By Bob Grant

Geoffrey West, Jim Brown, and Brian Enquist prefer to call their groundbreaking model "metabolic theory" and not "the metabolic theory of ecology," as some articles have referred to it. ¹ "It's unfortunate to associate it only with ecology," says Brown. Indeed, metabolic theory has branched from ecology, and its underlying principles and predictions have the potential to serve in a variety of contexts.

Urban Planning - This past month in the Harvard Business Review's "Breakthrough Ideas for 2007" issue, West wrote about power-law scaling relationships in urban areas. ² Looking at demographics, infrastructure dimensions, crime rates, intellectual innovation, and rates of disease spread in cities of all sizes around the world, he and his colleagues found that some urban features, including total length of electrical cables, miles of road surface, and number of gas stations, scale with exponents less than one, similar to biological networks such as the vascular and xylem systems. Therefore, as cities' populations double, they should require less than double of these infrastructure features. Some social aspects, however, scale to city size with an exponent greater than one. Measures of wealth and creativity such as GDP, wages, and number of patents filed actually increase more quickly as population increases.

Corporations - West says that some of the patterns true for cities may apply to corporations and industries as well, which would suggest that the larger companies get, the higher their per-employee rate of innovation. But, West writes: "The equations also predict that in the absence of continual major innovations, organizations will stop growing and may even contract, leading to either stagnation or ultimate collapse." ³

Drug Trials - According to West, if pharmaceutical researchers could use the predictions of metabolic theory to reliably scale drug dosage from model organisms to humans, much time and expense might be saved in development.

Tumor Growth - A paper in the Journal of Theoretical Biology reports that the principles of metabolic theory apply to tumor growth. ⁴ West suspects that tumors co-opt segments of the vascular system while maintaining an attachment to the wider transport network that determines the metabolic characteristics of the whole organism.

Human Fertility - Melanie Moses, a postdoc working with Brown, used metabolic theory to explore the scaling of human fertility with energy consumption. Analyzing more than 25 years of data from 100 countries, they showed that consumption of what they call "extrametabolic energy" strongly influences the number of offspring. This describes the use of resources such as oil, coal, gas, and electricity. Further, they found that human fertility rates decline with a scaling exponent of negative ¹/₃ as extrametabolic energy increases. This accounts for the reduced birth rates in industrialized nations, possibly due to parents considering potential tradeoffs between child number and the energy investment required.

Computer/Digital Network Design - Stephanie Forest, a computer scientist at the University of New Mexico, will be collaborating with Brown to explore how scaling power laws might inform computer and chip design. If measures such as optimal processing time and chip surface area can be modeled, computers and digital networks might be designed to function more efficiently.