From Molecules to Megacities: How Life Scales

Illustration by Nick Vokey, an ode to “Powers of Ten”


Geoffrey West’s monumental book “Scale” channels math and physics to explore the limits of our biology, our companies, and our civilization.

What’s the difference between a book and a book review? Both are composed of words, and both ideally have some kind of narrative arc: an initial premise or question, some explication and examples, and a satisfying conclusion or call for further study. Is one simply longer than the other? Is a book something like a collection of book reviews strung together? Or does its size require a different internal structure? In a book you can explain things such as the fractal fourth dimension; in a review, you generally can only assert them.

This question may sound pedestrian, but it scales to fundamental questions around the nature of life and the possibility of sustainability on earth. How do the things in a universe, all composed of atoms, change in behavior and structure as they get larger? How do things that are alive as units (i.e. animals) scale differently from things “alive” as interacting units (i.e. cities and companies)?

These are the kinds of deep questions theoretical physicist Geoffrey West addresses in Scale, a book that ruminates on his own mortality and that of all living creatures and the cities and companies they create.

This book is about science, but it is full of people — both humanity at large, and individuals who stood on each other’s shoulders to apply the laws of physics and to discover/define quantitative laws for the complexities of living things. That idea has been unfolding in an exciting way for a long time, and West has been in the middle of most of it, first at the Los Alamos National Laboratory, where his bosses allowed him to dabble in biology, and later at the Santa Fe Institute, where he still works.

The book cover of Geoffrey West's "Scale," depicting a black background with a globe showing North America at night.

At the scale of a book review, here is just a brief summary of West’s tour of a world perceived through the lens of physics and its laws of scaling. In essence, as we learned in school, if you double a line, it grows by a factor of two; double the side of a square, and its area grows by a factor of four; double the side of a cube, and its volume and mass will increase by a factor of eight.

Animals and cities and other organisms have complex internal structures whose different facets scale at different rates. For instance, as an animal’s overall mass grows, so do the length and size of its blood vessels, but the ending capillaries of a circulatory system are close to the same length and diameter in almost any animal, a function of the properties of blood. Similarly, rooms grow in number but not necessarily in size as a building gets larger. The electrical outlets are the same size throughout.

Big animals are not just like small ones but bigger; big ones live longer. The number of heartbeats in any animal’s lifetime is approximately the same — about 1.5 billion — so the hearts of large, long-lived animals beat much more slowly. A shrew’s heart beats roughly 1,500 times per minute, while the elephant operates at a ponderous 30 beats per minute. (Humans have become something of an outlier as we have extended our average lifespan to closer to 2.5 billion heartbeats with modern health measures — which may mean we have reached the limit. That’s a hotly debated question, of course.)

This all ties in with a different but complementary scaling in metabolic rates (how much energy it takes to keep a given mass of animal alive). For example, with each doubling of average weight, a species gets 25 percent more efficient metabolically and lives 25 percent longer. The physics of size and gravity also dictate certain other ratios: A mouse’s legs are tiny compared to its overall size, whereas an elephant needs broad stumps to stand on. Whales finesse the problem of supporting their mass by living in the sea.

For every doubling in residents, you need only 85 percent more infrastructure, but you get 115 percent more economic activity—and 115 percent more crime and disease.

West then proceeds to cities and companies, starting with humanity’s accelerating transition from hunting and gathering to farming to industry and urbanization and ultimately the digital everything/always-on phenomenon we’re dealing with now.

The big takeaway is that while companies get less innovative as they expand, cities foster innovation (presumably because of all the creative interactions). For every doubling in residents, you need only 85 percent more infrastructure, but you get 115 percent more economic activity—though you also get 115 percent more crime and disease.

As West puts it:

In biology, the network principles underlying economies of scale … constrain the pace of life … and limit growth [generally creating equilibrium]. In contrast, cities and economies are driven by social interactions whose feedback mechanisms lead to the opposite behavior. The pace of life systematically increases with [a city’s] population size: diseases spread faster, businesses are born and die more often, and people even walk faster in larger cities. … Moreover, the social network dynamic …. leads to open-ended-growth. … Continuous adaptation, not equilibrium, is the rule.

Yet these rates of increase cannot last, says West. Cities use resources at a troubling rate, and he wonders how we can avert environmental crisis.

Indeed, West’s biggest concern is the sustainability of the planet. He easily debunks the already debunked Malthus, who expected humanity to run out of food, but he notes the astounding growth in energy consumption of modern humans. The challenge is not to control the population but to figure out how to bend the curve of their increasing activity.

Perhaps because I’m not a physicist, I’m less troubled by all this than West is. Like hunter-gatherer tribes, cities may be a temporary phenomenon, to be replaced by whatever you get when cities all flow into one another and cover the planet. The fundamental questions concern what we can change in this setup — and what we will do on purpose, carefully. Or will the changes happen to us? The scaling laws describe what happens now, but they still don’t exactly explain how or why. In essence, West doesn’t yet have all the answers, but he’s asking the right questions.

If cities connect across the planet into multi-node urban agglomerations, what laws will govern their use of energy and the interactions of their parts? Will new corporate structures such as markets and platforms (like eBay and Uber and Airbnb) change the physics of corporate growth and senescence? Will the new platform companies take control and live forever? Or will governments apply antitrust laws and change the “natural” outcomes? Indeed, the role of government is oddly missing from West’s book. One might conclude that national governments are irrelevant because cities more directly influence how we live. Yet they matter, both for their own unnatural laws and their propagation of culture.

In short, this is a masterful work. It does not neatly explain everything; rather, it elucidates the regularities amid the messiness. Whatever the reader’s particular area of interest, there’s something in here that’s relevant and prompts further thought.

For example, although West explains individual human growth — and how it stops as we change from a growth metabolism into a sustaining metabolism — there’s another phenomenon left untouched. Diabetes and obesity — and the concomitant other chronic diseases — result from a disturbance of that delicate metabolism; the laws West propounds no longer apply as many individuals continue to grow past puberty. This may be as big a threat to our future as the broader environmental issues that trouble West more.

Perhaps both books and book reviews should end not just with conclusions but with questions. Ideally a book teaches you a lot and makes you want to know more, whereas a book review teaches you a little and makes you want to read the book.

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