The researchers found that the yellow and pink-painted scouts displayed waggle dances advertising for their respective nests. In addition, however, the scouts were also seen to make brief buzzing head-butts to one another’s head and thorax. Dancing bees tended to receive head-butts toward the end of their dances, suggesting that the head butts were a signal to stop dancing. The most interesting finding came when looking at who was head-butting whom. Yellow-marked bees tended to receive these putative stop signals from pink-marked bees, and vice versa. In other words, the two different populations were mutually inhibiting one another - one proposal pitted against another.
The result of this arrangement is that it amplifies small differences between different populations of scouts, setting up a kind of winner-take-all scenario. Without inhibitory stop signals, the hive would be able to sustain multiple competing interests, as different groups of scouts accumulate more and more votes until the hive reaches some stable, but divided state. With stop signals, divided hive states are far less stable. A slight preponderance of one group of scouts will translate into greater inhibition of other groups of scouts, turning an initially small numerical advantage into a more sizable one. Over several iterations of this process, an initial slight majority is amplified into a consensus.
Ideally, a follow-up experiment would have eliminated the bees’ stop signals and studied the consequences on the hive’s decision process. Since this is nearly impossible to do, Seeley and his colleagues opted for a simulation based approach instead. In their models of collective bee activity, cross-inhibitory stop signals were essential for breaking decision deadlocks between two equally attractive nests. If the stop signals were indiscriminate, or absent altogether, the hive remained split, and never converged on a consensus.
Seeley and his team propose that cross-inhibition may be a general strategy for decision making, and indeed, their findings in bees recapitulate features of decision making and pattern formation in other systems. The remarkable unifying theme in all of these systems is how an aggregate swarm intelligence is built from just a few kinds of simple, local interactions between agents. Both neurons and bees are presumably unaware of how their impulses and signals transcend the individual, and lay the substrate for a grander, collective intelligence.
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