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  • What is going on

  • in this baby's mind?

  • If you'd asked people this 30 years ago,

  • most people, including psychologists,

  • would have said that this baby was irrational,

  • illogical, egocentric --

  • that he couldn't take the perspective of another person

  • or understand cause and effect.

  • In the last 20 years,

  • developmental science has completely overturned that picture.

  • So in some ways,

  • we think that this baby's thinking

  • is like the thinking of the most brilliant scientists.

  • Let me give you just one example of this.

  • One thing that this baby could be thinking about,

  • that could be going on in his mind,

  • is trying to figure out

  • what's going on in the mind of that other baby.

  • After all, one of the things that's hardest for all of us to do

  • is to figure out what other people are thinking and feeling.

  • And maybe the hardest thing of all

  • is to figure out that what other people think and feel

  • isn't actually exactly like what we think and feel.

  • Anyone who's followed politics can testify

  • to how hard that is for some people to get.

  • We wanted to know

  • if babies and young children

  • could understand this really profound thing about other people.

  • Now the question is: How could we ask them?

  • Babies, after all, can't talk,

  • and if you ask a three year-old

  • to tell you what he thinks,

  • what you'll get is a beautiful stream of consciousness monologue

  • about ponies and birthdays and things like that.

  • So how do we actually ask them the question?

  • Well it turns out that the secret was broccoli.

  • What we did -- Betty Rapacholi, who was one of my students, and I --

  • was actually to give the babies two bowls of food:

  • one bowl of raw broccoli

  • and one bowl of delicious goldfish crackers.

  • Now all of the babies, even in Berkley,

  • like the crackers and don't like the raw broccoli.

  • (Laughter)

  • But then what Betty did

  • was to take a little taste of food from each bowl.

  • And she would act as if she liked it or she didn't.

  • So half the time, she acted

  • as if she liked the crackers and didn't like the broccoli --

  • just like a baby and any other sane person.

  • But half the time,

  • what she would do is take a little bit of the broccoli

  • and go, "Mmmmm, broccoli.

  • I tasted the broccoli. Mmmmm."

  • And then she would take a little bit of the crackers,

  • and she'd go, "Eww, yuck, crackers.

  • I tasted the crackers. Eww, yuck."

  • So she'd act as if what she wanted

  • was just the opposite of what the babies wanted.

  • We did this with 15 and 18 month-old babies.

  • And then she would simply put her hand out and say,

  • "Can you give me some?"

  • So the question is: What would the baby give her,

  • what they liked or what she liked?

  • And the remarkable thing was that 18 month-old babies,

  • just barely walking and talking,

  • would give her the crackers if she liked the crackers,

  • but they would give her the broccoli if she liked the broccoli.

  • On the other hand,

  • 15 month-olds would stare at her for a long time

  • if she acted as if she liked the broccoli,

  • like they couldn't figure this out.

  • But then after they stared for a long time,

  • they would just give her the crackers,

  • what they thought everybody must like.

  • So there are two really remarkable things about this.

  • The first one is that these little 18 month-old babies

  • have already discovered

  • this really profound fact about human nature,

  • that we don't always want the same thing.

  • And what's more, they felt that they should actually do things

  • to help other people get what they wanted.

  • Even more remarkably though,

  • the fact that 15 month-olds didn't do this

  • suggests that these 18 month-olds had learned

  • this deep, profound fact about human nature

  • in the three months from when they were 15 months old.

  • So children both know more and learn more

  • than we ever would have thought.

  • And this is just one of hundreds and hundreds of studies over the last 20 years

  • that's actually demonstrated it.

  • The question you might ask though is:

  • Why do children learn so much?

  • And how is it possible for them to learn so much

  • in such a short time?

  • I mean, after all, if you look at babies superficially,

  • they seem pretty useless.

  • And actually in many ways, they're worse than useless,

  • because we have to put so much time and energy

  • into just keeping them alive.

  • But if we turn to evolution

  • for an answer to this puzzle

  • of why we spend so much time

  • taking care of useless babies,

  • it turns out that there's actually an answer.

  • If we look across many, many different species of animals,

  • not just us primates,

  • but also including other mammals, birds,

  • even marsupials

  • like kangaroos and wombats,

  • it turns out that there's a relationship

  • between how long a childhood a species has

  • and how big their brains are compared to their bodies

  • and how smart and flexible they are.

  • And sort of the posterbirds for this idea are the birds up there.

  • On one side

  • is a New Caledonian crow.

  • And crows and other corvidae, ravens, rooks and so forth,

  • are incredibly smart birds.

  • They're as smart as chimpanzees in some respects.

  • And this is a bird on the cover of science

  • who's learned how to use a tool to get food.

  • On the other hand,

  • we have our friend the domestic chicken.

  • And chickens and ducks and geese and turkeys

  • are basically as dumb as dumps.

  • So they're very, very good at pecking for grain,

  • and they're not much good at doing anything else.

  • Well it turns out that the babies,

  • the New Caledonian crow babies, are fledglings.

  • They depend on their moms

  • to drop worms in their little open mouths

  • for as long as two years,

  • which is a really long time in the life of a bird.

  • Whereas the chickens are actually mature

  • within a couple of months.

  • So childhood is the reason

  • why the crows end up on the cover of Science

  • and the chickens end up in the soup pot.

  • There's something about that long childhood

  • that seems to be connected

  • to knowledge and learning.

  • Well what kind of explanation could we have for this?

  • Well some animals, like the chicken,

  • seem to be beautifully suited

  • to doing just one thing very well.

  • So they seem to be beautifully suited

  • to pecking grain in one environment.

  • Other creatures, like the crows,

  • aren't very good at doing anything in particular,

  • but they're extremely good

  • at learning about laws of different environments.

  • And of course, we human beings

  • are way out on the end of the distribution like the crows.

  • We have bigger brains relative to our bodies

  • by far than any other animal.

  • We're smarter, we're more flexible,

  • we can learn more,

  • we survive in more different environments,

  • we migrated to cover the world and even go to outer space.

  • And our babies and children are dependent on us

  • for much longer than the babies of any other species.

  • My son is 23.

  • (Laughter)

  • And at least until they're 23,

  • we're still popping those worms

  • into those little open mouths.

  • All right, why would we see this correlation?

  • Well an idea is that that strategy, that learning strategy,

  • is an extremely powerful, great strategy for getting on in the world,

  • but it has one big disadvantage.

  • And that one big disadvantage

  • is that, until you actually do all that learning,

  • you're going to be helpless.

  • So you don't want to have the mastodon charging at you

  • and be saying to yourself,

  • "A slingshot or maybe a spear might work. Which would actually be better?"

  • You want to know all that

  • before the mastodons actually show up.

  • And the way the evolutions seems to have solved that problem

  • is with a kind of division of labor.

  • So the idea is that we have this early period when we're completely protected.

  • We don't have to do anything. All we have to do is learn.

  • And then as adults,

  • we can take all those things that we learned when we were babies and children

  • and actually put them to work to do things out there in the world.

  • So one way of thinking about it

  • is that babies and young children

  • are like the research and development division of the human species.

  • So they're the protected blue sky guys

  • who just have to go out and learn and have good ideas,

  • and we're production and marketing.

  • We have to take all those ideas

  • that we learned when we were children

  • and actually put them to use.

  • Another way of thinking about it

  • is instead of thinking of babies and children

  • as being like defective grownups,

  • we should think about them

  • as being a different developmental stage of the same species --

  • kind of like caterpillars and butterflies --

  • except that they're actually the brilliant butterflies

  • who are flitting around the garden and exploring,

  • and we're the caterpillars

  • who are inching along our narrow, grownup, adult path.

  • If this is true, if these babies are designed to learn --

  • and this evolutionary story would say children are for learning,

  • that's what they're for --

  • we might expect

  • that they would have really powerful learning mechanisms.

  • And in fact, the baby's brain

  • seems to be the most powerful learning computer

  • on the planet.

  • But real computers are actually getting to be a lot better.

  • And there's been a revolution

  • in our understanding of machine learning recently.

  • And it all depends on the ideas of this guy,

  • the Reverend Thomas Bayes,

  • who was a statistician and mathematician in the 18th century.

  • And essentially what Bayes did

  • was to provide a mathematical way

  • using probability theory

  • to characterize, describe,

  • the way that scientists find out about the world.

  • So what scientists do

  • is they have a hypothesis that they think might be likely to start with.

  • They go out and test it against the evidence.

  • The evidence makes them change that hypothesis.

  • Then they test that new hypothesis

  • and so on and so forth.

  • And what Bayes showed was a mathematical way that you could do that.

  • And that mathematics is at the core

  • of the best machine learning programs that we have now.

  • And some 10 years ago,

  • I suggested that babies might be doing the same thing.

  • So if you want to know what's going on

  • underneath those beautiful brown eyes,

  • I think it actually looks something like this.

  • This is Reverend Bayes's notebook.

  • So I think those babies are actually making complicated calculations

  • with conditional probabilities that they're revising

  • to figure out how the world works.

  • All right, now that might seem like an even taller order to actually demonstrate.

  • Because after all, if you ask even grownups about statistics,

  • they look extremely stupid.

  • How could it be that children are doing statistics?

  • So to test this we used a machine that we have

  • called the Blicket Detector.

  • This is a box that lights up and plays music

  • when you put some things on it and not others.

  • And using this very simple machine,

  • my lab and others have done dozens of studies