The Light Eaters

zoë schlanger the light eaters

how the unseen world of plant intelligence offers a new understanding of life on earth.

in 1973, the book the secret life of plants tore a schism in plant-loving communities worldwide.

plants, claimed the authors peter tompkins and christopher byrd, were conscious.

like humans, they had emotions, preferred classical music to rock, and could feel pain.

but as people worldwide began leaving their speakers on for house ferns, botanists raged behind the scenes.

the book was heavily criticised for its lack of vigorous scientific methodology and its reliance on anecdotal evidence.

the concept that plants could be conscious had gripped popular culture.

but scientists were sceptical.

as a result, the scientific community remains wary of the term, preferring to focus on observable, measurable phenomena in plant behaviour and physiology.

as a result, the field of plant consciousness was sidelined, relegated to pseudoscience.

it's only recently that scientists have stumbled back into the notion of plant consciousness, often unwillingly.

to be clear, no one is claiming that the patch of moss in your backyard has human intelligence.

nor, scientists are quick to clarify, does it mean that plants can feel emotions or even think in the way we would use the term.

but it's becoming increasingly difficult to ignore the fact that plants possess complex communication systems, can respond to their environment in sophisticated ways, and even exhibit behaviours that suggest a form of memory.

these discoveries have reignited discussion about what it means to be conscious and whether the greenery around us has a form of awareness, however alien it is from our own.

in this chapter, we're going to delve into cutting-edge theories of plant neurobiology and discover how some scientists are drastically changing the way we look at the vegetation surrounding us.

by examining the work of leading scientists in the field, we aim to provide a comprehensive overview of the current state of knowledge on plant consciousness and the fascinating possibilities it presents.

in 1985, wildlife nutritionist wouter van hoven was tasked with solving a murder.

in the previous months, thousands of kudu in game ranches across the south african region of transvaal had suddenly dropped dead.

the kudu is a large african antelope known for its striking spiral horns and distinctive white body stripes.

now, their bodies littered the ground of every game ranch van hoven was called to.

what had caused such a die-off of these majestic creatures?

after weeks of collecting samples, van hoven found two things that he thought might explain what happened.

first, it had been a particularly dry winter, and stomach samples showed that the kudu had eaten mostly acacia leaves since the grass in the area was dry and dead.

this in itself isn't a problem.

acacia is part of a normal diet for the animals.

but these samples were different.

the second thing he found was that the stomach samples had a lethal dose of tannins.

when acacia are eaten, they begin to raise the tannins in their leaves to produce a bitter taste that deters the kudu from overeating.

but without any alternatives, the kudu continued to eat the leaves, and the plants continued to raise their tannin levels.

in fact, when the leaves were damaged, they released plumes of pheromones that alerted other trees in the area to start producing the tannins as well.

this, van hoven concluded, was a coordinated poisoning.

plants may seem passive to us, but they possess sophisticated mechanisms to respond to threats.

when faced with danger, plants can alter their physiology in ways that are both surprising and impressive.

rick carban is a biologist who started working with insects, but has become renowned for his work in demonstrating that plants truly can eavesdrop on distress signals from their neighbours.

when a plant is attacked by herbivores, it releases volatile organic compounds, also known as vocs, into the air.

nearby plants detect these vocs and preemptively bolster their own defences, producing chemicals that deter herbivores.

this form of communication is crucial for survival in environments where threats are unpredictable.

what's more, is that these vocs can be incredibly specific.

the sage bushes that carban works on are more responsive to chemical warnings to close genetic kin, and may tailor the signals they send out to benefit close relatives first.

they have also been shown to switch to a more general broadcast when in higher threat situations, where the whole community might be at risk.

this makes sense from an evolutionary point of view.

it's hard to be pollinated when you're standing in a field alone, but more curiously, it reveals a dynamic, responsive and highly adaptive form of life.

perhaps plants are far more attuned to their environment than previously thought, engaging in a silent but sophisticated battle for survival.

plants, though devoid of neurons, possess intricate electrical signalling systems that enable them to respond swiftly to environmental changes.

we can see this in plants such as the venus flytrap, which closes its modified leaves around its prey when an insect brushes against the trigger hairs twice in quick succession.

when these sensitive hairs are touched, an action potential is generated, an electrical impulse similar but unique to that we see within nerves.

in plants, action potentials propagate via ion movement across cell membranes, allowing rapid signal transmission across the plant.

intriguingly, the venus flytrap also responds to anesthetics, such as diethyl ether, as nerves.

when exposed to the drug, the electrical activity is suppressed, temporarily preventing the trap from closing.

so, what does it mean when a plant can be put to sleep, so to speak?

a plant has no central nervous system.

it has no brain where this information is collected and organised, meaning touch information is not processed in the same way it would be in animals.

so how could this be?

researchers like simon gilroy and shuhei toyota have uncovered the crucial role of electrical signalling in plant physiology.

by inserting a gene found in bioluminescent jellyfish, they have developed a way of tracking the electrical signals generated in a plant in real time.

when a leaf is damaged, a wave of electricity radiates from the wound in a ripple of light, triggering the production of defensive chemicals.

this does not mean the plant feels pain exactly.

pain is a way that these electrical signals are interpreted by the brain.

however, it does uncover the crucial role of electrical signalling in plant physiology to coordinate complex responses.

gilroy and toyota's research even show that electrical signals are modulated by the plant's metabolic state and environmental conditions.

these signals interact with chemical messengers, creating a communication network that integrates external stimuli with internal processes.

in other words, plants might be more aware of their surroundings than we've given them credit for.

so, the next time you brush up past a bush or walk across the grass, take a moment to think about if the plant can feel you too.

imagine these electrical waves rippling across the surface of the leaves, aware, in their own ways, of your presence.

the world is alive around you, a dynamic, responsive system capable of rapid communication and complex, reactive behaviours.

if a tree falls in a forest, can it hear the sound?

plants may not have ears, but they are remarkably attuned to the sounds around them.

recent research has shown that plants can hear vibrations and respond in ways that enhance their survival, revealing a new dimension of plant behaviour that challenges our understanding of sensory perception in the plant kingdom.

and, no, this doesn't mean you should start playing mozart to your houseplants.

but scientist rex cockroft's research has demonstrated that plants can detect and respond to the sound caused by insect herbivores.

sound, after all, is just a form of vibration propagated across space.

in one study, cockroft and his team used arabidopsis, a small flowering plant, to investigate how it responds to the sound of caterpillars munching on its leaves.

they discovered that the plant could distinguish between different types of vibrations.

when exposed to recordings of caterpillar feeding vibrations, the plants increased the production of mustard oils, chemicals that deter herbivores.

this response was specific to the feeding vibrations, as the plants did not react similarly to other environmental sounds, such as wind or insect song.

cockroft went on to collaborate with chemical ecologist heidi appel to explore exactly how plants respond to these acoustic cues to detect threats.

their research found that plants exposed to the vibrations of caterpillar feeding exhibited a primed defensive state, where they were better prepared to produce defensive chemicals more rapidly when actual herbivore attacks occurred.

this priming effect highlights a form of hearing that allows plants to anticipate and prepare for imminent danger.

interestingly, the ability of plants to respond to sound isn't limited to defensive actions.

other studies have shown that plants can also use sound waves to influence their growth and development.

a study by evolutionary biologist lilac hadani showed that the flowers of the evening primrose responded to the specific sound frequency of pollinator wingbeats.

the vibrations caused by honeybees in flight resonated with the structure of the flower, stimulating the plant to produce sweeter nectar in anticipation of their arrival.

interestingly, removing or damaging parts of the flower breaks this sympathetic resonance, decreasing the flower's capacity to anticipate the pollinator's presence.

in other words, the shape of the flowers themselves have evolved into a sort of ear, amplifying the sound waves to better prime the plant for the honeybee's arrival.

if plants do respond to sound, then it makes sense that they've evolved to listen to the parts of the world relevant to their survival.

so no, your houseplants probably don't care about your music taste.

but through fascinating studies like the ones we've talked about, we are beginning to understand the rich sensory lives of plants, showing that they are dynamic organisms capable of responding to the acoustic dimensions of their environment.

as we've mentioned, plants don't have a centralised brain to process and store information, such as pain or memories.

however, plants may still be able to remember past experiences and adjust their behaviour accordingly.

this form of memory, while fundamentally different from animal memory, allows plants to optimise their responses to recurring environmental challenges.

frantisek beluska studies how plants store and utilise information from their past.

his research focuses on the role of plant root tips as centres of sensory perception and signal processing, demonstrating that when roots encounter obstacles or changes in their environment, they can alter growth patterns in response to past experience.

for instance, beluska exposed roots to specific stimuli such as physical barriers or a chemical gradient in the soil, then removed the plant from these conditions.

after a period of time, they were re-exposed to the same or similar stimuli to observe if the plants responded more quickly the second time.

beluska's studies suggested that plants use electrical and chemical signalling to encode experiences in their cellular structure, allowing them to recall and learn from their past.

one of the most striking examples of plant memory is seen in the sensitive plant, mimosa pudica.

when touched, its leaves fold as a defensive response.

stefano mancuso conducted experiments where mimosas were repeatedly dropped but not harmed.

initially, the plants closed their leaves upon being dropped.

however, after several repetitions, the plants learned that the drop was not harmful and stopped closing their leaves.

this habituation process indicates a form of learning and memory, showing that plants can modify their behaviour based on past experiences.

further studies have shown that plants can remember environmental conditions and adjust their growth accordingly.

for instance, plants exposed to drought conditions will remember the stress and respond more quickly to future droughts by altering their water retention mechanisms.

this ability to anticipate and prepare for environmental stresses enhances their survival and adaptability.

the mechanisms underlying plant memory involve complex biochemical processes.

signalling molecules such as calcium ions, reactive oxygen species and phytohormones play crucial roles in encoding and retrieving memory.

these molecules create a dynamic feedback loop where past experiences influence future responses.

through the groundbreaking work of researchers like balusca and mancuso, we are beginning to unravel the mysteries of plant memory, revealing that these seemingly simple organisms possess an incredible capacity for learning and adaptation.

this insight not only deepens our understanding of plant biology but also inspires new ways of thinking about intelligence and memory in the natural world.

chatting with the neighbours we've talked a lot about plant physiology and how they can communicate between the same species, but within the complex web of life, plants might engage in even more sophisticated communication between different species and even with the animals that interact with them.

consuelo de moraes' research has been pivotal in uncovering the nuances of these multi-species interactions.

one of her most fascinating studies involves the parasitic plant cuscuta, commonly known as dodder.

dodder plants do not photosynthesise.

instead, they rely on other plants for sustenance.

de moraes discovered that dodder plants can sniff out their preferred hosts by detecting specific volatile organic compounds, vocs, emitted by the host plants.

this olfactory guidance allows dodder to locate and attach to suitable hosts, ensuring its survival.

another striking example of multi-species communication is the relationship between plants and pollinators.

de moraes' work highlights how plants emit floral scents to attract pollinators such as bees, butterflies and bats.

these scents are carefully tailored to the preferences of their target pollinators, ensuring successful pollination.

but it works the other way around too.

honeybees have been found to bite the leaves of plants when they are starving, before the flowers.

this seems strange at first.

the leaves don't provide nutrients, so bees seem to be wasting energy on something that doesn't benefit them.

but it's been shown that plants with bee-bite marks open their flowers faster, often months out of season.

the bites appear to be a sort of signal for the plants, who benefit from keeping their pollinators healthy in times of need.

but inter-species communication isn't always about pollination.

sometimes it's about defence.

some of de moraes' work explores how plants use chemical signals to enlist the help of predatory insects.

when attacked by herbivores, some plants release vocs that attract predatory insects, such as parasitic wasps.

these wasps then attack the herbivores, reducing the damage to the plant.

this form of indirect defence showcases a sophisticated strategy where plants recruit allies to fend off their enemies.

these examples of multi-species communication illustrate the complex and dynamic interactions between plants and animals.

the work of scientists like de moraes' reveal that plants are active participants in dialogue with their ecosystem, capable of sending and receiving sophisticated signals that iterate the interconnectedness of life.

in this chapter to the light eaters, by zoe schlanger, you've learned that plants are far more than passive green backdrops to our world.

they communicate, defend themselves, and even remember experiences, displaying a form of intelligence that challenges our traditional understanding of consciousness.

the groundbreaking research by scientists like rick carbon, simon gilroy, and consuelo de moraes has revealed that plants possess complex systems for electrical signaling, chemical communication, and inter-species interaction.

by altering our perspective and recognising the sophisticated behaviours of plants, we can better appreciate their crucial role in the ecosystem.

this newfound understanding encourages us to rethink our relationship with plants, emphasising the importance of preserving plant communities for the health of our planet.

as we continue to explore the mysterious and dynamic lives of plants, we are reminded that intelligence and awareness come in many forms, each contributing to the rich diversity of life on earth.

ok, that's it for this chapter.

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see you in the next chapter.