∞ generated and posted on 2016.09.10 ∞

Measure of the success of organisms in light of natural selection, typically determined in terms of reproductive success.

Fitness describes how many babies an organism has – that survive to have babies of their own – along with how soon in a organism's life those babies are made (with more babies, more reproductively successful babies, and sooner babies all contributing to a greater fitness).

The reproductive success of organisms can be measured either in terms of the number of progeny (babies) produced but more rigorously involves measurement of the number of progeny which go on to make progeny of their own. Additional, important components of fitness include survival to the point of reproduction, the number reproductive episodes, the clutch size per reproductive episode, and, coming full circle, the survival of progeny to reproductive maturity.

Note that an additional as well as crucial component of fitness is what is known as generation time, that is, how soon in an organism's life it reproduces, with sooner reproduction, greater survival, and greater numbers of progeny produced all contributing to higher fitness.

Note that fitness more formally can be described as a Darwinian fitness plus can be differentiated into an absolute fitness (how many progeny are produced per unit time) versus a relative fitness (how many progeny are produced, per unit time, relative to other members of the same population).