the most powerful, dangerous and subversive trait

that natural selection has ever devised.

It's a piece of neural audio technology

for rewiring other people's minds.

I'm talking about your language, of course,

because it allows you to implant a thought from your mind

directly into someone else's mind,

and they can attempt to do the same to you,

without either of you having to perform surgery.

Instead, when you speak,

you're actually using a form of telemetry

not so different

from the remote control device for your television.

It's just that, whereas that device

relies on pulses of infrared light,

your language relies on pulses,

discrete pulses, of sound.

And just as you use the remote control device

to alter the internal settings of your television

to suit your mood,

you use your language

to alter the settings inside someone else's brain

to suit your interests.

Languages are genes talking,

getting things that they want.

And just imagine the sense of wonder in a baby

when it first discovers that, merely by uttering a sound,

it can get objects to move across a room

as if by magic,

and maybe even into its mouth.

Now language's subversive power

has been recognized throughout the ages

in censorship, in books you can't read,

phrases you can't use

and words you can't say.

In fact, the Tower of Babel story in the Bible

is a fable and warning

about the power of language.

According to that story, early humans developed the conceit

that, by using their language to work together,

they could build a tower

that would take them all the way to heaven.

Now God, angered at this attempt to usurp his power,

destroyed the tower,

and then to ensure

that it would never be rebuilt,

he scattered the people by giving them different languages --

confused them by giving them different languages.

And this leads to the wonderful irony

that our languages exist to prevent us from communicating.

Even today,

we know that there are words we cannot use,

phrases we cannot say,

because if we do so,

we might be accosted, jailed,

or even killed.

And all of this from a puff of air

emanating from our mouths.

Now all this fuss about a single one of our traits

tells us there's something worth explaining.

And that is how and why

did this remarkable trait evolve,

and why did it evolve

only in our species?

Now it's a little bit of a surprise

that to get an answer to that question,

we have to go to tool use

in the chimpanzees.

Now these chimpanzees are using tools,

and we take that as a sign of their intelligence.

But if they really were intelligent,

why would they use a stick to extract termites from the ground

rather than a shovel?

And if they really were intelligent,

why would they crack open nuts with a rock?

Why wouldn't they just go to a shop and buy a bag of nuts

that somebody else had already cracked open for them?

Why not? I mean, that's what we do.

Now the reason the chimpanzees don't do that

is that they lack what psychologists and anthropologists call

social learning.

They seem to lack the ability

to learn from others

by copying or imitating

or simply watching.

As a result,

they can't improve on others' ideas

or learn from others' mistakes --

benefit from others' wisdom.

And so they just do the same thing

over and over and over again.

In fact, we could go away for a million years and come back

and these chimpanzees would be doing the same thing

with the same sticks for the termites

and the same rocks to crack open the nuts.

Now this may sound arrogant, or even full of hubris.

How do we know this?

Because this is exactly what our ancestors, the Homo erectus, did.

These upright apes

evolved on the African savanna

about two million years ago,

and they made these splendid hand axes

that fit wonderfully into your hands.

But if we look at the fossil record,

we see that they made the same hand axe

over and over and over again

for one million years.

You can follow it through the fossil record.

Now if we make some guesses about how long Homo erectus lived,

what their generation time was,

that's about 40,000 generations

of parents to offspring, and other individuals watching,

in which that hand axe didn't change.

It's not even clear

that our very close genetic relatives, the Neanderthals,

had social learning.

Sure enough, their tools were more complicated

than those of Homo erectus,

but they too showed very little change

over the 300,000 years or so

that those species, the Neanderthals,

lived in Eurasia.

Okay, so what this tells us

is that, contrary to the old adage,

"monkey see, monkey do,"

the surprise really is

that all of the other animals

really cannot do that -- at least not very much.

And even this picture

has the suspicious taint of being rigged about it --

something from a Barnum & Bailey circus.

But by comparison,

we can learn.

We can learn by watching other people

and copying or imitating

what they can do.

We can then choose, from among a range of options,

the best one.

We can benefit from others' ideas.

We can build on their wisdom.

And as a result, our ideas do accumulate,

and our technology progresses.

And this cumulative cultural adaptation,

as anthropologists call

this accumulation of ideas,

is responsible for everything around you

in your bustling and teeming everyday lives.

I mean the world has changed out of all proportion

to what we would recognize

even 1,000 or 2,000 years ago.

And all of this because of cumulative cultural adaptation.

The chairs you're sitting in, the lights in this auditorium,

my microphone, the iPads and iPods that you carry around with you --

all are a result

of cumulative cultural adaptation.

Now to many commentators,

cumulative cultural adaptation, or social learning,

is job done, end of story.

Our species can make stuff,

therefore we prospered in a way that no other species has.

In fact, we can even make the "stuff of life" --

as I just said, all the stuff around us.

But in fact, it turns out

that some time around 200,000 years ago,

when our species first arose

and acquired social learning,

that this was really the beginning of our story,

not the end of our story.

Because our acquisition of social learning

would create a social and evolutionary dilemma,

the resolution of which, it's fair to say,

would determine not only the future course of our psychology,

but the future course of the entire world.

And most importantly for this,

it'll tell us why we have language.

And the reason that dilemma arose

is, it turns out, that social learning is visual theft.

If I can learn by watching you,

I can steal your best ideas,

and I can benefit from your efforts,

without having to put in the time and energy that you did

into developing them.

If I can watch which lure you use to catch a fish,

or I can watch how you flake your hand axe

to make it better,

or if I follow you secretly to your mushroom patch,

I can benefit from your knowledge and wisdom and skills,

and maybe even catch that fish

before you do.

Social learning really is visual theft.

And in any species that acquired it,

it would behoove you

to hide your best ideas,

lest somebody steal them from you.

And so some time around 200,000 years ago,

our species confronted this crisis.

And we really had only two options

for dealing with the conflicts

that visual theft would bring.

One of those options

was that we could have retreated

into small family groups.

Because then the benefits of our ideas and knowledge

would flow just to our relatives.

Had we chosen this option,

sometime around 200,000 years ago,

we would probably still be living like the Neanderthals were

when we first entered Europe 40,000 years ago.

And this is because in small groups

there are fewer ideas, there are fewer innovations.

And small groups are more prone to accidents and bad luck.

So if we'd chosen that path,

our evolutionary path would have led into the forest --

and been a short one indeed.

The other option we could choose

was to develop the systems of communication

that would allow us to share ideas

and to cooperate amongst others.

Choosing this option would mean

that a vastly greater fund of accumulated knowledge and wisdom

would become available to any one individual

than would ever arise from within an individual family

or an individual person on their own.

Well, we chose the second option,

and language is the result.

Language evolved to solve the crisis

of visual theft.

Language is a piece of social technology

for enhancing the benefits of cooperation --

for reaching agreements, for striking deals

and for coordinating our activities.

And you can see that, in a developing society

that was beginning to acquire language,

not having language

would be a like a bird without wings.

Just as wings open up this sphere of air

for birds to exploit,

language opened up the sphere of cooperation

for humans to exploit.

And we take this utterly for granted,

because we're a species that is so at home with language,

but you have to realize

that even the simplest acts of exchange that we engage in

are utterly dependent upon language.

And to see why, consider two scenarios

from early in our evolution.

Let's imagine that you are really good

at making arrowheads,

but you're hopeless at making the wooden shafts

with the flight feathers attached.

Two other people you know are very good at making the wooden shafts,

but they're hopeless at making the arrowheads.

So what you do is --

one of those people has not really acquired language yet.

And let's pretend the other one is good at language skills.

So what you do one day is you take a pile of arrowheads,

and you walk up to the one that can't speak very well,

and you put the arrowheads down in front of him,

hoping that he'll get the idea that you want to trade your arrowheads