【经济学人】熊猫，你的亲戚有哪些？丨2017.01.21丨总第792期

CONVERGENT evolution—the arrival, independently, by different species at the same answer to a question posed by nature—is a topic of great interest to biologists. One aspect of the phenomenon which has not yet been much looked at, however, is its underlying genetics. In particular, an issue not previously addressed is how often such changes arise from similar mutations in the two convergent lines, and how often they have different genetic causes that happen to have similar effects on the organisms’ forms and functions. That has now been rectified by an examination of two creatures which, though only distantly related, share an unusual feeding habit, an unusual anatomical feature and an unusual name: panda.

趋同进化是生物学家们有着极大兴趣的话题，它是指在自然作用下，不同物种独立的共同进程。然而该现象在潜在基因方面尚未得到许多的关注。尤其是在两条趋势线中来自相似基因突变引起趋同变化的频率，以及不同基因对生物的形态功能起到相似作用的概率的方面，尚未得到解决。如今通过对两种生物的检验已得到纠正，虽然这两种动物是远亲，但他们都具有与众不同的饮食习性、解剖特性以及一个不寻常的名字：熊猫。

• mutation [mjuː'teɪʃ(ə)n]  n.突变

• anatomical [ænə'tɒmɪk(ə)l] adj.解剖的

注：convergent evolution——趋同进化：不同的物种在进化过程中，由于适应相似的环境而呈现出表型上的相似性。也指不同起源的蛋白质或核酸分子出现相似的结构和功能。

The giant panda is a black and white bear. The red panda is related to weasels, raccoons and skunks. Their habitats—mountainous areas of southern China and its neighbours—overlap, but their last common ancestor lived 43m years ago. They do, though, share a limited kinship, for both are members (along with dogs, cats, hyenas, mongooses, seals and so on) of the mammalian order Carnivora. Which is curious, because both are vegetarian.

大熊猫是一种黑白相间的熊。小熊猫与鼬鼠，浣熊和臭鼬具有亲属关系。他们的栖息地在华南山区且近亲重叠，在4300万年前，他们有着共同祖先。尽管如此，由于它们都是食肉目哺乳动物类（像狗，猫，鬣狗，猫鼬，海豹等），所以确实有一些相同的血缘关系。令人好奇的是它们都是食草动物。

• weasel ['wiːz(ə)l] n.鼬鼠

• skunk [skʌŋk] n.臭鼬

• hyena [haɪ'iːnə] n.鬣狗

• mongoose ['mɒŋguːs] n.猫鼬

• carnivora  [kɑr'nɪvərə] n.食肉类; 食肉目

浣熊

More intriguing still, both subsist almost entirely on bamboo (some etymologists think their mutual name is derived from the Nepali phrase nigalyaponya, meaning “bamboo-eater”). And most curiously of all, both have a sixth digit on their forepaws—a kind of ancillary thumb derived from one of the bones of the wrist that helps them hold bamboo stalks for consumption.These common features led Hu Yibo of the Institute of Zoology, in Beijing, and his colleagues, to wonder if the two vegetarian carnivores also shared genetic modifications that might explain those features. And, as Dr Hu observes in a paper just published in the Proceedings of the National Academy of Sciences, they do.

更有趣的是，它们几乎完全以竹子为食（一些词源学家认为它们的共同名字源于尼泊尔语nigalyaponya，指“食竹者”）。最令人惊奇的是，它们的前爪上都长有第六指，是从腕骨长出用来帮助它们在进食时拿住竹茎的辅助拇指。基于这些共同特征，北京动物研究所的胡一波和他的同事们设想，这两种食肉目食草动物是否共有一种能解释这些特征的修饰基因。正如胡博士刚刚在《美国国家科学院院报》发表的论文中所说的，它们确实共有。

• Intriguing ['ɪntriːgɪŋ] 有趣的

• Ancillary [æn'sɪlərɪ] 辅助的

To search for such genetic commonalities, Dr Hu and his colleagues compared the DNA of the two pandas with that of four other members of the Carnivora: polar bears (close relatives of giant pandas), ferrets (close relatives of red pandas), and tigers and dogs (close relatives of neither). If pandas share features of their DNA with each other, but not with the four comparison species, he reasoned, then it is likely that those features encode recent adaptations common to the two of them.

为了找到这样的遗传共性，胡博士团队将两只熊猫的DNA与另外4种食肉目动物（北极熊（大熊猫的近亲），白鼬（小熊猫的近亲），老虎和狗（非两者近亲））的DNA进行比较。如果熊猫们有相同的DNA特征，而四种对照物种没有熊猫所共有的DNA特征，他则推理很有可能这些DNA特征编码了它们两者间近代的共同特性。

• Ferret ['ferɪt] 雪貂

Altogether, the team identified 70 genes (out of the 20,000 or so that mammals have) which sport bits of DNA that seemed to be shared. They also found ten genes which have been disabled by crippling mutations in both of the pandas, but not in the other four species. Not all of the shared genetic features obviously tied in with the shared peculiarities of pandas, but some did. These fell into three categories: genes affecting anatomy, genes affecting appetite and genes affecting the digestion and metabolism of nutrients.

研究小组从哺乳动物约20000个基因中，确定了可以共有的70个DNA片段。他们也在两种熊猫中找到了十个因严重突变而丧失功能的基因，而其他四个物种中并未发现。尽管哺乳动物共有遗传特征并不都与熊猫的特性一致，但有些确实具有一定的关系。这分为三类：影响动物体结构的基因，影响食欲的基因和影响营养物质消化和新陈代谢的基因。

• peculiarity [pɪ,kjuːlɪ'ærɪtɪ] n.古怪; 怪癖; 特色; 奇形怪状;

• metabolism  [mɪ'tæbəlɪz(ə)m]  n.[生理]新陈代谢

The anatomy-related adaptations were those that seemed to control the development of the pandas’ second thumbs. Two genes in particular, DYNC2H1 and pericentrin, have mutations that cause identical changes in each type of panda in the proteins encoded by these genes. In mice, mutations in these genes are known to encourage extra digits to grow, so it is not unreasonable to suspect that they are also the cause of this in pandas.

与生物体结构相关的基因有可能控制熊猫第二拇指的生长。特别是DYNC2H1和中心粒周围蛋白这两种基因的突变，会导致在每种类型的熊猫中，由这两种基因控制编码的蛋白质产生相同变化。在小鼠中，这些基因的突变可导致小鼠额外足趾的生长，所以有理由认为熊猫第二拇指生长的原因也是基因突变。

• pericentrin  中心粒周蛋白

The appetite-modifying change involved one of the disabled genes. When working, this gene encodes a protein which forms part of the tongue’s taste buds for umami, a savoury “meatiness” separate from the other four tastes of sweetness, sourness, bitterness and saltiness. Umami perception is stimulated by glutamic acid, one of the 20 amino acids that make up proteins—but one that is more characteristic of animal proteins than plant ones. Sensitivity to umami is valuable to a carnivore but unnecessary (and possibly harmful) to a herbivore.

食欲修饰基因的改变是丧失功能的基因中的一个。该基因在工作时，会编码一种组成舌头味蕾中鲜味的蛋白质，是区别于酸甜苦咸四种味道的可口的“肉味”。鲜味感觉是由谷氨酸激发的产生的，它是组成蛋白质的20个氨基酸之一，但相比于植物蛋白，它更具有动物蛋白的特性。对鲜味的敏感程度对食肉动物而言非常重要，但对食草动物来说，这是不必要并且可能是有害的。

• umami [u'mɑmi] n.鲜味

• stimulate ['stɪmjʊleɪt]  v.刺激

• glutamic acid  谷氨酸

• amino acid [ə'miːnəʊ] [生化]氨基酸

• herbivore ['hɜːbɪvɔː] n.食草动物

蛋白质三维图

The other genetic convergences Dr Hu recorded were related to the digestion and metabolism of substances scarce in, or absent from, bamboo. He and his colleagues noted parallel changes in the genes for three digestive enzymes whose job is to liberate two particular amino acids, lysine and arginine, from proteins. Both lysine and arginine are abundant in meat, but in short supply in bamboo. The team also noted parallel changes in four genes that encode proteins involved in the metabolism of two vitamins, A and B12, and of arachidonic acid, a lipid essential for bodily function. All of these are scarce or non-existent in bamboo as well. Exactly how the genetic changes seen alter the effectiveness of the proteins involved remains to be determined. But the prediction would be that they enhance the availability of the nutrients in question.

胡博士记录的其他遗传转化与竹子中缺乏或缺失的物质的消化和代谢有关。他的团队发现三种消化酶基因相似的改变，这些消化酶的作用是从蛋白质中释放两种特殊的氨基酸，赖氨酸和精氨酸。肉类中富含赖氨酸和精氨酸，而在竹子中却很缺乏。该团队还注意到四种变化相同的基因，这些基因编码的蛋白质包括新陈代谢中所需的维生素A，维生素B12和机体功能必需的脂质-花生四烯酸。而这些在竹子中非常缺乏甚至不存在。基因变化具体是如何改变所涉及蛋白质的有效性仍有待确定。但可预测的是，它们增强了讨论中的营养素的可利用性。

• arachidonic acid  [ˈærəki'dɔnik] [ˈæsid] [有化]花生四烯酸

The upshot is that the two pandas do indeed seem to have similar genetics underlying their similar peculiarities. Such similarities are, admittedly, easier to find than different genetic routes to the same outcome would be. But Dr Hu has established that, at least in the case of pandas, natural selection has often taken the same paths to arrive at the same outcomes.

结论是：基于两类熊猫的相似特性，它们确实有相似基因。（期待您的翻译，明天会有针对这句话的长难句解析哟~）但是胡博士已经确定，至少在熊猫中，自然选择通常以相同的途径达到相同的结果。

• Upshot ['ʌpʃɒt] 结果

翻译 ▍hua外音、若水

审核 ▍云图

编辑 ▍璃儿