social circumstances. An...