How a new species of ancestors is changing our theory of human evolution | Juliet Brophy

Translator: Leslie Gauthier Reviewer: Krystian Aparta

譯者: Lilian Chiu 審譯者: Bruce Sung

Human origins.

人類起源。

Who are we?

我們是誰？

Where do we come from,

我們來自何處？

and how do we know?

我們怎麼知道的？

In my field, paleoanthropology,

在我的領域，古人類學，

we explore human origins --

我們探究的是人類的起源——

the "who" and "where" questions --

「誰」以及「何處」的問題——

by analyzing fossils that date back thousands and even millions of years.

做法是分析數千年 甚至數百萬年的化石。

In 2015, a team of colleagues and I named a new species in the genus Homo --

2015 年，我和同事組成的團隊

為一個新物種命名， 它隸屬「人屬」——

our genus --

和我們同屬——

Homo naledi.

納萊迪人（Homo naledi）。

Let's take a step back and put that into context.

咱們先倒帶一下，把情境帶進來。

The last common ancestors between humans and chimps

人類和黑猩猩的共同祖先 最後出現是在

date somewhere between six and eight million years.

約六百萬年前到八百萬年前之間。

The earliest hominins,

最早的人族，

or earliest human ancestors,

或說最早的人類祖先，

evolved into a group known as the australopithecines.

演化成為一般所知的南方古猿。

The australopithecines evolved into the genus Homo

南方古猿演化成為人屬，

and eventually modern humans -- us.

最終演化成現代人——我們。

With each new fossil discovery,

每發現一塊新化石，

we get a little bit closer to better understanding who we are

我們就稍微更進一步 了解我們是誰，

and where we came from.

及我們來自何處。

With these new fossil finds,

因為這些化石的新發現，

we realize we now have to make changes to this tree.

我們了解到，我們得要 修改這個樹狀圖。

Until this discovery,

在這個發現之前，

we thought we had a pretty good idea about the patterns of evolutionary change.

我們以為我們很清楚知道 演化改變的模式。

Current fossil evidence suggests

目前的化石證據指出

that the earliest populations of the genus Homo evolved in Africa

最早的人屬是在非洲演化出來的，

somewhere between two and three million years.

大約在兩百萬到三百萬年間。

Fast-forward to approximately 300,000 years to where we see the origins

快轉約三十萬年，

到我們看到最早的 現代人起源之處。

of the first modern humans.

While the fossil record between these time frames in Africa

雖然在非洲這些時間點 之間的化石記錄

is relatively sparse,

相對比較稀少，

the fossils nonetheless demonstrated certain trends

但不論如何，化石仍然 顯示出了某些趨勢，

from our earliest ancestors to modern humans.

從我們最早的祖先 到現代人的趨勢。

For example, our brains were becoming larger

比如，相對於我們的身體， 我們的大腦越來越大。

relative the rest of our body.

Our pelves were becoming more bowl-shaped,

我們的骨盆越來越像碗形，

and our hand-wrist morphology, or form,

我們手腕的形態學，或者說形式，

suggested a change in our grip as we began to make and use stone tools

顯示出我們的握法有所不同， 我們開始製造及使用石頭工具，

and spend less time in the trees.

花在爬樹上的時間變少。

These new fossils disrupt everything we thought we knew about these trends

這些新化石打斷了我們認為 我們對於這些趨勢所知的一切，

and force us to change the way that we think about human evolution.

強迫我們改變我們對於 人類演化的看法。

South Africa in general,

南非大部分的地方， 但特別是「人類的搖籃」地區，

but the Cradle of Humankind in particular,

contains numerous sites where hundreds of thousands of fossils have been found.

有許多地點都找出了數十萬件化石。

As an undergraduate student, I fell in love with one of them ...

我還是大學生時， 就愛上了其中一件……

Mrs. Ples.

普雷斯太太。

The skull of a 2.1-million-year-old early human ancestor.

這是 210 萬年前人類祖先的頭骨。

From that point on,

從那時起，

I was determined to go to South Africa and study human evolution.

我就下決心要到南非 以及研究人類演化。

I first traveled there in 2003,

2003 年，我初次到那裡，

and I did get to see my beloved Mrs. Ples.

我的確得以見到 我摯愛的普雷斯太太。

(Laughter)

（笑聲）

But words can hardly convey my excitement

但我的興奮無法言喻，

when I was chosen as an early career scientist

因為我被選為青年科學家，

by Lee Berger,

且是李貝加挑選的， 他是聞名世界的古人類學家，

a world-renowned paleoanthropologist,

to be one of the primary analysts of recently excavated unpublished fossils.

讓我擔任主要分析師之一，

分析近期挖出但尚未發佈的化石。

This treasure trove of fossils was being recovered from a new site

這些貴重的化石 是在一個新地點發現的，

called the Dinaledi Chamber in the Rising Star cave system.

這個地點叫做迪納萊迪洞穴， 屬於新星岩洞體系。

Species are often named based on a skull, a lower jaw,

物種通常是根據頭骨、 下顎來命名，

or, very rarely,

或，非常罕見的狀況，

a handful of postcranial, or below-the-neck, elements.

是用許多顱後或頸後元素來命名。

The fossils from Dinaledi were another story altogether.

來自迪納萊迪的化石全部 加在一起又是另一回事了。

An unprecedented approximately 1800 specimens --

前所未有，近一千八百個樣本——

so far --

只是截至目前為止——

have been excavated from the Rising Star system,

已經從新星岩洞體系挖出來，

representing at least 15 individual skeletons.

代表至少十五個人的骸骨。

The research team that I was invited to join

我被邀請加入一個研究團隊，

was tasked with describing, comparing and analyzing the fossils,

其工作任務是在描述、 比較、分析那些化石，

with the difficult goal of identifying to what species the fossils belonged.

且有個很困難的目標： 辨識出那些化石屬於什麼物種。

We were divided up into our different areas of expertise.

我們被依據專長領域分開來。

We were divided up in different areas of the lab, too.

我們也被分到實驗室的不同區域。

So there was "Hand Land," for the fossil hand people,

所以，研究化石手的人 在「手部大地」，

"Hip Heaven" for the pelvis ...

骨盆的人在「髖部天堂」……

I was in the "Tooth Booth."

我則是在「牙齒亭」。

(Laughter)

（笑聲）

And after long, intense days in the lab,

在實驗室中經過了漫長、 緊繃的白天之後，

the different teams would meet up at night and discuss our findings,

不同的團隊會在晚上見面， 討論我們的的發現，

still consumed by questions from our analyses.

仍然投注在我們的分析 所產生的問題上。

It was incredible how different the interpretations were.

大家的詮釋差異大到不可思議。

Each body part seemed to come from a different species,

每個身體部位似乎 都來自不同的物種，

based on what we knew from the fossil record.

詮釋根據是我們從化石 記錄習得的知識。

The suite of characteristics we were seeing didn't match any known species.

我們所看到的一系列特徵 並不符合任何已知物種。

And if we had only recovered the skull, we might have called it one thing;

如果我們只發現了頭骨， 我們可能會稱它是某樣東西；

if we had only recovered the pelvis, we might have called it another.

如果只發現了骨盆， 可能又會稱它是另一樣東西。

The anatomy of the skeletons didn't make sense

這些骨骸的解剖學並不合理，

with the framework of what we thought we knew of human evolution.

用我們對人類演化的既有 知識框架是說不通的。

Did it belong in the genus Homo?

它屬於人屬嗎？

Should it be an australopithecine?

它會不會是更新世靈長類動物？

Those bipedal, more apelike ancestors?

那些兩足動物，更像人猿的祖先？

Or perhaps it should be its own species.

或者，也許它自己另屬一種物種。

Ultimately, after much deliberation,

最終，經過許多的考量，

we decided the Rising Star specimens did indeed warrant a new species,

我們決定這些新星樣本 的確有理由成為一種新物種，

which we called "Homo naledi."

我們稱之為納萊迪人。

From the head to the feet,

從頭到腳，

the fossils present a mosaic of primitive, or ancestral,

這些化石呈現出混合了 原始的，或祖先的特徵

and derived or more modern-like features.

以及衍生的，或更像現代的特徵。

The skull is quite derived,

頭骨就很明顯是衍生的，

appearing most similar to early representatives of the genus Homo,

外觀上很類似早起的人屬代表，

like Homo habilis and Homo erectus.

比如巧人和直立人。

However, the brain is scarcely half the size of a modern human one.

然而，大腦幾乎不到 現代人大腦的一半。

One that is smaller than any other early Homo that has ever been found.

比所有已發現的其他 早期人類的大腦都還要小。

As someone who studies teeth,

身為研究牙齒的人，

I might argue these are the coolest fossils found at the site.

我可以主張從那個地點挖出的 化石中最酷的就是這些了。

(Laughter)

（笑聲）

The assemblage consists of 190 whole or fragmentary teeth

這一組化石包含了 190 個 完整或部分牙齒，

that range in age from very old to very young.

年齡從非常年輕到非常老都有。

Like the skeletons,

和骨骸一樣，

the teeth present a mix of primitive and derived traits.

牙齒也呈現出遠古和衍生的特性。

In modern humans,

就現代人類來說，

the third molar is typically the smallest, while the first molar is the biggest,

第三個臼齒通常 是最小的，第一個最大，

but Homo naledi has the primitive condition

但納萊迪人具有原始的狀態，

where the third molar is the biggest and the first molar is the smallest.

也就是第三個臼齒最大， 第一個最小。

The anterior teeth,

前面的牙齒，也就是門牙和犬齒，

or the incisors and canines,

are small for the genus Homo,

對於人屬來說很小。

and the lower canine has a cuspulid on it --

下犬齒上面有個尖處——

an extra cuspule that gives it a distinct mitten-like shape

額外的尖端讓它呈現 獨特的連指手套形狀，

that it shares with some specimens of the early human, Homo erectus.

一些早期人類的樣本 也有這個特性，

如直立人。

The overall shape of the teeth looked odd to me,

在我看來，牙齒的 整體形狀很奇特。

so I performed crown-shape analysis

所以我進行了冠形分析，

on the occlusal surfaces of deciduous teeth, or baby teeth --

分析乳牙的咬合表面——

on your left --

在你們的左邊——

and the permanent premolars and molars on your right.

還有你們右邊的 永久前臼齒及臼齒。

The deciduous teeth are especially narrow,

乳牙特別窄，

and the premolars are unique in their outline shape

與其他人類祖先相比，

前臼齒的輪廓形狀很獨特。

compared to other hominids.

In fact, when I compare the outlines,

事實上，我在比較輪廓時，

when I lay them on top of each other,

我把它們疊在一起時，

they look very similar.

它們看起來非常相似。

We say they have "low intraspecific variations,"

我們說，它們的「種內變異很低」。

so the variation within the species is low.

也就是在這個物種中的變異很低。

When I compare this to groups like the australopithecines,

當我把它和南方古猿 等族群做比較時，

the intraspecific variation is much larger.

種內變異就大很多。

Postcranially, the team concluded

顱後的部分，團隊的結論是

that the position of the shoulders suggesting naledi was a climber;

肩膀的位置，顯示出 納萊迪人會向上攀爬；

the flared pelvis and curved fingers are all primitive for the genus Homo.

就人屬來說，喇叭形的骨盆 和彎曲的手指都是原始的特徵。

On the other hand,

另一方面，

the humanlike wrist, long slender legs and modern feet

像人的手腕、修長的腿， 以及現代的腳，

are all consistent with other members of the genus.

都和同屬的其他物種一致。

In 2017, we announced more specimens of Homo naledi

2017 年，我們公佈了 更多納萊迪人的樣本，

from the nearby Lesedi Chamber,

是從附近的雷沙迪洞穴挖出來的，

also in the Rising Star cave system.

也是隸屬新星岩洞體系。

In addition, our geology team managed to produce an age estimate.

此外，我們的地質學團隊 做出了時代估計。

The date's a big deal because, up until now,

年代是很重要的， 因為，到目前為止，

we had based our analysis solely on the morphology of the specimens,

我們的分析全都立基在 樣本的形態學上，

without previous knowledge of how old something is --

事先完全不知道 什麼東西有多古老——

something which could unconsciously bias our interpretations.

我們的詮釋有可能 在不知不覺中受到偏見影響。

With its small brain and flared pelvis,

因為有很小的大腦 以及喇叭形的骨盆，

we would not have been surprised

如果最後確認這些化石 是兩百萬年前的，

if the fossils turned out to be two million years old.

我們也不會感到意外。

Instead, the fossils dated

結果，這些化石的時間

to 235 to 336 thousand years,

卻是 23 萬 5 千年 到 33 萬 6 千年之間，

an incredibly young date for such a small-brained individual.

就大腦這麼小的人來說， 年代這麼近是很不可思議的。

So think back to what I said earlier:

所以，回想一下我剛剛說的：

we thought that our brains were becoming larger relative to the rest of our body.

我們以為，相對於我們的身體， 我們的大腦變得越來越大。

Now we have a small-brained, young individual complicating this idea.

現在，我們找到了年代更近、 大腦卻很小的人，

讓這個想法變複雜了。

What does all this mean?

這一切意味著什麼？

Homo naledi has taught us

納萊迪人教我們的是，

that we need to reassess what it means to be in the genus Homo.

我們需要重新評估 身為人屬的意義。

We need to rethink what it means to be human.

我們需要重新思考 身為人類的意義。

In fact, most of the characteristics that we use to define the genus Homo,

事實上，我們用來 定義人屬的大部分特徵，

such as brain size and hip morphology,

比如大腦的大小和髖骨的形態學，

are no longer valid.

已經不再有效。

No other species exists with this mix of primitive and derived traits.

現存的物種當中，沒有一種 同時具有原始和衍生特性。

為什麼在人屬當中有 這麼大的形態學變異？

Why is there so much morphological variation in the genus Homo?

And what force is driving that variation?

是什麼力量造成了那樣的變異？

Another implication for these fossils is that for the first time,

這些化石還有一個意涵， 這是第一次，

we have concrete evidence of a species coexisting in Africa,

我們有具體證據證明三十萬年前

at 300,000 years,

在非洲有一個物種和現代人共存。

with modern humans.

Until this discovery,

在這個發現之前，

we only had large-brained modern humans that existed in Africa.

在非洲只有大腦很大的現代人存在。

Did they interbreed with each other?

他們曾彼此雜交嗎？

Did they compete with each other?

他們曾彼此競爭嗎？

Another implication that these fossils have

這些化石留了一個意涵

is for the archaeologists studying stone tools in South Africa.

給研究南非石製工具的考古學家。

Keep in mind that neither the Dinaledi nor the Lesedi Chambers

別忘了，在迧納萊迪 或雷沙迪洞穴中，

have any artifacts in them.

都沒有任何文物。

However, they do overlap in time with several stone-tool industries,

然而，他們所屬的時代和數個 石製工具產業的時代是重疊的，

the makers of which are considered to be either modern humans

那些工具的製造者被認為是現代人

or direct human ancestors.

或是人類的直屬祖先。

This begs the question:

這就帶出了一個問題：

Who made the stone tools of South Africa?

南非的石製工具是誰做的？

Brain size has historically played a key role

在歷史上，大腦的大小 扮演著關鍵角色，

in identifying a species as a tool user.

用來辨識物種是否 為工具的使用者。

The idea is that you need to have a large brain

想法是，你必須要有夠大的大腦，

to have even the capacity to make stone tools.

才有可能有能力做出石製工具。

But that notion has been questioned.

但，這個概念已經被質疑了。

Furthermore, Homo naledi, even with its small brain size,

此外，即使納萊迪人的大腦很小，

has a hand-wrist morphology similar to other species

他們的手腕形態學和其他

會製做和使用 石製工具的物種很相似，

that did make and use stone tools,

suggesting it had the capability.

意味著他們有這種能力。

With two species coexisting in Africa at 300,000 years,

三十萬年前， 兩個物種在非洲共存，

we can no longer assume we know the maker of tools

在沒有找到物種的工具發掘地點，

at sites with no associated species.

我們無法再假設 我們知道工具是誰製造的。

So where does Homo naledi fit in our human evolutionary lineage?

所以，納萊迪人應該放在 人類演化世系中的哪裡？

Who is it most closely related to?

他們和誰的關聯最近？

Who did it evolve from?

他們是從何演化來的？

We're still trying to figure all that out.

我們還在尋找這些答案。

It's ironic, because paleoanthropologists are renowned

很諷刺，因為古人類學家

以使用小樣本聞名。

for having small sample sizes.

We now have a large sample size,

我們現在有了很大的樣本，

and more questions than answers.

問題卻比答案還多。

Homo naledi has taught us,

納萊迪人教了我們很多，

has brought us a little bit closer

讓我們更進一步

to better understanding our evolutionary past.

了解我們的演化過往。

So while Mrs. Ples will always hold a special place in my heart,

所以，雖然普雷斯太太在我心中 一直佔有一個很特別的位置，

she now shares that space with several thousand others.

現在她得要把那個位置 和其他數千人共享了。

(Laughter)

（笑聲）

Thank you.

謝謝。

(Applause)

（掌聲）