Hidden Worlds

The British biologist and writer Merlin Sheldrake has been fascinated by the often mysterious world of fungi since he was a small boy. He used to bury himself in heaps of fallen leaves and inhale the piquant odor of rot. “I think of fungi as ecological connective tissue,” he says, “the living seam by which much of life is stitched into relation.”

Although we haven’t always known it, our lives have long been entangled with fungi, from microorganisms such as yeasts and molds to the more than ten thousand varieties of mushrooms. They are neither plants nor animals, occupying their own kingdom of eukaryotic organisms, and they make it possible to produce such foods and beverages as wine, beer, bread, cheese, vinegar, and soy sauce. Many medicines are the result of an engineered or naturally grown fungus, including penicillin, cyclosporine, and other antibiotics. Digesting food would be impossible without the fungal microbes that inhabit our gut. And if you’ve ever had athlete’s foot or tried to grow grain crops without pesticides, you know that fungi are not always our friends. “Fungi change the way we understand life,” Sheldrake says. They “illustrate that it is possible to solve complex problems without a brain. And human existence has been profoundly influenced by mind-altering drugs like psilocybin and alcohol, both derived from fungal life.”

He was frustrated growing up, Sheldrake says, because he wanted to study both the humanities and the sciences, and the education system forced students to go into one or the other. He had to work to find the places where the “artificial” barrier between the arts and the sciences was porous, and then spend as much time as he could there.

Sheldrake received a PhD in tropical ecology from Cambridge University for his work on underground fungal networks in the forests of Panama, where he was a predoctoral research fellow of the Smithsonian Tropical Research Institute. He recently published his first book, Entangled Life: How Fungi Make Our Worlds, Change Our Minds & Shape Our Futures (merlinsheldrake.com). He is also a musician and keen fermenter who filled his college dorm room with experiments in mead making and beer brewing, some of which went horribly wrong.

In 2013 I interviewed Sheldrake’s father, the scientist Rupert Sheldrake, for The Sun, and he told me tales of young Merlin’s precocious interest in mycology, or the study of mushrooms. When I read Entangled Life, I found Merlin’s description of the fungal world revelatory and his vision of future possibilities mind-boggling. After the pandemic made it impossible for him to undertake a planned U.S. speaking tour, I arranged to interview him by video chat. Despite our distance, his enthusiasm and curiosity for science came through loud and clear.

Leviton: You’ve said that fungi are possibly closer to animals than they are to plants.

Sheldrake: Yes, in the way their metabolism works. Unlike plants, which are what we call autotrophs — meaning they make their own energy and organic compounds from sunlight and carbon dioxide — fungi are heterotrophs. That means, like animals, they have to find organic matter in the world and digest it.

They’re also more closely related to animals in an evolutionary sense: they branch off the tree of life at a juncture closer to the animal branch than to the plant branch. Fungi are partly responsible for life moving from the ocean onto land, which at the time, around 500 million years ago, was a mainly hostile place. Temperatures fluctuated wildly, and most of the landscape was dusty and rocky. There was no real soil. The only organisms would have been a few photosynthetic bacteria and the fungi living in crusts. There was nothing like what we recognize today as plants. It was fungi that allowed plants to evolve from single-celled aquatic green algae into land-based life-forms with seeds, flowers, and so forth. So fungi are responsible for all macroscopic life on land today, because plants lie at the base of the food chain.

Leviton: Is it fair to say that plants can’t really exist without help from fungi?

Sheldrake: That’s correct. Even today 90 percent of plants depend on mycorrhizal relationships. [Mycorrhizae are symbiotic associations between plants and fungi — close biological relationships that benefit both partners. — Ed.] Mykes is Greek for “fungus,” and rhiza is “root.” All outdoor-grown plants that have been examined have fungi that live in their leaves and shoots.

What we call plants originated with algae that evolved to farm fungi, while at the same time the fungi evolved to farm algae. When you look at a plant, you’re looking at the outcome of that relationship.

Leviton: How is it that science is only now discovering this complex, infinitesimal reality?

Sheldrake: The process of discovery largely has to do with access. We studied plants first because we can touch and taste them. They’re macroscopic and immediately available to our senses. They very obviously shape our existence, whether as food or medicine or shelter materials. At the microscopic level there’s a fungal world and also a microbial world, and we have more access to these realms now because of new technologies like DNA sequencing, which allows us to grind up the DNA from a teaspoon of soil and find out who lives there — something we simply couldn’t do even a few decades ago.

Leviton: And these new tools are transforming the way we look at ecology?

Sheldrake: Absolutely. We have realized that all life-forms depend on microbes. Animals have trillions of microbes living in and on them, without which they could not grow and live.

Fungi have bacteria and viruses living inside them, too. Even large bacteria can have small bacteria living inside them, and bacteria can have viruses living inside them, and larger viruses can have smaller viruses living inside them. As biologist Lynn Margulis writes, all life is the story of “the long-lasting intimacy of strangers.”

As we find out more about the enormous role microbes play in evolution, we’re starting to reexamine some of the categories we took for granted in the past. Biology, the study of living organisms, is transforming into ecology, which is the study of the relationships among organisms, because each organism is itself a kind of ecology. We’re starting to see life as a series of nested relationships. It’s “relationships all the way down,” to borrow a concept from Hindu mythology that says the Earth rests on a giant turtle, which rests on another turtle, and so on. It’s turtles all the way down.

Leviton: What methods do fungi use to proliferate?

Sheldrake: Most fungi produce spores, which spread over large distances on the wind. In fact, fungal spores make up the largest portion of living material in the Earth’s atmosphere. Fifty million tons of fungal spores are produced every year, enough to influence the weather.

Fungi also have a powerful ability to regenerate. You can take a mycelium from a mycelial network, replant it, and generate an entirely new network. [Mycelia are the branching, threadlike “roots” of a fungus. — Ed.] That process can go on indefinitely, meaning that fungi are potentially immortal.

Leviton: The mycologist Paul Stamets describes a mycelial network as a “vast microscopic web, an infinite number of roads leading everywhere.” What do you see when you study these networks?

Sheldrake: It’s like a Zen koan: Are these large networks of fungi one organism or an interconnected set of individual organisms? Fungi play games with the notion of individuality from the cellular level upward. Most fungal networks can move cellular content through the network over long distances.

Large bacteria can have small bacteria living inside them, and bacteria can have viruses living inside them, and larger viruses can have smaller viruses living inside them. As biologist Lynn Margulis writes, all life is the story of “the long-lasting intimacy of strangers.”

Leviton: What do you mean by “cellular content”?

Sheldrake: The word cell was coined by Robert Hooke in the seventeenth century. While looking at cork plants under the microscope, he saw what looked like little rooms, each containing a nucleus and various parts, the way monks’ cells contained a bed and a desk. So we got the word cell to describe these neatly bounded subunits of life.

But in many types of fungal networks the nuclei are free to move through the network. So they’re not cellular in the traditional sense of the word. We sometimes refer to them as being in a “supracellular state.” You can have different types of nuclei traveling within one network, and one spore can have multiple, often genetically different, nuclei within it.

So there is a confusing question of where to draw the line and what criteria to use to define an individual fungal life. New discoveries suggest that “individuals” are not so much a natural fact as a category that depends on our point of view.

Leviton: It reminds me of how the brain of an octopus is dispersed throughout its body.

Sheldrake: Yes, you can cut off an octopus tentacle, and it can still explore its environment. They take advantage of a much more distributed brain and nervous system than we have.

Likewise, fungi are decentralized. They’re able to coordinate their behavior without anything resembling a brain. They can connect perception and action without having a special place to do so. The coordination somehow takes place everywhere at once, and also nowhere in particular.

Leviton: This brings up the question of how we define intelligence.

Sheldrake: We should assess all organisms’ intelligence on their terms, rather than on our terms, which reflect our human needs and sensibilities. Traditionally humans have been used as a yardstick to judge the intelligence of other organisms, placing us firmly at the center of the inquiry. It reveals our species’ narcissism.

There are a number of definitions of intelligence, but most refer to an organism’s ability to adapt to change, accomplish tasks, solve problems, decide between alternative courses of action, and process information from its environment in a way that helps meet its needs. By this measure, almost all organisms would qualify as intelligent to some degree.

This perspective is now quite widespread in biology. Scientists have started to ask not whether organisms have intelligence, but to what degree an organism displays intelligent behaviors and what kind. I think this helps to alleviate our human-centeredness and allows us to connect more with the unfolding event that is life.

I don’t know many serious scientists who would think of animals — human or otherwise — as mere stimulus-response machines at this point. It’s a welcome turn. As far as I can tell, the people who do still think like that do so not because they’ve carefully considered the matter, but because they haven’t.

Leviton: You also write about seeing our natural environment — the mountains, the rivers, the deserts, and so forth — as having a kind of spiritual life that connects them to humans.

Sheldrake: Yes, I quoted Robin Wall Kimmerer, a member of the Citizen Potawatomi Nation in Oklahoma, who points out all the ways the English language encourages us to view the universe as made up of unchanging things rather than of processes. The Potawatomi language is full of verb forms that attribute aliveness to the nonhuman world. The word for “hill,” for instance, means “to be a hill.” Hills are in the process of actively being.

Biological processes are never black-and-white. Context is crucial. Why should the stories and metaphors we use to make sense of the universe place us in a world of inanimate objects, of static things?

In biology, and within science in general, there’s a tension between what you might call a “substance ontology” — which posits that reality is made up of unchanging stuff, and that even we are sort of moving things — and another current, which posits that the universe is made up of constant change, of process. This idea of process is supported by modern physics, which understands atoms to be thrumming with fervent activity. Mass, in fact, is energy, when you boil it down, and energy is in constant process. We aren’t made of unchanging stuff. We are patterns of stability within a sea of change. This view seems to more accurately describe the way the living world works, and it helps coax us out of our little boxes.

Leviton: You give many examples in your book of fungi and plants attracting the right kind of insect or animal to help them spread, propagate, or gain protection. For instance, when broad-bean plants are attacked by aphids, they release volatile compounds that attract wasps who prey on aphids.

Sheldrake: One fungus called Ophiocordyceps unilateralis infects carpenter ants and strips them of their instinctive fear of heights. In a syndrome called “summit disease,” they climb higher than they normally would and bite the vein of a leaf, whereupon the fungus kills the ant and consumes it from the inside. Eventually a stalk bursts from the victim’s head, sprinkling spores over a considerable distance.

Leviton: Is it being anthropomorphic to say the fungi “decide” on this strategy for survival?

Sheldrake: We like to think of ourselves as being one of the few organisms that make decisions, but lots of organisms, when presented with options, make choices. They can behave differently when confronted with one environmental circumstance versus another. They wouldn’t be very successful if they behaved exactly the same way in a flood or a drought.

If we broaden our understanding of decision-making to include the decisions made by an organism without a brain, then I don’t think it’s too hard to accommodate these observations.

Leviton: It’s fairly easy to understand why an organism takes steps that are in its own best interest, but you and other scientists have observed behavior that may not be in the immediate interest of the individual. Rather it appears to be in the interest of the entire species, or of maintaining ecological connections.

Sheldrake: Yes, for example, when a fungus and a plant are engaged in a symbiotic relationship, both can exert some kind of control over that relationship. The fungus can provide phosphorus to a plant, and the plant can reward the fungus with more energy compounds: carbons and sugars. The fungus, in return, can supply more phosphorus. They finely manage their exchange in such a way that neither can hijack the relationship for their own exclusive benefit.

It’s a very intimate relationship, and an ancient one. The exchanges between fungus and plant have had hundreds of millions of years to evolve.

Traditionally humans have been used as a yardstick to judge the intelligence of other organisms, placing us firmly at the center of the inquiry. It reveals our species’ narcissism.

Leviton: But there are situations in which it’s more difficult to see what’s in it for one of the partners.

Sheldrake: Yes, there are mycorrhizal fungal networks through which nutrients can pass from plant to plant. People sometimes call it the “Wood Wide Web,” an underground network that connects trees and other plants. The nutrients that pass through it can be energy-containing carbon compounds or minerals like nitrogen and phosphorus and water. Even signaling compounds — molecules that transmit information between cells in bodies — can pass through a fungal network. The question is: How is this being controlled, and who stands to benefit?

Evolutionary theory doesn’t cope well with altruism, which in biological terms is when an organism assists another organism at a cost to itself. Within conventional evolutionary theory, if you assist a potential competitor at a cost to yourself, your competitor is more likely to survive, and your altruistic genes will soon be weeded out by natural selection.

But there are ways around this. One is kin selection: if an organism assists organisms that are related to it, then it can expect its genes to be passed on to the next generation. You can also have reciprocal altruism, in which organisms help each other at different times, such that both are ultimately more likely to survive.

This can help explain the behavior of shared mycorrhizal networks. Many orchids receive nutrition from fungal networks when they’re young, and only start to provide carbon to the fungus when they’re older. Some experiments have shown that plants tend to supply more carbon to neighbors who are their kin. That would explain it a little bit. But a lot of the time it happens among plants who aren’t kin. So the question remains.

So far we’re talking about the fungal network as a passive pipeline the plants use to send material back and forth, but we might also think about it from the point of view of the fungus, a living organism with its own needs and interests. It will survive better if it has a thriving community of plant partners. So it will support a plant partner that’s doing less well by harvesting nutrients from a plant partner that’s doing better. The fungus becomes a kind of broker, managing its clients for its own ends.

Leviton: But the theory of natural selection still says every organism is working only for its own survival or the survival of its kin.

Sheldrake: Yes, that’s the conventional view. But we see a lot of intimate cooperation as well as competition. Organisms have a multitude of organisms living in them and on them and somehow cooperating with each other or balancing their respective needs against the needs of the collective. From that perspective, the history of life has a lot more cooperation in it than we might read about in the more conventional natural histories, which frame life as unending conflict and competition. If you think about collaboration as being a combination of competition and cooperation, then there’s room for . . . well, more.

Leviton: It seems that, in so many areas — biology, botany, anthropology, psychology — there’s a new focus on the ability to cooperate. Maybe we’ve reached a point in our own evolution where we should reemphasize cooperation, because competition has done such damage to the global environment.

Sheldrake: For sure. Consider the evolutionary thinking in England in the late nineteenth century. T.H. Huxley was known as “Darwin’s bulldog” for his early and spirited defense of evolutionary theory. He talks about evolution as a gladiators’ competition, whereby the strongest and fittest live to fight another day. Such views of evolution mirror the views of social progress within an industrial-capitalist system.

In the Soviet Union in the twentieth century, however, there was a much greater emphasis on cooperation in evolution, which mirrored the views of the socialist/communist system there. The debate didn’t fall perfectly along East-West lines, but broadly speaking the split was noticeable.

Jan Sapp is a historian of symbiosis. He talks about the first international conference on symbiosis, which happened a few months after the Cuban Missile Crisis of 1962, when the U.S. and the Soviet Union almost went to war. The conference organizers said that global affairs might have led to their decision to hold the conference right then: they saw the need to cooperate. Maybe if scientists looked more closely at the way other organisms cooperate in the world, it would have a political or social impact.

Our scientific thinking mirrors contemporary views on human behavior. And then it feeds back on itself as humans try to justify their behavior as “natural.” You can learn a lot about humans by studying the history of how these different relationships are perceived: masters and slaves, men and women, the relationship between nations. This is why I have studied the history of science, the history of scientists as people, and how science has been influenced by culture. It’s a shame that so many scientists are taught science without being encouraged to think about its history. I think we’d get a lot farther in our knowledge, and scientists would have more fun, if they received a thorough history-of-science education.

Leviton: Darwin is such a giant figure in the history of science. Can you talk about his “root-brain hypothesis” and why it’s still relevant?

Sheldrake: He put forward the root-brain hypothesis at the very end of a book called The Power of Movement in Plants, which he cowrote with his son Francis. The idea was that the root tip appeared to be making the decisions about which way the root would grow. The tip was where the “inflection” would happen as the root changed direction to grow around an obstacle. The roots were “piloted” from there, as it were. Information from the rest of the plant was being integrated at the root tips, Darwin thought, making them the decision-making part of the plant — the root-brain. But you can argue the same about shoots aboveground, which behave in quite similar ways. Rather than having one brain like animals do, plants have lots of decision-making parts, all acting in a kind of swarm.

The root-brain hypothesis has caused a lot of controversy over the years. Some scientists think Darwin was brilliantly pushing us to think beyond our narrow human cerebrocentric framework. Others think it’s preposterous to say that plants have anything at all like a brain.

Leviton: Does this compare to the hyphae — the long, branching filaments of a fungus — and how they work?

Sheldrake: Yes, hyphae are piloted by their tips very much the way roots are. The tips are somehow able to integrate information from different parts of the fungus and make decisions about what to do next. Picture fluid flowing through a pipe, but the pipe can change and regulate the flow — using a valve, perhaps. The amount of work that the hyphal tip has to do is much greater, however. You could also think about mycelial networks as a swarm of hyphal tips, but of course it’s not a swarm, because they’re not individuals. They’re all actually connected.

Leviton: “Homing” is another factor in how mycelium grows. Can you talk about how it works?

Sheldrake: Say you have a mycelium growing on a plate. It will expand into a kind of fuzzy circle, the tips growing away from each other, avoiding other parts of the fungus. But at a certain point in the life cycle of this network their inclinations pivot, and they start to grow toward other hyphae, making more cross-connecting paths rather than these radial spokes. When they become attracted to each other, that’s a kind of homing. Very young hyphae of some types of fungi have pheromones that attract the others, so they can fuse to form a larger, more interconnected mycelium.

Leviton: Over the last few decades the study of the human brain has become the study of electrical activity, of neurons, those specialized cells that transmit nerve impulses. Do plants and fungi have neurons or an equivalent?

Sheldrake: There’s a lot of interest right now in electrical signaling in plants, fungi, and bacteria. We’ve known for a long time that plants produce waves of electrical activity that are analogous to the impulses in our nerves.

In the nineties a Swedish researcher named Stefan Olsson was working on mycelial networks, examining their foraging behavior. It struck him they might be using electrical signals, because they seemed to be able to coordinate their behavior too quickly for simple chemical communication to be in use. So he borrowed a microelectrode rig from a researcher who was using it to measure the impulses in moths’ brains. Olsson replaced the moth brain with a fungal network and found that rhythmic, spontaneous impulses passed along it. He was examining wood-rotting fungi, and when he put a block of wood on the network, the rate of firing of these impulses increased. This seemed to suggest that some fungi — especially those that form longer-lived networks over greater distances — had an increased need to coordinate their behavior and might be using electrical signals to do so. But there wasn’t much follow-up, and his findings were left in relative obscurity for twenty years or so. Thankfully people are starting to investigate the phenomenon now, an effort that coincides nicely with recent research finding that plants use electrical coordination to manage growth and development.

It turns out bacteria are electrically active beings, too. They live in colonies and what are called “biofilms,” where they stick to each other and to a surface. Dental plaque, for instance, is a biofilm. Bacteria can coordinate their activity across the colony with waves of electrical excitation.

We are beginning to understand that our brains didn’t evolve neurons from scratch; neurons reflect ancient properties that are present in most living cells. In our brains’ neurons the electrical excitability is more rapid and a lot more specialized, but the difference is in degree rather than in kind. Electrical signaling seems to be a fundamental property of living organisms in general.

Leviton: We sometimes talk about our “lizard brain” and how it still influences modern human behavior, but it’s a stretch for me to think of our ancestors as actually being plants.

Sheldrake: Well, if we’re talking about ancient properties of life, it all goes back to bacteria. Humans are a very specialized, optimized version of that early life.

Leviton: Let’s talk about the way yeasts, bacteria, and other microorganisms work in human bodies.

Sheldrake: All animals have what’s called a microbiome: an ecological community of microorganisms inside them. These microorganisms make it possible for us to live. We can’t exist without them: They guide the development of our immune systems. They help us digest food. They produce key molecules that regulate our behavior. They reduce toxins. We simply would not be who we are if we had zero bacteria living inside us.

Leviton: And when we ingest probiotic foods such as yogurt, sauerkraut, and kimchi, we are introducing health-enhancing bacteria into our bodies, correct?

Sheldrake: Yes, probiotics contain live microorganisms that help us digest, bolster our immune system, and so forth. Western medicine has gone for decades without a thorough understanding of how much we depend on our microbiomes. A lot of the things we do to stay well are actually terrible for our microbiomes. Antibiotics, for example, kill many bacteria that we need, as well as the bacteria that we want to get rid of. Microbiomes ravaged by antibiotics can become unhealthy.

One way to restore life to a ravaged gut is to take probiotic supplements, but what’s often most effective is a fecal-microbiota transplant. You have the feces of a healthy person added to your malfunctioning gut or colon through capsules or a tube. That way you get the full flora from a functioning gut, rather than just a few strains that were convenient to grow in a processing facility. It might sound strange, but for some patients it resolves 90 percent of severe problems due to a lack of bacteria in their digestive system.

Leviton: One aspect of what we consider “civilization” is the continual effort to be cleaner and get rid of dirt and vermin, but that’s had an unintended side effect: by distancing ourselves from dirt, we’ve made our bodies more vulnerable.

Sheldrake: Totally. Allergies, autoimmune disorders, and all sorts of other problems have their roots in oversanitization of our surroundings. Our immune systems developed in dialogue with the microbes that live around us, on us, and in us. If you take those microbes away, our immune systems don’t really learn what’s “us” and what’s “other,” or what’s a tolerable kind of other or an intolerable kind of other.

The germ theory of disease — that microorganisms from outside were interfering in the normal operation of our bodies — developed as early as the eleventh century in Europe, but it wasn’t widely accepted until the nineteenth century. Before that, the “miasma theory,” which held that disease was caused by “bad air,” was the operating science. Germ theory was a big step forward for modern medicine, but it also led us to wage total war on the microbes in our lives, without realizing that we were also killing microbes we need and depend on. We need a more targeted approach.

Leviton: And compounding the issue was a parallel development of pollution from fossil fuels and industries. We’ve been simultaneously cleaning up and befouling our environment.

Sheldrake: Exactly. Something similar happened in modern industrial agriculture, which failed to take into account the life of the soil, which you might think of as the guts of the planet. If you believe all fungi are bad for plants and you spray crops with fungicides, without also supplying organic matter to preserve the integrity of the living soil, then you cause damage. You breed crops that are unable to form high-functioning relationships with fungi. You create all sorts of dysfunction. And you get crop-disease epidemics. It mirrors the side effect of germ theory on human health.

Leviton: Speaking of fungi, let’s talk about mushrooms and lichens. I love that you call lichens “living riddles.” They cover 8 percent of the earth’s surface. There’s more lichen than there is rain forest.

Sheldrake: Yes, in terms of surface area, that’s true. Lichens prosper where other things can’t.

A lichen is a composite of fungus and algae. The Swiss botanist Simon Schwendener called the fungal partners “parasites, although with the wisdom of statesmen.” His “dual hypothesis” — that two different species could come together and build a new organism with its own separate identity — was opposed by many taxonomists. They argued that it was impossible for diverging branches of the tree of life to unexpectedly converge after millions of years.

Lichens play important ecological roles. They thrive on the scorched surface of deserts, where they prevent further desertification. They grow on bare rock. Their dead bodies generate soils in which other plants can then take root. Lichens are a kind of go-between linking the living and nonliving world. They are able to make energy from sunlight and air, to digest minerals from rock, and from that they produce organic tissue that becomes food for other organisms. Lichens occupy a very interesting station where inanimate geological cycles cross over into the metabolic cycles of the living.

Leviton: When you were studying lichens in British Columbia, did you go there with a preconceived sense of what they were doing, or were you surprised?

Sheldrake: I’m always surprised by lichens. [Laughs.] If you look at Ernst Haeckel’s illustrated 1904 book Art Forms in Nature, lichens are endlessly startling in their forms and shapes and colors. It’s like an alien landscape.

Lichens played a big role in the evolution of modern, Western scientific thought. They are gateway organisms to the idea of cooperation in nature. In 1877 the German botanist Albert Frank imported the word symbiosis into biology to describe lichens, because it had become clear that they weren’t just a type of “lower plant.” They had a photosynthetic component and a fungal component. Now we know that there can be multiple fungal and multiple photosynthetic components, as well as bacteria, in these living ecosystems.

Before the word symbiosis was coined, if you were sharing bodily space with another organism, it meant one of two things: parasitism or disease. The dual hypothesis seemed improbable at the time: How could you have a useful and invigorating parasitism? This was inconceivable. It meant evolution could no longer be thought of solely in terms of competition and conflict but had to include inter-kingdom cooperation.

After that 1877 discovery many new symbiotic relationships were uncovered. There were plants and their mycorrhizal partners, the symbiotic nature of corals, and so forth. The biologist who discovered bacterial viruses called them “micro-lichens.”

Leviton: It turns out lichens can help certain plants that cannot photosynthesize, right?

Sheldrake: That’s the mycorrhizal fungal network — the Wood Wide Web — which nourishes plants that have lost the ability to photosynthesize. Instead these plants pull nutrients from other plants through fungal networks.

Leviton: What would be the evolutionary advantage to losing the ability to photosynthesize? It seems like a very basic need for plants.

Sheldrake: Good question. For these plants the ability to get nutrition from other plants via fungal networks allows them to survive in heavily shaded understories, where very little light can reach. With not much sunlight penetrating the forest canopy, there was no advantage to maintaining their ability to photosynthesize. It just took a lot of nutrition and energy. Might as well ditch it. With that choice came this new dependence on the fungal networks.

Leviton: What do we know about our human ancestors’ use of mushrooms?

Sheldrake: Humans have been eating mushrooms and using them as medicine for many thousands of years. Ötzi the Iceman, whose frozen, mummified corpse was found by hikers in an Austrian glacier, lived sometime between 3400 and 3100 BCE. When he died — probably as a result of a wound from an arrow — he was carrying a type of fungus that grows on coniferous trees, and it was prepared quite carefully, kept in a bag strung around his neck. It was a “tinder fungus,” a mushroom that has been used for thousands of years to start and carry fire, an enormously important thing to be able to do.

He was also carrying a birch polypore, a mushroom that he probably used to treat disease and parasites. So he had a highly developed knowledge of the ways these fungi could be useful. It’s not that surprising, when you think about it, that a hunter-gatherer who depends entirely on the organisms that surround him would have a sophisticated working knowledge of how useful mushrooms can be.

It’s fascinating to examine the relationships that humans have formed with these organisms — how humans have used psychedelics, for example. Some cultures have a deep history with psychedelic mushrooms, which influence human thought and shape culture and religion.

I also love to learn about the use of mushrooms as medicines. Broadly speaking, China is a mycophilic, or mushroom-loving, culture. The Shennong Ben Cao Jing, written about 200 CE, is one of the first medical books ever produced. It features the reishi mushroom very prominently for its potential to prolong human life. The Chinese figured out how to cultivate shiitake mushrooms about the year 1000 CE, and at a temple festival in Qingyuan County, Zhejiang Province, they celebrate that discovery as a feast day every year. It’s hard to imagine that happening in England.

Leviton: We should talk about yeast as well.

Sheldrake: Yes, the history of agriculture is intimately entwined with yeast. It’s been debated for some time whether it was for bread or for beer that people first gave up their nomadic lifestyles and settled to grow grains.

Leviton: So the desire to brew beer may have been the start of modern civilization?

Sheldrake: The “beer before bread” hypothesis has been steadily gaining supporters. [Laughs.] In either case, humans feed yeast before they feed themselves. You can view this as us domesticating yeast or as yeast domesticating us.

About 10 million years ago a mutation in our genome gave us an enzyme that allows us much more efficiently to break down alcohol, which is the byproduct of the fermentation of grains, fruits, and other sources of sugar. Before this mutation alcohol was more toxic to us. The mutation seems to have allowed our primate ancestors to eat overripe fruits that had fallen to the forest floor, which may have played a part in our moving out of the trees and into a ground-dwelling existence.

Of course, everything is constantly tending toward rot and fermentation. Before refrigeration, food preservation was solely an effort to steer these metabolic processes in ways that were amenable to our culinary predilections and not just “off” and disgusting. Some of the greatest flavors in the world to this day are fermented: wines, cheeses, chocolate, olives, yogurts.

Fermentation is a basic feature of human life because it had to be. During that long period of time before we could artificially cool food and slow these metabolic processes, we learned to domesticate fermentation, to tame this chemical transformation, which is overseen by a chorus of microbial beings. I like fermenting foods because that jar in my kitchen reminds me we live in a world of metabolic processes that are mostly outside our notice.

Leviton: Psychopharmacologist Ronald Siegel at UCLA believed there is a strong biological drive to seek intoxication. Do you agree?

Sheldrake: It’s true that humans seek out intoxication. And not just humans: there are many examples of other animals seeking intoxication, too.

I think a pretty good case can be made that the desire for altered consciousness is a fundamental human trait. Andrew Weil cowrote, with Winifred Rosen, a book called From Chocolate to Morphine, in which he talks about how even young children have a tendency to alter their mental state by spinning around until they become dizzy. Whether or not we have a drug to assist us, we have an urge to somehow “get outside” our normal waking consciousness, which can lead us toward social, cultural, and spiritual enrichment and teach us something about what it means to be alive. Of course, psychoactive substances can cause problems. But mind alteration is here to stay.

Leviton: Let’s talk about a relatively new field: using fungi to clean up the environment by breaking down oil spills, plastic, and so forth.

Sheldrake: First of all, this idea is very old. Mycoremediation, as it’s called, has gone on forever. [Remediation in ecology is a reversal of environmental damage. — Ed.] Fungi are veteran survivors of ecological disruption, and they are prodigious decomposers. When you make alcohol, it is a kind of remediation: you’re encouraging yeast to remediate sugar into alcohol. When you make vinegar, you’re encouraging the remediation of alcohol into acetic acid. When you make miso, you’re encouraging a fungus to transform soybeans into a delicious, savory paste.

Now we are exploring how to harness the power of these fungal appetites to help us clean up pollutants. It’s not always straightforward, because you might find a fungus that can digest a pollutant in a petri dish, but that doesn’t mean you can just distribute this fungus into a full ecosystem and expect it will consume the contaminant, because there are all sorts of other organisms there. The fungus might not be able to get a foothold. For instance, the mycologist Peter McCoy trained Pleurotus mycelium to digest one of the most common types of litter: cigarette butts, which are saturated with toxic residues. His jam jar full of butts eventually broke down and transformed into an oyster mushroom. But can that process be applied to the 750,000 tons of cigarette butts thrown away every year?

And this big problem endures: just putting a fungus into an environment is not necessarily going to allow it to achieve a certain metabolic outcome. Some mycoremediation organizations and companies are now thinking that, instead of introducing a fungus into the environment, it’s better to divert waste streams into waiting fungal appetites. A company called Mycocycle is promoting a “closed-loop supply chain” to convert carbon waste into a usable byproduct. Asphalt roofing, for instance, is a huge source of landfill waste. Rather than wait until the pollutant is in the environment and then try to solve the problem, Mycocycle wants to divert old asphalt roofing into one of the company’s facilities, where fungi living in carefully controlled conditions are able to break it down in stages. This material is reduced to less-harmful byproducts, which might have a use or might just be safe to dispose of. This may be one of the most promising approaches to mycoremediation.

When the fungi break substances down, they do produce CO₂, and potentially methane. But the alternative is to have a poisonous substance contaminating the environment, and it will break down eventually. It’s better that we control that process rather than carelessly throw everything into a landfill where anything can happen.

Fungi are . . . sort of like cooks, combining ingredients. They lead us to see the world as made up of the relationships between organisms. We should be trying to understand organisms as wholes rather than as a list of their component parts.

Leviton: I interviewed your father for The Sun in 2013, and I see certain similarities in your work: You share his ability to avoid the straitjacket of rigid scientific thought. And you both value not only data and rigorous methodology, but intuition, enthusiasm, and emotion.

Sheldrake: My father’s a brilliant student of the living world and is endlessly curious about it. He has the ability to communicate that curiosity and awaken it in other people. Growing up with him as my father was an exciting experience, because he taught me to be curious about the world. He’s able to think very broadly, with little regard for the boundaries between disciplines. So he was an inspiring person and certainly encouraged my interest in biology and ecology. I learned from him to be suspicious of research programs that aim to reduce at all costs — meaning they want to break the world into pieces, chop up organisms and try to understand how they work by looking at the molecules that make them up. Reduction plays an important role in our efforts to understand the living world, but there’s a lot we can’t learn when we do that. We also need to look at the whole organism in its environment. We need to look at interactions between organisms.

Fungi are inherently integrative. They’re connected. They facilitate connections between other organisms. They’re sort of like cooks, combining ingredients. They lead us to see the world as made up of the relationships between organisms. We should be trying to understand organisms as wholes rather than as a list of their component parts.

Leviton: We have to critique how science functions in order to improve it, but we often see a rejection of science; a rejection of facts, statistics, probabilities. A U.S. president said, “I don’t think science knows” — in the middle of a global pandemic and increasingly widespread drought, hurricanes, and wildfires.

Sheldrake: Right. This has been a major issue for much of the history of science.

It’s not the first time that there have been these very vocal questions about what science is and should be: What is this discipline we call science? What’s it doing? What’s its role in society? How should it be funded? How does it relate to other aspects of human endeavor? How should we handle the evidence produced by scientists? Who are these people in our labs, universities, and medical establishments, and how are they taught?

There’s a good phrase I’ve run across that defines science as the “journey toward less uncertainty.” I think that’s a helpful way of understanding a lot of scientific endeavors. It’s not absolute certainty; it’s less uncertainty.

The universe was not made to be categorized, classified, systematized. We are wrestling with this unclassifiable, uncategorizable universe, and it’s messy. We can’t step outside the universe to observe it. There is no perfectly objective vantage point for us to observe from. The world is the biologist’s flask, and we’re in there with it.