Why monkeys (and humans) are wired for fairness

My first year in graduate school

studying cooperation in monkeys,

I spent a lot of time outside

just watching our groups
of Capuchin monkeys interact.

One afternoon, I was out back
feeding peanuts to one of our groups,

which required distracting
one of our males, Ozzie, enough

so that the other monkeys could get some.

Ozzie loved peanuts,

and he always tried to do
anything he could to grab some.

On that day, however,

he began trying to bring other things
from his enclosure to me

and trade them with me
in order to get a peanut.

Now Capuchins are smart,

so this wasn't necessarily a surprise.

But what was a surprise

was that some of the things
that he was bringing me

I was pretty sure he liked
better than peanuts.

First, he brought me
a piece of monkey chow,

which is like dried dog food,

it was even made by Purina,

and for a monkey,

is about as worthless as it gets.

Of course I didn't give him
a peanut for that.

But he kept trying,

and eventually he brought me
a quarter of an orange

and tried to trade it
with me for a peanut.

Now oranges are a valuable
monkey commodity,

so this trade seemed, shall I say,
a little bit nuts?

Now you may be wondering
how we know what monkeys prefer.

Well, we ask them,

by giving them a choice between two foods

and seeing which one they pick.

Generally speaking,

their preferences are a lot like ours.

The sweeter it is, the more they like it.

So, much like humans prefer
cupcakes to kale,

monkeys prefer fruits,
like oranges or grapes,

to vegetables like cucumbers

and all of this to monkey chow.

And peanuts are not bad.

However, they definitely don't prefer them
to a chunk of orange.

So when Ozzie tried to trade
a quarter of an orange for a peanut,

it was a surprise

and I began to wonder

if he suddenly wanted that peanut

because everybody else
in his group was getting one.

In case you're wondering,
I did give Ozzie his peanut.

But then I went straight
to my graduate adviser,

Frans de Waal,

and we began to design a study

to see how the monkeys would respond

when somebody else in their group
got a better reward than they did

for doing the same work.

It was a very simple study.

We took two monkeys from the same group

and had them sit side by side,

and they would do a task,

which was trading a token with me,

and if they did so successfully,

they got a reward.

The catch was that monkey
always got a piece of cucumber,

and the other monkey
sometimes got a piece of cucumber,

but sometimes got a grape.

And if you'll recall,

grapes are much preferred to cucumbers

on the Capuchin monkey hierarchy.

These are two of my Capuchin monkeys.

Winter, on the right,
is trading for a grape,

and Lance on the left,
is trading for a cucumber.

You can see that she --
and yes, Lance is actually a female --

is at first perfectly happy
with her cucumber,

until she sees Winter trading for a grape.

Suddenly, Lance is very
enthusiastic about trading.

She gets her cucumber,
takes a bite and then --

throws it right back out again.

Meanwhile, Winter trades again
and gets another grape

and has Lance's undivided attention
while she eats it.

This time,

Lance is not
so enthusiastic about trading.

But eventually she does so.

But when she gets the cucumber
this time around,

she doesn't even take a bite

before she throws it back out again.

Apparently, Lance only wants a cucumber

when she hasn't just watched
Winter eat a grape.

And Lance was not alone in this.

All of my Capuchins were perfectly happy
with their cucumbers

as long as the other monkeys
were getting cucumbers too.

But they often weren't so happy
with their cucumbers

when other monkeys were getting a grape.

The obvious question is why?

If they liked those cucumbers before,

what changed?

Now, I'm a scientist,

and scientists are famously shy
about reading too much into our studies,

especially when it comes
to what other animals

are thinking or feeling,

because we can't ask them.

But still, what I was seeing in my monkeys

looked an awful lot like what we humans
would call a sense of fairness.

After all,

the difference in that cucumber

was that it cam after Winter got a grape,

rather than before.

We humans are obsessed with fairness.

I have a younger sister,

and when we were little,

if my sister got a bigger
piece of the pie than me,

even by a crumb,

I was furious,

it wasn't fair.

And the childhood me is not alone.

We humans hate getting
less than another so much,

that one study found

that if humans were given
a hypothetical choice

between earning 50,000 dollars a year

while others earned 25,000 dollars

or earning 100,000 dollars a year

while others earned 250,000 dollars,

nearly half the subjects

prefer to earn 50,000 dollars
a year less money

to avoid earning relatively less
than someone else.

That's a pretty big price to pay.

What drives people

to this sort of apparently
irrational decision making?

After all,

throwing away your cucumber
because someone else got a grape

only makes sense
if it makes things more fair.

Otherwise, Winter has a grape,
and you have nothing.

Of course humans are not Capuchin monkeys.

But on the surface,

sacrificing 50,000 dollars

because somebody else
is going to earn more money than you

makes no more sense
than throwing away that cucumber.

Except, maybe it does.

Some economists think

that the sense of fairness in humans
is tied to cooperation.

In other words, we need
that sense of fairness

when we're working with somebody else

to know when we're getting
the short end of the stick.

Think about it this way.

Let's say you have a colleague at work
who's having a hard time

and needs a little extra help.

You're probably more
than happy to help out,

especially if she does
the same for you when you need it.

In other words, if things even out.

But now,

let's say that colleague
is always slacking off

and dumping extra work on you.

That's infuriating.

Or worse,

what if you're doing all the work

and she's getting paid more.

You're outraged, right?

As well you should be.

That righteous fury

is your sense of fairness
telling you that, well,

it's not fair.

You need to get your fair share
from the people you're working with

or it's exploitation, not cooperation.

You may not be able to leave every job
where you're treated unfairly,

but in a perfect world,

one without racism and sexism

and the frictions associated
with finding a new job,

it's your sense of fairness
that would let you know

when it was time to move on.

And if you couldn't?

Well, that smoldering frustration

might make you throw your cucumbers too.

And human are not alone in this.

In the previous study,

there was nothing Lance could do about it,

but what if there had been?

It turns out

that Capuchins simply refuse
to cooperate with other Capuchins

who don't give them their share
after they work together.

And refusing to work together
with another monkey

is a pretty straightforward way
of leveling the playing field.

Apparently, no monkey
getting anything at all

is better than another
monkey getting more.

But much like you and your coworker,

they're perfectly happy
with a little short-term inequality

as long as everything evens out
over the long run.

This economic connection
between fairness and cooperation

makes sense to me
as an evolutionary biologist.

After all,

your ancestors didn't get
to pass on their genes

because they did well
in some absolute sense,

but because they did better than others.

We don't call it survival of the fit,

we call it survival of the fittest.

As in, more fit than others.

It's all relative.

OK.

So my Capuchins don't like it
when they get less than another.

And they're perfectly happy
to sacrifice their cucumbers

to level the playing field.

That's great.

But what we would call
a sense of fairness in humans,

also means that we care
when we get more than someone else.

What about my monkeys?

It turns out

that primates do notice
when they get more than others.

Or at least, some of them do.

My Capuchins do not.

But in one of my studies

my chimpanzees would
sometimes refuse a grape

if another chimpanzee
in their group got a cucumber,

which is pretty impressive

given how much my chimpanzees like grapes.

However, they were still more upset
when they got less than another chimp

as compared to when they got more.

You may not think it's fair
when you have more than your neighbor,

but you really don't think it's fair

when your neighbor has more than you.

Here's an important question though.

Why do we care about
inequality or unfairness

when we are the ones
who are unfairly benefiting?

If evolution is about
survival of the fittest,

wouldn't it make sense to grab
any advantage you can get?

Here's the thing though.

I do better if I get more than you, sure.

But best of all is if you and I
can work together

and get more than either one of us
could have gotten on our own.

But why would you work with me

if you don't think I'm going to play fair?

But if you think I'm going to notice
when I've got more than you

and do something about it,

then you will work with me.

Evolution has selected us

to accept the occasional short-term loss

in order to maintain these all-important
long-term relationships.

This is true in chimpanzees,

but it is even more important in humans.

Humans are incredibly interconnected
and interdependent.

And we have the advanced
cognitive abilities

to be able to plan far into the future.

And to recognize the importance

of maintaining these
cooperative partnerships.

Indeed if anything,

I think we are likely underplaying

how important the sense
of fairness is for people.

One of the biggest differences
between humans and Capuchin monkeys

is the sheer magnitude and ubiquity
of cooperation in humans.

In other words,

we're a lot more cooperative
than Capuchin monkeys are.

Legal and economic systems
literally only exist

if we all agree to participate in them.

And if people feel left out
of the rewards and benefits

of those systems,

then they stop participating

and the whole system falls apart.

Many of the protests
and uprisings we're seeing,

both in the US and around the globe,

are explicitly framed
in terms of fairness,

which is not surprising to me.

Whether it's about disproportionate
access to resources,

or that some groups are being
disproportionately impacted

by the legal system
or the effects of a virus,

these protests are the logical outcome

of our long evolutionary tendency
to reject unfairness

combined with our long history
of social stratification.

And the systemic inequalities

that have resulted
from that stratification.

Layer on top of this the fact
that by many measures

economic inequality is skyrocketing.

Chris Boehm wrote a book
called "Hierarchy in the Forest"

in which he argued

that humans have reverse hierarchies

in which those at the bottom band together

to keep those at the top
from taking advantage of them.

Perhaps these protests
are simply the latest manifestation

of humans' tendency
to rebalance the hierarchy.

Perhaps the biggest difference
between us and Capuchin monkeys

is that we can recognize this problem

and actively work
to do something about it.

Of course we recognize
when we're disadvantaged.

But we can and we must also recognize

when we're advantaged
at the expense of someone else.

And recognize fairness

as the balance between
these two inequalities.

Because our society literally
depends upon it.

Indeed, my research shows

that not all primate species
care about inequality.

It's only those that rely on cooperation,

which most definitely includes humans.

We evolved to care about fairness

because we rely on each other
for our cooperative society.

And the more unfair the world gets,

and the less we care about each other,

the more peril we will face.

Our issues are more complex
than grapes and cucumbers,

but as the Capuchins have taught us,

we will all do better
when we all play fair.

Thank you.