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I think its pretty clear that there
is no consensus on the definition of

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intelligence.

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And we need to remember that the original
IQ test was developed at the beginning of

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the 20th century in France,
not to define intelligence, but

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to identify children who
are slow learners in school.

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Now, many of the modern
definitions of intelligence

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all include some level of
multiple intelligences.

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Now, I am not a psychologist.

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I don't have training in psychology, but
I just want to go over this very briefly,

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because I think it's important for
us, if we're gonna try to define

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plant intelligence to understand what
we think about intelligence in humans.

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So one of the very popular theories of

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multiple intelligences said that humans
have three types of intelligence.

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Analytical intelligence.

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This might be the type of intelligence
that we classically think of IQ tests,

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mathematical ability.

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Creative intelligence, and
what's termed practical intelligence,

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the ability to know how to do things.

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Other models further refine this and
add in two other types of intelligence.

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Emotional intelligence,
which has gotten a fair amount of press

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over the past number of years,
and social intelligence.

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The well-known psychologist,
Howard Gardner,

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has expanded this even further to where he
as nine different types of intelligences.

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So, theoretically, why not add
a tenth level of intelligence and

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we can define this as
vegetal intelligence.

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Plants clearly don't have social or
analytical intelligence but

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maybe there is a plant
type of intelligence.

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But even if we could define
a vegetal intelligence,

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does this really help us
understand plant biology?

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Maybe the question shouldn't be
whether plants are intelligent, but

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rather plants are aware.

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As I hope I've convinced
you in this course,

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plants are acutely aware
of the world around them.

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They are aware of their
visual environment.

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They differentiate between red, blue, far
red and UV lights and respond accordingly.

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They are aware of the aromas
surrounding them and

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respond to minute quantities of
volatile compounds wafting in the air.

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Plants know when they're being touched.

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They are aware of gravity.

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They can change their shapes to
ensure that their shoots grow up and

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that their roots grow down.

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And plants are aware of their past.

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They remember past infections, and
the conditions they've weathered, and

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then modify their current
physiology based on these memories.

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Now I have a confession.

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I did not want to call my
book What a Plant Knows.

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This was a title that was
actually suggested to me.

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My original response to this
title was not too dissimilar from

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what many of you have written in the
forums, but plants don't know anything.

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But whether plants know or
not is, I think,

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less important than what we
know what we're talking about.

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Whether or not plants know,

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I hope I've convinced you that
plants are infinitely complex.

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Rather than immobile, maybe even stupid
objects, I hope you now have a greater

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appreciation for the sophisticated
sensory machinery that powers a plant and

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enables it to survive in
every changing condition.

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Enables it to literally weather a storm.

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But is important for us to remember plants
are not aware of us as individuals.

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We are simply one of the many
external pressures that increase or

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decrease a plant's chances for
survival and reproductive success.

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A plant is aware of its environment, and

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indeed people are part
of this environment.

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But plants are not aware of
the gardeners or scientists

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who develop what they consider to be
personal relationships with their plants.

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While these relationships
may be meaningful for us,

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as a caretaker, they are not dissimilar
to a child and her imaginary friend.

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The meaning is unidirectional.

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And I say this as someone who has more
than once used anthropomorphic language

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in the lab with sentences such as, these
mutant plants don't look so happy today.

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Terms such as happy are our
own subjective assessment

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of a plant's decidedly
unemotional physiological status.

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For all the rich sensory
input that plants and

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people perceive, plant senses
are not manifested in emotion.

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That probably is one of the things
that defines us as humans.

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We project on plants our own
emotional interpretations and

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assume that a flower blooming is
happier than one that is wilting.

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Well, if happy can be defined as
an optimal physiological state,

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then perhaps this term fits.

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But I think that for all of us,

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happy depends on much more than
being in perfect physical health.

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Actually, I think we've all known people
who are afflicted with various ailments

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who consider themselves happy, or

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otherwise, very healthy individuals who
are actually miserable in their own mood.

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Happiness, I hope we can agree,
is a state of mind.

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So if humans and plants are similar
in that both are aware of complex

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light environments, intricate aromas,
different physical stimulations,

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if humans and
plants both have preferences, and

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if both remember, then do we see ourselves
when we're looking at the plant?

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What we must see, I think, is that
on a broad level, we share biology,

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not only with chimpanzees, and with dogs,
but also with begonias and sequoias.

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We should see a very long lost cousin when
we gaze at our rose bush in full bloom

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knowing that we can discern complex
environments just as it can.

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Knowing that we both share common genes.

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When we look at ivy clinging to a wall,
we are looking at what, save for

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some ancient stochastic event,
could have been our own fate.

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We are, as I hope you’ve learned in this
class, seeing another possible outcome

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of our own evolution, one that branched
off some two billion years ago.

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As we come to the end of our class,

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I wanna finish by reading the last
two paragraphs of our textbook,

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which sums up my own personal
take on what a plant knows.

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A shared genetic past does not
negate eons of separate evolution.

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While plants and humans maintain
parallel abilities to sense and

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be aware of the physical world,

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the independent paths of evolution
have led to a uniquely human capacity,

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beyond intelligence, that plants
don't have, the ability to care.

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So the next time you find yourself
on a stroll through a park,

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take a second to ask yourself,
what does the dandelion in the lawn see?

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What does the grass smell?

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Touch the leaves of an oak,

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knowing that the tree will
remember that it was touched.

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But it won't remember you.

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You, on the other hand,
can remember this particular tree and

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carry the memory of it with you forever.

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And now if you'll bear with me
a little bit more, if you want,

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you can come with me on a tour of my lab
and learn a little bit about my research.