Hunter-gatherers in Siberia died of a plague outbreak 5,500 years ago
Hunter-gatherers in Siberia died of a plague outbreak 5,500 years ago
5500年前，西伯利亚的狩猎采集者曾死于一场瘟疫爆发
Plague swept through groups of hunter-gatherers in southeastern Siberia 5,500 years ago, leaving dozens dead in its wake—with DNA from Yersinia pestis bacteria still trapped inside their teeth. University of Oxford ancient DNA researcher Ruairidh Macleod and his colleagues recently sequenced the telltale bacterial DNA in teeth from plague victims at four ancient cemeteries in the area around Russia’s Lake Baikal. The tragedy that befell these communities is now the earliest known plague outbreak, courtesy of the oldest strain of Y. pestis ever sequenced.
5500年前，一场瘟疫席卷了西伯利亚东南部的狩猎采集者群体，导致数十人死亡——而鼠疫杆菌（Yersinia pestis）的DNA至今仍残留在他们的牙齿中。牛津大学古DNA研究员鲁艾里·麦克劳德（Ruairidh Macleod）及其同事最近对俄罗斯贝加尔湖周边四个古代墓地的瘟疫受害者牙齿中的细菌DNA进行了测序。这些社区所遭遇的悲剧，如今被确认为已知最早的瘟疫爆发，这得益于科学家测序出的史上最古老的鼠疫杆菌菌株。
Unearthing a new backstory for the plague
发掘瘟疫的新背景
Until recently, scientists who study the evolution of diseases have held two fairly solid ideas about the origins of plague, the disease caused by Yersinia pestis bacteria. It’s a scourge so awful that it has gone down in history as not just a plague but “the plague.” The first idea is that the earliest strains didn’t have the right genetic traits to be really lethal. And the second is that the plague first began menacing humans when the first farmers settled in densely packed towns alongside rats and domestic animals.
直到最近，研究疾病演化的科学家们对于鼠疫（由鼠疫杆菌引起）的起源一直持有两个相当稳固的观点。这种灾难极其可怕，以至于在历史上它不仅仅被称为一种瘟疫，而是被称为“大瘟疫”（the plague）。第一个观点是，最早的菌株并不具备真正致命的遗传特征；第二个观点是，当第一批农民在人口稠密的城镇定居，并与老鼠和家畜共同生活时，瘟疫才开始威胁人类。
But the dead of Ust’-Ida I cemetery, near Lake Baikal, tell a very different story. “Our findings demonstrate that the earliest known outbreaks of plague occurred in prehistoric hunter-gatherers centuries before infections are observed in Neolithic farmers,” wrote Macleod and his colleagues in their recent paper. That challenges our previous assumption that plague spillover was a side effect of people taking up farming and settling in permanent villages and towns, living closer to each other and to an assortment of animals (and their fleas).
但贝加尔湖附近的Ust’-Ida I墓地的死者讲述了一个截然不同的故事。麦克劳德及其同事在最近的论文中写道：“我们的研究结果表明，已知最早的瘟疫爆发发生在史前狩猎采集者群体中，比在新石器时代农民身上观察到的感染早了几个世纪。”这挑战了我们之前的假设，即瘟疫的传播是人类开始务农、定居在永久村镇，并与他人及各种动物（及其携带的跳蚤）近距离接触后的副作用。
“Much of the accepted theory around epidemiology of disease in the past is that this kind of thing shouldn’t occur in hunter-gatherers because hunter-gatherers are constantly moving around the landscape because they’re in such small groups all the time,” said Macleod in a press conference. “The theory, at least, is that infectious disease can’t really take hold and devastate entire communities in this way.” So much for that theory.
“过去关于疾病流行病学的大部分公认理论认为，这种事情不应该发生在狩猎采集者身上，因为他们总是以极小的群体在各地不断迁徙，”麦克劳德在新闻发布会上说。“至少理论上认为，传染病无法以这种方式真正扎根并摧毁整个社区。”看来这个理论站不住脚了。
Welcome to the world’s first plague cemetery
欢迎来到世界上第一个瘟疫墓地
The Angara River flows from the depths of Lake Baikal. The people who lived along it thousands of years ago survived by hunting, foraging, and fishing. They would have lived in relatively small groups, but they seem to have stayed connected across hundreds of kilometers through marriage and family ties. Although their lifestyle would have been one of constant movement, they buried their dead in cemeteries such as Ust’-Ida, interring them with offerings of clay pots, stone tools, and bone and antler points.
安加拉河从贝加尔湖深处流出。几千年前生活在河边的人们依靠狩猎、采集和捕鱼为生。他们生活在相对较小的群体中，但似乎通过婚姻和家族纽带在数百公里的范围内保持着联系。尽管他们的生活方式是不断迁徙的，但他们会将死者安葬在像Ust’-Ida这样的墓地中，并随葬陶罐、石器以及骨制和鹿角制的尖头器。
At Ust’-Ida, archaeologists with the Baikal Archaeology Project unearthed a grim mystery: an unusually high number of dead children, a cluster of radiocarbon dates suggesting that many of the cemetery’s occupants died at around the same time, and no evidence of violence. Something tragic happened to this ancient hunter-gatherer community, but what? Archaeologists thought ancient DNA might shed some light on the mystery.
在Ust’-Ida，贝加尔考古项目的考古学家们发掘出一个严峻的谜团：这里有异常多的儿童遗骸，放射性碳测年结果显示墓地中的许多人死于同一时期，且没有暴力迹象。这个古代狩猎采集社区发生了悲剧，但究竟是什么呢？考古学家认为古DNA或许能揭开这个谜团。
Macleod and his colleagues started with shotgun sequencing, a technique used to identify the DNA sequences in a sample when scientists don’t know exactly which organisms they’re looking for. They used samples from the roots of 46 ancient people’s teeth from four different cemeteries along the Angara River. And to their complete surprise, they found plague.
麦克劳德及其同事首先使用了鸟枪测序法（shotgun sequencing），这是一种在科学家不确定样本中存在何种生物时，用于识别DNA序列的技术。他们使用了安加拉河沿岸四个不同墓地的46具古代人类牙齿根部的样本。令他们大吃一惊的是，他们发现了瘟疫。
Fun fact: Because dental roots are fed by lots of blood vessels, anything in your bloodstream is likely to pass through your teeth at some point, which means if you die with the plague, it may leave its DNA behind in your teeth. “This is really cool evidence that the plague was in the bloodstream, which is lethal,” said co-author Frederik Seersholm, a University of Copenhagen ancient DNA researcher who clearly knows a fun fact when he sees one, in a press conference.
有趣的事实：由于牙根由大量血管供血，血液中的任何物质都有可能在某个时刻流经牙齿，这意味着如果你死于瘟疫，它可能会在你的牙齿中留下DNA。“这是一个非常酷的证据，证明瘟疫存在于血液中，而这正是致命的原因，”合著者、哥本哈根大学古DNA研究员弗雷德里克·西尔斯霍尔姆（Frederik Seersholm）在新闻发布会上说，他显然很懂得如何分享有趣的科学事实。
About 11 of the 31 people Macleod and his colleagues tested at Ust’-Ida had Y. pestis DNA in their teeth, and Macleod says that’s “consistent with pretty much everybody [in the cemetery] having died of plague,” not just those 11. That’s because the detection rate for plague DNA in the remains at Ust’-Ida matches that at Smithfield’s, a known mass grave specifically for plague victims in London. It’s safe to assume everyone buried there had the plague.
在麦克劳德及其同事测试的Ust’-Ida的31人中，约有11人的牙齿中含有鼠疫杆菌DNA。麦克劳德表示，这“与墓地中几乎所有人都是死于瘟疫的情况相符”，而不仅仅是那11个人。这是因为Ust’-Ida遗骸中瘟疫DNA的检出率与伦敦史密斯菲尔德（Smithfield’s）的一处已知专门用于埋葬瘟疫受害者的乱葬岗的检出率相吻合。可以肯定地推断，埋葬在那里的每个人都患有瘟疫。
“We really didn’t know what to expect going into this, so it was a complete surprise that we discovered this really, really early evidence for large-scale lethal outbreaks of plague amongst these hunter-gatherer communities at this point in time,” said Macleod in the press conference.
“在进行这项研究时，我们真的不知道会发现什么，所以当我们发现这些狩猎采集社区在那个时期发生大规模致命瘟疫爆发的早期证据时，感到非常震惊，”麦克劳德在新闻发布会上说。
Ancient DNA and future outbreaks
古DNA与未来的爆发
Macleod and his colleagues managed to sequence a full Yersinia pestis genome from at least one of the samples, and it turns out to be the oldest strain of Y. pestis ever sequenced. According to the research, it’s very close to the base of the plague family tree, emerging just a few hundred years after Y. pestis last shared a common ancestor with another bacterium called Yersinia pseudotuberculosis. This ancient plague isn’t quite the one we’re familiar with today or the version that devastated medieval Europe.
麦克劳德及其同事成功地从至少一个样本中测序出了完整的鼠疫杆菌基因组，结果证明这是有史以来测序出的最古老的鼠疫杆菌菌株。根据研究，它非常接近瘟疫家族树的根部，出现在鼠疫杆菌与另一种名为假结核耶尔森菌（Yersinia pseudotuberculosis）的细菌最后一次拥有共同祖先后的几百年内。这种古老的瘟疫与我们今天熟悉的版本，或是摧毁中世纪欧洲的版本并不完全相同。