Fungi are in the thick of this scientific transformation, particularly those fungi involved in mutualistic relations with plants. These fungi bring water and nutrients to plants in exchange for carbohydrate meals.

Thinking through interspecies relations changes the game entirely for ecology, evolutionary theory, and developmental biology. Evolution, for example, is no longer imagined as a species-by-species affair. “Holobionts” are multispecies evolutionary units: they evolve together.

hope to convince you that fungi, which are a kind of organism that many people can’t imagine acting in lively, interactive ways with its fellow beings, are in fact doing just that.

every organism is actively making worlds all around us, worlds that we share, whether we notice them or not.

Like all forms of knowledge, our understandings of biology and its categories were shaped by the social conventions in which they were formed.

we have come to understand that much of the biological diversity of life is microscopic. We now know that microbes can share genetics with each other “horizontally,” that is, not only “vertically” from parent to child but from sibling to sibling and even between organisms that are considered different species.

The goal of a mechanistic view is to discover the mechanisms of life, the relations of cause and effect.

The main query of a mechanistic framework is always, at base, What is the mechanism?

our very world has been made possible by the daily actions of trillions of fungi that have shaped our planet for almost a billion years.

It was only as recently as 1969 that fungi were recognized by scientists as a separate kingdom from plants,

basically fungi are able to gather water and soil nutrients, which they exchange for photosynthetic sugars created by their plant partners. Thus, almost every plant is part of an underground fungal network.

while all the major climate change predictions completely ignore fungi, they are likely the most important actors in determining how carbon moves through soils—a source of carbon ten times more important than all land-based human processes. 23

I am interested in how actions create worldly effects rather than the internal motivation for such actions.

mainstream political theory largely views the world as consisting of dead matter, as a collection of objects that can be manipulated for human purposes.

world-making inquires into the particulars—the diverse and specific agencies—of various organisms. For instance, African elephants’ world-making will be totally different from the world-making of termites they share lands with, or even substantially different from that of their closer kin, the Asian elephants.

Scholars of ontology—which briefly means a theory about the nature of being or what it means to have existence—suggest that each cultural group lives in its own world, which necessarily presents the idea of plural worlds.

ontologists have sometimes criticized their fellow anthropologists for holding other cultural worlds at arm’s length (dismissing them as “myths,” “legends,” and “beliefs”) and conflating the world of their own culture as the world; ontologists, on the other hand, take other cultural worlds seriously in and of themselves, as fully rich worlds that are each unique.

Encounters prompt unexpected responses and improvised actions, as well as long-term negotiations with unforeseen outcomes,

I was intrigued, for example, to learn that some people in Japan have a unique enzyme that allows them to better digest seaweed, and the theory is that this enzyme is the result of a multispecies encounter. 51 I first assumed that this enzyme must have emerged from human DNA but later read that it was created by bacteria in the gut microbiota. Scientists think this enzyme became part of some people’s gut microbiota through a horizontal transfer of seaweed-eating bacteria a long time ago. Thus, rather than being digested in the stomach, these bacteria become part of human bodies. This is a powerful example of the physical manifestations that particular encounters can leave on the body.

world-making suggests that different species partake of their own significant and unique experience of living, and one can refer to each of these qualitatively different experiences as a kind of world.

much of the scientific and lay orientation toward microbes has focused on them as pathogens, as “germs.” This pathogenic bias toward microbes, however, is changing, in part through stories like those told in this book, which reveal how thriving life on Earth depends on microbial organisms and their complex interrelationships.

The pandemic has done a great deal to undermine a sense of human mastery and shows a virus’s power not only to attack and kill humans, but to compel people to reconfigure the global economy and nearly all aspects of social life to a degree unprecedented for a century (since the so-called Spanish flu epidemic of 1919).

in terms of net planetary effect, fungal mining could be more important than human mining. I suggest that the main reason why this is just emerging as a new scientific discovery is the tendency to imagine fungi as relatively passive, not as powerful world-makers.

While we are used to describing humans as dynamic actors whose abilities are shaped by their own experiences, we often imagine that other species have fixed responses that are neither learned nor enskilled, which diminishes a sense of their liveliness. Imagining fungi as active actors is even harder than imagining animals so because we don’t see fungi acting in animal-like ways. Yet their world-making liveliness in such behaviors as mining and rotting are highly active processes that are utterly essential to life; in the process of their own eating, they unlock nutrients and bring them from sinks into cycles for themselves and for others.

The particular partnership that fungi have developed with plants was to connect fungi’s fine hyphal threads with the plant’s coarse roots. This partnership is called mycorrhizae (for “fungus” and “root”),

hyphae can also obtain minerals that plants are not able to extract from the soil. In turn, plants send up to a quarter of their photosynthetically fixed, carbon-based sugars downward to fungi that cannot make sugars on their own. 24 In other words, when you look at a tree, one out of every four leaves is devoted to maintaining fungal relations.

Eventually, plants invented a new complex molecule that allowed for tremendous upward growth: lignin. This complex and tough structure became one of the key building blocks of wood. Without any kind of vein-like tubes or woody material, plants can reach only a very limited size, about the height of a tulip. The development of lignin completely transformed plant bodies into towering structures that could capture copious amounts of sunlight, which in turn created a whole new scale of vegetative potential: the tree.

after the arrival of lignin, for hundreds of millions of years nothing could break it down. This caused trees to become a new phenomenon: a biological dead end. That is, even trees that died from fire or disease could not be incorporated back into the cycle of life.

After repeated floods buried these swampscapes, massive amounts of undigested plant matter piled up and became subject to great forces of compression. In places with perfect conditions, the trees with their lignin and cellulose were compressed and then eventually turned into coal and petroleum. 26

the amount of coal and gas underground is proportional to the time gap between when plants developed lignin, which allowed them to become trees, and when fungi learned how to disassemble lignin and turn it into food. 27 If fungi had immediately figured out how to break lignin down, there would have been no gas or coal.

To recap: first, fungi spent perhaps six hundred million years converting rock into minerals and creating the basis for soil before plants arrived on land. Second, on land, fungi formed intimate relations with plant roots, which greatly enabled plants’ ability to grow in a much wider range of climates and conditions, while simultaneously providing fungi with food. Third, fungi learned to rot wood, a substance otherwise unpalatable to almost any other organism, and turned wood into organic matter and humus that created rich soil. This soil, in turn, became the basis for a new niche that spread virtually everywhere around the world.

Fungi that live within leaves, part of a world within plants, are called endophytic fungi (“ endo” for middle and “phytic” for plant), a term first coined in 1866. It is likely that many of the important chemicals that plants have—which help them live in extreme temperatures and deal with salinity and insect predators—are created by endophytic fungi and bacteria. It turns out that endophytic fungi are plentiful; since they were discovered, this study has exploded, and scientists have found endophytic fungi within every plant sample they have tested. 34

Whereas scientists had typically perceived most animals as individuals, there is growing recognition that all animals harbor teeming worlds of life within them, including bacteria but also fungi and others, so that each of us is a conglomerate of species.

dry rot, a kind of fungus that was accidentally transported from its original home in the Indian Himalayas to other parts of the world by British colonists, was the scourge of the British Navy and spread from ships to houses around the world.

our methods of monoculture agriculture have fostered fungal growth by giving fungi easy access to millions of genetically similar plants, so once a fungus starts eating one of these plants, it can easily spread by spore to others nearby. One of the most well-known examples is the devastation of Ireland’s potato crop. By 1600, potatoes had been brought from South America to Europe, where they thrived. Yet, like dry rot, a potato-eating fungus was unintentionally transported to Europe, where it started to wreak havoc in Ireland’s large potato fields. By 1845, this dreaded rot turned vast fields of potatoes into black goo.

Fungi have learned to become parasites of almost all known taxa of plants and animals40 and have thus coevolved in tandem with their immune and defense systems.

According to this new understanding, disease is caused less by the absence or presence of bad germs (bacterial, viral, or fungal) than as a result of an imbalanced ecology.

For a long time, botanists puzzled over how to explain why tropical forests are often diverse and why temperate forests are relatively homogeneous. One part of this history was revealed in the early 1900s after the industrialist Henry Ford planted a vast plantation of rubber trees in the Brazilian Amazon to “grow” tires for his Model T car. In the wild, rubber trees grow far apart, and rubber tappers have to spend a lot of time moving between trees. To make the harvest more efficient, he planted cleared forest lands with vast numbers of rubber seedlings. Soon, however, a particular fungus destroyed all the closely growing seedlings, revealing that the widely spaced distribution of rubber trees in the natural forest was shaped by the presence of fungi. Botanists now think that similar dynamics may be true for many other tropical trees: fungi eliminate those that grow closely together, and only those that are far enough apart survive.

Our industrial large-scale agriculture creates perfect conditions for fungi’s rapid proliferation.

new forms of plants, likely moss-like organisms, came out of the waters, together with fungi, and a miraculous partnership between plant roots and fungal bodies was formed.

around four hundred million years ago, lignin enabled plants to become soaring structures—trees—making new habitats and accelerating the breakdown of rocks into soil.

For sixty million years, tree bodies piled up on the landscape and fell into swamps, until fungi finally discovered how to unlock lignin and eat dead wood, initiating a seismic change in how ecologies functioned. Thus, fungi helped create the planet’s first forests. Fungi have kept these forests thriving today by assisting plant roots and leaves, as well as through their critical role in breaking down the dead and turning their bodies into nutrients for the living.

Evolution is often coevolution, always in relationship to other species that we eat and that eat us.

long before biology as a discipline came into being, linguistic conventions had already succeeded in effectively de-animating the nonhuman world.

in scientific language our terminology is used to define the boundaries of our knowing. What lies beyond our grasp remains unnamed. 3

physiological ecologist Scott Turner in his book The Extended Organism. 26 In it, he argues that scientists almost always assume that organisms adapt to their environment; relatively few consider how environments are also shaped by animals’ actions or, in other words, how animals perform a kind of world-making. Turner’s book shows, for example, how termites create structures that skillfully use wind currents for heating, cooling, and removing potentially harmful gases. These structures engage with the local environment and shape it to the termites’ benefit.

Active niche creation explores how organisms actively carry out efforts to enhance existing possibilities, or produce these niches.

This approach animates a landscape typically seen as fixed and enables us, instead, to view organisms as actively shaping their worlds, rather than as living a passive existence. We also see how niches are not isolated “bubbles” inhabited by just one species but can extend into large landscapes that contain many species.

all organisms, from bacteria to whales, live their lives and perpetuate themselves over the generations through their active engagements with others—not just as predator or prey—but through a wide range of relationships far more complex than the often reductive models of “beneficial species” or “antagonistic species.”

Fungal hyphae don’t just constantly exude digestive chemicals; they detect mineral prey and use powerful enzymes to dissolve these miniature rocks. Mycorrhizal fungi are effective in finding these nutrients and may provide their partners with up to 80 percent of the nitrogen and 100 percent of the phosphorus plants need to grow. 41

Umwelt is the subjective environment that each species perceives and creates, shaped by their distinctive sensory apparatus.

Neurologists now recognize at least nine human senses;

Uexküll’s notion that insects, for example, interpret the world and act as semiotic organisms

Ingold’s understanding of the umwelt as not a fixed sensorial apparatus but as an active engagement. 8 This conception of the umwelt understands sensing as the means by which organisms, including humans, don’t just passively know but also literally make sense of the world through their diverse senses. 9

I see the umwelt not as “a touchable and tangible category, but rather an array of subjective and perceptive elements.” 10

we may conflate our way of perceiving reality with reality itself.

For plants, light is food, and for fungi it is something different, but we don’t yet understand what it is for them, only that, in some ways, light helps mushrooms orient in time and space.

there is a gap in time between when something touches us and when we feel it. This gap can be noticed experimentally: tapping faster than sixteen times a second on a person’s arm is experienced as continuous touch. There is a name for this gap, a “moment,” a term we often use in a loose, impressionistic way but it is based on our umwelt, which is created according to the human nervous system. Anything slower will be experienced as tapping.

“Unlike most terrestrial mammals that communicate with pheromones, we depend on vision and privilege visual knowledge.… Human sensory organs make use of small portions of the electromagnetic, acoustic, and olfactory spectra for perception and communication.”

since Europeans created the vast majority of scientific instruments for exploring the world, it is no surprise that they mainly focused on enhancing sight (with such technologies as microscopes, telescopes, and X-rays). Even technologies that use vibration (like radar, sonar, and ultrasound) or smell (like gas chromatography) convert machine-made senses into visual representations, thus reinforcing and increasing our visual reliance.

This eyeless animal finds the way to her watchpoint [at the top of a tall blade of grass] with the help of only its skin’s general sensitivity to light. The approach of her prey becomes apparent to this blind and deaf bandit only through her sense of smell. The odor of butyric acid, which emanates from the sebaceous follicles of all mammals, works on the tick as a signal that causes her to abandon her post (on top of the blade of grass/ bush) and fall blindly downward toward her prey. If she is fortunate enough to fall on something warm (which she perceives by means of an organ sensible to a precise temperature) then she has attained her prey, the warm-blooded animal, and thereafter needs only the help of her sense of touch to find the least hairy spot possible and embed herself up to her head in the cutaneous tissue of her prey. She can now slowly suck up a stream of warm blood. 42

In Uexküll’s rendering, the tick’s umwelt has only three signifiers (things that matter to the tick’s universe): the smell of butyric acid, the warm temperature of mammals, and the hairiness of mammals.

Witzany argues that plants have an extensive chemical “vocabulary” that functions “as signals, messenger substances, information carriers, and memory medium in either solid, liquid, or gaseous form.” 47 Plants actively interpret signs, both biotic and abiotic, and Witzany suggests that they follow three kinds of rules, similar to human communication: participants interpret meanings through “syntactic (combinatorial), pragmatic (context dependent), and semantic (content-specific)” contexts. 48 He argues that air is often thick with communication, much of which is extraneous to the plants’ livelihood—what we might call “noise.” Plants can use more than twenty different types of chemical communication, and plant roots can produce more than one hundred thousand different chemicals. 49 Each of these chemicals can become a form of communication, and each chemical reacts with others to create novel signals.

The insight that plants actively interpret the world through the smell of airborne chemicals and the taste of herbivore saliva challenges conventional assumptions that plants are basically passive and inert. Scientists have also recently discovered that plants communicate not only through air but also through soil. Underground, they are especially reliant on their fungal partners. In these underground forms of communication, networks of fungal hyphae relay messages, sharing information between species. The older understanding of fungal mycorrhizae was that it was a connection between one mycelium and one plant, which moved water and nutrients back and forth. Newer understandings reveal a vast underground communication network, connecting many different species of trees and fungi, and that it not just circulates water and food but also plays an important role in plant communication. These signals greatly assist forest trees in alerting each other to impending insect damage and drought; this information is vital to maintaining a healthy forest in a dynamic world.

researchers found that multiple species of fungi did not attach only to a single tree but that they stitched multiple trees together into a network.

To explore the lives of fungi beyond a semiotic-only frame, I dove into the mycological literature to learn about how fungi interpret and interact in various diverse relationships: with tree roots, bacteria, a wide range of other fungi, underground insects like nematodes, and aboveground ones like sciarid flies. To view such diverse bodies in relationship can help move us beyond a focus on how organisms think—a semiotic-only approach—toward an understanding of how organisms live, how their bodies are engaged in many interactions, such as having sex and dying, eating and killing.

Fungi can also take over plant morphology and behavior, creating “zombie plants” that transform plant bodies through fungal action. Likely the most common example is huitlacoche (the Indigenous Nahuatl term from Latin America), known in English as “corn smut,” for this fungus grows on corn seeds, inducing them to grow into huge and almost comical shapes, which become filled with spores. 72

mushrooms, like animals and plants, are semiotic beings, creating signals and interpreting those they pick up from others. Fungi are also more than semiotic; they do more than think and communicate; like all organisms, they are embodied in their world-making. Underground or within other substrates like wood, mycelia are constantly seeking food and mates, dealing with disease and predation, deciding where to explore and when, if at all, to knit themselves together to make the mushroom that humans—and many others—might notice and come to find.

(1) all species have their own unique worlds that are informed by their bodies and their perception capacities, (2) all species must interpret their perceptions, and (3) there is a gap between perception and the world.

The recognition that our nervous system (compared to a housefly’s, for example) affects how we experience action, and therefore time, is surprising to many. It shows that we don’t experience the world as it is, but only as it is experienced in our specific body. We are compelled, in turn, to recognize that there is a great diversity of bodies, and thus a great diversity of ways of reckoning the world.

Uexküll offers us a sense of situated time, which exists only through the experiences of particular embodied organisms.

Uexküll’s work fostered the sensibility that other beings have their own ways of knowing the world, and from this, their own forms of communication. By adopting a model that moves beyond “the five senses,” and that attends to registers beyond human capacities, we can begin to learn what other species are saying. 81

For organisms to survive as a species, they must connect their lives with the lives of others—as predators, prey, and parasites; as flowers and pollinators; as sources of spores and agents of the spores’ dispersal; as coinhabitants.

Matsutake do not just exist in the world for humans as an object of the hunt, a commodity in the basket, and a meal on a plate; rather, they are living beings carrying out their own life projects, with specific forms of liveliness.

Matsutake fruit in response to a series of cold snaps in the fall, influenced more by the temperature of the soil than the temperature of the air.

fungal perception and communication are largely a chemical affair,

The chemical qualities of matsutake provide signals that travel through the air and soil and are detected by plants, animals, and fungi among others, luring in some species and likely repelling others. 13

A matsutake spore can germinate and grow into mycelium, but unless it finds another of a different mating type and exchanges its genes, it cannot produce mushrooms that can, in turn, make spores and spread through the air to new places.

matsutake mycelia can make relations with different plants to exchange minerals and water for photosynthetic sugars; indeed, they must.

Allotropa’s presence always means the presence of matsutake mycelium; it is one of the only reliable visual signs, and one that can easily enter the human umwelt, which is more attuned to sight than to smell. When young, Allotropa’s stalk is red with white stripes in a beautiful candy-stripe pattern, and it contains small white flowers that have a red center. The fact that it has no green is a bit of a giveaway that it does not create food from the sun; Allotropa eats from others, matsutake’s own water and minerals as well as the sugars of the mushroom’s life partners, the trees. Allotropa stalks are often eaten by animals when the plant is growing, but after death its stalks can persist for three years, making it a long-lasting sign of matsutake’s underground presence.

we might see how matsutake, like all forms of life, are always performing in relationship to both living and not-living others. Their performances include all the many acts required to stay alive: finding new sources of food and water; mediating attacks from bacteria, insects, and others; exchanging nutrients with trees; and growing and dying. As well, to carry on the next generation, the fungi actively lure in insects, mammals, or birds to carry their spores to new realms or propel them powerfully into swirling currents of air. Most of these actions are largely imperceptible to human umwelten because mushrooms often move too slowly for humans to notice. Time-lapse videos reveal mushrooms as active and moving subjects that we do not see as in motion with our limited perception and patience: popping into the air, unfurling their cap, and ejecting their spores. More difficult to see in underground terrain, slithering hyphae explore, drink up drops of water, and drill into grains of sand for their nutritious minerals.

One might imagine that as soon as a matsutake is severed from its network of underground mycelia, it dies and becomes a passive object under human regimes of mastery and control. But the mushroom is still alive, just weakening over time. It continues inhaling oxygen and exhaling carbon dioxide long after it is detached from the ground. That is part of the reason why mushrooms are not supposed to be stored in plastic bags: they might suffocate for lack of oxygen.

Previously, I had imagined the decay of vegetables or fungi as a passive or inevitable phenomenon, mainly because they were cut from their feeding structures. This is because I had failed to see how it was precisely the liveliness of bacteria (especially their actions of breaking down animal and fungal bodies) that was creating this process. 10 Thus, it is not only the Japanese desire for fresh matsutake but also some of the qualities of matsutake’s own world-making—such as the cluster of insects and bacteria that seek out these mushrooms to make worlds together—that compel the contours of Yi actions that make up this fast-paced, ice-pack-cooled, and highly attentive trade in these precious fungi.

those like Uexküll who presumed that all beings actively perceive and interpret the world, and do so with senses that we have yet to imagine. Yi experiments, however, also showed me a potential weakness in understanding the umwelt as a fixed sensory capacity; the Yi mushroom hunters I talked with saw insects as actively learning and coming up with new ways to act in the world in ways that mirrored their own improving abilities to find matsutake. They learned to attune their bodies to the places on the landscape that harbored matsutake, to poke at the mound that may belie the growing button underneath.

world-making is rarely just between two species but almost always involves forms of relationship with multiple kinds of liveliness all at once.

Compared to millet, barley helped Tibetan communities live another thousand meters higher, which dramatically expanded the places they could live. Barley allowed Tibetans to settle at altitudes up to thirty-four hundred meters, together enabling the world’s highest agricultural systems.

Barley began a focused relationship with people of the Fertile Crescent around ten thousand years ago, and somehow, along with millet, it ended up far away in the Sino-Tibetan borderlands around four thousand years ago.

Although so many scientists have worked for many years, spending many millions of dollars in the process, to encourage matsutake to make relations with pine trees and fruit in the lab or the forest, it seems that matsutake have refused. Despite many people’s efforts to domesticate matsutake, to make them reproduce and grow where we desire them to, the proposals for domestication we have made have all been rejected by the matsutake. This is despite human’s having learned about and provided for the needs of many other edible fungi, from shiitake to portabella to oyster mushrooms, mainly decomposers who eat dead matter, rather than mycorrhizal mushrooms that form relationships to living plants.

Over the past four thousand years, these landscapes have been made more by the efforts of yaks than by those of humans; yaks’ cumulative actions have changed the ecology, mainly through the plants they have eaten and the plants they have avoided. 38

matsutake have enabled them to build houses like never before, and to forge stronger connections throughout Tibetan territory and reclaim their place, once again, as masters of the caravan that connected them to the wider world more than a thousand years ago. Like before, they do not do so alone, but with intentional allies and unintentional participants in their lives, lived with and in tandem with yaks, barley, dogs, matsutake, and a number of others.

I, too, sometimes feel that the fungi are both literally enabling me to digest the world that I eat and at the same time metaphorically turning me into their substrate, their food, even as I advocate on their behalf.

the whole set of underlying assumptions and norms in the discipline of biology would be different, as the mycologist Alan Rayner has suggested, had it taken a symbiotic organism like a mycorrhizal matsutake mushroom and not a bounded individual, like a rat, as a model organism to generate the basic theories of life.

legal and economic systems that have been built on resourcism. Unraveling these centuries-old systems and building alternatives will take a lot of rethinking and a lot of work and will be met with deep resistance by the institutions that these systems benefit from.

we live in worlds created by other lively beings, whose actions far exceed the expectations of mechanistic theory. 14

As a form of life often engaged in intense symbiotic relations with others, fungi—existing as a lichen on a rock or tree, a mycorrhizal fungus living underground, or endophytic fungi living within plant leaves—help us challenge the premise that the world is full of individuals, rather than made and remade through relationships.

Fungal actions are a form of cumulative agency that helped enable plants to leave the oceans and join fungi in exploring forms of terrestrial life. Fungi helped push plants up into the atmosphere, where they could mine carbon from the air, sequestering some of it into their bodies and sharing some with their critical life partners. Aboveground, fungi are also eating plants, living and dead, and belowground they are eating rocks, as nutrients are once again cycled through living beings until they return again to the earth’s great oceanic sinks.

fungi’s wondrous alchemical abilities to turn xenobiotic (i.e., human-created and chemically novel) substances into food.

Fungi are necessary for us to live; they are critical life partners not only for mycorrhizal plants, but for all living beings, including us. This recognition allows us to see fungi not just as a commodity for exploitation but as a hidden source of life and a continuing wonder that challenges some of our animal-centric, anthropocentric, human exceptionalist, and resourcist ways of understanding.