Scale: The Universal Laws of Life and Death in Organisms, Cities and Companies

by Geoffrey West

Metabolic rate is the fundamental rate of biology, setting the pace of life for almost everything an organism does, from the biochemical reactions within its cells to the time it takes to reach maturity, and from the rate of uptake of carbon dioxide in a forest to the rate at which its litter breaks down.

the basal metabolic rate of the average human being is only about 90 watts, corresponding to a typical incandescent lightbulb and equivalent to the approxima...

else in a continuously challenging and evolving environment. We have been coevolving together in a never-ending multidimensional interplay of interaction, conflict, and adaptation.

Each organism, each of its organs and subsystems, each cell type and genome, has therefore evolved following its own unique history in its own ever-changing environmental niche.

Natural selection, or the “survival of the fittest,” is the gradual process by which a successful variation in some inheritable trait or characteristic becomes fixed in a population through the differential reproductive success of organisms that have developed this trait by interacting with their environment.

metabolic rate exhibits an extraordinarily systematic regularity across all organisms.

you can readily see that for every four orders of magnitude increase in mass (along the horizontal axis), metabolic rate increases by only three orders of magnitude (along the vertical axis), so the slope of the straight line is 3⁄4,

if the mass is increased by any arbitrary factor at any scale (100, in the example), then the metabolic rate increases by the same factor (32, in the example) no matter what the value of the initial mass is, that is, whether it’s that of a mouse, cat, cow, or whale.

if the size of an animal is doubled it doesn’t need 100 percent more energy to sustain it; it needs only about 75 percent more—thereby saving approximately 25 percent with each doubling.

the larger the organism the less energy has to be produced per cell per second to sustain a gram of tissue. Your

are primarily determined simply by its size. For example, the pace of biological life decreases systematically and predictably with increasing size: large mammals live longer, take longer to mature, have slower heart rates, and have cells that work less hard than those of small mammals, all to the same predictable degree.

allometric to describe how physiological and morphological characteristics of organisms scale with body size, though his focus was primarily on how that occurred during growth.

same,” and metric is derived from metrikos, meaning “measure.” Allometric, on the other hand, is derived from allo, meaning “different,” and refers to the typically more general situation where shapes and morphology change as body size increases and different dimensions scale differently.

most fundamental biochemical level metabolic energy is created in semiautonomous molecular units within cells called respiratory complexes.

The critical molecule that plays the central role in metabolism goes by the slightly forbidding name of adenosine triphosphate, usually referred to as ATP. The detailed biochemistry of metabolism is extremely complicated but in essence it involves the breaking down of ATP, which is relatively unstable in the cellular environment, from adenosine triphosphate (with three phosphates) into ADP, adenosine diphosphate (with just two phosphates), thereby releasing the energy stored in the binding of the additional phosphate. The energy derived from breaking this phosphate bond is the source of your metabolic energy and therefore what is keeping you alive.

The cycle of releasing energy from the breakup of ATP into ADP and its recycling back from ADP to store energy in ATP forms a continuous loop process much like the charging and recharging of a battery.

At any one time our bodies contain only about half a pound (about 250 g) of ATP, but here’s something truly extraordinary that you should know about yourself: every day you typically make about 2 × 1026 ATP molecules—that’s two hundred trillion trillion molecules—corresponding to a mass of about 80 kilograms

respiratory complexes, are situated on crinkly membranes inside mitochondria, which are potato-shaped objects floating around inside cells. Each mitochondrion contains about five hundred to one thousand of these respiratory complexes . . . and there about five hundred to one thousand of these mitochondria inside each of your cells, depending on the cell type and its energy needs.

Because muscles require greater access to energy, their cells are densely packed with mitochondria, whereas fat cells have many fewer.

So on average each cell in your body may have up to a million of these little engines distributed among its mitochondria working away night and day, collectively manufacturing the astronomical number o...

The rate at which the total number of these ATPs is produced is a measure ...

Your body is composed of about a hundred trillion (1014) cells. Even though they represent a broad ra...

these hundred trillion cells have to be organized into a multitude of subsystems such as your various organs, whose energy needs vary significantly depending on demand and function, thereby ensuring that you can do all of the various activities that constitute living, from thinking and dancing to having sex and repairing your DNA.

this entire interconnected multilevel dynamic structure has to be sufficiently robust and resilient to continue functioning for up to one hundred years!

This hugely multifaceted, multidimensional process that constitutes life is manifested and replicated in myriad forms across an enormous scale ranging over more than twenty orders of magnitude in mass.

A huge number of dynamical agents span and interconnect the vast hierarchy ranging from respiratory complexes and mitochondria to cells and multicellular organisms and up to community structures.

The fact that this has persisted and remained so robust, resilient, and sustainable for more than a billion years suggests that effective laws that govern the...

is within this context that we should view allometric scaling laws: their systematic regularity and universality provides a window onto these emergent laws and underlying principles.

Natural selection has solved this challenge in perhaps the simplest possible way by evolving hierarchical branching networks that distribute energy and materials between macroscopic reservoirs and microscopic sites.

why I loved being a scientist: the challenge of learning and developing concepts, figuring out what the important questions were, and occasionally being able to suggest insights and answers.

The classic case of Newton’s laws is a standard example. Only when it was possible to probe very small distances on the atomic scale or very large velocities on the scale of the speed of light did serious deviations from the predictions from Newton’s laws become apparent. And these led to the revolutionary discovery of quantum mechanics to describe the microscopic,

and to the theory of relativity to describe ultrahigh speeds comparable to the speed of light.

Quantum mechanics is the foundational theoretical framework for understanding materials and plays a seminal role in much of the high-tech machinery and equipment that we use.

stimulated the invention of the laser, whose many applications have changed our lives. Among them are bar code scanners, optical disk drives, laser printers, fiber-optic communications, laser surgery, and much more.

major challenge in constructing theories and models is to identify the important quantities that capture the essential dynamics at each organizational level of a system.

“toy model.” The strategy is to simplify a complicated system by abstracting its essential components, represented by a small number of dominant variables, from which its leading behavior can be determined.

temperature is similarly identified as the average kinetic energy of the molecules.

I were exploring when we embarked on our collaboration. Could we first construct a coarse-grained zeroth order theory for understanding the plethora of quarter-power allometric scaling relations based on generic underlying principles that would capture the essential features of organisms?

“technology gives us the tools to analyze organisms at all scales, but we are drowning in a sea of data and thirsting for some theoretical framework with which to understand it. . . . We need theory and a firm grasp on the nature of the objects we study to predict the rest.”

The frustrations and inefficiencies, the blind alleys, and the occasional eureka moments are all part and parcel of the creative process.

However, once the problem comes into focus and it’s been solved it is extremely satisfying and enormously exciting.

whatever the geometry and topology of the network is, it must service all local biologically active subunits of the organism or subsystem.

Our circulatory system is a classic hierarchical branching network in which the heart pumps blood through the many levels of the network beginning with the main arteries, passing through vessels of regularly decreasing size, ending with the capillaries, the smallest ones, before looping back to the heart through the venal network system.

Space filling is simply the statement that the capillaries, which are the terminal units or last branch of the network, have to service every cell in our body so as to efficiently sup...

that is required is for capillaries to be close enough to cells for sufficient oxygen to diffuse efficiently across capillary walls and thence t...

This simply means that the terminal units of a given network design, such as the capillaries of the circulatory system that we just discussed, all have approximately the same size and characteristics regardless of the size of the organism.

Terminal units are critical elements of the network because they are points of delivery and transmission where energy and resources are exchanged.

the capillaries of all mammals, whether children, adults, mice, elephants, or whales, are essentially all the same despite the enormous range and variation of body sizes.

difference between taxonomic groups, that is, between mammals, plants, and fish, for example, is characterized by different properties of the terminal units of their various corresponding networks.

The final postulate states that the continuous multiple feedback and fine-tuning mechanisms implicit in the ongoing processes of natural selection and which have been playing out over enormous periods of time have led to the network performance being “optimized.”