A measure of biological fitness expressed as the total number of gene copies transmitted to the subsequent generation or the total number of surviving offspring that an individual produces during its lifetime
In biology, Darwinian fitness or simply fitness of a biological trait describes how successful an organism has been at passing on its genes. It is different from physical fitness wherein the latter is concerned about the physical wellbeing of an organism. In Darwinian fitness, it is about the suitability of an organism to reproduce offspring. The more likely that an individual is able to survive and live longer to reproduce, the higher is the fitness of that individual. There are two ways through which fitness can be measured: (1) absolute fitness and (2) relative fitness.
In absolute fitness, the fitness of an organism involves the number of offspring that a fit organism would reproduce in its lifetime and that its offspring would reach reproductive age.
Absolute fitness (wabs) can be expressed as the total number of individuals, of phenotypes, or of genotypes. It can also be calculated as the product of the proportion survival and the average fecundity. An absolute fitness of > 1 means a growth in a particular genotype's abundance whereas an absolute fitness of <1 indicates decline.