An ancient murder-mystery

　　一个古老的谋杀之谜

　　What killed the woolly rhino?

　　是谁杀死了长毛犀牛?

　　From the moa in New Zealand to the dodo inMauritius, the arrival of humans has often spelled extinction for tasty butpreviously isolated animals. Many scientists had assumed that the woollyrhinoceros, a shaggy beast that sported an enormous horn, suffered the samefate. The animal was common in northern Europe and northern Asia 30,000 yearsago, when the first humans arrived. Shortly after, it disappeared.

　　从新西兰的恐鸟到毛里求斯的渡渡鸟，人类的到来往往意味着这些美味可口但曾与世隔绝的动物将惨遭灭绝。许多科学家认为，长毛犀牛(一种身披长毛、长着巨角的动物)也遭受了同样的命运。3万年前，在人们最早到来之际，长毛犀牛在北欧和北亚都很常见，但不久之后就灭绝了。

　　But Love Dalén, a professor at the Centrefor Palaeogenetics in Stockholm, and Edana Lord, one of Dr Dalén’s PhDstudents, are not so sure. In a paper published in Current Biology, they usedata from ancient DNA to argue that, this time at least, humans might beinnocent.

　　但是斯德哥尔摩古基因学中心的洛夫教授及其博士生伊达娜并不认为是人类致其灭绝的。在一篇发表在《当代生物学》上的论文中，他们利用来自远古时期DNA的数据证明，至少就这一次，人类或许被冤枉了。

　　Until recently, information on the fate ofthe great ice-age mammals had been limited to what could be gleaned fromfossilised bones. While useful, bones can only tell you so much. They canreveal the number of animals of different ages present at a specific locationat a specific time. With some species sex can be determined. Occasionally thecause of death can be detected.

　　直到最近，有关冰河时代大型哺乳动物命运的研究还仅限于从骨骼化石中收集信息。骨骼化石虽然有用，但所能得到的信息非常有限。它们可以揭示在特定时期、特定地点出现的不同年龄动物的数量。有些物种甚至可以利用骨骼化石来判断性别，有时利用骨骼化石还能推断出动物死因。

　　In the past couple of decades, though,scientists have learned to tap another, richer source of information: ancientgenomes. By itself, DNA degrades quickly, attacked by water and sunlight. ButDNA encased within bones and teeth can survive for longer, especially if thosebones and teeth are themselves encased in permafrost. It was this sort of DNAthat enabled Dr Dalén and Ms Lord to investigate the woolly rhino’sdisappearance.

　　不过，在过去几十年里，科学家们学会了另一种挖掘更多信息的方式：远古基因组。DNA在水和阳光的作用下会迅速降解。但包裹在骨骼和牙齿中的DNA可以留存恒久，尤其是当这些骨骼和牙齿还被埋藏在永久冻土中时。正是这种DNA使戴伦和洛德得以对长毛犀牛灭绝的原因展开调查。

　　Working with a team of colleagues, theresearchers obtained DNA from 12 woolly-rhinoceros bones collected frompermafrost in Siberia, dating from the beginning of the Late Pleistocene, about130,000 years ago, until the animals were on the verge of extinction. Extra DNAwas recovered from one sample of rhino hair and one piece of tissue found inthe stomach of a frozen wolf that had been preserved by the cold.

　　研究人员齐心协力从在西伯利亚永久冻土带采集的12块长毛犀牛骨骼中提取了DNA，这些骨骼最早可追溯至大约13万年前的更新世晚期，最晚至长毛犀牛濒临灭绝之时。此外，研究人员还从一头长毛犀牛的毛发样本以及在一只被冰冻的狼的胃里发现的一块长毛犀牛组织上提取到了DNA。

　　Analysing the genetic diversity of thesamples allowed the researchers to make a rough calculation of the size of thewoolly-rhino population over time. Rather than declining as humans arrived, thepopulation remained stable from 29,000 years ago until 18,500 years ago, just afew thousand years before the species went extinct.

　　通过对样本进行遗传多样性分析，研究人员能够粗略计算出长毛犀牛数量随时间变化的趋势。长毛犀牛的数量并没有随着人类的到来而减少，从2.9万年前至1.85万年前(此时距离长毛犀牛灭绝不过几千年)一直保持在一个稳定的水平。

　　That suggests that, far from being huntedto extinction, the rhinos co-existed stably with humans for around 10,000years. Perhaps the people who encountered the beasts found them unpalatable. Orperhaps the rhinos were simply too dangerous to hunt with their simple weapons.(They were the size of the modern white rhino, which is not an animal thattakes kindly to being stabbed with spears.)

　　这表明，长毛犀牛非但没有被人类猎杀至灭绝，反而与人类共同生存近1万年。或许是人们觉得长毛犀牛的肉不好吃。亦或是捕猎长毛犀牛太过危险，以致无法用简单的武器将其猎杀。(长毛犀牛的体型与现代白犀牛相当，而用长矛根本无法对白犀牛造成伤害)。

　　The researchers’ case is not quiteconclusive. It is possible that some sort of technological advance eventuallygave ancient humans the ability to hunt rhinos safely, and that extinctionfollowed after that breakthrough. On the other hand, the animals’ decline linesup suggestively with a rapid bout of global warming that began around 14,700years ago. The researchers argue that this was the more likely cause of theanimal’s disappearance. This time, it seems, it was Mother Nature whodunnit.

　　研究人员尚未得出确切结论。或许是某项技术的进步使古人类得以安全猎杀长毛犀牛，而长毛犀牛也就随着这项技术的突破惨遭灭绝。另一方面，1.47万年前，全球气候变暖趋势急剧加速，而这一时期恰恰是长毛犀牛数量锐减之时。研究人员认为，这更有可能是长毛犀牛灭绝的原因。这一次，大自然母亲或许才是真凶。

　　注：双语全文源自经济学人

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