and chemists unlocked secrets of the atom

that changed the world forever.

But life remained a profound mystery.

Among life's deepest secrets was inheritance.

Everyone knew that traits like the shape of a peapod

or the color of eyes and hair were passed

on from generation to generation.

But no one knew how

such information was stored or transmitted.

Scientists were convinced that there had

to be a biological molecule at the heart of the process.

And that molecule had to have some pretty special qualities.

[CARROLL:] The three dimensional arrangement of atoms

in those molecules had to explain the stability of life,

so that traits were passed faithfully from generation

to generation, and also the mutability of life.

You have to have change in order for evolution to happen.

[JUDSON:] The challenge

of solving this mysterious arrangement of atoms,

this fundamental "secret of life," was taken up in 1951

by two unknown scientists.

Less than 18 months later, they would make one

of the great discoveries of the twentieth century.

They met and joined forces at the Cavendish laboratory

in Cambridge, England.

One was a 23-year-old American named James Watson.

[OLBY:] He had a crew cut when he first came to Cambridge,

and that was very rare in Cambridge in those days.

He liked to wear what I call gym shoes

and leave the laces untied and things like that.

He was quite an enfant terrible I would say.

But behind that, of course, was his extreme, intense love

of science right from his early years, and his determination.

[JUDSON:] The other was an Englishman named Francis Crick.

Trained as a physicist,

his academic career had been interrupted by the outbreak

of the Second World War.

It wasn't until 1949 that he got back into academic science.

He was anxious to make up for lost time

and now interested in biology.

Crick and Watson connected instantly when they met in 1951.

They both loved to talk science.

[WATSON:] Francis and I both liked ideas.

And as long as I could talk to Francis, I, you know,

felt every day was worthwhile.

[JUDSON:] Crick was always ready to share his thoughts,

though he rarely did so quietly.

[WATSON:] Any room he was in he was going

to make more noise than anyone else.

[LUGER:] They would constantly throw crazy ideas at each other,

dismiss them, have another idea, follow that a little further,

dismiss that, but then something comes out of left field,

so it's kind of this give-and-take.

[CRICK:] We did have different backgrounds,

but we had the same interests.

We... we both thought that finding the structure

of the gene was the key problem.

[JUDSON:] The idea of the gene dates back

to Gregor Mendel's experiments with pea plants in the 1860s.

By the 1920s, genes had been convincingly located inside the

nucleus of cells, and associated

with structures called chromosomes.

It was also known that chromosomes are made

of proteins, and a nucleic acid, deoxyribonucleic acid, or DNA.

That meant that genes had to be made of either DNA or protein.

But which was it?

Protein seemed the better bet.

There are lots of different kinds of them and they do lots

of different stuff inside the cell.

In contrast, DNA didn't seem very interesting.

It's just repeated units of a sugar linked to a phosphate

and any of four bases.

The readiness to dismiss DNA was so entrenched

that it persisted even after Oswald Avery showed

that it can carry genetic information.

[CARROLL:] Avery had isolated a substance that conveyed a trait

from one bacterium to another.

And this "transforming principle," as he called it,

he showed that it was not destroyed

by a protein-digesting enzyme but was destroyed

by a DNA-digesting enzyme.

[JUDSON:] Watson and Crick were among the few

who found Avery's work persuasive.

They thought genes were made of DNA.

They also thought that solving the molecular structure

of the molecule would reveal how genetic information is stored

and passed on.

At the time, a powerful technique

for solving molecular structure was being perfected:

x-ray crystallography.

[LUGER:] At its best,

x-ray crystallography can determine the position

of every single atom in the molecule that you're analyzing

with respect to every other single atom.

[JUDSON:] Not that it's easy.

The picture you end up with is a "diffraction pattern,"

and to make sense of it--to work out where the atoms are--

involves interpreting lengthy calculations.

And in the 1950s, the equipment was primitive

and difficult to maintain.

The x-ray sources weren't very bright.

And on top of that, DNA is not an easy molecule to work with.

[LUGER:] Basically, you picture snot.

It's kind of hard to pick it up and do stuff

with it, and analyze it.

Polymers are not fun to work with from that point of view.

[JUDSON:] The Cavendish was famous

for x-ray crystallography.

But the director of the lab didn't want his staff

x-raying DNA.

He knew that a group at King's College

in London was already doing that and he didn't want

to be seen as competing.

[WATSON:] It just wasn't...

good manners.

[JUDSON:] The King's College scientist

who had initiated the work on DNA was Maurice Wilkins.

Like Crick, he was trained as a physicist

and had only recently become interested

in biological questions.

Though he was drawn to the problem of the gene,

Wilkins lacked Watson

and Crick's burning urgency to find a solution.

Complicating things for Wilkins was his relationship

with his colleague Rosalind Franklin.

She was a talented crystallographer,

but when she joined the team at Kings she believed

that she would be leading its DNA research.

[LUGER:] She had the notion that this was her project,

he had the notion it was his project, and if anything,

she should help him in his effort to solve the structure,

and so this is a recipe for disaster.

[JUDSON:] The times and their personalities worked

against an effective partnership.

[LUGER:] This was a time when it was very, very hard for women

in science to be taken seriously and so I would imagine

that Rosalind Franklin had to be perhaps quite assertive.

[JUDSON:] She certainly asserted her independence.

Wilkins, by all accounts a shy man, reluctantly agreed

that they would work separately.

London is only 75 miles from Cambridge.

That means that Watson and Crick could easily keep tabs

on the work being done at Kings.

But another potential competitor was thousands

of miles away, in California.

Linus Pauling was renowned

as the greatest physical chemist of his generation.

He was widely admired for his ability

to build accurate models of complex molecules.

Watson and Crick were convinced it was just a matter

of time before Pauling used this technique to solve DNA.

Biological molecules come in a variety of shapes.

Pauling, and Watson and Crick,

suspected DNA might be a helix of some kind.

But if so, how were the sugar, the phosphate

and the bases arranged?

Early in his collaboration with Watson, Crick had worked

out mathematically what the x-ray diffraction pattern

of a helical molecule should look like.

Shortly afterwards, Watson went to London

to hear Franklin report on some of her recent work.

When he got back, he told Crick what he remembered of her talk,

and they decided to build a model.

In a few days, they had one.

It was a helix, with three sugar-phosphate chains

on the inside, and the bases sticking out.

[LUGER:] At that time the only interesting thing

about the DNA molecule is the bases.

And so it made perfect sense, I mean,

only an idiot would put them inside

because then they're hidden.

[JUDSON:] They invited Wilkins and Franklin

to come and take a look.

Unfortunately, Watson had misremembered some

of her key measurements.

Franklin saw this immediately, and quickly

and derisively dismissed their effort.

She went to craft a mocking announcement

for the death of DNA as a helix.

It was an embarrassment that did not sit well

with the Cavendish leadership.

[WATSON:] We were forbidden in a sense to work on DNA.

[JUDSON:] The failure of the first model was painful,

but it can also be seen as just part of the scientific process.

[LUGER:] I would actually maintain that,

in order to arrive at the right solution, you have to put

out a couple of wrong ones.

And that's just the nature of discovery, and if you're afraid

of making a mistake, you're going to fail in this business.

[JUDSON:] Through 1952, Watson and Crick read and talked

over anything and everything that could prove relevant

for their ongoing-- but now underground--

quest to discover the structure of DNA.

[WATSON:] To me there was only one way I could be happy...

or two ways, you know: solve DNA or get a girlfriend...

[laughs] and I didn't get a girlfriend, so it was solve DNA.

[JUDSON:] The year ended with Watson and Crick thinking

about DNA, Franklin taking pictures of DNA,

Wilkins avoiding Franklin, and Pauling a distant

but worrisome presence.

Then, in January 1953, everything changed.

News came that Pauling was indeed preparing a paper

on the structure of DNA.

Watson secured a copy of the manuscript.

And found, to his great relief,

that Pauling was proposing a triple helix.

It was very similar to the one that he

and Crick had been shamed into abandoning the previous year.

Relieved, he headed to London to share the news

that the race for DNA wasn't over.

Only to find that Rosalind Franklin wasn't particularly

interested in what he had to say.

[OLBY:] Following his departure

from Rosalind Franklin's room he encountered Wilkins,

and Wilkins took him into his room and then took

out of a drawer a picture

which had been taken by Rosalind Franklin.

[JUDSON:] That picture would become one

of the most famous images in all biology: Franklin's Photo 51.

Jim Watson recognized the diffraction pattern

immediately-- it was a helix.

And based on this,

Watson thought it might have just two chains: a double helix.

About the same time, Francis Crick was shown a report

on Franklin's work that included an observation

on the symmetry of DNA.

This led Crick to a crucial insight

that Franklin had missed: the two backbones had to run

in opposite directions.

That led him to the conclusion

that the sugar-phosphate backbones had to be

on the outside with the bases inside.

So Watson started to build models again.

He experimented with pairing like-with-like:

adenine with adenine, thymine with thymine, and so on.

That would make each chain identical.

Watson thought that could explain how genetic information

is stored.

He thought he had the solution.

But then a Cambridge colleague told him

that the bases could not pair with themselves in that way.

And Crick pointed out that the model didn't take account

of something else that was known about DNA.

A few years earlier, another chemist interested in DNA,

Erwin Chargaff, had reported a puzzling fact