BrainStuff Classics: Are Plants Conscious?

Researchers have found evidence that plants have senses, memories, and can even communicate with each other. But does this mean they're conscious? Learn what science has to say in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of I Heart Radio. Hey
brain Stuff, I'm Lauren Vogelbaum, and this is another classic
episode from our former host, Christian Sager. This one deals
with a question to which the answer may seem obvious,
but research has made more complicated. Our plants conscious. Hey,

(00:23):
brain Stuff, it's Christian Sager. 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 to meet up with them, they seem
so slow that they're unable to move. Now, imagine that

(00:44):
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 plant life sped up, we see their
lively movement. But even though plants move and respond to stimuli,

(01:05):
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 might have heard of him,
and he once proposed something called the root brain hypothesis.

(01:25):
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 growing movement in science called
plant neurobiology, and it debates the way we think about

(01:47):
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 plants have a variety of sense, some
that can actually act as analogs to our site smell, touch, taste,

(02:12):
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 the sound is a recording and nothing is
eating the plant. Creepy, right, Plants can also communicate sometimes.

(02:35):
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. It's true in gardens,
no one can hear you scream. Now, when this distress

(02:55):
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 are eating the sage.
All right, So you hear the term plant neurobiology, and

(03:18):
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. Glutamate receptors
form memories and humans, and they're also found in plants,

(03:40):
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, like
prozac or meth amphetamines. They eat even produce their own ethylene,

(04:02):
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 signals.
So if plants have sort of brains, do they remember stuff? Well? Yeah,

(04:22):
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 mimosas fifteen centimeters onto foam, the

(04:45):
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 spons So, given what we know
about plants senses, communication, nervous systems, and memories, should we

(05:09):
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. Today's episode was written by Christian and

(05:32):
produced by Tyler Clang. Brain Stuff is a production of
I Heart Radio's How Stuff Works from more in this
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