Podcast Summary: In Our Time – "Slime Moulds"

In the January 30, 2025, episode of BBC Radio 4's "In Our Time," host Melvyn Bragg delves into the fascinating world of slime molds. Joined by experts Eleanor Thompson, Jonathan Chubb, Merlin Sheldrake, and Greg, the discussion unpacks the biology, behavior, and scientific significance of these enigmatic organisms.

Introduction to Slime Moulds

Melvyn Bragg opens the episode by painting a vivid picture of encountering slime molds in everyday environments:

Melvin Bragg [00:09]: "If you've ever seen a mysterious white or yellow blob on your garden compost heap or on a fallen tree in the local park, you'll have come across slime mold."

He highlights the longstanding debate over their classification, referencing Thomas Huxley's 1868 inquiry about whether slime molds are plants, animals, both, or neither.

What Are Slime Moulds?

Jonathan Chubb provides a foundational understanding of slime molds:

Jonathan Chubb [01:23]: "It's actually quite a vague, fuzzy term that encompasses a lot of different species."

He explains that slime molds are single-celled organisms capable of aggregating into multicellular structures under certain conditions. Their ability to form spores allows them to survive harsh environments for extended periods.

Types of Slime Moulds: Cellular vs. Acellular

The discussion distinguishes between the two primary types of slime molds:

Cellular Slime Moulds

Merlin Sheldrake elaborates on cellular slime molds, using Dictyostelium discoideum as a prime example:

Merlin Sheldrake [05:29]: "Cellular slime molds spend much of their life living as single-celled organisms. And when times get tough, food gets scarce, they come together to form a multicellular structure."

These organisms exhibit a remarkable life cycle where individual cells aggregate to form a "slug," which later differentiates into spores and stalks, demonstrating an early form of cellular differentiation and cooperation.

Acellular Slime Moulds

Melvin Bragg contrasts this with acellular slime molds, which form large, multinucleated cells known as plasmodia:

Melvin Bragg [11:06]: "These plasmodial or acellular slime molds can weigh as much as 20 kilos. They develop an internal circulation called cytoplasmic streaming to move materials efficiently within their vast single-cell structure."

Acellular slime molds navigate their environment through complex networks of vein-like structures, showcasing distributed problem-solving capabilities without centralized control.

Behavior and Intelligence

One of the most captivating aspects discussed is the problem-solving prowess of slime molds despite lacking a nervous system:

Merlin Sheldrake [12:54]: "Slime molds can navigate mazes, find the shortest paths, and even mimic the layout of complex networks like the Tokyo subway. Their ability to optimize routes rivals that of more 'intelligent' organisms."

The experts delve into how these behaviors emerge from simple, decentralized rules governing cell movement and aggregation.

Communication and Social Behavior

Eleanor Thompson and Greg explore the social dynamics within slime mold communities:

Greg [15:25]: "In cellular slime molds, around 20% of the cells sacrifice themselves to become stalk cells, facilitating the formation of spores. This self-sacrifice is orchestrated through chemical signaling and kin recognition mechanisms."

They discuss the presence of "cheater" cells that attempt to monopolize spore formation, highlighting the evolutionary balance between cooperation and selfishness within these organisms.

Scientific Relevance and Applications

The episode underscores the significance of slime molds in scientific research:

Greg [25:37]: "Slime molds like Dictyostelium discoideum have been instrumental in studying cell motility, chemotaxis, and even aspects of human disease. Their genetic similarities to human cells make them valuable models for understanding conditions like cancer, Alzheimer's, and Parkinson's."

Additionally, Merlin Sheldrake touches on innovative applications, including the use of slime molds in optimizing transportation networks and their potential role in space colonization experiments.

Future Research and Open Questions

Melvin Bragg addresses the complexities and future directions in slime mold research:

Melvin Bragg [31:49]: "We've amassed a vast amount of data on slime molds, but the challenge now is integrating this information to understand how cells process multiple signals simultaneously—much like navigating a busy street."

The conversation also touches on philosophical questions about intelligence, memory, and the nature of problem-solving in decentralized systems.

Conclusion: Rethinking Intelligence and Life

In wrapping up, Merlin Sheldrake and Greg reflect on the broader implications of slime mold studies:

Merlin Sheldrake [33:58]: "Slime molds challenge our human-centric definitions of intelligence and memory. They demonstrate that complex problem-solving can emerge from simple, distributed systems without a centralized brain."

Greg [39:26]: "Exploring amoebae helps us appreciate the sophistication of microbial life and its foundational role in the tapestry of life on Earth."

Melvin Bragg emphasizes the paradigm shift in biological understanding prompted by studying such organisms:

Melvin Bragg [40:54]: "Exposure to slime molds has allowed us to move away from rigid blueprint models of biology towards embracing emergence and self-organization as key principles in development."

This episode of "In Our Time" sheds light on the intricate and often overlooked world of slime molds, revealing their profound impact on scientific research and our understanding of life’s complexity.