by Daniel Kolitz
May 28, 2018
Illustration: Angelica Alzona
Animal rights activists have done stellar work in foregrounding the
question of creature-consciousness:
no meat-eater is now
ignorant of the fact that their food once lived, breathed, maybe
nuzzled its kin in a blood-soaked slaughterhouse.
Environmentalists have a
harder go of it.
Fracking footage will
always be less upsetting than your average fast food expose:
Plants, after all,
can't wail frantically as they're mowed down by the millions.
But does that mean
they're not conscious?
Is it sensible, or
desirable, to start anthropomorphizing crabgrass and dandelions, or
are plants really as insensitive as we all instinctively assume?
posed those questions to a number of environmental scientists and
philosophers - including a professor on the vanguard of something
called "plant neurobiology."
Plants may not be
able to wistfully reflect on their childhood, or hear/see anything
in a conventional sense, but they do, as it turns out, retain
information, and make "decisions" based on past experiences.
constitutes "consciousness" depends, as always, on how you define
Ikerbasque Research Professor,
Philosophy, University of the Basque
and author of
Plant-Thinking: A Philosophy of Vegetal Life,
among other works
definitely conscious, though in a different way than we, humans,
To find the
resources they need for living and thriving, they need to orient
themselves in above- and below-ground environments.
And so, plant
roots navigate the subterranean labyrinths of soil, rock, water,
bacteria and roots of other plants no less proficiently than
mice in search of food.
They must be
aware of dangers - the onset of drought, or invading herbivore
insects - in order to carry out the most essential life
activities, or to activate their defenses (for instance, by
releasing biochemical cues that call upon the predators who will
devour the threatening herbivores).
They have to
make complex decisions on the best time to blossom, juggling up
to twenty environmental factors, such as the length of day or
the warmth of the air, comparing the evolution of these
conditions over a span of at least a month.
In other words,
plants gather as much information about the world they live in
as possible and, attentive to changes in it, act with
consciousness literally means being "with knowledge," then
plants fit the bill perfectly.
Of course, they
do not have the sense organs we are used to, such as the eyes
and the ears, to receive stimuli from the environment.
But they do
have cells and tissues (say, photosensitive receptor cells) that
do the trick as well as - and sometimes better than - an animal
or human eye or ear would.
The data they
receive from the constantly changing world is essential for
In fact, they
change in tune with the world and with the seasons, growing when
the conditions are optimal, or shedding leaves and bringing life
to a minimum in the cold of winter.
We might say
that plant consciousness is saddled with tons of knowledge,
because plants live with an extreme sensitivity to the places
where they grow.
It is another
question whether plants are self-conscious. Before dismissing
the existence of this higher-level faculty in them outright, we
should consider what a plant self might be.
Plants are only
loosely integrated into a unity (take a cutting from a magnolia
stem, and it will grow independently!).
It stands to
reason that their sense of self would be equally dispersed.
Quite often, in fact, parts of a plant subject to danger (e.g.,
the leaves invaded by unwelcome insects) will communicate the
threat by releasing airborne biochemical substances to other
parts of the same plant.
The project of
an ongoing vegetal integration through feedback loops and other
communication strategies and mechanisms may be considered
analogous to what we, humans, define as self-consciousness.
The trick is to
let go of our fixed association of biological, if not
psychological, structures and the functions they fulfill,
imagining the possibilities of seeing and thinking otherwise
than with the eye and the brain.
Maybe once we
manage to do so, we will finally become conscious of plant
Professor, Environmental Sciences,
University of Toledo,
whose research focuses on how plants
recognize and respond
to insect herbivores with chemical
My view is that
they are not, even though they are aware of many aspects of the
environment in which they live.
My answer is
shaped by the common definitions of consciousness in the English
language, which all include the concept of mind and
self-awareness, in addition to being aware of one's environment.
The ability to
sense things in the environment and to integrate those
sensations into a beneficial response is not in itself
consciousness. Plants are not exceptional in being able to do
this - it's a trait of all life forms.
Plants are just
usually underestimated because they lack the specialized organs
that vertebrates possess to sense their environment.
suggested that since plants can form ‘memories' they are
therefore conscious beings.
retain information about what they experience, in that their
response to changes in their environment can depend on what
they've experienced previously.
may exhibit some traits that are influenced by what their
parents experienced. Retaining information within and between
generations of organisms is a trait of all living things, with
an increasingly well-understood genetic basis.
constitute ‘memories' depends on whether you define ‘memory' as
‘recall' or something more.
If we return to
common definitions in the English language, memory as commonly
defined does not require self-awareness, even though our
personal experience of memory as humans is certainly integrated
with the notion of self-awareness.
Dr. François Bouteau
problem with this question is the definition of what we call
If we consider
the definition of consciousness in a psychological sense, i.e.
made to describe different aspects of human life that would be
related to notions of knowledge, emotion, existence, intuition,
thought, psyche, subjectivity, sensation, reflexivity... it is
obviously difficult to answer the question for a plant.
doctors working on coma patients know that consciousness is not
binary and that there is a wide range of conscious states in
humans between the total loss and awakening state of a healthy
If we consider
a more general definition of consciousness as the ability to
perceive our own existence and the world around us, and accept
that we do not need a brain to have a consciousness, the matter
begins to be simpler.
have shown that plants perceive and interact with the world
around them, using complex behaviors.
As regards the
perception of their own existence, no one can say, but there is
growing evidence that plants are capable of a recognition of
kinship that could argue in favor of a capacity for
Another way to
approach the issue is to seek operational evidence of this
A classic way
to make a human being lose consciousness is to anesthetize him,
the very practical consequence during surgery being the loss of
perception of our existence and the world around us.
effectiveness on plants of anesthetics used during such
operations has been demonstrated for a very long time.
Although we do
not yet really know how these anesthetics work in plants or
animals, it seems, in a very interesting way, that the same
cellular mechanisms, including the functioning of ion channels
allowing the genesis of the action potential, are inhibited.
of argument is that plants, when injured, synthesize molecules
with anesthetic power.
like all living beings on earth have a form of consciousness is
very likely since it could correspond to an adaptive necessity
Entomology and Nematology, UC Davis
and author of
Plant Sensing and Communication
The answer to
this question depends entirely upon how you define
definitions include awareness of one's environment. By this
definition there can be little doubt that plants are conscious
organisms. Other definitions require the operation of a person's
obviously fail to meet these requirement as they are not persons
and lack brains.
evidence that plants are aware of their environments is
overwhelming. Anyone who has ever had a houseplant in a window
has observed that the plant grows towards the light. To achieve
this response it must perceive the direction of the light and
allocate resources preferentially.
perceive self and non-self and allocate resources differently
when they encounter tissues of these two types.
differentiate the quality of shade cast by a green competitor
and respond more strongly to this threat than to an inanimate
anticipate future conditions and respond to the light cast by
competitors before actually being shaded.
Plants not only
perceive light but many other qualities of their environments
that affect their survival and ability to reproduce. However,
there is no credible scientific evidence that they perceive
music or prefer classical music rather than rock.
for nutrients in the soil, growing dense roots in rich areas and
abandoning poor ones.
microbes that they come in contact with and reward those
associations that are beneficial to them while actively
defending against those that are harmful.
actively defend themselves against insects and other larger
herbivores which make their own living feeding on plants.
They respond to
actual damage, as well as a variety of reliable cues that
predict future risk by elevating sophisticated and often costly
include airborne chemicals that are emitted by their own damaged
tissues or those of their neighbors.
They respond to
chemicals associated with mating and egg-laying of insects as
well as insect footsteps, insect saliva, and vibrations caused
by insect chewing.
have experienced damage remember those experiences and respond
more rapidly and more strongly to subsequent attacks.
In some cases,
this memory persists for several plant generations.
Dean, George S. Wise Faculty of Life
Director, Manna Center for Plant
Tel Aviv University
obviously aware of their visual environment, and of smells in
know if they're being touched
have different types of memories
can differentiate between up and down,
that doesn't mean that plants are conscious.
I can use the
aware of their environment.
organisms are aware of their environment - you have to be in
order to survive.
even bacteria, have to be able to find the exact niche that will
enable them to survive. It's not anything that's unique to
Of course, this
also falls into the question of intelligence.
can't even agree on a definition of intelligence for
The bottom line
as I see it is that plants are incredibly complex organisms that
have evolved for the past two billion years completely
differently than animals have, and we don't need to
anthropomorphize them in order to appreciate their complexity.
have nerves, and plants don't have brains, but they still
integrate signals from their roots and their leaves and their
flowers, and know how much light there is and what the
temperature is and how many bugs are in the area, and they
integrate all of this information to yield a plant that is
exquisitely adapted to its environment, and they do it all
without a brain.
So, what's that
say about the need for a brain?
In other words:
you can eat your plants without feeling guilty.