Are Plants Conscious?

Scientists have found evidence that plants have senses, memories, and can even communicate with each other. But does this mean they're conscious?

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
it's Christian Seger. So there's this old episode of Star
Trek called Wink of an Eye. You may have seen it.
There's this race of aliens that live in hyper sped
up acceleration. So when the crew of the Enterprise appears

(00:22):
to meet up with them, they seem so slow that
they're unable to move. Now, imagine that scenario. If you
were the aliens, wouldn't you assume humans were inert objects
with no consciousness. Now let's take this and apply it
to our relationship with plants. When we watch videos of

(00:42):
plant life sped up, we see their lively movement. But
even though plants move and respond to stimuli, they're not conscious. Right, Otherwise,
every time we ate vegetables, we'd be causing them pain. Wait,
wait a minute, can plants feel pain? Well? Okay, there
was this guy once. His name was Charles Darwin. You

(01:04):
might have heard of him, and he once proposed something
called the root brain hypothesis. He proposed that the tip
of a plant's root could act like a brain does
in some animals, receiving sensory input and directing movement. In
the years since Darwin made this proposal. There's been a

(01:24):
growing movement in science called plant neurobiology, and it debates
the way we think about plants and consciousness. Other scientists
hate this term, but who cares, because here's some of
the things we know about plants because of this really
unusual research. Let's start with plant senses. We know that

(01:47):
plants have a variety of sense some that can actually
act as analogs to our site smell, touch, taste, and hearing.
In fact, there's evidence that when plants hear the sound
of a caterpillar chewing on a leaf, they respond defensively
by producing chemicals like mustard oil. This happens even if

(02:11):
the sound is a recording and nothing is eating the plant. Creepy, right.
Plants can also communicate sometimes. Plant chemical production is like
a method of communicating with other plants. So here's an example.
That smell of freshly cut grass that we all know
that's actually a distress call to warn other plants of danger.

(02:34):
It's true in gardens, no one can hear you scream. Now,
when this distress call reaches other plants, they will also
emit the chemicals to warn their neighbors as well. And
these calls can even work on different species of plant.
For instance, a sage plant can signal a tobacco plant
to emit an odor that's not just to animals that

(02:57):
are eating the sage. All right, So you hear the
term plant neurobiology and you say, but plants don't have brains. Well,
one of the reasons why many scientists hate that term
is because plants don't have neurons, but they do produce
neuroactive chemicals that act like those in the human brain.

(03:19):
Glutamate receptors form memories in humans, and they're also found
in plants, and some hormones are transported around plants similar
to how neurotransmitters move through animal brains. Likewise, some plants
are vulnerable to drugs that disrupt neurotransmitters in the human brain,

(03:40):
like prozac or meth amphetamines. They even produce their own ethylene,
which is possibly used as an anesthetic when they're stressed out.
Plants even have a kind of nervous system, and that
may allow information to travel around the plant via electrical
sick mills. So if plants have sort of brains, do

(04:04):
they remember stuff? Well, yeah, plants also have their own
kind of memory. In fact, there's a plant called the
Mimosa pudica plant, and it closes its leaflets immediately after
they're touched, but because this requires energy, the plant won't
do it if it's unnecessary. However, when researchers dropped potted

(04:26):
mimosas fifteen centimeters onto foam, the plants learned that the
fall wasn't dangerous, so they stopped closing their leaves. Even crazier,
after one month, the plants still remember that the drop
wasn't dangerous and they wouldn't close their leaves in response. So,
given what we know about plants, senses, communication, nervous systems,

(04:51):
and memories, should we consider them to be either conscious
or intelligent? What about pain? Does the fact that plants
react to danger indicate that they feel pain? Well, some
scientists argue yes, while others loudly say no. Check out

(05:14):
the brainstuff channel on YouTube, and for more on this
and thousands of other topics, visit how stuff works dot
com