经济学人下载:法医动物学 保护大象刻不容缓

Science and technology
科学技术

Forensic zoology
法医动物学

The elephant in the room
房间里的大象—保护大象，刻不容缓！

Dating ivory has just become easier. Poachers beware
确定象牙年代已变得更容易了，偷猎者们要小心喽！

FEW megafauna are more charismatic than elephants, and that charisma gives them political clout.
在大型动物里，没有几种动物可以匹敌大象的魅力，这种魅力让大象很有政治影响。

On July 1st, for example, Barack Obama used the Tanzanian leg of his tour of Africa to announce an executive order intended to give teeth to America's obligation, as a party to the Convention on International Trade in Endangered Species, to prevent the smuggling of poached ivory.
比如说今年7月1日，奥巴马总统在非洲行程中的坦桑尼亚站宣布了一项行政命令，该命令旨在通过强制实施有效手段来更好地履行美国《濒危野生动植物种国际贸易公约》的一员防止偷运偷猎象牙的义务。

The rules on trading ivory, though, are hard to enforce, for if it comes from an animal killed before 1990 such trade is legal.
但是，针对象牙贸易的规定很难实行，因为如果象牙来自的大象是在1990年之前被杀的，那么这种贸易是合法的。

Not surprisingly, a cottage industry in making ivory look older than it is has grown up.
因此，让象牙看起来比实际年代更久的家庭手工业的发展壮大就并不奇怪了。

But a paper published in the Proceedings of the National Academy of Sciences, by Kevin Uno of the University of Utah and his colleagues, may deal with that.
犹他大学的Kevin Uno和他的同事发表在《美国国家科学院院刊》上的一篇论文可以解决这个问题。

For Dr Uno has worked out how to use one of science's less glorious episodes, the atmospheric testing of nuclear weapons, to work out exactly how old a piece of ivory really is.
因为Uno博士研究出了如何利用科学不甚光彩的一段—核武器大气层实验，来算出一节象牙的真实年代是多少。

Dr Uno's method uses the ivory's carbon-14 content in a way that was not previously employed.
博士Uno的方法用到了象牙的碳-14含量，他利用碳-14含量的方式从来没人用过。

What radiochemists call 14C forms naturally in the atmosphere by the action of cosmic rays on nitrogen atoms.
被放射化学家称作碳-14的物质是宇宙射线撞击空气中的氮原子而在大气中自然形成的，

It has a half-life of 5,730 years, which makes it ideal for dating objects pertinent to human history, and it can do so to within a few decades of their true age—which is great for archaeology.
其半衰期约为5,730年，这让其十分适合测量与人类历史有关事物的年代，其测量误差不超过其真实年代前后几十年。

It is not, though, much use for finding out whether a particular piece of ivory was detached from the elephant that grew it before or after a specific date just over 20 years ago.
但碳定年法在测量象牙年代，看其生长的时期是在20年前的之前还是之后，则并无甚用武之地。

But Dr Uno realised there has recently been a second source of 14C—those bomb tests. And they give him the precision he requires.
但是Uno博士意识到最近碳-14还有另一个来源—那些核爆试验，而这些试验给了他他所想要的精度。

Normally, the amount of 14C in the atmosphere is governed by the rate at which cosmic radiation creates it and the rate at which things like photosynthesis absorb it.
通常来说，大气中碳-14的数量取决于宇宙射线产生碳-14的速率和像光合作用一类的反应吸收碳-14的速率。

Between 1952 and 1962, however, when bomb tests above ground were commonplace, the amount of 14C in the air shot up until it was nearly double the normal level.
但是，在1952至1962年间，地面上的核爆试验十分普遍，因此空气中的碳-14数量骤升，达到了近正常值的两倍。

Since then it has fallen, also quite steeply, as plants have absorbed the surplus.
但自那以后，碳-14的数量也急剧下降，因为植物把剩余的碳-14吸收掉了。

And it will continue to fall until the old equilibrium reasserts itself.
并且碳-14的值会不断下降，直到降到原来的平衡值。

This bomb curve, as it is known, changes so fast that year-by-year differences in the 14C levels of recent specimens should be detectable.
我们知道，这种爆炸曲线的变化如此之快，因此我们就可以探测出近期空气中每年碳-14值的不同。

To test this hypothesis, Dr Uno and his colleagues looked at 29 specimens of known age, from 1905 to 2008.
为对这一假想进行测试，Uno博士和他的同事研究了已知年代，即从1905年至2008年的29个样品。

These included elephants' tusks, teeth and tail hair, and hippopotamus teeth.
这其中包括大象的长牙、牙齿和尾部的毛发，还有河马的牙齿。

They measured the specimens' 14C content using a sensitive technique called accelerator mass spectrometry.
他们使用一项被称作加速器质谱的高灵敏度技术来测量样品中碳-14的含量。

For those tissues that had grown after 1955 the 14C concentration did, as the researchers hoped it would, closely match the bomb curve.
正如研究者们所预料的那样，对于1955年以后生长的组织，其碳-14浓度与爆炸曲线严格吻合。

Indeed, for these the match was so good that their ages could be determined to within a year of the truth.
的确，对于这些样品来说，吻合度如此之高，以至于对其年代的确定可精确到一年以内。

At the moment Dr Uno's technique costs 1,000 a pop, so some places, particularly poorer countries in Africa, might be reluctant to deploy it.
由于Uno博士的技术每次要耗费一千美元，因此有些地方，尤其是非洲更贫困的地区就可能不愿使用这种技术了。

But in the context of an illegal trade in ivory reckoned to be worth about 1 billion a year, that is not a huge amount of money.
但是，鉴于非法象牙贸易一年约价值十亿美元，这就不是一个大的数目了。

And if it helps preserve elephants, whose numbers in Africa have fallen from 1.3m to 600,000 in the past 40 years, many would see it as money well spent.
而且，如果这种技术有助于保护大象，那么很多人会认为这个钱花得很值，因为在过去的40年里，大象的数量已从一百三十万下降到了六十万。