Aelius Galenus, better known to us as Galen, was an Ancient medical writer. He wrote in Ancient Greek, but belonged to the Ancient Roman Empire.
Galen is hardly well-known today. Most will know him as a punching bag, used to describe the ignorant and silly medical theories of ye olden days. The fact that Galen was deeply influential for over a millennium of history was not a testament to his skill and insight as a writer about medicine; rather, in our worldview, it is a serious indictment of the stubbornness, lack of curiosity and dogmatism of pre-modern science.
Galen is responsible for popularising medicine based on four temperaments, hot, cold, wet and dry, which always exist in balanced or imbalanced mixtures (krasis). An imbalance between these four qualities is an important cause of disease in the Galenic worldview. These are easily confused with the ‘four humours’, more frequently talked about, which consist of yellow bile, black bile, phlegm and blood. These bodily fluids do appear in Galenic writing, but they don’t seem to have interested him nearly as much as the more fundamental, elemental mixtures.
It is fair to say that a few things have changed since we took Galen seriously as a medical authority, rather than seeing him as a primary source for cultural and scientific history. It’s hard to summarise all of this, and most of it will be obvious already: germ theory, the idea of pathogens entering the body and causing problems; autoimmune diseases, the idea of the body’s own protective system attacking its own cells, and so on, are all examples of changes in our medical worldview. These changes are complex because we have replaced unifying theories that have to do with the world at large with a bunch of specific explanations for different types of disease, some intrinsic, some extrinsic.
Even in this summary, however, we begin to treat Galen unfairly. Galen did not see all disease as a result of the imbalance of the krasis (dyskrasis). He acknowledged several other routes for disease in his writing. The inability to access certain types of equipment, such as precision optics (microscopes) obviously hindered someone like Galen. The fact is, Galen did try to look out at the world honestly, and with logical rigour. He was empirical in the sense that a modern scientist is, but the techniques of his empiricism, and some of the assumptions he made, were indeed fatally flawed by our point of view.
A fascinating example is Galen’s comments on hair growth, temperament and climate. Because of the ‘global’ aspect of the Ancient Roman Empire, Galen saw many different types of people in his lifetime. He saw Egyptians, Scythians, Celts, Germans and Africans. Galen noticed that the hair growth, quality and colour of all these peoples were somewhat different, and he immediately connected it with the climates in which these people lived. This makes complete sense; we do the same thing today. Unfortunately, his theory of causation in this respect all hinges on an analogy between human body hair and the green stuff that comes out of the ground: grass.
Galen’s idea on hair growth was that the wetness, coldness, hotness and dryness of various places explains grass growth (e.g. wetness plus hotness leads to big grass growth) and thus it also explains hair growth. People from a eukratic (well balanced) climate such as those of the Italian peninsula (hmm) happen to have perfect hair because, like with grass, the growth is not excessive where the climate is neither excessively hot nor wet not cold nor dry.
The problem here is not the fundamental idea that hair grows, nor that the fact that it might grow in reaction to the climate at some level. No, the problem is his assumption that hair grows like grass, that is, in immediate response to weather conditions and nutrients. Hair grows in response to climate conditions but the pattern is set over an evolutionary timescale. Galen’s barking up the wrong tree with value judgements about hair as if he’s talking about well or poorly kept lawns are quite amusing, but could we possibly expect otherwise? How could Galen have favoured a mechanism that was slower and more complex than what was visually obvious to him, especially when the two mechanisms share basic principles?
Galen does seem to have had a special talent for observation, even if his conclusions were flawed. His writing on the ‘thinning diet’ is fascinating, and in some ways correct. He singles out garlic, onions, and mustard as being powerful ‘thinners’ for their hot effects on the body, purging us of excessive wetness and coldness (compared with the ‘thickening’ effects of cucumber). The clever part here is that Galen is alighting on the special compounds within those plants which indeed have a burning effect, allicin (in the aliums like onions) and allyl isothiocyanate, in the strong brassica, mustard.
It is, however, a losing battle to find many different ideas from Galen’s writings and try and defend their credibility from a historical perspective. Ultimately, there are just far too many things Galen wrote about (and he wrote about a LOT). Galen’s surviving corpus extends to about four million words. As one protests more and more, it becomes clearer and clearer that he was just ‘wrong’ about many specific things. This, to be clear, is not that surprising. It’s also not much of a ‘victory’ over the past. Disagreeing with Galen’s ideas is like rocket-launchering anchovies in a tin.
More serious and more interesting is the humbling lesson that one should take from Galen. We, too, continually use relatively ‘simple’ frames with which to understand all features of the observable world, just like Galen was wedded to his elegant quaternary view of the universe. Most people —and here I mean non-scientists—understand the basic concepts of evolution, and we apply these all over the place. We apply these concepts without checking the assumptions we are making, and without being aware that even the evolutionary frame (which is a powerful one) can mislead us.
The evolutionary process means that many features of the human body are indeed accidents. The ‘design’ without a designer is neither beautiful nor consistent at all times, and it comes up with some extraordinary oversights. A good example of this is the nerve, the recurrent laryngeal nerve1, which travels all the way down our necks from the brain, loops back around the heart, and returns to the head to reach the oesophagus very close by. The reason it does this is because it made sense in fish, from whom we evolved, where the heart and gills were close to one another. Go figure. If one applies the evolutionary ‘frame’ without first checking the facts of nature, then none would assume that this unhinged detour fulfils some crucial function.
It is worth taking Galen seriously, then, not because he will give you good advice about your headache or desire for weight loss. Rather, take Galen seriously to understand just how difficult it is to observe the world without making assumptions. Assumptions are necessary to understand anything and everything, and yet assumptions always have flaws lurking somewhere.
An amusing titbit here is that the RLN was actually named by Galen.