Dawn of the Din

鳴き声の進化 それは虫の声から始まった

By Michael B. Habib M. B. ハビブ
English 日本語 日本語
We take it for granted that virtually every habitat on Earth is alive with the sounds of animals, from the haunting songs of whales in the oceans to the riotous symphony of birds, frogs and insects in forests to the hubbub of humans and our technological creations in cities the world over. Yet for most of our planet’s history the only sounds were those of the wind, rain and waves.  地球上のほぼすべての生息地が動物の音でにぎやかなのは当然だと思える。海ではクジラのしみじみとした歌声,森では鳥やカエル,昆虫による大合唱,世界各地の都市では人間と人工物が立てる騒音が聞こえる。だが地球史の大半の期間,音を立てるのは風と雨,波だけだった。
In my work as a paleontologist, I seek to understand the lives of extinct animals—how they moved, what they ate, the sounds they might have made. I also serve as an animation and creature-design consultant for exhibits, television, movies and games. Among the most common topics I have been asked to tackle for these projects are those pertaining to animal sounds. Whether someone is reconstructing long-vanished pterosaurs for an academic study or designing a creature for a blockbuster film, sound is paramount in bringing both past and imaginary worlds to life.  私は古生物学者として絶滅動物が生きていたときの様子を,つまりどのように動き,何を食べ,どんな音を立てていたのかを理解しようとしている。また,展覧会やテレビ,映画,ゲームに使われるアニメーションや生物デザインのコンサルタントを務めている。そこでよく受ける相談の1つが,動物が立てる音に関するものだ。学術研究のためにはるか昔に絶滅した翼竜を再現するのであれ,超大作映画のために生物をデザインするのであれ,音は過去の世界や想像上の世界に生気を吹き込むのに最も重要な要素だ。
Recent insights into the evolution of animal acoustics have led to a new understanding of how our modern-day soundscapes came to be. Fossils reveal when the major types of sound-production—and sound-detection—structures appeared in the forerunners of today’s invertebrate and vertebrate creatures. And in some cases, clever modeling has allowed scientists to re-create the ancient sounds themselves. Many details remain to be worked out, but we can now begin to piece together the dawn of the din.  動物の音の進化に関する最近の知見から,現代の音風景(サウンドスケープ)がどのように作り上げられたのかに関する新たな理解が得られた。化石から,発音器官と聴覚器官の主なタイプが無脊椎動物と脊椎動物の祖先でそれぞれいつ出現したかが明らかになった。また,優れた模型を作ることによって古生物の音そのものを再現した研究例もある。詳細の多くはまだわかっていないが,地球がにぎやかになり始めた時代の様子が浮かび上がってきた。
The fossil record indicates that life on Earth got its start 3.7 billion years ago. But those earliest organisms—including microbes and, much later, soft-bodied animals similar to today’s jellies—were a quiet bunch. It was not until the evolutionary burst that occurred in the Cambrian period, between 541 million and 485.4 million years ago, that animals acquired some basic sound-making behaviors related to locomotion and predation. Yet even then the hush under water, where these creatures lived, was probably punctuated only by the skittering of arthropod feet across sand or the faint grinding of a cephalopod breaking a shell. Meanwhile the terrestrial realm remained essentially silent. More than 200 million years passed before the buzzing of insects started to fill the air, giving rise to an entirely new acoustic world.

The oldest-known putative insect dates to 408 million years ago and was probably soundless and deaf. Scientists do not know exactly when insects started to first make or hear sounds, but the fossil record provides a minimum date: a katydid from around 250 million years ago has the sound-producing anatomy characteristic of this group. The earliest-known fossils of cicada relatives also date to this time. These insects can generate exceptionally loud sounds by rapidly buckling and unbuckling drumlike structures on their bodies called tymbals.  知られる限り最古の昆虫とみられる生物は4億800万年前のものだが,おそらく音を出すことも聞くこともできなかった。昆虫が音を出したり聞いたりし始めた正確な時期は不明だが,化石記録から2億5000万年前よりも前であることがわかっている。この時期のキリギリスにはこのグループ特有の音を出すための解剖学的特徴があった。既知で最古のセミの近縁種の化石もまたこの時期のものだ。セミは「発音膜」という太鼓のような器官を高速で振動させることで非常に大きな音を出すことができる。