Life and the Art of Networks

Contents Viewpoints Molecular Networks: The Top-Down View D. Bray Biological Networks: The Tinkerer as an Engineer U. Alon Social Insect Networks J. H. Fewell Reviews Communication in Neuronal Networks S. B. Laughlin and T. J. Sejnowski A Bacterial Cell-Cycle Regulatory Network Operating in Time and Space H. H. McAdams and L. Shapiro Also see related material on Science's STKE.

In the world at large, it is easy to see the impact of networks and the relevance of network theory. Steve Strogatz recently called the massive power failure in the United States the "grid's immune response" and called for the utilization of technology to have parts of the grid talk to each other and make decisions that would benefit the entire network rather than individual power plants (S. Strogatz, "How the blackout came to life," New York Times, 25 August 2003, p. A21). The impact of this way of thinking is percolating into fundamental biological research with increasing speed, and this issue of Science focuses on how we are making that transition. A Viewpoint by Bray (p. 1864) gives an overview of basic network properties. Alon's Viewpoint (p. 1866) notes the striking similarity of biological and human-made machines, which suggests that engineers and biologists may now find their efforts converging.

Biologists are striving to move beyond a "parts list" to more fully understand the ways in which network components interact with one another to influence complex processes. Thus attention has turned to the analysis of networks that operate at many levels. At the scale of networks of interacting proteins that govern cellular function, the flagellated bacterium Caulobacter crescentus has been a model system for cell cycle regulation for at least 25 years. McAdams and Shapiro (p. 1874) review the spatial and temporal controls that must be appreciated to understand how global regulators might operate. One assumes that biological regulatory networks are the result of crafting by natural selection. But are they? Wagner (Science's STKE 2003, pe41) grapples with this question and possible mechanisms by which signaling networks develop in an associated Perspective at Science's STKE.

The design principles for efficient coordination of cells that work together in organ systems are also under scrutiny. Laughlin and Sejnowski (p. 1870) describe the characteristics of brain cells in the cerebral cortex. Energy efficiency and the capability for dynamic reorganization emerge as key properties of these neuronal networks. Individual organisms act together in societal networks. As described by Fewell (p. 1867), studies of social insect behavior have the potential to shed light on how interactions between individuals affect the group and how behavioral networks evolve.

The idea that molecular signaling cascades share fundamental properties with colonies of ants and Internet communication systems is adding new meaning to the idea of interdisciplinary science. By dissecting the properties of networks, we are beginning to determine how network architecture affects the function of its components. As A.-L. Barabási fervently concludes in his popular book Linked (Perseus, 2002), "These laws, applying equally well to the cell and the ecosystem, demonstrate how unavoidable nature's laws are and how deeply self-organization shapes the world around us." The potential for the future is that we will be able to intervene and modify networks, using the same underlying rules to affect disease states or even ecological crises.