Survival of the fittest

"Survival of the fittest" is a phrase which is shorthand for a concept relating to competition for survival or predominance. Originally applied by Herbert Spencer in his Principles of Biology of 1864, Spencer drew parallels to his ideas of economics with Charles Darwin's theory of evolution by what Darwin termed natural selection.

Darwin first used Spencer's phrase "survival of the fittest" as a synonym for "natural selection" in the fifth edition of On the Origin of Species, published in 1869.^[1][2] It is a metaphor, not a scientific description,^[3] and is both incomplete and misleading. Survival is only one component of selection, and for example where a number of males survive to reproductive age, but only a few ever mate, the difference in reproductive success stems mainly from ability to attract mates rather than ability to survive. In an evolutionary sense, fitness is the average reproductive output of a class of genetic variants in a gene pool, and should not be confused with physically fit meaning biggest, fastest or strongest, which does not necessarily lead to reproductive success.^[4] It is not generally used by modern biologists, who use the phrase "natural selection" almost exclusively.

An interpretation of the phrase to mean "only the fittest organisms will prevail" (a view sometimes derided as "social Darwinism") is not consistent with the actual theory of evolution. Any individual organism which succeeds in reproducing itself is "fit" and will contribute to survival of its species, not just the "fittest" ones, though some of the population will be better adapted to the circumstances than others. A more accurate characterization of evolution would be "survival of the fit enough."^[5]

The phrase "survival of the fittest" is sometimes misunderstood to simply mean "survival of those who are better equipped for surviving," which is a rhetorical tautology. What Darwin meant was "better adapted for immediate, local environment", tracking changing environments by differential preservation of organisms better adapted to live in them. The theory is not tautological as it contains an independent criterion of fitness.