Ronald A. Fisher > Quotes

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

“To consult the statistician after an experiment is finished is often merely to ask him to conduct a post mortem examination. He can perhaps say what the experiment died of.”
― Ronald A. Fisher

“The value for which P=0.05, or 1 in 20, is 1.96 or nearly 2; it is convenient to take this point as a limit in judging whether a deviation ought to be considered significant or not. Deviations exceeding twice the standard deviation are thus formally regarded as significant. Using this criterion we should be led to follow up a false indication only once in 22 trials, even if the statistics were the only guide available. Small effects will still escape notice if the data are insufficiently numerous to bring them out, but no lowering of the standard of significance would meet this difficulty.”
― Ronald A. Fisher, The Design of Experiments

“It will be noticed that the fundamental theorem proved above bears some remarkable resemblances to the second law of thermodynamics. Both are properties of populations, or aggregates, true irrespective of the nature of the units which compose them; both are statistical laws; each requires the constant increase of a measurable quantity, in the one case the entropy of a physical system and in the other the fitness, measured by m, of a biological population. As in the physical world we can conceive the theoretical systems in which dissipative forces are wholly absent, and in which the entropy consequently remains constant, so we can conceive, though we need not expect to find, biological populations in which the genetic variance is absolutely zero, and in which fitness does not increase. Professor Eddington has recently remarked that 'The law that entropy always increases—the second law of thermodynamics—holds, I think, the supreme position among the laws of nature'. It is not a little instructive that so similar a law should hold the supreme position among the biological sciences. While it is possible that both may ultimately be absorbed by some more general principle, for the present we should note that the laws as they stand present profound differences—-(1) The systems considered in thermodynamics are permanent; species on the contrary are liable to extinction, although biological improvement must be expected to occur up to the end of their existence. (2) Fitness, although measured by a uniform method, is qualitatively different for every different organism, whereas entropy, like temperature, is taken to have the same meaning for all physical systems. (3) Fitness may be increased or decreased by changes in the environment, without reacting quantitatively upon that environment. (4) Entropy changes are exceptional in the physical world in being irreversible, while irreversible evolutionary changes form no exception among biological phenomena. Finally, (5) entropy changes lead to a progressive disorganization of the physical world, at least from the human standpoint of the utilization of energy, while evolutionary changes are generally recognized as producing progressively higher organization in the organic world.”
― Ronald A. Fisher, The Genetical Theory of Natural Selection

“We are quite in danger of sending highly trained and intelligent young men out in the word with tables of erroneous numbers under their arms, and with a dense fog in the place where their brains ought to be.”
― Ronald A. Fisher, Collected papers of R. A. Fisher

“The supposed conflict between heredity and environment is quite superficial; the two are connected by double ties: first that the surest and probably the quickest way to improve environment is to secure a sound stock; and secondly that, for the eugenist, the best environment is that which effects the most rapid racial improvements. The ordinary social reformer sets out with a belief that no environement can be too good for humanity; it is without contradicting this, that the eugenist may add that man can never be too good for the environment.”
― Ronald A. Fisher