In this chapter, we explore the hidden networks of life that underpin our understanding of intelligence, revealing how the intricate relationships between fungi, neural networks, and early animal forms suggest a profound connection that may redefine our view of evolution.

 

Opening Statement

In the quest to understand the origins of intelligence, a revolutionary hypothesis emerges: the potential fungal ancestry of animal neurons. This groundbreaking theory posits that the intricate neural networks found in animals may trace their roots back to ancient fungal organisms. This is not merely an academic exercise; it represents a profound shift in our understanding of evolution and intelligence itself.

For decades, the evolution of intelligence has been viewed through the lens of animal lineage, with emphasis placed on the gradual development of neural structures. However, the suggestion that fungi, some of the oldest and most resilient life forms on Earth, could have influenced the emergence of animal neural systems opens up a fascinating new chapter in evolutionary biology. This theory invites us to reconsider the foundational building blocks of intelligence, suggesting that the early interactions between fungi and primitive life forms may have laid the groundwork for the complex brains we see today.

The implications of this hypothesis are vast. If true, it not only rewrites the narrative of animal evolution but also offers profound insights into how we might design artificial intelligence systems. By understanding the neural architectures that have evolved through symbiotic relationships in nature, we can create AI that mimics these efficient, adaptive systems. This connection to AI further underscores the relevance of the hypothesis in contemporary discussions about technology and evolution.

As we explore the intricate networks that exist beneath our feet and the evolutionary pathways that connect diverse life forms, we find ourselves at the intersection of biology, technology, and philosophy. This exploration is not just about understanding where we come from; it is about shaping the future of intelligence itself. The potential fungal ancestry of animal neurons invites us to engage with the past to inform our future, paving the way for a new understanding of the cognitive superorganism that humanity may become in collaboration with AI.

 

1.1 The Hidden Networks Beneath Our Feet

Long before the first animals roamed the planet, Earth was dominated by a web of interconnected life forms that silently thrived beneath the surface. Fungi, some of the oldest life forms on Earth, emerged around 1.5 billion years ago, well before the appearance of multicellular animals. Their role in shaping life on Earth has been profound and largely hidden from view. Today, these ancient life forms continue to serve as a vital part of ecosystems, yet they go unnoticed by most of us.

At the heart of fungal biology lies the mycelium, an intricate web of thread-like structures called hyphae. These mycelial networks stretch for miles underground, quietly breaking down organic material and recycling nutrients. Some scientists even refer to these networks as the “Wood Wide Web” due to their ability to connect not only fungi but also plants, trees, and other organisms in an ecosystem. Just as the internet connects computers across the globe, mycelium links life in forests, creating a shared resource distribution system that fosters cooperation and survival.

But these hidden networks do much more than feed plants or recycle dead matter—they communicate. Recent studies have revealed that fungi transmit electrical impulses across their hyphal networks in ways eerily similar to how neurons fire in the brains of animals. These impulses help regulate nutrient flow, allowing fungi to adapt to their surroundings and even share resources between plants in a mutually beneficial exchange. This is the earliest example of a distributed, decentralized system capable of complex, intelligent behavior, long before the evolution of the first nervous systems in animals.

It’s easy to see the parallels between mycelial networks and the neural networks we associate with intelligence today. Both systems are decentralized, rely on electrical signaling, and adapt based on feedback from the environment. Fungal networks evolved a sort of “primitive intelligence,” capable of making decisions about resource allocation and environmental response. Although they lack brains or consciousness, these fungi have evolved a way to make their networked systems highly efficient—a trait that would later emerge as a foundational characteristic of neural networks in animals.

Imagine a world billions of years ago, where Earth’s surface was dominated by sprawling fungal networks, silently shaping ecosystems. In this ancient landscape, fungi may have been laying the groundwork for something far more complex to emerge—something that would eventually lead to the rise of nervous systems and intelligence in animals.

 

1.2 Nematodes and the Soil Ecosystem

Here, we’ll explore how early simple animals like nematodes interacted with these hidden networks. This will set the stage for understanding the role of mutualism between fungi and primitive animals.

While fungi silently built their underground networks, another player began to emerge on the stage of life—simple animals like nematodes. Nematodes, often referred to as roundworms, are among the most ancient and abundant forms of life on Earth. Fossil records suggest that they have been around for over 500 million years, thriving in environments from the ocean floor to deep underground soil ecosystems. Despite their simplicity, nematodes are incredibly successful, and their symbiotic relationship with fungi may be one reason for that success.

In the vast underground ecosystems where mycelial networks dominated, early nematodes found themselves in a nutrient-rich world. These primitive creatures, tiny tube-like organisms, moved through the soil, feeding on bacteria, organic matter, and potentially fungi. Nematodes were not just passive consumers, though. As they burrowed through the soil and ingested nutrients, they helped break down organic material, making nutrients more accessible to the fungal networks.

But nematodes also relied on the mycelial networks for survival. Fungi broke down tough plant material that nematodes could not digest on their own, and in return, nematodes played a crucial role in helping fungi disperse their spores across the soil. This early form of mutualism—where both species benefited from their relationship—may have been one of the driving forces behind the early evolution of these soil ecosystems.

Moreover, nematodes were among the first animals to develop a primitive nervous system capable of responding to their environment. Their simple neural circuits allowed them to sense chemical cues in the soil, enabling them to detect food sources or avoid threats. Over time, the evolution of chemical signaling between nematodes and fungi may have played a key role in shaping these early neural pathways. The need to navigate the complex, resource-rich environments created by fungi likely exerted evolutionary pressure on nematodes to develop more refined sensory systems.

In this ancient ecosystem, mutualism between fungi and nematodes helped to create a feedback loop of biological innovation. As nematodes evolved more complex neural systems, they became better equipped to exploit the resources made available by fungi. In turn, fungi may have evolved in response, creating more intricate networks to distribute nutrients and protect themselves from harm. This mutualistic relationship is one of the earliest examples of how cooperation between different life forms can drive evolutionary innovation, setting the stage for the development of more complex nervous systems in animals.

Nematodes also offer us a glimpse into how early neural networks may have evolved in response to environmental pressures. Although their nervous systems were simple compared to those of modern animals, they represented a significant leap forward in the evolution of biological complexity. Their ability to sense, respond to, and interact with the fungal networks around them laid the groundwork for future innovations in neural architecture.

1.3 Hyphae as a Blueprint for Neural Networks

In this section, we’ll explore how the structure and function of fungal mycelium served as an early “blueprint” for more advanced communication systems in animals, potentially influencing the evolution of neural networks.

Fungi have existed for over 1.5 billion years, long before the emergence of complex animals, and during that time, they developed one of the most intricate and efficient communication networks in the natural world: mycelium. These vast underground networks of hyphae (the thread-like structures that make up the mycelium) not only absorb nutrients but also transfer information through electrical impulses, a process that bears a striking resemblance to the way neurons transmit signals in animal nervous systems.

Hyphae are the microscopic filaments that extend through soil, decaying plant matter, and other organic material, forming the backbone of fungal networks. Mycelium can span vast distances underground, creating complex webs that link entire ecosystems. These webs are capable of transporting water, nutrients, and even chemical signals between plants, fungi, and other organisms, essentially creating a form of communication that links different parts of the environment. In many ways, mycelium networks act as the underground internet of the natural world, facilitating interactions that are vital to the health of ecosystems.

But mycelium does more than just facilitate nutrient exchange. Modern research has revealed that mycelial networks are capable of transmitting electrical signals across long distances, much like neurons. These signals can influence how fungi grow, how they interact with their surroundings, and how they communicate with other organisms. In fact, some studies suggest that fungal networks exhibit behaviors akin to problem-solving, memory, and adaptation—traits typically associated with animal intelligence.

Given these capabilities, it’s not hard to imagine that the intricate signaling systems of fungal networks may have served as an early model for the development of neural circuits in animals. Early life forms, such as nematodes and flatworms, lived in close proximity to these fungal networks, and it’s possible that they “borrowed” or mirrored some of these mechanisms when developing their own systems of communication. As we delve into the origins of neurons, the parallels between fungal mycelium and early nervous systems become increasingly hard to ignore.

The striking resemblance between mycelial signaling and neural transmission suggests that fungi may have had an indirect but profound influence on the evolution of nervous systems. Both systems rely on the rapid transmission of information across networks, whether through electrical impulses in neurons or chemical signals in hyphae. Both systems exhibit a remarkable ability to adapt and change in response to environmental conditions, allowing organisms to better navigate and survive in their environments.

Just as mycelium networks allowed fungi to process information from their surroundings and make adaptive decisions, early nervous systems likely evolved to serve a similar purpose in animals. Primitive animals like nematodes and flatworms needed to sense changes in their environment, detect food, and avoid predators—all tasks that required a form of information processing. The evolutionary leap from simple chemical signaling to more complex electrical signaling may have been influenced by the well-established systems of fungi that had been thriving for hundreds of millions of years before animals even appeared.

This idea—that mycelium acted as a blueprint for neural networks—invites us to rethink the traditional narrative of animal evolution. It suggests that the evolutionary innovations we associate with animals, such as the nervous system, may have been shaped, in part, by the life forms that dominated the planet long before animals existed. Fungi, with their vast experience in creating networks of communication and nutrient exchange, may have provided the template for more complex systems to evolve in early animals.

The possibility that early animals borrowed from the fungal playbook is more than a mere speculation; it is supported by the shared biochemical pathways between fungi and animals. Both rely on similar signaling molecules and pathways to transmit information across cells. This biochemical commonality hints at an evolutionary link that may go back to the dawn of life on Earth. In the soil, where fungi and simple animals coexisted, mutualistic relationships between the two life forms may have accelerated the evolution of neural complexity.

As we explore the origins of neural networks, we must consider that the web of life, as it evolved underground through mycelial networks, laid the foundation for more sophisticated communication systems. Fungal networks, with their ability to process and transmit information, could have been the hidden architects of the neural complexity that would later define the animal kingdom.

The next section will delve into the evolutionary paths that led from fungal-like communication systems to the complex neural networks that we see in modern animals.

 

1.4 Divergent Evolution: From Hyphae to Neurons

Evolution often follows divergent paths, with organisms adapting to their environments in unique ways based on available resources, competition, and ecological pressures. Fungi and animals, though vastly different in form and function today, may have shared a common ancestor or at least shared biochemical mechanisms that allowed them to communicate with their environments. As evolution unfolded, these two groups of organisms took separate trajectories: one remaining rooted in the soil, processing nutrients and exchanging information through mycelial networks, and the other evolving mobility, centralized nervous systems, and complex brains.

The question of how and why these divergent paths occurred is a fascinating one. In the case of fungi, evolution selected for a sprawling, decentralized communication network that could spread over vast distances underground, sensing and responding to changes in the environment. In contrast, early animals developed more centralized systems of communication, driven by the need to move, hunt, and respond quickly to stimuli in their surroundings. Both of these evolutionary paths were driven by the same fundamental need: to process information and respond adaptively to the environment.

Fungi developed their mycelial networks to maximize efficiency in nutrient absorption and communication within their local ecosystems. These networks, composed of hyphae, are remarkably efficient at distributing resources and signals across large areas. The decentralized nature of these networks allows fungi to remain flexible and adaptable, capable of responding to multiple environmental inputs simultaneously. In this way, fungi exhibit a kind of “distributed intelligence,” where decision-making is spread across the entire network rather than being concentrated in a single location, much like the decentralized nature of the internet today.

Meanwhile, animals, particularly early flatworms, faced different evolutionary pressures. Mobility and the ability to react quickly to changes in the environment were crucial for survival. To achieve this, animals needed a more centralized communication system that could rapidly process sensory information and direct physical responses. This necessity led to the evolution of primitive nervous systems, with neurons clustering in centralized regions such as the brain, allowing for faster processing and more coordinated movement.

Divergent evolution thus gave rise to two very different solutions to the same problem: how to gather, process, and respond to information. For fungi, the solution was a decentralized network capable of processing multiple inputs at once, spreading across an ecosystem and adapting to changing conditions. For animals, the solution was a more centralized system, where specialized neurons took on the role of processing sensory information and sending signals to muscles to initiate movement.

Yet, despite these divergent evolutionary paths, the parallels between mycelial networks and neural systems are striking. Both systems rely on the transmission of electrical impulses to communicate across networks. Both are capable of adapting to environmental changes, learning from past experiences, and responding with remarkable efficiency. These similarities suggest that the basic principles of network communication—whether through hyphae or neurons—are deeply rooted in the evolution of life on Earth.

One intriguing possibility is that early neural systems evolved by co-opting some of the same biochemical pathways that fungi had already perfected over hundreds of millions of years. As we saw in the previous section, fungal networks were capable of transmitting electrical signals and even storing information. It’s possible that early animals, living in close proximity to these fungal networks, borrowed or mirrored some of these mechanisms as they evolved their own systems of communication.

The idea of divergent evolution also opens the door to thinking about how different life forms solve similar problems in unique ways. While fungi remained stationary, using their extensive networks to gather resources and communicate across ecosystems, animals moved into new environments, using neural networks to navigate, hunt, and form social bonds. Both strategies were wildly successful, allowing fungi and animals to become two of the most widespread and diverse groups of organisms on the planet.

As we explore the rise of neural networks in animals, it’s important to remember that this evolutionary path did not happen in isolation. The early Earth was teeming with life, much of it microbial or fungal, and these life forms interacted with one another in ways that likely influenced their evolution. The communication systems we see in animals today may have evolved alongside, or even because of, the networks that fungi had already established.

Ultimately, the divergent paths taken by fungi and animals highlight the incredible diversity of solutions that evolution can produce. While neural networks in animals may seem far removed from the mycelial networks of fungi, both are built on the same fundamental principles of communication and adaptation. These principles, shaped by billions of years of evolution, continue to drive the development of complex systems—whether in nature or in the technological networks we build today.

In the next section we’ll explore the deep biochemical links between fungi, early animals, and the evolutionary leap that led to neural complexity.

 

1.5 The Ancient Biochemical Connections

Beneath the visible differences between fungi and animals lies an ancient biochemical connection that may have helped pave the way for the evolution of neural networks. These connections offer an intriguing insight into how life’s building blocks were repurposed over millions of years to create new biological systems.

At the heart of this evolutionary leap are the shared molecular pathways that both fungi and animals utilize to communicate and adapt to their environments. One of the most critical of these pathways is the use of electrical signaling. Long before animals developed neurons, fungi were already using electrical impulses to transmit information across their mycelial networks. This discovery has profound implications for understanding how the ability to transmit signals might have evolved in early animals.

Recent research shows that fungi use electrical signals to regulate the flow of nutrients across their networks, much like neurons use electrical impulses to relay information between different parts of the nervous system. The similarities between these two systems are striking: both fungi and animals rely on ion channels to propagate electrical signals, and both systems exhibit patterns of oscillatory signaling that allow them to respond dynamically to environmental changes. Could it be that the ability to transmit electrical impulses, a hallmark of the nervous system, had its evolutionary origins in the humble mycelial networks of fungi?

This biochemical connection between fungi and animals doesn’t stop at electrical signaling. Both groups of organisms also share several important signaling molecules that play a role in regulating cellular processes. For example, serotonin, a neurotransmitter in animals that plays a crucial role in mood regulation, is also found in fungi, where it helps regulate spore germination and mycelial growth. The presence of such shared molecules suggests that early neural networks may have evolved by repurposing biochemical tools that fungi had already been using for millions of years.

The shared use of signaling molecules and electrical impulses hints at a deep evolutionary connection between fungi and the nervous systems of animals. But how did these biochemical tools get transferred from one organism to another? One possibility lies in the process of horizontal gene transfer, where genetic material is exchanged between unrelated species. This process, which is facilitated by viruses, has been observed in a variety of organisms and may have played a crucial role in the early evolution of complex biological systems.

Retroviruses, in particular, are known to integrate themselves into the genomes of their hosts, sometimes transferring useful genetic material in the process. In the case of early animals, it’s possible that retroviruses facilitated the transfer of genes related to signal transmission from fungi to primitive organisms like flatworms. Over time, these genes could have been co-opted to help build the first neural circuits, allowing early animals to sense and respond to their environments more effectively.

Another key player in this biochemical exchange is the microbiome—the diverse community of microbes that live in and around all living organisms. In modern animals, the microbiome plays a crucial role in regulating many aspects of health, including digestion, immune function, and even mood. It’s now understood that the gut microbiome communicates directly with the nervous system, influencing behavior and cognitive function. This “gut-brain axis” is an area of intense scientific interest, and it may provide clues about how early neural networks evolved in the context of mutualistic relationships with microorganisms.

The gut microbiome itself is a product of millions of years of co-evolution between animals and microbes. Early in vertebrate evolution, the immune system developed new ways to interact with beneficial bacteria, helping to regulate this complex community while maintaining protection against pathogens. One of the most remarkable innovations in this process was the evolution of the protein AID (Activation-Induced Cytidine Deaminase), which enables the immune system to adapt to new threats through targeted DNA mutations. AID also allows the immune system to support a diverse microbiome, which in turn contributes to overall health and even brain function.

The evolutionary leap enabled by AID illustrates a broader theme in evolution: the ability to repurpose existing biochemical tools for new functions. In the same way that AID helped regulate the gut microbiome, early neural systems may have evolved by co-opting biochemical mechanisms from fungi and other microorganisms. This mutualistic relationship between animals and their microbial partners provided the biochemical foundation for more complex systems to evolve, including the brain.

The interplay between these ancient biochemical connections and the rise of neural networks is a fascinating example of how evolution works in unexpected ways. By building on existing systems and adapting them for new purposes, life on Earth has continuously reinvented itself, creating ever more complex forms of communication and organization.

Today, these ancient biochemical connections remain at the core of how living organisms function. The nervous systems of animals, including humans, still rely on many of the same signaling molecules and pathways that existed in early fungi. This continuity across billions of years of evolution highlights the deep interconnectedness of life on Earth, reminding us that even the most advanced biological systems are rooted in the simple, ancient processes that first evolved in the primordial seas.

As we move forward into the age of artificial intelligence, it’s worth reflecting on these ancient biochemical connections. Just as early life forms borrowed and adapted from one another to evolve new capabilities, we are now borrowing from nature to build new technologies. The parallels between the evolution of neural networks in animals and the development of artificial neural networks in machines are becoming increasingly clear. And just as fungi played a role in shaping the evolution of biological neural networks, they may also inspire the next generation of technological innovation.

As we conclude our exploration of these foundational networks, it becomes clear that the potential fungal ancestry of animal neurons represents a groundbreaking hypothesis that challenges conventional evolutionary narratives and invites us to rethink the origins of intelligence itself.