Entangled Life

Fungi are one of life's kingdoms, a category every bit as broad and busy as the animals or the plants, and yet they are almost entirely overlooked. As you read these words, Sheldrake writes, fungi are "changing the way that life happens, as they have done for more than a billion years." They are eating rock and making soil, digesting pollutants and surviving in the vacuum of space, nourishing some plants while killing others, inducing visions, producing food and medicines, manipulating the behavior of animals, and shaping the very composition of the Earth's atmosphere. And still more than ninety percent of their species remain undocumented. We live inside a fungal world that we have only barely begun to see, which is why the deeper Sheldrake looks, the more he finds that the familiar world makes less and less sense without them.

The visible mushroom is a fraud of scale. Just as an apple is a small part of a much larger tree, a mushroom is only the fruiting body of a fungus, the place where its spores are made, and most fungi never bother to make one at all. Beneath and behind the mushroom lies the fungus proper: mycelium, a fine, branching, fusing web of tubular cells called hyphae. Mycelium, Sheldrake insists, is best understood "not as a thing but as a process: an exploratory, irregular tendency." Water, nutrients, and even waves of electrical activity flow through it. It is the fungal way of life, and it is a way of life that "challenges our animal imaginations."

Fungi are metabolic wizards, and "metabolism is the art of chemical transformation," a craft at which their range is rivaled only by bacteria. Using cocktails of enzymes and acids they break down lignin, rock, crude oil, polyurethane, and even the explosive TNT. A radiation-resistant species thrives inside the ruined Chernobyl reactor and actually grows toward radioactive particles, apparently harnessing radiation as an energy source in the way that plants harness sunlight. Their spores are the largest source of living particles in the air, some fifty megatons a year, roughly the weight of half a million blue whales, and they drift up into clouds where they help to trigger rain and snow. A few species discharge their spores explosively, accelerating ten thousand times faster than a space shuttle at launch.

Fungi are also, surprisingly, more closely related to animals than to plants, which is itself a good example of the "category mistake" researchers keep making with them. That deep kinship is precisely why fungal chemistry works so well inside our own bodies. Penicillin, cyclosporine (the drug that makes organ transplants possible), statins, antivirals, the cancer drug Taxol, alcohol, and psilocybin are all fungal gifts, and roughly sixty percent of industrial enzymes and fifteen percent of vaccines come from fungi as well. But this book is not a catalogue of uses. It makes a stranger and larger argument, that fungi trick us out of our preconceptions, and that in the process they can change the way we think.

Two frontiers of biology guide the whole inquiry. The first is the discovery of sophisticated, problem-solving behavior in brainless organisms. The poster child is the slime mold Physarum, an amoeba rather than a true fungus, which has no nervous system and yet can find the shortest path through a maze. Released onto a map of Greater Tokyo with oat flakes marking the cities, it grew a network almost identical to the actual rail system, and in other trials it faithfully recreated the US motorway network and the roads of the Roman Empire. Classical definitions of intelligence use humans as the yardstick, arranging life into a "great chain of intelligence" inherited from the ancient Greeks, and they place such organisms firmly at the bottom. But these creatures prompt us to rethink what it means to "solve problems," "communicate," "decide," "learn," and "remember." As those old hierarchies soften, Sheldrake suggests, "our ruinous attitudes toward the more-than-human world may start to change."

Sheldrake writes from inside the questions. A lifelong fungal obsessive who grew mushrooms in his bedroom and brewed alcohol as a teenager, he took his PhD studying mycorrhizal networks in the tropical forests of Panama, where he became entranced by a small blue flower called Voyria that had abandoned photosynthesis entirely and lived off the fungal web. He even took part in a clinical LSD study, lying in a hospital bed and wondering "what it was like to be a fungus" while picturing the soil as "a horizonless external gut." His aim is never to reduce fungi to "ticking, spinning, bleeping mechanisms." It is to let them "press against the limits of my understanding," and to give himself "permission to be amazed, and confused, by their entangled lives."

A truffle is a fungus with a problem. It is the underground fruiting body of a mycorrhizal fungus, and because its spores are packed away in the soil they cannot be caught by the wind or seen by any animal. Its solution is smell. To be found at all, a truffle must be pungent enough to penetrate the soil, distinctive enough to stand out amid a whole forest's worth of competing scents, and delicious enough that an animal will dig it up, eat it, and carry its spores away in its feces. A truffle's aroma, Sheldrake writes, is therefore "an evolutionary portrait in scent of animal fascination," a depiction of animal tastes refined over hundreds of thousands of years and worth as much as twelve thousand euros a kilogram.

Smell is the door through which we can enter the fungal world, because fungi live "bathed in a rich field of chemical information." The human nose can distinguish well over a trillion odors, far more than the millions of colors our eyes can see. But a fungus has no nose and no brain. Instead its entire surface is chemically sensitive, so that "a mycelial network is one large chemically sensitive membrane." A molecule binding anywhere on it can trigger a signaling cascade that changes the fungus's behavior. To smell a truffle, then, is to be briefly included in the chemical ecology by which fungi conduct so much of their lives.

Sheldrake goes truffle-hunting in the hills near Bologna with two rival hunters, Paride, who trains his dog Kika through play, and Daniele, who trains his dog through hunger, and later in Oregon with the truffle scientist Charles Lefevre. Truffles, he learns, "bring out the dark side of people," since prized forests are poached, trained dogs worth thousands of euros are stolen, and in 2010 a French farmer shot a thief dead. The lure runs deep and wide. Bears and elk dig for matsutake, some orchids mimic the very scent of a mushroom to fool the flies that pollinate them, orchid bees blend fungal compounds into the perfumes they spend a lifetime assembling to court their mates, and agarwood, which is a fungal infection of a tree, is worth more per gram than gold.

The chemical world is not always benign. Some fungi are subtle predators. Nematode-hunting fungi spend most of their lives as decomposers, but when food runs short and they sense worms nearby, they deploy an arsenal of traps: adhesive nets; hyphal nooses that inflate in a tenth of a second to snare a passing worm; toxic droplets (the common oyster mushroom paralyzes nematodes this way, then grows in through the mouth); and harpoon-like "gun cells." A fungus, faced with many options, must choose between them.

Imagine you could pass through two doors at once. It is inconceivable, and yet fungi do it all the time. Faced with a forked path, a hypha does not choose one way or the other; it branches and takes both. Watch its tips explore a microscopic maze and "one tip becomes two, becomes four, becomes eight, yet all remain connected in one mycelial network." Is the organism singular or plural? Sheldrake finds himself "forced to admit that it is somehow, improbably, both." Mycelium, he writes, is "ecological connective tissue, the living seam by which much of the world is stitched into relation," running through soil and ocean sediments, along coral reefs, through bodies both alive and dead, into rubbish dumps and floorboards, and across the canvases of old master paintings hanging in museums.

Lynne Boddy, a microbial ecologist at Cardiff, has spent decades watching mycelium forage. Grow a wood-rotting fungus from a single block of wood and it spreads outward in every direction as a fuzzy exploratory disc. Let it find a second block, and the whole network transforms itself, withdrawing the fruitless links and thickening the one connection that leads to food, "completely remodeling itself" in the process. Move the original block away and the fungus grows back toward the place where the new block had been, which suggests that it possesses a kind of directional memory. Boddy has even grown mycelium into the shape of Britain, with blocks of wood standing in for the cities: "the fungi grew out and made the motorway network. You could see the M5, M4, M1, M6."

How does one part of a network "know" what a distant part is doing? A mycelial network has no head and no brain. "Fungi, like plants, are decentralized organisms. There are no operational centers, no capital cities, no seats of government. Control is dispersed," so that "mycelial coordination takes place both everywhere at once and nowhere in particular." A single fragment can regenerate the whole, which means that one mycelial individual, "if you're brave enough to use that word," is potentially immortal. The Swedish mycologist Stefan Olsson, studying a bioluminescent fungus, once watched a wave of light sweep across a network in seconds, far too fast to be carried by any chemical signal. Borrowing a moth-brain neuroscience rig, he replaced the moth brains with living mycelium and found what almost no one expected: hyphae fire electrical impulses, much as nerve cells do. Lay a block of wood on the network and the firing rate doubles. Lay down an inedible plastic block of the same size and weight, and nothing at all happens.

And a network with no eyes can still be exquisitely sensitive. The Nobel biophysicist Max Delbrück called the fungus Phycomyces "the most intelligent" of the simple multicellular organisms, since its fruiting stalks detect light as faint as that of a single star and are only dazzled by full sun, a sensitivity that rivals the human eye. It also performs a strange "avoidance response," bending away from a nearby object without ever touching it, an enigma that decades of study have failed to solve. Most fungi sense light in color, using the same opsin pigments found in animal eyes, along with temperature, moisture, the texture of a surface (down to grooves three times shallower than the tracks on a CD), gravity, and electrical fields. "Fungal lives are lived in a flood of sensory information," and it is integrated not in a brain but across the hyphal tips, which the Darwins, writing about root tips in 1880, likened to "the brain of one of the lower animals." Where the network needs to move water or nutrients quickly, it builds cords, pipelines of bundled hyphae that can run for hundreds of meters, and one dry-rot fungus was found feeding at a rotting floor and fruiting in an oven eight meters away.

Is any of this "intelligence"? The word's Latin root means "to choose between," and Darwin took a pragmatic line, holding that intelligence is "how efficient a species becomes at doing the things they need to survive." Complex information processing, it turns out, is not confined to brains at all. A flatworm retains a memory even after its head has been cut off and regrown, and most of an octopus's nerves live not in its brain but in its tentacles, which taste and grasp entirely on their own. "A dynamic and responsive network is all that's needed." Mycelium may in fact be one of the oldest such networks, since in 2017 fossilized filaments that "touch and entangle each other" were found in ancient lava flows and dated to 2.4 billion years ago, more than a billion years before fungi were thought to have existed at all.

Sheldrake reaches for music to describe it. In the Aka recording "Women Gathering Mushrooms," each woman sings a different melody as she wanders the forest, and though no voice leads and none surrenders its identity, "yet a form emerges." Mycelium, he writes, "is polyphony in bodily form." And it is never static. Hyphae grow only at their tips, laying down fresh material like the artist Francis Alÿs trailing blue paint behind him through a city, so that the growing tip is the present moment while the winding network behind it is a map of the fungus's history. As the geneticist William Bateson observed, organisms are "really systems through which matter is continually passing," which is exactly why all life-forms, Sheldrake insists, "are in fact processes not things."

In 2016, a spacecraft returned from the International Space Station carrying, beneath the astronauts' seats, a box of lichens that had spent a year and a half exposed to open space, drenched in unfiltered cosmic rays and cycling from −120°C to +120°C every single day. Most of them survived, and lichens are among the only organisms that can. But their real strangeness is closer to home. Since the nineteenth century, lichens have "provoked fierce debate about what constitutes an autonomous individual," and the closer we look at them the stranger they seem, and the more they dissolve our very concept of the self.

In 1869 the botanist Simon Schwendener proposed a scandalous idea, that a lichen is not one organism at all but two, a fungus and an alga (or sometimes a photosynthetic bacterium) living together. The fungus builds the body and gathers minerals, while the photosynthetic partner harvests light to make sugars, and together they thrive in places where neither could survive alone. Fellow lichenologists were appalled, one of them spluttering "Who ever before heard of such a thing?", and Beatrix Potter herself wrote, "we do not believe in Schwendener's theory." The threat cut to the very shape of life. Darwin's tree of life was made of branches that diverge, forking apart over time, and here instead were branches converging, two distant lineages fusing into a single body. To name this strange new kind of relationship, Albert Frank coined a word in 1877: symbiosis.

Lichens became "a gateway organism to the idea of symbiosis," and symbiosis went on to rewrite the history of life itself. In the 1960s Lynn Margulis argued, against fierce opposition that saw her paper rejected fifteen times, that the complex eukaryotic cell arose by endosymbiosis. An ancient cell engulfed a bacterium, which stayed on to become the mitochondrion, the cell's power plant, and plants later acquired photosynthetic bacteria that became their chloroplasts. "All complex life that followed, human life included, was a story of the long-lasting intimacy of strangers." Around the same time, Joshua Lederberg showed that bacteria trade genes horizontally, acquiring traits "ready-made" without inheriting them from a parent at all. Both discoveries told the same startling truth, that branches of the tree of life which had diverged for eons can converge again inside a single body.

Follow this logic all the way down and the individual comes apart in your hands. You cannot be defined anatomically, since you are made of more microbial cells than the cells you would call "your own." You cannot be defined developmentally, since your body's growth is steered in part by your symbionts. You cannot be defined genetically, since your mitochondria carry their own genome, at least eight percent of the human genome came from viruses, and mothers and fetuses swap cells in the womb to become "chimeras." You cannot even be defined immunologically, since your immune system seems built to enable microbial colonization rather than simply to repel invaders. Researchers use the word holobiont, from the Greek for "whole," for an assemblage of organisms that behaves as a single unit. It is no utopia, since "collaboration is always a blend of competition and cooperation." But the conclusion of one landmark paper is unambiguous.

The most inventive manipulators of animal behavior are fungi that live inside insects. The best-studied is Ophiocordyceps unilateralis, which hijacks carpenter ants. An infected ant loses its instinctive fear of heights, leaves the nest, and climbs a plant, and then, at a height of exactly twenty-five centimeters, oriented to the sun, at noon, it clamps its jaws around a leaf vein in what is known as a "death grip." Mycelium stitches its feet to the surface, digests its body, and sprouts a stalk from its head that showers spores on the ants passing below. Ninety-eight percent of the time the ant bites down on a major vein. Yet when David Hughes reconstructed the fungus inside the ant, he found that it filled as much as forty percent of the ant's body mass while remaining entirely absent from the brain. It controls the ant chemically, from a distance, as "a fungus in ant's clothing."

Which brings us to the fungi that manipulate our minds. Psilocybin, the active compound in "magic" mushrooms, is at once a psychedelic, a word meaning "mind-manifesting," and an entheogen, a substance that elicits "the divine within." Humans have wrapped these mushrooms in ritual since antiquity, and the Aztecs called them "flesh of the gods." Sheldrake takes part in a clinical LSD study, wrestling with a questionnaire that asks him to rate, on a scale of one to five, "your experience of pure Being" and "your sense of fusion into a larger whole." These are qualities rather than quantities, and "yet science deals in quantities." The mushrooms confound our concepts, he realizes, "including the most fundamental concept of all, that of our selves."

Since the 2000s, rigorous trials have confirmed what traditional cultures long knew. In two 2016 studies, terminal-cancer patients suffering depression, anxiety, and existential distress were given a single dose of psilocybin. Eighty percent showed substantial, lasting relief; more than seventy percent rated the session among the five most meaningful experiences of their lives, comparing it to the birth of a child. What changed was a "movement from feelings of separateness to interconnectedness." How can one experience heal so durably?

Brain scans revealed the mechanism, and it comes as a surprise. Psilocybin does not rev the brain up. Instead it quiets one specific system, the default mode network (DMN), the "corporate executive" that keeps order and hums away whenever we self-reflect or ruminate. Shut down the DMN and "the brain is let off the leash," so that connectivity explodes and regions which never normally speak to one another light up together. Aldous Huxley called ordinary consciousness a "reducing valve," and psilocybin opens it. The people who experienced the greatest loss of self, the state known as "ego dissolution," were the ones whose DMN had quieted the most.

Terence McKenna went further still, proposing the "stoned ape" hypothesis, the idea that psilocybin ignited the first flickerings of human self-reflection, language, and spirituality back in the Paleolithic, so that "mushrooms were the original tree of knowledge." The evidence, a possible mushroom-deity painted into the 9,000-year-old Tassili rock art of the Sahara, is ambiguous, and "as with most origin stories it is difficult to prove either way." But as Sheldrake notes, "the absence of evidence does not provide evidence of absence," and the philosopher William James long ago warned that "no account of the universe in its totality can be final which leaves these other forms of consciousness quite disregarded."

Did psilocybin evolve for this? Probably not, and certainly not for us, since it arose some 75 million years before there were any humans, in fungi that live in dung and rotting wood alongside the insects that "eat or compete" with them. But once humans arrived, the mushroom's fortunes changed, because we can barely overdose on it and we have carried it around the world by seeking it out. If a fungus could wear our minds and enjoy "splashing around in our consciousness," Sheldrake asks, what would we expect to see? "Songs sung about mushrooms, statues of mushrooms, paintings of mushrooms, ceremonies built around the celebration of mushrooms… and people like Terence McKenna who claim to be able to speak English for fungi."

Roughly five hundred million years ago, green algae hauled themselves out of the water and onto a scorched, soilless land where the nutrients were still locked away in solid rock. They had no roots, no way to store water, and no way to mine minerals. How did they manage the passage? On this question, Sheldrake writes, "one piece of academic consensus stands out," which is that they could only do it "by striking up new relationships with fungi." Those alliances became what we now call mycorrhizal relationships, from the Greek words for fungus (mykes) and root (rhiza). Today more than ninety percent of plants depend on them, which makes the partnership "a more fundamental part of planthood than fruit, flowers, leaves, wood, or even roots."

The deal is elegant. Plants can do something that fungi cannot, namely photosynthesis, packing sunlight and air into energy-rich sugars and lipids. Fungi can do something that plants cannot, foraging the dark, textured "rotscape" of the soil for water and scarce minerals. So the two of them trade, with the plant feeding the fungus carbon and the fungus feeding the plant its nutrients. "By partnering, plants gain a prosthetic fungus, and fungi gain a prosthetic plant." Inside a root the two clasp each other in structures called arbuscules, which means "little trees," and it is here that the exchange actually takes place.

This ancient trade did nothing less than shape the planet's climate. In the Devonian, as fungus-fed plants boomed and grew from ankle-height to thirty-meter trees, mycorrhizal fungi mined the phosphorus and minerals that let them flourish; the plants drew down carbon dioxide, which was buried as they died. Atmospheric CO₂ fell by ninety percent, cooling the whole Earth. When the researcher Katie Field put mycorrhizal "symbiotic efficiency" into a climate model, she could shift the entire global climate just by turning it up or down. "Our results suggest that mycorrhizal relationships have played a role in the evolution of much of life on Earth."

The partnership even reaches your dinner plate. Grow the same strawberry with different fungal partners and you change its flavor, its juiciness, and even how attractive its flowers are to bees, and different fungi alter the oils in basil, the sweetness of tomatoes, the medicinal compounds in echinacea, and the crumb of a loaf of bread. And the trade is no simple handshake. Toby Kiers, tracing carbon and phosphorus with radioactive labels, found that neither partner fully controls the exchange, since plants send more carbon to the fungi that deliver more phosphorus, and fungi that receive more carbon deliver more phosphorus back in turn. Expose one fungus to an unequal supply of phosphorus and it begins to play the market, adopting a strategy of "buy low, sell high" and hauling nutrients from where they are abundant and cheap toward where they are scarce and dear. "Same fungus, same plant, different setting, different outcome."

In the shaded forests of the Pacific Northwest, ghostly white plants push up through the fir needles. They have no leaves and no green at all, because Monotropa, the "ghost pipe," has abandoned photosynthesis entirely. So where does its energy come from? It can only come from other plants, pumped to it through a shared fungal network in the soil. Ghost pipes are living proof that plants are wired together underground. As the botanist David Read showed in 1984, carbon really does pass between plants through fungal channels, and in 1997 Suzanne Simard proved it in a living forest by tracing carbon as it flowed from birch to fir. Read gave the phenomenon its famous name, printed on the cover of Nature, and called it the wood wide web.

It is more than a metaphor. "It is the difference between having twenty acquaintances," Sheldrake writes, "and having twenty acquaintances with whom one shares a circulatory system." When Kevin Beiler genetically fingerprinted every tree and fungus in a plot of Douglas fir, he found that the network was not woven evenly at all. Young trees had only a few links, while the ancient trees were richly connected hubs, and the busiest single tree was linked to forty-seven others. This is a "scale-free" pattern, the same one found in the World Wide Web, in air-travel routes, and in the neurons of a brain, where a few well-connected hubs let you cross the whole network in a handful of steps. That very structure makes forests resilient, and it also makes them dangerously vulnerable to the targeted removal of their biggest and oldest trees.

What flows through the web? Carbon, certainly, and one study measured 280 kilograms of it per hectare moving between trees, enough to power a home for a week, but also nitrogen, phosphorus, water, hormones, and even warnings. When Lucy Gilbert and David Johnson let aphids attack a single bean plant, its neighbors, connected to it only by a shared fungal network, ramped up their chemical defenses and summoned parasitic wasps before the aphids had ever reached them. But the same web can carry poison just as easily, and toxins leaching from walnut leaves travel a "fungal fast lane" to stunt rival plants. The wood wide web is no utopia. It is a "complex amplifier" of interactions, cooperative and competitive at one and the same time.

This is the book's crucial correction. In nearly every story of the wood wide web, the plants are the heroes and the fungi are mere "plumbing." But fungi are not passive cables at all, for they solve spatial problems, pump resources in any direction, reward and punish, and hoard and share. Shared mycorrhizal networks are complex adaptive systems, "ongoing happenings rather than things," in the same family as brains, cities, termite colonies, and financial markets. We keep reaching for metaphors, wondering whether this is socialism in the soil, or a forest stock exchange, or mother trees nursing their seedlings, and each metaphor, Sheldrake warns, quietly smuggles in our own politics. Perhaps the wiser path is Toby Spribille's, to "let the lichen be a lichen," and to let these webs "be questions, rather than answers known in advance."

"We live and breathe in the space that decomposition leaves behind." If decomposition stopped tomorrow, Sheldrake writes, the planet would pile "kilometers deep in bodies," and yet from a fungal point of view that would simply be "an enormous heap of opportunities." Fungi are the great unmakers, and their supreme act of unmaking is the decomposition of wood. Wood is mostly lignin, the substance that is "what makes wood wood," a haphazard and tightly bonded matrix that almost nothing on Earth can digest. Almost nothing, that is, except the white rot fungi, which crack it open with nonspecific enzymes that release a torrent of free radicals, a process of "enzymatic combustion" that amounts, fittingly, to a kind of radical chemistry. "Radical," Sheldrake notes, "has it right."

If fungi are appetite in bodily form, then our mess looks to them like a feast, and a growing movement of radical mycologists means to introduce them. Peter McCoy, an anarchist and self-taught mycologist, trained oyster mushrooms to digest used cigarette butts by weaning them off their usual food, at which point the fungus "learned," or rather remembered, dusting off a dormant enzyme, since many toxic pollutants resemble the very by-products of breaking down lignin. In mycoremediation, fungi break down crude oil, pesticides, TNT, plastics, and nerve agents, and Paul Stamets's collaborators once trained turkey tail and a psilocybin species to eat a component of VX gas. In mycofiltration, mats of mycelium strain heavy metals and E. coli from water. The catch is always that a dish is not an ecosystem, and as Sheldrake puts it, "the wine barrel is a contaminated ecosystem, and we're inside it."

None of this is new to nature. African Macrotermes termites have farmed white rot fungi in "fungus combs" inside towering mounds, structures Sheldrake calls "giant, externalized guts," for more than twenty million years, far longer than the genus Homo has existed. And Paul Stamets, the movement's tireless evangelist, may have found a way for fungi to save the honeybee, since extracts of wood-rotting fungi, which are rich in antivirals, cut deformed-wing virus in bees eighty-fold and another virus 45,000-fold. His eureka moment came from remembering bees feeding on the mycelium in his own woodpile decades earlier. As Sheldrake reflects, "somewhere deep in the psycho-spiritual compost heap of his dream world, Stamets metabolized an old radical mycological solution into a new one."

The fungi with the most intimate history with humans are yeasts, single cells that live on our skin and in our guts and that oversee "one of the most dramatic cultural transformations in human history." Yeast turns sugar into alcohol and carbon dioxide, and it may well have turned us from wandering foragers into settled farmers. The Neolithic transition, Sheldrake writes, "can be understood, at least in part, as a cultural response to yeast," because whether it was for bread or, as many scholars now believe, for beer, "in the preparation of either, humans feed yeast before they feed themselves." Fermentation is "domesticated decomposition," which is to say rot rehoused. You can lure it, but you can never coerce it. "In many ways, you might argue, yeasts have domesticated us."

Fungi have always defied our attempts to sort them. Linnaeus threw up his hands in 1751, declaring that "the order of Fungi is still Chaos, a scandal of art, no botanist knowing what is a Species and what is a Variety." Bacteria and fungi were classed as plants until the 1960s, and one modern mycologist has argued that we should abandon the concept of fungal species altogether. The Wassons split all human cultures into the mycophilic, meaning fungus-loving, and the mycophobic, meaning fungus-fearing, and Darwin's own daughter, Aunt Etty, hunted stinkhorns down in order to burn them "in the deepest secrecy… because of the morals of the maids." As Sheldrake notes, "the ways that we try to make sense of fungi often tell us as much about ourselves as the fungi that we try to understand."

Nowhere is that clearer than in the science of symbiosis, which "behaves like a prism through which our own social values are often dispersed." Is nature fundamentally competitive, or is it cooperative? For a century the dominant story mirrored industrial capitalism, a vision of "Nature, red in tooth and claw," and cooperation was kept "close to the margins of polite biological society." The great riposte came from the anarchist Peter Kropotkin in his 1902 book Mutual Aid, with its ringing instruction to "Don't compete! Practice mutual aid!" The first international symbiosis conference met in London in 1963, only six months after the Cuban Missile Crisis had brought the world to the edge of nuclear war, which was, its editors admitted, "no accident."

Our fungal entanglement runs in our very biology. Around ten million years ago, an ancestor we share with gorillas and chimps evolved a version of the alcohol-digesting enzyme ADH4 that was forty times more efficient, and the "drunken monkey hypothesis" holds that we love alcohol because our tree-dwelling ancestors followed the scent of yeast to the overripe, fermenting fruit on the forest floor. Sheldrake closes the chapter by fermenting the apples of Cambridge's clone of Newton's own apple tree, a myth "affirmed and denied at the same time," whose keeper refused to let him pick the fruit because "the apples have to be seen by the tourists to fall from the tree, to add verisimilitude to the myth." He brews the windfalls with their own wild yeast and names the cider Gravity, so that by the end he is "intoxicated with a story, comforted by it, constrained by it, dissolved in it."

As a child, Sheldrake built enormous piles of autumn leaves and buried himself in them, until, week by week, the piles shrank and the leaves at the bottom turned to soil. Where was the pile sinking to? His father proposed an experiment, a clear bottle of layered soil, sand, leaves, and worms, and over the following days the hard layers dissolved into one another. "Composers make pieces of music," his father explained. "These were decomposers, who unmake pieces of life. Nothing could happen without them." That single reversal, the discovery of arrows pointing in both directions at once, "changed the way I understood the world," and it grew in time into his lifelong fascination with fungi.

Out of this "compost heap of questions and fascinations," Sheldrake writes, "this book has composed itself. There have been so many questions, so few answers, and this feels exciting." Ambiguity no longer itches as it once did, and it is easier now "to resist the temptation to remedy uncertainty with certainty." He has become a go-between among far-flung fields, "sometimes carrying a few grains of sand into the soil, sometimes a few clumps of soil into the sand." The pile of questions is bigger than when he began, "and it smells just as mysterious." His parting line folds the reader into the fungal world for good.