The weird history of the "sex chromosomes"

The common thinking on biological sex goes like this: females have two X chromosomes in their cells, while males have one X and one Y. In this myth-busting talk, science writer and podcaster Molly Webster shows why the so-called "sex chromosomes" are more complicated than this simple definition -- and reveals why we should think about them differently.

OK.

So we are going to start in 1891,

when a German scientist
was looking through a microscope

at insect cells.

And he saw something kind of funny.

At the center of the cells,
there was this dark stuff.

No one had ever seen it before.

And he noticed that as the cells
would multiply and divide,

it would go into some of the new cells

but not the others.

He didn't know what it was,
so he gave it a really great name.

He called it the "X element."

(Laughter)

And he was like,
"We'll just fill in that X later."

And then, fast-forward 10 years later,

and there is an American scientist,

and she is looking through her microscope,

also at insect cells.

And she sees something funny.

There's more of this dark stuff.

And it's kind of tiny,

it's hanging out near the X element.

And eventually, someone was like,

"Well, if that one thing's called X,

should we call this other thing Y?"

And like that, (Snaps fingers)

the sex chromosomes had been discovered.

So chromosomes,

you probably all know what they are,

but I will tell you anyways.

They're made up of DNA --

everything has it,
it's the blueprint of life,

we've got rats, we've got trees,

we've got insects, we've got humans.

And in the case of human chromosomes,

geneticist Melissa Wilson
broke it down for me like this.

(Audio) Melissa Wilson: Typically,
you'll get one copy of every chromosome

from your genetic mom

and one copy of every chromosome
from your genetic dad,

and we have 22 of these

that you get one copy from mom
and one copy from dad.

And then there's a 23rd pair, X and Y.

Molly Webster: So while all
the other chromosomes are numbered,

one through 22,

we do not call X and Y 23.

I like to think that they are waiting
for, like, a LeBron James to come along.

But in this instance, they were like,

"We're just going to keep the letters,

and then we'll give them a title."

They called them the sex chromosomes.

Now I would wager
that in the United States,

these are the most well-known chromosomes

for one simple fact:

that we say X equals "girl,"
and Y equals "boy" --

that they are responsible for sex.

And -- and I had to learn this --

but when I'm talking about "sex" here,

I'm talking about the way biology
gives us gonads,

which are our ovaries and our testes --

I'm not talking about gender,
which is how we identify.

And so, as a reporter at the show --

"Radiolab," the audio documentary
program I work for --

I was like, what's up
with these sex chromosomes?

You know, that's kind of my job,
I think things are weird,

and then I get to call people about them

and ask questions,
and then hopefully they answer.

And in this case,
a lot of people answered.

And in the two years I had
of reporting on X and Y,

as part of "Gonads,"
the series on sex and gender

I ended up doing for "Radiolab,"

I found out that these two chromosomes
live in a world that is unexpected,

a little unsettling;

where things that I thought were facts

were, like, twisted in ways
I hadn't seen before.

And the world goes so far
beyond the boundaries of sex,

I was like,

"Maybe we should all talk about this."

So, you're you all,

we're all going to talk about it.

And for me,

the true story of X and Y
starts with their name.

So within years of being discovered,

these two little chromosomes
had acquired more than 10 different names.

There was diplosome and heterochromosome

and idiochromosome,

and most of the names had to do
with their structure, their shape,

their size.

And then there was "sex chromosome,"

which they had been given
because of the fact

that we had started seeing that the X
would go with the females,

and the Y would often go with the males.

But scientists were like,

"Do we really want
to call them sex chromosomes?"

And science historian Sarah Richardson
is the one who told me this story.

(Audio) Sarah Richardson:
For three decades, scientists were like,

"You should not call them
the sex chromosomes.

The X and Y have many functions,

and you wouldn't assume
that a single chromosome

controls a single trait.

Imagine calling one chromosome
the 'urogenital chromosome,'

or the 'liver chromosome.'"

MW: Scientists, if you dig
into the history --

it's really cool, you should --

were hesitant to, like,
commit to such a specific name

and such a powerfully connotated name.

There was a fear that it would
actually be really limiting --

maybe to science, maybe to society --

but the fear was in the room.

And you can see they ended up
getting "sex chromosome" --

it's like a pretty juicy title,

it popularized genetics, you know?

But in the 100-year history
since we settled on that name,

you can see it starts
to get a little complicated.

So around 1960 --

this is going to be our first stop

on the complicated world
of the sex chromosomes --

so around 1960,

we had discovered that you could be XYY.

They discovered an XYY man.

And to digress a little here,

it turns out that the model
of "X equals girl and Y equals boy"

is really simplistic.

You can actually be a whole bunch
of different combinations of X and Y,

giving you, like, different types
of biological sex.

You could be two Xs and two Ys together.

You could be four Xs,
you could be five Xs,

you could be XO.

And so I thought that was pretty crazy,

because I was like,

"Wow, this really upends
a model of biological sex

I think most of us in this room
have been taught."

So a few years after they realized
that you can be XYY,

researchers go to a prison in Scotland,

and they do genetic analysis
of a bunch of the male prisoners.

And they find a number
of people who are XYY.

And according to Sarah:

(Audio) SR: They just rushed
to publish a theory

suggesting that this extra Y chromosome

could explain criminality in some men.

MW: Yeah.

So the logic goes like this:

By this point, we're thinking Y is male.

We think male is aggressive,

so Y must be aggression.

If you've got an extra Y,
you must be crazy.

And like, we went nuts with this theory.

We called it the supermale,

they started scanning more prisoners,

serial killers, boys.

And in all seriousness,

there was actually a suggestion
that we consider aborting XYY fetuses.

So in 1980,

this theory pretty much toppled,
for a number of reasons.

One,

there had been this really large study

that basically showed
there was no connection

between Y and violence,

I think we all saw that coming.

And then, there was one other thing.

(Audio) SR: Going back
and looking at those original findings

in that high-security
psychiatric institution,

they had also found
a high number of individuals

with an extra X chromosome.

So these are XXY, as opposed to XYY.

(Audio) MW: Really?

(Audio) SR: Yeah.
Now, they never claimed

that the individuals
with an extra X chromosome

were superfemales.

They never investigated
whether they had higher rates of violence.

MW: Seems like kind of an oversight.

I don't know.

But I think it's interesting,

because what you see is if you start
looking at these chromosomes

through the lens of sex,

what naturally falls in place behind

is we look at them
through the lens of gender,

and the traits
that we associate with gender.

So men were violent,

and Y explained why they were in prison.

The X did not do that,

because like, you know, what's X?

We don't associate it with violence.

And while we don't believe
in supermales today --

God, I hope we don't --

we don't believe in supermales today,

there is a very similar conversation
that's still happening

around inherent violence
in boys and biology.

So my next stop
on the weird world of X and Y,

or things feeling
a little topsy-turvy, is 1985.

The World University Games
were set to happen in Japan,

and the Spanish hurdler María José
Martínez-Patiño was scheduled to run.

She was like a hot shot,
a rising superstar.

And the night before her race,
they had her DNA scanned.

Now at the time, this was a thing
that they were doing,

because they were like,

"OK, we don't want men
covertly racing as women,

so we're going to scan the women

and make sure all their Xs line up."

And so I heard this story
from Ruth Padawer

who was a New York Times Magazine reporter

and she reported on María.

(Audio) Ruth Padawer: So they tell her
the chromosome test results were abnormal.

Although on the outside,
she was fully female,

she had XY chromosomes
and these internal testes.

MW: They were like,

"We hate to break it to you, María,
but you're actually a dude.

You can't race with the ladies."

(Audio) RP: And so she's thrown
off the national team,

she's expelled from
the athletics residence,

she's denied her scholarship,

a bunch of her friends dump her,

fellow athletes abandon her,

she loses her medals,
her records are revoked.

MW: So it turns out --

remember when I told you

you can be a bunch of different
combinations of X and Y --

you can also be XY and be female.

You can be XX and male.

In María's case, she was something called
androgen insensitive.

Which means that she did have
some sort of internal testes --

they were making testosterone --

but her body couldn't use it.

And so if you thought of testosterone
as, like, a superpower,

she was not benefiting from it.

And so eventually,

sports authorities, like, let her back in,

but her career was done.

And in this instance you see how,

if you assign sex
to a specific place in the body,

or at least, like,
this is what I saw, right?

If you assign sex
to a specific place in the body,

it somehow makes us think
that we can go into a body,

look at a specific place

and tell someone we know
something more about them

than they know about themselves.

And that feels terrifying to me.

And we don't genetically test
female athletes anymore,

but you can see very similar
conversations happening

when we talk about testosterone in sports,

you can also see it in suggestions
that we take transgender individuals

and we genetically analyze them
and we tell them who they are.

That is real,

that is a conversation
that has happened recently.

The last place that I'll share with you

where these chromosomes
got complicated for me

is this one thing that Melissa told me.

(Audio) Wilson: You can't
survive without an X chromosome.

No matter your gonads,
no matter your identity,

every single human being
has to have an X chromosome,

because without one,
the rest of your body doesn't develop.

MW: Why do we call this
the female chromosome?

OK, this is something
I had never though about,

but literally, every single person
in this audience has an X chromosome,

I'm not lying.

Every single person on the planet
has an X chromosome,

but no one is going around like,
"This is the every-person chromosome."

You know?

Like, somehow it's over here,
the Y is over there,

and they must be really different,

and I'm just like,
it would be so much better

if it was the every-person chromosome.

And not just because I'm like,
love you all and I want you all in,

but because of what we're overlooking
by the fact that we consider it female.

Because I'm going to tell you
one of the craziest things I found out.

Which is, when you think
about the X chromosome,

of the almost 1,100 genes
on the X chromosome,

how many do you think have to do
with sex and reproduction?

Like, get a number in your head.

Four percent.

That means 96 percent
of the rest of that chromosome

is doing something that has nothing
to do with your gonads.

And I guess as all of these,

sort of, some of them social stories,

some of them scientific stories,
some of these facts,

started to add up, I just thought, like,

why are we calling these
the sex chromosomes?

Or if we are, like,
maybe we all like that name,

should we just allow ourselves
to think about them

a little more broadly?

Because if we do,

like, what insights would we gain,
as people, as scientists?

And we're at this point
where we're thinking about, like,

how do we want to teach science,

what do we want to fund,

like, who do we want to be
as a society, you know?

And I just wondered if it wasn't a moment
to rethink the biology of X and Y,

and at the very least,

to remember, like,
the footnotes of history,

which is that the dude who came up
with the phrase "sex chromosome,"

actually was like, "Hey, everyone,
just remember, this is just,"

and I quote, "a form of shorthand."

We should not take it literally.

Thank you.

(Applause)