to the task of describing living things. As Lawrence Slobodkin says: “Almost any prepackaged mathematical structure used in biology was designed for something else. Biology wears these clothes like hand-me-downs.”

The fields of chaos, complexity, and emergence being studied by researchers at the Santa Fe Institute and elsewhere came about through the efforts of biologists such as Ludwig von Bertalanffy to think like physicists, and of the biology envy of physicists such as Robert May and Geoff West. As a result of their efforts, we are starting to understand how large groups of simple units can interact to produce complex behavior. One of the fruits of this new science has been an understanding of the links between power laws and fractal geometry. Power laws run through biology—in metabolism and other allometries, and in patterns of species diversity, rarity, and commonness. The laws are equally ubiquitous in the physical processes that shape life’s environment. Many theories of biology and physics work at some scales but not others—but power laws show how the same principles can apply across scales from mitochondria to sequoias. Scientists have only just begun to exploit fractal geometry and power laws as ways of describing and unifying nature.

Attempts at deriving general laws for biology have always met with skepticism and controversy. Often this skepticism proves justified. Most of the patterns proposed as general laws of nature—such as Rubner’s surface law, Pearl’s rate-of-life hypothesis, Kyoji Yoda’s self-thinning in plants, and Evelyn Hutchinson’s ratios—have turned out to be not as general, or as accurate, as their advocates first thought. Metabolic ecology is science in the making, not received wisdom like the laws of natural selection, motion, and thermodynamics. The current state of the theory is probably not the last word on the matter, but then nothing in science ever is. “People end up being well known more for the questions they ask than for the answers they provide,” comments David Tilman. “West, Brown, and Enquist are asking the right questions.”

West, Brown, and Enquist are not the first of biology’s unifiers to