Echo Chambers

In the late 70’s, French anthropologist Bruno Latour set off to do some interesting fieldwork. He spent time observing the daily rituals and customs of scientists in situ, in the laboratory of Roger Guillemin, discoverer of TRF, at the Salk Institute. The results of his anthropological study was a book called “Laboratory Life” which was published in 1979. It was one of the first descriptions of the day to day functioning of a science lab and of the act of doing science itself. Anyone that has worked in a lab will recognize the descriptions of laboratory dynamics, the role of funding in scientific research and in the selection of what scientific questions are considered important, the role of the PI’s prestige in determining which data gets published where and how “believable” it is, how hypotheses sometimes become unspoken assumptions without any real data to back them up, and in general how scientific facts become constructed by the human enterprise of science. Latour’s conclusion is somewhat extreme – that all scientific facts are socially constructed. I think most scientists would agree that this is not the case, that while many of the observations that Latour makes can influence scientific conclusions, in the end there is a real fact that is eventually shed light upon by the science and is continuously refined by the process of scientific consensus. Nevertheless, its a great book (a bit dry at times) that everyone should take a look at. However, there are some cases where scientific facts have been almost entirely socially constructed, and have even persisted for over a thousand years, despite large evidence to the contrary. One of my favorite examples relates to the structure and function of the human heart.

In the second century C.E. the Roman physician Galen wrote what became the seminal medical text for the next thousand years or so. In it he described the human heart as the source of the body’s heat and described the heart as having two chambers, the right was associated with the liver and contained “nutritive blood” which was made by the liver and consumed by the different organs. The left chamber was involved in making vital spirits which were distributed to organs by arteries. Both the left and the right chambers were supposed to be connected by tiny pores in the heart’s septum where both types of humors could mix. It’s not clear to me how Galen drew these conclusions about the structure opf the heart. Although he never did dissect human hearts, he did dissect hearts of multiple animals, and its pretty obvious in these that, like human hearts, they have four chambers. Maybe he was trying to fit the evidence to his prevailing world view. Galen’s book was translated into multiple languages and went unquestioned in medical circles for centuries. Even Avicenna, the famous medieval Persian physician deferred to Galen when it came to the structure and function of the heart, and any evidence of pulmonary circulation or the fact that the heart actually had four chambers was usually ignored because it contradicted the accepted cannon, and Galen’s “facts” just propagated from textbook to textbook.

Fig 1. Galen's conception of the heart and blood.

It wasn’t until the Renaissance when the practice of studying human anatomy from direct observation (rather than from texts) became popular. Yet even then, some anatomical drawings, allegedly drawn from real life still show the heart with two chambers and pores in the septum. Take a look at this drawing by Leonardo Da Vinci. For the most part it’s an anatomically accurate description of the heart and organs. But look at the heart – it has two chambers and tiny pores in the septum. Again deference to authority still seemed more important than actual observation.

Fig 2. Anatomical drawing of the heart by Leonardo Da Vinci. Notice the two-chambered heart and the pores in the septum.

Finally in 1543 Andreas Vesalius published one of the first modern anatomy texts, De Humani Corporis Fabrica, in which all anatomical descriptions were drawn from real cadavers, and where it is recognized that the heart has four chambers and no septal pores. This is a beautiful and compelling book. My university library has an original copy of this book which is bound in human skin. It’s a wild and creepy experience to leaf through it.

Despite a revised anatomical picture of the heart, there was still confusion about its function. This was settled about 100 years later when English physician William Harvey published his seminal study on blood circulation. Harvey started from modern anatomical views of the heart and performed a series of comparative experiments in hearts of various animals, and concluded that the heart was actually pumping blood. He further measured the capacity of the heart and multiplied it by the heart rate and figured that there was no way that the liver and heart could produce so much blood to be consumed by the organs in a single day. Thus, he proposed that blood actually circulated from the lungs to the heart to the body, then back to the heart and again to the lungs. He showed that blood vessels had valves which would ensure unidirectional circulation. This he demonstrated by a variety of simple experiments, one which you can do yourself. Right now! So: 1) Find a vein on your arm or back of your hand. 2) Press on it with a finger on the end closer to your body,  use another finger to squeeze the blood out. You will see that as soon as you do this it will fill up immediately. 3) Press now on the side of the vein closer to your fingertips. Squeeze the blood out. You will see that the vein remains empty until you release your other finger and then fills up. This is because venous blood blood flows towards the heart, as opposed to the Galenic view that both types of blood flow to the organs to be consumed.

Fig 2. Harvey's little vein experiment. From "De Motu Cordis".

Thus with actual observation, an integrative scientific approach and demonstrable experiments, as well as information from the latest literature, Harvey was able to overturn a thousand year-old “fact”. It’s not that he he had fancy new equipment not available to Galen, but rather lived in a time where a scientific world view was prevalent. And it was just a matter of time. If he hadn’t resolved the discrepancy between theory and data, someone else would have.

This is obviously an extreme case where deference to authority distorts scientific facts. But in reality this occurs all the time in more subtle ways in modern scientific practice. Part of learning to do science is to be able to identify these types of biases and avoid them as much as possible.

Further Reading

Bruno Latour (1986, 2d Ed.), “Laboratory Life: The construction of scientific facts“.

Andreas Vesalius (1543). “De humani corporis fabrica“. (click link for browsable version!)

William Harvey (1628). “De motu cordis” (On the motion of the heart and blood).

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4 Responses to Echo Chambers

  1. drugmonkey says:

    I love that experiment. It is way better than twiddling your thumbs when bored.

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  3. Arlenna says:

    What an awesome post. Being trained as a chemist means you never learn this stuff.

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