The phrase survival of the fittest is not generally used by modern biologists as the term does not accurately describe the mechanism of natural selection as biologists conceive it.
https://en.wikipedia.org/wiki/Survival_of_the_fittest
But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient.”. Herbert Spencer (1820-1903) was the eldest of nine children, all the rest of whom died in infancy.
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Spencer and the Fittest. Herbert Spencer was a 19th-century philosopher and social idealist. He was known to be a strong supporter of Darwin's methods of evolution and a supporter of the evolutionary process by way of his writings and critiques of others.
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In the first four editions of On the Origin of Species, Darwin had used the phrase natural selection. In Chapter 4 of the 5th edition of The Origin published in 1869, Darwin implies again the synonym: Natural Selection, or the Survival of the Fittest.
https://en.wikipedia.org/wiki/Survival_of_the_fittest
Himmelfarb, discussing this essay, asserts even more directly that. the phrase, 'survival of the fittest' was used here for the first. time.8 James Rogers, citing A Theory of Population, affirms. that Herbert Spencer used the phrase 'survival of the fittest' as.
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Darwin wrote 'survival of the fit' to imply that those who were fit would live long enough to pass on their genes. Spencer wrote 'survival of the fittest,' implying those who were most fit would survive the social world due to some biological mechanism that made them superior.
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Who coined the phrase “the survival of the fittest”? Herbert Spencer. Spencer was an engineer, philosopher, and psychologist, who in his day was as famous as Darwin. He first coined the phrase “survival of the fittest” in his Principles of Biology (1864), having been inspired by Darwin’s theory of natural selection.
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Darwin and the Fit. Charles Darwin published On the Origin of Species which included the oft misquoted line 'survival of the fit.' Fit, not fittest, was originally written. The idea here was that one merely needed to be fit enough to reproduce to pass on its genetics in the form of a new generation.
http://study.com/academy/lesson/survival-of-the-fittest-herbert-spencer-definition-examples-quiz.html
For other uses, see Survival of the fittest (disambiguation). Herbert Spencer coined the phrase survival of the fittest. Survival of the fittest is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success.
https://en.wikipedia.org/wiki/Survival_of_the_fittest
In the early 1850s, according to historian Richard Hofstadter, Herbert Spencer . . . coined the phrase survival of the fittest.. Spencer's phrase referred to competition both in human. economics and in animal life.
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who coined the term  survival of the fittest?
Herbert Spencer coined the term survival of the fittest.  