In this episode of Stuff You Should Know, the hosts explore the fascinating world of slime molds, organisms that defy traditional biological classification. Though they were once thought to be fungi, these ancient life forms belong to the kingdom Protista and can exist as both single cells and large masses. Despite lacking a nervous system, slime molds demonstrate remarkable capabilities, including solving mazes, finding efficient paths to food, and sharing information between colonies.
The episode also examines how researchers are applying slime mold behavior to modern challenges. Studies have shown that these organisms can recreate efficient transportation networks, with patterns matching existing systems like the Tokyo railway. Their problem-solving abilities have applications in urban planning, and the tech sector is investigating how to use slime mold behavior patterns in artificial intelligence development and complex systems modeling.

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Slime molds challenge traditional biological classification systems, as they exhibit characteristics spanning multiple kingdoms. Originally classified as fungi, they are now recognized as members of the kingdom Protista, representing some of Earth's most ancient life forms. These organisms can exist either as single cells or as large cytoplasmic masses, reaching sizes comparable to a medium pizza while maintaining a single cellular structure with multiple nuclei.
Despite lacking a nervous system, slime molds display remarkable intelligence. Dr. Toshiyuki Nakagaki's research revealed their ability to solve mazes and find efficient paths to food sources. These organisms can even share learned information between colonies and demonstrate collective decision-making through chemical signaling. The slime mold Dictyostellium discoideum exhibits altruistic behavior, with some cells sacrificing themselves to form structures that help disperse spores, ensuring species survival.
Researchers have found fascinating applications for slime mold behavior in modern problem-solving. At Hokkaido University, Atsushi Taro demonstrated that slime molds can recreate efficient transportation networks, developing patterns that mirror existing systems like the Tokyo railway. These organisms have even helped map ancient Roman roads, suggesting potential applications in urban planning. The tech community is now exploring ways to reverse-engineer slime mold behavior for AI development and complex systems modeling, highlighting the potential for nature-inspired solutions to modern challenges.
1-Page Summary
Understanding slime molds requires rethinking traditional categories, as these organisms bridge characteristics across different kingdoms.
Slime molds present a biological classification conundrum, having traits likened to fungi, animals, and neither. Once considered members of the kingdom Fungi, slime molds are reclassified into the kingdom Protista, according to the present biological consensus. Even though mycologists, who traditionally studied fungi, continue their research on slime molds, these organisms are identified as some of the most ancient life forms.
The confusion regarding slime mold classification stems from their spore-producing nature and their congregation into large clumps that mirror fungal appearances. However, these seemingly fungal attributes fall short of defining them. It's clarified that slime molds are neither animals nor fungi and should be understood within their distinct category—a testament to their deep evolutionary roots.
The range of slime mold configurations include both single-celled organisms and expansive, wall-less cellular masses.
These plasmodial slime molds can grow impressively large, equivalent to the size of a medium pizza. Yet, despite their size, they maintain themselves as a single cellular structure containing millions of nuclei and organelles without individual cell walls. This structure enables dynamic and coordinated movements towards nutrients by oscillating in response to their environment, resembling a single sheet of living tissue.
Al ...
The Biology and Classification of Slime Mold
Slime mold, a simple organism devoid of a nervous system, exhibits a range of behaviors that suggest a form of intelligence and the capability for adaptive decision-making usually attributed to more complex life forms.
Japanese researchers, including Dr. Toshiyuki Nakagaki, discovered that slime molds, such as Physarum polycephalum, can move in deliberate ways, spread out strategically, and even solve mazes to find food.
In a notable experiment, Dr. Toshiyuki Nakagaki observed how slime mold managed to find the most efficient path through a maze to reach its food. The slime molds displayed the ability to learn and navigate around a bridge with a noxious substance, and once accustomed, they could transfer this knowledge to naive, unexposed slime molds, indicating a form of information sharing.
As Josh Clark describes, slime molds search for food by creating fan-like formations that move fractally toward food sources through a process of contraction and expansion. They exhibit a decentralized form of decision-making where cells closest to food emit cyclic AMP signals, prompting a collective movement toward the food without needing a leader or central cont ...
The Intelligent and Adaptive Behaviors of Slime Mold
In the realm of scientific inquiry, researchers are finding that the humble slime mold may hold solutions to some of the most complex and modern problems in urban planning and technology.
Recent studies have shown that the movement and growth patterns of slime molds can guide the optimization of transportation and other networks.
Researchers have utilized slime molds to recreate ancient and modern transportation systems. In one experiment, Atsushi Taro from Hokkaido University placed oat flakes, representing Tokyo neighborhoods, in a petri dish and observed slime molds growing networks between these oat flakes. Remarkably, the patterns closely resembled the Tokyo railway commuter system, which exemplifies the mold's ability to naturally develop efficient pathways. This holds the promise of utilizing slime mold behavior as a blueprint for optimizing urban designs.
Similarly, in experiments signifying ancient Roman cities, slime molds (fisarium) mimicked the layouts of long-forgotten Roman roads, uncovering lost routes and affirming known ones. Clarke and Bryant have humorously posited that someday every city planner might rely on a slime mold researcher for infrastructural guidance.
The Potential Applications of Slime Mold Research
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