survival of the fittest the continued existence of organisms which are best adapted to their environment, with the extinction of others, as a concept in the Darwinian theory of evolution.

☞ The phrase was coined by the English philosopher and sociologist Herbert Spencer (1820–1903) in Principles of Biology (1865). Besides its formal scientific use, the phrase is often used loosely and humorously in contexts relating to physical fitness (or the lack of it).