but we don't normally think of cancer

ガンはなにも特別な疾病ではありません

as being a contagious disease.

しかし通常 ガンが感染するとは

The Tasmanian devil has shown us

考えられていません

that, not only can cancer be a contagious disease,

タスマニアデビルの事例によって

but it can also threaten

ガンは感染する可能性があるだけではなく

an entire species with extinction.

種の存続を脅かす可能性があることも

So first of all, what is a Tasmanian devil?

明らかとなりました

Many of you might be familiar with Taz, the cartoon character,

まず タスマニアデビルとは何でしょう？

the one that spins around and around and around.

クルクル回るアニメキャラのタズを

But not many people know

ご存知の方も多いでしょう

that there actually is a real animal called the Tasmanian devil,

しかし実際に世界最大の肉食有袋類の

and it's the world's largest carnivorous marsupial.

タスマニアデビルという動物が存在することを

A marsupial is a mammal with a pouch

知っている方は多くありません

like a kangaroo.

有袋類とはカンガルーのように

The Tasmanian devil got its name

腹部に袋をもつ哺乳類です

from the terrifying nocturnal scream that it makes.

タスマニアデビルという名前は

(Screaming)

夜に発する恐ろしい叫び声に由来しています

(Laughter)

(叫び声)

The Tasmanian devil is predominantly a scavenger,

(笑)

and it uses its powerful jaws

タスマニアデビルは清掃動物で

and its sharp teeth

強力なあごと

to chomp on the bones of rotting dead animals.

鋭い歯で

[The] Tasmanian devil is found only on the island of Tasmania,

動物の腐った死骸をかみ砕きます

which is that small island

タスマニアデビルはオーストラリア南部に

just to the south of the mainland of Australia.

位置するタスマニア島という

And despite their ferocious appearance,

小さな島だけに生息しています

Tasmanian devils are actually

凶暴な外見にもかかわらず

quite adorable little animals.

タスマニアデビルは実際は

In fact, growing up in Tasmania,

愛らしい小さな動物です

it always was incredibly exciting

実際タスマニアで育った私も

when we got a chance to see

野生のタスマニアデビルに

a Tasmanian devil in the wild.

出会った時は いつも

But the Tasmanian devil population

本当に興奮したものです

has been undergoing a really extremely fast decline.

しかしタスマニアデビルの数は

And in fact, there's concern

ものすごい勢いで減少しています

that the species could go extinct in the wild

実際に20〜30年以内に

within 20 to 30 years.

野生のタスマニアデビルが絶減するのではと

And the reason for that

懸念されています

is the emergence of a new disease,

この原因は

a contagious cancer.

ある感染性のガンの

The story begins in 1996

出現です

when a wildlife photographer took this photograph here

始まりは 1996年に

of a Tasmanian devil

野生動物の写真家が撮った

with a large tumor on its face.

顔に大きな腫瘍のある

At the time, this was thought to be a one-off.

タスマニアデビルの写真でした

Animals, just like humans,

当時は偶発的なものと考えられていました

sometimes get strange tumors.

動物にも人間同様に

However, we now believe

奇怪な腫瘍ができることがあります

that this is the first sighting of a new disease,

しかし私たちは

which is now an epidemic spreading through Tasmania.

これこそが現在タスマニアで蔓延している

The disease was first sighted

新型のガンの最初の事例であったと確信しています

in the northeast of Tasmania in 1996

この病気は1996年に

and has spread across Tasmania like a huge wave.

タスマニア北東部で初めて確認されて以来

Now there's only a small part of the population,

大きな波のようにタスマニア中に広がりました

which remains unaffected.

現在感染せずに残っているデビルは

This disease appears first as tumors,

ほんの一握りです

usually on the face or inside the mouth

タスマニアデビルがこのガンを発症すると

of affected Tasmanian devils.

通常 顔面もしくは口内に

These tumors inevitably grow into larger tumors,

腫瘍ができます

such as these ones here.

これらの腫瘍は この写真のように

And the next image I'm going to show

大きくなってしまいます

is quite gruesome.

次にお見せする写真は

But inevitably, these tumors progress

本当にひどいものです

towards being enormous, ulcerating tumors like this one here.

これらの腫瘍は否応なしに

This one in particular sticks in my mind,

このように大きな潰瘍性の腫瘍に進行するのです

because this is the first case of this disease

これは私が実際に

that I saw myself.

目にした初めての事例だったので

And I remember the horror of seeing this little female devil

特に印象に残っています

with this huge ulcerating, foul-smelling tumor

悪臭を放つ潰瘍性巨大腫瘍のために

inside her mouth

下あごが外れてしまった

that had actually cracked off her entire lower jaw.

このメスデビルを

She hadn't eaten for days.

目の当たりにした恐怖は今でも覚えています

Her guts were swimming with parasitic worms.

何日も物は食べていません

Her body was riddled with secondary tumors.

内臓は寄生虫でいっぱいでした

And yet, she was feeding three little baby Tasmanian devils

腫瘍は体中に転移しています

in her pouch.

それでも彼女は小さな３匹の赤ん坊に

Of course, they died along with the mother.

母乳を与えていました

They were too young to survive without their mother.

もちろん赤ん坊も死んでしまいました

In fact, in the area where she comes from,

幼すぎて母親なしでは生き残れなかったのです

more than 90 percent of the Tasmanian devil population

このメスが生息していた地域では

has already died of this disease.

90％以上のタスマニアデビルが

Scientists around the world

この病気で死んでしまっています

were intrigued by this cancer,

タスマニアデビルを襲う

this infectious cancer,

この感染性のガンに

that was spreading through the Tasmanian devil population.

世界中の科学者たちが

And our minds immediately turned to cervical cancer in women,

大変な興味を示しました

which is spread by a virus,

私達はすぐにウィルスで感染する

and to the AIDS epidemic,

子宮頚ガンや

which is associated with a number of different types of cancer.

色々なガンと関連のある

All the evidence suggested that this devil cancer

AIDSの流行のことを考えました

was spread by a virus.

状況から このガンがウィルスによって

However, we now know -- and I'll tell you right now --

感染しているように思われたからです

that we know that this cancer is not spread by a virus.

しかしウイルス感染症でないことが

In fact, the infectious agent of disease in this cancer

今ではわかっています

is something altogether more sinister,

実はこのガンの感染源は

and something that we hadn't really thought of before.

思いもしなかった

But in order for me to explain what that is,

恐ろしいものでした

I need to spend just a couple of minutes

この原因を説明するために

talking more about cancer itself.

まずガン自体について

Cancer is a disease

もう少しお話しなくてはいけません

that affects millions of people around the world every year.

ガンは世界規模で毎年

One in three people in this room

何百万人もが発症する疾病です

will develop cancer at some stage in their lives.

この部屋にいる方の ３分の１は

I myself had a tumor removed from my large intestine

いつかガンにかかるでしょう

when I was only 14.

私自身は14歳の時

Cancer occurs

大腸の腫瘍を摘出しました

when a single cell in your body

ガンは 遺伝子内で

acquires a set of random mutations in important genes

突然変異を生じた

that cause that cell to start to produce

1つの細胞がガン化し

more and more and more copies of itself.

次々に増殖することで

Paradoxically, once established,

発生します

natural selection actually favors

自然選択は適者生存のはずですが

the continued growth of cancer.

おかしなことにこれが

Natural selection is survival of the fittest.

増殖するガンに対して

And when you have a population of fast-dividing cancer cells,

有利に働いてしまうのです

if one of them acquires new mutations,

増殖力の高いガン細胞の一つが

which allow them to grow more quickly,

一つ突然変異すると それは

acquire nutrients more successfully,

より効果的に栄養を吸収し

invade the body,

増殖力が増します

they'll be selected for by evolution.

その細胞は自然選択の対象となり

That's why cancer is such a difficult disease to treat.

体中に一層蔓延するのです

It evolves.

このようにガンは自然選択を通じ進化するので

Throw a drug at it,

治療が難しいのです

and resistant cells will grow back.

薬物を投与しても

An amazing fact is that,

耐性細胞を成長させるだけです

given the right environment and the right nutrients,

驚くことに

a cancer cell has the potential

適切な環境と栄養があれば

to go on growing forever.

ガンは永遠に

However cancer is constrained

成長することが可能なのです

by living inside our bodies,

しかしガンは生物の身体を

and its continued growth,

離れることはできません

its spreading through our bodies

ガンが増殖を続けて

and eating away at our tissues,

体中の組織を

leads to the death of the cancer patient

むしばんでしまえば

and also to the death of the cancer itself.

患者の身体もガンそのものも

So cancer could be thought of

死んでしまうのです

as a strange, short-lived, self-destructive life form --

ガンは短命で奇妙な

an evolutionary dead end.

自減的側面を持つ進化論的−

But that is where the Tasmanian devil cancer

行き詰まりとでも言えましょう

has acquired an absolutely amazing

しかしガンが

evolutionary adaptation.

驚くべき進化の適応を果たしたのが

And the answer came from studying

タスマニアデビルの事例だったのです

the Tasmanian devil cancer's DNA.

DNAを解析することで

This was work from many people,

この謎が解けました

but I'm going to explain it through a confirmatory experiment

多くの人との共同研究ですが

that I did a few years ago.

私が数年前に行った

The next slide is going to be gruesome.

確認実験を通して説明します

This is Jonas.

次のスライドは悲惨です

He's a Tasmanian devil that we found

これはジョナスです

with a large tumor on his face.

私達の発見した 顔に大きな腫瘍ができた

And being a geneticist,

タスマニアデビルです

I'm always interested to look at DNA and mutations.

私は遺伝学者として

So I took this opportunity

DNAや突然変異の分析には興味があります

to collect some samples from Jonas' tumor

この機会にジョナスの顔の腫瘍と

and also some samples from other parts of his body.

身体からいくらか

I took these back to the lab.

サンプルを取りました

I extracted DNA from them.

研究所に持ち帰って

And when I looked at the sequence of the DNA,

ここからDNAを抽出しました

and compared the sequence of Jonas' tumor

ジョナスの顔にできた腫瘍のDNAと

to that of the rest of his body,

身体から採取したDNAを

I discovered that they had a completely different genetic profile.

比較してみると

In fact, Jonas and his tumor

遺伝子プロファイルは全く異なっていました

were as different from each other

事実　ジョナスと

as you and the person sitting next to you.

彼にできた腫瘍は 皆さん自身と

What this told us was that Jonas' tumor

皆さんの隣に座っている人ほど違っていました

did not arise from cells of his own body.

つまりジョナスの腫瘍は

In fact, more genetic profiling

自身の体内で生成されたものではなかったのです

told us that this tumor in Jonas

更に遺伝子プロファイルを分析していくと

actually probably first arose

ジョナスの腫瘍はおそらく

from the cells of a female Tasmanian devil --

まずメスのデビルから

and Jonas was clearly a male.

生じたものだと判明しました

So how come

ジョナスは明らかにオスなのに

a tumor that arose from the cells of another individual

ではなぜ他の個体で