The first people who populated the Americas
定居在美洲大陆的第一批人

Many thousands of years ago, not a single human being lived in the Americas.

几千几万年前，美洲没有人类居住。

This only changed during the last Ice Age. It was a time when most of North America was covered with a thick sheet of ice, which made the Americas difficult to inhabit.

在最后一个冰河时代，这一情况才发生变化。当时北美大部分地区都覆盖着厚厚的冰块，人类很难在此居住。

But at some point during this time, adventurous humans started their journey into a new world.

但在这个时代的某个时刻，富有冒险精神的人开始进入这个新世界。

今天许多美洲原住民是克洛维斯人的直系后裔

They probably came on foot from Siberia across the Bering Land Bridge, which existed between Alaska and Eurasia from the end of the last Ice Age until about 10,000 years ago. The area is now submerged by water.

他们很可能是从西伯利亚步行穿过白令陆桥（Bering Land Bridge）来到美洲。白令陆桥位于阿拉斯加和欧亚大陆之间，形成于最后一次冰河世纪末，消失于一万年前。它现在被海水浸没。

There is still debate about when these first Americans actually arrived and where they came from. But we are now getting closer to uncovering the original narrative, and finding out who these first Americans really were.

关于这些第一批美洲原住民何时到达以及他们来自哪里，仍然存在争议。但是，我们现在越来越接近揭示原本的事实经过和确定他们的真实身份。

During the peak of the last Ice Age about 20,000 years ago, a journey from Asia into the Americas would not have been particularly desirable. North America was covered in icy permafrost and tall glaciers. But, paradoxically, the presence of so much ice meant that the journey was, in a way, easier than it would be today.

在大约两万年前，正值最后一个冰河时代的高峰期，从亚洲进入美洲的旅程并不特别吸引人。北美洲覆盖着永久冻结带和高大的冰川。但是，具有讽刺意味的是，这么多冰的存在意味着当时的旅程在某种程度上比今天更容易。

The abundance of ice meant that sea levels were much lower than they are now, and a stretch of land emerged between Siberia and Alaska. Humans and animals could simply walk from Asia to North America. The land bridge was called Beringia.

大量的冰意味着海平面远远低于现在，而且在西伯利亚与阿拉斯加之间出现了一片土地。人类和动物可以从亚洲走到北美。这座陆桥被称为白令陆桥（Beringia）。

At some point around this time – known as the Last Glacial Maximum – groups of hunter-gatherers moved east from what is now Siberia to set up camp there.

在这个时期的某个时间点——被称为末次冰盛期（Last Glacial Maximum）——大批狩猎采集者从现在的西伯利亚向东移动，在那里建立营地。

"The first people who arrived in Beringia were probably small, highly mobile groups evolving in a large landscape, probably depending on the availability of seasonal resources," says Lauriane Bourgeon of the University of Montreal, Canada.

加拿大蒙特利尔大学（University of Montreal）的劳瑞安·布容尔（Lauriane Bourgeon）说："到达白令陆桥的第一批人可能是规模较小、流动性很高的群体，他们在较大的环境中繁育，并可能仰赖季节性资源。"

These people did well to seek refuge there. Central Beringia was a much more desirable environment than the icy lands they had left behind. The climate was a bit damper. Vegetation, in the form of woody shrubs, would have given them access to wood that they could burn to keep warm.

这些人在那里发现了很好的庇护所。白令陆桥中央地区的环境远比他们原先的冰冷土地更加理想。气候会有点潮湿。植被以木本灌木为主，这是他们木材的来源，让他们能够燃烧木柴以保持取暖。

Beringia was also an ideal environment for large grazing mammals, giving early hunter-gathers something to hunt, says Scott Elias of Royal Holloway, University London in the UK, who reconstructs past climates.

白令陆桥也是大型草食哺乳动物的理想环境，这给早期的猎人提供了一些猎物，英国伦敦大学皇家哈洛威学院（Royal Holloway, University London）的斯科特·埃利亚斯（Scott Elias）说。他研究历史气候的重建。

"Our hypothesis is that people were using the woody shrubs from the land bridge to ignite bones on the landscape. The bones of big animals contain lots of fatty deposits of marrow, and they will burn."

"我们的假设是当时的人用陆桥上的灌木点燃动物的骨头。大型动物的骨头含有大量的富含脂肪的骨髓沉积物，它是可燃物。"

When humans got to Beringia, they would have had little choice but to set up camp there. The vast Laurentide and Cordilleran ice sheets further east cut them off from North America.

当人类到达白令陆桥时，他们几乎别无选择，只能在那里扎营。东边广阔的洛朗第（Laurentide）和科迪勒拉冰盖（Cordilleranice sheets）把他们与北美隔开。

It is now becoming clear that they made Beringia their home, staying put for several thousand years. This idea is called the Beringian Standstill Hypothesis. This standstill helped these isolated groups of people to become genetically distinct from those they had left behind, according to a 2007 study.

现在越来越清楚的是他们把白令陆桥当成家园，住在这里几千年。这个想法被称为"白令陆桥滞留假说"。根据2007年的一项研究，这次滞留导致这些隔离的群体出现了不同于其原先群体的遗传基因。

This long standstill therefore meant that the people who arrived in the Americas – when the ice finally retreated and allowed entry – were genetically different to the individuals who had left Siberia thousands of years earlier. "Arguably one of the most important parts of the process is what happened in Beringia. That's when they differentiated from Asians and started becoming Native Americans," says Connie Mulligan of the University of Florida in Gainesville, US, who took part in this early analysis.

因此，这次长期滞留意味着到达美洲的人——当冰块终于退缩并允许人类进入美洲时——与几千年前离开西伯利亚时的人具有不同的基因。佛罗里达大学盖恩斯维尔分校（University of Florida in Gainesville）的康妮·穆里根（Connie Mulligan）说："可以说，这个过程最重要的部分之一就是在白令陆桥发生了什么事情。当时他们与亚洲人区别开来，开始成为美洲原住民。"她参与了早期的分析工作。

Since then, other genetic insights have further supported the standstill hypothesis. Elias and colleagues even propose that people stayed in Beringia for as long as 10,000 years.

自此此后，其他遗传方面的发现进一步支持了滞留假说。埃利亚斯和他的同事甚至提出，人类在白令陆桥居住了长达一万年。

When the ice finally started to retreat, groups of people then travelled to different pockets of the Americas.

当冰块终于开始退缩时，不同群体的人类前往不同的美洲的各个地区。

There has long been debate over whether these early settlers arrived from several migrations from different areas, or just one.

长期以来的一个争论是这些早期定居者是否从不同地区分多次迁移到美洲，还是仅来自一个地方。

Over 20 years ago, Mulligan proposed that there was just one migration from Beringia into the "New World". She came to this conclusion by analysing the genetic variation in the DNA of modern-day Native Americans and comparing it with the variation in Asia. The same rare pattern appeared in all the Native Americans she studied, but very rarely appeared in modern-day Asians. This meant Native Americans likely arose from a single population of people who had lived in Beringia, isolated for many years.

20多年前，穆里根提出，只发生了一次从白令陆桥到"新世界"的迁徙。她通过分析现代美洲原住民的DNA遗传变异，并将其与亚洲的遗传变异进行比较，得出了这一结论。她所研究的所有美洲印第安人都出现了同样的罕见模式，但这种模式很少出现在现代亚洲人当中。这意味着美洲原住民很可能仅仅来自居住在白令陆桥的人类，因为他们在那里与世隔绝很多年。

In 2015, a study using more advanced genetic techniques came to a similar conclusion. Rasmus Nielsen of the University of California, Berkeley, US, and colleagues found that the "vast majority" of Native Americans must have originated from just one colonisation event.

2015年的一项研究通过使用更先进的遗传技术得出了类似的结论。美国加利福尼亚大学伯克利分校的拉斯姆斯·尼尔森（Rasmus Nielsen）及其同事发现，美洲原住民中的"绝大多数人"肯定仅仅源于一次殖民事件。

"There's been no turnover or change in the population group as some people had previously hypothesised," says Nielsen. In fact, about 80% of Native Americans today are direct descendants of the Clovis people, who lived across North America about 13,000 years ago. This discovery came from a 2014 genetic study of a one-year-old Clovis boy who died about 12,700 years ago.

尼尔森说："正如此前有些人的假设，人口并没有发生更替或变化。事实上，今天约有80％的美洲原住民是克洛维斯人（Clovis）的直系后裔，他们在大约13,000年前在北美洲生活。这一发现来自2014年的基因研究。该研究是关于一名克洛维斯一岁男婴，他大约在12,700年前死亡。

But we now know there must have been staggered migrations from Beringia.

但是，我们现在知道从白令陆桥来的移民一定是分批次的。

That is because there are small groups of people in the Amazonian region of South America – such as the Suruí and Karitiana – with additional mysterious "arctic gene flow", unrelated to the Clovis boy. Another 2015 study therefore proposed there was more than one "founding population of the Americas".

那是因为在南美洲的亚马逊地区有小规模的族群带有神秘的"北极基因流"，比如苏鲁人（Suruí）和卡利吉亚纳（Karitiana）。他们与克洛维斯男婴无关。因此，2015年另一份研究报告提出有不止一批"美洲始祖"。

The indigenous populations of the Americas, the team found, have distant genetic links in common with people of Australia, Papua New Guinea and the Andaman Islands.

该研究团队发现，美洲的土著人口与澳大利亚、巴布亚新几内亚（Papua New Guinea）和安达曼群岛（Andaman Islands）的人有着遥远的基因联系。

This means, says Pontus Skoglund of Harvard University in Boston, Massachusetts, that people came into Beringia over different times during the "standstill" and went on to populate different parts of the Americas. Those early dispersals are still reflected by differences in the genomes of people living today.

马萨诸塞州波士顿哈佛大学（Harvard University in Boston, Massachusetts）的蓬托斯·斯各格兰德（Pontus Skoglund）说，这意味着，来到白令陆桥的人们在"滞留"期的不同时间继续前进，占据了美洲的不同地区。人口的早期分散仍然体现在今天生活在这里的人群的基因组差异中。

"It wasn't simply a single homogenous founding population. There must have been some type of patchwork of people, and maybe there were multiple pulses," says Skoglund.

斯各格兰德说："始祖不是单一的族群，而是多个族群拼凑起来的。"

In other words, the Beringian inhabitants did not all arrive or leave at the same time.

换句话说，白令陆桥的居民并不是在同一时间到达或离开。

This makes sense when you consider that Beringia was not a narrow land bridge with ocean on either side. "It was a huge region about twice the size of Texas," says Elias. The people living there would have had no idea that it was a land bridge at all. "There were no sign posts saying they were leaving Siberia."

当考虑到白令陆桥不是一座两面临海的狭窄陆桥时，这就可以说得通。"这是一块巨大的地区，是德克萨斯州的两倍。"埃利亚斯说。居住在那里的人根本不知道这是一座陆桥。 "没有任何路牌提醒说他们正在离开西伯利亚。"

This makes it highly likely that there were different groups of Beringian inhabitants that never met.

所以，很有可能不同的白令族群从未相遇。

A study published in February 2017 strengthens this idea further. After examining the shapes of 800- to 500-year-old skulls from Mexico, researchers found they were so distinct, the people the skulls belonged to must have remained genetically isolated for at least 20,000 years.

2017年2月发表的一项研究进一步加强了这一看法。研究人员检查了墨西哥500至800年前的头骨形状，结果发现这些头骨非常独特，其遗传分离发生在至少两万年前。

To understand who the first Americans really were, we have to consider when they arrived. While the exact timing is hard to pin down. Nielsen's work gives some insight. By sequencing the genomes of people from the Americas, Siberia, and Oceania, he and colleagues could understand when these populations diverged. The team concludes that the ancestors of the first Americans came to Beringia at some point between 23,000 years and 13,000 years ago.

要了解第一批美洲人的实际身份，我们必须考虑他们是什么时候到达的，虽然确切的时间很难确定。尼尔森的工作提供了一些有价值的看法。通过对美洲、西伯利亚和大洋洲人的基因组进行排序，他和同事们了解了这些人口何时分道扬镳。该团队得出结论，第一批美洲人的祖先在23,000年至13,000年前的某个时刻来到了白令陆桥。

We now have archaeological evidence to suggest that the people who left Siberia – and then Beringia – did so even earlier than the 23,000-year-limit proposed by Nielsen and colleagues. In January 2017, Lauriane Bourgeon and her team found evidence of people living in a cave system in the northern Yukon Territory of western Canada, called the Bluefish Caves, that dates to as early as 24,000 years ago. It was previously believed that people had only arrived in this area 10,000 years later.

我们现在有考古证据表明，先离开西伯利亚，然后离开白令陆桥的人的迁徙时间比尼尔森及其同事提出的23,000年的极限更早。2017年1月，劳里安·布尔根及其小组发现证据表明，在加拿大西部育空地区（Yukon Territory）"蓝鱼洞"系统中早在24,000年前就有人类活动了。以前，据信人类在一万年后才到达这个地区。

"They reached Beringia as early as 24,000 years ago, and they remained genetically and geographically isolated until about 16-15,000 years ago, before dispersing south of the ice sheets that covered most of North America during this period," says Bourgeon.

布尔根说："他们早在24,000年前就到达了白令陆桥，并在遗传和地理上保持隔离，直到大约16,000至15,000年前，此后分散到这个时期覆盖北美大部分地区的冰盖的南部。

The caves "were only used on brief occasions for hunting activities", she says. "We found cut marks on bones from horse, caribou and wapiti, so we know that humans were relying on those species."

这些洞穴"只用于短暂的狩猎活动"，她说，"我们发现马、驯鹿和麋鹿的骨头上有切痕，所以我们知道人类仰赖这些物种生存。"

This work provides further evidence that people were in the Beringia area at this early date. But it does not reveal the exact dates these people first ventured further south.

这项研究提供了进一步的证据表明，人类早就来到白令陆桥。但这并未揭示这些人第一次进一步向南进发的确切日期。 

For that, we can turn to archaeological evidence. For decades, stone tools left by the Clovis people have been found throughout North America. Some date to as early as 13,000 years ago. This might suggest that humans moved south very late. But in recent years evidence has begun to emerge that questions this idea.

为此，我们可以转向考古证据。几十年来，克洛维斯人留下的石器遍及北美。有些可以追溯到13,000年前。这可能表明人类南迁可能很晚。但是近年来开始出现一些证据对这个看法提出质疑。

For instance, at a site called Monte Verde in southern Chile, there is evidence of human occupation that dates between 14,500 and 18,500 years ago. We know these people built fires, ate seafood and used stone tools – but because they did not leave any human remains behind, much about this early group remains mysterious.

例如，在智利南部的蒙泰韦尔德区（Monte Verde），人类活动的证据可以追溯到14,500年至18,500年前。我们知道这些人会生火，吃海鲜，使用石器——但是由于他们没有留下任何人类的遗迹，所以这个早期人群的大部分情况依然很神秘。

"We really know little about them, because most preserved remains are stone tools and sometimes bones of animals, thus technology and diet," explains Tom Dillehay of Vanderbilt University in Tennessee, US, who is studying these people. "Monte Verde in south-central Chile, where I am at present, has several organic remains – animal hide, meat, plant remains that reveal a wider diet, wood technology – but these types of sites are rare to find."

美国田纳西州范德堡大学（Vanderbilt University in Tennessee, US）的汤姆·迪耶尔（Tom Dillehay）解释说："我们对他们知之甚少，因为大部分保存下来的遗迹都是石器，还有动物的骨头，所以只能了解他们的技术和饮食。智利中南部的蒙泰韦尔德区目前发现了几处有机遗骸——兽皮、肉、植物遗迹，这显示出更广泛的饮食和木工水平——但是这种遗迹很难找到。"

Another conundrum remains. Ice sheets still covered North America 18,500 years ago, making journeying south difficult. How did people arrive in southern Chile so early?

另一个难题仍然存在。18,500年前，冰盖仍然覆盖着北美，前往南部很难。人类如何那么早抵达智利南部？

A leading idea had been that an ice-free corridor opened up, which allowed humans to travel south. However, the latest evidence suggests this corridor only opened about 12,600 years ago, long after these early Chileans arrived.

一个主导的思路是，当时开出了一条无冰的走廊，使人们能够向南迁徙。然而，最新的证据表明，这条走廊只可能在大约12,600多年前开放，但在那之前很久人类就已经到达智利了。

Elias also points out how difficult this journey would have been. "Even if there was a small gap in between these enormous ice sheets, the environment left in that gap would have been so horrible, with mud, ice, meltwater and slush. It would not have been a habitable place for people or the animals they would have wanted to follow," he says.

埃利亚斯还指出了这次旅程的难度。"即使这些巨大的冰盖之间存在很小的距离，在这个缝隙中的环境是非常可怕的，到处都是泥、冰、融水和泥浆。寻找宜居之地的人或动物是不会顺着这条路走的。"他说。

There is an alternative. These early people could have travelled by boat, taking a route along the Pacific coast. There is no archaeological evidence to support this idea, but that is not entirely unexpected: wooden boats are rarely preserved in the archaeological record.

还有一个选择是这些早期的人类可以沿着太平洋海岸乘船往南。没有考古证据支持这个看法，但这并不是完全意想不到的：木船在考古记录中很少能保存下来。

There are still many unanswered questions, but Mulligan says that studying how and when early hunter-gatherers spread across the Americas can help us to understand the process of migration itself. That is, how population sizes change and which genetic traits persist.

仍然有许多尚未得到解答的问题。但是，穆里根说，研究早期的狩猎采集者如何以及何时遍布美洲可以帮助我们了解人类迁徙过程本身。也就是说，人口规模如何变化以及遗传特征如何延续。

In many ways, the peopling of America presents scientists with a golden opportunity to study these processes. There have been multiple migrations both into and out of other regions of the world – Africa, Europe and Asia, for instance. But the people who moved into the Americas were on a one-way journey. "We know the original inhabitants came from Asia into the New World with no other people there, and no major back migrations, so it's the simplest model you can conceive of."

在许多方面，人类迁入美洲为科学家们提供了研究这些过程的良机。在世界其他地区，例如非洲、欧洲和亚洲，人类进行了多次迁移。但是，进入美洲的人进行的是单程旅行。"我们知道最早的居民是从亚洲来到新世界的，当时的美洲没有人类生活，后来也没有发生重大的回迁，所以这是你可以想到的最简单的模式。"

That it was a one-way journey, coupled with the increased interest in studying the genetics of these ancient people, means we should soon understand even more about who these first Americans really were, and exactly when they arrived.

这是一次单程旅行，加上研究者对这些古代人的遗传学研究的兴趣越来越强烈：这意味着我们应该很快就能进一步了解第一批美洲人真正的身份以及他们具体是何时到达美洲。

来源：好英语网