Tumor Cities and Science Metaphors
Scaling abstract concepts into ideas
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Tumor cities
Cities are sustained by similar network systems such as roads, railways, and electrical lines that transport people, energy, and resources and whose flow is therefore a manifestation of the metabolism of the city.
That is a quote from the 2017 book Scale by British theoretical physicist Geoffrey West. It’s one of the most idea-rich non-fiction books I have read in several years. In his book, West tackles the fallacy of believing in infinite exponential growth, Black Swan events, big data, science policy, and - as the title suggests - the quest to find general principles that shape systems at different scales — cells, humans, cities, economies…
It sounds weird, though, doesn’t it, to talk about the ‘metabolism’ of a city the way West does in the quote1?
But the metaphor turns out to have merit.
In a recent study, researchers model the development of London and Syndey over roughly the last 180 years. What they end up with2 are growth dynamics that look strikingly like angiogenesis — a fancy term that means the formation of new blood vessels. As you can imagine, angiogenesis is important in the normal development of our bodies, but it also plays a big role in certain health issues. For example, angiogenesis is a crucial factor in tumor growth, so much so that angiogenesis inhibitors are a distinct class of cancer medications.
The city modelers even found that:
In particular, urban dynamics show striking similarities with tumor angiogenesis where a first stage of in situ, diffusion-limited growth is followed by neovascularization and development of solid malignant tumors.
Cities are tumors.
Metaphors in science
Can you see it? The city as a tumor, growing through roads and railway tracks followed by a suburban sprawl and people metastasizing (sorry, moving) to the suburbs?
Science is full of metaphors. If we restrict ourselves to biology: DNA is a recipe or blueprint and mitochondria are power plants in the cell. We have evolutionary ‘trees’, food ‘webs’ or ‘pyramids’, and ecological ‘footprints’. Feel free to drop others in the comments!
Why? We see science as this cold, rational, analytic endeavor (not true, by the way), so what place could the linguistic trickery of metaphors have in it?
The very first sentences of this paper on the use of metaphors in synthetic biology already provide a good attempt at an answer:
Metaphors are not just decorative rhetorical devices that make speech pretty. They are fundamental tools for thinking about the world and acting on the world.
Metaphors help us make the invisible mentally visible. They turn something abstract into a mental concept that is more tangible. It doesn’t have to be visual, though I would guess that a lot of metaphors have a visual component for many people, myself included. (If someone with aphantasia is reading this: I’d be very interested to hear your take on the use of metaphors!)
Those of you who have actually seen DNA know that, if you’re doing the extraction correctly, it looks like a slimy booger in a test tube. Hard to figure out what it does that way. However, if you can conceive of it as a recipe encoded in a double helix that is a sequence of letters, it becomes easier to imagine how it could be used for building proteins.
For scientists themselves, metaphors can be powerful tools too. Philosopher of science Thomas Kuhn wrote about metaphors in science in 1979, where he suggests that:
Metaphor plays an essential role in establishing links between scientific language and the world. Those links are not, however, given once and for all.
A more recent paper by a duo of biologists makes the point even more explicit:
… their [metaphors’] generative potential cannot be ignored. It is, in fact, metaphor that makes theory possible, and a great number of scientific revolutions have been initiated through novel comparisons between natural phenomena and everyday experiences
Metaphors do not only help in communicating about science; they might be helpful for the science itself.
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Metaphorical breakdown
But metaphors are not without danger. The quote by Kuhn already alludes to this, and he pointed out that when a scientific paradigm shifts3, so do the metaphors.
Once, DNA was a blueprint. Recent research, however, suggests that ‘blueprint’ is too inflexible. These days, DNA is often seen as a recipe — something you can more easily tweak and adjust to context. Once, electrons traveled along stable and contained orbits around an atomic nucleus. Then, quantum mechanics turned everything fuzzy, and now we’re dipping into electron clouds.
Overall, I think there are three main challenges when using metaphors in science: choice, change, and context.
Choice: the metaphor you use needs to elucidate what you want it to. How do you go from ‘slimy booger in test tube’ to ‘heritable information-carrying molecule’? Well, think of that booger as a recipe.
Change: at which point in theory development or scientific discovery do you update the metaphor? When does an orbit become a cloud?
Context: language and culture change. For example, a lot of ant species that were described in the 1800s are known as ‘slave-making’ ants. Some people might consider this a metaphor or even an accurate description of the behavior of ant species that raid nests to steal away the larvae and pupae to raise a generation of workers. Other people might consider this an insensitive and historically loaded metaphor. In this case, should we update the metaphor? What do you think?
From the earlier linked biologists’ paper:
For all of their problems, metaphors are indispensable tools for both practicing and communicating science. No metaphor is perfect, and incongruities between target and source meanings are unavoidable.
Solid (metaphorically).
If you want a fictional treatment of the idea, check out N. K. Jemisin’s urban fantasy book The City We Became, in which cities that grow large enough come alive through human avatars (NYC obviously has five avatars).
“… a minimalist reaction-diffusion model coupled with economic constraints and an adaptive transport network,” if you’re into that kind of thing.
The idea of paradigm shifts in science is what Kuhn is most remembered for, but whether or not those paradigm shifts are as clear-cut as he (initially) claimed is not something everyone agrees with.
I think metaphors are used in science to make the information easier to understand (by using our senses to "see" or "smell" it) -- and just as much, easier to empathize with. When something resonates with us on a deeper level, like a simple metaphor might, we empathize with the topic in a different way than when we use our rational mind to understand cognitively abstract (scientific) concepts.
'Cities as tumors' is simply brilliant. I never thought of it like that and now I cannot un-see it.
Human body as classic car that can be endlessly repaired, brain as digital :)