A Hundred Years After the Verdict

Paul Kammerer and science’s duty to judge — and to doubt

A specimen lies in a laboratory.

It is supposed to demonstrate something remarkable: that an animal can develop a trait as a consequence of the environment in which it lives, and that this trait can subsequently be inherited.

But someone examines the specimen more closely.

It has been manipulated.

What, then, do we know?

That question was asked in 1926. A hundred years later, it is still not as easy to answer as one might think.

The midwife toad

Paul Kammerer was an Austrian zoologist, born in Vienna in 1880. He worked at the Biologische Versuchsanstalt, an institute known for ambitious experimental biology. Kammerer studied salamanders, cave-dwelling olms, sea squirts and other organisms.

But he became famous because of a small toad.

The midwife toad, Alytes obstetricans, has an unusual mode of reproduction. Unlike many other amphibians, it normally mates on land. The male winds the strings of eggs around his hind legs and carries them until they are ready to hatch.

Kammerer attempted to alter this behaviour through changes in the environment. By keeping the animals at higher temperatures, he claimed that he could induce them to seek water for mating. After several generations, he maintained that the males developed dark, thickened areas on their forelimbs — so-called nuptial pads — which in aquatic amphibians help the male grip the female.

More remarkable still was his claim that the induced characteristics could be passed on to subsequent generations.

This was not merely a curious story about toads. Kammerer’s experiments went straight to the heart of one of the great biological controversies of his time: Can characteristics acquired through an organism’s interaction with its environment in some way be inherited?

Kammerer believed that the answer might be yes.

Others believed that the entire idea belonged to a biology that science was in the process of leaving behind.

A specimen with India ink

In the summer of 1926, the American zoologist Gladwyn Kingsley Noble examined the last preserved specimen said to demonstrate Kammerer’s famous nuptial pads.

He found something serious.

The darkened area contained what was identified as India ink, introduced beneath the skin. Noble also failed to find the anatomical structure he would have expected if this had truly been a normally developed nuptial pad.

On 7 August 1926, Nature published his findings.

The specimen had been manipulated.

That is a fact we need not relativize. But already we must be careful with our language. The fact that the specimen had been manipulated is not the same as knowing who manipulated it. Nor does it mean that all of Kammerer’s earlier experiments were therefore false.

Kammerer examined the specimen himself and acknowledged the manipulation. But he denied having carried it out.

A few weeks later, on 23 September 1926, he took his own life.

And so a story emerged that would follow him through the history of science: the scientist who committed fraud, was exposed, and then killed himself.

The story is simple.

Perhaps too simple.

From finding to verdict

Hans Przibram, who had been Kammerer’s superior in Vienna, tried shortly afterwards to distinguish between questions that could easily become confused: What caused Kammerer’s suicide? Who had manipulated the specimen? And what could now be said about the validity of his earlier experiments?

A hundred years later, that distinction remains crucial.

There is no reasonable basis for doubting that the specimen was manipulated. But who did it has never been established. Kammerer denied having done so. At the same time, there are serious scientific problems with several of the results he published, and we do not know with certainty why he took his own life.

Yet these different questions have often merged into a single moral narrative. Kammerer became the fraudster.

Something interesting happens here in the language:

“This specimen has been manipulated.”

“Kammerer manipulated the specimen.”

“Kammerer was a fraud.”

The sentences may look like three steps in the same argument, but they are three different kinds of claim. The first concerns an object that can be examined. The second concerns an action and the person who performed it. The third characterizes a human being.

They do not require the same evidence.

Arthur Koestler reopened the Kammerer case in his 1971 book The Case of the Midwife Toad, arguing, among other things, that it had never been proved that Kammerer himself manipulated the specimen. The question of who did so remains unresolved.

But this does not make the problems with Kammerer’s research disappear. Later researchers have identified biological and statistical difficulties in his material. Jacques van Alphen and Jan Arntzen analysed Kammerer’s published results and found, among other things, distributions suspiciously close to expected Mendelian ratios. In their assessment, parts of the material were so regular that it was difficult to believe they were genuine.

Another problem also remains: Kammerer’s classic results with the midwife toad have never been convincingly replicated.

There are therefore good scientific reasons for scepticism. To say that it has not been proved that Kammerer manipulated the specimen is not to say that his research has thereby been rehabilitated.

Science must judge

It would be tempting to turn Kammerer into the victim of an arrogant scientific establishment incapable of understanding a researcher who was ahead of his time.

That would be a poor story.

For Noble did precisely what science is supposed to do. He examined a specimen, found evidence of manipulation and published his findings so that others could evaluate them.

Scientific integrity requires such judgements. If a specimen has been manipulated, this must be said. If data have been fabricated, they must be rejected. If an experiment cannot be reproduced, that must affect the degree of confidence we place in its results.

Being open to doubt does not mean that all explanations are equally good. Nor does it mean that scientific misconduct should be relativized into a matter of perspective.

Science has a duty to judge.

But it also has a duty to know what it has judged.

Then came epigenetics

The story eventually took an unexpected turn.

For much of the twentieth century, the idea that acquired characteristics could be inherited was commonly associated with an outdated Lamarckism. Heredity came to be understood through genes and DNA, and the distinction between heredity and environment could appear far sharper than it does today.

Then epigenetics developed.

We now know that environmental influences can, under certain conditions, alter the way genes are regulated without changing the DNA sequence itself. In some circumstances, such epigenetic effects can also influence subsequent generations.

Suddenly, some of the questions Kammerer had asked seemed less alien.

In 2009, Alexander Vargas argued that some of Kammerer’s results could be reconsidered in the light of epigenetic mechanisms. But here too we must resist the temptation to tell an overly simple story. Epigenetics has not proved that Kammerer was right. The historian of science Sander Gliboff, among others, has argued that modern epigenetic interpretations do not fit straightforwardly with what Kammerer actually described in his original experiments.

What modern biology has done is therefore something more modest — and perhaps more interesting. It has made some of the questions Kammerer asked scientifically relevant again.

A question can be good even if the answer once given to it was wrong.

A hundred years later

On 14 September 2026, evolutionary biologist Max Telford published an essay about Kammerer in Nature. Almost a hundred years had passed since Kammerer’s suicide.

Its title is revealing: Fraud sealed the fate of controversial zoologist Paul Kammerer — 100 years on, his ideas deserve revisiting.

Notice the final words: His ideas deserve revisiting.

Not that Kammerer has been exonerated. Not that his experiments have been confirmed. Not that Noble was wrong.

The ideas deserve to be examined again.

There is something profoundly scientific about this formulation. The strength of science does not lie in never being wrong. It lies, among other things, in the possibility of returning to a question that once appeared settled when new theories, new methods or new arguments provide reason to do so.

Being able to be wrong

Karl Popper made fallibility a fundamental characteristic of scientific knowledge. A scientific theory is not scientific because it has been conclusively proved, but because it exposes itself to the possibility of being contradicted by experience.

The same applies to science’s own judgements.

This does not mean that we should doubt everything. Such universal scepticism would make both science and action impossible. Researchers must act on the basis of the best knowledge available now.

But now is an important word.

Scientific knowledge is provisional without therefore being arbitrary. A journal may have to retract a paper. A university may have to act. A scientific community may have to reject results. Such decisions cannot be postponed for a hundred years while we wait for absolute certainty.

Yet a judgement must be precise enough not to claim more than the evidence allows.

Practical philosophy

This is where the midwife toad leaves the laboratory.

For this problem does not belong only to the history of science. We encounter it whenever we have to take a position before we know everything. In professional practice, in the legal system, in politics and in our judgements of other people, we constantly have to act on incomplete knowledge.

We cannot always wait.

But neither can we therefore pretend to know more than we do.

Practical philosophy concerns precisely this difficult territory between principle and action: How do we judge fairly when a judgement is necessary? How much knowledge is enough before we must act? And how do we retain the ability to correct ourselves after we have acted?

It requires two virtues that can easily come into conflict. One is decisiveness: the willingness to say that something is wrong when the evidence warrants it. The other is intellectual humility: the ability to recognize the limits of our knowledge.

The Kammerer case is an exercise in both.

The judgement and the human being

When scientific misconduct is uncovered, we need categories such as manipulation, fabrication, falsification and misconduct. They are necessary because science depends on trust. A researcher must be able to trust that a colleague’s data really are the data that colleague claims them to be.

The problem arises when a category describing an action gradually begins to describe the whole person. A researcher who has fabricated data becomes a fraudster. The name begins to stand for the act. After a few decades, we may no longer remember what was actually proved, what was probable and what was merely assumed. We remember the verdict.

Kammerer shows how difficult this transition can be. A hundred years later, we can still say with considerable confidence that the specimen was manipulated. When we ask who did it, our certainty diminishes. And when we attempt to sum up the entire human being Paul Kammerer with a single moral concept, we have moved still further away from what Noble could actually see through his microscope.

This does not mean that actions and human beings can be completely separated. We are responsible for what we do. But a just judgement should not be greater than the knowledge supporting it allows.

That applies to the researcher.

It applies to science.

And it applies to us.

A hundred years have passed

It is tempting to end the Kammerer case with a verdict. Perhaps that is precisely what I should not do.

I do not know whether Paul Kammerer manipulated the midwife toad.

I know that the specimen was manipulated. I also know that there are serious reasons to doubt parts of his research. And I know that some of the questions he asked are, a hundred years later, once again being discussed in biology.

The rest is less certain.

In 1926, Nature published the investigation that helped seal Kammerer’s scientific reputation. A hundred years later, the same journal has returned to him.

It is not an acquittal.

Nor is it a new verdict.

It is a question reopened.

Perhaps this is science at its best: not when it refuses to judge, but when it can make a necessary judgement and still preserve the possibility that one day it may have to look at that judgement again.

To judge when we must — and to doubt when we should.

That is not only science.

It is practical philosophy.

References

Gliboff, S. (2010). Did Paul Kammerer discover epigenetic inheritance? A modern look at the controversial midwife toad experiments. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 314B(8), 616–624.

Koestler, A. (1971). The case of the midwife toad. Hutchinson.

Noble, G. K. (1926). Kammerer’s Alytes. Nature, 118, 209–211.

Popper, K. R. (1959). The logic of scientific discovery. Hutchinson.

Przibram, H. (1926). Prof. Paul Kammerer. Nature, 118, 555.

Telford, M. J. (2026). Fraud sealed the fate of controversial zoologist Paul Kammerer — 100 years on, his ideas deserve revisiting. Nature.

van Alphen, J. J. M., & Arntzen, J. W. (2017). The case of the midwife toad revisited. Contributions to Zoology, 86(4), 365–374.

Vargas, A. O. (2009). Did Paul Kammerer discover epigenetic inheritance? A modern look at the controversial midwife toad experiments. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 312B(7), 667–678.