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friday :: august 25, 2006
evolutionary path: scale-free networks

The architecture that pervades biological networks gives them an evolutionary edge by allowing them to evolve to perform new functions more rapidly than an alternative network design, according to computer simulations conducted at the University of Chicago.

Scientists have found the same intricate network architecture of evolution just about everywhere they look. This architecture characterizes the interaction network of proteins in yeast, worms, fruit flies and viruses, to name a few. But this same architecture also pervades social networks and even computer networks, affecting, for example, the functioning of the World Wide Web.

“These results highlight an organizing principle that governs the evolution of complex networks and that can improve the design of engineered systems,” wrote co-authors, Panos Oikonomou and Philippe Cluzel.

This organizing principle is what scientists call a “scale-free design.” A diagram of this design resembles the route maps of airline companies. “You have hubs that are highly linked with airplanes going in and out of those hubs,” Oikonomou said. But then smaller airports also exist that have far fewer connections, and there are various scales of connections in between.

Oikonomou and Cluzel initiated his project to find out if network design conferred any kind of evolutionary advantage. They created a Darwinian computer simulation to compare the evolvability of this scale-free network design with a more random design in which all network components have approximately the same number of connections. They programmed this computer world to have random mutations and natural selection operate on its digital populations, then compared how long it took the two types of networks to evolve the ability to perform a new task.

The populations organized in scale-free networks evolved rapidly and smoothly, while randomly organized networks evolved slowly and in spurts following a succession of rare and beneficial random events. “They followed drastically different evolutionary paths,” Cluzel said. Cluzel plans to conduct laboratory experiments on bacteria to test the validity of the organizing principle he and Oikonomou have identified via their simulations.

Their goal was to better understand biological evolution, but social and economic networks also display a scale-free architecture. “These networks can be people, they can be molecules, they can be whatever you like,” Cluzel said. >from *Digital World Reveals Architecture of Evolution*. August 7, 2006

related context
social network theory to the test. the interaction between social network structure and collective problem solving. august 10, 2006
> coupled oscillators -that is, entities capable of responding to each other's signals- will spontaneously self-organize. april 9, 2003
> small-world networking. february 4, 2003
> organizing principles of networks. november 11, 2002
> the new science of networks. june 6, 2002

tim miller gets trapped in a free-scale network hub

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