by Quentin Long
©2008 Quentin Long
I just learned something unspeakably cool: Slime molds got memory!
Details are in the paper Amoebae Anticipate Periodic Events, by Tetsu Saigusa, Atsushi Tero & Toshiyuki Nakagaki, and Yoshiki Kuramoto (downloadable PDF here). When left to themselves, slime molds just kinda spread out at a more-or-less constant rate; what Saigusa & Co. did was, they took a colony of the slime mold Physarum polycephalum, and once an hour, they hit said colony with a ten-minute-long Coldness/Dryness combo. Since slime molds prefer Warm and Wet, it shouldnt surprise anybody that the Physarum colony slowed its advance during each Cold/Dry period. However, theres a couple of weird bits which should surprise people.
Weirdness #1: After Saigusa & Co. stopped the periodic Cold/Dry treatments, the colony slowed itself down once an hour. Not indefinitely, mind youthe self-inflicted hourly braking did go away after conditions stabilized for a whilebut even so, a slime mold is a unicellular life-form, okay? And youve got to wonder how a single-celled critter can possibly manage to keep to an hourly schedule at all
Weirdness #2: Some time after letting things stabilize, Saigusa & Co. hit the colony with a single Cold/Dry treatmentat which point, the colony returned to slowing itself down once an hour!
In short: Yes, Virginia, unicellular life-forms can exhibit behavior which is awfully hard to explain without the notion that theyre capable of both (a) recalling past events, and (b) recognizing a regular-recurring pattern. How cool is that?
Of course, there are a few unanswered questions. Like, what the heck is that Physarum colony actually doinghow does it store information, and how does it retrieve that information at whichever later moment? At this point, nobody knows (Saigusa & Co. included)! But what we do know, is that single-celled critters can exhibit behavior which was previously thought to be the exclusive province of multi-cellular beasties with distinct brains. Again: How cool is that?
This finding has implications for the origin of intelligent life but in addition to that, it also opens up new possibilities for writers. Were all familiar with multi-cellular critters which have a number of specialized cell-types (i.e., skin cells, heart cells, etc), each of which has its own particular role to play in the ongoing business of keeping the whole organism alive; indeed, we are multi-cellular critters of that kind! What Saigusa & Co. have shown is that its possible for cells to play at least some of those particular roles without being explicitly specialized to do that. Perhaps the most obvious possibility here is the notion of a sentient amboid, a creature whose physical form is subject to change without notice; another is a creature which is apparently indestructible because when its attacked, it immediately sloughs off any/all damaged cells, and whatever those cells may have been doing before the attack, intact cells from elsewhere in its body take over without skipping a beat.
You might say its the Harvard Law of BiologyUnder the most rigorously controlled conditions of pressure, temperature, volume, humidity, and other variables, the organism will do as it damn well pleasesas applied to entire species, not just individual life-forms