There is a great, third kingdom of life lying hidden at our feet – that of the fungi. So ubiquitous are they that they also lie hidden in our feet: around a hundred species have been recorded on the human foot alone. The other two kingdoms of multicellular life – plants and animals – are obvious to us. If we think about fungi at all, we tend to associate them with plants. But fungi are in fact more closely related to animals, and this relationship is reflected in their chemistry. For example, both fungi and animals produce the light-sensitive proteins known as opsins that are present in the rod and cone cells of animal eyes. Astonishingly, these proteins allow fungi to “see” colour.
According to Merlin Sheldrake’s passionately and convincingly argued Entangled Life, we have fundamentally misunderstood fungi. It is not mushrooms, but the “wood wide web”, the ecosystem highway and the fungal mind that we should think of when we hear the word “fungi”. It’s hard to believe that Entangled Life is Sheldrake’s first book. A pioneer of soil fungal research in the tropics, Sheldrake has the rare ability of translating his own and others’ highly technical findings into riveting prose. With its delightful illustrations, all drawn using ink derived from the shaggy ink cap mushroom, the book is a sensory as well as an intellectual pleasure.
Entangled Life begins with a disquisition on my favourite food – the European white truffle. I am not alone in my enchantment with this fungus: in 2007, a single white truffle weighing around 2lb sold for $330,000, making it far more expensive than gold. In its appeal to the human nose, Sheldrake informs us, the white truffle is a rarity among its kind. Of the thousand truffle species inhabiting North America, few are appetising to humans. One produces a stench reminiscent of baby diarrhoea, revolting the human truffle hunters who encounter it – though not their dogs, who find the pong irresistible.
Truffles are the reproductive organs of fungi that ripen deep in the soil. To successfully reproduce, the hidden fungus must induce its target species to labour at locating and unearthing it. The evolutionary dance between fungal scent and the mammalian nose is necessarily slow, taking thousands of generations of trial and error to reach the aromatic perfection possessed by the white truffle. Perhaps the fungus first refined its perfume on Homo erectus, who entered Europe around two million years ago.
Fossils indicate that the kingdom of fungi may have been in existence for more than two billion years. More certain is that they peaked some 400 million years ago, when forests of great Prototaxites fungi, with trunks eight metres high and a metre thick, colonised the land. How strange that lost fungal era must have been, with its damp, fragrant, silent forests of tree-shaped mushrooms, inhabited only by millipedes, centipedes and scorpions. Within a few tens of millions of years, the earliest land plants had replaced the great fungi, forcing their descendants into subterranean and other obscure habitats.
Today’s fungi may be less imposing than Prototaxites, but they are probably more prevalent. The mycelium of the mycorrhizal fungi (those associated with plant roots) alone make up between a third and half of the weight of the soil. So abundant are they, and so vigorous is their growth, that over a million years their mycelium would exceed the diameter of the known universe. Fungi are just as widespread outside the soil, inhabiting animals and plants alike. Nobody knows how many species exist, but the current tally of named types is surely the tip of the iceberg.
The third kingdom is so profoundly important to the Earth’s ecosystems that it is hard to imagine plants and animals thriving without it. More than 90 per cent of plant species depend upon fungi for their existence. From the wood wide web, which redistributes carbon and vital minerals such as phosphorous to plants across kilometres, to the fungi that rot cellulose, to those that thrive in the depths of the sea and the dry valleys of Antarctica, fungi play a vital part. Some may even have a role in remediating a post-apocalyptic age: a kind of fungi that was discovered thriving around the ruins of the nuclear reactor at Chernobyl uses radioactive waste as food.
Fungi specialise in decomposing things and are expert at breaking down resistant materials such as rocks and cellulose. But they are not mere passive agents. Indeed, they have so many ways of sensing the world that Sheldrake describes them as living “in a flood of sensory information”. And like animals, fungi appear to utilise electrical impulses to communicate, spreading information across a mycelium network far more rapidly than could be achieved using chemicals. Neurologists tend to steer clear of terms such as “brain” when discussing the ways fungi integrate information to decide on actions; but it is indisputable that, like brains, fungal mycelia consist of fantastically complex networks of electrically excitable cells, and that these networks can complete complex transactions.
Experiments have shown fungi can trade rare nutrients including phosphorus with plants in exchange for carbon-based energy. The trade is sophisticated, rewarding the fungi’s most cooperative trading partners and hoarding minerals when the exchange rate falls too low. This is possible because fungi can move minerals around their network in any direction, regardless of density gradients. They are even capable of running “take now, pay later” schemes with various plant partners.
The evolutionary relatedness of fungi and animals may have given fungi some extraordinary opportunities denied to plants. Some fungi, for example, are active hunters, capturing nematodes – a kind of worm – by a variety of means including nets, poisoned droplets, harpoons and swimming spores. Some fungi even hunt bigger prey: one of the most remarkable is surely Ophiocordyceps unilateralis, which organises its life around carpenter ants. The ants become infected when fungal spores land on them, and soon start exhibiting strange behaviours. Carpenter ants have a natural fear of heights, but when infected by the fungus, they become as fearless as tightrope walkers and, in a syndrome known as “summit disease”, climb the nearest plant. When an ant reaches an altitude at which the temperature and humidity is optimal for the fungus, it bites into the vein of a leaf – and never lets go. The fungus then grows out through the ant’s feet, stitching them to the plant, and begins consuming it from the inside. Eventually, a mushroom bursts from the victim’s head, sprinkling spores over a vast area to spread the infection anew.
It was long believed that the Ophiocordyceps fungus controlled the ant’s mind. But in 2017 researchers examined ants as they made their “death bite” into a leaf. By slicing the ants into thin sections, they showed that almost every organ was laced with fungal hyphae – except the brain. The fungus, it seems, can puppeteer the ants’ movements using chemical signals: an ant may desperately want to return to the warmth and comfort of the nest, but finds itself marching to ever more dizzying heights, until it is forced to make its suicidal bite and endure all that follows.
Upon reading this gruesome passage, and newly cognisant of the fungi lacing my entire body, I sought reassurance in the superior immune systems of vertebrates like myself, which protect us from fungal takeover. My sense of comfort was, alas, momentary. In the very next paragraph, Sheldrake informed me that Ophiocordyceps is a close relative of the ergot fungus, which notoriously poisoned barley during the Middle Ages, causing hallucinations and compulsive dancing in people that lasted for days. Ergot is, in a sense, still with us, for its psychoactive compounds were used to make the first LSD.
The fungus Massospora offers a second extraordinary example of fungal control. It infects cicadas, causing the entire rear third of their bodies to rot away. Despite their complete loss of genitals, the cicadas are seized with an insatiable desire for sex. Massospora produces both cathinone (the active ingredient in the stimulant khat) and psilocybin (the active ingredient in magic mushrooms). Stimulated, hallucinating and raging with desire, the frenzied, emasculated cicadas are transformed into, as one researcher put it, “flying saltshakers of death”.
Ophiocordyceps doesn’t care what animals think: it simply takes over an ant’s body. But Massospora clearly takes a great interest in the mind of its victim. In the light of the ability of certain mushrooms – such as magic mushrooms – to modify human behaviour, could it be that some fungi have an interest in the way we think? Another way of putting the question is whether some fungi have evolved an ability to alter our minds in order to benefit themselves, by inducing us to consume and disperse their spores.
In what researchers consider some of the most effective psychiatric interventions in the history of modern medicine, psilocybin was used to treat anxiety, depression and existential distress in people with terminal cancer. The response was dramatic, with 80 per cent of participants in the trials reporting substantial reductions in their symptoms, and 70 per cent describing the effect of the mushrooms as one of the five most meaningful experiences of their life.
Such profound changes in people’s minds are rare. Psilocybin appears to work by shutting down the brain’s default mode network (DMN). Described as the “corporate executive” of the brain, the DMN is involved in giving us our sense of self. Intriguingly, the profound, mystical experience of awe – a sense of everything being interconnected – reported by participants was accompanied by the loss of a sense of a clearly defined self. Scientific investigation into fungal influences on the human brain is in its infancy. But as Entangled Life makes clear, it is a research area of enormous potential importance.
Accomplished, riveting and surprising at every turn, Entangled Life explains the importance of fungi to our world. It is a fascinating tribute to organisms that, in comparison to plants and animals, remain almost unknown to science. Such is the complexity and diversity of fungi that none but a practising mycologist could have written such a work. We owe a great debt to Sheldrake for lifting his eyes from the microscope for long enough to enlighten us about the wonders of fungi.
Entangled Life: How Fungi Make our Worlds, Change our Minds, and Shape our Futures
Bodley Head, 368pp, £20