Technology Collective behavior Follow my leader
科技 集体行为 跟领导走
A group's “intelligence” depends in part on its members'ignorance
HUMAN beings like to think of themselves asthe animal kingdom's smartest alecks.
It may come as a surprise to some,therefore, that Iain Couzin of Princeton University believes they havesomething to learn from lesser creatures that move about in a large crowd.
As he told the AAAS meeting in Washington, DC, groups of animals often make whatlook like wise decisions,
正如他在华盛顿AAAS（American Association forthe Advancement of Science，美国科学促进会）召开的会议上所说的，虽然群居动物中的大部分成员对接下来会发生什么一无所知，
even when most of the members of those groups areignorant of what is going on.
Coming to that conclusion was not easy. Beforelessons can be drawn from critters perched on the lower rungs of theevolutionary ladder, their behaviour must first be understood.
One way to dothis is to tag them with devices that follow them around—motion-capturesensors, radio transmitters or global-positioning-system detectors that can puta precise figure on their movements.
Unfortunately, it is impossible to tag morethan a few individuals in a herd, flock or swarm.
Researchers have thereforetended to extrapolate from these few results by using various computer models.
Dr Couzin has done quite a bit of this himself.
Most recently, he has modelledthe behaviour of shoals of fish.
He posited that how they swim will depend oneach individual's competing tendencies to stick close to the others (and thusmove in the same direction as them) while not actually getting too close to anyparticular other fish.
It turns out that by fiddling with these tendencies, avirtual shoal can be made to swirl spontaneously in a circle, just like somereal species do.
That is a start. But real shoals do not existto swim in circles.
Their purpose is to help their members eat and avoid beingeaten.
At any one time, however, only some individuals know about—and can thusreact to—food and threats.
Dr Couzin therefore wanted to find out how suchtemporary leaders influence the behaviour of the rest.
He discovered that leadership is extremelyefficient.
The larger a shoal is, the smaller is the proportion of it thatneeds to know what is actually going on for it to feed and avoid predationeffectively.
Indeed, having too many leaders with conflicting opinions resultsin confusion.
At least, that is true in the model. He is now testing it inreality.
Tracking individual fish in a shoal is hard.
Fortunately, advances in pattern-recognition software mean it is no longerimpossible.
Systems designed to follow people are now clever enough not only totrack a person in a crowd, but also to tell in which direction his head isturned.
Since, from above, the oval shape of a human head is not unlike theoblong body of a fish, this software can, with a little tweaking, followpiscine antics, too.
Dr Couzin has been using a program developedby Colin Twomey, a graduate student at his laboratory, to track individual fishin a tank.
The result is not just a model of shoaling fish, but a precisenumerical representation of their actual movements and fields of vision.
That means it is possible to investigate whether real-life fishy leaders have thesame effect on a group as their virtual kin.
Alas, merely observing a shoal does not makeit clear which individuals lead and which follow.
Instead, Dr Couzin has builta biddable robot three-spined stickleback.
A preliminary study of a shoal often flesh-and-blood sticklebacks shows that they do indeed mingle with therobot and that they follow its leadership cues as predicted.
He is now making arobot predator to see how the shoal reacts to less benign intruders.
If the models are anything to go by, the bestoutcome for the group—in this case, not being eaten—seems to depend on mostmembers' being blissfully unaware of the world outside the shoal and simplytaking their cue from others.
This phenomenon, Dr Couzin argues, applies to allmanner of organisms, from individual cells in a tissue to (rather worryingly)voters in the democratic process.
His team has already begun probing thequestion of voting patterns.
But is ignorance really political bliss?
DrCouzin's models do not yet capture what happens when the leaders themselvesturn out to be sharks.