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Patterns in Nature’s Networks

  • By Mark Zastrow
  • Posted 07.24.14
  • NOVA

From food webs to Facebook—even inside our own brains—the networks that bind us exhibit an all too familiar hub-and-spoke pattern. It appears over and over again. Connected clusters link people or species, cities, or neurons. This pattern is nature’s way of allowing resources and activity to course through the network, maximizing efficiency.

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Transcript

The Pattern in Nature’s Networks

Posted: July 24, 2014

What does a social network look like? You know, the links of friendship between people. It often feels like we make friends through a random series of chance encounters. So, you might think that social networks should look random, too. Something like this.

But it turns out real life social networks don't look like that. They look more like this. There’s a pattern here, a sort of hub-and-spoke shape. People cluster into groups and are linked to each other through a few hubs. You know who these hubs are—the social butterflies who introduce everyone to everyone else.

A network that looks like this is called a “small world network” because, through these key people, we're all connected to each other in just a few steps. It’s the classic idea of six degrees of separation. And if you’re thinking this sort of network shape looks familiar‚ you're right. Many of the networks that engineers design‚ like airline routes and power grids and the servers that power the Internet—they all have the same pattern. And that’s because small world networks have a special feature: they maximize connectivity while minimizing the number of connections. Fewer connections mean resources can travel through the network more efficiently.

In fact, scientists now know that this pattern appears spontaneously all the time in nature. It’s found in places like rivers, the food webs of ecosystems, and even inside our own bodies. Why? For the same reason we organize our power grid this way—it gives you the most connectivity for your wiring cost.

Take your brain, for example. Its 10 billion neurons are wired in a network that scientists call the connectome. The brain needs different regions to be able to communicate effectively, so it makes sense for the connectome to have a small world pattern. In fact, the brain seems to want to wire itself this way. Things like brain tumors can break up the formation, but when the brain tries to recover, it goes back to a small-world shape, rewiring and regenerating its network. We also know that children's brains start off looking randomly connected. But as they age and their brains develop, connections are lost, and it becomes more small world-like and structured. On the other hand, people with neurological disorders like autism have brains that look like big worlds, missing those key connections between clusters. If it's the connections in our brains that matter, maybe consciousness itself emerges from small world architecture.

It might seem almost magical that this hub-and-spoke pattern keeps appearing all over the universe. But it’s not magical, it’s mathematical. We see other kinds of patterns, too, appearing and reappearing everywhere in nature. Take the bell curve, for example, which describes natural randomness in all sorts of things, from breeding populations to the velocities of stars. Or the Fibonacci sequence, which shows up in the number of spirals you count on the head of a sunflower. These patterns hint at the math and physics lying underneath reality. It’s a signal that the gears of the universe are churning away. In that way, our small-world social networks don’t just connect us to each other—they also reflect the mechanics of the cosmos.

Credits

PRODUCTION CREDITS

Writer, Producer, and Narrator
Mark Zastrow
Music by
Mark Zastrow
Editorial Help from
Anna Rothschild
Original Footage
© WGBH Educational Foundation 2014

MEDIA CREDITS

Mississippi River watershed
National Park Service
Diffusion tensor images
Human Connectome Project, NIH, Massachusetts General Hospital, Meredith Reid (University of Alabama–Birmingham)
Neurons, In Vitro Color!
Flickr /thelunch_box (CC BY-NC 2.0)
Small world neural network
based on figure from van den Heuvel and Sporns (2011) / The Journal of Neuroscience 31(44):15775–15786
Autism spectrum disorder networks
Barttfeld et al. (2011) / Neuropsychologia 49 (2011) 254–263
The Formation of Stars and Brown Dwarfs and the Truncation of Protoplanetary Discs in a Star Cluster
Matthew R. Bate, Ian A. Bonnell, and Volker Bromm, UK Astrophysical Fluids Facility
Floral Art
Flickr / Louise Docker (CC BY 2.0)
Dark matter filaments
Ralf Kaehler, Oliver Hahn and Tom Abel, Kavli Institute for Particle Astrophysics and Cosmology (Stanford)
Millennium Simulation flythroughs
Springel et al. (2005)

IMAGE

(main image: small world network)
© WGBH Educational Foundation 2014

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