Mushrooms and other kinds of fungi are often associated with witchcraft and are the subjects of longstanding superstitions. Witches dance inside fairy rings of mushrooms according to German folklore, while a French fable warns that anyone foolish enough to step inside these ‘sorcerer’s rings’ will be cursed by enormous toads with bulging eyes. These impressions come from the poisonous and psychoactive peculiarities of some species, as well as the overnight appearance of toadstool ring-formations.
Given the magical reputation of the fungi, claiming that they might be conscious is dangerous territory for a credentialled scientist. But in recent years, a body of remarkable experiments have shown that fungi operate as individuals, engage in decision-making, are capable of learning, and possess short-term memory. These findings highlight the spectacular sensitivity of such ‘simple’ organisms, and situate the human version of the mind within a spectrum of consciousness that might well span the entire natural world.
Before we explore the evidence for fungal intelligence, we need to consider the slippery vocabulary of cognitive science. Consciousness implies awareness, evidence of which might be expressed in an organism’s responsiveness or sensitivity to its surroundings. There is an implicit hierarchy here, with consciousness present in a smaller subset of species, while sensitivity applies to every living thing.
Until recently, most philosophers and scientists awarded consciousness to big-brained animals and excluded other forms of life from this honour. The problem with this favouritism, as the cognitive psychologist Arthur Reber has pointed out, is that it’s impossible to identify a threshold level of awareness or responsiveness that separates conscious animals from the unconscious. We can escape this dilemma, however, once we allow ourselves to identify different versions of consciousness across a continuum of species, from apes to amoebas.
That’s not to imply that all organisms possess rich emotional lives and are capable of thinking, although fungi do appear to express the biological rudiments of these faculties.
Just what are mushrooms? It turns out that this question doesn’t have a simple answer. Mushrooms are the reproductive organs produced by fungi that spend most of their lives below ground in the form of microscopic filaments called hyphae. These hyphae, in turn, branch to form colonies called mycelia. Mycelia spread out in three dimensions within soil and leaf litter, absorbing water and feeding on roots, wood, and the bodies of dead insects and other animals. Each of the hyphae in a mycelium is a tube filled with pressurised fluid, and extends at its tip.
The materials that power this elongation are conveyed in little packages called vesicles, whose motion is guided along an interior system of rails by proteins that operate as motors. The speed and direction of hyphal extension, as well as the positions of branch formation, are determined by patterns of vesicle delivery. This growth mechanism responds, second by second, to changes in temperature, water availability, and other opportunities and hardships imposed by the surrounding environment.
Each mycelium is like a snowflake, with a shape that arises at one place and time in the Universe
Hyphae can detect ridges on surfaces, grow around obstacles, and deploy a patch-and-repair system if they’re damaged. These actions draw upon an array of protein sensors and signalling pathways that link the external physical or chemical inputs to cellular response.
The electrical activity of the cell is also sensitive to changes in the environment. Oscillations in the voltage across the hyphal membrane have been likened to nerve impulses in animals, but their function in fungi is poorly understood. Hyphae react to confinement too, altering their growth rate, becoming narrower and branching less frequently.
The fungus adapts to the texture of the soil and the anatomy of plant and animal tissues as it pushes ahead and forages for food. It’s not thinking in the sense that a brained animal thinks – but the fundamental mechanisms that allow a hypha to process information are the same as those at work in our bodies