Through the Wormhole

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 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.