in the 45 years since the introduction of the automated teller machine,

those vending machines that dispense cash,

the number of human bank tellers employed in the United States

has roughly doubled,

from about a quarter of a million to a half a million.

A quarter of a million in 1970 to about a half a million today,

with 100,000 added since the year 2000.

These facts, revealed in a recent book

by Boston University economist James Bessen,

raise an intriguing question:

what are all those tellers doing,

and why hasn't automation eliminated their employment by now?

If you think about it,

many of the great inventions of the last 200 years

were designed to replace human labor.

Tractors were developed

to substitute mechanical power for human physical toil.

Assembly lines were engineered

to replace inconsistent human handiwork

with machine perfection.

Computers were programmed to swap out

error-prone, inconsistent human calculation

with digital perfection.

These inventions have worked.

We no longer dig ditches by hand,

pound tools out of wrought iron

or do bookkeeping using actual books.

And yet, the fraction of US adults employed in the labor market

is higher now in 2016

than it was 125 years ago, in 1890,

and it's risen in just about every decade

in the intervening 125 years.

This poses a paradox.

Our machines increasingly do our work for us.

Why doesn't this make our labor redundant and our skills obsolete?

Why are there still so many jobs?

(Laughter)

I'm going to try to answer that question tonight,

and along the way, I'm going to tell you what this means for the future of work

and the challenges that automation does and does not pose

for our society.

Why are there so many jobs?

There are actually two fundamental economic principles at stake.

One has to do with human genius

and creativity.

The other has to do with human insatiability,

or greed, if you like.

I'm going to call the first of these the O-ring principle,

and it determines the type of work that we do.

The second principle is the never-get-enough principle,

and it determines how many jobs there actually are.

Let's start with the O-ring.

ATMs, automated teller machines,

had two countervailing effects on bank teller employment.

As you would expect, they replaced a lot of teller tasks.

The number of tellers per branch fell by about a third.

But banks quickly discovered that it also was cheaper to open new branches,

and the number of bank branches increased by about 40 percent

in the same time period.

The net result was more branches and more tellers.

But those tellers were doing somewhat different work.

As their routine, cash-handling tasks receded,

they became less like checkout clerks

and more like salespeople,

forging relationships with customers,

solving problems

and introducing them to new products like credit cards, loans and investments:

more tellers doing a more cognitively demanding job.

There's a general principle here.

Most of the work that we do

requires a multiplicity of skills,

and brains and brawn,

technical expertise and intuitive mastery,

perspiration and inspiration in the words of Thomas Edison.

In general, automating some subset of those tasks

doesn't make the other ones unnecessary.

In fact, it makes them more important.

It increases their economic value.

Let me give you a stark example.

In 1986, the space shuttle Challenger

exploded and crashed back down to Earth

less than two minutes after takeoff.

The cause of that crash, it turned out,

was an inexpensive rubber O-ring in the booster rocket

that had frozen on the launchpad the night before

and failed catastrophically moments after takeoff.

In this multibillion dollar enterprise

that simple rubber O-ring

made the difference between mission success

and the calamitous death of seven astronauts.

An ingenious metaphor for this tragic setting

is the O-ring production function,

named by Harvard economist Michael Kremer

after the Challenger disaster.

The O-ring production function conceives of the work

as a series of interlocking steps,

links in a chain.

Every one of those links must hold for the mission to succeed.

If any of them fails,

the mission, or the product or the service,

comes crashing down.

This precarious situation has a surprisingly positive implication,

which is that improvements

in the reliability of any one link in the chain

increases the value of improving any of the other links.

Concretely, if most of the links are brittle and prone to breakage,

the fact that your link is not that reliable

is not that important.

Probably something else will break anyway.

But as all the other links become robust and reliable,

the importance of your link becomes more essential.

In the limit, everything depends upon it.

The reason the O-ring was critical to space shuttle Challenger

is because everything else worked perfectly.

If the Challenger were kind of the space era equivalent

of Microsoft Windows 2000 --

(Laughter)

the reliability of the O-ring wouldn't have mattered

because the machine would have crashed.

(Laughter)

Here's the broader point.

In much of the work that we do, we are the O-rings.

Yes, ATMs could do certain cash-handling tasks

faster and better than tellers,

but that didn't make tellers superfluous.

It increased the importance of their problem-solving skills

and their relationships with customers.

The same principle applies if we're building a building,

if we're diagnosing and caring for a patient,

or if we are teaching a class

to a roomful of high schoolers.

As our tools improve,

technology magnifies our leverage

and increases the importance of our expertise

and our judgment and our creativity.

And that brings me to the second principle:

never get enough.

You may be thinking, OK, O-ring, got it,

that says the jobs that people do will be important.

They can't be done by machines, but they still need to be done.

But that doesn't tell me how many jobs there will need to be.

If you think about it, isn't it kind of self-evident

that once we get sufficiently productive at something,

we've basically worked our way out of a job?

In 1900, 40 percent of all US employment

was on farms.

Today, it's less than two percent.

Why are there so few farmers today?

It's not because we're eating less.

(Laughter)

A century of productivity growth in farming

means that now, a couple of million farmers

can feed a nation of 320 million.

That's amazing progress,

but it also means there are only so many O-ring jobs left in farming.

So clearly, technology can eliminate jobs.

Farming is only one example.

There are many others like it.

But what's true about a single product or service or industry

has never been true about the economy as a whole.

Many of the industries in which we now work --

health and medicine,

finance and insurance,

electronics and computing --

were tiny or barely existent a century ago.

Many of the products that we spend a lot of our money on --

air conditioners, sport utility vehicles,

computers and mobile devices --

were unattainably expensive,

or just hadn't been invented a century ago.

As automation frees our time, increases the scope of what is possible,

we invent new products, new ideas, new services

that command our attention,

occupy our time

and spur consumption.

You may think some of these things are frivolous --

extreme yoga, adventure tourism,

Pokémon GO --

and I might agree with you.

But people desire these things, and they're willing to work hard for them.

The average worker in 2015

wanting to attain the average living standard in 1915

could do so by working just 17 weeks a year,

one third of the time.

But most people don't choose to do that.

They are willing to work hard

to harvest the technological bounty that is available to them.

Material abundance has never eliminated perceived scarcity.

In the words of economist Thorstein Veblen,

invention is the mother of necessity.

Now ...

So if you accept these two principles,

the O-ring principle and the never-get-enough principle,

then you agree with me.

There will be jobs.

Does that mean there's nothing to worry about?

Automation, employment, robots and jobs --

it'll all take care of itself?

No.

That is not my argument.

Automation creates wealth

by allowing us to do more work in less time.

There is no economic law

that says that we will use that wealth well,

and that is worth worrying about.

Consider two countries,

Norway and Saudi Arabia.

Both oil-rich nations,

it's like they have money spurting out of a hole in the ground.

(Laughter)

But they haven't used that wealth equally well to foster human prosperity,

human prospering.

Norway is a thriving democracy.

By and large, its citizens work and play well together.

It's typically numbered between first and fourth

in rankings of national happiness.

Saudi Arabia is an absolute monarchy

in which many citizens lack a path for personal advancement.

It's typically ranked 35th among nations in happiness,

which is low for such a wealthy nation.

Just by way of comparison,

the US is typically ranked around 12th or 13th.

The difference between these two countries

is not their wealth

and it's not their technology.

It's their institutions.

Norway has invested to build a society

with opportunity and economic mobility.

Saudi Arabia has raised living standards

while frustrating many other human strivings.

Two countries, both wealthy,

not equally well off.

And this brings me to the challenge that we face today,

the challenge that automation poses for us.

The challenge is not that we're running out of work.

The US has added 14 million jobs

since the depths of the Great Recession.

The challenge is that many of those jobs

are not good jobs,

and many citizens cannot qualify for the good jobs

that are being created.

Employment growth in the United States and in much of the developed world

looks something like a barbell

with increasing poundage on either end of the bar.

On the one hand,

you have high-education, high-wage jobs

like doctors and nurses, programmers and engineers,

marketing and sales managers.

Employment is robust in these jobs, employment growth.

Similarly, employment growth is robust in many low-skill,

low-education jobs like food service,

cleaning, security,

home health aids.

Simultaneously, employment is shrinking