Photo by Nicki Mannix, via Flickr
Photo by Nicki Mannix, via Flickr

Pavlov’s Obscure, Retracted, and Lasting Endorsement of Lamarckian Inheritance

Most people know the Russian scientist Ivan Petrovich Pavlov for his famous dog experiments. Around the turn of the 20th century, Pavlov reported that if dogs are repeatedly given food just after hearing a bell, then eventually they will drool at the sound of the bell alone. That phenomenon, known as classical conditioning, is at the heart of most animal behavior studies today.

A couple of weeks ago, Pavlov’s name came up on this blog in a surprising context. I was writing about a new study in which researchers reported that mice inherit specific smell memories from their fathers, even if they’ve never encountered the smell before. Taken at face value, the study bolsters a theory, championed by French naturalist Jean-Baptiste Lamarck in the early 19th century, saying that an organism can acquire a trait during its life and pass that trait on to its children. Lamarck used the giraffe as an example: A giraffe might be born with a relatively short neck, but it would stretch over years reaching for high tree branches. Its extended neck would then be passed down to its offspring.

That theory quickly fell out of favor as evidence accumulated for Charles Darwin’s theory of natural selection. Darwin’s explanation for the giraffe’s long neck had nothing to do with stretching over time; rather, it was that the giraffes lucky enough to be born with the longest necks would be more likely to survive. As he wrote in On the Origin of Species:

So under nature with the nascent giraffe, the individuals which were the highest browsers and were able during dearths to reach even an inch or two above the others, will often have been preserved; for they will have roamed over the whole country in search of food. That the individuals of the same species often differ slightly in the relative lengths of all their parts may be seen in many works of natural history, in which careful measurements are given. These slight proportional differences, due to the laws of growth and variation, are not of the slightest use or importance to most species. But it will have been otherwise with the nascent giraffe, considering its probable habits of life; for those individuals which had some one part or several parts of their bodies rather more elongated than usual, would generally have survived. These will have intercrossed and left offspring, either inheriting the same bodily peculiarities, or with a tendency to vary again in the same manner; while the individuals less favoured in the same respects will have been the most liable to perish.

Darwin died in 1882. Over the next few decades, scientists recognized that Darwin’s ideas about evolution meshed well with Gregor Mendel’s ideas about genes (a marriage that’s responsible for pretty much all of modern biology). Lamarck was a fading memory beginning to lose his appeal.*

Alright, so back to Pavlov. He published his famous work on dogs and bells in 1903. The next year he won the Nobel Prize for research on the physiology of the digestive tract. And 19 years after that, in 1923, this incredibly famous, rigorous, and highly respected scientist made some shockingly supportive statements regarding Lamarckian inheritance.

That summer Pavlov gave three scientific talks — in Edinburgh, Chicago, and Battle Creek, Michigan (my hometown!) — that were all essentially the same, according to a fascinating review published in 1958 by one of Pavlov’s contemporaries, Gregory Razran.

In those three talks, Pavlov described unpublished experiments from his lab in which he trained mice to run to their food bowls when they heard a bell. This learned behavior, he claimed, was inherited by future generations. Here’s a snippet of his Battle Creek talk, which was published in Sciencepublished in Science later that year:

The first generation of white mice required 300 lessons. Three hundred times was it necessary to combine the feeding of the mice with the ringing of the bell in order to accustom them to run to the feeding place on hearing the bell ring. The second generation required, for the same result, only 100 lessons. The third generation learned to do it after 30 lessons. The fourth generation required only 10 lessons.

The last generation which I saw before leaving Petrograd learned the lesson after 5 repetitions. The sixth generation will be tested after my return. I think it very probably that after some time a new generation of mice will run to the feeding place on hearing the bell with no previous lesson.

Pavlov was seeing giraffe necks grow before his eyes.

These claims reverberated among scientists — and, interestingly, Soviets — for more than three decades, as is outlined in Razran’s excellent review. (The rest of this post is really a summary of what Razran found, so do go read the original if you have access to it.)

“There was some consternation in 1923,” wrote biologist Thomas Hunt Morgan two years later, “when the great Russian physiologist, Pawlow, reported the results of experiments that go far beyond what most Lamarckians have dared hope.”

Soon enough, though, Pavlov expressed his own doubts, albeit very, very quietly. In a preface to a 1927 English edition of a book of his lectures, Pavlov wrote in a footnote that the inheritance experiments “have been found to be very complicated, uncertain and moreover extremely difficult to control.” And continued:

They are at present being subjected to further investigation under more stringent conditions. At present the question of hereditary transmission of conditioned reflexes and of the hereditary transmission of their acquirement must be left entirely open.

He never mentioned the experiments in public again.

In private, though, he did. W. Horsley Gantt, one of Pavlov’s friends and collaborators, once told another biologist that Pavlov considered his claims about inherited traits to be one of the biggest scientific errors of his life. In 1934, Razran asked Pavlov directly what he thought about the work. As Razran recounts in his review: “His answer was a shoulder shrug coupled with the sound of a typical Russian ‘Ekh,’ which to me meant, ‘Don’t ask,’ and I preferred not to pursue the question.”

You might consider this whole story as a trip down the rabbit hole of the annals of science, and maybe it is. But I can’t help but think of this tale in light of our growing acknowledgement of scientific mistakes (honest or not) and the retractions that result.

Pavlov never published his faulty experiments, but his lectures were nevertheless published in Science and other publications. And they’re still being cited by respected scientists today. Perhaps there’s advice in all this for the modern scientist (and the modern journalist, too): When you’ve made an error, don’t shrug it off. A formal retraction can be a good thing — the faster and louder, the better.

*UPDATE (12/13/13, 1:36pm): As Razib Khan pointed out to me on Facebook, some legit evolutionary biologists such as Ernst Mayr held Lamarckian views even in the 1920s. “It wasn’t quackery from what I know,” Razib said. “It took the modern synthesis to really kill off Lamarckianism in the 30s and 40s.” I think it’s probably fair to say that there was quite a bit of controversy over Lamarck by the time Pavlov gave his lectures, which would explain Morgan’s response to them in his 1925 book.

Many thanks to Marcus Pembrey, emeritus professor of paediatric genetics at University College London. Pembrey was the one who cited Pavlov’s experiments in my previous post, and also the one who swiftly alerted me to their possible retraction. As Pembrey put it to me, this Pavlov stuff “could turn out to be a quite a story in its own right!” Indeed.