is what we can learn from studying the genomes

我們從研究

of living people

活著的人

and extinct humans.

和滅絕人種的基因組中可以學到什麼。

But before doing that,

但在那之前，

I just briefly want to remind you about what you already know:

我要提醒你們一些你們已經知道的事：

that our genomes, our genetic material,

我們的基因組，我們的基因物質，

are stored in almost all cells in our bodies in chromosomes

存在於我們身上幾乎所有細胞內的染色體中，

in the form of DNA,

以DNA的形式存在，

which is this famous double-helical molecule.

即著名的雙重螺旋分子結構。

And the genetic information

而且這些基因資料

is contained in the form of a sequence

是以四種簡稱為

of four bases

Ａ、Ｔ、Ｃ、Ｇ的鹼基

abbreviated with the letters A, T, C and G.

組成的序列。

And the information is there twice --

基因資料有兩組──

one on each strand --

一股(線)上一組──

which is important,

這點很重要，

because when new cells are formed, these strands come apart,

因為當新細胞形成時，DNA的雙股會分開，

new strands are synthesized with the old ones as templates

單股各自為模板，與(複製出的)新股合成為兩條雙股DNA

in an almost perfect process.

這是一個近乎完美的複製過程。

But nothing, of course, in nature

當然!自然界沒有任何東西

is totally perfect,

是完美無瑕的。

so sometimes an error is made

因此有時會出錯而

and a wrong letter is built in.

置入錯誤的字母(鹼基)。

And we can then see the result

舉例來說，當我們比較

of such mutations

演說廳內所有人的DNA序列，

when we compare DNA sequences

我們就會看到

among us here in the room, for example.

這類突變的結果。

If we compare my genome to the genome of you,

拿我的基因組跟你們的比較，

approximately every 1,200, 1,300 letters

在我們之中，大約每1,200或1,300個鹼基

will differ between us.

就會出現不同之處。

And these mutations accumulate

而且這些突變

approximately as a function of time.

有大概的週期，隨歲月不斷積累。

So if we add in a chimpanzee here, we will see more differences.

所以若加入黑猩猩來比對，差異又更大了。

Approximately one letter in a hundred

大約每一百個字母(鹼基)就有一個

will differ from a chimpanzee.

跟大猩猩不同。

And if you're then interested in the history

而且若你對一段DNA

of a piece of DNA, or the whole genome,

或是整個基因組的進化史有興趣的話，

you can reconstruct the history of the DNA

可以利用這些觀測到的差異

with those differences you observe.

來重現DNA的進化史。

And generally we depict our ideas about this history

一般我們以這樣的樹狀圖

in the form of trees like this.

來繪製我們對進化史的概念。

In this case, it's very simple.

以這個例子來說，就是個簡單的例子。

The two human DNA sequences

這兩個人類DNA序列

go back to a common ancestor quite recently.

可追溯到最近的同源祖先。

Farther back is there one shared with chimpanzees.

時間再往回推，就可推出和黑猩猩有同源祖先。

And because these mutations

而且因為這些突變的發生

happen approximately as a function of time,

可依時間作大概推算，

you can transform these differences

你們可以把這些差異

to estimates of time,

轉換成估算的時間，

where the two humans, typically,

一般而論，這兩個人類

will share a common ancestor about half a million years ago,

可被推算出在大約五十萬年前有同源祖先，

and with the chimpanzees,

跟黑猩猩的話，

it will be in the order of five million years ago.

推算出的時間是在五百萬年前左右。

So what has now happened in the last few years

這麼說吧，這些年來發生的事──

is that there are account technologies around

精密科技的問世

that allow you to see many, many pieces of DNA very quickly.

讓我們得以非常快速地檢視很多、很多的DNA。

So we can now, in a matter of hours,

所以僅僅幾個小時，我們就可以

determine a whole human genome.

檢測出全套人類基因組。

Each of us, of course, contains two human genomes --

當然人類每個個體都有兩組基因組：

one from our mothers and one from our fathers.

一組來自母親，一組來自父親。

And they are around three billion such letters long.

而且約三十億字母(鹼基)的長度。

And we will find that the two genomes in me,

大家會在我身上找到兩組基因組，

or one genome of mine we want to use,

我們拿其中一組基因組來檢驗，

will have about three million differences

約有三百萬不同之處

in the order of that.

大概是這個數字。

And what you can then also begin to do

然後你也可以開始研究

is to say, "How are these genetic differences

這些基因的差異

distributed across the world?"

在這世界的分佈情形。

And if you do that,

而且若這麼做，

you find a certain amount of genetic variation in Africa.

你會發現在非洲有某一數量的基因變異(突變)。

And if you look outside Africa,

若你研究非洲以外的地區，

you actually find less genetic variation.

你觀察到的基因變異較少。

This is surprising, of course,

奇怪吧!

because in the order of six to eight times fewer people

因為在非洲的人比在非洲外的人

live in Africa than outside Africa.

少了約七、八倍。

Yet the people inside Africa

然而非洲內的人

have more genetic variation.

發生更多的基因變異(突變)

Moreover, almost all these genetic variants

況且，我們在非洲外發現

we see outside Africa

幾乎所有基因變異

have closely related DNA sequences

與在非洲內找到的DNA序列

that you find inside Africa.

有密切關係。

But if you look in Africa,

但若你們看看非洲內，

there is a component of the genetic variation

有處基因變異

that has no close relatives outside.

在非洲外完全沒有相近的排列。

So a model to explain this

那麼可以解釋這個的模式是

is that a part of the African variation, but not all of it,

部分基因變異的非洲人，而非全基因變異人口，

[has] gone out and colonized the rest of the world.

移居到地球其他地方。

And together with the methods to date these genetic differences,

再加上利用基因差異斷定時間的技術，

this has led to the insight

讓我們對現代人類

that modern humans --

有這樣的了解：

humans that are essentially indistinguishable from you and me --

根本上難分你我的人類

evolved in Africa, quite recently,

是最近約十萬至二十萬年前

between 100 and 200,000 years ago.

在非洲進化而來的。

And later, between 100 and 50,000 years ago or so,

稍後約五萬到十萬年前

went out of Africa

離開非洲

to colonize the rest of the world.

到世界其他地方殖民。

So what I often like to say

所以我常喜歡說

is that, from a genomic perspective,

以基因組的觀點來看，

we are all Africans.

我們都是非洲人。

We either live inside Africa today,

我們不是現今住在非洲內

or in quite recent exile.

就是最近出走非洲的那群。

Another consequence

另一個現代人類的

of this recent origin of modern humans

最近起源的推論是

is that genetic variants

基因變異

are generally distributed widely in the world,

廣泛地分佈在全球

in many places,

各個地方，

and they tend to vary as gradients,

而且以全版面的角度來看

from a bird's-eye perspective at least.

往往呈梯度變化。

And since there are many genetic variants,

由於有很多基因變異，

and they have different such gradients,

就有不同的梯度變化，

this means that if we determine a DNA sequence --

這意味著若我們可以測出DNA序列──

a genome from one individual --

個體的基因組──

we can quite accurately estimate

我們可以相當準確地判斷

where that person comes from,

這個人是從哪裡來的，

provided that its parents or grandparents

若其父母或祖父母

haven't moved around too much.

沒有經常四處遷徙。

But does this then mean,

但這是不是表示

as many people tend to think,

如很多人想的那樣

that there are huge genetic differences between groups of people --

不同族群的人，基因差異很大，

on different continents, for example?

是不是不同洲的人差異會更大?

Well we can begin to ask those questions also.

嗯，我們也可以開始問這樣的問題。

There is, for example, a project that's underway

舉個例子，有個計畫在執行中

to sequence a thousand individuals --

要為世界不同地方的一千個人

their genomes -- from different parts of the world.

排列基因組。

They've sequenced 185 Africans

研究人員已經在非洲兩個族群中

from two populations in Africa.

完成185個人的DNA序列。

[They've] sequenced approximately equally [as] many people

在歐洲和在中國已排出序列的

in Europe and in China.

人數也大概同樣多。

And we can begin to say how much variance do we find,

那麼我們便可開始指出找到多少基因變異，

how many letters that vary

在這些個體DNA排序中，

in at least one of those individual sequences.

單一個人的鹼基有多少變化。

And it's a lot: 38 million variable positions.

答案是很多：有三千八百萬個變異處。

But we can then ask: Are there any absolute differences

但我們也可以問：非洲人和非非洲人

between Africans and non-Africans?

有任何完全差異嗎?

Perhaps the biggest difference

也許我們大部份的人會想到的

most of us would imagine existed.

最大差異曾經存在過。

And with absolute difference --

而「完全差異」

and I mean a difference

我所指的差異是

where people inside Africa at a certain position,

非洲內的人在某個「特定位置」，

where all individuals -- 100 percent -- have one letter,

「百分之百」有「相同的字母(鹼基)」，

and everybody outside Africa has another letter.

而每個在非洲外的人則有「另一個字母(鹼基)」。

And the answer to that, among those millions of differences,

這個問題的答案是，數百萬的差異之中，

is that there is not a single such position.

沒有這樣一個「完全差異」的位置。

This may be surprising.

這也許出人意料。

Maybe a single individual is misclassified or so.

也許有某個人的序列被弄錯了。

So we can relax the criterion a bit

所以我們可以稍稍放寬條件來問：

and say: How many positions do we find

我們發現有多少位置是

where 95 percent of people in Africa have

95%非洲內的人

one variant,

有「相同變異」，

95 percent another variant,

而在同樣的位置，95%非洲境外人則有「另一變異」，

and the number of that is 12.

得到的數字是12。

So this is very surprising.

所以很意外吧

It means that when we look at people

這意味著當我們看著人群，

and see a person from Africa

看到某個來自非洲的人、

and a person from Europe or Asia,

看到某個來自歐洲或亞州的人，

we cannot, for a single position in the genome with 100 percent accuracy,

我們不能百分之百說中

predict what the person would carry.

「某人」基因組之「某處」具有「何種鹼基」。

And only for 12 positions

而且只有12個位置

can we hope to be 95 percent right.

我們能期望有九成五的正確率。

This may be surprising,

這也許令人驚訝。

because we can, of course, look at these people

我們當然可以用肉眼盯著這些人

and quite easily say where they or their ancestors came from.

並相當容易地分辨他們或其祖先從哪裡來。

So what this means now

也就是說

is that those traits we then look at

我們看到的這些特徵

and so readily see --

是很容易就看得到的──

facial features, skin color, hair structure --

相貌特色、髮色質量、皮膚顏色──

are not determined by single genes with big effects,

並非由各類單一、重要的基因決定其作用，

but are determined by many different genetic variants

而是由很多不同的基因變異決定，

that seem to vary in frequency

且這些變異似乎在世界各地

between different parts of the world.

發生的頻率(次數)也不同。

There is another thing with those traits

另外一件事與我們可以很容易地

that we so easily observe in each other

在彼此身上看得到的特徵有關。

that I think is worthwhile to consider,

我認為值得想想，

and that is that, in a very literal sense,

就字義來說，

they're really on the surface of our bodies.

這些特徵的確是在我們身體表面。

They are what we just said --

如我剛剛說的

facial features, hair structure, skin color.

相貌特色、髮色質量、皮膚顏色。

There are also a number of features

然而各洲間還存有諸如此類的不同特色

that vary between continents like that

可說是不勝枚舉，

that have to do with how we metabolize food that we ingest,

像是我們如何代謝我們吃進去的食物

or that have to do

或是

with how our immune systems deal with microbes

我們的免疫系統如何應付

that try to invade our bodies.

企圖侵犯我們身體的病菌。

But so those are all parts of our bodies

然而這些是我們身體的各部

where we very directly interact with our environment,

直接與周圍環境互動，

in a direct confrontation, if you like.

你也可以說是「正面對峙」。

It's easy to imagine

很容易想像

how particularly those parts of our bodies

何以身體特定的某些部份

were quickly influenced by selection from the environment

一受到「環境淘汰(選擇)」威脅

and shifted frequencies of genes

就轉換這些受環境衝擊

that are involved in them.

的基因頻率。

But if we look on other parts of our bodies

但若我們看身體其他

where we don't directly interact with the environment --

不直接與環境互動的部份，

our kidneys, our livers, our hearts --

我們的腎臟、肝臟、心臟，

there is no way to say,

就很難

by just looking at these organs,

憑這些器官

where in the world they would come from.

判斷他們來自世界的何處。

So there's another interesting thing

所以有這層了解，我們發現

that comes from this realization

另一件有趣的事

that humans have a recent common origin in Africa,

人類最近共同的起源在非洲，

and that is that when those humans emerged

而且當時這些人類出現

around 100,000 years ago or so,

距今大約十萬年前，

they were not alone on the planet.

他們並不是單獨存在地球上。

There were other forms of humans around,

那時候有其他人種存在，

most famously perhaps, Neanderthals --

最有名的大概是「尼安德塔人」──

these robust forms of humans,

在左邊

compared to the left here

較健壯的人型，

with a modern human skeleton on the right --

右邊的是現代人類骨骼──

that existed in Western Asia and Europe

在幾十萬年前

since several hundreds of thousands of years.

就生活在西亞和歐洲。

So an interesting question is,

所以有個有趣的問題，

what happened when we met?

那時我們相遇，發生了什麼事?

What happened to the Neanderthals?

尼安德塔人怎麼了?

And to begin to answer such questions,

為了回答這樣的問題，

my research group -- since over 25 years now --

我的研究團隊在過去25年來

works on methods to extract DNA

研究如何從尼安德塔人

from remains of Neanderthals

和絕種動物

and extinct animals

的幾萬年遺骸

that are tens of thousands of years old.

萃取DNA。

So this involves a lot of technical issues

所以這牽涉到許多技術性問題

in how you extract the DNA,

像是如何萃取DNA，

how you convert it to a form you can sequence.

如何把它轉化成可以排序的形式。

You have to work very carefully

操作必須非常小心謹慎

to avoid contamination of experiments

以避免自己造成的

with DNA from yourself.

實驗污染DNA。

And this then, in conjunction with these methods

結合這些可以快速

that allow very many DNA molecules to be sequenced very rapidly,

排列出大量DNA分子的方法

allowed us last year

讓我們在去年

to present the first version of the Neanderthal genome,

得以呈現首版尼安德塔人基因組，

so that any one of you

所以你們任何人

can now look on the Internet, on the Neanderthal genome,

都可以在網路上找到尼安德塔人基因組，

or at least on the 55 percent of it

或至少看得到目前能重現的

that we've been able to reconstruct so far.

55%尼安德塔人基因組。

And you can begin to compare it to the genomes

你們可以開始將之

of people who live today.

與現今活著的人類基因組做比較。

And one question

接著你們也許

that you may then want to ask

想問一個問題

is, what happened when we met?

現代人類和尼安德塔人相遇時，發生什麼事?

Did we mix or not?

有沒有混種？

And the way to ask that question

提問的科學路徑是

is to look at the Neanderthal that comes from Southern Europe

去看南歐出土的尼安德塔人之基因組

and compare it to genomes

然後將其基因組

of people who live today.

與現今活著的人類作比對。

So we then look

所以我們接著

to do this with pairs of individuals,

分析一對對的個體

starting with two Africans,

以兩個非洲人開始，

looking at the two African genomes,

看這兩個非洲人的基因組，

finding places where they differ from each other,

找出他們互不相同的地方，

and in each case ask: What is a Neanderthal like?

並在每個案例中提問：尼安德塔人是怎麼樣的人?

Does it match one African or the other African?

其基因組與這個非洲人吻合或是另一個?

We would expect there to be no difference,