If you drop a frog in a pot of boiling water, it will of course frantically try to clamber out. But if you place it gently in a pot of tepid water and turn the heat on low, it will float there quite placidly. As the water gradually heats up, the frog will sink into a tranquil stupor, exactly like one of us in a hot bath, and before long, with a smile on its face, it will unresistingly allow itself to be boiled to death. — from Daniel Quinn’s “The Story of B” (1996)
You may have heard of the boiling frog tale, often used as a cautionary anecdote about the dangers of inaction, letting harmful but gradual change get the better of us before realizing too late.
This “tale” is not that old, the idea probably starting to circulate in the 1970s. If the idea is true, it does make quite an apt parable, so people have naturally wondered about its accuracy. Since 1995, a few scientists have chipped in and boldly proclaimed that the premise is false. Here’s what has been said by different modern scientists:
If you put a frog in boiling water, it won’t jump out. It will die. If you put it in cold water, it will jump before it gets hot—they don’t sit still for you.
If a frog had a means of getting out, it certainly would get out.
The legend is entirely incorrect! The ‘critical thermal maxima’ 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 2 degrees Fahrenheit [about 1.1 degrees Celsius] 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. If the container size and opening allow the frog to jump out, it will do so.
It seems pretty conclusive then. Only a fool would have believed the idea anyway; it sounds inherently ridiculous in the first place that a frog wouldn’t notice themselves being cooked to death. And that’s what the internet has concluded, smugly knowing that they can refute any use of the boiling frog analogy from hereon.
The last quote is the response from an expert on frogs. I don’t doubt his technical knowledge, but his conclusion is wrong.
Here’s the thing. In the late 19th century, several people were doing tests that related in some way to this topic. At least three of those experimenters directly claim that it is possible to have a frog in cold water and heat the water gradually to the point that the frog dies without it trying to escape. Sure, their understanding of physiology was highly speculative back then, but mostly what they did was perform lots of experiments. They also came up with theories to explain their results, but there was a lot left unexplained, plenty of disagreement, and a lack of technology to prove anything for sure (“it only remains for the microscope to detect the structural peculiarities of these three kinds of nervous end-organs”). We can summarize some independent results as follows:
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. In his experiment, Goltz had raised the temperature of the water from 17.5 °C to 56 °C in about ten minutes, or 3.8 °C per minute.
An 1872 experiment by Heinzmann was said to show that a normal frog would not attempt to escape if the water was heated slowly enough, which was corroborated in 1875 by Fratscher. 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.
It is easy to prove, and is practically admitted by all observers, that under heating which is at all entitled to be called “gradual,” the immersion of an actively reflex frog suspended as described above and immersed to the fore limbs or to the anus, will bring about such a state of things that the animal will pass into heat rigor without making a single movement of consequence.
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 repose of the normal frog under any circumstances, though it will do so for the reflex frog if only enough of his skin be immersed…
There’s obviously a contradiction. Our modern scientists are saying the boiling frog tale is a completely myth, but if that’s true, how do you explain those 19th century experiments? It really makes me angry to consider that one scientist or other must be talking out of their ass. Thankfully, I’ve found that that isn’t quite the case.
There’s no academic dishonesty going on; our modern scientists, who have stated their opinions without any experimentation, are simply uneducated in this matter. Many people have wrongly assumed that our modern scientists who have made those comments are even aware of those 19th century experiments. I guarantee you they haven’t read those papers either. You can’t refute a hypothesis if you’ve misunderstood it or don’t even know what it states. The facts go roughly like this:
- Boiling water will kill a frog very quickly.
- Being exposed to excessive temperatures leads to irreversible stiffening of a frog’s muscle tissue.
- The fatal temperature for a frog is below boiling point, more like up to 40 °C.
- A frog will “violently” try to escape out of water being heated at a moderate rate. This was demonstrated in the 19th century experiments as well as more recently.
- The important question is whether there exists a gradual rate at which a frog wouldn’t react.
So, if a frog can be heated in water from 20 °C to 40 °C without attempting to escape, then it will likely have already died by that point. We could say it has been “boiled to death”, even if the water never comes to a boil. (Analogy: replace frog with human and 40 °C with a 60 °C spa, and you would call that boiling to death.)
I read William Sedgwick’s article (“On the Variation of Reflex Excitability in the Frog induced by changes of Temperature“) that summarizes the experiments going on (including his own) during that the late 19th century. It’s clear that these experiments were not made up, and that many experiments were being performed. I even secured a copy of Heinzmann’s paper (which is in German), in which he details 27 separate experiments. I don’t know much about Sedgwick, but he’s reputable and it’s apparent from his writing that he’s no fool. These experiments were real, performed by various discerning individuals, and they were investigating details far more controversial than the boiling frog parable itself (which probably didn’t even exist at the time). It’s true that they obtained many conflicting results, but only in their more nuanced experiments; Sedgwick talks about the premise of the boiling frog as if everyone working on the topic knows or has probably verified it for themselves. At least Heinzmann, Fratscher, and Sedgwick have replicated the experiment, and probably also Foster, Tarchanow, and others. No modern scientist has taken the idea seriously enough and read the past literature to bother replicating the experiment, so it seems unjustified to claim those 19th century results were invalid with no real basis.
So, for all those smart alecks that have concluded that the tale is a lie, they don’t have a single shred of relevant evidence for it.
I must admit, one reason why people find it easy to jump to the conclusion that the 19th century experiments were a sham is because of a single miscitation from a book author, who also gets misquoted on Wikipedia. This, when combined with the uninformed assumption that the experiments ended at boiling point, could easily trigger some false alarms.
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.”
Sedgwick never wrote such a thing, and the experiment described was performed by Heinzmann, not Sedgwick. This is a quote from Edward Scripture’s (“The New Psychology”). But apparently Scripture’s German is so terrible that he can’t read numbers, since the proper figure is 0.2 °C per minute, and the experiments did not take over two hours. And so we get this comment from a science broadcaster:
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?
Several people have jumped this bandwagon and dismissed all those experiments as bogus in one fell swoop, neglecting the fact that 40 °C is already fatal and that those past researchers were never trying to boil frogs nor prove a tale that didn’t even exist at the time. My goodness, this is how misinformation gets spread… when individuals think they’re smart enough to judge a whole series of experiments by a single (seemingly contradictory in this case) detail.
In cooking, tepid water is defined as one part boiling water plus two parts cold water, which results in a mixture of about 40 °C. That’s probably defined for convenience though. American National Standards Institute (ANSI) defines tepid water as being 60–100 ºF (15.6–37.8 ºC). If I were to argue for the non-believers, I’d probably suggest that most people would think of tepid water as being warmer than room temperature, so anything hotter than 25 ºC might be uncomfortable enough for a frog to jump out from the get go, depending on the frog.
So is it proven then?
Unfortunately I can’t read German, so there is some remaining doubt. In those 19th century experiments, they usually (if not always) suspended frogs mechanically. In other words, the frog wasn’t exactly free to jump around. What they observed was whether the frog’s muscles twitched at all. Does not twitching a single time for 90 minutes while suspended and being heated to death equate to not moving at all without any physical restrictions, or did the physical restriction decrease conscious impulse? Someone probably knows or knew this, but I don’t know for sure.
I’m just gonna leave this as a mess.
Occurrence of “boiling frog” as a term.
Links to a lot of the papers.
Quote from the expert
Edward Scripture’s book (page 300)
Online discussion thread
At least one amphibian biologist was willing to admit he couldn’t know the answer without there being an experiment
Someone closer to my opinion
Missing the point about temperatures
40 degrees is probably the limit
Supposed debunking, completely missing the point