Original subtitles

Boy or girl?

It's the eternal question.

But that question may have more than two answers.

Science is finding the line

between male and female bodies is blurred,

identifying the hallmarks of a transgender brain

and studying people who seem to change sex spontaneously.

Are some people neither male nor female?

Are there more than two sexes?

Space, time, life itself.

The secrets of the cosmos lie through the wormhole.

Captions by vitac... www.Vitac.Com

captions paid for by Discovery communications

Everyone who ever lived was created

from the genes of one man and one woman.

Those genes blended together to make a unique child...

With dad's dark hair and mom's curls,

or with mom's lips that curl into dad's smile.

One thing, however, isn't a blend...

The child's sex.

It's either male or female.

But is there something in between?

Many transgender people, their friends and families

say there is.

But what does science say?

Today, that question is playing out

in a very public arena.

For more then 100 years,

athletes have pushed themselves to the limit

to be the strongest, the fastest.

And for almost as long,

some have been doing whatever it takes to gain

that winning edge.

But endocrinologist Richard Holt is watching them.

He's a pioneer of tests designed to spot athletes

seeking an unfair advantage.

The difference between somebody winning

and somebody not winning is absolutely tiny.

We're talking about maybe less than 1%.

There are a number of athletes who might be

just that little bit away, and they think,

"well, maybe if I just take a little bit of extra

then I'll be able to reach the pinnacle of the career."

Richard's human growth hormone test debuted

at the 2012 London Olympics,

but lately he's entered a more controversial arena...

Verifying athletes' sexes.

Indian sprinter Dutee Chand grew up as a woman

and runs against them.

But on the eve of the 2014 Commonwealth games,

she ran into a problem.

She was found to have high levels

of testosterone in her blood,

and fell foul of the regulations.

She was banned from competition.

Men and women both make testosterone naturally

but in very different quantities.

According to international athletic rules,

Chand fell outside the female reference range.

She did not fit the definition of a woman.

Imagine we had two athletes, a man and a woman,

and we looked at the two together.

We'd see that, on average,

the man would be taller than the woman,

he'd have broader shoulders than the woman,

he'd have bigger hands than the woman.

Men, on average,

have much more lean body mass than women.

If you've got more lean body mass,

you've got a stronger engine.

To avoid men sneaking into women's events,

sporting federations began

in the 1960s to certify women as women.

They did this the old-fashioned way...

By visual inspection.

But this led to controversy.

Athletes thought the practice was indecent and disrespectful.

Since the 2000s, some women have,

instead, been subjected to testosterone tests.

But a recent large study

of more than 800 elite athletes found

that testosterone tests can't always tell men from women.

What they found was that there are about 15% of men

that had testosterone levels

that were below the typical normal reference range

and there are about 30% of women whose testosterone

were above the upper limits of the female range.

In other words, there's no clear dividing line

between male and female testosterone levels.

In fact, there's no evidence that naturally high testosterone

even gives you a performance advantage.

If testosterone was really key to athletic performance,

what we would expect is that, among men,

men with the highest level testosterone,

those men were winning the races,

but I can tell you,

some of them had very, very low testosterone levels,

and despite having very low testosterone levels,

they were still capable of competing

at the very, very highest level.

Dutee Chand fought the ruling against her,

claiming it was discriminatory to ban her

for a naturally occurring condition.

In 2015, she won back the right to compete.

Testosterone screening for female athletes

has been suspended for the moment,

but there's no agreement on what should replace it.

I think the best way of actually determining

whether a woman should be able to compete

as a woman is the way that she self-identifies.

If she's always seen herself as a woman,

regardless of what her testosterone levels are,

I think she should be allowed to compete as a woman.

Sporting federations are still wrestling

with how to draw the line between male and female bodies.

But Israeli neuroscientist Daphna Joel has been looking

for telltale differences in another place...

our brains.

There are many studies finding differences

between men and women, in brain structure,

brain connectivity, brain function,

and also in behaviors, attitudes, et cetera.

But the question is whether these differences

add up to create two types of people.

Do the differences between the ways men

and women behave trace back

to physical differences in their brains?

Science has asked this question for generations.

In the 18th century, anatomists noticed that men,

on average, had larger skulls.

In the 19th century,

they discovered that the brains of men

tended to weigh more than those of women.

These differences quickly become politicized.

They started using this to explain female inferiority

when they discovered that the brain

of males were, on average,

larger than the brains of females.

Then again, this was used to explain

why women are not as intelligent.

There's a long history of science

being used to justify

and maintain the social order.

Today, we think we're too sophisticated

to make that mistake.

Studies show that more men than women like soccer.

We now know, that doesn't make soccer

an exclusively male sport.

But when we talk about the brain,

we still fall back on male and female stereotypes.

For example, scientists have found that,

on average, a brain structure

called the amygdala is larger in men.

Because the amygdala is linked to aggression,

you often hear people say aggression is a male trait.

The idea that there is a male brain and female brain

is so popular that people that write books

about this get to be millionaires.

These ideas depend on one big assumption...

That you can look at any brain

and tell whether it belongs to a man or a woman.

Daphna set out to test whether this is really true.

She analyzed MRI scans from more than 1,400 men and women.

She wasn't looking at averages,

she was looking at each individual brain.

Imagine your brain is an ice-cream sundae.

You get something blue for each brain structure

that follows the male pattern.

You get something pink

for each structure that looks female.

Many different brain structures go into the sundae.

We assume that all the differences add up,

one to the other, to create one type of person...

Men with a male brain and woman with a female brain.

Daphna's study put this idea to the test.

If you're female, will every part of your brain

look female in the MRI?

If you're male, will every part of your brain look male?

Looking at brains one by one,

Daphna saw nothing like that.

These sundaes should all look the same

because they are all of women,

but what we actually see when we look closely,

is that most people had a brain

which was a mosaic, mosaic of features.

The majority of brains has a mixture of both male

and female characteristics.

Brains do not have sex,

and we should stop using

the male-brain/ female-brain idea

to explain why men and women are fundamentally different,

because they are not.

In body and mind, we are all mosaics...

Pixelated images of both man and woman.

There's no denying that most of us grow up

knowing which sex we are,

but on a deep genetic level,

we could be wrong.

Where does our sex come from?

Well, like any biological trait,

the answer lies in our DNA.

There are two sex chromosomes...

One's called the x,

and its little sidekick is the y.

Usually, women have two x's,

and men have one y and one x.

But a small percentage of babies are born with chromosomes

in neither of these arrangements.

The more we learn about the biology of sex,

the less it seems like there are only two sexes.

Geneticist Eric Vilain works

with an unusual group of patients.

They do not fit our normal definitions of male and female.

One term for them is "intersex."

I see patients with intersex conditions.

Their biological sex does not match

their appearance, their chest, their genitals.

And sometimes they're in between.

Their genitalia are ambiguous.

About one in 100 people

have some degree of intersex condition.

That's roughly the odds

of having green eyes or red hair.

While those qualities are visible to the naked eye,

some intersex people aren't even aware of their condition.

In his research, Eric found one particularly striking case.

So, I had a patient, young girl, 17 years of age.

Let's call her Eileen.

And she came to my office

because she didn't have any periods.

Unlike all her friends, month after month,

she was waiting... Nothing.

Eileen looked like a completely typical girl...

She was tall, she was good-looking,

she was well put-together.

Even though she looked completely female,

there's one thing that was not working properly...

She could not produce eggs,

and she could not produce female hormones.

We sent some tests for Eileen,

and the first test we sent for her were chromosomes,

and that's when we discovered

that she had an x-y pair of chromosome,

and not an x-x.

Eileen was actually male...

At least, according to her genes.

The human genome is an incredibly complex molecule.

It's the source of the many millions of instructions

which our bodies follow as they grow.

The determination of which sex we are is just one of them.

In each cell of the human body,

there are 46 chromosomes...

Like this one...

Containing millions of base pairs,

but only one has something to do with determining sex.

Our 46 chromosomes come in 23 pairs.

Half of each pair comes from our mother,

the other from our father.

Within the chromosomes,

our genes determine everything from eye color

to the shape of our earlobes.

Hidden among these pillars of our existence

is one pair of sex chromosomes.

Their combination determines

whether we become male or female.

Women are x-x, men... x-y.

But if Eileen was male, why didn't she look male?

Eric went looking for the root of the problem.

We sent for another series of tests

looking for mutations in genes

important for sexual development.

One of these tests looked

for mutations in a critical gene on the y chromosome

called SRY.

On the y chromosome,

there is this small gene called SRY

that's only 887 base pairs in the determined sex.

It was once believed that many genes

on the y chromosome worked together

in the womb to make you male.

But we now know that the tiny SRY gene

does that job all by itself.

If SRY doesn't work correctly,

the child can grow up looking female.

We identified one base pair

that was different in Eileen.

This one mutation was responsible

for her being not a boy.

Out of three billion base pairs

in the human genome,

a single one had switched places with the one beside it.

It's called a point mutation...

The smallest possible alteration that can be made to a gene.

Since mutations can be inherited,

Eric invited Eileen's relatives

to come for testing.

He found two more females who were genetically x-y.

Like Eileen, they had never had periods

and could not bear children.

Because of one tiny mutation,

they'd lived as women for their entire lives.

When it comes to SRY, the main sex-determining gene,

there is no room for error.

One base-pair mutation

and the sexual development switches

from male to female.

For this handful of patients,

along with millions of intersex people

around the world,

learning the truth about their genes

can mark the beginning of a difficult process.

They're really ashamed of their situation,

and that's something that I can't stress enough.

Despite the fact that these conditions are rare,

they're not unique.

If they're not alone,

then this sense of shame disappears,

and then they can embrace their conditions

rather than be ashamed of it.

Most of us can't imagine the anguish

that the intersexed 1% must go through,

but some people have even more challenging transitions...

They hit puberty and their sex seems to suddenly switch.

We all know that time changes us.

First, we grow taller, then a little shorter.

We lose our baby fat,

and then we get a little of it back.

But for most of us, one thing doesn't change... our sex.

As we age, we learn to wear our masculinity

and femininity like an old suit.

But that's not true for everyone.

Pediatric endocrinologist Chris Houk lives

on 150 acres in south Carolina.

In this grand laboratory of nature,

he encourages his kids to study the birds and the bees.

We live here with chickens

and a horse and bees

and soon-to-be goats.

It allows kids to connect with nature.

The eggs hatch, and then they grow up

and become mature male or female,

and then they make more babies.

And the circle of life continues.

Chris' research focuses on the biological process

of growing up... How girls become women

and boys become men.

A few decades ago, some intriguing evidence emerged

that not everyone follows those facts.

Back in the early 70s,

there was a rumor that circulated,

that there was a village in the Dominican Republic

where girls turned into boys at the age of puberty.

The villagers seemed to know about this.

They had multiple generations,

seven or eight generations,

that they could document at the time,

to the point that they had created a terminology for it

called "guevedoce," which means "penis at 12."

Before their daughters hit puberty,

the villagers trusted their eyes

and raised them as girls.

But when they hit puberty,

sometimes things went a little haywire.

Similar to humans, chickens go through puberty...

Testosterone's what initiates chicken puberty

and establishes sexual maturity,

the ability to reproduce.

To use this analogy, in guevedoce,

a chick that appears to be becoming a hen

takes on some of the secondary sexual characteristics

that one would only see in a rooster.

When researchers tested the guevedoces,

they found high levels of testosterone,

and their sex chromosomes were x-y.

Biologically, they were male.

Puberty had somehow revealed their underlying genetic sex.

But how?

Let's use this egg, for a moment,

to talk about human development.

We'll pretend that this egg is a womb.

Within it is contained the fetus

and all the materials needed to make a male or a female.

If we wanted to make a female, this would be the end of it.

We're done. We can scramble this up,

we can sunny-side-up, we can over-medium.

That is a girl egg.

Making a female is a simple recipe...

Just leave nature's goodness alone.

But male development calls for more ingredients.

At a very early time in human development,

we would need to add testosterone,

and that will have a tremendous effect.

But if this is all you do,

you're internal anatomy will be male,

but no on will know it.

In the guevedoces, this was the stage

where male development went off course.

They were missing a crucial extra ingredient.

You need another, more potent activator of maleness,

and that would be a hormone called DHT.

This hormone is at least 100 times as potent

as regular testosterone,

and it's critical for what we call male development.

In the womb,

DHT is made from regular testosterone.

It takes an enzyme called 5-Alpha reductase

to do this job.

In a normal male embryo,

DHT creates structures we associate with maleness.

At the end of the process, a baby boy is born.

In guevedoces, a genetic mutation

prevented them from making DHT.

They looked female until puberty,

when a surge of testosterone

finally transformed their bodies into male ones.

This strange discovery led researchers

to a deep psychological question...

How will a male see himself

if he's raised as a girl?

We have these two terms, "sex" and "gender."

They're often used interchangeably.

But to us in medicine, they are two distinct things.

Sex generally refers to the physical appearance

of an individual.

Gender is something totally different.

It's something sort of ethereal.

It's this internal sense of "I'm a male"

or "I'm a female"

or "I'm neither, something in between."

Well into the 20th century,

gender was seen as something parents

could assign to children.

Raise a girl in a female role

and she will see herself as female.

But the children in this Dominican

village shattered this idea.

Of the guevedoces raised as female,

95% transitioned to live as male.

This sort of challenged that prevailing view

that we could assign a gender.

We could assign sex...

You know, how you would raise the child...

But you could not really assign gender,

that there's something internal,

something innate about gender.

Our mental sense of whether we are male or female

is not just an idea we get from the influence of others.

Gender is rooted, biologically, deep inside us.

So, what happens in our minds

when our gender and our sex don't match?

Biology says that sex

is not as simple as male and female.

Approximately 1 in 300 people

identify themselves as transgender.

Transgender people feel their biological sex

doesn't match who they truly are up here,

which raises a fascinating scientific question...

Why do body and mind disagree?

Transgender people are becoming

much more visible in recent years

thanks to evolving social norms.

Many go to great lengths to alter their bodies,

and ask their families to accept a different version of them.

But where does the urge

to change one's body come from?

Neuroscientist Ivanka Savi? is trying to understand

the roots of transgender feelings in the brain.

She studies how we perceive our bodies

and feel at home in them.

This is a very complex process for the brain

because it involves several different areas

that have to do with cognition, self.

"Who am I?" Is a very high-level cognitive process.

Ivanka believes this cognitive process

might be different in transgender people.

Transgender people, they look at themselves in the mirror

every morning and feel uncomfortable

because they, of course, recognize the image,

but they don't feel this is the image that represents them.

In a way, they see somebody else.

As a neural scientist,

Ivanka knows that connecting

with your own body is a complex mental ballet.

Our visual world overflows with information...

Colors, forms, movements...

But our brains impose a kind of order,

identifying those things which are most important to us.

It starts with the visual cortex,

which takes in everything we see.

That information flows

to more specialized brain regions...

One identifies bodies, another identifies faces.

And yet another region,

the temporo-parietal junction,

identifies whether those faces and bodies belong to us.

But it takes one more region

to pull all these I.D.S together...

The brain's identity center.

The prefrontal cortex must conclude

"this image feels like me."

This is the mental network

that allows us to recognize our own bodies

and feel at home in them.

And it operates completely unconsciously.

This all-body perception is so automatic,

so we don't even consciously reflect upon it.

I look at my hand. It's my hand.

I look at my face. It's my face.

To recognize and know ourselves

is something we take for granted everyday.

But in some people, it may work a little differently.

Many transgender people do not identify

with the bodies they are born with.

And in many cases,

it doesn't seem to be a matter of choice.

In many, many people who are transgender,

this occurs very early during the childhood,

and it's very strong.

And that's why it's very important

to take this seriously.

Ivanka thought transgender people might see

in their mind's eye

a body that's different from their physical image.

In an experiment, she showed transgender subjects

photos of themselves.

In some of these photos,

she had subtlety altered their physiques.

Many, many body images are presented

during a very short time,

and for each image, they have to determine

"how much is it me?"

Ivanka gave her subjects very little time to reflect,

but they consistently identified with the photos

that altered their outward sex characteristics,

and they made their choices so quickly,

Ivanka suspected the unconscious process

of own-body perception

was working differently for them.

So she used MRI imaging to look

at the connections in their brains.

Think about what it takes to make a self-portrait.

It's a dialogue between what your eyes tell you

and what you think should be there.

That's not unlike the unconscious dialogue

that goes on between regions of your brain.

People with transgender feelings

don't have any visual impairment.

They don't see the world any differently,

but when Ivanka looked at their brains,

she noticed two regions

that weren't communicating in the usual way.

We could see that there was a weaker connection

between the area of the brain

that represents self and the area of the brain

that represents their own body.

It could, somehow, explain these perceptions

of seeing own body, recognize own body,

but at the same time,

feeling that this is not part of the self.

The struggle to feel like yourself

when you look at your own body

is at the core of trans identity.

Ivanka's research has uncovered the roots

of this struggle in the brain.

To live happier lives,

transgender people often correct

their physical appearance

through hormone therapy or surgery.

It's a tall order to switch sex anatomically,

but new research is showing it soon could get easier

because, on a hidden level,

our bodies are constantly trying to switch.

Hermaphrodite... it's an animal that has both male

and female sex organs,

like these snails.

When they mate,

either one can take on the biological role

of the male or the female.

New research is revealing

that we all might be hermaphrodites, in a sense.

Down at the level of our cells,

there's a war between male and female

raging inside all of us.

Geneticist David Zarkower looks

at how cells in our reproductive organs

choose to be one sex or the other,

and whether they can change their minds.

Our interest is in how sexual differentiation happens,

so how cells come to be either male or female.

And so what we do is we find genes

that might play an important role in that process,

and we break them, and we see what happens.

SRY is the gene on the y chromosome that decides

whether you'll become male or female,

and if SRY has been active, male development occurs.

But David and his team decided to look beyond SRY

to another gene called dmrt1.

Dmrt1 helps the testes develop,

but David wondered why it stayed active in adulthood.

If the sex of male cells

is supposed to be fixed before birth,

why was this gene still working?

David works on mice as stand-ins for humans,

as their biology is very similar.

And he did what geneticists do,

he let mice grow to adulthood,

then broke the dmrt1 gene to see what would happen.

In this microscopy room, we look at mouse tissue samples,

and we use specific stains to ask whether male-

or female-specific proteins are active.

The color scheme is simple...

Green for male cells, pink for female.

When David eliminated the dmrt1 gene

then looked at the gonads of his mice,

he saw something surprising.

You can see that there's still some male cells...

Which is these... But there are many,

many more intensely pink staining cells.

Deleting just one gene

caused the cells to change sex.

Ovaries were developing in the bodies of males.

And he found this process works in both directions.

At first we didn't really believe it,

because this was supposed to be a testis,

but there was all this expression

of female-specific genes,

and so we repeated the experiment,

but it was clearly true.

This testis was, essentially, directly transforming

into something that was very much like an ovary.

It's a discovery that shakes the very foundations of sex.

The cells which makes us male or female

don't have to stay that way.

Could a woman produce sperm

to make a baby with another woman?

And could a man produce eggs?

We all start with genes

that could pull us toward male or female.

For the first six weeks in the womb,

a tenuous balance exists,

neither side is winning.

The embryo seems neither male nor female.

But after six weeks,

if the embryo has a y chromosome,

the SRY gene kicks into action.

The gene called SRY is the difference-maker.

With SRY as anchor,

the pro-male genes swing into action...

Overwhelming their competition,

pulling the fetus to develop as male.

With sex determination complete, SRY hands over the reins.

Here you go.

Dmrt1 sees to it that a male child remains male.

But if dmrt1 should ever leave his post,

a gene called foxl2

will seize the opportunity

and start working to make the body...

Let's go, ladies.

Female.

Like SRY, foxl2 spurs other genes into action...

One, two, three, pull.

Which overpower the male genes

and start making female cells.

We have this lifelong battle between dmrt1 and foxl2

over whether the gonad will remain male

or will, instead, become female.

This is really different from the way

we thought about things previously.

Dave's genetic tinkering found a battle

of the sexes going on inside us

that never truly ends.

In theory, an adult human body can be coaxed

to make opposite-sex hormones.

A new era of gender therapy is on the horizon.

But consider the dark side.

Could this technology be misused?

Could people with anomalies

in their sex chromosomes be forced

to accept genetic alteration,

to make them fit into traditional male

and female molds?

Children who are intersex may be coerced

into being assigned one sex or the other.

This has been a historical problem.

This technology could potentially make that worse.

So it'll have to be used responsibly.

On the other hand,

this new knowledge offers immense hope

for transgender and intersex people

who want to transition from one sex to another.

The ultimate goal of gender transformation

would be to allow somebody to become

a reproductive individual of the opposite sex.

It's a ways off, but now there's some reason to think

that it might be possible for two men to have a baby,

with one making sperm and the other one making eggs.

Some day, our society

may contain many new kinds of happy families.

Our children may be born

with more ways of changing their bodies' sex,

if it doesn't seem to fit.

Sex could soon be more fluid

than we ever thought possible.

But the animal kingdom is already showing

that our understanding of sex

could evolve even further.

These scientists are exploring a world

where making babies

needs more than one male and one female.

Sex and gender were long seen as male or female.

However you thought of yourself,

you could only use one bathroom door,

but we now know the gender you feel you are

can disagree with your anatomy.

As a society, we're beginning to accept that sex

and gender can be male,

female, both, or somewhere in between.

But in the future,

we may choose to make sex even more complex than that,

creating more than one type of male and female

and even more possibilities in between.

Good morning.

Hey. Would you like to get a colony out?

Sure.

Biologist Joel Parker

and evolutionary ecologist Sara Helms Cahan

were once classmates.

Now a tiny species has brought them back together...

a species which could reveal where we ourselves are headed.

- Okay. - Are you ready to touch 'em?

- Yeah, well, don't get stung. Ah, remember... yes.

You're braver than I am.

I remember you were always squeamish about this.

Throughout the desert southwest,

there are many different species of seed-harvester ants.

One of the most common is a pogonomyrmex.

It means "bearded ant."

"Pogo" meaning "beard."

It was here, in the pogo's desert habitat,

that Joel came across a paradox.

He found two different species of pogos,

a red type and a black type.

Their colonies looked normal,

with reproductive queens and males

and hoards of sterile workers.

But the two species shared a mysterious quirk.

If you mated a queen with a male from her colony,

you wouldn't get all the offspring the colony needed,

you would only get female reproductives.

You wouldn't get workers.

So where did those workers all come from?

Did they fall from outer space?

Or did their appearance on the scene

have a more earthy explanation?

It was a mystery Joel and Sara were determined to solve.

A normal ant colony gets started

when a newly mated queen goes off after she mates

and digs a little hole.

She'll crawl into the hole then lay eggs

that will become the first generation of workers.

Workers are the backbone of an ant colony.

These sisters forage for food

and maintain the nest,

but they can't reproduce.

Reproductive females come later,

and then the colony is established.

They're cared for and fussed over

like the future queens they are destined to be.

You could think of them as princesses.

And finally come the males, the colony's lowliest members.

Males have a very sorry lot in the insect world.

They're very small.

They basically only have two functions in life...

To fly and to mate.

But mating for these two species

is where the system appears to break down.

Joel discovered that each species

wasn't being faithful to its own kind.

They were flying off to have flings

with the species next door.

In a pogo mating swarm,

different couplings produce different types of offspring.

When a female mates with her own species,

she makes another reproductive female,

a future queen.

But to make one of the much-needed workers,

she must mate with a male from the other species.

Usually when you think of a sexual system,

you think of males and females.

With our ants, we have a situation

where there's two different types of males

and two different types of females

that are required to keep this population going.

So you can think of it as like one species,

then, that has four different sexes.

In a species with four sexes,

there is more than simply male and female.

Joel and Sara believe this system

helps ants in a colony

become more specialized in their roles,

and they think it offers a preview

of what may happen with humans,

in the future.

The thing that blows me away about ants is

when you actually start looking at 'em

from a biological point of view,

they are more highly advanced evolutionarily than humans.

Ants started farming 100 million years before we did.

They don't have to be taught how to farm.

It's all in their genes.

We have ranching, we keep cattle.

Ants tend their own kind of cattle,

which are tiny little insects called aphids.

We have soldiers that we send out to fight our wars.

Ants also have soldiers

that they send out to fight their wars.

Where ants have gone, humanity has followed.

Joel and Sara think it is happening again.

Today, every human baby is made from the genes

of just two people.

But we are now experimenting

with modifying the human genome,

inserting genes from other sources.

A baby made this way would have more than just two parents.

I can't even think what our sexual system will be like

when we start using some of these new technologies

to put foreign DNA into our germ line.

But when that happens, how many parents are we gonna have?

I think we are going to move beyond

the simple binary of mother and father.

I could see it becoming more difficult

to be able to easily define

who is the parent of a given child.

The poet Audre Lorde once wrote,

"it is not our differences that divide us,"

it is our inability to recognize, accept,

"and celebrate those differences."

One day, we may find ourselves

embracing a rainbow of different sex identities.

Medical techniques could expand the definitions of sex

and allow us to accelerate the evolution of our species.

Perhaps the question isn't

whether there are more than two sexes,

but whether there are more possibilities

than we ever imagined.

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