‘Solving mazes and complex routing problems are non-trivial exercises,’ Sheldrake writes.
‘This is why mazes have long been used to assess the problem-solving abilities of many organisms, from octopuses to bees to humans.’
Fungi ace these puzzles because ‘solving spatial and geometrical problems is what they have evolved to do.’
They are diffuse, plastic beings: they reform themselves around the problem at hand. ‘Mycelium’, says Sheldrake, is a body without limits: ‘a body without a plan’.
With a decentralised body that grows independently at every extremity, how does a fungus know when to change itself?
When a hyphal tip discovers a tasty block of wood, how is this information conveyed to the rest of the network-body? Through chemical transport, perhaps?
Fungi are known to produce and respond to chemicals that can act as cues, and mycelial networks transport water and nutrients rapidly through their hyphae in ‘micro-tubules’, which function hydraulically and are highly pressure-sensitive.
They can also direct the flow towards particular areas: when it is time to produce a mushroom, for instance, the mycelium propels water into the growing fruit, sometimes under great pressure.
A fruiting stinkhorn mushroom can crack through asphalt, exerting a force sufficient to lift about 130 kg.
However, as methods of communication go, chemical plumes and microflows of pressurised liquid aren’t very fast – and the mycelium of some fungi can extend for kilometres.
Would electricity fit the bill? In the 1990s, the Swedish mycologist Stefan Olsson began to investigate.
Adapting techniques used to research the brains of insects, he inserted glass microelectrodes into the body of the honey fungus, a species that creates huge mycelial networks.
Sure enough, the mycelium was producing electrical impulses ‘at a rate very close to that of animals’ sensory neurons’, which travelled through the network along the hyphae.
When a block of wood – a food source – was placed in contact with the wired-up mycelium, the rate of firing doubled; it returned to normal when the wood was removed.
Controls with a plastic block of similar size showed that the fungus was identifying the wood, rather than merely responding to weight or contact.
Olsson repeated the experiment with other species of fungi, obtaining the same results: he concluded that fungi use electrical signals for internal communication, reporting on what the hyphae find or what is happening around them.
They are, Sheldrake writes, ‘fantastically complex networks of electrically excitable cells’.
Some researchers compare mycelial networks to brains, others to computers.
Both images are seductive: the first suggests fantastical beings, extending themselves in contemplative ingestion through forest and field; the second invites speculation that mycelium’s ability to sample and report on its surroundings might somehow be harnessed as a kind of ‘biocomputing’, capable of providing finely textured real-time reports on the health of the environment.
Sheldrake cautions that neither metaphor truly gets close to the reality of mycelial lives, but he seems quite taken with them nonetheless.
Likewise, Olsson dismisses the brain analogy, yet when observing that hyphal branching creates junctions that could act as ‘decision gates’ to integrate the streams of impulses from the foraging tips, he can’t resist wondering if mycelium might indeed act like ‘a “brain” that could learn and remember’.
Whether or not mycelium in fact behaves like a neural network, fungi certainly seem to have a highly evolved interest in the brains and nervous systems of others.
The psychoactive effects that psilocybin-producing mushrooms have on humans are well known (though seriously under-researched), but the most virtuosic feats of mind alteration – if that is the right way to describe it – are performed by the numerous species of fungus that can control the minds and bodies of insects.
These are sometimes called ‘zombie fungi’, and they act with what Sheldrake describes as ‘exquisite precision’.
The fungus Ophiocordyceps infects carpenter ants. Inside the body of an infected ant, it begins to develop a mycelial network. Hyphae travel through the ant’s body cavities, into its limbs and organs: an infected insect becomes about 40 per cent fungus.
Once this fungal growth is complete, the normally ground-dwelling ant leaves its nest and climbs the nearest plant.
At a height of around 25 centimetres – ‘a zone with just the right temperature and humidity to allow the fungus to fruit’ – it orients itself towards the sun; at high noon, it clamps its jaws round a leaf vein, in a ‘death grip’.
Mycelium grows out of the ant’s feet, plastering it to the leaf. Sutured into place, jaws rigid, the ant’s body is then digested by the fungus: a small mushroom grows out of the ant’s head, releasing spores which drift down onto the ants passing below, beginning the cycle again.
Massospora, a species completely unrelated to Ophiocordyceps, infects cicadas: it rots away the abdomen of an infected insect, leaving it tipped with a yellowish plug of spores that looks like a mass of pollen.
Infected cicadas are not incapacitated or ill: in fact they become ‘hyperactive and hypersexual despite the fact that their genitals have long since crumbled away’.
Rushing between mates, they become ‘flying salt-shakers of death’, dusting other cicadas with Massospora’s spores.
It’s unclear how such exact behavioural changes are effected. Ophiocordyceps fills an ant’s body with hyphae and takes control of its actions, but it doesn’t invade the ant’s brain, which is left intact;
Massospora confines itself pretty much to the cicada’s abdomen, leaving the rest of the body alone, in order that the insect can continue to move around and attempt to mate while the fungus completes its life-cycle.
It is possible that the control is achieved by means of minutely precise pharmacological interventions in the brains of the hosts:
Massospora manufactures both psilocybin and cathinone, a stimulant related to the recreational drug mephedrone, which is otherwise found only in plants such as khat (Catha edulis, whose leaves are chewed widely in East Africa and beyond).
So the fungus is perhaps administering both amphetamines and psychedelics to its cicada. But nobody really understands quite how this would work.
The mechanism by which Ophiocordyceps produces exact and perfectly timed bodily actions in an infected ant is also a profound mystery, except that it most probably involves ‘fine-tuning’ the ant’s ‘chemical secretions in real time’.
Precise and complex effects of this sort are far beyond the reach of human medical pharmacology; Sheldrake compares the way these fungi command their hosts to phenomena such as spirit possession or the speech of mediums.
Like an incorporeal spirit, the fungus does not have a body, instead entering and possessing something else’s.
The ascent up the plant and the death grip are not the behaviour of the carpenter ant but of the fungus, which is using the insect as a kind of exo-suit:
‘For part of its life, Ophiocordyceps must wear an ant’s body.’ How rapidly, how finely must the network be communicating and acting to puppeteer the central nervous system of a living creature, to measure distance and conditions, to determine direction and time of day?
The question of fungal sentience hovers in the background, like the ambiguous ghosts of spirit photography.
These ideas spill over into a discussion of the effects of psilocybin on humans.
Sheldrake’s parents were friends with Terence McKenna, the ethnobotanist, renegade philosopher and advocate of psychedelics, and it was on a visit to McKenna’s Hawaiian home – whose grounds were a sort of Wonka Factory of psychoactive plants – that the young Merlin first learned that ‘humans can alter their minds by eating other organisms.’
McKenna speculated that psilocybin mushrooms lay at the root of human cultural development: it was consuming them which spurred the creation of art, culture, religion and even language.
But he also believed that by means of a big enough dose of psilocybin, mushroom consciousness could manifest inside a human partner, and even communicate to the outside world:
‘With psilocybin as a chemical messenger,’ fungi could ‘borrow a human body, and use its brain and senses to speak and think through.’
‘Do psilocybin fungi wear our minds, as Ophiocordyceps and Massospora wear insect bodies?’ Sheldrake asks. It’s a marvellous, disorientating notion. But his answer is a qualified ‘no’: science has not found any evidence of a long-term evolutionary advantage for fungi in using psilocybin to form a symbiotic relationship with humans or their minds.
Our eating them doesn’t appear to help them in evolutionary terms; the timescales of human intervention are too short, and psilocybin-producing fungi have been around too long to care much about people.
More likely, the compound developed to interfere with other beings, probably fungivorous insects.
But then again, Sheldrake writes, ‘perhaps we shouldn’t be too hasty’ in giving up McKenna’s notion. Sheldrake may, one suspects, have taken too many shrooms with too much fascination and joy to surrender the prospect that psilocybin might give us genuine insight into, or even a proxy experience of, fungal lives.
Tripping on mushrooms is just too mushroom-y, too psychomycelial, to be set aside when trying to think about what fungi are up to.
In the human brain, psilocybin suppresses what is called the ‘default mode network’, the interconnected brain areas responsible for self-reflection and self-consciousness, thinking about past and future, and for regulating other cerebral processes.
The DMN, Sheldrake says, keeps a kind of order: ‘a schoolteacher in a chaotic classroom’.
In neural terms, psilocybin and LSD let the brain ‘off the leash. Cerebral connectivity explodes, and a tumult of new neuronal pathways arise. Networks of activity previously distant from one another link up.’
The experience of this for the user involves all the stereotypical (but reliably real) sensations: mystical gnosis, the revelation of the interconnectedness of all things, and so on.
Put like that, the patterns of thought experienced by someone taking psilocybin seem strikingly analogous to its neurological effects.
And both seem profoundly similar to what we know of mycelium and its habits.
The explosive growth of interconnections, the development of flexible new relationships, the filling of spaces with a tangle of new pathways, novel and powerful exchanges and flows of information coursing through an electrically excitable network:
what else but this would a fungus do if it really did seize hold of your mind? And if a fungus were sentient or somehow like a brain, isn’t this perhaps just how it would think – in an entanglement of intimate, sudden, pulsing, fresh connections between the things around it?