Cities obey the laws of living beings

WHo would disagree with Dickens that the green spaces of London are the “lungs” of the city? A city is a sleeping animal, although some never do it, like New York or Hong Kong. All cities are some sort of creatures. Some have several “faces” they present in the world, most have a “beating heart” where the action takes place, and it is a rare city that has no dark “belly”.

The analogy of the city as a living organization is so established, in fact, that it has gone through the field of scientific investigation. For at least a decade, researchers have attempted to decode sustainable planning lessons could emerge from the thought of cities as living beings.

Now, a team of scientists from the Federal Polytechnic School of Lausanne (EPFL) has found that all cities – that Tokyo, Lagos or Zurich – did not oblige according to the predictable principles that govern animal biology in the natural world. In the process, they have challenged a long -standing hypothesis: that large cities are more durable than small.

“Large cities are often considered” better “, explains Gabriele Manoli, study author and chief of the laboratory of urban and environmental systems of EPFL, in an email. “However, these laws depend on the definition of a city.” The results, reported in the Proceedings of the National Academy of Sciencescould influence the way urban planners design the cities of the future.

Cities self-organize as they develop regardless of the context and without central planning.

Planners have long applied that the larger is better because large urban areas require less resources and energy per capita and generate more wealth. But that was difficult to model because of the way in which the limits of the city are often traced. Where is the real edge of a city? To solve this problem, Manoli and his colleagues “re-evaluated” 100 cities around the world, breaking them into units that they called pixels which could be more equitably compared in the urban areas of diversity.

Then, they hung millions of data from these different units of the city and found a law of scale which links the size of the population to transport networks and economic activity and at CO₂ shows. The relationship between these variables follows the same curve for all the cities, large and small, they found, and echo the law of Kleiber, a principle that emerges in biology when the sizes of animals are seen in relation to their metabolic rates.

In the 1930s, Max Kleiber noted that the energy whose animals required daily to maintain their body (their metabolic rate) extended in proportion to their size. Mice have a lower metabolic rate than elephants, and tiny microscopic creatures require even less energy. The law has proven a useful tool.

Veterinarians use Kleiber’s law to determine the amount of drugs to give an animal, while conservation scientists use it to assess the needs of different species. By simply knowing the size of an animal, it can deduce its metabolic rate and determine the amount of food and water it needs to survive. This helps manage ecosystems and fauna reserves to ensure that a habitat can support a specific animal population.

For cities, the size of the population is similar to the mass of an animal, the economic activity of the metabolic rate of the animal and the roads towards its circulatory system, offer researchers. The relationship is universal and independent of geographic, political and historical differences, they say: cities self-organize as they develop, naturally optimizing for energy flow and distribution of resources, whatever the context and without central planning.

The authors of the study hope that for cities, the relationship revealed in the study can help urban planners with sustainable design planners. “Thanks to the large amount of data available, cities offer fertile land to test new theories inspired by biology and ecology,” explains Manoli.

Perhaps the new mathematics will allow planners to better understand how to keep the animals that are our cities hum as they grow and evolve.

Main image: Alicia Crespo Montañes, Epfl cities

• Elena Kazamia

  Published on September 5, 2025

  Elena Kazamia is a scientific writer from Greece. She holds a master’s degree in conservation of the University College of London and a doctorate. in the vegetable sciences of the University of Cambridge in the United Kingdom