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I love a great mystery,

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and I'm fascinated by the greatest
unsolved mystery in science,

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perhaps because it's personal.

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It's about who we are,

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and I can't help but be curious.

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The mystery is this:

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What is the relationship
between your brain

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and your conscious experiences,

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such as your experience
of the taste of chocolate

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or the feeling of velvet?

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Now, this mystery is not new.

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In 1868, Thomas Huxley wrote,

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"How it is that anything so remarkable
as a state of consciousness comes about

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as the result of irritating nervous tissue

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is just as unaccountable

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as the appearance of the genie
when Aladdin rubbed his lamp."

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Now, Huxley knew that brain activity

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and conscious experiences are correlated,

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but he didn't know why.

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To the science of his day,
it was a mystery.

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In the years since Huxley,

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science has learned a lot
about brain activity,

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but the relationship
between brain activity

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and conscious experiences
is still a mystery.

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Why? Why have we made so little progress?

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Well, some experts think
that we can't solve this problem

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because we lack the necessary
concepts and intelligence.

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We don't expect monkeys to solve
problems in quantum mechanics,

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and as it happens, we can't expect
our species to solve this problem either.

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Well, I disagree. I'm more optimistic.

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I think we've simply
made a false assumption.

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Once we fix it, we just
might solve this problem.

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Today, I'd like tell you
what that assumption is,

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why it's false, and how to fix it.

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Let's begin with a question:

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Do we see reality as it is?

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I open my eyes

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and I have an experience that I describe
as a red tomato a meter away.

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As a result, I come to believe
that in reality,

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there's a red tomato a meter away.

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I then close my eyes, and my experience
changes to a gray field,

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but is it still the case that in reality,
there's a red tomato a meter away?

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I think so, but could I be wrong?

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Could I be misinterpreting
the nature of my perceptions?

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We have misinterpreted
our perceptions before.

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We used to think the Earth is flat,
because it looks that way.

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Pythagorus discovered that we were wrong.

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Then we thought that the Earth
is the unmoving center of the Universe,

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again because it looks that way.

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Copernicus and Galileo discovered,
again, that we were wrong.

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Galileo then wondered if we might
be misinterpreting our experiences

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in other ways.

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He wrote: "I think that tastes,
odors, colors, and so on

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reside in consciousness.

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Hence if the living creature were removed,
all these qualities would be annihilated."

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Now, that's a stunning claim.

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Could Galileo be right?

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Could we really be misinterpreting
our experiences that badly?

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What does modern science
have to say about this?

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Well, neuroscientists tell us
that about a third of the brain's cortex

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is engaged in vision.

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When you simply open your eyes
and look about this room,

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billions of neurons
and trillions of synapses are engaged.

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Now, this is a bit surprising,

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because to the extent that
we think about vision at all,

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we think of it as like a camera.

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It just takes a picture
of objective reality as it is.

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Now, there is a part of vision
that's like a camera:

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the eye has a lens that focuses
an image on the back of the eye

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where there are 130 million
photoreceptors,

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so the eye is like a 130-megapixel camera.

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But that doesn't explain
the billions of neurons

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and trillions of synapses
that are engaged in vision.

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What are these neurons up to?

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Well, neuroscientists tell us
that they are creating, in real time,

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all the shapes, objects, colors,
and motions that we see.

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It feels like we're just taking a snapshot
of this room the way it is,

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but in fact, we're constructing
everything that we see.

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We don't construct
the whole world at once.

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We construct what we need in the moment.

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Now, there are many demonstrations
that are quite compelling

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that we construct what we see.

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I'll just show you two.

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In this example, you see some red discs
with bits cut out of them,

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but if I just rotate
the disks a little bit,

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suddenly, you see a 3D cube
pop out of the screen.

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Now, the screen of course is flat,

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so the three-dimensional cube
that you're experiencing

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must be your construction.

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In this next example,

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you see glowing blue bars
with pretty sharp edges

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moving across a field of dots.

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In fact, no dots move.

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All I'm doing from frame to frame
is changing the colors of dots

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from blue to black or black to blue.

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But when I do this quickly,

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your visual system creates
the glowing blue bars

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with the sharp edges and the motion.

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There are many more examples,
but these are just two

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that you construct what you see.

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But neuroscientists go further.

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They say that we reconstruct reality.

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So, when I have an experience
that I describe as a red tomato,

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that experience is actually
an accurate reconstruction

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of the properties of a real red tomato

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that would exist
even if I weren't looking.

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Now, why would neuroscientists
say that we don't just construct,

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we reconstruct?

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Well, the standard argument given

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is usually an evolutionary one.

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Those of our ancestors
who saw more accurately

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had a competitive advantage compared
to those who saw less accurately,

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and therefore they were more likely
to pass on their genes.

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We are the offspring of those
who saw more accurately,

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and so we can be confident that,
in the normal case,

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our perceptions are accurate.

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You see this in the standard textbooks.

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One textbook says, for example,

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"Evolutionarily speaking,

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vision is useful precisely
because it is so accurate."

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So the idea is that accurate perceptions
are fitter perceptions.

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They give you a survival advantage.

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Now, is this correct?

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Is this the right interpretation
of evolutionary theory?

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Well, let's first look at a couple
of examples in nature.

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The Australian jewel beetle

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is dimpled, glossy and brown.

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The female is flightless.

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The male flies, looking,
of course, for a hot female.

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When he finds one, he alights and mates.

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There's another species in the outback,

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Homo sapiens.

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The male of this species
has a massive brain

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that he uses to hunt for cold beer.

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(Laughter)

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And when he finds one, he drains it,

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and sometimes throws the bottle
into the outback.

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Now, as it happens, these bottles
are dimpled, glossy,

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and just the right shade of brown
to tickle the fancy of these beetles.

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The males swarm all over
the bottles trying to mate.

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They lose all interest
in the real females.

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Classic case of the male
leaving the female for the bottle.

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(Laughter) (Applause)

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The species almost went extinct.

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Australia had to change its bottles
to save its beetles.

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(Laughter)

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Now, the males had successfully
found females for thousands,

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perhaps millions of years.

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It looked like they saw reality
as it is, but apparently not.

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Evolution had given them a hack.

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A female is anything dimpled,
glossy and brown,

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the bigger the better.

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(Laughter)

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Even when crawling all over the bottle,
the male couldn't discover his mistake.

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Now, you might say, beetles, sure,
they're very simple creatures,

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but surely not mammals.

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Mammals don't rely on tricks.

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Well, I won't dwell on this,
but you get the idea. (Laughter)

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So this raises an important
technical question:

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Does natural selection really favor
seeing reality as it is?

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Fortunately, we don't have
to wave our hands and guess;

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evolution is a mathematically
precise theory.

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We can use the equations of evolution
to check this out.

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We can have various organisms
in artificial worlds compete

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and see which survive and which thrive,

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which sensory systems are more fit.

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A key notion in those
equations is fitness.

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Consider this steak:

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What does this steak do
for the fitness of an animal?

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Well, for a hungry lion looking to eat,
it enhances fitness.

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For a well-fed lion looking to mate,
it doesn't enhance fitness.

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And for a rabbit in any state,
it doesn't enhance fitness,

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so fitness does depend
on reality as it is, yes,

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but also on the organism,
its state and its action.

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Fitness is not the same thing
as reality as it is,

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and it's fitness,
and not reality as it is,

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that figures centrally
in the equations of evolution.

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So, in my lab,

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we have run hundreds of thousands
of evolutionary game simulations

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with lots of different
randomly chosen worlds

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and organisms that compete
for resources in those worlds.

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Some of the organisms
see all of the reality,

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others see just part of the reality,

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and some see none of the reality,

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only fitness.

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Who wins?

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Well, I hate to break it to you,
but perception of reality goes extinct.

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In almost every simulation,

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organisms that see none of reality

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but are just tuned to fitness

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drive to extinction all the organisms
that perceive reality as it is.

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So the bottom line is, evolution
does not favor veridical,

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or accurate perceptions.

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Those perceptions of reality go extinct.

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Now, this is a bit stunning.

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How can it be that not seeing
the world accurately

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gives us a survival advantage?

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That is a bit counterintuitive.

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But remember the jewel beetle.

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The jewel beetle survived
for thousands, perhaps millions of years,

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using simple tricks and hacks.

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What the equations
of evolution are telling us

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is that all organisms, including us, 
are in the same boat as the jewel beetle.

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We do not see reality as it is.

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We're shaped with tricks
and hacks that keep us alive.

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Still,

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we need some help with our intuitions.

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How can not perceiving
reality as it is be useful?

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Well, fortunately, we have
a very helpful metaphor:

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the desktop interface on your computer.

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Consider that blue icon
for a TED Talk that you're writing.

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Now, the icon is blue and rectangular

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and in the lower right corner
of the desktop.

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Does that mean that the text file itself
in the computer is blue,

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rectangular, and in the lower
right-hand corner of the computer?

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Of course not.

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Anyone who thought that misinterprets
the purpose of the interface.

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It's not there to show you
the reality of the computer.

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In fact, it's there to hide that reality.

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You don't want to know about the diodes

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and resistors and all
the megabytes of software.

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If you had to deal with that,
you could never write your text file

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or edit your photo.

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So the idea is that evolution
has given us an interface

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that hides reality and guides
adaptive behavior.

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Space and time, as you
perceive them right now,

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are your desktop.

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Physical objects are simply icons
in that desktop.

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There's an obvious objection.

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Hoffman, if you think that train
coming down the track at 200 MPH

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is just an icon of your desktop,

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why don't you step in front of it?

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And after you're gone,
and your theory with you,

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we'll know that there's more
to that train than just an icon.

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Well, I wouldn't step
in front of that train

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for the same reason

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that I wouldn't carelessly drag
that icon to the trash can:

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not because I take the icon literally --

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the file is not literally blue
or rectangular --

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but I do take it seriously.

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I could lose weeks of work.

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Similarly, evolution has shaped us

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with perceptual symbols
that are designed to keep us alive.

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We'd better take them seriously.

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If you see a snake, don't pick it up.

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If you see a cliff, don't jump off.

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00:13:43,150 --> 00:13:46,726
They're designed to keep us safe,
and we should take them seriously.

248
00:13:46,726 --> 00:13:49,417
That does not mean that we
should take them literally.

249
00:13:49,417 --> 00:13:51,671
That's a logical error.

250
00:13:51,671 --> 00:13:54,876
Another objection: There's
nothing really new here.

251
00:13:54,876 --> 00:13:58,800
Physicists have told us for a long time
that the metal of that train looks solid

252
00:13:58,800 --> 00:14:03,188
but really it's mostly empty space
with microscopic particles zipping around.

253
00:14:03,188 --> 00:14:04,676
There's nothing new here.

254
00:14:04,676 --> 00:14:06,880
Well, not exactly.

255
00:14:06,880 --> 00:14:10,920
It's like saying, I know that
that blue icon on the desktop

256
00:14:10,920 --> 00:14:13,219
is not the reality of the computer,

257
00:14:13,219 --> 00:14:16,678
but if I pull out my trusty
magnifying glass and look really closely,

258
00:14:16,678 --> 00:14:18,489
I see little pixels,

259
00:14:18,489 --> 00:14:20,950
and that's the reality of the computer.

260
00:14:20,950 --> 00:14:24,758
Well, not really -- you're still
on the desktop, and that's the point.

261
00:14:24,758 --> 00:14:27,754
Those microscopic particles
are still in space and time:

262
00:14:27,754 --> 00:14:30,145
they're still in the user interface.

263
00:14:30,145 --> 00:14:33,907
So I'm saying something far more radical
than those physicists.

264
00:14:34,727 --> 00:14:36,200
Finally, you might object,

265
00:14:36,200 --> 00:14:38,759
look, we all see the train,

266
00:14:38,759 --> 00:14:41,801
therefore none of us constructs the train.

267
00:14:41,801 --> 00:14:43,891
But remember this example.

268
00:14:43,891 --> 00:14:46,607
In this example, we all see a cube,

269
00:14:47,597 --> 00:14:49,690
but the screen is flat,

270
00:14:49,690 --> 00:14:52,427
so the cube that you see
is the cube that you construct.

271
00:14:53,736 --> 00:14:55,779
We all see a cube

272
00:14:55,779 --> 00:15:00,638
because we all, each one of us,
constructs the cube that we see.

273
00:15:00,638 --> 00:15:02,698
The same is true of the train.

274
00:15:02,698 --> 00:15:07,180
We all see a train because
we each see the train that we construct,

275
00:15:07,180 --> 00:15:10,733
and the same is true
of all physical objects.

276
00:15:12,343 --> 00:15:17,396
We're inclined to think that perception
is like a window on reality as it is.

277
00:15:17,396 --> 00:15:22,400
The theory of evolution is telling us
that this is an incorrect interpretation

278
00:15:22,400 --> 00:15:23,865
of our perceptions.

279
00:15:25,095 --> 00:15:28,639
Instead, reality is more like a 3D desktop

280
00:15:28,639 --> 00:15:31,936
that's designed to hide
the complexity of the real world

281
00:15:31,936 --> 00:15:33,802
and guide adaptive behavior.

282
00:15:34,282 --> 00:15:37,210
Space as you perceive it is your desktop.

283
00:15:37,210 --> 00:15:40,236
Physical objects are just
the icons in that desktop.

284
00:15:41,456 --> 00:15:45,126
We used to think that the Earth is flat
because it looks that way.

285
00:15:45,520 --> 00:15:48,654
Then we thought that the Earth
is the unmoving center of reality

286
00:15:48,654 --> 00:15:50,378
because it looks that way.

287
00:15:50,378 --> 00:15:51,520
We were wrong.

288
00:15:51,520 --> 00:15:54,190
We had misinterpreted our perceptions.

289
00:15:54,910 --> 00:15:58,319
Now we believe that spacetime and objects

290
00:15:58,319 --> 00:16:00,933
are the nature of reality as it is.

291
00:16:01,453 --> 00:16:05,377
The theory of evolution is telling us
that once again, we're wrong.

292
00:16:05,377 --> 00:16:10,416
We're misinterpreting the content
of our perceptual experiences.

293
00:16:10,416 --> 00:16:12,947
There's something that exists
when you don't look,

294
00:16:12,947 --> 00:16:16,350
but it's not spacetime
and physical objects.

295
00:16:16,350 --> 00:16:19,378
It's as hard for us to let go
of spacetime and objects

296
00:16:19,378 --> 00:16:22,861
as it is for the jewel beetle
to let go of its bottle.

297
00:16:22,861 --> 00:16:27,279
Why? Because we're blind
to our own blindnesses.

298
00:16:28,409 --> 00:16:30,756
But we have an advantage
over the jewel beetle:

299
00:16:30,756 --> 00:16:32,544
our science and technology.

300
00:16:32,544 --> 00:16:34,935
By peering through the lens of a telescope

301
00:16:34,935 --> 00:16:39,571
we discovered that the Earth
is not the unmoving center of reality,

302
00:16:39,571 --> 00:16:42,449
and by peering through the lens
of the theory of evolution

303
00:16:42,449 --> 00:16:44,771
we discovered that spacetime and objects

304
00:16:44,771 --> 00:16:47,139
are not the nature of reality.

305
00:16:47,139 --> 00:16:51,424
When I have a perceptual experience
that I describe as a red tomato,

306
00:16:51,424 --> 00:16:54,361
I am interacting with reality,

307
00:16:54,361 --> 00:16:59,571
but that reality is not a red tomato
and is nothing like a red tomato.

308
00:16:59,571 --> 00:17:04,972
Similarly, when I have an experience
that I describe as a lion or a steak,

309
00:17:04,972 --> 00:17:06,820
I'm interacting with reality,

310
00:17:06,820 --> 00:17:09,978
but that reality is not a lion or a steak.

311
00:17:09,978 --> 00:17:11,998
And here's the kicker:

312
00:17:11,998 --> 00:17:16,688
When I have a perceptual experience
that I describe as a brain, or neurons,

313
00:17:16,688 --> 00:17:18,778
I am interacting with reality,

314
00:17:18,778 --> 00:17:22,307
but that reality is not a brain or neurons

315
00:17:22,307 --> 00:17:25,805
and is nothing like a brain or neurons.

316
00:17:25,805 --> 00:17:30,584
And that reality, whatever it is,

317
00:17:30,584 --> 00:17:34,195
is the real source of cause and effect

318
00:17:34,195 --> 00:17:38,227
in the world -- not brains, not neurons.

319
00:17:38,227 --> 00:17:40,827
Brains and neurons
have no causal powers.

320
00:17:40,827 --> 00:17:43,428
They cause none of our
perceptual experiences,

321
00:17:43,428 --> 00:17:45,216
and none of our behavior.

322
00:17:45,216 --> 00:17:50,592
Brains and neurons are a species-specific
set of symbols, a hack.

323
00:17:50,592 --> 00:17:53,273
What does this mean
for the mystery of consciousness?

324
00:17:53,923 --> 00:17:57,916
Well, it opens up new possibilities.

325
00:17:57,916 --> 00:17:59,611
For instance,

326
00:17:59,611 --> 00:18:06,590
perhaps reality is some vast machine
that causes our conscious experiences.

327
00:18:06,590 --> 00:18:10,260
I doubt this, but it's worth exploring.

328
00:18:10,260 --> 00:18:15,609
Perhaps reality is some vast,
interacting network of conscious agents,

329
00:18:15,609 --> 00:18:21,182
simple and complex, that cause
each other's conscious experiences.

330
00:18:21,182 --> 00:18:24,432
Actually, this isn't as crazy
an idea as it seems,

331
00:18:24,432 --> 00:18:26,052
and I'm currently exploring it.

332
00:18:26,592 --> 00:18:28,658
But here's the point:

333
00:18:28,658 --> 00:18:31,979
Once we let go of our massively intuitive

334
00:18:31,979 --> 00:18:35,903
but massively false assumption
about the nature of reality,

335
00:18:35,903 --> 00:18:40,291
it opens up new ways to think
about life's greatest mystery.

336
00:18:41,251 --> 00:18:45,860
I bet that reality will end up
turning out to be more fascinating

337
00:18:45,860 --> 00:18:49,834
and unexpected than we've ever imagined.

338
00:18:49,834 --> 00:18:54,222
The theory of evolution presents us
with the ultimate dare:

339
00:18:54,222 --> 00:18:59,364
Dare to recognize that perception
is not about seeing truth,

340
00:18:59,364 --> 00:19:03,460
it's about having kids.

341
00:19:03,460 --> 00:19:08,200
And by the way, even this TED
is just in your head.

342
00:19:08,200 --> 00:19:10,244
Thank you very much.

343
00:19:10,244 --> 00:19:13,632
(Applause)

344
00:19:20,786 --> 00:19:24,221
Chris Anderson: If that's
really you there, thank you.

345
00:19:24,221 --> 00:19:27,152
So there's so much from this.

346
00:19:27,152 --> 00:19:30,421
I mean, first of all, some people
may just be profoundly depressed

347
00:19:30,421 --> 00:19:35,970
at the thought that,
if evolution does not favor reality,

348
00:19:35,970 --> 00:19:39,300
I mean, doesn't that to some extent
undermine all our endeavors here,

349
00:19:39,300 --> 00:19:41,984
all our ability to think
that we can think the truth,

350
00:19:41,984 --> 00:19:45,490
possibly even including
your own theory, if you go there?

351
00:19:45,490 --> 00:19:49,944
Donald Hoffman: Well, this does not
stop us from a successful science.

352
00:19:49,944 --> 00:19:52,756
What we have is one theory
that turned out to be false,

353
00:19:52,756 --> 00:19:57,215
that perception is like reality
and reality is like our perceptions.

354
00:19:57,215 --> 00:19:58,900
That theory turns out to be false.

355
00:19:58,900 --> 00:20:00,318
Okay, throw that theory away.

356
00:20:00,318 --> 00:20:03,572
That doesn't stop us from now postulating
all sorts of other theories

357
00:20:03,572 --> 00:20:04,930
about the nature of reality,

358
00:20:04,930 --> 00:20:08,535
so it's actually progress to recognize
that one of our theories was false.

359
00:20:08,535 --> 00:20:11,193
So science continues as normal.
There's no problem here.

360
00:20:11,193 --> 00:20:13,794
CA: So you think it's possible
-- (Laughter) --

361
00:20:13,794 --> 00:20:17,904
This is cool, but what you're saying
I think is it's possible that evolution

362
00:20:17,904 --> 00:20:20,551
can still get you to reason.

363
00:20:20,551 --> 00:20:22,864
DH: Yes. Now that's a very,
very good point.

364
00:20:22,864 --> 00:20:27,391
The evolutionary game simulations that I
showed were specifically about perception,

365
00:20:27,391 --> 00:20:29,969
and they do show that our perceptions
have been shaped

366
00:20:29,969 --> 00:20:31,849
not to show us reality as it is,

367
00:20:31,849 --> 00:20:36,122
but that does not mean the same thing
about our logic or mathematics.

368
00:20:36,122 --> 00:20:39,744
We haven't done these simulations,
but my bet is that we'll find

369
00:20:39,744 --> 00:20:43,366
that there are some selection pressures
for our logic and our mathematics

370
00:20:43,366 --> 00:20:45,572
to be at least in the direction of truth.

371
00:20:45,572 --> 00:20:48,219
I mean, if you're like me,
math and logic is not easy.

372
00:20:48,219 --> 00:20:51,570
We don't get it all right, but at least
the selection pressures are not

373
00:20:51,570 --> 00:20:53,908
uniformly away from true math and logic.

374
00:20:53,908 --> 00:20:57,228
So I think that we'll find that we have
to look at each cognitive faculty

375
00:20:57,228 --> 00:20:59,852
one at a time and see
what evolution does to it.

376
00:20:59,852 --> 00:21:03,613
What's true about perception may not
be true about math and logic.

377
00:21:03,613 --> 00:21:07,607
CA: I mean, really what you're proposing
is a kind of modern-day Bishop Berkeley

378
00:21:07,607 --> 00:21:09,998
interpretation of the world:

379
00:21:09,998 --> 00:21:12,947
consciousness causes matter,
not the other way around.

380
00:21:12,947 --> 00:21:15,339
DH: Well, it's slightly
different than Berkeley.

381
00:21:15,339 --> 00:21:18,701
Berkeley thought that, he was a deist,
and he thought that the ultimate

382
00:21:18,701 --> 00:21:20,740
nature of reality is God
and so forth,

383
00:21:20,740 --> 00:21:23,850
and I don't need to go
where Berkeley's going,

384
00:21:23,850 --> 00:21:26,545
so it's quite a bit
different from Berkeley.

385
00:21:27,725 --> 00:21:31,235
I call this conscious realism.
It's actually a very different approach.

386
00:21:31,235 --> 00:21:34,825
CA: Don, I could literally talk with you
for hours, and I hope to do that.


387
00:21:34,825 --> 00:21:37,298
Thanks so much for that.
DH: Thank you. (Applause)