Summary: In the mid-1990s physicists Geoffrey West and Louis Bettencourt collaborated with biologists to study allometric scaling laws, where it is generally found that larger organisms are more efficient consumers of energy than smaller ones. After mathematically explaining these laws through fractal network effects, the researchers began applying them to the human built environment, particularly cities. Certain environmentalists and sustainability advocates mistook the significance of these results, leading to decades of policy work and investments in urban growth that, West now admits, are doomed to fail. The fact that so many, including the originators of the work, got this story wrong reflects the cultural blinders and techno-biases that typify most of us living in high energy modernity. Doing the opposite of our conditioned response to the overshoot predicament will likely lead to more favorable outcomes.
I fell in love with biology as a kid. It answered questions that naturally came to mind as I explored my suburban backyard, such as, “Why are insects so much smaller than birds and mammals?” The answer lies in fascinating details of their anatomy and the laws of physics that underpin evolutionary biology and ecology.
This childhood love put me on the path to get both a BS and PhD in biology, and my studies have since turned towards how humans can live in ways that support the broader community of life and propagate a culture that may endure. So I find it jarring when the science I know well is mis-applied to the critical human questions, all related to how we as a society and species may persist or not, in what form and where, through the stresses of the Anthropocene with myriad poly-perma-metacrises unfurling into a Great Unraveling and/or Great Simplification. Let me get back to some biology basics to explain.
Insects don’t have hearts and lungs and circulatory systems to transfer blood with oxygen like vertebrates do. Instead, they have a network of tubes that allows air to diffuse into their bodies and surround each cell. Gas exchange in insects is a passive process, not an active one. This limits how large they can be, because as a body gets larger, its surface area relative to its volume gets smaller. Up to a certain size, adequate oxygen can get to the interior of a body, but beyond that size, cells experience oxygen starvation. This knowledge made me an insufferable little critic of B horror movies depicting ginormous insects such as Mothra.
The largest animals on the planet are vertebrates like us. In contrast to insects, vertebrates have a circulatory system of arteries and veins and a heart that pumps blood throughout the entire body bringing oxygen to cells and removing carbon dioxide waste through the lungs. This setup overcomes the surface area to volume constraint that insects face and makes possible massive dinosaurs, elephants, and whales (although even with a heart and lungs, Godzilla is way beyond the scale possible for radioactive fire breathing sea monsters).
Alas, the removal of one constraint means you end up running into another. A case in point is the metabolic systems of different classes of vertebrates. On the one hand you have vertebrates like mammals and birds, which are known as warm-blooded (technically called endotherms). These animals use metabolic work to maintain a nearly constant body temperature. By contrast the cold-blooded vertebrates, such as reptiles and amphibians, appear sluggish much of the time, as they often require a sunny day to warm their bodies (ectotherms).
The metabolism of mammals and birds allows them to be active in the environment almost any time–moving, feeding, mating, fighting. This trait can be a tremendous advantage and often allows warm-blooded animals to out compete cold-blooded ones. They are less constrained by environmental temperatures, but at a price. A warm-blooded lifestyle requires a prodigious amount of energy inputs to maintain.
As a kid I had cats as pets, and if I didn’t feed them twice a day I’d expect them to claw my eyes out while I slept. But I noticed that a friend of mine with a snake of roughly the same size only fed it once a week or so. If you’re a reptile and food becomes scarce, you can probably wait it out and be fine. Mammals and birds, on the other hand, have a built-in demand for power. If food becomes scarce locally, they need to go somewhere else and find more, or they will starve. This explains the great movements of mammals and birds, especially birds who will fly thousands of miles to be where food is abundant, and why we don’t talk about seasonal lizard migrations between continents, though that would be cool.
A well-known fable covers this biological distinction well. I’m talking about the famous race between the tortoise and the hare, animals with the same mass but contrasting baseline metabolic demands. The tortoise represents team “Cold-blooded Reptiles”, and is preposterously slow compared to the hare. With rapid fire muscles and legendary speed, one would expect the “Hot-blooded Mammals” entrant to demolish the tortoise in a race. The whole setup illustrates, at least to a biology nerd like me, metabolic trade-offs, the nature of power, and what might be meant by the term efficiency.
A 19th-century illustration of La Fontaine’s Fables by Jean Grandville (public domain, care of Wikimedia)
The tortoise runs the race in the only mode it has, low-power, which means it does the work of moving its body without using much energy per unit time. The hare, by contrast, runs the race in high-power mode, burning calories prodigiously to accomplish the same task quickly. If you look at basic research on metabolic rates you find that warm-blooded creatures use roughly ten times the power of cold-blooded ones. Hence the danger of hungry cats.
If both runners are disciplined and follow the course, the hare will be time-efficient and energy-inefficient, while the tortoise will be energy-efficient in its travel but slow, and therefore time-inefficient. The assumption that time is the metric being optimized in a race may reflect our upbringing in peak-but-now-waning modernity, but in other cultures (and life in general), that isn’t always so. In many ecological situations, energy or materials are the constraint. (Is a cactus in a hurry?) The twist in the fable is that the tortoise wins by time as well, because the hare is too cocky and screws up somehow. Oh my gosh, it’s not just a biology lesson!
Fig 1. Adapted from White et al. (2006). Reprinted with permission of author. Note: Standard metabolic rate (SMR), in units of oxygen consumption per hour, is shown as a function of body mass (grams) in vertebrates. For a given body size, the metabolic rate of endotherms (birds and mammals) is about an order of magnitude higher than that of ectotherms (amphibians, fish and reptiles). For example, a 10,000 gram reptile has the same metabolic rate as a 1,000 gram mammal. This allometric scaling relationship is known as Kleiber’s Law.
The relevance of this biology lesson in scaling laws in urban sustainability discussions comes through the study of Urban Metabolism. An animal’s metabolism is composed of the networks of vessels, nerves, and feedback systems that allow a collection of millions to trillions of cells to coordinate and be an organism. Key activities include ingesting food, distributing energy and raw materials to build and maintain the body, moving about and performing work, and evacuating waste. As expected (and shown in Fig 1), larger animals consume energy at a faster pace (i.e., demand more power) than smaller animals, but the scaling relationship is sublinear, meaning that larger animals consume proportionally less energy per mass than smaller ones do. At the extreme ends of the size spectrum, this sublinear scaling relationship makes a big difference in metabolic terms. A 10 gram mammal (e.g., a modest-sized shrew) has a standard metabolic rate (SMR) of 20, while a 100,000 gram mammal (e.g., a large man) consumes at 10,000 SMR.
Cities have metabolic functions that are analogous to living organisms. Transportation and communication networks are like a city’s circulatory system. Fuels and electricity are like food. In cities metabolic functions are paid for by trips to the grocery store and gas station; taxes and fees to the water, sewer, road, and utility districts; bills from internet and phone companies; and the mobsters who handle solid waste. Physicists Geoffrey West and Louis Bettencourt of the Santa Fe Institute famously showed that the same scaling laws that work in biological systems also explain the analogous metabolic networks of human cities and economies. In other words, the energy and material demands of big cities are higher than those of smaller cities, but follow the same sublinear scaling laws as biological systems – making bigger cities appear more efficient. In the city analogue, people are akin to cells in a body, and as an urban agglomeration gets larger, it delivers goods and services with fewer per capita resources. As a bonus, some desirable metrics like innovation and wages per capita scale superlinearly with size, i.e., scale at a rate higher than one. Bigger seems doubly better.
This fascinating work by renowned physicists from an esteemed institution was met by urban sustainability gurus with glee. The common interpretation goes something like this:
Cities are a key invention for humanity to become a more sustainable species on Earth. Policies need to bolster investment in new, retrofitted, and enlarged megacities that will more efficiently supply human flourishing needs and foster greater rates of innovation. The global trend of urbanization and rural depopulation is a good thing for the planet, as it frees up space for wildlife and makes us richer and smarter.
In 2024, Nate Hagens interviewed Geoffrey West and posed the question that can be paraphrased as: Should we put most people into a few hyper-efficient megacities and free up the rest of the planet for nature restoration along the lines of E.O. Wilson’s Half Earth proposal? West’s response can be summarized as: The megacities actually need a network of smaller cities distributed globally to function, but we can expect more people to indeed move into big cities, especially in developing countries that still have a sizable rural proportion. Rural areas in developed nations only have 20% of the population so that may be near the lower limit. The big risk West is worried about is the need to constantly innovate, at accelerating rates even, to solve the compounding crises brought on by resource demands and pollution. Because of superlinear scaling of innovation, cities are the best places to make that happen, but he recognizes this is impossible to maintain in the long run, leading to a “socioeconomic heart attack.” West appears to be describing much of the plot of one of my favorite sci-fi stories, The Machine Stops.
The Hagens interview is interesting as West is expressing more concerns and caveats than in the past. In 2017, he said about cities:
“They create most of civilization’s problems, but they are capable of solving problems even faster than they create them.”
Now that he apparently believes our development pattern ends in collapse, West does not offer an alternative program. His legacy of “urban scaling laws” acts as another intellectual weight behind the settled belief by ecomodernists that investing in big urbanism will somehow produce both continuous growth and, crossing fingers, elucidate never ending sets of miracle technologies towards sustainability.
Rendering of The Line. Image captured from NEOM website.
This reasoning justifies megaprojects such as The Line in Saudi Arabia, and seems to give book authors license to make urban utopian claims (see One Billion Americans by Ygelsias and Abundance by Klein and Thompson). Here is how The Line is described on its website:
“THE LINE will eventually accommodate 9 million people and will be built on a footprint of just 34 square kilometers. This will mean a reduced infrastructure footprint, creating never-before-seen efficiencies in city functions. The ideal climate all-year-round will ensure that residents can enjoy the surrounding nature. Residents will also have access to all daily essentials within a five-minute walk, in addition to high-speed rail – with an end-to-end transit of 20 minutes” (accessed April 2025).
(I want to note that the simple notion that “bigger cities are more efficient” that permeates public discourse is not settled science, but as you will learn below that doesn’t really matter for my larger point. For a more up-to-date and nuanced view, with geek-out worthy graphs, see this paper.)
Now I have also dabbled in utopian manifesto writing with the aim of solving our great predicament. In my version, humans are selected and genetically engineered over 10 to 15 generations to become the size of a very small monkey. This lowers per capita footprints dramatically and allows our population to continue growing a lot. Fortunately, my manifesto is an absurd joke. Unfortunately, the view that we need to double down on high-energy urbanism is equally absurd, yet taken seriously by a lot of normal and smart people, who, if I met in person, I’d probably really like.
I will explain in some detail why people who can generally be considered sane and thoughtful get this wrong. The reason is rather straightforward and can be summarized as: We are committed to being hares instead of tortoises. In nerd words, on those metabolic graphs, we shouldn’t place all our attention on the sublinear slope of the lines. We should pay more attention to the Y-axis differences between different classes of organisms.
But first I want to share some really basic information that should have nipped this discussion in the bud long ago. If the hypothesis is that big-city people are less resource-demanding than country people, then a graph showing per capita energy use by nation on the X-axis with population percentage urbanized on the Y-axis should provide rock-solid evidence. For the hypothesis to be supported, more urbanized nations should use less energy. I made that graph, so take a look (Fig 2).
Fig 2. Per capita energy consumption and rural population by country (2008). The percentage of population that is rural is plotted with respect to per capita energy consumption and shows that in general, countries with high energy use tend to be more urbanized. Some of the largest countries are highlighted, and outliers tend to be small island nations. Sourced from Bradford 2019.
The data appear to tell an opposite story: Nations that adopt modern industrial infrastructure and complex, globally integrated economies will increase energy consumption per capita in proportion to their level of urbanization/industrialization. It is truly remarkable that we can tell ourselves a story that is clearly falsified by facts on the ground. But the “cities are efficient” meme is a self-serving narrative, as it justifies our way of life. My BS (that’s “bullshit,” not “bachelor of science”) detector looks at Fig 2 and asks, “What can I learn from the people who don’t use oil?” as opposed to, “How can I move rural peasants into the global economy?”
Now to be clear, I am not saying West and Bettencourt are wrong, only that their results lack full context, and thus the standard interpretation of them is, how can I put this delicately… “ass backwards.” And I am not advocating for suburban sprawl instead of more Green Manhattans. Neither will suffice, because the issue I’m getting at is more fundamental.
Back to some basic biology and some weird aspects of Homo sapiens. Humans, as a species, are unique in how they relate to energy. The metabolic charts discussed in the scaling law context do not capture what people do. It may have all started with the discovery of meat cooked by a lighting fire, but it has led to big evolutionary scale changes. To a degree unlike any other creatures, we rely on exosomatic energy, namely, energy not of our bodies, to thrive.
A typical sedentary person needs 2,000 food calories per day to maintain a metabolism of 100 watts. These numbers regularly double or triple with high-activity behaviors (strongman Halfthor Bjornsson ingests 10,000 calories a day). Now here is the shocker. Agrarian societies prior to the fossil-fueled industrial era typically had access to non-human exosomatic power on the order of 10 to 1. That is, a person living prior to fossil fuel exploitation could, by gathering wood, capturing energy from the flow of rivers, harnessing oxen, etc., utilize ten times the energy output of their own bodies (endosomatic) to aid in survival and comfort. That is equivalent to the metabolism of a horse). Isn’t that crazy? Even before the age of steam engines, jet engines, and nuclear power plants, we used 10 times our metabolic power. Today, however, the typical person in a so-called developed nation uses hundreds of times more power than their body’s output. According to West, metabolically we are equivalent to a dozen elephants, and yet it somehow smells fine in the house.
Houston aerial view, by Halina, care of Adobe Stock.
At least it smells fine if the urban metabolic demands are met. Look at a big city from space at night and admire the lights. Those lines denote networks built of steel, concrete, copper, asphalt, plastic, and glass, which are non-biological in origin and subject to entropy. Unlike a living organism, they can’t maintain and repair themselves, so cities need to be fed all the time. Modern cities especially have a built-in power demand that is very high, way beyond any preindustrial city. They can’t rest and slow their metabolism like a reptile, but must always be very active, like a mammal or bird. What is the rule of thumb for modern city livability without electricity or trucking services? Isn’t it three days?
I don’t necessarily envision a series of megadisasters wiping out megacities (we can at least rest assured that we’re safe from Mothra attacks), though some storms and fires will play their parts. Instead I foresee deaths by a thousand cuts as infrastructure decays, replacement costs rise, and things fall apart, bit by bit. Think of what happened to Detroit, Michigan, becoming the norm over the rest of this century.
Now some of you reading this may be thinking, “Renewables are going to become cheap and take over from fossil fuels, and life will go on like before, only electrified.” I know all about this point of view but don’t share it, and am not up for arguing (and have gone over this elsewhere). All I ask is please humor me a while and consider a scenario where the PV arrays and grid batteries fail to arrive in time and at scale, while fossil fuel extraction sputters, the arteries of the global economy get blocked, and the financial system locks up. In such a situation where would you want to live, and what livelihood would you like to have?
Personally, I find this is all very depressing, and maybe you do too and crave something more than doom and gloom from me. Are you thinking it is time for solutions? Yes, it is. I just want to admit I am a bit nervous because you might hate what I suggest. Why? Because what it takes to respond wisely to our situation, which I can define as massive ecological overshoot, is pretty much the opposite of what we did to make this mess. Does that make intuitive sense? No doubling down. No doing the same things and expecting a different outcome. I attest to being a sane, responsible, and caring adult here. Not totally free of delusions, but generally allergic to BS (again, the kind that flows from bovines, not colleges) my whole life, which makes paying attention awfully hard for sure.
I will ease into this by an example and analogy many can follow and agree with. I do not like Confined Animal Feeding Operations (aka CAFOs or feedlots) as a general rule. Not great for the animals and also ecologically uncouth, to put it lightly. In a feedlot, gobs of exosomatic energy are needed to keep the animals alive. Water is piped in. Feed is trucked in and delivered to troughs via a powered auger. Excrement is scooped and hauled off by tractors with buckets and dump trucks. Without cheap energy, especially diesel, this would be ridiculous, and nobody would do it.
Feedlot from Google Earth near Greeley Colorado.
Instead I advocate a different, more traditional system for raising livestock. Cattle, for example, can walk around under their own power and consume grasses, clovers, and forbs. When they eliminate waste, it is a helpful fertilizer, not a pollutant, and the pasture grows back and makes more feed on its own in a lovely, life-affirming, solar-powered cycle. Disease risk is low, as population density is low, and the feed isn’t spiked with antibiotics. The stress levels are measurably lower too, so everyone seems to be happy with this arrangement (vegans aside).
What can we say about the pasture system in contrast to the feedlot? It is biological and regenerative, not mechanical and degenerative. Resource sourcing is local, not global. The animal population is relatively small and dispersed, not large and centralized. The operation is more passive in terms of human intervention, rather than very active. Infrastructure consists of few parts and could be classified as simple, rather than complex. Energy is from current sunlight not fossils.
Sheep and cattle on pasture near Corvallis, Oregon. Photo care of author, Jason Bradford.
Wow, I’m a true believer and might consider walking around with a sandwich board that says “Free-range cows now!” But you’d probably have to pay me to do so.
Let’s turn back to human systems using The Lord of the Rings as an example. You know what my favorite place is in the saga? You probably guessed it, the Shire. When I graduated from college, I did one of those European backpack tours, and the places I recall most fondly are the villages and small towns. Their construction was of natural and local materials. You could easily walk from the town square to the defined edge, maybe a wall, and look out over farms and woodlands. One could imagine these beautiful settlements persisting over the centuries with or without modern technologies because they had originally evolved prior to the Industrial Revolution. Sure, they lacked the selection of discotheques available in the megacities, but the surface area to volume ratio intuitively felt right to me. In a village, materials, energy, and waste can flow in and out almost passively like an insect breathing.
Maybe we need T-shirts that read “Free-range people now!” I’ll wear it at no charge.
Yes, what I am getting at is if we truly understood the scaling laws, in their proper energy context, we would not be doubling down on urbanism (or suburban sprawl). The megacities evolved because they are energy-efficient (and that is still up for debate) only in the context of industrialism, which is like a new class of organisms, the species Homo colossus on the metabolic chart. Modern cities may only look good when comparing a small energy-hogging city with a bigger energy-hogging city, all nested within a global network that includes small towns and depopulated farmland and forests.
Relictual rural human residents are responsible for managing the vast flows of resources into and wastes out of cities using gigantic machines where one person can harness the equivalent of thousands of human laborers. The idea that we can put most people in cities and make space for nature belies the reality that we now completely depend upon relatively few people running mostly diesel-fueled engines to survive, and these machines and remaining people have little capacity to care for watershed restoration, populations of endangered and keystone species, or soil and forest carbon. With some nice exceptions, they think of themselves as a kind of factory worker making raw commodity inputs for the global economy.
So the broader reason modern cities exist is because we hit the fossil fuel lottery, started burning ancient sunlight, and energy became available in superhero-strength amounts where each citizen is like Tony Stark in his exosomatic Iron Man suit. Time became the metric we came to care most about, not energy or materials, which suddenly became “overproduced.” This is the first and only era in history when we can build grandiose human feedlots and call that progress.
A sustainable scale is the opposite of our current instincts for bigness. Can we proactively reverse course and invest in ruralism? And can we do so not by replicating the Homo colossus rural lifestyles of most Americans, which tend to be more resource-intensive than their urban compatriots? For any ruralism to make sense, rural folks need to behave like tortoises, hobbits, historic European villagers, or contemporary peasant communities.
For a lot more on this, I recommend this previous publication of mine, but offer a quote:
The circulatory system of a modern city is very active, and it requires high energy inputs to keep the city-dwellers fed and prevent the buildup of wastes. This infrastructure locks-in high energy demand compared to locations with simpler systems to manage basic needs. In highly urbanized nations, this high-energy lock-in applies to the countryside as well. The rural residents in places like the United States are living with a depauperate associative economy, characterized by the lack of nearby services. They often make their living driving around the countryside managing expansive tracts of land with big machines. Their lives are not ones of frugality and self-sufficiency, but instead are tied into the global economy where cheap, concentrated, and prodigious use of energy, or what together I will refer to as extreme energy, is taken for granted.
I’ll conclude by admitting I don’t know what is going to happen. We are at some historic tipping point, and past trends are no longer guides. I’m saying our culture doesn’t even see the predicament for what it is, and the terms we might want to use for the socio-political systems that could helpfully emerge are not widely recognized. In other words, the world is going bonkers, any number of crazy-frightening events may derail civilization, and we don’t generally acknowledge the concepts or use the vocabulary for how to respond reasonably.
But if I can outline a possible non-catastrophic scenario, using terminology I hope becomes common, it might be as follows: Cities will eventually shrink from under-investing, either by choice or because entropy overwhelms. A shift towards rural villages and towns will happen, ideally with active planning and support. Perhaps by 2100 (but I don’t know!) we are back to 1950 levels of rural population (70% from 45% today), of mostly self-provisioning communities. So I can happily imagine ruralization as a slow process, mirroring the rate of urbanization (Fig 3). And if pioneers of the alternatives I envision are correct (e.g. Living Energy Farm), we can live decently in rural communities with a fraction of the exosomatic energy of today.
Fig 3. Trends in global rural and urban population percentages from 1950 to 2018 and with United Nations projections to 2050. From Bradford (2019).
Cities would not be gone by any means, but they would be more frugal and capable of living with intermittent power. Industry would be downscaled and focused on basic functions. Some visions and pilot projects along these lines include the 2000 Watt Society, and Retrosuburbia. And if certain strains of economic thought are right, this does not relegate most to crushing poverty, but instead covers material needs for all with a much smaller formal economy. Things like advanced medical equipment and telecommunication are more likely to survive if we give up pool noodles, fast fashion, and luxury SUVs.
If the ecological footprint of cities is reduced to a fraction of today’s, and most people are engaged in rural livelihoods, then we can better undertake the restoration ecology needed to stabilize and increase biodiversity and draw down atmospheric carbon with ecosystem sinks. I know from personal experience, which is backed by research, that small, diverse, regenerative, and organic farms that people make by hand are welcoming to wild beings. In fact, as Robin Wall Kimmerer explains, the worldview of people living in nature is one of partnership and reciprocity. So yeah, let us rewild half (or I’d say almost all) the Earth, with people integrated into ecologically functional landscapes. There is much to be anxious about in the future, but I hope the prospect of people becoming Indigenous to a place again motivates us to work on this more gracious possibility.
