100 Greatest Discoveries

An empire billions of years in the making.

A carnival of natural wonders.

Societies of cells.

Simple and complex.

All connected by an astonishing web of molecular processes and global ecological systems.

A web of life.

These are the greatest discoveries in the history of biology.

In the early sixteen hundreds, basic microscopes were used throughout Europe.

Gentleman scientists were held spell bound by their ability to enlarge the universe of the very small.

Then in 1665, an English scientist named Robert Hook...

observed the tiny boxes in a sliver of cork and called them cells.

Because they reminded him of the small room lived in by monks.

Hook’s observation set the stage for our first great discovery.

Antoine Leeuwenhoek was a Dutch merchant fascinated with science.

Upon learning about Hook’s microscope, he decided to build one for himself.

Doctor Gaul.

To find out what happened next, I paid a visit to Joseph Gaul.

A cell biologist at the Carnegie Institution in Baltimore Maryland

Antoine Leeuwenhoek, What did he discover.

Leeuwenhoek discovered quite a few things. But what he's most famous for are discovering protozoa.

That’s small single cell animals living in pond water.

How did he do that.

He did it using a microscope of his own construction.

Then would you like to see Oh yes.

You have a Leeuwenhoek microscope.

Not original. I have a replica of a Leeuwenhoek microscope.

It consists of two brass plates with a small piece of glass which is the lens.

And when you use this, it’s to put the specimen on the pin here.

And then you hold your eye up very close to the lens on this side.

And when you do that you can see the point of the pin.

And you can put the specimen, whether it's an insect or whatever on that pin.

- Would you like to take a look at it? - Oh yeah.

- It’s kind of heavy, cause it’s brass. - It’s brass.

In 1675, then Leeuwenhoek was using his microscope to examine a bead of water.

When he observed something extraordinary.

A world full of creatures that no human had ever seen.

Microorganisms.

So with this, with all due respect, primitive gismo, yes.

He discovered single cell animals. We take for granted.

What he's most famous for are discovering protozoa...

bacteria...

and sperm.

This thing is brilliant.

It’s got a mechanical stage, it’s got a focusing device.

It's got all of the things that you need to look at a specimen.

And it works.

Did they know what they were seeing ? Do you what I mean like did they understand.

Well I doubt that they really understood what they were seeing in the modern sense.

But they were impressed at all these little things that were alive in water.

And people had no idea that water was teeming with organisms.

I guess I just had no idea the thing was this small and delicate...

and frankly, so elegant.

Because it’s the palm of your hand.

And what you see on the tip of that pin changes the world. It does, indeed.

It was an enlargement of our understanding of nature, nature of the natural world.

That, that the world out there was not just dead things, but it was teeming with life.

Our next great discovery occurred in 1831.

English naturalist Robert brown was studying the different types of plant species he collected during a voyage to Australia.

Brown has an exquisite eye for detail.

The cells of the plants were of particular interest to him.

On examining them under the microscope, he saw something intriguing.

In each cell, a similar structure, circular, opaque.

He called it the nucleus.

Upon learning of brown’s observations

German physiologist Theodor Schwann...

began looking for a similar structure in the cells of tadpoles.

And he found it.

Each and every cell of the tadpole had a nucleus as well.

It was a revolutionary breakthrough.

Here was evidence that all life was connected.

In this book, Schwann describes various cell types from all sorts of organisms.

And identifies them by the fact that they have a nucleus in them.

How would you say the discovery of the nucleus was a great discovery.

The realization that there was a unit of structure to all organisms.

This was a unit of structure not only in plants but in animals.

So it united both the plant and animals kingdom into something that had similarities to each other.

More than a century after the discovery of the cell nucleus.

It was believed that there were two fundamental types of life on earth.

Bacteria and everything else.

Bacteria were classified as prokaryote.

These were simple, single cell organisms with their DNA contained not within a nucleus but by the cell wall.

All other life forms were classified as eukaryote.

Their cells carried their DNA enclosed within the nucleus.

But this simple classification system was in for a shock.

In 1977, biologist Carl Woese was studying the genetic make-up of a methane-producing microbe.

When he realized it was different from any known bacteria.

Its cell wall was unique. It produced unusual enzymes.

And its genetic sequence was unlike anything he’d ever seen.

It became apparent within the scope an hour.

That there was something a third thing out there.

This was the moment of discovery

Carl Woese had found a third form of life.

A group of single celled organism that he called archaea.

We used to think that there were two primary kingdoms on this planet.

Now we know there are three.

That was the shift, the shift.

Because all of the microbiology have been structured on the idea that all bacteria are fundamentally the same not in their details...

but in their essence, their ancestry and their basic cell organization...

here is something that every microbiologist and biologist firmly believed in and it wasn’t true...

so, it does make you smile. Yeah, look what I found...

what he found was a life form able to live anywhere on the planet...

including the most extreme environments.

Some archaea even call this home.

Hydrothermal vents on the ocean floor.

Temperatures here fluctuate wildly within just a few inches.

Going from freezing to a scorching 760 degrees Fahrenheit.

Archaea have also been found living miles inside the earth.

Thriving in lakes of acid where even iron minerals dissolve.

Today, some biologists believe...

that archaea are the common ancestor from which eukeryotes evolved.

And that includes you and me.

For Carl Woese, the discovery of archaea remains a sweet memory.

It was picked up when published by the New York time first.

And other newspapers and TV came in.

And I can remember walking outside my house one night...

When all this was happening and, tonight, the world belongs to you.

Our next great discovery sought to answer the question at the heart of biology.

How cells form new life.

In the course of human events.

This is all pretty recent. Right Yes.

We found nuclei, the cells around nuclei.

Animals and plants have cells Yes.

And what happened next.

After a gap of some 30 years or so, people began to see cells dividing.

Cell division is the process that the cell or plant or animal goes through to duplicate itself.

While scientists had known about the process for decades

German zoologist Walter Fleming was the first to describe it and to publish his findings.

And his book was published in 1881.

This book is momentous and extremely important in the history of cell biology.

Because Fleming described cell division in a way...

which would be acceptable in a modern journal

Fleming observed the process of cell division in great detail.

With the help of a powerful new microscope and new dyed staining techniques.

With these innovations, he was able to identify structures that later were named chromosomes.

And then his great discovery.

During cell division, the chromosomes undergo dynamic change.

They divide into two identical parts. One for each daughter cell.

Fleming called this process mitosis.

So, that’s the whole process of mitosis as he described it in 1881.

- In a tadpole tail. - In a tadpole tail, yes.

And he knew to go to the tail because the tail is growing...

- and the back of tadpole there's a lot going on - Exactly.

He knew that if you're going to see cell division in detail, "in de tail"...

- Sorry for the pun. - I like the pun, kookie for the pun.

Then, that was one of the places to look.

The splitting of chromosomes during mitosis was a breakthrough discovery.

It opened the door for scientists to begin understanding.

How one cell can turn into a complex organism, made of many interacting cells.

Around the time that Walter Fleming was studying the cell division process.

Biologists already knew that fertilization resulted from the union of two sex cells...

sperm and egg...

what they didn’t know was why these were the only type of cells in the body capable of reproducing new life...

what made them different.

The first answer was provided in 1883 by Belgian zoologist Edward van Beneden

Van Beneden was studying a species of roundworm.

when he discovered that nearly all of its cells contained four chromosomes.

The only exceptions were the roundworm’s sex cells.

The male’s sperm and the female’s egg, these cells had only two chromosomes.

Then Beneden observed that once two of the sex cells came together.

A full set of four chromosomes appeared in the fertilized egg.

But just why the sex cells had only half number of the chromosomes compared to the all the other cells was still a mystery.

Then in 1887, German biologist August Weismann entered the picture.

He knew about the work of van Beneden who had shown that the sperm and egg bring an equal number of chromosomes.

But van beneden’s work had not really worked out the details of how the chromosomes were reduced in number.

He saw them go in half and he saw them recombine.

He saw the sperm and egg brought in half the number of chromosomes into the body cell...

But he didn’t really know how they got rid of the half that they got rid of.

So Weismann discussed how this might happen from a theoretical standpoint.

And he said, well, what you could have would be that...

either every one of the chromosomes would just split in half and half would go off one way and half would go another way.

Or, you could have more complicated, that the chromosomes could pair and then, instead of splitting, they just separate again.

After years of studying the behavior of chromosomes

Weismann determined that at some point, a developing organism signals its sex cells.

To divide their number of chromosomes in half

Weismann called this very special form of cell division meiosis.

I think they would look back and see this as the golden age of biology.

Because let’s say 200 years between 1800-2000.

We went from not knowing what distinguished the stone from a frog.

Ok.

And now we know the difference between a stone and the frog.

That’s pretty good.

So that, in a real sense, we’ve answered the old philosophical question, what is life.

Maybe not to everybody’s satisfaction but we are well on the way.

Our next great discovery answered another question about the biology of life.

In the late 19th century...

Biologists knew that during the formation of the embryo, the cells of most organisms became differentiated.

That is they received their assignments for specific jobs in the adult organisms.

Arms, legs. Eyes.

But when did this differentiation happen?

German biologist Hans Driesch was determined to find the answer.

In a lab experiment with sea urchins...

He observed that in the early stages of an embryo's development.

Its cells are not yet differentiated.

They can still develop into all cell types.

Today, scientists call cells that can develop into all or many cell types, stem cells..

- Hi bill. - Hi.

To find out more, I paid a visit to Helen Blau.

Who is directing stem cell research at Stanford University’s genetic pharmacology lab.

Everybody is talking about stem cells.

Cells start out, they're fertilized and then they start to divide.