PBS高端访谈:DNA革命帮助揭开远古人类之谜（在线收听）

JUDY WOODRUFF: Now: who we are and how we got here. Jeffrey Brown takes a time traveling look at how modern researchers are using the latest DNA sequencing technology to understand the movements and interactions of very ancient humans. It is the latest in our weekly science series, the Leading Edge.

JEFFREY BROWN: It's a trip into the deep human past in a lab at the Harvard Medical School, disposable Tyvek suits, gloves, headgear, all required to avoid contamination of the ancient bones being studied here.

DAVID REICH, Harvard Medical School: The bones that we're looking at right now are about 5,000- or 6,000-year-old samples from Italy. And we're trying to understand population transformations in Italy over time.

JEFFREY BROWN: David Reich, who heads this lab, is at the forefront of a revolution in DNA studies, now providing new insight into human history as old as 40,000 years.

DAVID REICH: We can open up an ancient skeleton from 10,000 years ago, sequence its genome, have as much information from that ancient individual as we would have from a person living today.

JEFFREY BROWN: And tell a story about them and their movement, and their relations to others?

DAVID REICH: Exactly. And the power of this information is evident from the fact that the stories are always so surprising.

JEFFREY BROWN: Finding our roots is all the rage these days. There's a deep human interest in where we come from. Reich and his colleagues go deeper, much deeper into the past, powered by enormous advances in sequencing technology in the last decade. He's using it to answer very big questions. The title of his new book, "Who We Are and How We Got Here."

DAVID REICH: We're looking at the history of humans and how we got to all the different places we are in the world today, and it's not something that's been possible to look at before this technology. And, really, what the ancient DNA has done, and the ability to look with high resolution at human variation has done, is, it's opened up a whole Pandora's box of archaic humans, and ancient mixtures, that we didn't know about before, but that we already can see some of them.

JEFFREY BROWN: Reich and his team work on bones collected around the world, brought to them by archaeologists and museums.

WOMAN: I think that might be an ossicle.

JEFFREY BROWN: In the so-called clean lab, we watched as an ancient skull fragment was sandblasted to isolate the cochlea, or inner ear. The petrous bone surrounding this area can retain traces of DNA for thousands of years. In another room, we met Harold the robot.

WOMAN: He prepares all of our libraries for us and our DNA so we can sequence it.

JEFFREY BROWN: Reich was part of a group of scientists which confirmed that ancient humans and Neanderthals mixed and mated until some 40,000 years ago, and that some living humans today still carry traces of Neanderthal DNA. A cave in Siberia produced another surprise, a species later dubbed Denisovans.

DAVID REICH: My colleagues obtained DNA from a finger bone from Siberia that they thought was a modern human. But when they sequenced its DNA, it was from a population that was neither Neanderthal nor modern human. So this was an incredible revelation to all of us.

JEFFREY BROWN: That suggests and that's what I wanted to ask you that there are still yet to be found, other kinds of archaic humans?

DAVID REICH: That's right. You know, I think we're alone on the planet now, but 50,000 years ago, it would have been much like the scene in Star Wars, with many, many different humans, all similar to each other and comprehensible to each other in some ways, many of them as big-brained as us, but much more different from each other than people who live today.

JEFFREY BROWN: Perhaps the biggest surprise in the ancient DNA research, though, is in more recent human history. We may think mass migration and mixing of cultures is a modern phenomenon, but it turns out to be the story of our species. We have always moved and always mixed.

DAVID REICH: The idea that human populations today might correspond to age-old separations, tens of thousands of years old, that have existed from time immemorial, has now been profoundly undermined by genetics. What the genetic data shows is that groups that we see today, and that we recognize, in fact are the results of profound mixtures, and that none of these groups are pure in any sense at all.

JEFFREY BROWN: Original populations in most regions of the world have been replaced, sometimes several times over. Europe, for example, saw what Reich calls a collision of three very different populations over the last 9,000 years, the last of them part of a great migration that began far to the east, in what we now call the Russian Steppes. To make this more concrete, Reich points to the iconic site of Stonehenge, which reached its final form around 4,500 years ago, constructed by people who descended by Europe's first farmers.

DAVID REICH: But within 100 years or 200 years, Stonehenge was taken over by these new people who were not the same people genetically.

JEFFREY BROWN: So if you're living in Britain today and you're thinking, my ancestors built Stonehenge, you're wrong?

DAVID REICH: You're basically wrong, or maybe only 10 percent of your ancestors or fewer did. And so I think that this is sort of an example of this point, which is that people today are almost never directly descended from the people who first lived in those places. There's waves and waves of population replacement, and that we're all interconnected.

JEFFREY BROWN: That, of course, blows up concepts of pure races and national identity, ideas of genetics misused by the Nazis and many others into our own time. Differences? Yes. But more connections and mixing than we'd known. It's hardly the end of the story. Reich says the ancient DNA revolution is just beginning. And there's plenty the DNA doesn't tell us, just why people migrated at a given time, for example, what, in fact, where they thinking? New secrets, he says, will continue to be unlocked.

DAVID REICH: It's gonna really profoundly change the way we do archaeology, history, linguistics, sociology, even demography, and even sort of economic history, because we will be able to learn things about, for example, how population sizes have changed over time.

JEFFREY BROWN: It's all there in the ancient bones. For the "PBS NewsHour," I'm Jeffrey Brown at the Harvard Medical School in Cambridge, Massachusetts.

朱蒂·伍德拉夫：现在：我们是谁，又如何来到这里。杰弗里·布朗耗时游历，看现代研究人员如何利用最新的DNA测序技术来了解远古人类的迁徙及相互作用。这是我们每周系列科学节目《前沿》的最新一期。

杰弗里·布朗：我深入哈佛大学医学院实验室，开启了一场深入人类过去的旅行，身着一次性特卫强套装，手套，头罩，以保证正在这里接受研究的远古人类骸骨免遭污染。

戴维·瑞奇，哈佛大学医学院：现在我们看到的骨骼来自意大利，距今大约已有5000到6000年的历史。我们正试图了解长久以来意大利人口的变化情况。

杰弗里·布朗：这一实验室的负责人是戴维·瑞奇，这里的研究正处于DNA研究的革命前沿，现在这些研究成果为人类长达40,000年的历史提供新的洞察力。

戴维·瑞奇：我们可以开启距今10,000年之久的古老人类遗骨，对它的基因组进行测序，从中所得到的信息堪比在现存人类身上所获得的信息。

杰弗里·布朗：我们可以了解他们的故事，他们的迁徙情况以及他们与他人之间关系？

戴维·瑞奇：没错。而这些故事总是令人惊讶万分，这种信息的力量因此显而易见。

杰弗里·布朗：寻根研究在当下非常流行。我们来自何方，人类对此总充满浓厚的兴趣。瑞奇和他的同事经过了十年的深入研究，在测序技术方面取得了巨大进展。他用测序技术来回答非常大的问题。他新书的标题是《我们是谁，又如何来到这里》。

戴维·瑞奇：我们正在研究人类的历史，探寻我们如何到达今天世界上各个不同的地方，而在这项技术应用以前，这些我们无从而知。而且，真的，古老的DNA，以及研究人类变异时的高分辨能力，打开了古人类的潘多拉魔盒，揭开了古代人类相互融合的谜团，这些我们以前从未知晓，但现在已经可以了解到其中的一些。

杰弗里·布朗：瑞奇和他的团队从世界各地收集人类骸骨，将它们呈递给考古学家和博物馆。

女人：我想这可能是一块听小骨。

杰弗里·布朗：在所谓的无菌实验室里，我们看到了一块古人类颅骨碎片被喷砂以及进行耳蜗或内耳隔离的过程。这一区域四周的岩骨可将DNA痕迹保存数千年之久。在另一个房间里，我们遇见了机器人哈罗德。

女人：他为我们和我们的DNA提供了各种图书馆资源，以便我们可以对其进行排序。

杰弗里·布朗：瑞奇是科学家团队的一员。这个团队证实了古代人类曾在约40,000年前与尼安德特人混合交配，现存人类中，仍有一些携带尼安德特人DNA痕迹。西伯利亚的一个洞穴又为我们带来了一个惊喜，这一人种后来被称为丹尼索瓦人。

戴维·瑞奇：我的同事从西伯利亚的一根手指骨中获取了DNA，他们以为这属于现代人类。但当他们对DNA进行测序时，发现它来自一个既不是尼安德特人也不是现代人类的群体。所以这给了我们所有人一个不可思议的启迪。

杰弗里·布朗：这就表明了，也是我想问你的，是否还存在我们尚未发现的远古人类？

戴维·瑞奇：没错。你知道，现在我们认为在这个星球上的人类只此一种，但50,000年前，也许就像星球大战中的场景一样，有许许多多不同的人类物种，它们彼此相似，在某种程度上互相理解，它们中的许多与我们的脑容量相当。但与现在的人有很大的不同。

杰弗里·布朗：但也许在古代DNA研究中，最大的惊喜仍存在于近代人类历史的研究上。我们可能认为大规模迁移和文化融合是一种现代现象，但事实证明这些现象在很早以前就已经发生了。我们的迁徙与融合从未停止。

戴维·瑞奇：人们此前曾认为，现代人口可能与由来已久的隔离相契合，这些隔离，早在远古时代就已经存在，但这种想法现在已被遗传学大大地打破了。遗传数据显示，我们今天看到和认识到的人类群体，事实上，已经经过了深度混合，绝无纯粹血统可言。

杰弗里·布朗：世界上大部分地区的原始种群已经被取代，有时还会被多次取代。例如，欧洲在过去9,000年里，三个截然不同的人口种群，发生了瑞奇所谓的碰撞，他们中的最后一个，进行了一次从远东开始的大迁移，那个地区我们现称之为俄罗斯草原。为了使这更加具体，瑞奇指出了标志性地点巨石阵，4,500年前后，这里形成了如今的样式，它们由欧洲最早一批农民的后裔建造。

戴维·瑞奇：但在距今100年或200年内，巨石阵被一些新人接管了，从基因上来讲，他们不是同一人种。

杰弗里·布朗：所以，如果今天你住在英国，你在想，我的祖先建造了巨石阵，你错了吗？

戴维·瑞奇：你基本上错了，或者也许这些建造者只有10%或更少是你的祖先。所以我认为这是这个观点的一个例子，这就是今天的人类几乎都不是曾经原住民的直接后裔。人口更迭接连不断，我们所有人都相互关联。

杰弗里·布朗：当然，这与纯粹种族和民族身份的概念形成了对立，遗传学思想遭到了纳粹以及当今很多现代人的滥用。差异？是的。但更多的是联系与融合，这些超乎我们所知。还有后文。瑞奇说古代DNA革命才刚刚开始。还有很多东西，DNA并没有告诉我们，例如，人们为什么在特定时间进行迁移，他们在想什么，事实上，在哪里？他说，我们还将揭开更多新的秘密。

戴维·瑞奇：这将深刻地改变我们考古学、历史、语言学、社会学，甚至人口统计学，乃至经济史的研究方式，因为我们将能够了解一些关于，比如，人口规模随时间推移而变化的内容。

杰弗里·布朗：一切尽在远古遗骸身上。PBS新闻一小时，我是杰弗里·布朗，曼彻斯特剑桥哈佛大学医学院为您报道。