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Sir Ronald Aylmer Fisher (17 Feb 1890 - 29 Jul 1962) British statistician, geneticist and evolutionary biologist who contributed to mathematical statistics, but also initiated biometric genetics and investigated dominance, backed up with practical breeding experiments. He published his fundamental theorem of natural selection in 1918. Short biography of Sir Ronald Aylmer Fisher >>

Ronald Aylmer Fisher
“Natural selection is a mechanism for…improbability.”

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“Natural selection is a mechanism for generating an exceedingly high degree of improbability.”

— Ronald Aylmer Fisher

From Evolution as a Process (1954).

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Although this is well-known, and seen as a quote which various sources ascribe to Ronald Fisher, these words were actually written by Julian Huxley, to summarize Fisher's idea made in longer quote. Both forms appear in the book Evolution as a Process (1954) which Huxley co-edited. The shorter version was provided by Huxley early in the book to introduce Huxley's concept. It appears in full, later in the book, in the essay by Fisher, “Retrospect of the Criticisms of the Theory of Natural Selection.” The shorter quote is clearly not verbatim, but in Huxley’s words, when compared with the statement as it was actually written by Fisher:

“It was Darwin’s chief contribution, not only to Biology but to the whole of natural science, to have brought to light a process by which contingencies a priori improbable are given, in the process of time, an increasing probability, until it is their non-occurrence, rather than their occurrence, which becomes highly improbable.”

The essay itself is written to look back at what Fisher identifies as historically four successive “comparatively distinct periods” when “objections and difficulties in respect of Darwin’s views” were aired. Fisher considers these periods to be:

(a) “the difficulties which he himself felt during the period the theory was developing in his mind”, (b) objections from scientific friends discussed “as difficulties of the theory in the sixth chapter of the Origin”, (c) the reactions expressed in the essays of “the more conservative or recalcitrant biologists … to the growing acceptance of Darwin’s views” and (d) when the early geneticists widely disseminated the assumption “that the discovery of Mendel’s laws of inheritance was unfavorable, or even fatal, to the theory of natural selection.”

Midway through his essay, Fisher addresses one of these difficulties “with respect to organs of extreme perfection, of which Darwin chooses the eye as an example.” Darwin recognized that this only became a difficulty to understand if imagination is too limited. Quoting Darwin from chapter 6 of the Origin:

“Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory.”

The subject quote (given at the top) by Fisher is part of his remarks to expand on the idea, which in the essay followed the Darwin quote.

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Nature bears long with those who wrong her. She is patient under abuse. But when abuse has gone too far, when the time of reckoning finally comes, she is equally slow to be appeased and to turn away her wrath. (1882) -- Nathaniel Egleston, who was writing then about deforestation, but speaks equally well about the danger of climate change today.

Carl Sagan: In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) ...(more by Sagan)

Albert Einstein: I used to wonder how it comes about that the electron is negative. Negative-positive—these are perfectly symmetric in physics. There is no reason whatever to prefer one to the other. Then why is the electron negative? I thought about this for a long time and at last all I could think was “It won the fight!” ...(more by Einstein)

Richard Feynman: It is the facts that matter, not the proofs. Physics can progress without the proofs, but we can't go on without the facts ... if the facts are right, then the proofs are a matter of playing around with the algebra correctly. ...(more by Feynman)

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