Slime Mold Revisited

In this episode, Rik from Planet Vulcan reports on the ongoing research into the behavior of Physarum, aka slime mold.  The behavior of slime mold is an awe-inspiring and humbling example of the evolved wisdom of nature.  This simple superorganism forages efficiently and knows when it is time to produce spores, all based on mechanical and chemical signals.

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Transcript

Slime Mold Update

 Good day to you, and welcome to Fascinating!  I am your host Rik, from Planet Vulcan.  My ongoing mission on Planet Earth:  to plant seeds of a way of thinking, a way that is based on an understanding of evolutionary processes, with the ultimate aim of helping to sustain and increase the momentum of Earth’s long arc towards prosperous and happy societies, founded on ideals of liberty and justice.

 In Season 1, episode 3, senior contributing editor Prego de Nada wrote about slime mold, among other natural examples of spontaneous self-organization, such as ant colonies, fish schools, grazing herds and bird flocks in what we refer to as the “natural world”; and in the world of human society, the self-organization of automobile traffic and markets. 

 Although we should emphasize that from a Vulcan’s-eye view, there really is no meaningful distinction between the natural world and the world of human society; it’s all natural, as much as Earthlings love to believe they are somehow special - separate and apart from mere animals and the natural world.

The phenomenon of spontaneous self-organization and emergent order are things that most Earthlings are still not familiar with; they are surprised when presented with this idea and find it difficult to believe.  Such ideas are not routinely taught in school, even though emergent order is ubiquitous in both nature and society if you just learn how to recognize it.

 The organization we observe in nature, and in much of human society as well, results from unguided actions; the order we see on a macro scale emerges from behavior on a micro scale, as the individual components of a system behave under a simple system of local rules, such as the rules assigning right-of-way to automobile drivers.

 About Physarum, Prego wrote, “the behavior of slime mold is quite possibly the most astonishing demonstration of spontaneous order in all of nature, more astonishing than the order evident in gatherings of other creatures, because physarum does not have a nervous system, nor does it have muscles.  It can exist as a single-celled organism resembling an amoeba, and it can join with others into a blob with numerous nuclei but no internal cell walls.  Flows of cytoplasm within this mass are created by contractions of the outer membrane to create movement.  In ways that are still being investigated by today’s scientists, physarum can forage effectively, it can remember where it found food, and forms fruiting bodies that produce spores”.

 Earthling scientists have continued to do research on Physarum, also known as slime mold, and I asked my chatbot to describe the results of the most recent investigations.  

 The bot reported on collaborative research efforts currently underway involving participants from Harvard University’s Wyss Institute and participants from the Allen Discovery Institute at nearby Tufts University.  Here is a summary of their recent findings about this remarkable organism:

 Mechanosensation and Decision-Making:  the researchers found that Physarum can sense mechanical cues in its environment, and make decisions on growth direction based on what it senses.  It uses its outer membrane to detect slight deformations, called strain patterns, in substrates, and it prefers smoother substrates over rougher substrates.

 Network Adaptation and Information Processing:  Physarum forms smart networks by dynamically and continuously adjusting its tubular network in response to environmental changes.  The contractile tubes respond to both mechanical and chemical signals.  This enables the organism to effectively process information about its immediate environment and produce well-informed behaviors.

 Learning and Habituation:  Physarum can learn from experience and retain memories, in spite of not having a conventional nervous system.  For example, if it repeatedly encounters an irritant in its environment without undergoing damage, it will habituate to the irritant and decrease its avoidance behavior.

 What about the fruiting bodies and the production of spores, which Prego also mentioned?  

 How does Physarum know when the time is right to do this?

Researchers have noted that spore production tends to occur when the organism is environmentally stressed, such as when it gets too cold, when it gets too dry, or when it cannot find enough food. 

 Specific genes become activated in response to the chemical signals that the stress creates, and this triggers a cascade of molecular events which ultimately lead to spore production.

 Nature has selected for behavior where it is as if the organism is thinking, “I am in mortal danger and might very well perish, so just in case I do die, I will ensure that new organisms will develop from my spores when the spores sense that times have gotten better, and they awaken from their dormant state and grow into the single-celled organisms that will combine into a new superorganism.

 Here's another fascinating anecdote, which illustrates the ability of Physarum to in effect perform sophisticated mathematical calculations.

 There is a much-studied problem in network optimization called the “Traveling Salesman Problem”, stated thusly:  "Given a list of cities and the distances between each pair of cities, what is the shortest possible route that visits each city exactly once and returns to the starting city?"

 Solving this problem algorithmically has proven so far to be intractable, particularly as the number of cities becomes large, because the possible combinations of routes increases factorially with the number of cities.  Brute force computing, even with the power of today’s computers, has not so far been successful at solving the Traveling Salesman Problem beyond dealing with a small number of cities.

 But Physarum routinely, and quickly, creates networks among food sources that approach optimality, without necessarily arriving at the ultimate solution.  

 Achieving optimality in a network solution is analogous to achieving profit maximization in the world of business.  Physarum tries to maximize the difference between energy expenditure and nutrient value, while a business enterprise seeks to maximize the difference between the cost of production and the market value of output.

 In both cases, maximization is usually not perfectly attained, but an approximation is usually sufficient.  Economists call it “satisficing”.

 Social insects, such as bees, ants and termites also effectively solve network problems related to their foraging activities.

 Nature is endlessly fascinating, and is way smarter than any of us, even with our supercomputers to help us.  It’s been doing this sort of thing successfully for a long time, driven by the need for organisms to survive and replicate.

 If the ideas of self-organization and emergent order are new to you, I urge you to listen to the second and third podcast essays from Season 1, where these foundational concepts and their significance are introduced.

 I also highly recommend Heather Barnett’s Ted Talk titled, “What Humans Can Learn from Semi-Intelligent Slime”, which you can find on YouTube. 

 Ms. Barnett is an artist who works with slime mold as a medium, and she is the founder of the Slime Mould Collective, which promotes collaborative investigation of slime mold among people from many different backgrounds.

 Among other interesting facts, Heather relates the story of an experiment that researchers ran, where they placed oat flakes (slime mold’s favorite food) in a pattern that replicates the stops on the rail transport network of the city of Tokyo.  Over the course of just over one 24-hour day, the mold created a network that almost exactly reproduces the rail network.

 I invite you to have a listen to the next Fascinating! podcast and a look at the next video on our YouTube channel.  You can find access to all podcasts and videos on our web page, fascinatingpodcast.com.

 Please recommend Fascinating! to your friends if you find the lessons from nature in these essays personally valuable.

 Theme music:  Helium, with thanks to TrackTribe.

 Live long and prosper.

 Practice the art of winning without defeating anyone.

 Savor your experiences.

 Treasure your memories.

 Anticipate a happy and rewarding future.

 And respect nature’s wisdom.