Boiling frog

The boiling frog is an anecdote describing a frog slowly being boiled alive. The premise is that if a frog is put suddenly into boiling water, it will jump out, but if the frog is put in cold water which is then brought to a boil slowly, it will not perceive the danger and will be cooked to death. The story is often used as a metaphor for the inability or unwillingness of people to react to or be aware of threats that arise gradually.

While some 19th-century experiments suggested that the underlying premise is true if the heating is sufficiently gradual, according to contemporary biologists the premise is false: a frog that is gradually heated will jump out. Indeed, thermoregulation by changing location is a fundamentally necessary survival strategy for frogs and other ectotherms.

As part of advancing science, several experiments observing the reaction of frogs to slowly heated water took place in the 19th century. In 1869, while doing experiments searching for the location of the soul, German physiologist Friedrich Goltz demonstrated that a frog that has had its brain removed will remain in slowly heated water, but an intact frog attempted to escape the water when it reached 25 °C.

Other experiments showed that frogs did not attempt to escape gradually heated water. An 1872 experiment by Heinzmann demonstrated that a normal frog would not attempt to escape if the water was heated slowly enough, which was corroborated in 1875 by Fratscher.

Goltz raised the temperature of the water from 17.5 °C to 56 °C in about ten minutes, or 3.8 °C per minute, in his experiment which prompted normal frogs to attempt to escape, whereas Heinzmann heated the frogs over the course of 90 minutes from about 21 °C to 37.5 °C, a rate of less than 0.2 °C per minute. In "On the Variation of Reflex Excitability in the Frog induced by changes of Temperature" (1882) William Thompson Sedgwick writes: "in one experiment by Scripture the temperature was raised at a rate of 0.002°C per second, and the frog was found dead at the end of 2½ hours without having moved."

In 1888 Sedgwick explained the apparent contradiction between the results of these experiments as a consequence of different heating rates used in the experiments: "The truth appears to be that if the heating be sufficiently gradual, no reflex movements will be produced even in the normal frog; if it be more rapid, yet take place at such a rate as to be fairly called 'gradual', it will not secure the response of the normal frog under any circumstances".

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Wikipedia