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team will also track individuals with mac-ular degeneration to determine how longit takes for changes to occur in the visualcortex. —B. BOWER

Sizing Up Complex WebsClose or far, manynetworks look the same

Researchers have discovered that aremarkable diversity of complex networks,including the World Wide Web and pat-terns in cellular biochemistry, have a com-mon architecture with snowflakes and trees.These networks all display similar patterns,whether viewed from up close or far away.

“It’s a fundamental advance,” says Albert-László Barabási, a physicist who studiesnetworks at the University of Notre Damein Indiana. The question of whether com-plex networks can show such a fractal pat-tern, also known as self-similarity, “has beenbugging us for a while,” he says.

In recent years, researchers have found

that a surprising range of networks has acommon structure: a few major hubs withmany connections and many minor nodeswith only a few connections. In the WorldWide Web, for instance, tens of thousandsof sites link to a few popular Web sites,such as Google and Yahoo, while there areoften just a few links to an individual’shome page.

Now, in a surprising finding, researchershave identified self-similarity in four typesof complex networks: the World WideWeb, a network of actors who have beenin films together, networks of proteins withlinks between those that can bind to eachother, and networks of other cellular mol-ecules with links between moleculesinvolved in the same biochemical reac-tions.

The researchers note that they discov-ered this wide-ranging characteristic byfiguring out how to “zoom out” and look atnetworks from farther and farther away.They started by using computer analysisto cover each network with non-overlap-ping boxes, each of which contained a clus-ter of nodes separated by less than a spec-ified number of links. Next, theinvestigators essentially blurred theirvision, paying attention to how the boxes—rather than the individual nodes—wereconnected.

By repeating this procedure manytimes, the researchers could observe thestructure of a network on many levels. Inthe Jan. 27 Nature, Hernán Makse of theCity College of New York and his cowork-

ers report that all the blurred networkshave connectivity patterns similar to thoseof the original network.

Ordinarily, Barabási says, objects withfractal structures fit into a finite-dimen-sional space, such as a flat plane or a three-dimensional space. By contrast, mathe-maticians have modeled complex networkssuch as the World Wide Web as infinitedimensional because there’s no realistic wayto fit such a network, with hubs having somany links, into a finite-dimensional space.This property led Barabási and many otherresearchers to assume that complex net-works cannot be self-similar.

“If you had asked me yesterday, I wouldhave said they are surely not self-similar,”Barabási says.

Understanding the architecture of com-plex networks is important, for example, forprotecting the World Wide Web from hackerattacks and for designing drugs with fewside effects, Barabási says. However, the con-tribution of the new finding to thoseadvances isn’t yet clear, he says.

“They’ve found something new here, butwe don’t know yet whether it is a Rosettastone that will let us translate the myster-ies of networks into something we under-stand,” says Steven Strogatz, a mathemati-cian at Cornell University. —E. KLARREICH

Good ExposureContact with babies mightlessen MS risk

People who grow up with younger siblingsclose to them in age are less likely to develop(MS) than are people without such siblings,a new study finds.

The finding supports the idea thatsloppy kisses from baby brothers and sis-ters might fend off disease in later years.As such, it adds to evidence in support ofthe hygiene hypothesis, which holds thatearly, frequent exposure to infectiousagents prepares the immune system tofight off diseases rather than to turnagainst a person’s own tissues, as occurs inautoimmune diseases, say Anne-LouisePonsonby of Australian National Univer-sity in Canberra and her colleagues.

Most researchers consider MS—whichis marked by tremors, pain, loss of musclecoordination, and slurred speech—to be anautoimmune disease. It appears when fattysheaths that insulate nerve fibers are dam-aged, as if by an errant immune attack.What would trigger such an immune mis-fire is unclear, but scientists suspect somecombination of a person’s genetics andexposure to pathogens.

The new study suggests that childhoodexposure to infants and the infections theyspread could reduce the risk of a person

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SCIENCENEWSThis Week

FRACTAL BURST In the World Wide Web, links between individual nodes follow patternssimilar to those of links between clusters of nodes, between clusters of clusters, and so on.

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