请勿随地乱吐口香糖

ABC Gum

被人嚼过的口香糖你可能不是特别感兴趣,但是对考古学家来说,只要口香糖年代够久远,就是一座基因的金矿。瑞典乌普萨拉大学的考古学研究生纳塔莉雅说这就像侏罗纪公园。她提到电影当中的著名桥段,侏罗纪公园的科学家从琥珀里的蚊子标本当中提取血液,找到了恐龙的基因。

只是纳塔莉雅找到的人类基因不在琥珀里,而在瑞典西海岸一个捕猎渔村遗址发掘出的年代异常久远的口香糖里。

这些样本看上去就像一坨坨被嚼过的现代口香糖。当然,跟绿箭口香糖不一样,考古学家发现的是从白桦树树皮中蒸馏出的焦油残渣,又黑又稠。纳塔莉雅说,我嚼过这种口香糖的现代版,再不想尝第二场,除非有人给我钱。

那古人干嘛要嚼这么难吃的东西,他们可能并不是为了让口气更清新,而是用口香糖来封补船只或者盆盆罐罐的缺口,所以古人的口香糖一般是日常用途。这些口香糖很多都留下了齿印,很可能是古人通过咀嚼让口香糖成形,久而久之嚼成了习惯,就像当代也有一些人习惯咀嚼烟草一样,只是味道不可同日而语。

纳塔莉雅的研究团队从古老的口香糖中提取基因进行排序,结果发现嚼口香糖的一共三人,两女一男。这是在斯堪迪纳维亚发现的最古老的人类基因样本,可以追溯到大约公元前八千年。这些基因更像是来自西欧采猎部族,而不是东欧。这也为我们研究古人如何来到现在的瑞典提供了一些线索。这项研究发表在通讯生物学杂志上。

发掘出的口香糖可能还会带来其它线索,比如古人的饮食,古人的口腔细菌等等。既然可以从古人的口香糖中发现如此多信息,我们现在把它们粘在桌椅底下,对未来的考古学家来说岂不更好。纳塔莉雅说,我们不能乱吐口香糖,应该把口香糖扔进垃圾箱里,不过,她说一万年前的古人随地乱吐就没问题。他们当时就该随地乱吐,他们吐得很好。

原文

You're probably not too interested in what some people call ABC gum - already been chewed. But for archaeologists, such gum - as long as it's really old - is a genetic gold mine. "It's a bit like Jurassic Park." Natalija Kashuba, a graduate student in archaeology at Uppsala University in Sweden. She's referring to that famous clip from the movie, about how Jurassic Park scientists extract blood from a mosquito trapped in amber, "and bingo, dino DNA."

Except in this case it's human DNA, and it's trapped not in amber, but in exceptionally old chewing gums found at the site of an ancient hunting and fishing village on the west coast of Sweden. The samples look just like chewed-up wads of modern-day gum. But don't think Wrigley's - his detritus is black, sticky tar distilled from birch bark. Kashuba has tasted modern-day versions and isn't eager to try it again. "Not unless I'm paid for it."

So why chew something so unpleasant? Maybe because their gum wasn't for fresh breath. "You could use it to seal your boat, or like seal your pots, so it's an everyday-use type of substance." Many of the gums have teeth marks, too, so perhaps they chewed it to help shape it and in turn developed a habit, despite the taste, that today's tobacco chewers might relate to.

Kashuba's team extracted and sequenced DNA from the ancient gum, and they found genetic evidence of three different gum chewers - two women and a man. It's the oldest human DNA found in Scandinavia, dating to about 8,000 B.C. And because it more closely resembles the DNA of hunter-gatherers from western Europe than from eastern Europe, it also provides hints about how people ended up in what's now Sweden. The results are in the journal Communications Biology.

The gum could still hold other clues about ancient diets or the bacteria these people had in their mouths. Given that we can learn so much from chewing gum, is it really so bad to stick it to the bottom of chairs and tables? You know, for the benefit of future archaeologists? "I think you should definitely throw it in the bin. But I won't blame these guys who spat it out 10,000 years ago. They did a good job then."

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