How did you come up with the idea of applying the laws of biology to cities?
It’s a long story, but let’s say it all started when, along with a group of colleagues, we became interested in “scaling laws”. We then discovered that simple, mathematical laws governed the growth of living organisms. If you double the size of an animal, it won’t need twice the resources to grow and survive. It will need about 25% less in terms of resources. And this is true for all animals and all indicators: size, lifespan, number of offspring, etc.
And you had the idea of transposing this law to cities?
Actually, I first thought about analysing companies, but a social science colleague at the University of Santa Fe encouraged me to look at cities. Cities are often compared to living organisms: they metabolise, grow, use energy.
And the law worked?
Exactly! We often approach cities in a narrative way, but rarely by measuring them. That’s what we have done. We collected a lot of data: the number of petrol stations, restaurants, power lines, kilometres of transport networks, to check whether cities experienced this scaling phenomenon. And we found that beyond geographical or cultural differences, there was indeed a universal structure of cities and a scaling phenomenon comparable to that found in biology: Paris is a bigger version of Marseille, which is a bigger version of Avignon, etc.
The only change, compared with the growth of living organisms, is that cities spend only 15% less resources by doubling in size, and not 25%. But the other discovery is that when we look at the social and societal impacts, we see that as cities grow, we produce “surplus growth”, an “economy of scale”. In a city twice the size, the number of patent filings (a good indicator of the level of innovation) is twice as high, +15%. This is what I call “superlinear scaling”. Unfortunately, this rule also applies to dangerous social phenomena: a city twice the size means twice the crime, twice the disease, +15%.
"There is a common structure to cities: Paris is a bigger version of Marseille, which is a bigger version of Avignon, etc. And this is true in Asia, Europe and Africa."
How can this finding be applied?
In biology, we work on growth mechanisms. We are born, we grow, we stop growing. The networks (blood network, respiratory system, nervous system) that underlie this growth slow down with age. But cities are growing steadily and more and more quickly, a growth underpinned by interactions between people, social networks, the increased speed of transport.
The bigger cities are, the faster life gets. Is this model sustainable when cities dominate the planet and are largely responsible for global warming? What new paradigm can be invented to get out of this race for speed? I am convinced that a true “science of cities” can allow decision-makers to look holistically at cities to create scenarios for a sustainable future.