It's been said that once the cell evolved, everything else in life is but a detail. It sounds like glib reference to the fact that all life (well, all cellular life--viruses excluded) is cellular. But as we've noted in an earlier post on cognition in bacteria, and in our books and writing, even single-celled organisms have complex abilities to evaluate and respond to their environments. Those abilities include, in many or even perhaps most such organisms, the ability to form multicellular organisms under some conditions (slime mold, bacterial biofilms, and others).
In fact, this is not a trivial kind of exception, but a profound one. The same kinds of mechanisms that make you a single, multicellular entity lead otherwise single-celled organisms to do remarkable things. These 'simple' cells have sophisticated ways to monitor their environment, respond collectively (even sometimes as collections of different species) in response. That is, they are adaptable, one of the basic principles of life.
An example that has been noted by others, but that we learned about this week on the BBC World Service radio program, The Forum, with biologist Brian J Ford, is the amoeba called Difflugia coronata. This single celled organism, living in ponds or other watery worlds, builds a house of sand which it lives in and carries around as it moves. The house is 150 thousandths of a millimeter in diameter, but apparently carefully constructed in a replicable form. As the amoeba grows, it ingests sand of varying sizes and when it divides to reproduce, one of the daughter cells inherits the house and the other gets the ingested sand so that it can build a house of its own. You can read more about it in the book, Built by Animals: The Natural History of Animal Architecture by Mike Hansell [Oxford University Press. 2008] (which can be found online in abbreviated Google form here). This gorgeous picture of one Difflugia's house is from that book.
It's not only the amoeba, of course. Cells of red algae even circle around a wounded peer, protecting it from the outside environment and providing its physiological needs until it recovers. And so on.
If we think about life in this way, and not in terms of exceptionalism for 'higher' organisms, life becomes more of a unitary phenomenon. Also, many things, including perhaps especially behaviors, that we might wish to credit adaptive evolution for having produced in our own precious ancestry as a species, have been around billions of years before the first hominids had that lusty gleam in their eyes. And, with little doubt, these 'primitive' amoebae and algae will still have their orderly social life eons after we advanced creatures have departed this Earth.