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When friends pick a restaurant or movie, group decision making can get tricky. So how do flocks stick together in the animal world? As this ScienCentral News video explains, one researcher says they can do it without even communicating.
Birds of a Feather Decide Together
You've been there before, stuck at an impasse with friends, unable to decide where to eat or which movie to see. Suggestions fly as time slips away, the gang still undecided. For folks atop the food chain, complex communication doesn't always serve us well, especially considering that sheep, fish and bees continuously make snap decisions that move their groups in unison without much fuss or muss.
Scientists have long wondered how such animals do it. Now, one researcher believes he's found clues that point to an answer far simpler than anyone once thought. "You don't need [individual animals] to have to signal to one another," says Iain Couzin, a mathematical biologist and lead author of a study on decision-making in animal groups that was published in the journal Natureand highlighted in Discover Magazine. "You don't need individuals to actually recognize one another... and they can even collectively come to consensus," he explains. All the group needs, he says, is a few individuals with a directional preference. When they turn, one of two things happen: either the group follows or the stray individual rejoins the group.
Couzin, who splits his time between Princeton University and University of Oxford in England, says in animals that flock, herd or school, rules are at play. To decipher them, he and his colleagues first fished for clues in tanks, where they filmed fish swimming. Then the team created computer software that automatically tracked fish as they moved, helping translate darts and turns into mathematical formulas. "We can create these virtual animals," Couzin says of his experiment. "Then what we can do is we can abstract. We can make a simplified version of reality... we then look at the basic kinds of interactions that fish use."
And just like in our schools, fish follow rules in theirs. These include individuals moving apart when they get too close, turning at certain rates and interacting at given ranges, amongst what Couzin says are only some local rules that serve more as cues than signals. So important is group behavior that, alone, fish are incapable of doing things they do in a group. "As individuals, they have very good memory and they can learn navigation routes. But there's another level at which they can interpret their environment and that's at the collective level... by interacting with other individuals and responding to the movements of other individuals, they're acting as a super sensor," explains Couzin. "They're able to form tasks that are not possible for the individual in isolation."
image: Milton Love
But what happens when there are individual preferences that threaten to split a group in two directions? Here's where fish get diplomatic.
Couzin showed that if the percentage vying to go their way is equal, half of the time one of the groups will win. The other half of the time the other group will win, but only if there is a big difference in opinion about which way to go. For smaller differences of opinion, the whole group follows a route that's an average of the two directions. But, as Couzin explains, "If you have six percent in one group and five percent in the other, we find that one group with a tiny majority... will tend to win out almost all of the time. So, the group can collectively sense that majority."
People unconsciously behave in similar ways in crowds. "When you're walking along a sidewalk and other individuals are coming towards you, you'll tend to... perform all these avoidance maneuvers without really knowing about it," Couzin says, adding that other scenarios, like those where we should be communicating most, can handicap us. "In an evacuating building there could be the sound of an alarm, a fire and people might be panicking and therefore not capable of making a rational decision about where to go," he says.
Couzin's team has already started dissecting how we operate in such instances. "We're doing a simplified experiment with crowds of students whereby some students are given information about where to go and others are naive and no one knows who has this information," he says. "What we find is that people behave a lot like our model... so we're beginning to get an idea of how these ideas could be important, not only in understanding how people evacuate buildings or move on sidewalks, but also in terms of the spread of ideas... and how a few individuals can influence the behavior of many."
Such findings may shed light on how charismatic leaders intent on evil shape seemingly sane populations---think Hitler---perhaps someday purging the world of those who lead their flock down a wayward path.