The idea that microorganisms (diatoms in this case) might be capable of social behavior is new to me. I have a picture in mind of vast colonies of cells coalescing in evolutionary time to form higher organisms, as if social behavior was the natural prototype of a central nervous system.
Pelagic diatoms communicate through synchronized beacon natural fluorescence signaling
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Tidewater News and Opinion Forum 
At least thirty years ago I read about a professor who had spent his entire career studying slime mold. I was similarly surprised. The basic revelation is that slime is not just being slimy. The organisms at one end of the pipe or wall or whatever are communicating with other parts of the colony. Later, I read about how fungi on the roots of one tree seem to be communicating with the fungi on the roots of the next tree. The whole forest seems to be communicating more than we thought.
I think the basic rule is, if anything advantageous shows up, i.e. something more likely to survive, then that thing will become the norm.
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