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  • When I was a student here in Oxford in the 1970s,

  • the future of the world was bleak.

  • The population explosion was unstoppable.

  • Global famine was inevitable.

  • A cancer epidemic caused by chemicals in the environment

  • was going to shorten our lives.

  • The acid rain was falling on the forests.

  • The desert was advancing by a mile or two a year.

  • The oil was running out,

  • and a nuclear winter would finish us off.

  • None of those things happened,

  • (Laughter)

  • and astonishingly, if you look at what actually happened in my lifetime,

  • the average per-capita income

  • of the average person on the planet,

  • in real terms, adjusted for inflation,

  • has tripled.

  • Lifespan is up by 30 percent in my lifetime.

  • Child mortality is down by two-thirds.

  • Per-capita food production

  • is up by a third.

  • And all this at a time when the population has doubled.

  • How did we achieve that, whether you think it's a good thing or not?

  • How did we achieve that?

  • How did we become

  • the only species

  • that becomes more prosperous

  • as it becomes more populous?

  • The size of the blob in this graph represents the size of the population,

  • and the level of the graph

  • represents GDP per capita.

  • I think to answer that question

  • you need to understand

  • how human beings bring together their brains

  • and enable their ideas to combine and recombine,

  • to meet and, indeed, to mate.

  • In other words, you need to understand

  • how ideas have sex.

  • I want you to imagine

  • how we got from making objects like this

  • to making objects like this.

  • These are both real objects.

  • One is an Acheulean hand axe from half a million years ago

  • of the kind made by Homo erectus.

  • The other is obviously a computer mouse.

  • They're both exactly the same size and shape to an uncanny degree.

  • I've tried to work out which is bigger,

  • and it's almost impossible.

  • And that's because they're both designed to fit the human hand.

  • They're both technologies. In the end, their similarity is not that interesting.

  • It just tells you they were both designed to fit the human hand.

  • The differences are what interest me,

  • because the one on the left was made to a pretty unvarying design

  • for about a million years --

  • from one-and-a-half million years ago to half a million years ago.

  • Homo erectus made the same tool

  • for 30,000 generations.

  • Of course there were a few changes,

  • but tools changed slower than skeletons in those days.

  • There was no progress, no innovation.

  • It's an extraordinary phenomenon, but it's true.

  • Whereas the object on the right is obsolete after five years.

  • And there's another difference too,

  • which is the object on the left is made from one substance.

  • The object on the right is made from

  • a confection of different substances,

  • from silicon and metal and plastic and so on.

  • And more than that, it's a confection of different ideas,

  • the idea of plastic, the idea of a laser,

  • the idea of transistors.

  • They've all been combined together in this technology.

  • And it's this combination,

  • this cumulative technology, that intrigues me,

  • because I think it's the secret to understanding

  • what's happening in the world.

  • My body's an accumulation of ideas too:

  • the idea of skin cells, the idea of brain cells, the idea of liver cells.

  • They've come together.

  • How does evolution do cumulative, combinatorial things?

  • Well, it uses sexual reproduction.

  • In an asexual species, if you get two different mutations in different creatures,

  • a green one and a red one,

  • then one has to be better than the other.

  • One goes extinct for the other to survive.

  • But if you have a sexual species,

  • then it's possible for an individual

  • to inherit both mutations

  • from different lineages.

  • So what sex does is it enables the individual

  • to draw upon

  • the genetic innovations of the whole species.

  • It's not confined to its own lineage.

  • What's the process that's having the same effect

  • in cultural evolution

  • as sex is having in biological evolution?

  • And I think the answer is exchange,

  • the habit of exchanging one thing for another.

  • It's a unique human feature.

  • No other animal does it.

  • You can teach them in the laboratory to do a little bit of exchange --

  • and indeed there's reciprocity in other animals --

  • But the exchange of one object for another never happens.

  • As Adam Smith said, "No man ever saw a dog

  • make a fair exchange of a bone with another dog."

  • (Laughter)

  • You can have culture without exchange.

  • You can have, as it were, asexual culture.

  • Chimpanzees, killer whales, these kinds of creatures, they have culture.

  • They teach each other traditions

  • which are handed down from parent to offspring.

  • In this case, chimpanzees teaching each other

  • how to crack nuts with rocks.

  • But the difference is

  • that these cultures never expand, never grow,

  • never accumulate, never become combinatorial,

  • and the reason is because

  • there is no sex, as it were,

  • there is no exchange of ideas.

  • Chimpanzee troops have different cultures in different troops.

  • There's no exchange of ideas between them.

  • And why does exchange raise living standards?

  • Well, the answer came from David Ricardo in 1817.

  • And here is a Stone Age version of his story,

  • although he told it in terms of trade between countries.

  • Adam takes four hours to make a spear and three hours to make an axe.

  • Oz takes one hour to make a spear and two hours to make an axe.

  • So Oz is better at both spears and axes than Adam.

  • He doesn't need Adam.

  • He can make his own spears and axes.

  • Well no, because if you think about it,

  • if Oz makes two spears and Adam make two axes,

  • and then they trade,

  • then they will each have saved an hour of work.

  • And the more they do this, the more true it's going to be,

  • because the more they do this, the better Adam is going to get at making axes

  • and the better Oz is going to get at making spears.

  • So the gains from trade are only going to grow.

  • And this is one of the beauties of exchange,

  • is it actually creates the momentum

  • for more specialization,

  • which creates the momentum for more exchange and so on.

  • Adam and Oz both saved an hour of time.

  • That is prosperity, the saving of time

  • in satisfying your needs.

  • Ask yourself how long you would have to work

  • to provide for yourself

  • an hour of reading light this evening to read a book by.

  • If you had to start from scratch, let's say you go out into the countryside.

  • You find a sheep. You kill it. You get the fat out of it.

  • You render it down. You make a candle, etc. etc.

  • How long is it going to take you? Quite a long time.

  • How long do you actually have to work

  • to earn an hour of reading light

  • if you're on the average wage in Britain today?

  • And the answer is about half a second.

  • Back in 1950,

  • you would have had to work for eight seconds on the average wage

  • to acquire that much light.

  • And that's seven and a half seconds of prosperity that you've gained

  • since 1950, as it were,

  • because that's seven and a half seconds in which you can do something else,

  • or you can acquire another good or service.

  • And back in 1880,

  • it would have been 15 minutes

  • to earn that amount of light on the average wage.

  • Back in 1800,

  • you'd have had to work six hours

  • to earn a candle that could burn for an hour.

  • In other words, the average person on the average wage

  • could not afford a candle in 1800.

  • Go back to this image of the axe and the mouse,

  • and ask yourself: "Who made them and for who?"

  • The stone axe was made by someone for himself.

  • It was self-sufficiency.

  • We call that poverty these days.

  • But the object on the right

  • was made for me by other people.

  • How many other people?

  • Tens? Hundreds? Thousands?

  • You know, I think it's probably millions.

  • Because you've got to include the man who grew the coffee,

  • which was brewed for the man who was on the oil rig,

  • who was drilling for oil, which was going to be made into the plastic, etc.

  • They were all working for me,

  • to make a mouse for me.

  • And that's the way society works.

  • That's what we've achieved as a species.

  • In the old days, if you were rich,

  • you literally had people working for you.

  • That's how you got to be rich; you employed them.

  • Louis XIV had a lot of people working for him.

  • They made his silly outfits, like this,

  • (Laughter)

  • and they did his silly hairstyles, or whatever.

  • He had 498 people

  • to prepare his dinner every night.

  • But a modern tourist going around the palace of Versailles

  • and looking at Louis XIV's pictures,

  • he has 498 people doing his dinner tonight too.

  • They're in bistros and cafes and restaurants

  • and shops all over Paris,

  • and they're all ready to serve you at an hour's notice with an excellent meal

  • that's probably got higher quality

  • than Louis XIV even had.

  • And that's what we've done, because we're all working for each other.

  • We're able to draw upon specialization and exchange

  • to raise each other's living standards.

  • Now, you do get other animals working for each other too.

  • Ants are a classic example; workers work for queens and queens work for workers.

  • But there's a big difference,

  • which is that it only happens within the colony.

  • There's no working for each other across the colonies.

  • And the reason for that is because there's a reproductive division of labor.

  • That is to say, they specialize with respect to reproduction.

  • The queen does it all.

  • In our species, we don't like doing that.

  • It's the one thing we insist on doing for ourselves, is reproduction.

  • (Laughter)

  • Even in England, we don't leave reproduction to the Queen.

  • (Applause)

  • So when did this habit start?

  • And how long has it been going on? And what does it mean?

  • Well, I think, probably, the oldest version of this

  • is probably the sexual division of labor.

  • But I've got no evidence for that.

  • It just looks like the first thing we did

  • was work male for female and female for male.

  • In all hunter-gatherer societies today,

  • there's a foraging division of labor

  • between, on the whole, hunting males and gathering females.

  • It isn't always quite that simple,

  • but there's a distinction between

  • specialized roles for males and females.

  • And the beauty of this system

  • is that it benefits both sides.

  • The woman knows

  • that, in the Hadzas' case here --

  • digging roots to share with men in exchange for meat --

  • she knows that all she has to do to get access to protein

  • is to dig some extra roots and trade them for meat.

  • And she doesn't have to go on an exhausting hunt

  • and try and kill a warthog.

  • And the man knows that he doesn't have to do any digging

  • to get roots.

  • All he has to do is make sure that when he kills a warthog

  • it's big enough to share some.

  • And so both sides raise each other's standards of living

  • through the sexual division of labor.

  • When did this happen? We don't know, but it's possible