Humans appeared about 200,000 years ago.
And I believe we count as a threshold in this great story. Let me explain why.
We've seen that DNA learns in a sense,it accumulates information.But it is so slow.
DNA accumulates information through random errors, some of which just happen to work.
But DNA had actually generated a faster way of learning: it had produced organisms with brains, and those organisms can learn in real time.
They accumulate information, they learn.
The sad thing is, when they die,the information dies with them.
Now what makes humans different is human language.
We are blessed with a language,a system of communication,so powerful and so precise
that we can share what we've learned with such precision that it can accumulate in the collective memory.
And that means it can outlast the individuals who learned that information, and it can accumulate from generation to generation.
And that's why, as a species, we're so creative and so powerful,and that's why we have a history.
We seem to be the only species in four billion years to have this gift.
I call this ability collective learning.It's what makes us different.
We can see it at work in the earliest stages of human history.
We evolved as a species in the savanna lands of Africa,
but then you see humans migrating into new environments,
into desert lands, into jungles,into the Ice Age tundra of Siberia --tough, tough environment --into the Americas, into Australasia.
Each migration involved learning --learning new ways of exploiting the environment,new ways of dealing with their surroundings.
Then 10,000 years ago,exploiting a sudden change in global climate with the end of the last ice age,humans learned to farm.
Farming was an energy bonanza.
And exploiting that energy,human populations multiplied.Human societies got larger,denser, more interconnected.
And then from about 500 years ago,humans began to link up globally through shipping, through trains,through telegraph, through the Internet,
until now we seem to forma single global brain of almost seven billion individuals.
And that brain is learning at warp speed.
And in the last 200 years,something else has happened. We've stumbled on another energy bonanza in fossil fuels.
So fossil fuels and collective learning together explain the staggering complexity we see around us.
So --Here we are,back at the convention center.
We've been on a journey,a return journey, of 13.7 billion years.
I hope you agree this is a powerful story.
And it's a story in which humans play an astonishing and creative role.
But it also contains warnings.
Collective learning is a very, very powerful force, and it's not clear that we humans are in charge of it.
I remember very vividly as a child growing up in England, living through the Cuban Missile Crisis.
For a few days, the entire biosphere seemed to be on the verge of destruction.
And the same weapons are still here, and they are still armed.
If we avoid that trap,others are waiting for us.
We're burning fossil fuels at such a rate
that we seem to be undermining the Goldilocks conditions that made it possible for human civilizations to flourish over the last 10,000 years.
So what big history can do is show us the nature of our complexity and fragility and the dangers that face us,
but it can also show us our power with collective learning.
And now, finally --this is what I want.
I want my grandson, Daniel, and his friends and his generation, throughout the world, to know the story of big history,
and to know it so well that they understand both the challenges that face us and the opportunities that face us.
And that's why a group of us are building a free, online syllabus in big history for high-school students throughout the world.
We believe that big history will be a vital intellectual tool for them,
as Daniel and his generation face the huge challenges and also the huge opportunities ahead of them
at this threshold moment in the history of our beautiful planet.
I thank you for your attention.