Fungi are the most successful life form in Earth's history, having survived all five mass extinction events (Ordovician, Devonian, Permian, Triassic, and Cretaceous) without experiencing a mass extinction of their own. Unlike plants that depend on sunlight for photosynthesis, fungi are heterotrophs that digest organic matter externally and absorb nutrients through their hyphae, allowing them to thrive when photosynthesis-based ecosystems collapse. Fungi colonized land before any plants or animals, built the first soils, and established the mycorrhizal networks that support over 90% of land plant species. Despite an estimated 2.2-6 million fungal species on Earth, only about 150,000 have been formally described, representing just 2-7% of total diversity. This kingdom, which has been on Earth for close to a billion years, remains largely unknown to science and continues to be studied as one of the most complex and underexplored areas of biology.
The Organism That Outlived EverythingAdded:
Consider what it takes to outlive an extinction. Not one extinction, not two, five mass extinctions spread across 500 million years of Earth's history. Each one rewriting the catalog of life so completely that the world emerging from the other side bore almost no resemblance to the world that preceded it.
The Ordovician, the Devonian, the Permian, which killed more than 90% of all species on Earth, the Triassic, the Cretaceous, which ended the age of non-avian dinosaurs and reshaped the trajectory of vertebrate life on this planet.
Five separate events in which the dominant organisms of their era were erased, and the ecosystems built around them collapsed.
Through every one of them, one kingdom survived without a mass extinction of its own. Not the insects, though they came close. Not the bacteria, though they are the obvious answer. The kingdom that passed through each of these events and emerged each time as the first major biological presence rebuilding the dead world belongs to a group of organisms most people cannot name beyond a handful of species, the kingdom fungi. The organisms we put on pizza, the organisms we treat as pests in our homes, the organisms whose living body we typically never see, only the temporary reproductive structures they push above ground when conditions are right. The most successful life form in Earth's history grows in the dark, underground, in the tissues of other living things, and in the material left behind by everything that dies.
In the sediment record immediately following the Permian-Triassic extinction, the most severe dying event in the geologic record at approximately 252 million years ago, there is an extraordinary spike [music] in fungal spores, an abundance of fungal material at the exact boundary where more than 90% of marine species and 70% of land vertebrates disappear.
The forests that had blanketed the supercontinent of Pangea were gone. The animals that lived in them were gone.
What the fossil record shows flourishing in their place is a kingdom of organisms [music] built to metabolize death.
Scientists studying that sediment layer have described the global landscape of that period as resembling a massive compost heap.
The fungi had inherited the Earth. They would do it again.
After the Cretaceous-Triassic extinction 66 million years ago, molecular phylogenetic analyses of more than 5,000 Agaricomycetes species show no detectable mass [music] extinction signal in fungal evolution at that boundary.
The event that ended the non-avian dinosaurs did not register in the fungal lineage as a population collapse. Other kingdoms lost dominant lineages, [music] fungi continued. Most living things depend on sunlight directly or indirectly.
Photosynthesis [music] drives the foundational energy budget of nearly every ecosystem on land.
In a post-extinction world where debris clouds block solar radiation for months or years and the photosynthetic base of the food web collapses, organisms built around sunlight die.
Organisms built around death do not.
Every mass extinction is, from the fungal perspective, an expansion event.
What we are going to examine in this film is not the story most people have been told about fungi.
It is not primarily about mushrooms or bread or the penicillin that Alexander Fleming observed growing on a Petri dish in 1928.
Those are chapters.
The full story is larger and stranger and older than almost anything else in natural history.
It is the story of a kingdom that colonized land before any plant or animal made the crossing, that built some of the largest organisms on Earth before trees existed, that established the underground infrastructure on which terrestrial life depends, >> [music] >> and that today lives inside the bodies of nearly every plant and animal species on the planet, including us.
Fungi are not a background element [music] of the natural world.
In a meaningful biological sense, they are the foundation of it.
And our understanding of what they are, how they operate, and what they are doing inside [music] the ecosystems we think we understand remains remarkably incomplete.
The current estimate for the total number of fungal species on Earth sits between 2.2 and 6 million. Approximately 150,000 have been formally described. The rest remain undiscovered.
The kingdom that has been here for close to a billion years is still largely unknown to science.
This film is an attempt to reckon with that. To follow the fungi from their origins in ancient oceans through the moment they stepped onto bare rock and helped build the first soils. Through every extinction they survived, into the networks running beneath every forest, into the electrical signals moving through their hyphae, into the gut of every animal alive today, and into the compounds derived from fungi that reshaped human medicine and are currently being studied at some of the most serious neuroscience research institutions in the world.
The question running beneath all of it is not simply a biological one. It is a question about what success means for a living thing, and why the organism that answers it most definitively is one we have spent most of history ignoring.
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For most of recorded scientific history, fungi were classified as plants. Not informally, not loosely, but formally and officially as a recognized subkingdom of the the kingdom.
They were grouped alongside mosses and algae in a category called cryptogamia, a Latin construction meaning roughly hidden reproduction, used to collect organisms that did not fit neatly into the plant categories scientists understood best.
Ferns were in there, lichens were in there, and fungi, across centuries of botanical literature, were treated as a variant of plant life that simply happened to grow differently.
This classification persisted well into the 20th century.
It was not meaningfully challenged until the latter half of it.
For context, the space program began before mycology had formally separated fungi into their own kingdom of life.
The reclassification, when it came, was not subtle. Fungi are not plants. They are not a type of plant, a degenerate form of plant, or a plant that lost something along the way.
They are a separate kingdom of life, as distinct from plants as animals are, and in certain fundamental respects more closely related to animals than to the organisms they spent centuries being confused with.
The distinction begins with how they eat.
Plants produce their own food. Through photosynthesis, they capture energy from sunlight, combine it with carbon dioxide from the air and water drawn up through their roots, and synthesize [music] the organic compounds that fuel their growth.
The plant is, in metabolic terms, self-contained.
It converts environmental energy into biological material with no requirement for external organic matter as a fuel source.
Fungi cannot do this. They have no chlorophyll. They have no mechanism for capturing solar energy.
They are heterotrophs, meaning they depend on consuming organic matter produced by other organisms, and the mechanism [music] by which they do this is unlike anything plants or animals do.
A fungus does not ingest food the way an animal does.
It secretes digestive enzymes directly into the surrounding material, whether that is dead wood, soil, a living leaf, or an insect, and breaks that material down chemically outside its own body.
It then absorbs the dissolved nutrients through the walls of its hyphae, the thread-like filaments that make up the fungal body.
Digestion happens outside the organism.
Absorption happens through the surface of it.
The fungus, in a sense, eats by becoming part of what it consumes.
This is not a variation on plant metabolism. It is a fundamentally different strategy for extracting energy from the world, and it explains a great deal about why fungi survive where other organisms cannot.
They are not dependent on sunlight.
They're not dependent on soil nutrients in the way plants are. They require only organic matter and moisture, >> [music] >> and organic matter is available in vast quantities wherever life has been.
Including in the aftermath of mass extinctions, when organic matter accumulates faster than anything else can process it.
The genetic evidence complicates the picture further. Phylogenetic analyses, examining the actual evolutionary relationships encoded in DNA, place fungi closer to the animal kingdom than to plants.
Fungi and animals share a more recent common ancestor than either shares with plants.
The divergence between the lineage that produced fungi and the lineage that produced animals occurred after the split from plants. In evolutionary terms, a mushroom is your more distant cousin than it is a tree's.
This fact tends to produce a particular kind of discomfort when people first encounter it.
Our intuitions about biological similarity are built largely on what we can see, and what we can see of a mushroom looks nothing like an animal.
But visible morphology is not a reliable guide to evolutionary history.
The structural features we use to sort organisms intuitively, shape, size, whether something moves, whether it has roots, whether it is green, are frequently the products of convergent evolution or shared environmental pressures rather than genuine kinship.
Beneath those features, at the level of genetics and cellular machinery, fungi and animals share a range of molecular mechanisms that plants do not.
The practical consequences of this misidentification were significant. If fungi are plants, they belong to botany.
If they belong to botany, they are studied by botanists, funded through botanical research programs, and evaluated by the standards and priorities of plant biology.
Mycology, the dedicated scientific study of fungi, developed slowly and incompletely within that framework, and the underfunding has never fully resolved itself.
Current estimates suggest the total number of fungal species on Earth falls somewhere between 2.2 and 6 million.
Approximately 150,000 have been formally described and named.
On a percentage basis, that means somewhere between 2 and 7% of all fungal species on Earth have been identified by science.
Every other major kingdom of complex life has been cataloged with considerably greater completeness.
A 2023 guest-edited collection on fungal evolution and diversity published in Scientific Reports noted that the discovery and classification of fungi remain in high flux, and that modern molecular methods continue [music] to reveal diversity that conventional taxonomy had no way to anticipate.
What was true in 2023 is more true now.
The more precisely we look at fungal communities in soil, in water, and in the tissues of living organisms, the more species appear that match nothing in the existing catalog.
The term mycobiome, used to describe the fungal component of the microbial communities living in and on animal bodies, was first coined in 2009.
A search of the scientific literature for that term returns 10 results in 2013.
The field of gut mycology, examining what the fungi living inside the human body are actually doing, is, by any [music] measure, in its early stages.
We have been carrying these organisms inside us for our entire evolutionary history, and we've been studying them systematically for less than two decades.
None of this represents a failure of any individual scientist or institution.
It represents something more structural.
The organisms that shaped the terrestrial world, that made it possible for plants and animals to exist on land, that survived every catastrophic reset the planet produces, spent centuries being filed under the wrong category.
And the intellectual infrastructure built around that error has been slow to dismantle itself.
The living body of a fungus is almost entirely invisible in its primary form.
The mycelium, the branching network of hyphae that constitutes the actual organism, grows underground, inside wood, or embedded in the tissues of a host.
What emerges above the surface, the structure we typically call a mushroom, is a fruiting body, the temporary reproductive apparatus the fungus produces to disperse spores. It is, in terms, closer to a flower than to the plant itself.
The plant in this analogy is underground and largely unseen.
Biology, historically, has paid attention to what it can observe.
And the most consequential parts of the fungal kingdom have spent the entirety of their existence outside the field of view.
To understand what fungi are, it helps to understand how long they have been here.
Not in the vague sense in which we sometimes say that bacteria are ancient, or that life predates complex biology by billions of years, but in the specific sense of following what the fossil record and the molecular clock actually show, because the timeline, once laid out plainly, changes the [music] frame through which everything else in this story must be read.
The earliest fossils possessing [music] features characteristic of fungi date to the Paleoproterozoic Era, approximately 2.4 billion years ago.
That number is difficult to hold in the mind at ordinary scale.
For reference, the dinosaurs appeared roughly 230 million years ago and were gone by 66 million years ago.
A reign of approximately 165 million years.
The fungi were already hundreds of millions of years old before the first dinosaur existed and were already hundreds of millions of [music] years older than that when the Paleoproterozoic fossils that we now recognize as fungal were being deposited.
The fossil record for fungi at that range is sparse and contested as it is for most life from that period, but the molecular evidence supports origins in the range of 1 billion years ago, placing fungi firmly in the Proterozoic as aquatic organisms living in ancient seas long before the terrestrial [music] world was biologically colonized.
This is where the standard account of life on land tends to begin with the ocean.
Complex multicellular life develops in water.
Photosynthesis in the oceans produces the oxygen that slowly transforms the atmosphere.
Eventually, life crosses onto land and the terrestrial ecosystems we recognize begin to take shape.
The standard narrative then moves to plants, the first land colonizers, followed by the animals that followed them.
What the fossil record actually shows is that this sequence is missing its opening chapter.
Tortotubus protuberans is a filamentous fungus found in fossil deposits dating to the early Silurian period, >> [music] >> approximately 440 million years ago.
It is currently regarded as the oldest known fossil of a terrestrial organism.
Not the oldest plant fossil, not the oldest animal fossil.
The oldest fossil of any organism adapted to life on land of any kind belongs to a fungus.
Before mosses, before liverworts, before any vascular plant had developed the structures needed to stand upright in open air, before any animal had solved the physiological problems of breathing, desiccation, and locomotion outside of water, a fungus was already living on land.
The implications of this are not merely chronological. Bare rock and mineral substrate do not constitute a habitat in any meaningful ecological sense.
The terrestrial environment that the first plants would eventually colonize was not a prepared ground.
There was no soil in the modern sense, no established nutrient cycling, no decomposing organic layer.
Whatever happened in the gap between the first fungal colonization of land and the arrival of plants involved fungi working on rock, breaking it down chemically, contributing to the early formation of the substrate [music] that would later support plant life.
Fungi did not move into a world that was ready for them. They helped make a world that was ready for everything else.
What that early terrestrial world looked like is one of paleontology's more contested questions, and one of its stranger answers involves a group of structures called Prototaxites. [music] Prototaxites were large, spire-like organisms that stood across [music] the landscape during the Devonian period, from approximately 419 to 359 million years ago.
They were common across most regions of the world. Some reached heights of 8 to 10 m, making them by far the largest structures produced [music] by any living organism during that geological period.
For over a century after their discovery, scientists debated what they were. They are clearly not animals. They have no vascular structure consistent with plants.
Various proposals [music] were advanced over the decades: giant algae, rolled mats of liverworts, something without a clear modern analogue.
The current interpretation, supported by the work of Christine Strullu Darian and colleagues, published in New Phytologist in 2018, is that Prototaxites were most likely large saprotrophic fungi, or in some cases gigantic algal-fungal symbiosis, similar in principle to modern lichens, but on a vastly larger scale.
If this interpretation is correct, then for tens of millions of years during the Devonian period, the largest organisms on land were fungi, not trees, which had not yet evolved, not insects, >> [music] >> which were small and early. Fungi, standing up to 10 m tall, dominating a landscape that had no other organisms remotely approaching their scale.
The Devonian is sometimes called the age of fishes for the extraordinary diversification of fish species occurring in its oceans.
On land, it could just accurately be called the age of fungi.
The terrestrial world during that period was a place of low-lying plant life, early forests just beginning to develop, and enormous fungal structures rising above them.
The fungi were not part of the landscape.
For a significant portion of Earth's middle history, they were the landscape.
The evolutionary trajectory from those early terrestrial colonizers to the diversity of fungal forms living today runs through a long series of divergences and adaptations that are only partially reconstructed.
What the fossil record makes clear is that the fungal body plan, the hyphal network, the external digestion, the spore-based reproduction, has been a functional and stable solution to the problem of survival for an extraordinary length of time.
The basic architecture has changed relatively little across hundreds of millions of years of environmental upheaval.
The oldest mushroom-forming fungi in the fossil record, a species called Archaeomarasmius leggetti, are preserved in amber from the mid-Cretaceous period, [music] approximately 90 million years ago.
By that point, the flowering plants had already diversified substantially. The mycorrhizal partnerships between fungi and plant roots were well-established, and the basic ecological structure of terrestrial ecosystems was in something approaching its modern form.
The mushroom that appears in that amber is recognizable.
It belongs to a lineage that had already been operating for hundreds of millions of years before the Cretaceous, and that would outlast the extinction event of the end of it without noticeable disruption.
There is something genuinely disorienting about holding this timeline in mind.
When we talk about organisms that shaped the natural world, we tend to mean plants that produced oxygen, or animals that drove evolutionary pressure through predation, or microbes that transformed the chemistry of the oceans.
Fungi rarely appear in that accounting, but the terrestrial world that all of those organisms eventually inhabited was, in its earliest form, built by fungi.
They arrived first. They processed the bare rock. They established the first biological presence on land, and the largest things moving across that land for tens of millions of years were not what we picture when we imagine ancient life.
The question of what came before [music] plants and animals on land has a clear answer.
It has had a clear answer for long enough that it should feel settled. It does not feel settled, largely because the organism that the answer names has spent most of its history out of sight.
The story of how life colonized land is one of the most frequently told in biology, and it is almost always told with the same cast of characters.
Fish developing limbs at the water's edge, primitive plants spreading across rock and mud, building the first thin soils, animals following the plants onto the land because the plants came first and the energy was there.
The narrative is built around visible actors [music] doing visible things, and it carries the implicit assumption that colonization was something life accomplished by developing new capabilities, new structures, new solutions to the problem of surviving outside the ocean.
That account is accurate as far as [music] it goes. It does not go far enough.
The largest contributor to the transition of complex life onto land is not in the standard version of the story, because the largest contributor spent that entire transition underground, inside the tissues of the organisms we do talk about, doing work that made everything else possible.
To understand what the earliest land plants were actually dealing with, it helps to be precise about the environment they were entering.
The terrestrial surface of the early Paleozoic was not hospitable in any of the ways we associate with land today.
There was no soil in the modern sense.
Soil, as it currently [music] exists, is a product of billions of years of biological activity.
Decomposed organic matter, mineral particles broken down by chemical weathering and biological acid production, accumulated [music] fungal biomass, bacterial communities, the physical churning of organisms moving through it.
In the early Silurian and Ordovician, none of that existed.
What land offered was bare mineral substrate, periodic water from rain and meltwater, and atmospheric carbon dioxide.
That was essentially the entire resource base.
The plants entering this environment were not the vascular plants we tend to picture when we imagine ancient flora.
They were small, rootless, and [music] leafless, with absorbing structures called rhizoids rather than true roots.
These rhizoids could anchor a plant and draw in some moisture, but they were limited in what they could extract from bare rock and mineral substrate.
Phosphorus, essential for cellular growth and energy transfer, was locked in mineral form.
Without a mechanism to access it, even a plant that had solved the problem of desiccation and structural support [music] would struggle to grow at any significant scale.
The leading hypothesis, now by converging lines of fossil, genomic, and experimental evidence, is that fungi provided the mechanism that plants could not provide for themselves.
Mycorrhizal symbiosis, the partnership in which fungal hyphae colonize plant root systems and dramatically extend their reach into surrounding substrate, [music] appears to have preceded the development of true roots. The fungi were already in the soil, already threading through mineral material, and extracting nutrients through enzymatic digestion before plants had the architecture to do anything similar.
The plant-fungus partnership did not emerge after plants figured out [music] how to survive on land.
It appears to have been a precondition for that survival. [music] The evidence embedded in rock makes this argument difficult to dispute.
In the Rhynie chert, a deposit of early Devonian silicified rock in Aberdeenshire, Scotland, [music] dated to approximately 407 million years ago, some of the most detailed fossil preservation in the geological record captures early land plant tissues in three dimensions at cellular resolution.
Within those tissues, researchers have found the unmistakable structures of mycorrhizal fungi, hyphae threading between plant cells and arbuscules, the highly branched fungal structures that form inside plant cells and serve as the [music] interface for nutrient and carbon exchange between the two organisms.
The partnership was not incipient or primitive. It was already fully formed, already operating [music] at the cellular level with the same basic architecture it uses in plants today.
In 2025, a study published in New Phytologist by researchers from the Natural History Museum and the Sainsbury [music] Laboratory at Cambridge University, described a new species of arbuscular mycorrhizal fungus, Rugosospora maceres, Lavoisierae, preserved within one of those 407 million-year-old Rhynie chert plant fossils.
It was identified living inside the early land plant Aglaophyton major alongside a second, previously known fungal species.
Two distinct fungal partners living simultaneously within a single early plant 407 million years ago.
The researchers described the preservation as providing the most detailed three-dimensional evidence to date that early land plants engaged in complex symbiotic relationships with multiple fungal species simultaneously.
The plant was not carrying one fungal partner onto land. It was carrying a community.
The genomic evidence points in the same direction.
A 2021 study published in Science provided the first experimental evidence for one of the central claims of the mycorrhizal landing hypothesis.
That the symbiotic relationship between plants and mycorrhizal fungi is not a recent or derived adaptation, but an ancestral trait inherited from the common ancestor of all land plants.
The researchers working with liverworts, some of the closest living relatives of the first plants to colonize land, found that these ancient lineages respond to mycorrhizal fungi using the same genes and molecular machinery as modern flowering plants.
Genes involved in hormone production, infection responses, and lipid transfer shared across the entire span of land plant evolution activated by fungal contact in the same way in a liverwort as in an oak tree.
The implication is that the common ancestor of all land plants was already engaged in mycorrhizal symbiosis. The partnership is not something plants developed. It is something they inherited. Today, mycorrhizal fungi associate [music] with over 90% of land plant species.
The University of Guelph's research program on mycorrhizal evolution, summarized in 2022, frames this figure [music] in terms that clarify its significance.
If you fast forward from the Ordovician to the present day, plants dominate [music] the terrestrial habitat, and over 90% of plant species maintain these symbioses with mycorrhizal fungi.
The relationship has survived every extinction event, every climate shift, every continental reorganization of the past 500 million years.
It is not a niche adaptation. It is the foundational operating condition of terrestrial plant life.
The conventional framing of this [music] relationship describes fungi as benefiting plants. That is accurate. The fungi extend the plant's effective root zone by orders of magnitude, accessing water and mineral nutrients, particularly phosphorus and nitrogen, from volumes of soil the plant's own roots could never reach.
In exchange, the plant provides the fungus with carbohydrates derived from photosynthesis and lipids used in building fungal cell membranes.
The exchange is metabolically significant for both parties.
But the framing that describes fungi as helping plants obscures the more fundamental point. The earliest land plants had no roots. They had rhizoids.
The fungal hyphae were already present in the substrate before anything resembling a modern root evolved.
The partnership was not something a plant developed roots in order to engage in.
It was something that was already operating through rhizoid contact and tissue penetration before roots were a biological option.
The plants did not bring fungi with them as a useful [music] tool. They arrived already embedded in a relationship that the fossil record suggests was already ancient by the time the first terrestrial plant fossils were deposited.
The narrative of land colonization that biology has taught for most of the past century is built around the visible actors.
The plants that spread, the animals that followed, the environments that changed in response. The infrastructure that made those actors capable of surviving is underground, cellular, and almost entirely invisible. And without it, the terrestrial world as it exists today would not have become biologically possible.
Fungi did not colonize land alongside plants.
In the most accurate version of the sequence, they were already there.
Once life had established itself on land, once the forests had developed and the soil had deepened, and the animal lineages had diversified into the forms that would dominate successive eras of Earth's history, the planet began producing another kind of event entirely.
Not the slow grind of evolutionary competition, in which lineages rise and fall across millions of years of incremental change, but sudden, catastrophic, global collapses of the biological order.
Events in which the conditions sustaining complex life were disrupted so severely and so quickly that the ecosystems built across hundreds of millions of years of evolution were effectively erased.
There were five of them.
And the kingdom that processed the wreckage after each one was the same kingdom that had been there before any of the ecosystems those extinctions destroyed had existed.
The Permian-Triassic extinction, approximately 252 million years ago, is the benchmark against which every other mass dying in Earth's history is measured.
Nothing else approaches its scale.
Current estimates place species loss in the marine environment at above 90%. On land, the gymnosperm and seed fern forests that had spread across the supercontinent of Pangaea [music] were devastated. The cause remains debated, with massive volcanic activity in what is now Siberia considered the primary driver, releasing carbon dioxide and sulfur [music] dioxide in quantities sufficient to acidify the oceans and raise global temperatures [music] to the edge of what most complex organisms could tolerate.
The world that existed before the Permian-Triassic boundary and the world that existed after it were, in ecological terms, barely recognizable as the same planet.
In the sediment record at that boundary, researchers have found what is now referred to as the fungal spike, an extraordinary concentration of fungal spores and mycelial material at the exact geological horizon where the Permian ends and the Triassic begins, documented in studies including peer-reviewed analyses published in the journal Geoscience Frontiers in 2017.
The interpretation is not difficult to construct. When the forests of Pangaea died, they did not vanish. They fell.
They accumulated. Hundreds of millions of years of forest biomass collapsed into an unprocessed mass of dead organic material distributed across the land surface of the planet.
Something had to metabolize it.
The organisms positioned to do so were not the surviving plants, which were reduced to scattered refugia.
They were the fungi, which do not require living ecosystems to operate.
They require dead matter.
In that moment, dead matter was the predominant biological product of the terrestrial world.
Scientists studying that sediment boundary have described the global landscape of the early Triassic as resembling, in function if not in scale, a massive compost heap.
The fungal bloom that followed the Permian extinction was not a survival story in the ordinary sense. It was an ecological takeover of a dead world by the one kingdom specifically adapted to process death at scale.
The Cretaceous-Tertiary extinction, 66 million years ago, is the event that most people know.
The asteroid impact that ended the non-avian dinosaurs triggered global firestorms and injected enough particulate matter into the atmosphere to suppress sunlight for years.
The immediate ecological consequence on land was the collapse of photosynthesis-dependent food webs.
Plants died. The herbivores that depended on them died. The predators that depended on those herbivores died.
The extinction pulse moved through the trophic levels of terrestrial ecosystems with a speed and completeness that left most large animal lineages without a viable future.
The fungal record at the Cretaceous-Tertiary boundary shows again an immediate increase in fungal evidence. But the more significant finding is what the molecular phylogenetic data reveals about the fungal lineage across that boundary.
Phylogenetic comparative analyses of more than 5,000 Agaricomycetes species, the group that includes most of the mushroom-producing fungi, show no detectable signal of a mass extinction event in fungal evolution around the Cretaceous-Tertiary boundary.
The statistical signature that indicates population collapse and lineage loss, clearly visible in the evolutionary record of other kingdoms at this boundary, is absent in the fungi.
The event that ended the dinosaurs did not produce a measurable collapse in fungal biodiversity.
This is not a subtle distinction. It is the difference between an extinction event that restructured a kingdom's evolutionary trajectory and an extinction event that passed through that kingdom without leaving a mark.
For the fungi, the end of the Cretaceous was, in evolutionary terms, unremarkable.
The metabolic explanation for this pattern is the same one that applies to the Permian event and to the Devonian, the Ordovician, and the Triassic extinctions that bracket the others.
Fungi do not depend on sunlight. The currency they operate in is organic matter, and organic matter does not disappear during a mass extinction. It accumulates.
When photosynthesis collapses and the living organisms that depend on solar energy begin to die in large numbers, the fungi are not deprived of resources.
They are supplied with them. Every mass extinction represents, from the perspective of fungal ecology, not a crisis, but an abundance.
The conditions that kill kingdoms built on light are precisely the conditions that favor kingdoms built on decomposition.
This structural advantage has had consequences that extend beyond mere survival.
The Permian-Triassic extinction did not only provide fungi with an abundance of dead material to process.
It cleared ecological space.
The lineages that had occupied terrestrial niches were gone, and the survivors, including the fungi, were positioned to diversify into a reorganized world.
A 2024 preprint in bioRxiv, analyzing genome-wide phylogenetic patterns across fungal lineages, found that carnivorous nematode-trapping fungi emerged in the period following the Permian-Triassic extinction and subsequently radiated into multiple distinct lineages, each developing different mechanical structures for capturing [music] free-living nematodes.
These are fungi that evolved the ability to hunt animals in the ecological sense by constructing hyphal snares, adhesive networks, and constricting rings that immobilize and consume small worms moving through the soil.
They did not exist before the Permian extinction. They emerged into the ecological vacuum it created. Carnivory is not a trait we typically associate with fungi, and the nematode-trapping lineages represent a small fraction of fungal diversity.
But their origin in the aftermath of a mass extinction is a precise illustration of a pattern repeated across the fossil record.
The extinctions that devastated other kingdoms created the conditions under which entirely new fungal strategies became viable.
The disasters were, for the fungi, evolutionary opportunities.
There is a lesson embedded in this record that operates at [music] a level broader than mycology.
The organisms that built the most visible dominance in any given era, the organisms [music] that drove evolutionary pressure, controlled the most resources, and defined what the living world looked like at any given moment, are not the organisms [music] that survived the resets. The survivors were the processors, the decomposers, the organisms positioned at the interface of death and renewal, whose function became most essential precisely when the organisms above them in any food web collapsed.
Resilience in evolutionary history has not belonged to the dominant. It has belonged to the indispensable. And no kingdom in the history of life has made itself more consistently indispensable than the one that feeds on what everything else leaves behind.
The five extinctions that mark the most catastrophic episodes in the history of complex life are, in the fungal record, barely visible as interruptions.
They are, in some cases, visible only as expansions. To understand why fungi survived what they survived, it helps to understand what a fungus actually is, physically, as a body.
Because the way we typically picture fungi, the mushroom cap, the stem, the gills underneath, the object we find in the refrigerator or spot growing from the base of a tree, is not the fungus.
It is the part of the fungus that became temporarily visible for the purpose of reproduction.
The structure we call a mushroom is a fruiting body. Its function in the life of a fungus is analogous to the function of a fruit on a tree, a temporary structure produced to disperse reproductive material, in this case spores, into the surrounding environment.
>> [music] >> The tree is not the apple. The fungus is not the mushroom. The mushroom can be removed entirely and the fungus will continue.
In most species, fruiting bodies represent a small fraction of the organism's total biomass, produced only when environmental conditions, moisture, temperature, nutrient availability, favor spore dispersal and retracted or abandoned when those conditions change.
The actual body of a fungus is the mycelium, a branching, three-dimensional network of thread-like filaments called hyphae, extending through whatever substrate the fungus inhabits. [music] In soil-dwelling species, the mycelium spreads outward through the soil in all directions simultaneously. Each hypha growing at its tip, branching when it encounters an obstacle or a nutrient gradient worth exploring, and fusing with other hyphae from the same organism to create a continuously self-reorganizing network.
In wood-decay species, the hyphae penetrate the cellular structure of dead or living wood, secreting the enzymes that break down cellulose and lignin and absorbing the products.
In parasitic species, the hyphae grow directly through or between the cells of a host organism, extracting nutrients from living tissue, while the host remains, for a time, functional.
The physical scale of this structure ranges from the microscopic to the genuinely difficult to comprehend.
Individual hyphae are between 1 and 30 micrometers in diameter, thinner than a human hair by a factor of two to 20, depending on the species.
At that scale, a single hypha is invisible to the naked eye.
But, hyphae do not grow alone.
They grow as networks, and those networks can expand across distances that place fungi among the largest organisms ever documented on Earth.
In Malheur National Forest in Eastern Oregon, a single individual of the species Armillaria ostoyae, the honey fungus, has been mapped across an area of approximately 2,385 acres, or 965 hectares.
It occupies nearly 10 square kilometers of forest soil, connected through a continuous mycelial network that has been genetically confirmed as a single organism.
Its estimated age is approximately 8,000 years, placing its origin at roughly the same period as the earliest agricultural civilizations in the Fertile Crescent.
It was already old when writing was invented. It has been growing continuously through drought and fire seasons and the succession of entire forest communities above it for longer than most human institutions have existed.
This individual is not the only candidate for the title of largest organism on Earth.
Estimates for several other fungal networks and for the interconnected root systems of certain clonal plant colonies challenge the ranking depending on how individual organisms are defined.
But, Armillaria ostoyae in Oregon remains one of the most thoroughly documented and genetically verified examples, and its scale illustrates something about the fungal body plan that the statistics alone do not quite capture.
This is not a large organism in the way that a blue whale or a giant sequoia is large, with mass concentrated in a structure you can stand next to and measure.
It is large the way a city's water infrastructure is large, distributed across an enormous area, invisible at the surface, continuously functional through 10,000 simultaneous contact points with the environment around it.
That distributed architecture is not incidental to what fungi are.
It is the defining feature of the fungal body plan, and it has architectural implications that run deeper than scale.
In most animal tissues, cells are discrete, bounded structures separated by membranes, each containing its own nucleus, and managing its own metabolic processes [music] within a body that is controlled and coordinated by a central nervous system. The animal body has a center. It has a headquarters.
Damage to that headquarters is catastrophic in a way that damage to the periphery is not.
Fungi in many species do not operate [music] this way. In a substantial portion of fungal lineages, hyphal networks are coenocytic, meaning the internal divisions between adjacent hyphal compartments called septa are perforated rather than sealed. Nuclei, organelles, and cytoplasm can migrate through these pores across the entire length of the mycelial network.
The fungus does not have discrete cells in the way an animal does. It has a continuous shared internal environment distributed across a branching network of tubes with genetic material flowing through that network in response to local conditions and requirements.
There is no single point of control.
There is no structure whose destruction would constitute the death of the organism in the way that the destruction of a brain constitutes the death of an animal.
If one section of the mycelial network is destroyed by a competitor organism, by physical disturbance, or by the death of a local nutrient source, the rest of the network continues. The organism reorganizes around the loss. It reroutes. It grows in other directions.
The resilience is not behavioral, it is structural. It is built into the architecture of the body itself.
This body plan has remained largely stable across hundreds of millions of years of Earth history.
The basic elements of the fungal form, the hyphal network, the external digestion, the spore-based reproduction, the absence of centralized control appear in fossil material from the Silurian and Devonian in a form recognizable as continuous with what exists today.
Every major extinction event produced fundamental reorganizations of the dominant animal and plant body plans.
Lineages that had existed for hundreds of millions of years were eliminated and the survivors that repopulated the post-extinction world often bore little structural resemblance to their predecessors.
The fungal body plan did not require that kind of reorganization. It persisted because it worked and it worked because it was not organized around the assumptions that make other body plans vulnerable.
Complexity in the biological systems we tend to study most closely tends to flow towards centralization.
Brains, hearts, root systems that converge into a central structure.
The assumption embedded in the way we understand complex organisms is that coordination requires a center. That a sufficiently large and capable organism will necessarily develop something like a headquarters.
Fungi have spent close to a billion years demonstrating that this assumption is not a biological necessity. It is a design choice and it is not the design choice that produced the most durable form of multicellular life on Earth.
The most successful body plan in the history of terrestrial life has no center.
It is all periphery and the periphery is everywhere.
The mycelial network described in the previous section does not simply extend through soil and substrate in isolation.
In forest ecosystems it connects.
The hyphae of mycorrhizal fungi colonize the root systems of multiple trees simultaneously threading between them through the soil creating a continuous underground structure that links individual plants across an area that can span the entirety of a mature forest.
What moves through that structure is not only fungal biomass. It is carbon. It is phosphorus. It is nitrogen. It is water.
The resources that determine whether a given plant lives or dies in a given season can travel through the fungal network from one plant to another. And the direction and quantity of that transfer is not fixed, but responds to conditions across the network as a whole.
This is the system that has come to be called the wood wide web, a name coined by the popular science press in the late 1990s, following a paper that shifted how ecologists understood the functional organization of forests.
In 1997, Suzanne Simard, then a doctoral researcher at the University of British Columbia, published findings in the journal Nature demonstrating that paper birch and Douglas fir trees in British Columbia were transferring carbon to one another through shared mycorrhizal networks.
The experimental design used radioactive and stable carbon isotopes to trace the movement of carbon from one species to another, and the results showed bidirectional transfer. Carbon moving from birch into fir under certain conditions, and from fir into birch under others.
The trees were not simply coexisting in the same soil. They were exchanging resources through a shared fungal infrastructure.
The finding was significant for several reasons, not all of them immediately obvious.
The dominant model of forest ecology at the time treated trees primarily as competitors, each individual maximizing its own access to [music] light, water, and soil nutrients at the expense of neighbors.
The mycorrhizal transfer data complicated that picture.
If trees were exchanging carbon through underground networks, then the forest [music] was not simply a collection of competing individuals organized by the rules of natural selection operating on each plant in isolation.
It was a system with connections, and those connections had functional consequences for the distribution of resources across the whole. Simard's subsequent research over the following decades extended these findings and introduced additional concepts, including the proposal that certain large well-connected trees, which she termed mother trees or hub trees, occupied more central positions in mycorrhizal networks and transferred disproportionate quantities of carbon to neighboring plants, particularly to seedlings of the species growing in shade.
The implication carried through her 2021 book and a body of peer-reviewed work is that forest regeneration may depend in part on resource subsidies flowing from established trees to juvenile plants through the mycorrhizal network, and that the removal of large hub trees during logging operations may therefore affect seedling survival rates in ways not captured by conventional forestry models.
This body of research has been influential, broadly cited, and genuinely important to the development of forest ecology.
It has also generated scientific debate, and that debate is worth describing accurately rather than eliding.
The core finding that plants exchange carbon and other resources through shared mycorrhizal networks is well documented and not seriously contested.
The mycorrhizal network is real.
The bidirectional transfer of carbon between plant species via shared fungal hyphae has been replicated across multiple experimental systems. That is established science.
What remains under active research and genuine scientific discussion is the interpretation of this transfer as intentional resource sharing, communication, or coordinated mutualism between individual trees.
The fungal network does not have intentions.
The question of whether the carbon transfers that occur through mycorrhizal networks constitute something meaningfully described as trees helping one another, or whether they are better understood [music] as consequences of the fungus managing its own carbon and nutrient flows across a network that happens to include multiple plant hosts, [music] is not settled.
The language of the wood wide web, with its implication of deliberate connectivity and information sharing modeled on human communication networks has been criticized by some ecologists as importing assumptions about intentionality that the data does not support. A 2023 review in Nature Ecology and Evolution examined the evidentiary basis for the strongest claims made about mycorrhizal networks in popular science writing and found that some of those claims, particularly the idea that trees deliberately share resources with relatives or coordinate responses to stress through the network were not well supported by the existing experimental literature.
The review did not challenge the existence of the networks or the documented resource transfers.
It challenged the interpretive leap from documented transfer [music] to deliberate coordination.
This is a distinction worth holding on to because the actual documented phenomenon is remarkable enough without the interpretive additions.
Mycorrhizal networks connect the root systems [music] of most trees in a mature forest through a continuous fungal structure that facilitates the movement [music] of carbon, phosphorus, nitrogen, and water between plants according to gradients of concentration, demand, and fungal metabolic [music] activity.
Seedlings growing in shade with limited access to sunlight and therefore limited photosynthetic output have been shown in experimental conditions to receive net carbon inputs from the network which may support their survival during the period before they grow tall enough to access direct light. [music] Whether this constitutes the established trees actively subsidizing their offspring or a passive consequence of carbon gradient dynamics within the fungal network is a question that current methods cannot definitively resolve.
What can be said without interpretive controversy is this, [music] the mycorrhizal network beneath a mature forest represents a functional infrastructure that predates the forest growing above it.
The individual trees that constitute the visible forest will live and die across time scales of decades [music] to centuries.
The mycorrhizal network they are connected to operates across time scales that exceed the lifespan of any individual tree in it.
The network is not a product of the forest. [music] The forest is, in a real sense, a product of the network. The trees grow where the network supports [music] their growth. Their survival through drought, through nutrient poor soil conditions, through the shaded early years of a seedling's life, is mediated in part by access to a fungal infrastructure that was present before they germinated and will persist after [music] they die.
The fungi running beneath a forest are not passengers in that ecosystem.
They're not even partners in the standard sense in which two organisms with separate interests arrive at a mutually beneficial arrangement.
They are the substrate on which the forest functional organization depends.
The forest, from this perspective, [music] is something the fungal network is doing.
The trees are one of its outputs. That reframing is not metaphor. It is a reasonable description of what the ecological evidence, carefully [music] read, actually shows.
If the mycorrhizal network is moving carbon and phosphorus through a forest, the question that follows [music] is whether it is moving anything else.
Resources flow through the network because the fungal hyphae connecting plant root systems are living tissue with cytoplasm and membrane potential and the full biochemical machinery of a metabolically active cell.
>> [music] >> Any living tissue capable of conducting resources is also, in principle, capable of conducting signals. [music] The question of whether the fungal network does this, whether something more than nutrients moves through the mycelium, has generated some of the most contested research in contemporary mycology.
The electrical dimension of fungal biology was not, in its origins, a fringe proposition.
In 1984, research published in the Journal of General Microbiology documented transhyphal electrical currents [music] in fungi.
Further work through the 1990s showed action potential like activity in fungal mycelia that was sensitive to external stimulation.
The basic observation that fungal hyphae generate and transmit electrical signals was established and reproducible.
[music] What those signals were doing was not understood.
In 2018, Andrew Adamatzky, a researcher [music] at the University of the West of England specializing in unconventional computing, published findings in Scientific Reports demonstrating that oyster types of oscillating [music] electrical impulses transmitted through the mycelium.
These were not simple voltage noise.
They were structured [music] recurring patterns of electrical activity with characteristics similar to action potentials in animal neurons, sharp rises in voltage followed by decay traveling along hyphal filaments.
Adamatzky framed these as spiking [music] activity and began investigating whether the patterns carried information.
The follow-up work published in Royal Society Open Science in 2022 became the study that attracted [music] the widest public attention.
Adamatzky analyzed the electrical spiking activity of four fungal species, ghost fungi, enoki fungi, split gill fungi, and caterpillar fungi.
He found that the spikes were not random. They occurred in clusters with measurable intervals between them and the statistical [music] distribution of those clusters showed structural properties comparable to the vocabulary distribution found in human languages.
Spike duration across [music] the four species ranged from 1 to 21 hours and amplitude ranged from 0.03 to 2.1 millivolts.
The variation was species specific suggesting that the characteristics of the electrical activity [music] were not environmental artifacts but biological properties of each organism.
Adamatzky proposed that these spike [music] trains represented a form of information exchange between distant parts of the fungal colony and that the structural [music] resemblance to human language vocabulary might indicate something functionally analogous to communication.
The claim attracted significant scientific scrutiny, as it warranted.
Subsequent research from Prasina and colleagues in 2022 showed that mycelial networks of oyster fungi could discriminate between different electrical frequencies applied externally, responding differently to signals of different frequency, rather than passing all input through the network equivalently.
This suggested that the fungal network was not simply a passive conductor of electrical activity, but had some capacity to process incoming signals differentially.
The finding added a layer of complexity to the picture without resolving the central interpretive question.
That question was addressed directly in a 2023 commentary in EMBO reports, which examined the state of the evidence and placed it in the context of what is known about electrical signaling in other organisms.
The commentary noted that the electrical activity documented by Adamatzky is real and reproducible.
The spikes exist.
They travel through hyphal networks.
They show species-specific characteristics. None of that is seriously contested.
What the commentary challenged was the interpretation of this activity as a language in any meaningful sense, and the framing of the spike patterns as evidence of communication between distinct parts of the organism.
The core objection is one of evidence sufficiency.
Plants also use electrical signals to coordinate [music] responses to mechanical damage, drought stress, and pathogen attack.
The existence of structured electrical activity in a biological system does not, in itself, establish that the activity carries information in the way language carries information, or that it constitutes communication between the parts of the organism generating it, let alone between separate organisms.
The structural resemblance that Adamatzky documented between fungal spike distributions and human language vocabulary distributions is a statistical observation about pattern, not a demonstration of function.
The same statistical structure could emerge from physical or biological processes that have nothing to do with communication.
A further methodological concern raised by subsequent researchers involves the difficulty of separating [music] genuine biological electrical signals from abiotic fluctuations in the substrate when using the electrode configurations employed in some of the published studies.
A 2025 review of electrical signaling in fungi published in FEMS Microbiology Reviews examined the experimental record and noted that reproducible [music] detection of fungal electrical signals remains technically demanding and that the interpretation of recorded signals requires careful controls that not all published work has included.
What the field is left with at present is a genuinely open question that resists both confident affirmation and confident dismissal.
Fungal networks generate and transmit structured electrical signals.
The signals have characteristics that vary by species and respond to external stimuli.
The networks can process incoming electrical frequencies differentially.
Whether these properties amount to communication in any biologically meaningful sense of that term is not established. The philosophical dimension of that uncertainty is worth sitting with for a moment. The question of whether fungi communicate is at its foundation a question about what communication requires.
At the molecular level, all biological signaling is either chemical or electrical.
The signal that travels down a neuron in the human nervous system and the spike that travels along a fungal hypha are both voltage changes propagating through a biological membrane.
The difference between them is not categorical.
It is a question of speed, amplitude, the complexity of the networks they operate in, and the range of responses they can produce. The neuron is embedded in a system of extraordinary computational complexity. The hypha is embedded in a network whose computational properties, if it has any, are almost entirely uncharacterized.
Whether that difference in complexity is sufficient to place fungal electrical activity in a different category from animal neural activity, or whether it simply represents a different position on a continuous spectrum of biological signaling, is not a that current science can definitively answer. That it cannot be answered definitively is itself a finding worth noting. The organisms that have been on Earth for close to a billion years, that have survived every catastrophic reset the planet has produced, are generating electrical signals through networks spanning enormous distances, and we do not yet know what those signals are for.
That is not a small unknown. It is one of the significant open questions in contemporary biology.
The electrical signaling question sits at one boundary of what fungi might be capable of. A different boundary, harder to dispute and considerably more unsettling in its implications, is illustrated by what certain parasitic fungi are already documented to do to the organisms they infect.
In tropical forests across Central [music] and South America, Southeast Asia, and parts of Africa, carpenter ants of the genus Camponotini occasionally begin behaving in ways that serve no identifiable interest of their own.
An infected ant leaves the colony, abandons the foraging trails and social structures that define ant behavior, and moves upward onto low vegetation.
It finds a leaf at a specific height above the forest floor, typically between 10 and 30 cm, [music] bites into the underside of the leaf's central vein with a force that locks the mandibles in position, and dies.
From the base of the ant's head, a fungal stalk emerges over the following days and weeks, growing upward before rupturing to release spores onto the forest floor below, where other Camponotini ants are foraging.
The organism responsible is Ophiocordyceps [music] unilateralis, a parasitic fungus whose entire reproductive strategy depends on the precise manipulation of another organism's body.
It is not the only fungus that manipulates host behavior. It is the most thoroughly studied and the most precisely characterized, and the mechanism it uses to achieve what [music] it achieves represents something that has no clear parallel in the biological literature.
What makes the behavioral manipulation of Ophiocordyceps unilateralis remarkable is not simply that it occurs.
Parasites that alter host behavior are documented across many lineages.
Parasitic wasps that reprogram caterpillar defensive behavior, hairworms that compel crickets to seek water and drown, protozoan parasites that alter rodent responses to predator scent.
Behavioral manipulation by parasites is a recognized ecological phenomenon.
What distinguishes Ophiocordyceps is the specificity and precision of the manipulation it produces.
The infected ant does not simply behave abnormally. It behaves with a precision that reflects the reproductive requirements of the fungus rather than the survival requirements of the ant.
The height at which the ant bites, the orientation of the bite relative to the leaf surface, the microhabitat selected in terms of temperature and humidity, all correspond to the conditions optimal for fungal spore production and dispersal, not to any location that would benefit a living ant. The ant is directed to a specific set of environmental coordinates by a process it cannot resist and does not control, and it executes that direction with its own muscles, its own legs, its own mandibles before dying in the exact position the fungus requires.
Research conducted at Penn State University, led by David Hughes, has examined the mechanism by which Ophiocordyceps achieves this control.
And the findings are more precise and more philosophically disorienting than the popular account of the zombie ant fungus typically conveys.
The fungus penetrates the ant's body and colonizes its muscle tissue extensively.
In experimental analyses of infected ants, fungal cells were found distributed throughout the major muscle groups involved in locomotion and mandible function.
The brain tissue, however, was found to be largely intact and largely free of fungal colonization.
The fungus was not, in the straightforward sense, invading the ant's nervous system and issuing commands through neural architecture it had taken over.
It was colonizing the muscles directly and, through a combination of chemical secretion and physical presence, manipulating the contractile tissue that produces movement without rooting that manipulation through the ant's own decision-making apparatus.
The ant is not, in this picture, being neurologically overridden. It is being physically operated. The distinction is not merely semantic. If the fungus were producing behavioral changes by hijacking the nervous system, the ant would be analogous to a machine whose controller had been replaced.
What the Hughes lab data suggests is something different. That the fungus colonizes the output layer of the ant's motor system and drives behavior through the muscles themselves, bypassing the nervous system's role as intermediary.
The ant's brain may remain functional throughout the process. It may be receiving sensory information and generating behavioral outputs that the fungal tissue in its muscles is overriding or redirecting at the point of execution.
The genus Ophiocordyceps contains over 400 described species, and the specialization pattern across those species is among the most striking features of this lineage.
Each species tends to infect a single host species or a narrow group of closely related host species, and the behavioral manipulation each produces is calibrated to that specific host's neuromuscular architecture, movement patterns, and habitat.
The system is not a generalist strategy that fungi stumbled upon and applied broadly.
It is a collection of highly refined species-specific solutions to the problem of achieving precise behavioral control over another organism.
Each solution independently evolved for a different target.
A 2011 in PLoS One by Evans, Elliot, and Hughes documented four new species of Ophiocordyceps in a single region of Atlantic rainforest in Brazil, each specific to a different carpenter ant species, each producing a morphologically distinct fruiting body suited to a different microhabitat.
The diversity of this genus in a single forest fragment suggests that the total number of Ophiocordyceps species across tropical ecosystems may be substantially higher than current estimates account for.
The philosophical question embedded in this system is one that the biology does not resolve and is not designed to resolve.
An ant infected with Ophiocordyceps walks through the forest under its own power.
It uses its own muscles to climb the vegetation it was directed toward. It uses its own mandibles to bite into the leaf it was [music] positioned to bite.
The body producing all of this movement belongs to the ant.
The agenda driving all of this movement belongs to the fungus. What the organism doing the moving is in that situation is not a question with a clean answer.
The boundary between an organism and a parasite that has colonized its motor tissue is not a line that biology draws clearly.
The ant is still alive when the manipulation occurs.
The fungus is not yet a separate body.
They occupy the same physical space with the ant's muscles under fungal chemical and physical influence, and the ant's brain, possibly still functioning, unable to override the result.
The organism that appears to be acting is not in any operationally meaningful sense the organism in control.
That is a finding about the nature of agency that extends well beyond mycology.
If behavior can be produced by an organism without originating in that organism's own interests or decision-making, then the relationship between a body and the actions of that body is less fixed than the way we typically talk about living things assume.
The Ophiocordyceps story involves a fungus operating inside the body of another organism, using that organism's own physical architecture to serve fungal reproductive ends. It is an extreme case evolved over millions of years of host-specific refinement, and it is tempting [music] to treat it as a biological curiosity, a specialist strategy that applies to certain tropical ants in certain forest environments, and has no bearing on the broader relationship between fungi [music] and animal bodies.
That temptation should be resisted.
Not because fungi are doing to human bodies what Ophiocordyceps does to ants, but because the premise of the Ophiocordyceps story, that fungi live inside animal bodies and exert influence on the biological processes occurring there, is not a specialist phenomenon.
It is the default condition of complex animal life, [music] including human life.
The human gut is not a sterile environment. It harbors a dense and diverse community of microorganisms, bacteria, archaea, viruses, [music] protozoa, and fungi, collectively constituting a microbial ecosystem whose composition [music] and activity have measurable effects on the physiology of the person carrying it.
This community has been studied with increasing intensity since the early 2000s, when advances in genomic sequencing made it possible to characterize microbial populations without the requirement of culturing them in a laboratory, a method that left the majority of gut microorganisms undetectable because most do not survive the culturing [music] process.
The bacterial component of the gut microbiome has received the preponderance of research attention. The fungal component, the mycobiome, has received considerably less, and the reasons for that disparity are partly practical and partly historical.
The term mycobiome itself was not coined until 2009.
A literature search for that term returns 10 results in 2013.
The scientific infrastructure for characterizing gut fungal communities, the reference genome databases, the computational methods for distinguishing fungal sequences from bacterial ones in metagenomic data, the experimental frameworks for studying fungal-bacterial host interactions simultaneously has been built in pieces over the past 15 years and remains incomplete.
What that infrastructure has revealed in the time it has existed is a picture considerably more complex than the early assumption that gut fungi were primarily opportunistic pathogens, organisms that cause problems only when the immune system was compromised or the bacterial microbiome was disrupted. A 2022 review published in the Lancet Microbe examined the compositional and functional diversity of the gut mycobiome across healthy populations from birth to adulthood and found that [music] intestinal fungi regulate host homeostasis, interact dynamically with the co-residing bacterial microbiome, and play roles in immune function that are not reducible to their effects when they cause [music] disease.
The dominant fungal genera detected in the human gut across multiple studies are Candida, Saccharomyces, and Penicillium, though the specific composition varies [music] substantially between individuals and is influenced by diet, geography, antibiotic use, and age.
Fungi appear to act as [music] early colonizers of the infant gut with fungal communities detectable in newborns and with evidence suggesting [music] that these early fungal populations exert influence on the developing immune system during a period when the basic parameters of immune response are being calibrated.
A 2025 review published in a peer-reviewed journal on gut microbiota interactions describes fungi as a [music] critical component of the gut microbiota despite representing a modest fraction of its total biomass, noting their role in mediating immune responses and shaping the broader [music] microbial ecology of the gastrointestinal tract.
The interactions between fungi and bacteria in the gut are not passive coexistence. They involve direct competition for resources and space, [music] production of chemical compounds that inhibit or stimulate the growth of neighboring organisms, and coordinated effects on the immune [music] system that neither population produces in isolation.
Fungi mediate the activation of immune pathways including TH17 cell activation, a branch of the inflammatory response [music] implicated in both protective immunity and in the pathology of autoimmune and inflammatory conditions.
Dysbiosis of the gut microbiome, meaning disruption of the normal fungal community composition, has been associated with inflammatory bowel disease, >> [music] >> Crohn's disease, graft-versus-host disease following bone marrow transplantation, and certain liver conditions.
A 2024 study published in Cell took the most comprehensive approach to characterizing the gut mycobiome yet attempted.
Researchers compiled what they called the cultivated gut fungi catalog.
760 fungal genomes derived from the feces of healthy individuals spanning 206 species [music] across 48 families, of which 69 species had not been previously identified or described.
They then used this catalog to analyze over 11,000 fecal metagenomes from populations in China and elsewhere, constructing a phylogenetic map of gut mycobiome composition at a scale that earlier methods could not approach.
The analysis confirmed significant variation in microbiome composition associated with inflammatory bowel disease and other conditions and identified fungal signatures in the metagenomic data that correlated with disease states in ways that the bacterial microbiome data alone had not captured.
The implication is not that fungi cause these conditions in a simple or direct sense.
The gut ecosystem is a system of interactions and attributing specific outcomes to specific members of that system requires the kind of mechanistic experimental work that the field is still developing the tools to conduct.
What the data shows is that the fungal component of the gut community is not a background presence.
It is an active participant in the ecology of the gut and changes in that participation correlate with changes in host health in ways that are beginning to be measurable.
We have been carrying these organisms inside us for our entire evolutionary history.
The fungi in the human gut today are not newcomers. They are members of a kingdom that has been living in association with animal bodies for as long as animal bodies have existed and that has shaped its strategies for surviving inside biological hosts across hundreds of millions of years of coevolution.
We have been studying them systematically for roughly 15 years.
The boundary of the human body defined anatomically as the skin and the mucosal surfaces of the gut and respiratory tract is in biological terms a negotiated territory.
The organisms living on and within it are not passengers. They are functional components of the system contributing to immune calibration, metabolic processing, and microbial competition in ways that affect the physiology of the person containing them.
The question of where the human organism ends and the microbial community it harbors begins is not one that biology can answer cleanly because the functional answer depends on processes that operate across that boundary continuously.
The kingdom that survived every extinction, that built the infrastructure of terrestrial ecosystems, that operates inside the tissues of 90% of land plants, has been operating inside us as well.
The scale of what we do not yet know about that operation is, given what the past 15 years of research have already produced, considerable.
The relationship between fungi and human civilization is not recent, and it is not peripheral.
It runs through the center of medicine, agriculture, food production, and in ways that contemporary neuroscience is only beginning to formalize the study of consciousness itself.
The kingdom that most people associate primarily with mold and mushrooms is the source of some of the most consequential chemical compounds in human history. And the inventory of what it has produced is not closed.
The starting point for any account of fungi and medicine is a Petri dish in London in 1928.
Alexander Fleming, a bacteriologist at St. Mary's Hospital, returned from a period away to find one of his bacterial cultures contaminated by a mold.
The mold had produced a clearing in the bacterial growth around it.
A zone in which the staphylococcus bacteria he'd been culturing had been killed.
The mold was penicillium notatum, now reclassified as penicillium chrysogenum.
The compound it had produced, which Fleming named penicillin, was a secondary metabolite of the fungus, a chemical it generated not as a primary product of its own metabolism, but as a compound with ecological function. In this case, the suppression of competing bacteria in its immediate environment.
The subsequent development of penicillin into a clinical antibiotic, primarily through the work of Howard Florey and Ernst Chain at Oxford in the late 1930s and early 1940s, produced a drug that is conservatively estimated to have saved hundreds of millions of lives across the following decades.
The antibiotic era it inaugurated transformed the practice of medicine so fundamentally that the pre-antibiotic and post-antibiotic periods are effectively different epochs of medical history.
The compound that accomplished this was not synthesized in a laboratory.
It was discovered in a fungus.
Penicillin is the most widely known instance of a pattern that extends across the fungal pharmacopoeia.
In 1969, a soil sample collected in Norway contained a fungus called Tolypocladium inflatum.
The compound extracted from it, cyclosporin A, was found to possess a highly specific immunosuppressive property. [music] It inhibits the activation of T lymphocytes without broadly suppressing the immune system in the way that earlier immunosuppressants did.
The clinical consequence of this specificity was that organ transplantation, which had been limited by the immune system's rejection of foreign tissue despite aggressive and broadly damaging immunosuppressant regimens, became viable as a routine medical procedure.
The modern transplant program, which sustains the lives of hundreds of thousands of patients annually, depends on a drug derived from a soil fungus collected from a Norwegian hillside.
[music] Statins, the class of drugs used to lower low-density lipoprotein cholesterol and reduce cardiovascular disease risk, are among the most widely prescribed pharmaceuticals on Earth.
The first statin in clinical [music] use, lovastatin, was isolated from Aspergillus terreus, a fungus found in soil.
The compound works by inhibiting a key enzyme in the cholesterol biosynthesis pathway, a mechanism first characterized through the study of the natural product rather than through rational drug design.
The fungus was producing a cholesterol-modulating compound for its own ecological purposes.
Pharmacology found it and characterized what it did in human biology.
The pattern across these three cases is not coincidental. Fungi have spent hundreds of millions of years in chemical competition with bacteria, other fungi, insects, and the immune systems of the plants and animals they inhabit.
The secondary metabolites they have evolved to produce in that competition are a vast library of biologically active compounds, shaped by selection pressure to interfere with or modulate specific biological processes in other organisms.
What pharmacology does when it screens fungi for drug candidates is, in a real sense, reading that library.
And the library is large.
The fermentation dimension of the fungal contribution to human civilization is older than the pharmaceutical one by several thousand years.
Saccharomyces cerevisiae, brewer's yeast, is a fungus.
Its capacity to metabolize sugars and produce ethanol as a byproduct has been exploited by human societies across every continent for at least 10,000 years, predating written language, predating most organized state structures, predating agriculture itself in some regional sequences.
Beer, wine, bread, and a substantial proportion of the world's cheeses are products of fungal activity.
The dietary and cultural technologies that organized early human civilization were, in significant part, fungal technologies.
The most recent addition to the account of what fungi have given human understanding sits in a different register from the pharmaceutical and the nutritional, and it involves a compound that is, in its clinical implications, still being characterized.
Psilocybin is a naturally occurring psychoactive compound produced by certain species of fungi, primarily members of the genus Psilocybe. Its chemical structure allows it to cross the blood-brain barrier and interact with serotonin receptors in the central nervous system, producing alterations in perception, cognition, and the sense of self that are, by clinical report, among the most psychologically significant experiences most people who undergo them describe.
The Johns Hopkins Center for Psychedelic and Consciousness Research, one of the most prominent institutional settings for the clinical study of psilocybin has published findings demonstrating that psilocybin-assisted therapy can produce substantial reductions in major depressive disorder symptoms that persist for more than a year in some patients.
A 2023 prospective longitudinal study published in Frontiers in Psychiatry involving researchers from Johns Hopkins documented associations between naturalistic psilocybin use and persisting improvements [music] in mental health and well-being across a large sample.
A 2022 study from the same institution examined a different question.
Whether a psychedelic experience alters not just mood, but the attribution of consciousness to other living things.
The findings showed that among people who described a single psychedelic experience as having changed their beliefs, attribution of consciousness to fungi increased from 21% before the experience to 56% after it.
A compound produced by fungi when it enters the human nervous system and temporarily reorganizes the functional connectivity of the brain makes people substantially more likely to consider that fungi might be conscious.
Whatever one makes of that finding as a statement about fungal consciousness, it is a precise illustration of the reach of fungal chemistry into human cognitive life.
The compounds fungi produce have shaped what we eat, how we treat bacterial infection, how organ transplantation is possible, what cardiovascular disease prevention looks like, and what a significant number of people believe about the nature of mind.
We built our medicine from fungi. We built our food systems from fungi.
The frontier of what else the fungal pharmacopoeia contains has not been reached. The inventory, by any reasonable assessment, is not complete.
Every section of this film has in some form arrived at the same boundary, the edge of what is currently known. The mycorrhizal network is documented, but its full functional scope is debated.
The electrical signals in fungal hyphae are measured, but their purpose is uncharacterized.
The mycobiome is being cataloged, but its mechanistic role in human health is only beginning to be understood. The behavioral manipulation produced by Ophiocordyceps is observed in detail, but the precise chemical mechanism that produces it in the ant's muscle tissue is not fully resolved.
At each point, the known opens into a much larger space of the unknown.
The shape of that space, its actual dimensions, is itself one of the more striking features of mycology as a scientific field.
The numbers are a useful starting point.
Current estimates for the total number of fungal species on Earth range from 2.2 million to 6 million, depending on the methodology and assumptions of the estimate.
Approximately 150,000 have been formally described and named.
That figure represents somewhere between 2 and 7% of the estimated total, depending on which estimate is used. For context, mammal species are essentially fully cataloged. Approximately 6,500 species of mammals are known, and the discovery of a new mammal species is a significant scientific event covered by the specialist press.
New fungal species are discovered in quantities large enough that the discovery of individual species rarely receives attention outside mycological journals.
The disparity in what is known between the most studied and least studied kingdoms of complex multicellular life is not a gap. It is a chasm.
The discovery pipeline shows no signs of narrowing that chasm. It shows signs of widening it in the sense that [music] as detection methods improve, the number of unidentified fungal sequences appearing in environmental samples increases rather than decreases.
Environmental DNA sampling, the technique of extracting and sequencing genetic material directly from soil, water, or tissue samples without culturing organisms in a laboratory, routinely produces fungal sequences that match nothing in existing reference databases.
Every systematic survey of a new ecosystem, every metagenomic analysis of a poorly studied soil type, every analysis of a deep-sea sediment sample, or a high-altitude glacier core returns fungal genetic material from organisms that have no formal name and no characterized biology.
They exist. They are genetically detectable.
What they are doing in the ecosystems they inhabit is in most cases entirely unknown.
The 2025 New Phytologist study that identified Rugososporomyces Lavoisier in a 407 million-year-old fossil is an instructive case in a different register.
The Rhynie chert has been studied by paleobotanists and paleomycologists for over a century. [music] It is one of the most thoroughly examined fossil deposits in the world, valued precisely because of its extraordinary cellular preservation of early Devonian organisms.
>> [music] >> And within a plant fossil from that deposit, using imaging techniques not previously applied to those samples, researchers found a fungal species that had not previously been described living in symbiosis with an early land plant alongside a second fungal species that had been known.
A site that has been examined for 100 years, using improved methods, revealed new species.
The implication for how much remains undiscovered in less thoroughly examined ecosystems is not difficult to draw.
The functional unknowns compound the taxonomic ones.
Knowing that a species exists is a different category of knowledge from knowing what it does.
For the approximately 150,000 described fungal species, functional characterization ranges from detailed for the commercially or medically significant species to essentially absent for the majority.
The ecological roles of most described fungi, the specific substrates they decompose, the organisms they associate with, the compounds they produce, the interactions they mediate in the soil, communities they inhabit, are not documented with any completeness.
Taxonomy has outpaced functional biology in the fungal kingdom, and functional biology has itself barely begun.
The open questions are not confined to the undescribed species.
Within the systems this film has examined, the gaps in current knowledge are substantial.
The mechanism by which Ophiocordyceps unilateralis achieves the behavioral specificity it produces in infected ants, the precise combination of compounds acting on specific muscle groups to direct the ant to the correct height and position, has been partially characterized and is actively investigated, but is not fully resolved.
The question of whether the electrical signals in fungal networks carry information within the organism, and if so, what kind of information, has not been answered.
The functional significance of the mycobiome in human health, beyond the associations documented so far, requires the mechanistic experimental work that the field is still building the infrastructure to conduct.
The scale of these unknowns, taken together, describes a kingdom of life that has been on Earth for close to a billion years, that has shaped [music] terrestrial ecosystems since before plants existed, that lives inside the bodies of nearly every complex organism alive, that produces compounds that have restructured the practice of medicine, and that remains in the majority of its diversity and in much of its functional biology uncharacterized by science.
[music] That is not a failure of mycology.
The scientist working in this field have produced, >> [music] >> in a relatively short period of dedicated research, findings that have fundamentally revised how biology understands land colonization, forest ecology, microbial communities, and pharmaceutical chemistry.
The unknowns are large not because the field [music] has failed to investigate them, but because the organism being studied is, at the scale of its diversity and the depth [music] of its integration into biological systems, genuinely that complex.
The kingdom is large, the science is young, the distance between those two facts is where the next generation of mycological research will operate.
The question this film opened with was not primarily a biological one. It was framed in biological terms through extinction events and survival records and the age of fossil deposits, but the question underneath all of those facts was something older and more general.
What does it actually mean to succeed as a living thing?
Biology tends to answer that question with the organisms that dominate, the ones that are largest, most numerous, most visible, most studied. Dinosaurs for the Mesozoic, flowering plants for the Cenozoic, mammals for the present era. The organisms we place at the center of the narrative of life on Earth are the ones that, at a given moment, appear to be winning by the most visible measures: [music] size, abundance, ecological control, structural complexity.
These are the organisms that fill the textbooks. They are the ones whose extinctions we treat as the pivotal moments in the history of life.
Fungi do not appear in that narrative in any central role. They appear as background, [music] as decomposers, a functional category that tends to be defined by what it is not rather than by what it is.
Not a producer, not a predator, not a builder of the structures we call ecosystems.
The decomposers are what remains after the real actors have finished. They clean up.
The full account of fungal biology, laid out across the sections of this film, is an argument against that framing. Not a rhetorical argument, but an evidential one.
The terrestrial ecosystem did not produce fungi in its background as a cleanup crew.
The terrestrial ecosystem was built on fungi from the first moment any organism crossed from the ocean onto bare rock.
The plants that generate the primary productivity of every forest on earth carry fungal partners in their roots that have been continuous in the plant lineage since before plants had roots.
The animals that constitute the [music] visible fauna of every terrestrial ecosystem carry fungi inside their gut that mediate the immune responses those animals depend on.
The soils that make the growth of all terrestrial life possible are products, in significant part, of hundreds of millions of years of fungal decomposition and mineral processing.
The organisms we call dominant [music] in any given era are, in many cases, downstream products of fungal infrastructure. They exist in the form they exist in because fungi made the conditions for their existence possible.
When the conditions for their existence are destroyed, as they were five times in the history of complex life, the fungi process the resulting mass of dead biological material and make the conditions for the next era of life possible.
The pattern has repeated across half a billion years without a significant break in the fungal record.
Fungi are not undefeated because they are invincible.
No single organism is invincible.
They are undefeated because the conditions that destroy other kingdoms are, for a kingdom built on decomposition, the conditions of abundance.
And they are undefeated because no terrestrial ecosystem, at any point in the history of life on land, has been able to function without them. They are not part [music] of the system. In the most accurate biological sense available, they are what the system runs on.
Success in the evolutionary record turns out to look different from what dominant [music] suggests.
The organisms that have accumulated the longest unbroken record of survival and ecological centrality are not the ones that grew largest or moved fastest or developed the most elaborate structures.
They are the ones that positioned themselves where they could not be removed at the intersection of death and renewal, at the interface between what a living system produces and what that production requires.
The organisms that are indispensable survive the events that eliminate the organisms that are merely dominant.
We began this film with an image from the geological record, the extraordinary concentration of fungal spores at the sediment boundary of the Permian-Triassic extinction, [music] 252 million years ago.
The forests were dead. The animals were [music] dead.
The ecosystems that had organized the land surface of the planet for the preceding hundreds of millions of years were gone.
And in that dead world, in the sediment layer that recorded it, what the fossil record shows flourishing is a fungal bloom, spreading across a planet of fallen biomass, processing it, metabolizing it, cycling the carbon and the phosphorus and the nitrogen locked in dead tissue back into a form that living organisms could use.
That process did not end at the Triassic boundary. It has not ended.
It is occurring right now in the soil beneath every forest, in the decomposing wood of every fallen tree, in the roots of every [music] plant with a mycorrhizal partner, in the gut of every mammal, in the walls of buildings, in stored grain, in aging fruit, in the bread made from the fermentation of a fungus that human populations have maintained in continuous cultivation for thousands of years.
The kingdom that was present before the terrestrial world was habitable, that made it habitable, that survived every catastrophic reset it underwent, is present in essentially every biological context on Earth at this moment.
The most successful life form in Earth's history is not a dramatic organism.
It does not have a face or a sound or a visible body in most of the contexts where it operates. It does not compete for the ecological positions that produce the organisms we name and study and celebrate.
It occupies a different position entirely. The one that cannot be filled by anything else. The one that every other position in every ecosystem depends upon.
It has been here for close to a billion years.
It was here before us. It is inside us now.
And for most of that time, we did not have a name for the part of it that lives in our own gut.
Because the field of research required to find it did not exist until 15 years ago.
The organism that has outlived is not one we discovered. It is one we are very slowly beginning to see.
>> [music] [music]
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