4. MYCELIAL MINDS

There is a world beyond ours…That world talks. It has a language of its own. I report what it says. The sacred mushroom takes me by the hand and brings me to the world where everything is known…I ask them and they answer me.

—MARÍA SABINA

ON A SCALE of one to five—one being “not at all,” and five being “extreme”—how would you rate the sense of loss of your usual identity? How would you rate your experience of pure Being? How would you rate your sense of fusion into a larger whole?

I lay on my bed in the clinical-drug testing unit, toward the end of my LSD trip, and puzzled over these questions. The walls appeared to breathe gently, and I found it difficult to focus on the words on the screen. There was a soft murmuring around my stomach, and the willow trees outside swayed, green and vivid.

LSD, like psilocybin—the active ingredient in many species of “magic” mushrooms—is classified as both a psychedelic (or “mind-manifesting”) and an entheogen (a substance that can elicit an experience of “the divine within”). With effects ranging from auditory and visual hallucinations and dreamlike, ecstatic states to powerful shifts in cognitive and emotional perspective and a dissolving of time and space, these chemicals loosen the grip of our everyday perceptions, reach into our consciousness, and touch us somewhere deep. Many users report mystical experiences or a connection with divine beings or entities, a feeling of oneness with the natural world, and a loss of a neatly bounded sense of self.

The psychometric questionnaire I was struggling to complete had been designed to assess this kind of experience. But the more I tried to cram my sensations into a five-point scale on a page, the more confused I became. How can one measure the experience of timelessness? How can one measure the experience of unity with an ultimate reality? These are qualities, not quantities. Yet science deals in quantities.

I squirmed, took several deep breaths, and tried to approach the questions from a different angle. How do you rate your experience of amazement? The bed seemed to sway gently, and a school of thoughts scattered through my mind like startled minnows. How do you rate your experience of infinity? I could feel the scientific procedure groaning under the strain of what seemed to be an impossible task. How do you rate the loss of your usual sense of time? I succumbed to a fit of uncontrollable laughter—a common effect of LSD, I had been warned in a preparatory risk assessment. How do you rate the loss of your usual awareness about where you are?

I recovered from my laughter and looked up at the ceiling. Come to think of it, how had I ended up here? A fungus had evolved a chemical that had been used to make a drug. Quite by accident, this drug had been discovered to alter human experience. For seven decades or so, LSD’s peculiar effects on our minds had generated astonishment, confusion, evangelical zeal, moral panic, and everything in between. As it filtered through the twentieth century, it had left an indelible cultural residue that we still struggle to make sense of. I was lying in this hospital room as part of a clinical trial because its effects remained as bewildering as they had always been.

No wonder I was baffled. LSD and psilocybin are fungal molecules that have found themselves entangled within human life in complicated ways exactly because they confound our concepts and structures, including the most fundamental concept of all: that of our selves. It is their ability to pull our minds into unexpected places that has caused psilocybin-producing magic mushrooms to be enveloped within the ritual and spiritual doctrines of human societies since antiquity. It is their ability to soften the rigid habits of our minds that makes these chemicals powerful medicines capable of relieving severe addictive behaviors, otherwise incurable depression, and the existential distress that can follow the diagnosis of terminal illness. And it is their ability to modify the inner experience of our minds that has helped to change the way that the very nature of mind is understood within modern scientific frameworks. Yet why certain fungal species evolved these abilities remains a source of puzzlement and speculation.

I rubbed my eyes, rolled over, and plucked up the courage to look once more at the words on the screen. How do you rate your sense that the experience cannot be described adequately in words?

THE MOST PROLIFIC and inventive manipulators of animal behavior are a group of fungi that live within the bodies of insects. These “zombie fungi” are able to modify their host’s behavior in ways that bring a clear benefit: By hijacking an insect, the fungus is able to disperse its spores and complete its lifecycle.

One of the best-studied cases is that of the fungus Ophiocordyceps unilateralis, which organizes its life around carpenter ants. Once infected by the fungus, ants are stripped of their instinctive fear of heights, leave the relative safety of their nests, and climb up the nearest plant—a syndrome known as “summit disease.” In due course the fungus forces the ant to clamp its jaws around the plant in a “death grip.” Mycelium grows from the ant’s feet and stitches them to the plant’s surface. The fungus then digests the ant’s body and sprouts a stalk out of its head, from which spores shower down on ants passing below. If the spores miss their targets, they produce secondary sticky spores that extend outward on threads that act like trip wires.

Zombie fungi control the behavior of their insect hosts with exquisite precision. Ophiocordyceps compels ants to perform the death grip in a zone with just the right temperature and humidity to allow the fungus to fruit: a height of twenty-five centimeters above the forest floor. The fungus orients ants according to the direction of the sun, and infected ants bite in synchrony, at noon. They don’t bite any old spot on the leaf’s underside. Ninety-eight percent of the time, the ants clamp onto a major vein.

How zombie fungi are able to control the minds of their insect hosts has long puzzled researchers. In 2017, a team headed by David Hughes, a leading expert on fungal manipulative behaviors, infected ants with Ophiocordyceps in the lab. The researchers preserved the ants’ bodies at the moment of their death bite, sliced them into thin pieces, and reconstructed a three-dimensional picture of the fungus living within their tissues. They found that the fungus becomes, to an unsettling degree, a prosthetic organ of ants’ bodies. As much as forty percent of the biomass of an infected ant is fungus. Hyphae wind through their body cavities, from heads to legs, enmesh their muscle fibers, and coordinate their activity via an interconnected mycelial network. However, in the ants’ brains, the fungus is conspicuous by its absence. To Hughes and his team, this was unexpected. They anticipated that the fungus would have to be present in the brain to exert such fine control over the ants’ behavior.

Instead, the fungus’s approach appears to be pharmacological. The researchers suspect that the fungus is able to puppeteer the ants’ movements by secreting chemicals that act on their muscles and central nervous system even if the fungus does not have a physical presence in their brains. Exactly what chemicals these are isn’t known. Nor is it known whether the fungus is able to cut the ant’s brain off from its body and coordinate its muscle contractions directly. However, Ophiocordyceps is closely related to the ergot fungi, from which the Swiss chemist Albert Hofmann originally isolated the compounds used to make LSD, and is able to produce the family of chemicals that LSD derives from—a group known as “ergot alkaloids.” Inside infected ants the parts of the Ophiocordyceps genome responsible for the production of these alkaloids are activated, suggesting that they might have a role to play in the manipulation of ant behavior.

However they do it, these fungal interventions are remarkable by any human standard. After decades of research, and many billions of dollars of investment, the ability to regulate human behavior using drugs is anything but fine-tuned. Antipsychotic drugs, for example, don’t target specific behaviors; they just tranquilize. Compare this with the ninety-eight percent success rate of Ophiocordyceps in causing an ant not just to climb upward or perform its death bite—these always happen—but to bite onto the specific part of the leaf with the best conditions for the fungus to fruit. To be fair, Ophiocordyceps, like many zombie fungi, have had a long time to fine-tune their methods. The behaviors of infected ants don’t pass without a trace. Ants’ death grips leave distinctive scars on leaf veins, and fossilized scars push the origins of this behavior back into the Eocene epoch, forty-eight million years ago. It is likely that fungi have been manipulating animal minds for much of the time that there have been minds to manipulate.

I WAS SEVEN when I discovered that humans can alter their minds by eating other organisms. My parents took me and my brother to stay in Hawaii with a friend of theirs, the eccentric author, philosopher, and ethnobotanist Terence McKenna. His great passion was mind-altering plants and fungi. He had been a hashish smuggler in Bombay, a butterfly collector in Indonesia, and a psilocybin mushroom grower in Northern California. Now he lived in an offbeat bolt-hole called Botanical Dimensions, several kilometers up a potholed road on the slopes of the volcano Mauna Loa. He had set up the land in Hawaii as a forest garden, a living library of rare and not so rare psychoactive and medicinal plants harvested from many corners of the tropical world. To reach the outhouse, one had to walk along a winding trail through the forest, ducking under dripping leaves and lianas. A few kilometers down the road, streams of lava flowed into the sea and made it froth and boil.

McKenna reserved his greatest enthusiasm for psilocybin mushrooms. He had first eaten them while traveling in the Colombian Amazon with his brother, Dennis, in the early 1970s. In the years that followed, fueled by regular “heroic” doses of mushrooms, McKenna discovered a rare gift of the gab and flair for public speaking. “I realized that my innate Irish ability to rave had been turbo-charged by years of psilocybin mushroom use,” he recalled. “I could talk to small groups of people with what appeared to be electrifying effect about…peculiarly transcendental matters.” McKenna’s bardic musings—eloquent and widely broadcast—remain celebrated and denounced in more or less equal measure.

After a few days at Botanical Dimensions, I came down with a fever. I remember lying under a mosquito net, watching as McKenna ground up a preparation in a large pestle and mortar. I assumed it was a remedy for my sickness and asked what he was doing. In his zany metallic drawl, he explained that it was no such thing. This plant, like some types of mushroom, could make us dream. If we were lucky these organisms could even speak to us. These were powerful medicines that humans had used for a long time, but they could also be scary. He grinned a languorous smile. When I was older, he said, I could try some of the preparation—a mind-altering cousin of sage called Salvia divinorum, as it turned out. But not now. I was transfixed.

There are many examples of intoxication in the animal world—birds eat inebriating berries, lemurs lick millipedes, moths drink the nectar of psychoactive flowers—and it is likely that we have been using mind-altering drugs for longer than we have been human. The effects of these substances are “frequently inexplicable, and indeed uncanny,” wrote Richard Evans Schultes, a professor of biology at Harvard and a leading authority on psychoactive plants and fungi. “Without any doubt, [these compounds] have been known and employed in human experience since earliest man’s experimentation with his ambient vegetation.” Many have “strange, mystical and confounding” effects, and like psilocybin mushrooms, are intimately bound up within human cultures and spiritual practices.

A number of fungi have mind-altering properties. The iconic red-and-white-spotted mushroom Amanita muscaria, eaten by shamans in parts of Siberia, elicits euphoria and hallucinatory dreams. Ergot fungi induce a grisly portfolio of effects from hallucinations to convulsions to a sensation of unbearable burning. Involuntary muscle twitching is one of the primary symptoms of ergotism, and the ability of ergot alkaloids to induce muscle contractions in humans may mirror their role in ants infected by Ophiocordyceps. A number of the horrors depicted by the Renaissance painter Hieronymus Bosch are thought to have been inspired by the symptoms of ergot poisoning, and some hypothesize that the numerous outbreaks of “dancing mania” between the fourteenth and seventeenth centuries, in which hundreds of townspeople took to dancing for days without rest, were caused by convulsive ergotism.

The longest well-documented use of psilocybin mushrooms is in Mexico. The Dominican friar Diego Durán reported that mind-altering mushrooms—known as “flesh of the gods”—were served at the coronation of the Aztec emperor in 1486. Francisco Hernández, the physician to the King of Spain, described mushrooms that “when eaten cause not death but madness that on occasion is lasting, of which the symptom is a kind of uncontrolled laughter…There are others again which, without inducing laughter, bring before the eyes all kinds of visions, such as wars and the likeness of demons.” The Franciscan friar Bernardino de Sahagún (1499–1590) provided one of the most vivid accounts of mushroom use:

They ate these little mushrooms with honey, and when they began to be excited by them, they began to dance, some singing, others weeping…Some did not want to sing but sat down in their quarters and remained there as if in a meditative mood. Some saw themselves dying in a vision and wept; others saw themselves being eaten by a wild beast…When the intoxication from the little mushrooms had passed, they talked over among themselves the visions which they had seen.

Unequivocal records of mushroom consumption in Central America stretch back to the fifteenth century, but the use of psilocybin mushrooms in the region almost certainly predates this. Hundreds of mushroom-shaped statues have been found, dating from the second millennium BCE, and codices from before the Spanish conquest depict mushrooms being eaten and held aloft by feathered deities.

In McKenna’s view, human consumption of psilocybin mushrooms was an even more ancient phenomenon and lay at the root of human biological, cultural, and spiritual evolution. Evidence of religion, complex social organization, commerce, and the earliest art arises within a relatively short period in human history around fifty to seventy thousand years ago. What triggered these developments is not known. Some scholars attribute them to the invention of complex language. Others hypothesize that genetic mutations brought about changes in brain structure. For McKenna, it was psilocybin mushrooms that had ignited the first flickerings of human self-reflection, language, and spirituality, somewhere in the proto-cultural fog of the Paleolithic. Mushrooms were the original tree of knowledge.

Cave paintings preserved by the dry heat of the Sahara desert in southern Algeria provided McKenna with the most impressive evidence for ancient mushroom consumption. Dating from between 9000 and 7000 BCE, the Tassili paintings include a figure of a deity with an animal’s head and mushroom-like forms sprouting from its shoulders and arms. As our ancestors roamed “the mushroom-dotted grasslands of tropical and subtropical Africa,” McKenna conjectured, “the psilocybin-containing mushrooms were encountered, consumed and deified. Language, poetry, ritual, and thought emerged from the darkness of the hominid mind.”

There are many variations on the “stoned ape” hypothesis, but as with most origin stories it is difficult to prove either way. A rich bloom of speculation proliferates around psilocybin mushrooms wherever they are eaten. Surviving texts and artifacts are patchy, and almost always ambiguous. Does the Tassili painting represent a mushroom deity? It might. Then again, it might not. The evidence from Neanderthal tooth plaque, the Iceman, and other well-preserved corpses provides proof that human knowledge of mushrooms as food and medicine stretches back many thousands of years. However, none of these bodies have been found with traces of psilocybin mushrooms. A number of primate species are known to seek out and consume mushrooms as food, and there are anecdotal accounts of primates consuming psilocybin mushrooms, but no well-documented instances. Some suspect that ancient Eurasian populations used psilocybin mushrooms as part of religious ceremonies, the best-known being the Eleusinian Mysteries, secretive rites celebrated in ancient Greece and thought to have been attended by many luminaries, including Plato. But once again there’s no definitive record. And yet the absence of evidence does not provide evidence of absence. This makes speculation inevitable. And McKenna, turbo-charged by psilocybin, was a master of the art.

OPHIOCORDYCEPS HAS BEEN the inspiration for at least two fictional monsters: the cannibals in the video game The Last of Us and the zombies in the book The Girl with All the Gifts. It sounds like a strange but true special case—one of evolution’s left-field outcomes. However, Ophiocordyceps is just one well-studied example. This type of manipulative behavior is not exceptional. It has evolved multiple times across the fungal kingdom in unrelated lineages, and there are numerous non-fungal parasites that are also able to manipulate the minds of their hosts.

Fungi use a variety of approaches to tweak the biochemical dials that regulate their hosts’ behavior. Some use immunosuppressants to override the insects’ defensive responses. Two such compounds have found their way into mainstream medicine for these very reasons. Cyclosporine is an immunosuppressant drug that makes organ transplants possible. Myriocine has become the blockbuster multiple sclerosis drug fingolimod and was originally extracted from fungus-infested wasps that are eaten in parts of China as a nostrum for eternal youth.

In 2018, researchers at the University of California at Berkeley published a study documenting a startling technique used by Entomophthora, a mind-manipulating fungus that infects flies. There are parallels with Ophiocordyceps. Infected flies climb up high. When they extend their mouthparts to feed, a glue produced by the fungus sticks them to whatever surface they touch. When the fungus has consumed the fly’s body, starting with the fatty parts and finishing with the vital organs, it pushes a stalk out of the fly’s back and ejects spores into the air.

The researchers were surprised to find that the Entomophthora fungus carries around a type of virus that infects insects, not fungi. The lead author of the study reported it to be “one of the whackiest discoveries” of his time in science. What’s whacky is the implication: that the fungus uses the virus to manipulate the mind of insects. It’s still a hypothesis, but it’s plausible. A number of related viruses specialize in modifying insect behavior. One such virus is injected by parasitic wasps into ladybirds, which tremble, remain rooted to the spot, and become guardians for the wasp’s eggs. Another similar virus makes honeybees more aggressive. By harnessing a mind-manipulating virus, the fungus wouldn’t have to evolve the ability to modify the mind of its insect host.

One of the more surprising twists in the story of zombie fungi came from research carried out by Matt Kasson and his team at West Virginia University. Kasson studies the fungus Massospora, which infects cicadas and causes the rear third of their bodies to disintegrate, allowing it to discharge its spores out of their ruptured back ends. Infected male cicadas—“flying saltshakers of death,” in Kasson’s words—become hyperactive and hypersexual despite the fact that their genitals have long since crumbled away, a testament to how expertly the fungus is able to arrange their deterioration. Within their decaying bodies, their central nervous systems remain intact.

In 2018, Kasson and his team analyzed the chemical profile of the “plugs” of fungus that sprout from the cicadas’ broken bodies. They were amazed to find that the fungus produced cathinone, an amphetamine in the same class as the recreational drug mephedrone. Cathinone naturally occurs in the leaves of khat (Catha edulis), a plant cultivated in the Horn of Africa and the Middle East, which has been chewed for centuries by humans for its stimulant effects. Cathinone had never before been found outside of plants. More astonishing was the presence of psilocybin, which was one of the most abundant chemicals in the fungal plugs—although one would have to eat several hundred infected cicadas to notice any effect. It’s surprising because Massospora sits in an entirely different division of the fungal kingdom from the species known to produce psilocybin, separated by a gulf of hundreds of millions of years. Few suspected that psilocybin would show up in such a distant part of the fungal evolutionary tree, playing a behavior-modifying role in a very different story.

What exactly is Massospora able to accomplish by drugging its hosts with a psychedelic and an amphetamine? The researchers presume that these drugs play a part in the fungal manipulation of the insect. But how, exactly, isn’t known.

ACCOUNTS OF PSYCHEDELIC experiences frequently involve hybrid beings and interspecies transformations. Myths and fairy tales, too, are full of composite animals from werewolves and centaurs to sphinxes and chimeras. Ovid’s Metamorphoses is a catalogue of transformations from one creature into another and even includes a land where “men grew from rainswept fungus.” In many traditional cultures, it is believed that composite creatures exist, and that the boundaries between organisms are fluid. The anthropologist Eduardo Viveiros de Castro reports that shamans in indigenous Amazonian societies believe they can temporarily inhabit the mind and body of other animals and plants. Among the Yukaghir people in northern Siberia, writes the anthropologist Rane Willerslev, humans dress and behave like elk when they hunt elk.

These accounts seem to stretch the limits of biological possibility and are rarely taken seriously within modern scientific circles. However, the study of symbiosis reveals that life is full of hybrid life-forms, such as lichens, which are composed of several different organisms. Indeed, all plants, fungi, and animals, including ourselves, are composite beings to some extent: Eukaryotic cells are hybrids, and we all inhabit bodies that we share with a multitude of microbes without which we could not grow, behave, and reproduce as we do. It’s possible that many of these beneficial microbes share some of the manipulative abilities of parasites like Ophiocordyceps. A growing number of studies have made a link between animal behavior and the trillions of bacteria and fungi that live in their guts, many of which produce chemicals that influence animal nervous systems. The interaction between gut microbes and brains—the “microbiome-gut-brain axis”—is far-reaching enough to have birthed a new field: neuromicrobiology. However, mind-manipulating fungi remain some of the most dramatic examples of composite organisms. In the words of Hughes, an infected ant is a “fungus in ant’s clothing.”

It’s possible to make sense of this sort of shape-shifting within a scientific framework. In The Extended Phenotype, Richard Dawkins points out that genes don’t just provide the instructions to build the body of an organism. They also provide instructions to build certain behaviors. A bird’s nest is part of the outward expression of the bird’s genome. A beaver’s dam is part of the outward expression of a beaver’s genome. And an ant’s death grip is part of the outward expression of the genome of Ophiocordyceps fungi. Through inherited behaviors, Dawkins argues, the outward expression of an organism’s genes—known as its “phenotype”—extends into the world.

Dawkins was careful to place “stringent requirements” on the idea of the extended phenotype. Although it is a speculative concept, he dutifully reminds us, it is a “tightly limited speculation.” There are three crucial criteria that have to be met to prevent phenotypes becoming too extended (if a beaver’s dam is an expression of the beaver’s genome, then what about the pond that forms upstream of the dam, and the fish that live in the pond, and…).

First, extended traits must be inherited—Ophiocordyceps, for example, inherits a pharmacological talent for infecting and manipulating ants. Second, extended traits must vary from generation to generation—some Ophiocordyceps are more precise manipulators of ant behavior than others. Third, and most important, variation must affect an organism’s ability to survive and reproduce, a quality known as its “fitness”—Ophiocordyceps that can more precisely control their insect’s movements are better able to spread their spores. Provided these three conditions are met—traits must be inherited, they must vary, and their variation must affect an organism’s fitness—extended characteristics will be subject to natural selection and will evolve in an analogous way to their bodily characteristics. Beavers that make better dams are more likely to survive and pass on the ability to make better dams. But human dams—or any human building for that matter—don’t count as part of our extended phenotype because we aren’t born with an instinct to build specific structures that directly affect our fitness.

Summit disease and the death grip, on the other hand, fully qualify as fungal behaviors, not ant behaviors. The fungus doesn’t have a twitchy, muscular, animal body with a centralized nervous system or an ability to walk, bite, or fly. So it commandeers one. It is a strategy that works so well that it has lost the ability to survive without it. For part of its life, Ophiocordyceps must wear an ant’s body. In nineteenth-century spiritualist circles, human mediums were understood to become possessed by the spirits of the dead. Lacking their own bodies or voices, spirits were said to borrow a human body to speak and act through. In an analogous way, mind-manipulating fungi possess the insects that they infect. Infected ants stop behaving like ants and become mediums for the fungi. It is in this sense that Hughes referred to an ant infected with Ophiocordyceps as a “fungus in ant’s clothing.” Impelled by the fungus, the ant veers off the tracks of its own evolutionary story—tracks that guide its behaviors and relationships to the world and other ants—and onto the tracks of the evolutionary story of Ophiocordyceps. In physiological, behavioral, and evolutionary terms, the ant becomes fungus.

OPHIOCORDYCEPS AND OTHER insect-manipulating fungi have evolved a remarkable ability to cause harm to the animals they influence. Psilocybin mushrooms, as a growing number of studies report, have evolved an astonishing ability to cure a wide range of human problems. In one sense, this is news: Since the 2000s, rigorously controlled trials and the latest brain-scanning techniques have helped researchers interpret psychedelic experiences using the language of modern science—it was this new wave of psychedelic research that brought me into the hospital for the LSD study. These recent findings have broadly confirmed the opinions of many researchers in the 1950s and ’60s, who came to regard LSD and psilocybin as miracle cures for a wide range of psychiatric conditions. In another sense, however, much of the research that has taken place in modern scientific contexts broadly confirms what is well-known to the traditional cultures who have used psychoactive plants and fungi as medicines and psycho-spiritual tools for an unknowably long time. From this point of view, modern science is simply catching up.

Many recent findings are extraordinary by the standards of conventional pharmaceutical interventions. In 2016, two sister studies at New York University and Johns Hopkins University administered psilocybin alongside a course of psychotherapy to patients suffering from anxiety, depression, and “existential distress” following diagnoses with terminal cancer. After a single dose of psilocybin, eighty percent of patients showed substantial reductions in their psychological symptoms, reductions that persisted for at least six months after the dose. Psilocybin reduced “demoralization and hopelessness, improved spiritual well-being, and increased quality of life.” Participants described “exalted feelings of joy, bliss, and love,” and “a movement from feelings of separateness to interconnectedness.” More than seventy percent of participants rated their experiences as one of the top five most meaningful experiences in their lives. “You may say, what does that mean?” Roland Griffiths, a senior researcher on the study, remarked in an interview. “Initially I wondered if they had pretty dull lives. But no.” Participants compared their experiences to the birth of their first child or the death of a parent. These studies are considered to be some of the most effective psychiatric interventions in the history of modern medicine.

Profound changes in people’s minds and personalities are rare; that they should happen over the course of such a short experience is striking. Nonetheless, these aren’t anomalous findings. Several recent studies report the dramatic effects of psilocybin on people’s minds, outlooks, and perspectives. Using some of the psychometric questionnaires that I had contended with, many of these studies have found that psilocybin can reliably induce experiences classified as “mystical.” Mystical experiences include feelings of awe; of everything being interconnected; of transcending time and space; of profound intuitive understanding about the nature of reality; and of deeply felt love, peace, or joy. They often include the loss of a clearly defined sense of self.

Psilocybin can leave a lasting impression on people’s minds, like the grin on the Cheshire Cat in Alice’s Adventures in Wonderland, which “remained some time after the rest of it had gone.” In one study, researchers found that a single high dose of psilocybin increased the openness to new experiences, psychological well-being, and life satisfaction of healthy volunteers, a change that persisted in most cases for more than a year. Some studies have found that experiences with psilocybin have helped smokers or alcoholics break their addictions. Other studies have reported enduring increases in subjects’ sense of connection with the natural world.

Out of the flurry of recent research into psilocybin some themes are starting to emerge. One of the most interesting is the way that participants in psilocybin trials make sense of their experiences. As Michael Pollan reports in How to Change Your Mind, most of the people who take psilocybin don’t interpret their experiences in modern biology’s mechanistic terms, of molecules moving around their brains. Quite the opposite. Pollan found that many of those he interviewed had “started out stone-cold materialists or atheists…and yet several had had ‘mystical experiences’ that left them with the unshakable conviction that there was something more than we know—a ‘beyond’ of some kind that transcended the physical universe.” These effects pose a riddle. That a chemical can induce a profound mystical experience appears to support the prevailing scientific view that our subjective worlds are underpinned by the chemical activity of our brains; that the world of spiritual beliefs and experience of the divine can spring from a material, biochemical phenomenon. However, as Pollan points out, the very same experiences are so powerful as to convince people that a nonmaterial reality—the raw ingredient of religious belief—exists.

OPHIOCORDYCEPS AND GUT-DWELLING microbes influence animal minds by living inside their bodies, fine-tuning their chemical secretions in real time. This is not the case with psilocybin mushrooms. One can inject a person with synthetic psilocybin and elicit the full range of psycho-spiritual effects. How does it work?

Once inside the body, psilocybin is converted to the chemical psilocin. Psilocin slips into the workings of the brain by stimulating receptors normally stimulated by the neurotransmitter serotonin. By mimicking one of our most widely used chemical messengers, psilocybin, like LSD, infiltrates our nervous systems, intervenes directly in the passage of electrical signals around our bodies, and can even change the growth and structure of neurons.

How exactly psilocybin changes patterns of neuronal activity wasn’t known until the late 2000s, when researchers from the Beckley/Imperial Psychedelic Research Programme gave subjects psilocybin and monitored the activity of their brains. Their findings were surprising. The scans revealed that psilocybin didn’t increase the activity of the brain as one might expect, given its dramatic effects on people’s minds and cognition. Rather, it reduced the activity of certain key areas.

The type of brain activity reduced by psilocybin forms the basis of what is termed the default mode network (DMN). When we’re not focusing on much, when our minds are wandering idly, when we’re self-reflecting, when we’re thinking of the past or making plans about the future, it’s our DMN that’s active. The DMN has been described by researchers as the “capital city” or “corporate executive” of the brain. In the riot of cerebral processes going on at any one time, the DMN is understood to keep a kind of order—a schoolteacher in a chaotic classroom.

The study showed that subjects who reported the strongest sense of “ego-dissolution,” or loss of a sense of self, on psilocybin had the most dramatic reductions in the activity of their DMNs. Shut down the DMN, and the brain is let off the leash. Cerebral connectivity explodes, and a tumult of new neuronal pathways arise. Networks of activity previously distant from one another link up. In the terms of the metaphor used by Aldous Huxley in his seminal exploration of psychedelic experience, The Doors of Perception, psilocybin appears to shut down a “reducing valve” in our consciousness. The outcome? An “unconstrained style of cognition.” The authors conclude that psilocybin’s ability to change people’s minds is related to these states of cerebral flux.

Brain-imaging studies provide an important description of the way that psychedelics act on our bodies, but they don’t do much to explain participants’ feelings. After all, it is people who have experiences, not brains. And it is exactly people’s experiences that seem to underpin the therapeutic effects of psilocybin. In the studies that measured the effects of psilocybin on terminally ill cancer patients, it was those who had the strongest mystical experiences who showed the most pronounced reductions in symptoms of depression and anxiety. Similarly, in a study of psilocybin and tobacco addiction, the patients with the best results were those who had undergone the most powerful mystical experiences. Psilocybin appears to take effect not by pushing a set of biochemical buttons but by opening patients’ minds to new ways of thinking about their lives and behaviors.

It is a finding that echoes much of the research into LSD and psilocybin that took place during the first wave of modern psychedelic research in the mid-twentieth century. Abram Hoffer, a Canadian psychiatrist and researcher into the effects of LSD in the 1950s, remarked that “from the first, we considered not the chemical, but the experience as a key factor in therapy.” This may sound like common sense, but from the standpoint of mechanistic medicine at the time it was a radical notion. The conventional approach was—and remains to a large degree—to use stuff, whether drugs or a surgical tool, to treat the stuff that the body is made out of, just as we might use tools to repair a machine. Drugs are normally understood to work through a pharmacological circuit that bypasses the conscious mind entirely: A drug affects a receptor, which triggers a change in symptoms. By contrast, psilocybin—like LSD and other psychedelics—appears to act on symptoms of mental illness via the mind. The standard circuit is enlarged: A drug affects a receptor, which triggers a change of mind, which triggers a change in symptoms. Patients’ psychedelic experiences themselves appear to be the cure.

In the words of Matthew Johnson, a psychiatrist and researcher at Johns Hopkins, psychedelics like psilocybin “dope-slap people out of their story. It’s literally a reboot of the system…Psychedelics open a window of mental flexibility in which people can let go of the mental models we use to organize reality.” Toughened habits, such as those that give rise to substance addiction, or those that add up to the “rigid pessimism” of depression, become more pliable. By softening the categories that organize human experience, psilocybin and other psychedelics are able to open up new cognitive possibilities.

One of our most robust mental models is that of the self. It is exactly this sense of self that psilocybin and other psychedelics seem to disrupt. Some call it ego dissolution. Some simply report that they lost track of where they ended and their surroundings began. The well-defended “I” that humans depend on for so much can vanish entirely, or just dwindle, shading off into otherness gradually. The result? Feelings of merging with something greater, and a reimagined sense of one’s relationship to the world. In many instances—from lichens, to the boundary-stretching behavior of mycelium—fungi challenge our well-worn concepts of identity and individuality. Psilocybin-producing mushrooms, like LSD, do so too, but in the most intimate possible setting: the inside of our own minds.

IN THE CASE of Ophiocordyceps, an infected ant’s behavior can be thought of as fungal behavior. The death grip, summit disease—these are extended characteristics of the fungus, part of its extended phenotype. Can the alterations in human consciousness and behavior brought about by psilocybin mushrooms be thought of as part of the extended phenotype of the fungus? The extended behavior of Ophiocordyceps leaves an imprint in the world in the form of fossilized scars on the underside of leaves. Can the extended behavior of psilocybin mushrooms be thought of as leaving an imprint in the world in the form of ceremonies, rituals, chants, and the other cultural and technological outgrowths of our altered states? Do psilocybin fungi wear our minds, as Ophiocordyceps and Massospora wear insect bodies?

Terence McKenna was a great advocate of this view. Given a sufficiently large dose, he asserted, the mushroom could be expected to speak, plainly and clearly, talking “eloquently of itself in the cool night of the mind.” Fungi have no hands with which to manipulate the world, but with psilocybin as a chemical messenger, they could borrow a human body and use its brain and senses to think and speak through. McKenna thought fungi could wear our minds, occupy our senses, and, most important, impart knowledge about the world out there. Among other things, fungi could use psilocybin to influence humans in an attempt to deflect our destructive habits as a species. For McKenna, this was a symbiotic partnership that presented possibilities “richer and even more baroque” than those available to humans or fungi alone.

As Dawkins reminds us, how far we’re willing to go depends on how far we’re willing to speculate. How we speculate in turn depends on how we arrange our biases. “You think the world is what it looks like in fine weather at noon day,” the philosopher Alfred North Whitehead once observed to his former student Bertrand Russell. “I think it is what it seems like in the early morning when one first wakes from deep sleep.” In Whitehead’s terms, Dawkins speculates in fine weather at noon day. He takes pains to ensure that his speculation about extended phenotypes remains “disciplined” and “tightly limited.” He is clear that phenotypes can extend beyond the body, but they can’t be too extended. By contrast, McKenna speculates at dawn. His requirements are less stringent, his explanations less tightly limited. Between the two poles lies a continent of possible opinion.

How do psilocybin mushrooms stand up to Dawkins’s three “stringent requirements”?

A mushroom’s ability to produce psilocybin is certainly inherited. It is also an ability that varies from mushroom species to mushroom species, and between individual mushrooms. However, for the bemushroomed state—the visions, the mystical experiences, the ego dissolution, the loss of a sense of self—to count as part of the extended phenotype of the fungi, the final key condition must be met. Fungi that orchestrate “better” altered states—whatever that means—must pass on their genes more successfully. Fungi must differ in the ability to influence humans, and the ones that provide more fulsome and desirable experiences must benefit at the expense of those providing less desirable experiences.

At a glance, this third requirement seems to decide the issue. Psilocybin-producing fungi may influence human behavior, but unlike Ophiocordyceps, they don’t live on within our bodies. Moreover, McKenna’s speculation is hard to reconcile with the fact that humans are latecomers to the psilocybin story. Psilocybin was produced by fungi for tens of millions of years before the genus Homo evolved—the current best estimate puts the origin of the first “magic” mushroom at around seventy-five million years ago. For more than ninety percent of their evolutionary history, psilocybin-producing fungi have lived on a human-free planet and have done just fine. If the fungi do indeed benefit from our altered states, they can’t have done so for very long.

Then what did psilocybin do for those fungi that evolved an ability to produce it? Why bother to make it in the first place? It’s a question that has been pored over for decades by mycologists and magic-mushroom enthusiasts alike.

It’s possible that psilocybin didn’t do much at all for the fungi that made it until humans came along. There are lots of compounds in fungi and plants that accumulate in biochemical backwaters playing Z-list roles as incidental metabolic by-products. Sometimes these “secondary compounds” encounter an animal that they attract, confound, or kill, at which point they might start to benefit the fungus and become an evolutionary adaptation. However, sometimes they don’t do much more than provide variations on a biochemical theme that might one day prove useful, or not.

Two studies published in 2018 suggest that psilocybin did provide a benefit to the fungi that could make it. Analysis of the DNA of psilocybin-producing fungal species reveals that the ability to make psilocybin evolved more than once. More surprising was the finding that the cluster of genes needed to make psilocybin has jumped between fungal lineages by horizontal gene transfer several times over the course of its history. As we’ve seen, horizontal gene transfer is the process by which genes and the characteristics they underpin move between organisms without the need to have sex and produce offspring. It is an everyday occurrence in bacteria—and how antibiotic resistance can spread rapidly through bacterial populations—but it is rare in mushroom-forming fungi. It is even more rare for complex clusters of metabolic genes to remain intact as they jump between species. The fact that the psilocybin gene cluster remained in one piece as it moved around suggests that it provided a significant advantage to any fungi who expressed it. If it didn’t, the trait would have quickly degenerated.

But what could this advantage have been? The psilocybin gene cluster jumped between species of fungus that lived similar lifestyles in rotting wood and animal dung. These habitats are also the home of numerous insects that “eat or compete” with fungi, all of whom should be sensitive to the potent neurological activity of psilocybin. It seems probable that the evolutionary value of psilocybin lay in its ability to influence animal behavior. But how, exactly, isn’t clear. Fungi and insects share a long and complicated history. Some fungi, like Ophiocordyceps or Massospora, kill. Some cooperate over immense tracts of evolutionary time, like those that live with leaf-cutter ants and termites. In either case, fungi use chemicals to change insect behavior. Massospora even goes so far as to use psilocybin to accomplish its purpose. Which way did psilocybin swing? Opinion is divided. Monitoring the effects of psilocybin on the organisms that consume it isn’t straightforward even with humans, who can at least attempt to talk about their experience and fill out psychometric questionnaires. What chance do we have of finding out what psilocybin might do to the mind of an insect? Animal studies on the subject are scarce, which makes matters worse.

Could psilocybin be a deterrent produced by fungi to fuddle the wits of their insect pests? If so, it doesn’t seem to be very effective. There are species of gnat and fly that routinely make their homes within magic mushrooms. Snails and slugs devour them without apparent ill-effect. And leaf-cutter ants have been observed to actively forage for a certain type of psilocybin mushroom, carrying them back to their nests in one piece. These findings have led some to suppose that far from being a deterrent, psilocybin served as a lure, somehow changing insect behavior in ways that benefited the fungus.

The answer probably falls somewhere in between. Psilocybin mushrooms that are toxic to some animals could still make a good meal for those able to develop resistance. Some species of fly are resistant to the poisons produced by the death cap mushroom, for instance, and have near exclusive access as a result. Could these psilocybin-tolerant insects serve the fungus by helping to spread its spores? By defending it from other pests? Once again, we’re left speculating.

WE MIGHT NOT know how psilocybin served fungal interests for the first several million years of its existence. But from our current vantage point, it is clear that the interaction of psilocybin with human minds has transformed the evolutionary fortunes of those mushrooms that produce it. Psilocybin-producing fungi develop an easy rapport with humans. Far from acting as a repellent—to stand a chance of overdosing, a human would have to eat a thousand times more mushrooms than required for an average trip—psilocybin has caused humans to seek out the mushrooms, carry them from place to place, and develop methods to cultivate them. In doing so, we have helped to spread their spores, which are both light enough to travel over great distances in the air and numerous: Left on any surface for just a few hours, a single mushroom will eject enough spores to leave a thick black smear. In colliding with a new type of animal, a chemical that might once have served to baffle and deter pests has been transformed into a glittering lure in a few swift moves. The passage of magic mushrooms from obscurity to international stardom over a few decades in the twentieth century is one of the most dramatic stories in the long history of human relationships with fungi.

In the 1930s, the Harvard botanist Richard Evans Schultes read the fifteenth-century accounts of the “flesh of the gods” written by the Spanish friars and became intrigued. From the few sources that survived, it was clear that in parts of Central America psilocybin mushrooms had grown into cultural and spiritual centers of gravity. They had found their way into the hands of the local deities, and their consumption had fueled a conception of the divine in which the mushrooms themselves featured heavily.

Could these mushrooms still be found growing in modern-day Mexico? Schultes received a tip-off from a Mexican botanist, and in 1938 set off for the remote valleys in northeastern Oaxaca to find out. (This was the same year that Albert Hofmann first isolated LSD from ergot fungi in a pharmaceutical lab in Switzerland.) Schultes found mushroom use among the Mazatec people to be alive and well. Curanderos, or healers, held regular mushroom vigils to heal the sick, locate lost property, and give advice. Mushrooms were common in the pastures surrounding the villages. Schultes collected specimens and published his findings. He reported that consumption of these mushrooms resulted in “hilarity, incoherent talking, and…fantastic visions in brilliant colors.”

In 1952, Gordon Wasson, an amateur mycologist and a vice president of the bank J. P. Morgan, received a letter from the poet and scholar Robert Graves describing Schultes’s report. Wasson was fascinated by Graves’s news of the mind-altering “flesh of the gods” and traveled to Oaxaca in search of the mushrooms. There, Wasson met a curandera called María Sabina, who invited him to a mushroom vigil. Wasson described his experience as “soul shattering.” In 1957, he published an account of his experience in Life magazine. The article was titled “Seeking the Magic Mushroom: A New York Banker Goes to Mexico’s Mountains to Participate in the Age-Old Rituals of Indians Who Chew Strange Growths that Produce Visions.”

Wasson’s article was a sensation and read by millions. By this time, the mind-altering properties of LSD had been known about for fourteen years, and there was an active community of researchers conducting studies into its effects. Nonetheless, Wasson’s was among the very first accounts of a psychedelic mind-altering substance to reach the general public. “Magic mushrooms” became a household term—and gateway concept—more or less overnight. In his autobiography, Dennis McKenna remembers his brother, Terence, then a precocious ten-year-old, “trailing our mother as she did her housework, waving the magazine demanding to know more. But of course she had nothing to add.”

Things moved quickly. Hofmann was sent a sample of the magic mushrooms by a member of Wasson’s expedition, and had soon identified, synthesized, and named the active ingredient: psilocybin. In 1960, the well-respected Harvard academic Timothy Leary heard of the magic mushrooms through a friend and went to Mexico to try them. His experience, a “visionary voyage,” had a profound impact on him, and he returned “a changed man.” Back at Harvard, inspired by his experience with the mushrooms, Leary abandoned his research program and set up the Harvard Psilocybin Project. “Since eating seven mushrooms in a garden in Mexico,” he later wrote of his gateway experience, “I have devoted all my time and energy to the exploration and description of these strange deep realms.”

Leary’s methods proved controversial. He left Harvard and began in earnest to promote his vision that cultural revolution and spiritual enlightenment could be attained via the consumption of psychedelics, and soon became notorious. In numerous TV and radio appearances, he evangelized about LSD and its many benefits. In an interview with Playboy he advised that on an average acid trip women could expect to have a thousand orgasms. He ran against Ronald Reagan for governor of California and lost. Fueled in part by Leary’s proselytizing, the countercultural movement of the 1960s picked up momentum. In 1967, in San Francisco, Leary, by now “High Priest” of the psychedelic movement, addressed the Human Be-In that was attended by tens of thousands. Soon afterward, in a haze of backlash and scandal, LSD and psilocybin were made illegal. By the end of the decade, almost all of the research taking place into the effects of psychedelics had been shut down or driven underground.

THE OUTLAWING OF psilocybin and LSD marked the start of a new chapter in the evolutionary history of psilocybin mushrooms. Most of the psychedelic research of the 1950s and ’60s had taken place with LSD or synthetic psilocybin in pill form, much of it produced by Hofmann in Switzerland. But by the early 1970s, in part because of the legal risks associated with pure psilocybin and LSD, and in part due to their scarcity, interest in magic mushrooms grew. By the mid-1970s, species of psilocybin mushrooms had been discovered growing in many parts of the world, from the United States to Australia. However, the supply of wild mushrooms is limited by seasonal conditions and location. When they returned from Colombia in the early 1970s, Terence and Dennis McKenna sought a steadier supply. Their solution was radical. In 1976, the McKennas published a short book entitled Psilocybin: Magic Mushroom Grower’s Guide. Armed with this slim volume, the brothers advised, with little more than jars and a pressure cooker, anyone could produce unlimited quantities of a powerful psychedelic from the comfort of their garden shed. The process was only a little bit more complicated than making jam, and even a novice could soon find themselves, in Terence’s words, “neck deep in alchemical gold.”

The McKennas were not the first to cultivate psilocybin mushrooms, but they were the first to publish a reliable method for growing large quantities of mushrooms without specialist laboratory equipment. The Grower’s Guide was a runaway success and went on to sell more than a hundred thousand copies in the five years following its release. It kick-started a new field of DIY mycology and influenced a young mycologist named Paul Stamets, the discoverer of four new species of psilocybin mushroom and author of a guidebook to psilocybin mushroom identification.

Stamets was already working on new ways to cultivate a range of “gourmet and medicinal” mushrooms, and in 1983, he published The Mushroom Cultivator, which simplified growing techniques even further. In the 1990s, as online forums for magic mushroom growers sprang up, Dutch entrepreneurs spotted a loophole in the law that allowed them to sell psilocybin mushrooms openly, and many Dutch growers of edible supermarket mushrooms switched over to psychedelic mushroom production. By the early 2000s, the craze had spread to England, and crates of fresh psilocybin mushrooms were being sold on London high streets. By 2004, the Camden Mushroom Company alone was shifting a hundred kilograms of fresh mushrooms a week, equivalent to about twenty-five thousand trips. Fresh psilocybin mushrooms were made illegal soon afterward, but the secret was out. Today, just-add-water kits are readily available online. Crosses between fungal strains are producing new varieties, from “Golden Teacher” to “Mc Kennai,” each with subtly different effects.

For as long as humans have sought out psilocybin mushrooms—thus serving as enthusiastic agents of spore dispersal—the fungi have benefited from their ability to tinker with our consciousness. Since the 1930s, these benefits have multiplied many times over. Before Wasson’s trip to Mexico, few people outside indigenous communities in Central America knew of the existence of psilocybin mushrooms. Yet within two decades of their arrival in North America, a new story of domestication was underway. In cupboards, bedrooms, and warehouses, a handful of tropical fungal species found new lives in otherwise inhospitable temperate climates.

What’s more, since Schultes’s first paper in the late 1930s, more than two hundred new species of psilocybin-producing fungi have been described, including a psilocybin-producing lichen that grows in the Ecuadorian rainforest. It turns out that there are few environments where these mushrooms don’t grow, given sufficient rainfall. As one researcher observes, psilocybin mushrooms “occur in abundance wherever mycologists abound.” Guidebooks make it possible for humans to find, identify, and pick—and thus disperse—psilocybin mushrooms that would have been off the radar a few decades ago. Several of these species seem to have a fondness for disturbed habitats and find an easy home in our messy wake. As Stamets wryly confides, many have an affection for public spaces, including “parks, housing developments, schools, churches, golf courses, industrial complexes, nurseries, gardens, freeway rest areas and government buildings—including county and state courthouses and jails.”

DO THE EVENTS of the last several decades bring us any closer to satisfying Dawkins’s third criterion? Can these fungi be thought of as borrowing a human brain to think with, a human consciousness to experience with? Does a human under the influence of mushrooms really fall under their influence, as an infected ant falls under the influence of Ophiocordyceps?

For our altered states to count as an extended phenotype of the fungi, the bemushroomed human would need to serve the reproductive interests of the very fungi they had eaten. However, this doesn’t seem to be the case. Only a small number of species are cultivated, and for a large part, the decision of which fungal strains to grow is made on the basis of which are the easiest to cultivate and provide the biggest yields—it’s not clear that “better” mind-alterers are selected over “worse” mind-alterers. More problematic is that if all humans were made extinct in a single instant, most species of psilocybin mushroom would carry on untroubled. Psilocybin-producing fungi don’t depend entirely on our altered states, as Ophiocordyceps depends entirely on the altered behavior of ants. For tens of millions of years, they have grown and reproduced perfectly well without humans, and would probably continue to do so.

Does it really matter? “One might think that with the isolation…of psilocybin and psilocin, the mushrooms of Mexico had lost their magic,” wrote Schultes and Hofmann in 1992. With the domestication of psilocybin-producing fungi, hundreds of kilograms of mushrooms can be grown in warehouses in Amsterdam. With the isolation of psilocybin, the default mode network can be disabled on demand in brain scanners. Mystical experiences, awe, and a loss of one’s sense of self can be elicited in a hospital bed. How much closer do these advances propel us toward an understanding of the way that psilocybin influences human minds?

For Schultes and Hofmann, the answer was “not very.” Mystical experiences are those by definition resistant to rational explanation. They don’t readily fit within numbered scales on psychometric questionnaires. They confound and enthrall. And they undoubtedly occur. As Schultes and Hofmann observe, scientific investigation into the identity and structure of psilocybin and psilocin had “merely shown that the magic properties of the mushrooms are the properties of two crystalline compounds.” It is a finding that does little more than kick the question down the road. “Their effect on the human mind is just as inexplicable, and just as magical, as that of the mushrooms themselves.”

The effects of psilocybin mushrooms might not count as an extended phenotype in a strict sense, but does this mean we should dismiss the speculation of Terence McKenna? Perhaps we shouldn’t be too hasty. “Our normal waking consciousness,” wrote the philosopher and psychologist William James in 1902, “is but one special type of consciousness, whilst all about it, parted from it by the filmiest of screens, there lie potential forms of consciousness entirely different.” For reasons that are poorly understood, certain fungi lead humans out of familiar stories into forms of consciousness that are entirely different, and toward the edge of new questions. “No account of the universe in its totality can be final which leaves these other forms of consciousness quite disregarded,” James concluded.

Whether for a researcher, a patient, or just an interested bystander, the curious thing about these fungal chemicals is exactly the experiences that they elicit. McKenna’s mushroom-fueled speculation may stretch the limits of mental and biological possibility. But that is precisely the point: The effects of psilocybin on human minds stretch the limits of what seems possible. In Mazatec culture, it is self-evident that mushrooms speak; anyone who takes them can experience this for themselves. Theirs is a view shared by many traditional cultures that ritually use entheogenic plants or fungi. And it is a view commonly reported by contemporary users in nontraditional settings, many of whom report a thinning of the boundaries between “self” and “other,” and an experience of “merging” with other organisms.

Is the world what it looks like in fine weather at noon day? Or is it what it seems to be at dawn when we first wake from sleep? Perhaps there are things that everyone can agree on. Whether or not fungi actually speak through humans and occupy our senses, the impact of psilocybin mushrooms on our thoughts and beliefs is real enough. If we imagined that a fungus could wear our minds and enjoyed splashing around in our consciousness, what would we expect to see? There might be songs sung about mushrooms, statues of mushrooms, paintings of mushrooms, myths and stories in which mushrooms play leading roles, ceremonies built around the celebration of mushrooms, a global community of DIY mycologists developing new ways to cultivate mushrooms in their homes, mycological evangelists like Paul Stamets talking to large audiences about how mushrooms can save the world. And people like Terence McKenna who claim to be able to speak English for fungi.