Smart Swarm: Using Animal Behaviour to Organise Our World. Don Tapscott

Чтение книги онлайн.

СКАЧАТЬ out that the waggle dance—or “tail-wagging dance” as he called it—was in fact a sophisticated form of communication (he won a Nobel Prize for this research in 1973). When a foraging bee danced, von Frisch had discovered, she wasn’t just advertising a source of food, she was also providing precise directions to locate it. To perform such a dance, a bee would run forward a short distance on the hive’s comb while vibrating her abdomen in a “waggle.” Then she’d return to her starting point in a figure-eight and repeat this over and over, as if reenacting her flight to the flower patch. The length of her dance indicated how far away the food was, and the angle of her dance (relative to vertical) corresponded with the direction of the food (relative to the sun). If a bee danced in a direction thirty degrees to the right of vertical, for example—picture the number 1 on a clock—the flower patch could be found by flying in a direction thirty degrees to the right of the sun. It was an ingenious system, but it had never been linked to house hunting before.

      By carefully studying several swarms—sometimes running beneath them as they flew across the Bavarian countryside—Lindauer determined that the bees dancing on the swarm cluster were scouts that had been out searching for a nest site. Some were still powdered with red-brick dust from having explored a hole in a building, or blackened with soot from having checked out a chimney. Just as foraging bees used the waggle dance to share news about food sources, so the scouts were using it to report on potential real estate. At first, many of the scouts danced in different directions, apparently announcing various options. But after some hours, fewer and fewer sites were mentioned until, finally, all the dancers were pointing in the same direction. Soon after that, the swarm lifted off from its bivouac and flew to its new home, which Lindauer was able to locate by reading the code of the dances.

      The bees had reached a consensus, he theorized, because the liveliest scouts had persuaded the rest to go along with their choice. They did this by getting rivals to visit their preferred site, where, confronted with the superior qualities of the site, the former competitors simply changed their minds. One by one they were won over, he speculated, and the disagreement went away.

      In this respect, at least, Lindauer got it wrong. It wasn’t quite that simple. Researchers have since established that only a small percentage of scouts ever visit more than one site. The group’s decision does not rely on individual scouts changing their minds, but rather on a process that combines the judgments of hundreds of scouts—one that would remain a mystery for fifty years.

      That’s where Tom Seeley and Kirk Visscher came in. Beginning in the late 1990s, they picked up where Lindauer left off, this time using video cameras to record every aspect of the swarm’s behavior. They also brought some new ideas about honeybee deliberation. Given the large number of individuals that take part in house hunting, they doubted that bees’ decision making was based on consensus. It just seemed too complicated, like trying to get a large group of friends to agree on which movie to watch. More likely, they figured, the process relied on some form of competition. Instead of trying to work through their differences with one another, scouts dancing on the swarm cluster appeared to be actively lobbying for different sites. It wasn’t a meeting of minds at all, but a race to build up supporters—with the winners taking all.

      In that sense, the bees’ system was more like a stock market, in which the value of a security rises or falls according to the collective judgment of the group. Scouts watching another scout dance, like brokers, might be persuaded to do their own research on the site being advertised, and if they liked what they saw, they could buy into the site by dancing for it themselves. If they didn’t like it, they didn’t have to. The more bees that joined in, the greater the likelihood the site would be selected.

      But how did the process work, exactly? What were the mechanisms that enabled the bees to choose so accurately?

      To find out, Seeley and Visscher conducted a series of experiments. After preparing a swarm for house hunting, they placed five plywood nest boxes an equal distance from the bees on Appledore Island—four representing mediocre choices for a new nest and one that was excellent. What made the fifth box better than the rest was that it offered the bees an ideal amount of living space—about forty quarts, compared to fifteen quarts for the others, which was not enough to store honey, raise brood, and meet the other needs of an expanding colony. To track the bees during the decision-making process, Seeley and Visscher labeled all four thousand individuals in each swarm with tiny numbered disks on their thoraxes and dabs of paint on their abdomens, a tedious process that involved chilling batches of twenty bees at a time to render them docile enough to be handled. But it was worth it in the end, because, when they looked at video tapes of the swarms later, they could tell which bees had visited which nest boxes and which ones had danced for which boxes at the main cluster. The shape of the decision-making process emerged.

      The key, it turned out, was the brilliant way the bees exploited their diversity of knowledge—the second major principle of a smart swarm. Just as Deborah Gordon’s ant colonies used self-organization to adjust to changes in the environment, so the honeybees used diversity of knowledge to make good decisions. By diversity of knowledge, in this case, I mean a broad sampling of the swarm’s options. The more choices, the better. By sending out hundreds of scouts at the same time, each swarm collected a wealth of information about the neighborhood and the nest boxes, and it did so in a distributed and decentralized way. None of the bees tried to visit all five of the boxes to rate which one was the best. Nor did they submit their findings to some executive committee for a final decision, as workers in a corporation might do. Instead, these hundreds of scouts each provided unique information about the various sites to the group as a whole in what Seeley and Visscher described as a “friendly competition of ideas.”

      Equally important, every scout evaluated nest sites for herself. If a scout was impressed by another scout’s dance, she might fly to the box being advertised and conduct her own inspection, which could last as long as an hour. But she would never blindly follow another scout’s opinion by dancing for a site she hadn’t visited. That would open the door to untested information being spread like a rumor. Or, to use the stock-broker analogy, a bee wouldn’t invest in a company just because its stock was on the rise. She’d check out its fundamentals first.

      Meanwhile, as the scout bees continued their search, the swarm was busily ranking each option. This was determined by the number of bees visiting each site. The more visitors, the more “votes” for the site. Though the best nest box wasn’t discovered first by the scouts, it quickly attracted the attention of numerous bees. Scouts returning from the excellent box had no trouble convincing others to check it out, largely because they danced for it so vigorously—performing as many as a hundred dance circuits each, compared to only a dozen or so danced by bees for lesser sites. A dance of that length could take five minutes, compared with thirty seconds for a shorter dance, so it was much more likely to be noticed by scouts walking around on the surface of the cluster. And once the number of bees advertising the best box increased, support for it shot up, as interest in the mediocre sites faded away.

      “This careful tuning of dance strength by the scouts created a powerful positive feedback,” Seeley explained, “which caused support for the best site to snowball exponentially.” This was a crucial mechanism, because it meant that even small differences in the quality of nests were exaggerated—their “signals” were amplified—making it much more likely that support for the best site would surge ahead.

      As more and more bees gathered at the first-rate box, fewer and fewer lingered at the others. That was because scouts returning from boxes for the second or third time were dancing fewer circuits for them each time, whether they’d visited the excellent box or the mediocre ones. Scouts that had visited poor sites quit dancing first. Seeley and Visscher described this mechanism as the dance “decay rate.” It meant that support for less attractive boxes would dwindle automatically—even as the number of bees collecting at the superior box kept growing—in a decision-making process that lasted from two to five hours during the test. In technical terms, this represented a balancing, or negative feedback, СКАЧАТЬ