Slime moulds present a classification challenge for scientists, questioning whether they fit into the plant, animal, or neither category.
Despite lacking a brain, slime moulds exhibit problem-solving abilities by efficiently navigating mazes and modeling urban infrastructures.
The social behavior of cellular slime moulds, involving chemical communication and cell sacrifice, offers insights into cooperation and altruism in biology.
Deep dives
Understanding Slime Mold Diversity
Slime molds are diverse single-celled organisms that often exist in both free-living and aggregated forms. They can vary greatly in size, with some species being microscopic while others can grow nearly a meter across. These organisms feed predominantly on bacteria and can produce environmentally lasting spores when conditions become unfavorable, allowing them to survive for years. Their intriguing appearances, such as vibrant colors and unique shapes, contribute to their classification, with notable forms like wolf's milk and the infamous 'dog's vomit' mold standing out for their visual distinctiveness.
Life Cycles and Behavior
Slime molds exhibit fascinating life cycles that can be categorized into cellular and acellular types, each with distinct behaviors. Cellular slime molds, like Dictyostelium discoideum, exist primarily as single cells but can aggregate into a multicellular structure during food scarcity. In contrast, acellular slime molds can form a single, large cell with multiple nuclei, challenging conventional notions of cellular structure. These life stages allow them to adapt to their environment, demonstrating behaviors that include coordinated movement towards food sources.
Navigational Intelligence
Despite lacking a brain, slime molds display sophisticated intelligence in navigating complex environments, often finding the shortest path through mazes. Experiments show that when placed in artificial environments representing cities or road networks, slime molds can efficiently connect food sources, achieving navigational efficiency comparable to human-designed systems. This capability illustrates their unique form of decentralized problem-solving, wherein they can strengthen connections to food and retract unnecessary paths. Their behavior raises profound questions about intelligence and decision-making in organisms without centralized nervous systems.
Cell Communication and Sacrifice
In the social behavior of cellular slime molds, communication plays a critical role in their transition from unicellular to multicellular organisms. As individual cells aggregate, a portion sacrifices itself to form stalk cells while others become spores, highlighting an intricate social structure. This process involves chemical signaling that ensures a coordinated evolutionary strategy for survival and reproduction. Such behaviors prompt interest in understanding kin recognition and communal decision-making, suggesting lessons about cooperation and altruism in other biological systems.
Slime Molds in Scientific Research
Scientists leverage slime molds for research in various fields, notably in studying human diseases like cancer, Alzheimer's, and Parkinson's. The model organism, Dictyostelium discoideum, shares significant genetic similarities with human cells, making it a valuable tool for investigating cellular behaviors and disease pathways. Their behavior in navigating environments parallels human immune responses and neurodegenerative conditions, allowing researchers to explore cellular movements and interactions. This research highlights the broader relevance of slime molds in comprehending biological systems on both micro and macro scales.
Melvyn Bragg and guests discuss slime mould, a basic organism that grows on logs, cowpats and compost heaps. Scientists have found difficult to categorise slime mould: in 1868, the biologist Thomas Huxley asked: ‘Is this a plant, or is it an animal? Is it both or is it neither?’ and there is a great deal scientists still don’t know about it.
But despite not having a brain, slime mould can solve complex problems: it can find the most efficient way round a maze and has been used to map Tokyo’s rail network. Researchers are using it to help find treatments for cancer, Parkinson's and Alzheimer's disease, and computer scientists have designed an algorithm based on slime mould behaviour to learn about dark matter. It’s even been sent to the international space station to help study the effects of weightlessness.
With
Jonathan Chubb
Professor of Quantitative Cell Biology at University College, London
Elinor Thompson
Reader in microbiology and plant science at the University of Greenwich
And
Merlin Sheldrake
Biologist and writer
Producer: Eliane Glaser
In Our Time is a BBC Studios Audio production
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