鸟鸣之源

The melodious call of many birds comes from a mysterious organ buried deep within their chests: a one-of-a-kind voice box called a syrinx.

很多鸟儿们动听的叫声是来自于一个深埋在它们胸腔内的神秘器官：一种独特的音箱，叫做鸣管。

Now, scientists have concluded that this voice box evolved only once, and that it represents a rare example of a true evolutionary novelty.

如今，科学家们已经得出结论，这种音箱只进化出过一次，而且它是一种真正的进化的新颖性的罕见代表。

“It’s something that comes out of nothing,” says Denis Dubuole, a geneticist at the University of Geneva in Switzerland who was not involved with the work.

“它属于那种无中生有的事物，”丹尼斯.杜博说道，他是瑞典日内瓦大学的一名遗传学家，并未参与此次研究。

“There is nothing that looks like a syrinx in any related animal groups in vertebrates. This is very bizarre.”

“在任何有亲缘关系的脊椎动物种群中，没有什么像这个鸣管一样。这是令人匪夷所思的。”

Reptiles, amphibians, and mammals all have a larynx, a voice box at the top of the throat that protects the airways.

爬行类，两栖类和哺乳类动物都有喉部，这是位于咽喉顶部的可以保护气道的音箱。

Folds of tissue there—the vocal cords—can also vibrate to enable humans to talk, pigs to grunt, and lions to roar.

那里层叠的组织—声带—可以振动，使得人类可以说话，猪可以咕哝，狮子可以咆哮。

Birds have larynxes, too.

鸟类也有喉部。

But the organ they use to sing their tunes is lower down—where the windpipe splits to go into the two lungs.

不过它们用来唱出音调的器官位置更低—气管在哪里分裂进入两个肺。

The syrinx, named in 1872 after a Greek nymph who was transformed into panpipes, has a similar structure: Both are tubes supported by cartilage with folds of tissue.

鸣管，是在1872年以一个希腊女神来命名的，她被变成了牧笛，鸣管拥有类似的结构：和声带一样都是由软骨支撑的层叠的组织。

The oldest known syrinx belongs to a bird fossil some 67 million years old; that’s about the same time all modern bird groups became established.

最古老的鸣管属于一只六千七百万年前的鸟化石；那大概是现代鸟类开始建立的时间。

To figure out where the bizarre organ came from, Julia Clarke, a paleontologist at the University of Texas in Austin, who made the syrinx discovery in 2013, assembled a team of developmental biologists, evolutionary biologists, and other researchers.

为了找出这种奇异的器官从何而来，茱莉亚.克拉克，一名德克萨斯州立大学奥斯汀分校的考古学家，她在2013年对鸣管有所发现，她组建了一个由发育生物学家，进化生物学家和其他研究员组成的团队。

The group combed the literature and compared the anatomy, genetics, and development of bird syrinxes and larynxes from a range of modern reptiles.

这支团队梳理了文献，并对比了鸟类鸣管和一系列现代爬行类的声带的解剖学，进化学和发育学内容。

The organs are quite different—even more so than early biologists believed—they discovered.

他们发现，这种器官是非常不同的—甚至比之前生物学家们预计的更甚。

To work the vocal cords, larynxes depend on muscles that attach to that organ’s cartilage.

为了让声带振动，喉部要以来那些黏附到该器官的软骨的肌肉。

But the syrinx relies, at least in part, on muscles that in other animals extend from the back of the tongue to the bones that connect the arms to the body.

而鸣管依赖的，至少一部分，是那些在其它动物中从舌头背部延伸到连接胳膊和躯干的骨头的肌肉。

The two organs also appear to develop differently.

这两种器官似乎发育过程也有异。

The larynx is made from a mix of mesoderm and neural crest cells, which make up muscles and some facial bone and nerve cells, respectively.

喉部似乎是由中胚层和神经嵴细胞组成的，它们分别可以组成肌肉和其他的面部骨骼和神经细胞。

But the syrinx is made of just mesoderm cells—there are no neural crest cells involved.

而鸣管全部是由中胚层细胞组成—没有涉及到神经鞘细胞。

“It presents a rather interesting rare case of how new structures and developmental programs evolve,” Clarke says.

“这就代表了一种非常有趣而罕见的情况，表明新的结构和发育程序进化了出来，”克拉克说道。

These differences, however, still resulted in organs with the same function.

然而，这种差异仍然造就了同样功能的器官。

Clarke and her colleagues suspect the ancestors of modern birds also had a larynx.

克拉克和她的同事们怀疑现代鸟类的祖先也是有喉部的。

Then, at some point before birds became birds, the cartilage in the windpipe just above the lungs expanded to form the syrinx.

后来，在鸟类真正进化为鸟类之前，气管中肺部上方的软骨进行了延伸从而形成了鸣管。

This expansion may have initially provided additional support for the split in the windpipe; eventually, it developed rings of muscle that enabled the complex avian sound repertoire heard today.

这种延伸可能最初为气道的分裂提供了额外的支撑；最后，它发展出了环状的肌肉成就了如今听到的复杂的鸟类的声音曲调。

Over millions of years, the syrinx took over sound production from the larynx, possibly because the syrinx was more versatile at producing a wide variety of sounds.

在百万年的时间里，鸣管渐渐取代了声带的发声功能，也许是因为鸣管在发出各种多样的声音发面更为万能。

This means that the syrinx is an evolutionary novelty, Clarke and her colleagues reported last week in the Proceedings of the National Academy of Sciences.

这意味着鸣管是一种进化的创新，克拉克和她的同事们上周在美国国家科学院院刊上发表了论文。

True novelties in evolution are hard to come by.

进化上真正的新事物是很难遇到的。

They are innovations—new traits or new structures—that arise without any clear connections to existing traits or structures.

它们是一种创新—新的特点或新的结构—它们的产生与已有的特点或结构并没有任何明显的联系。

Most previously suspected novelties, such as fingers and toes in land animals, have turned out to be the result of evolution tinkering with something that already exists, like fish fins in the case of fingers and toes.

大部分以前认为是创新的东西，比如陆地动物的手指和脚趾，最后证明是已经存在的事物的进化调整，比如在手指和脚趾的情况中，是从鱼鳍进行调整得来的。

Such new innovations can “trigger further evolutionary steps,” says Johannes Müller, a paleozoologist at the Museum of Natural History in Berlin.

而这种新的创新则“可以引发进一步的进化阶段，”乔纳斯.穆勒说道，他是柏林的自然历史博物馆的一名古动物学家。

By enabling songs to get more complex, he adds, the syrinx could have prompted birds with new variations of their songs to split into new species.

通过使得鸣唱更加复杂，他补充道，鸣管还推动了鸟类发展出新的变异，分裂成了不同的新品种。

And the study may have implications beyond avian crooners.

这项研究的意义可能不仅仅局限于鸟叫声。

Behavioral ecologist Richard Vogt from the National Institute of Amazonian Research in Manaus, Brazil, says it gives him a starting point to search for the structures that make sounds in turtles.

来自巴西玛瑙斯的亚马逊国家研究所的行为生态学家理查德.沃格特说，这给了他一个开始寻找龟类发声结构的起点。

Since 2008, Vogt and conservation biologist Camila Rudge Ferrara of the Wildlife Conservation Society in Manaus have shown that turtles, particularly social species, make a variety of sounds, even in their egg cases.

从2008年起，沃格特和来自玛瑙斯的野生动物保育协会的保育生物学家卡梅莉亚.鲁奇.费拉拉就曾表明了，海龟，尤其是群居的海龟，会发出各种各样的声音，甚至是在它们的蛋壳里。

It’s currently unclear whether they are using their larynx or generating these noises in just their mouths.

目前还不清楚它们是用声带还是仅仅靠嘴来发出声音。

Neither turtles nor the later-evolving crocodiles has a syrinx, says Nicolas Mathevon, an ethologist at the University of Lyon/St. Etienne in France, who studies the sounds crocodiles and their relatives—the only modern representatives of dinosaurs apart from birds—make.

而无论海龟还是后来进化出的鳄鱼都没有鸣管，尼古拉斯.马特凡说，他是法国里昂/圣埃蒂安大学的一名生态学家，他研究的是鳄鱼和它们的近亲—它们是除了鸟类之外恐龙的唯一现代代表—的发声。

Crocodiles diverged from birds 240 million years ago, and many are famous for their calls.

大约两亿四千万年前，鳄鱼从鸟类中分支出来，很多的鳄鱼都以其叫声而闻名。

But crocs have a very basic larynx, with structures that vibrate in airflow.

但是鳄鱼们拥有的非常基础的喉部，其中带有能在气流中振动的结构。

If the syrinx evolved as birds came into existence, then “some dinosaurs may have had two sound sources,” Mathevon says.

假如鸣管是随着鸟类出现而进化的，那么“有些恐龙可能就会有两种声音来源，”马特凡说道。

“Maybe one day we will find a fossil of a dinosaur with a larynx together with a syrinx.”

“也许有一天，我们会找到一个既有喉部又有鸣管的恐龙的化石。”

对于鸟类鸣管的进化，朋友们有什么看法呢？欢迎给amber留言哦！

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