Survival of the fittest

"Survival of the fittest" is a phrase that originated in evolutionary theory as a way of describing the mechanism of natural selection. It is more commonly used today in other contexts, to refer to a supposed greater probability that "fit" as opposed to "unfit" individuals will survive some test. In this contexts, "fit" refers to "most well adapted to the current environment," which differs from common notions of the binary 'fit' and 'unfit.'^{[citation needed]}

Herbert Spencer first used the phrase – after reading Charles Darwin's On the Origin of Species – in his Principles of Biology (1864), in which he drew parallels between his own economic theories and Darwin's biological ones, writing, "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favoured races in the struggle for life."

Darwin first used Spencer's new phrase "survival of the fittest" alongside "natural selection" in the fifth edition of On the Origin of Species, published in 1869, intending it to mean "better designed for an immediate, local environment".

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