Iain Couzin

Behavioral Ecologist

Emerging Explorer

Picture of Iain Couzin

Photograph by Simon Garnier

Can understanding a swarm of cannibalistic locusts help solve world hunger? Can a million migrating wildebeests help explain why cancer spreads? Can a school of fish help invent robots that locate oil spills? Ask Iain Couzin. He's exploring how collective behavior in animals can be quantified and analyzed to give us new insights into the patterns of nature—and ourselves.

"We're realizing that animals have highly coordinated social systems and make decisions together," Couzin says. "They can do things collectively that no individual could do alone. It's still a very unexplored area of animal behavior." Couzin blends fieldwork, lab experiments, computer simulations, and complex mathematical models to test theories about how and why cells, animals, and humans organize and work together.

"I never had special training in math or computer science, but I realized the power of using computational tools, so I basically taught myself programming." He discovered that video game cards loaded with next-generation graphics processing power would be the perfect supercomputers for his work. "These cards let us explore hypothetical virtual worlds within computer simulations; tracking thousands of animals in real time. One new technique even allows us to see the world from an animal's perspective, giving us a whole new understanding of how sensory input and environmental factors affect collective behavior."

Couzin notes that behaviors such as swarming locusts, flocking birds, or schooling fish may look the same on the surface, but be driven by entirely different biological pressures. During plague years, massive locust swarms invade more than one-fifth of the world's land cover, affecting the livelihood of one in ten people on the planet. Couzin presumed the insects were somehow transmitting information and perhaps acting cooperatively. In fact, his research revealed that they were responding to a lack of essential protein and salt in their diet.

"When those resources run low, locusts eat each other," he explains. "All the nutrition they crave is perfectly packaged in the tissue and blood of other locusts. They run away to avoid cannibalization from behind, and run forward to catch and devour those ahead. This triggers the onset of vast swarms, many miles long. Now that we understand the important role of nutrition, we hope to use satellite data and ground-based sensing to understand where protein may be environmentally limited and predict outbreaks in the future."

Couzin discovered the secret behind the swarms by building a small racetrack in the lab where locusts march for eight hours a day while software follows their movement and interactions. "This kind of detailed, quantitative tracking leads to all kinds of surprises."

His fieldwork studying army ants revealed highly complex, coordinated behavior between a million nearly blind individuals. The voracious carnivores quickly decimate all prey in any area, so they constantly move on, forming traffic lanes that minimize congestion and optimize traffic flow. "Unlike humans, they've unselfishly evolved an efficient strategy that benefits the whole colony." They also form incredible living architectures to keep the swarm moving, including bridges of interconnected individuals and modular nests shielded by five-foot-high walls of interwoven ants.

"This gives us new clues about how to design modular robotics. We may be able to mimic what we see in nature to create machines that can dynamically respond and adapt in the face of change, just as the ants spontaneously create robust yet very flexible structures," he says. "We're working with engineers to develop biologically inspired robots that can very effectively search for oil spills, phytoplankton plumes, or other anomalies in the ocean."

Other research may reveal crucial data on how habitat fragmentation caused by humans affects long-distance animal migrations. Couzin's mathematical models predict a critical point at which migration, once severely disrupted, cannot be regained. "You can't just recover the habitat and expect the migrations to resume—they won't. If our models are right, we must be extremely cautious about transforming land to the degree where systems collapse."

Animal migration also demonstrates the power of collective intelligence. "If one individual is confused, it can follow others. When its own magnetic sensing or memory is stronger, it in turn becomes influential. So you have ever changing leadership according to the quality of information each individual possesses."

Could this allow us to see how cancer cells migrate and spread throughout the body? Couzin hopes so. "I'm fascinated by the idea that our work could ultimately help explain how tumors progress. Basic principles we're unraveling may give us new insights into the collective motion of cells or interactions between neurons."

Couzin tests many predictions in fish tanks at his lab. There, he and his team trained different groups of fish to have varying degrees of preference for different targets. Fish with the strongest "opinions" dictated the movement of the entire group, even when they were only a small minority. But as fish with no preferences were added, a tipping point was reached, and group behavior flipped back to majority control.

"Our experiments showed that individuals without a preference actually promote democracy, increase the chance of consensus, and prevent extremist minorities from fragmenting the group," he says. "At this stage we can't claim this relates to political outcomes or decisions in humans, but we're ready to test our mathematical principle with other systems, including people. The health-care community is increasingly interested in the underpinnings of how opinions are transferred. It could have important consequences for everything from the probability of giving up smoking to the likelihood of obesity."

Couzin's studies aren't limited to bugs and birds. He's placed actors within crowds of people at train stations, told them when to turn their heads as though looking at something, and prompted chain reactions in the crowd. "This kind of socially contagious behavior is common in humans, as is our ability to sense something out of the ordinary," he reports. To demonstrate that, he placed suspicious-looking individuals in a crowd and documented how others detected and responded to the suspects. "You may not be aware of it, but you are subtly, socially engaging with other individuals in crowds all the time."

Although an animal lover since childhood, for Couzin, it's all about the math. "By analytically quantifying all these examples of collective behavior, we can translate knowledge from one system to another—from locusts to wildebeest to people. Scientists are realizing how little we know, yet how important it is to gain knowledge about group dynamics. Sometimes nature surprises us with solutions more elegant than anything we could imagine. There could be completely unknown applications we haven't even dreamed of yet."

Inside National Geographic Magazine

  • swarm-theory.jpg

    Swarm Theory

    A single ant or bee isn't smart, but their colonies are. The study of swarm intelligence is providing insights that can help humans manage complex systems, from truck routing to military robots.


  • The Pattern Maker

    A look into Iain Couzin's mathematical approach to collective behavior.

  • Centered version

    Studies on Migration

    How do individuals balance the cost and benefits of migration? What is the role of social interaction? What are the principles that underlie the evolution of collective migration?

In Their Words

From invasive cells to schooling fish to human cultures, groups can accomplish what solitary individuals cannot. Collective behavior is one of the most basic, yet unexplored, aspects of life.

—Iain Couzin


  • swarm-behavior-couzin.jpg

    Swarm Behavior

    The study of swarm intelligence is providing insights that can help humans manage complex systems.



Listen to Iain Couzin

Hear an interview with Iain Couzin on National Geographic Weekend.

  • 00:09:00 Iain Couzin

    Iain Couzin studies collective behavior, from insect swarms to schools of fish to groups of humans. His study of locust swarms surprisingly revealed that the insects are often more intent on devouring each other than on eating crops.

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