slime mold!

Slime mold has long sparked the interest and imagination of scientists, philosophers and mathematicians concerned with emergent behavior, spontaneous order, and self-organization.  The basic concept behind these fields is that complex systems and unexpected behavior can arise out of a profusion of relatively simple interactions.  Central to all these theories is the notion that such organization takes place without any overarching control.  For example: schools of anchovies move in giant seething formations as if they were a single much larger fish, but though the school may react like a single organism it has no brain, no central nervous system, no leader, only the individual actions of each of its constituent members based on how the fish around it are reacting.  Other examples of emergent behavior include termite and ant colonies, swarms of locust, weather patterns and traffic jams.  Because these systems rely on the aggregate actions of individual components and/or actors these theories are closely tided to chaos theory.

There are actually two major types of slime mold – plasmodal slime molds and cellular slime molds.  Once thought to be related to fungi, slime molds tend to live in decaying plant matter and feed on bacteria.  Plasmodal slime molds (like the yellow one on the videos) begin life as unicellular amoeba.  When they encounter another amoeba, they fuse to form a larger multi-nucleic organism – basically a single giant cell – that feeds by engulfing its food (bacteria).   As you can see in the time-lapse video it travels in fan like patterns by streaming its cytoplasm (or is it technically protoplasm?) through vein like fingers.  Once it has exhausted its resources, or conditions become too harsh it will produce fruiting bodies and spores, which germinate into new amoebae.

The second type, cellular slime molds, is even stranger.  They too begin life as single “swarm cells” that will form together into slug-like blobs in order to locomote and reproduce via spore, but with one crucial difference – they retain their cell walls and individual identity.  When food is low individuals send out chemical signals telling nearby cells to group together to form a blob capable of migrating to better conditions and producing spores.  When conditions are correct to form fruiting bodies, some cells will form into stalks, while others become the “fruit”.  For a long time it was something of a mystery (and fodder for critics of evolution) why some cells would sacrifice their genes so that others might reproduce.  After all, since they were autonomous cells it seemed impossible that stalk forming genes would be selected for since such genes would preclude reproduction and thus passing on of those genes.  It is now thought that, rather than possessing different genes, it is the cells timing in joining the blob and thus their position within it that determines whether a given cell becomes a stalk or a fruit.

What I find so fascinating about slime molds and similar systems is how predominant they are in nature, and yet how utterly alien they are to traditional notions of consciousness.  Even in a very well defined emergent system capable of being accurately modeled mathematically there seems to be a huge gulf between the linear language used to describe such systems and the aggregate of simultaneous, autonomous, actions. One can understand the components of a system.  One can understand the rules that govern it.  One can understand how the rule is applied to each of the components in any given case.  But one cannot simply intuit the emergent form any more than any individual component within the system can know how its actions affect the overall group dynamic.  In order to understand the emergent form one must physically go through the procedure for creating it. An algorithm must be applied to each component one after another step by step making this as much of an empirical pursuit as a mathematical one. Perhaps that is why the complexity of such emergent systems is so surprising.

Further reading on slime molds and a bit of emergence:

http://www.youtube.com/watch?v=VWGA7kIeE0Q documentary on cellular slime mold (In German).

Conover, Adele. Hunting Slime Molds: They’re not animals and they’re not plants, and biologists want to know a lot more about them. Smithsonian magazine, March 2001 http://www.smithsonianmag.com/science-nature/phenom_mar01.html
Barone, Jennifer. Slime Molds Show Surprising Degree of Intelligence: A creature with no brain can learn from and even anticipate events. Discover January 2009 http://discovermagazine.com/2009/jan/071
StarLogo – modeling environment for exploring properties of emergent systems including slime molds http://education.mit.edu/starlogo/
Hofstadter, Douglas.  I am a Strange Loop.  2007.  Basic Books – Very accessibly book about emergent systems and their relationship with consciousness and identity.  His postulate of consciousness as an emergent phenomenon leads to an interesting discussion of how one can understand neurochemistry or physics to be deterministic and yet perceive conscious thought as a free act of the will.

One more video: not slime mold but quite beautiful: