字幕表 動画を再生する
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Translator: Joseph Geni Reviewer: Morton Bast
翻訳: Chiaki Takeuchi 校正: Misaki Sato
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This is poo,
これはフンです
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and what I want to do today is share my passion
今日はフンに懸ける私の思いを
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for poo with you,
共感して頂きたいと思います
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which might be quite difficult,
できなくても構いません
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but I think what you might find more fascinating
しかしこの小さな生物と フンの関係には
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is the way these small animals deal with poo.
興味を持てるのでは ないでしょうか
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So this animal here has got a brain
この生物の脳は
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about the size of a grain of rice, and yet it can do things
米粒ほどの大きさです しかし人間なら
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that you and I couldn't possibly entertain the idea of doing.
試みることもないことを 彼らはするのです
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And basically it's all evolved to handle its food source,
つまり彼らの食糧源である
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which is dung.
フンの扱い方です
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So the question is, where do we start this story?
さて何から話しましょう?
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And it seems appropriate to start at the end,
やはりここはお尻からが いいでしょう
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because this is a waste product that comes out
これは他の動物が出す 排泄物ですが
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of other animals, but it still contains nutrients
まだ栄養が残っています
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and there are sufficient nutrients in there
フンコロガシが生きていくのに
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for dung beetles basically to make a living,
十分な量の栄養素です
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and so dung beetles eat dung, and their larvae
彼らはフンを餌とし その幼虫も
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are also dung-feeders.
またフンを食べます
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They are grown completely in a ball of dung.
フンだけを餌にして 成長するのです
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Within South Africa, we've got about 800 species of dung beetles,
南アフリカには800種の フンコロガシがいます
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in Africa we've got 2,000 species of dung beetles,
アフリカ全体では2000種
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and in the world we have about 6,000 species of dung beetles.
世界では6000種です
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So, according to dung beetles, dung is pretty good.
彼らにとってフンは 相当のごちそうです
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Unless you're prepared to get dung under your fingernails
指でフンをほじくれなければ
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and root through the dung itself, you'll never see
フンコロガシ種の9割は
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90 percent of the dung beetle species,
お目にかかれません
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because they go directly into the dung,
彼らはフンの奥に
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straight down below it, and then they shuttle back and forth
入り込み 地上のフンと
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between the dung at the soil surface
地中の巣との間を
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and a nest they make underground.
何度も往復するからです
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So the question is, how do they deal with this material?
では 彼らはフンを どう扱うのでしょう?
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And most dung beetles actually wrap it into a package of some sort.
大半は何かしらの形にまとめます
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Ten percent of the species actually make a ball,
1割方は フンをボールのようにして
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and this ball they roll away from the dung source,
元のフンから離れた 場所へと転がし
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usually bury it at a remote place away from the dung source,
地中に埋めます
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and they have a very particular behavior
彼らは独特の行動を取りますが
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by which they are able to roll their balls.
その行動によってフンが転がせるのです
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So this is a very proud owner of a beautiful dung ball.
ここに自慢げなフンの持ち主がいます
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You can see it's a male
オスです
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because he's got a little hair on the back of his legs there,
足の後ろに毛が生えていますからね
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and he's clearly very pleased about what he's sitting on there.
彼はこの美しいフンの玉に ご満悦のようです
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And then he's about to become a victim
ところが悲劇です
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of a vicious smash-and-grab. (Laughter)
卑劣な強盗の 犠牲者となりました
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And this is a clear indication
この行為はフンが貴重な
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that this is a valuable resource.
食糧源であることの表れです
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And so valuable resources have to be looked after
貴重な食糧源は特別な方法で
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and guarded in a particular way, and we think
守る必要があります だからフンを遠くに
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the reason they roll the balls away is because of this,
転がすのではないでしょうか?
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because of the competition that is involved
フン獲得の競争が
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in getting hold of that dung.
激しいからです
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So this dung pat was actually -- well, it was a dung pat
このフンの塊--もはや過去形ですね
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15 minutes before this photograph was taken,
この写真を撮影する15分前は塊でした
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and we think it's the intense competition
この激しい競争こそフンコロガシが
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that makes the beetles so well-adapted
フンを転がすに至った
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to rolling balls of dung.
理由ではないかと思うのです
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So what you've got to imagine here is this animal here
ではこの生物がアフリカの
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moving across the African veld.
草原を横切る姿を想像して下さい
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Its head is down. It's walking backwards.
頭を下に 後ろ向きに歩いています
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It's the most bizarre way to actually transport your food in any particular direction,
食糧の運び方として これ以上ないほど突飛です
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and at the same time it's got to deal with the heat.
しかも熱との戦いもあります
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This is Africa. It's hot.
アフリカは暑いです
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So what I want to share with you now
ではここで私と同僚が行った
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are some of the experiments that myself and my colleagues
実験についてお話します
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have used to investigate how dung beetles
フンコロガシは運搬と熱に
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deal with these problems.
どう対処しているのでしょう
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So watch this beetle,
このフンコロガシを見てください
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and there's two things that I would like you to be aware of.
二つの点に注目して下さい 一つは
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The first is how it deals with this obstacle
置かれた障害物に対する
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that we've put in its way. See, look, it does a little dance,
対処法です ちょっと踊りましたね
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and then it carries on in exactly the same direction
そして最初に向かっていた方向と
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that it took in the first place.
全く同じ方向に歩いていきます
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A little dance, and then heads off in a particular direction.
一瞬踊ってから 目的の方向へと進みます
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So clearly this animal knows where it's going
彼らは行き先が 分かっているのです
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and it knows where it wants to go,
行きたいところがわかっています
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and that's a very, very important thing,
これは非常に重要なことです
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because if you think about it, you're at the dung pile,
例えば自分が大きなフンの塊の中にいて
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you've got this great big pie that you want to get away from everybody else,
ご馳走を独り占めしたい 遠くに運びたいわけです
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and the quickest way to do it is in a straight line.
直進するのが 一番手っ取り早いですよね
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So we gave them some more tasks to deal with,
そこで私達はこの子に 更に課題を与えました
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and what we did here is we turned the world
彼の足元を回転させたのです
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under their feet. And watch its response.
彼の反応に注目して下さい
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So this animal has actually had the whole world
彼の世界は足元で今回転しました
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turned under its feet. It's turned by 90 degrees.
90度回転したのです
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But it doesn't flinch. It knows exactly where it wants to go,
しかし全く動じません 行きたい方向に
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and it heads off in that particular direction.
再び向かっていきます
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So our next question then was,
ではどうやって彼らは
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how are they doing this?
行き先を認識しているのか?
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What are they doing? And there was a cue that was available to us.
何をしているのか? 私達は気がつきました
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It was that every now and then they'd climb on top of the ball
彼らは時々ボールの上に登るのです
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and they'd take a look at the world around them.
そして辺りを見回します
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And what do you think they could be looking at
ボールの頂上に登って
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as they climb on top of the ball?
彼らは一体何を見ているのでしょう?
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What are the obvious cues that this animal could use
動物が利用できる手掛かりは
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to direct its movement? And the most obvious one
何でしょう? 一番分かりやすいのは
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is to look at the sky, and so we thought,
空でしょう では空の何を
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now what could they be looking at in the sky?
見ているのでしょう?
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And the obvious thing to look at is the sun.
空と言えば太陽です
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So a classic experiment here,
そこで典型的な実験をしました
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in that what we did was we moved the sun.
太陽を動かしたのです
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What we're going to do now is shade the sun with a board
板を使って太陽を遮ります
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and then move the sun with a mirror
そして鏡を使って全く違う
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to a completely different position.
位置に太陽を動かします
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And look at what the beetle does.
フンコロガシの反応を見てください
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It does a little double dance,
少し踊って
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and then it heads back in exactly the same direction
元の方向と全く同じ方向へ
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it went in the first place.
歩いていきます
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What happens now? So clearly they're looking at the sun.
彼らが太陽を見ていることが 明らかになりました
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The sun is a very important cue in the sky for them.
彼らにとって太陽は 重要な手掛かりなのです
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The thing is the sun is not always available to you,
でもいつも太陽があるとは限りません
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because at sunset it disappears below the horizon.
日没後は水平線の下に 隠れてしまいます
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What is happening in the sky here
空には私達には見えない
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is that there's a great big pattern of polarized light in the sky
偏光の大きなパターンがあります
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that you and I can't see. It's the way our eyes are built.
人間の目では感知できません
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But the sun is at the horizon over here
しかし太陽は 水平線上にあります
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and we know that when the sun is at the horizon,
太陽が水平線上にある時は--
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say it's over on this side,
例えばこちら側にあるとすると
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there is a north-south, a huge pathway across the sky
南北に大きな帯状の
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of polarized light that we can't see
偏光パタ―ンができます 人間には見えません
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that the beetles can see.
でもフンコロガシには 見えるのです
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So how do we test that? Well, that's easy.
ではそれを証明しましょう
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What we do is we get a great big polarization filter,
大きな偏光フィルターを用意します
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pop the beetle underneath it, and the filter is at right angles
その下にフンコロガシを入れます フィルターは
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to the polarization pattern of the sky.
空の偏光パターンの向きと 直角に置きます
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The beetle comes out from underneath the filter
フンコロガシは フィルターの下から
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and it does a right-hand turn,
出てきて 右に曲がります
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because it comes back under the sky
元々の向きのパターンの
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that it was originally orientated to
空の下に戻ったので
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and then reorientates itself back
元々の方角へと
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to the direction it was originally going in.
体の向きを変えたのです
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So obviously beetles can see polarized light.
彼らには光の偏光が わかるのです
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Okay, so what we've got so far is,
ここまでのおさらいをすると
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what are beetles doing? They're rolling balls.
フンコロガシはボールを転がします
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How are they doing it? Well, they're rolling them in a straight line.
しかも直線で転がします
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How are they maintaining it in a particular straight line?
何故曲がらずに 移動できるのか?
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Well, they're looking at celestial cues in the sky,
それは私達の目には見えない
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some of which you and I can't see.
天空の手掛かりを 使っているからです
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But how do they pick up those celestial cues?
ではその手掛かりは どう感知するのか?
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That was what was of interest to us next.
それがまさに次の疑問でした
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And it was this particular little behavior, the dance,
そしてこの踊りこそが 重要なのではないかと
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that we thought was important, because look,
考えたのです 何故なら
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it takes a pause every now and then,
このように時々休憩しています
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and then heads off in the direction that it wants to go in.
そして再び行きたい方角へと 向かいます
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So what are they doing when they do this dance?
この踊りが持つ意味は何なのか?
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How far can we push them before they will reorientate themselves?
何が起こると彼らは向きを 変えるのでしょう?
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And in this experiment here, what we did was we forced them
こちらの実験では まず無理矢理彼を
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into a channel, and you can see he wasn't
この溝に誘導します 良く見ると特に
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particularly forced into this particular channel,
無理強いはされていませんね
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and we gradually displaced the beetle by 180 degrees
そして徐々に 180度ずらしていき
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until this individual ends up going in exactly the opposite direction
最終的に元の方向とは
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that it wanted to go in, in the first place.
逆方向へと向かわせます
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And let's see what his reaction is
彼の反応を見てみましょう
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as he's headed through 90 degrees here,
90度の場所を通り過ぎ
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and now he's going to -- when he ends up down here,
歩き続け 最終的には
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he's going to be 180 degrees in the wrong direction.
元の方向とは 180度反対方向を向きます
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And see what his response is.
彼の反応を見てみると
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He does a little dance, he turns around,
少し踊って 回転して
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and heads back in this. He knows exactly where he's going.
再び溝の中を進みます
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He knows exactly what the problem is,
彼は何が問題なのか理解し
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and he knows exactly how to deal with it,
かつ対処法も心得ているのです
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and the dance is this transition behavior
そしてこの踊りを転機に
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that allows them to reorientate themselves.
彼らは正しい方向に 向き直るのです
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So that's the dance, but after spending many years
以上が踊りについてです しかし灼熱のアフリカで
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sitting in the African bush watching dung beetles on nice hot days,
何年もフンコロガシを 観察しているうちに
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we noticed that there was another behavior
踊りに関連するもう一つの
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associated with the dance behavior.
ある行動に気がついたのです
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Every now and then, when they climb on top of the ball,
ボールに登ると彼らは時たま
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they wipe their face.
顔を拭くのです
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And you see him do it again.
またやりましたね
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Now we thought, now what could be going on here?
これは一体どういうことなのでしょう?
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Clearly the ground is very hot, and when the ground is hot,
明らかに地面は熱いです 地面が熱いと
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they dance more often, and when they do this particular dance,
踊る回数が増えます そして踊ると
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they wipe the bottom of their face.
顔の下の方を拭くのです
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And we thought that it could be a thermoregulatory behavior.
これは温度調節をしているのではないか
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We thought that maybe what they're doing is trying to
熱い砂を払い 顔に唾をかけて
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get off the hot soil and also spitting onto their face
頭を冷やしているのではないかと
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to cool their head down.
私達は考えたのです
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So what we did was design a couple of arenas.
そこで二つの舞台を作りました
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one was hot, one was cold.
一つは熱く 一つは涼しい状態です
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We shaded this one. We left that one hot.
こちらは日陰に もう一つは日向に置きました
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And then what we did was we filmed them with a thermal camera.
そして熱探知カメラで 撮影しました
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So what you're looking at here is a heat image
今映っているのは 熱を映像化したものです
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of the system, and what you can see here emerging
そしてフンの中から低温の
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from the poo is a cool dung ball.
フンコロガシが出てきました
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So the truth is, if you look at the temperature over here,
フンコロガシは低温 つまりクール
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dung is cool. (Laughter)
かっこいい奴なのです(笑)
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So all we're interested in here is comparing the temperature
私達の関心はフンコロガシと
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of the beetle against the background.
周囲との温度差です
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So the background here is around about 50 degrees centigrade.
周囲はおよそ50℃です
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The beetle itself and the ball are probably around about
フンコロガシとボールはおよそ
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30 to 35 degrees centigrade,
30℃から35℃くらいでしょう
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so this is a great big ball of ice cream
例えるなら 大きな アイスクリームの塊を
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that this beetle is now transporting across the hot veld.
熱い草原の上を転がしていく ようなものです
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It isn't climbing. It isn't dancing, because
まだ登っていません 踊っていません
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its body temperature is actually relatively low.
体温が比較的低いからです
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It's about the same as yours and mine.
私達の体温とほぼ同じです
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And what's of interest here is that little brain is quite cool.
そして小さな脳みそも かなり低温です
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But if we contrast now what happens in a hot environment,
ところが周りが熱くなると
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look at the temperature of the soil.
地面の温度を見てください
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It's up around 55 to 60 degrees centigrade.
55℃から60℃です
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Watch how often the beetle dances.
頻繁に踊り始めましたね
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And look at its front legs. They're roaringly hot.
前足を見てください 相当熱そうです
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So the ball leaves a little thermal shadow,
ボールは熱の影を残しています
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and the beetle climbs on top of the ball
そしてフンコロガシは ボールに登ります
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and wipes its face, and all the time it's trying to cool itself down,
顔を拭き 常に体温を下げ 熱い砂を
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we think, and avoid the hot sand that it's walking across.
避けようとしていると考えられます
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And what we did then was put little boots on these legs,
そこで靴を履かせてみました
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because this was a way to test if the legs
地面の温度を足で知覚するのか
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were involved in sensing the temperature of the soil.
確認するためです
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And if you look over here, with boots they climb onto the ball
ここを見て下さい 靴を履くとボールに登る
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far less often when they had no boots on.
回数が格段に少なくなります
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So we described these as cool boots.
クールブーツと命名しました
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It was a dental compound that we used to make these boots.
靴は歯科治療用の 材料で作りました
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And we also cooled down the dung ball, so we were able
またフンのボールも冷やしました
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to put the ball in the fridge, gave them a nice cool dung ball,
冷蔵庫で冷やしたフンを与えたのです
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and they climbed onto that ball far less often
するとボールが熱い時と比べて
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than when they had a hot ball.
登る回数がかなり減りました
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So this is called stilting. It's a thermal behavior
「高床歩き」です 人間も熱い砂浜を
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that you and I do if we cross the beach,
歩くときにします
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we jump onto a towel, somebody has this towel --
他人のタオルに飛び乗り
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"Sorry, I've jumped onto your towel." --
「失礼 踏んでしまいました」 と言って
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and then you scuttle across onto somebody else's towel,
別の人のタオルに 飛び移る
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and that way you don't burn your feet.
足を火傷せずに済みます
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And that's exactly what the beetles are doing here.
フンコロガシの行為も全く同じことです
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However, there's one more story I'd like to share with you,
もう一つお話をしたいと思います
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and that's this particular species.
それはこの種についてです
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It's from a genus called Pachysoma.
パキソーマ亜属と呼ばれ
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There are 13 species in the genus, and they have
13種が存在します 彼らには
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a particular behavior that I think you will find interesting.
興味深い習性があります
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This is a dung beetle. Watch what he's doing.
これはフンコロガシです 見てください
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Can you spot the difference?
違いが分かりますか?
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They don't normally go this slowly. It's in slow motion.
この映像は通常の 速度ではありませんが
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but it's walking forwards,
ポイントは前向きに 歩いている点です
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and it's actually taking a pellet of dry dung with it.
しかも乾燥した 小さなフンを運んでいます
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This is a different species in the same genus
同じ属の違う種ですが