Flash mobs had their 15 minutes of fame a few years back.
In the early (pre-Twitter) days, individuals would receive e-mails or text messages with specific instructions to gather at a particular place and time, for a very particular purpose -- all to demonstrate the viability of technology-enabled social networking.
For example: "Thursday, 2:30-2:45 PM, on the steps of the museum. Be ready to disco John-Travolta-in-Saturday-Night-Fever style. Bell bottoms preferable."
To make the stunt work, those who arrived early knew to lie low until the appointed hour. With an appropriately-sized, suddenly-amassed crowd, the events were surprising and effective spectacles.
But when early arrivals gave the plan away, authorities were able to stop an event before it gathered steam. A critical mass of players was key. Without it, what could have been a powerful demonstration was nothing more than a few dopey weirdoes causing trouble.
Wikipedia will tell you the first flash mob occurred in Manhattan in 2003. However, in her lecture at the technology conference TED2009 a few weeks ago, Princeton University molecular biologist Bonnie Bassler made it clear there is nothing either new or original about these events.
Not only is the concept that coordinated group activity kicks in when critical mass is achieved not new, but we humans are late to this party. Bacteria were the first to figure it out.
In her compelling talk, Bassler explained that bacteria are both very chatty and quite capable of organizing groups to act up when -- and only when -- their team efforts will be most noticeable.
This bacteria conversation is known, quite reasonably, as quorum sensing.
Most bacteria, Bassler said, exist solely to reproduce. Humans are always playing host to myriad bacteria species, which are generally benign in small doses.
However, when some of these little "beasts" successfully reproduce rapidly enough to overwhelm our defense mechanisms, they change their behavior in ways that cause any number of problems, ranging from annoying infection to death.
The key for these bacteria is to hold their fire until there are enough of them to trounce our immune system. When enough of them "radio" back that sufficient reinforcements are in place, these bacteria, in unison, release their toxic payloads into the host and the problems emerge.
For example, Bassler said, vibrio fischeri, marine bacteria found in squid, appear to do little when measured in low concentrations. However, when enough of them are packed in together, they "flip the switch" and then glow.
Unfortunately, this group on/off switch doesn't just work for glowing sea creatures. Bassler's team has found evidence of quorum-sensing communication in bacteria responsible for cholera, the black plague and other fatal illnesses.
These bacteria use a chemical signaling mechanism, based on molecules called autoinducers to measure their own concentration by "chatting" with others. Once they have established that their concentration in the host has reached a critical mass, these bacteria do something they didn't do when the concentration was below the threshold.
One particular type of autoinducer, the AI-2, which requires the presence of a single gene, the LuxS, is found in many different bacteria strains. It is the AI-2 molecule that enables conversations not only among but also between bacteria species.