I'll Have What She's Having by R. Alexander Bentley & Mark Earls & Michael J. O'Brien

Author:R. Alexander Bentley & Mark Earls & Michael J. O'Brien [Bentley, Alex]
Language: eng
Format: epub
ISBN: 9780262297981
Publisher: MIT Press
Published: 2011-06-15T00:00:00+00:00

This was part of a larger cascade in the 1990s, a frenzied rush of discoveries of “power law” distributions (some rather dubious, it must be said) in social data—economic markets, the then still new World Wide Web, Hollywood actor networks, and university research funding. Marketers were not immune to this fashion. “Direct-response” marketers—those using mail and other direct-response media—jumped aboard the trend to justify the way they valued certain customer groups without acknowledging the underlying instability. Indeed, many asserted the “fixed” and enduring location of different groups of customers along the distribution. Power laws were indeed suddenly everywhere, and it all went a bit too far, with a Nature paper describing a “power law” in hospital waiting lines and arcane navel-gazing pursuits such as finding a “power law” probability distribution of line shifts in a word processor when text was inserted.

Avalanches and Wildfires

Despite some overeagerness, the new complexity science injected energy into a classic debate regarding the “punctuated equilibrium” described by paleobiologists Niles Eldredge and Stephen J. Gould. The debate was over whether fossil species extinctions were somehow interconnected not through extreme external events (such as an asteroid impact) but rather through small triggering events cascading through the vast tangle of ecological interdependency among species. A prevailing analogy was to think of evolution as being like a pile of sand, with more sand slowly being poured onto the peak. Usually the grains land without much disturbance, but occasionally one grain can trigger a massive sandslide. Like the addition of a grain of sand to the sandpile, the extinction of a single species could cause the extinction of other species that are ecologically dependent on it.

According to the late Danish theoretical physicist Per Bak, both evolution and sandpiles exhibit “self-organized criticality”—a property of systems that are in continual flux but precariously balanced between the buildup of interdependencies. In sandpiles and evolution, change occurs intermittently rather than smoothly and gradually. “Critical” points are reached, which trigger bursts, or avalanches, that extend over a wide range of magnitudes.

The analogy of the sandpile was a seductive start, but Bak and his colleague Kim Sneppen made the model even simpler and in the process more satisfying. They modeled an “ecosystem” through the arrangement of index numbers (“species”) in a circle, such that each agent interacted with its two nearest neighbors. Each agent was represented by a fitness value between 0 and 1, chosen at random to start the simulation. Their simulation then ran in a series of steps. At each time step, the lowest fitness value in the circle was selected against and assigned a new random value. The two nearest neighbors of the chosen agent were also randomly assigned new fitness values, equaling the “adaptation” of dependent agents. It was all so simple. At each time step in the simulation, the smallest fitness, together with the fitnesses of the two neighbors, were replaced with new random fitnesses. The step was repeated again and again. And from this there seemed to unravel a secret of the complex universe.

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