Frog Fable Brought to Boil

By Dr. Karl S. Kruszelnicki

If you plunge a frog into boiling water, it will immediately jump out. But if you place the frog into cool water and slowly heat it to boiling, the frog won’t notice and will slowly cook to death. So claims the myth. Indeed, everyone—from corporate consultants to politicians to environmental activists—cites the frog fable as proof that people often don’t see change happening and cannot deal with it in the aftermath.

So how did this myth begin? Maybe it arose because frogs are cold-blooded. We humans are warm-blooded: our internal thermometers measure the local temperature, and then we shiver or sweat to maintain a body temperature of around 37 degrees Celsius. But a cold-blooded frog maintains the temperature of its immediate environment. Perhaps somebody once wrongly thought that this meant frogs had an inferior or inadequate thermometer.

Or perhaps the story began with E.W. Scripture, who wrote The New Psychology in 1897. He cited earlier German research: “. . . a live frog can actually be boiled without a movement if the water is heated slowly enough; in one experiment, the temperature was raised at the rate of 0.002 [degrees Celsius] per second, and the frog was found dead at the end of 2.5 hours without having moved.

Well, the numbers just don’t seem right. If the water comes to a boil, that means a final temperature of 100 degrees Celsius. In that case, the frog would have to have been put into the water at 82 degrees Celsius. Surely, the frog would have died immediately. Scripture also wrote that the frog was found “without having moved.” How do you convince a frog not to move for more than two hours?

Then there’s the issue of the real-life behavior of frogs. First, a frog cannot jump out of boiling water. Remember the last time you dropped some egg white into boiling water: the proteins coagulated into a mess of thin, white strands. Unfortunately, the proteins in the frog’s skinny legs would do the same thing. So the frog in boiling water could not jump anywhere. It would die a nasty death.

Dr. George R. Zug, curator of reptiles and amphibians at the American Museum of Natural History in New York, and Professor Doug Melton of Harvard University both agree on this point.

Second, a frog would notice the water getting hot. Dr. Victor Hutchison, a herpetologist at the University of Oklahoma, has dealt with frogs throughout his professional life. Indeed, one of his current research interests is “the physiological ecology of thermal relations of amphibians and reptiles.” Professor Hutchison states, “The legend is entirely incorrect! The ‘critical thermal maxima’ [the maximum temperature an animal can bear] of many species of frogs have been determined by several investigators. In this procedure, the water in which a frog is submerged is heated gradually at about 2 degrees Fahrenheit per minute. As the temperature of the water is gradually increased, the frog will eventually become more and more active in attempts to escape the heated water.”

So real-life experiments show that the frog-in-boiling-water story is wrong. If only this fact could make it into real life, too. ❧

DR. KARL KRUSZELNICKI is an Australian Science broadcaster and the author of 30 popular science books. For more info, visit: This article was adapted from his book “It Ain’t necessarily So… Bro”



  • Steven Earl Salmony April 9, 2011 at 6:13 pm

    In search of sustainability for humankind…

    Would professionals with appropriate expertise please examine the extant science regarding human population dynamics and human overpopulation of Earth? How can this knowledge be used to move the human community from the dangerous and patently unsustainable ‘trajectory’ it is on now to sustainable lifestyles and right-sized corporate enterprises?

    —–Original Message—–
    Sir John Sulston, Chair
    People and the Planet Working Group
    UK Royal Society
    March 31, 2011

    Dear Sir John Sulston:

    Your recent comments regarding the review of research on the human population and its impact on the planet we inhabit by a high level panel of experts give rise to hope for the future of children everywhere. Thanks for all you, the Planet and the People Working Group and the UK Royal Society are doing to protect biodiversity from massive extirpation, the environment from irreversible degradation and the Earth from wanton dissipation of its finite resources by the human species. I am especially appreciative for two quotes from you,

    …… “we’ve got to make sure that population is recognized… as a multiplier of many others. We’ve got to make sure that population really does peak out when we hope it will.”

    …….”what we want to do is to see the issue of population in the open, dispassionately discussed…. and then we’ll see where it goes.”

    Inasmuch as you and an esteemed group of professionals with appropriate expertise are examining scientific evidence regarding the unbridled increase of absolute global human population numbers, please note there is research that has been summarily dismissed by many too many of our colleagues regarding human population dynamics and human overpopulation which I would like to bring to your attention. For the past ten years I have been unsuccessfully attempting to draw attention to certain evidence that to date remains both unchallenged and ignored by virtually every top-rank professional. They appear unable to refute the evidence and simultaneously unwilling to believe it. Their unexpected conspiracy of silence has served to conceal certain research by David Pimentel and Russell Hopfenberg. How else can it be that so many established professionals with adequate expertise act as if they are willfully blind, hysterically deaf and electively mute in the face of scientific evidence of human population dynamics and human overpopulation? The conscious denial of what could somehow be real about the growth of the human population in our time is not doing anything that can be construed as somehow right and good for future human wellbeing and environmental health, I suppose. It appears as if we could be witnesses to the most colossal failure of intellectual honesty, moral courage and nerve in human history.

    Peer-reviewed professional publications, letters to the editor, slideshow presentations et cetera can be found at the following link,

    Thank you for attending to this request for careful, skillful and rigorous scrutiny of research from two outstanding scientists. Please know I am holding onto a ray of hope that the research of Hopfenberg and Pimentel is fundamentally flawed; that human population dynamics is different from, not essentially similar to, the population dynamics of other species; and that human population numbers are not primarily a function of an available supply of food necessary for human existence. That would be the best news.

    Sometime soon, I trust, many scientists will speak up with regard to apparently unforeseen and unfortunately unwelcome science of human population dynamics and human overpopulation the way people in huge numbers in the Mid-East are calling out for democracy now.

    Respectfully yours,

    Steve Salmony

    Steven Earl Salmony
    AWAREness Campaign on The Human Population,
    Established 2001


  • a frog preferring not boiled December 7, 2011 at 1:16 pm

    The New Psychology(1897) cited it was saying “it found dead” and not saying “it was dead in boiling water”.

    So, 0.002 [degree Celsius] per second (18 degree/2.5h) is not strange.

    That makes whole sentence of this article weird.

    I read a reference about Critical Thermal Maximum part on Wikipedia, but I want to see a result at 0.002 experiment to make sure if it’s wrong.

    Is there anything at 0.002?


    • really? January 22, 2012 at 4:16 pm

      I agree, the article never stated that it was boiling according the what has been posted. Also we need to figure out the difference between .002 degrees CELSIUS per SECOND to 2 degrees FAHRENHEIT per MINUTE


    • George Hallaway July 28, 2015 at 8:22 pm

      Well, at 0.002 C per second, the frog might overheat and pass out of hyperthermia well before the water became uncomfortably hot. Once unconscious, the frog won’t be going anywhere…


  • felix August 10, 2012 at 6:28 pm

    It really doesn’t matter one way or the other: the truth is the undeniable. We will all die
    We humans with our power/blessing/curse of denial accomplish the equivalent: inertia prevents action. It was nice to be alive for awhile, i guess
    Who is really at fault? God, maybe?
    Isn’t religion wonderful?
    Good luck


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