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要約 |
>Top
0. Introduction:
- 543 million years ago (ma): Cambrian explosion
The Big Bang in animal evolution was perhaps the most dramatic event in the history of life on Earth.
- All the major animal groups found today evolved hard parts and became district shapes, simultaneously and for the first time.
- We don't know why it happened.
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0. 序章:
- 5.43億年前：カンブリア紀爆発
生命の歴史において、動物の進化のビックバンほどドラマティックな出来事はない。
- 今日発見されたすべての主な動物種は、同時にかつ初めて、堅い殻と明確な体形とを進化させた。
- 我々は、それがなぜ起こったのかを知らない。
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>Top 1. Evolutions's Big Bang:
- 38 animal phyla have evolved on Earth.
- The first fossils from the time 543 to 490 ma were found in the Cambrian Hills in Wales (known as the Cambrian period)
- There were perhaps three phyla at 543 ma.
- During five-million-year interval beginning 543 ma, all animal phyla attained complex external forms. (the Cambrian explosion)
- The Earth formed some 4,600 ma, and life came into existence around 3,900 ma. But during the first 3,000 my of life's history, the Earth was populated only by bacteria, algae and single-celled animals.
- >Top Chapters 1 to 3 in the history of life - the first cells:
- Black smokers: very primitive bacteria can tolerate temperatures of up to 110 degrees Celsius in today's black smokers.
- Iron sulphide globules provided the reducing environment necessary to sustain the first life forms.
- Chapter 3: cyanobacteria (erroneously called blue-algae algae). As the cyanobacteria removed hydrogen from the Earth's water, oxygen remained and entered the atmosphere.
- Hamelin Pool in Shark Bay in West Australia: stromatolites (stony carpet in Greek)
- >Top Chapter 4 and 5 in the history of life - the nucleus and the grouping of cells.
- The first cells with a nucleus appeared around 1,200 ma and belonged to a group of single-celled organisms called protists.
- The key feature of nucleared cell reproduction is that genes are shuffled around. Genes are distributed to daughter cells from two parents rather than one. (origin of sexuality)
- Chapter 6 to 8 in the history of life - appearance of the true multicelled animals.
- Sponge have open-topped, sack-like bodies which are fixed to the sea floor. Water is filled through the body and food is filtered out. Sponges also lack a nervous system and muscle fibre.
- Cnidarians and comb jellies have two thin but clearly modified tissue layers separated by a gelatinous material One layer is protected and surrounds the body; the other has a digestive function and forms the lining of a gut.
- Chapter7: Flatworms have an inner tissue layer that produces muscles and some other organs, but they are without a blood circulatory system.
- Chapter 8: next evolutional innovation takes place - a body with three modified layers of tissue, a blood space in the form of blood vessels and an internal body space, in which the gut is suspended.
- The Ediacaran enigma. Dickinsonia: grew to about a meter in length yet was less than 3 mm thick.
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1. 進化のビッグバン:
- 38の動物門が地球上で進化してきた。
- 最初の化石は543から490百万年前のカンブリア紀
- 543百万年前にはわずか３部門
- 543百万年前からわずか500万年の間に、すべての動物は複雑な外部組織を持った。 (カンブリア紀の爆発)
- 地球は約46億年に形成し、生命は39億年前に誕生した。生命の最初の30億年間は、バクテリア、藻類、単細胞動物のみ。
- 生命史第１〜３章：最初の細胞
- ブラックスモーカー：110度Cの中で、原始バクテリアが生存
- 硫化鉄粒子による還元環境が最初の生命を支えた。
- 第３章：シアノバクテリア (藍藻と呼ぶのは間違い)。水から水素を取り去ることで酸素を放出
- 西豪州シャークベイのハメリンプール：ストロマトライト (ギリシャ後で石のカーペットの意)
- 生命史第４〜５章：細胞核と細胞の合体
- 核を持った最初の細胞は1,200 maに現れ、原生動物と呼ばれる単細胞生物を構成する。
- 生命史第６〜８章：真の多細胞動物の登場
- 海綿動物：上部に開いた口を持つ袋状態で海底に付着。海水を体内に取り入れ、食物を濾し取っている。海綿動物には神経系も筋組織もない。
- 刺胞動物や有櫛動物には、薄いけれど異なる二種類の組織層あり、ゼラチン質で隔てられている。一つは体の保護膜で、一つは消化機能を持つ消化膜。
- 第７章：扁形動物は、筋肉その他の器官を形成する組織層はあるが、血液循環システムはない。
- 第８章：次の進化上の大変革が起きる。三種類の組織層を持つ。血液腔の中の血管および消化膜を備えた体腔である。
- エディアカラ動物の謎：ディッキンソニア
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>Top The Cambrian Explosion 515 ma.
- The Cambrian explosion is a milestone in evolution that can be matched in significance only by the beginning of life itself.
- A burst of creativity: animals with teeth and tentacles and claws and jaws suddenly appeared.
- Darwin became puzzled by the sudden appearance of hard-shelled fossils about 542 ma. Darwin had only micro-evolution to work with.
- >Top Burgess shale fauna: (515ma)
Fossils of the Burgess Shale have been regarded either as the predecessors of today's fauna and flora or as enigmatic species that belong to phyla that did not survive the Cambrian.
- >Top Pikaia, a swimming worm that was the first known member of the phylum to which we belong. If Pikaia had not survived the Cambrian period, the story goes, then we would not be here today.
- Ten phyla are represented by the Burgess fauna: sponges, cnidarians, comb jellies, lamp shells, molluscs, hyolith, priapulid worms, bristle worms, velvet worms, arthropods, echinoderms and chordates (to which we belong)
- 1907-1924: Charles Doolittle Walcott, Head scientist at US National Museum of Natural History, recovered 65,000 fossils.
- 1924-1930: Percy raymond, Harvard University
- 1960: Alberto Simonetta, Italian biologist
- 1960s: Harry Whittington, authority on trilobites
- 1972: Drek Briggs and Simon Conway morris, Cambridge project.
- 1989: Stephen Jay Gould, publish 'Wonderful Life'. Gould's curtain came down on Pikaia, the first known member of the phylum to which we belong.
- Ten to twelve phyla are represented by the Burgess fauna: sponges, cnidarians, comb jellies, lamp shells, molluscs, hyoliths, priapulid worms, bristle worms, velvet worms, arthropods, echinoderms and chordates (to which we belong).
- >Top 1984: Chengjiang fauna in Yunnan province: 525 ma. Chengjiang fauna predates the Burgess fauna by ten million years.
- >Top 543 -538 ma:
- What the Cambrian explosion is: It is the sudden acquisition of hard external parts by all the animal phyla found today (except the sponges, comb jellies and cnidarians) It happened in a blink of an eye on the geological timescale known as phenotypes.
- What caused the Cambrian explosion? The development of complex, hard external parts from an embryo requires more energy - why spend more energy than is necessary?
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カンブリア紀大爆発
- 生命の誕生にも匹敵する大事件。
- 歯、触手、爪、顎をもった動物がと突如出現
- ダーウィンはその出現に当惑。ダーウィンが取り組んでいたのは小進化だけだった。
- バージェス動物群(515 ma)は、現存の動物門の祖先とする説とカンブリア紀だけで絶滅した動物門を多数有しているという説とがある。
- 1907-1924:チャールズ・D・ウォルコット、米国国立自然史博物館長
- 1924-1930：パーシー・レイモンド、ハーバード大学
- 1960：アルベルト・シモネッタ
- 1960年代：ハリー・ウィッチントン、ハーバード大学
- 1972：デレク・ブリッグスと・サイモン・コンウェイ・モリス、ケンブリッジ・プロジェクト
- 1989：スティーブン・ジェイ・グールドの名著ワンダフルライフ。我々と同じ脊椎動物門の祖先：ピカイアの話で締め括る。
- バージェス動物群10-12動物門：海綿動物、刺胞動物、有櫛動物、腕足動物、軟体動物、ヒオリテス、鰓曳動物、環形動物、有爪動物、節足動物、棘皮動物、そして脊索動物 (ヒトはここに属する)である。
- 1984: 中国雲南省澄江(チェンジャン) のカンブリア紀の化石。525 ma. バージェス動物群より1000万年古い。
- 543-538 ma:
- カンブリア紀の爆発とは：すべての動物門が突如として硬い殻を獲得した出来事である (海綿動物、有櫛動物、刺胞動物を除き)。これは地史学的には一瞬の間に表現型の変化として起こった。
- 何が引き金となったのだろうか？硬い外装を胚からは発生させるには多くのエネルギーを要する。その必要がなければエネルギーを消費する理由はないはず。
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>Top
2. The Virtual LIfe of Fossils:
- Fossils are factual. They are literally hard facts that we cannot ignore.
- The application of engineering, physics, chemistry and biology can indeed transform a load of old bones into a virtual 3D world where animals run, fly, gallop, burrow, eat and avoid being eaten.
- Reconstructing ancient environments:
- A point on the Earth's crust can change its longitude and latitude: latitudinal change is more significant. The biggest clues to a fossilized animal's precise environment can be found in the surrounding fossils, particularly the plants.
- Cambrian life was exclusively marine; photosynthetic algae in a fossil indicated the photic zone (up to 90 m in depth)
- Structure of exoskeleton could be considered an indicator of temperature, etc.
- Distinct inverse relationship between the concentration of carbon dioxide in the atmosphere and the density of pores on leaves. 300 million years of atmospheric temperature has been discerned.
- Period of low carbon dioxide prevailed between 296 - 275 ma, between 30 -20 ma, and during the past 8 ma.
- Paleontology - the first forensic science:
- The word 'fossil' means something dug up.
- Ammonoids were a group of molluscs, long extinct, related to the octopus and squid. (derived from Amon, Egyptian god)
- Ammonoid: Recent studies have revealed a further adaptation in a nautilus living in deep water (up to 600m) - its shell can behave like a Scuba tank.
- >Top Trace fossils:
- Footprints of dinosaurs are known as trace fossil - not part of the ancient animals, but impressions made by movement, feeding and lifestyles.
- The sloppiness of the mud had preserved a 3D foot print. It preserved the entry and exit wounds made by the foot, following comparisons with living animals. It could potentially provide data on the movement of dinosaur feet through the air.
- This provided evidence that, compared to birds, the theropod stride was more strongly powered by the femur, while the lower leg and foot provided more of the power thrust.
- This continued to feed the debate as to whether or not dinosaurs were birds.
- Adding further flesh to the bones:
- We identify the food of dinosaurs via the dentition of their jaws, the often fateful teeth marks left behind in bones, and their dung. The dinosaur dung has provided further information on ancient lifestyle and evolution - that of dung beetles. Dung beetles evolved with herbivorous dinosaurs.
- Paleontology meets modern engineering:
- CAD provides the advantage of enabling an object to be viewed in 3D and from all angles. The fossils were to be ground away, a hair's width by a hair's width. After each serial grind, a photograph was taken of the newly exposed section of the fossil. Bit by bit fossils can grow virtual outer skins, fill with virtual blood, and walk across the computer monitor in search of specific virtual food.
- >Top Taking our tools to the Cambrian:
- Our fossil finds since Darwin's days have increased a hundredfold But we are still without Precambrian signs of the characteristic external parts of animals today.
- "The study of fossils ... can be made to reveal the way of life of animals now extinct." (The Theory of Evolution, by John Maynard Smith)
- Light and evolution:
- Light is certainly a major force in governing the behavior of animals today. Light must have been a considerable factor of evolution in the past.
- Camouflage and shadows:
- Many beetles living on leaves are hemispherical in shape. This is a physical adaptation to light. A sphere will always cast a shadow, but from most positions a hemisphere will not.
- >Top Structural colors:
- The Romans were highly skilled in the art of glass making. The colors possessed a metallic appearance. The glass plate had an extremely thin, fragile coating. It is literally a thin film.
- Simply put, a thin film is a thin layer of material. It only has upper and lower surfaces. About 4% of the rays in the original beam reflect from each surface of the thin film, and 92 % pass through the film.
- Remember pigments appear as less than 1% reflection.
- Liquid crystals contain helical molecules, slotting together like a row of tiny springs. That is, half the wavelength of the light that is reflected from the structure - LC can appear strongly colored.
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2. 化石のバーチャル生命:
- 化石は事実そのもの。文字通り無視できない強固な事実である。
- 工学、物理、科学、生物学を駆使して、古い骨格から3Dのバーチャル映像を作成し、化石を蘇らせる。
- 古い環境の再構築:
- 地殻移動：緯度変化の方が影響大
- カンブリア紀は海生層のみ。光合成植物の存在は、海底90mまでを示す。
- 外骨格によって気温状態がわかる。
- 二酸化炭素濃度の植物の気孔密度とは反比例の関係
- 低二酸化炭素濃度の時期：296-275 ma, 30-20 ma、および過去800万年前から
- 古生物学は最初の法医学:
- fossileとは掘られたものの意
- アンモナイトは、600mの深海にまで適応。巻き貝を浮力として。
- 生痕化石:
- 恐竜の足跡など動物本体以外の化石
- ぬかるんだ泥には、足跡が３Dとして保存されていた。現存の動物と比較することで、空中での恐竜の足の動きのデータが明らかになった。
- 鳥類と比較して、獣脚類は、大腿骨によって勢いをつけて踏みだし、下肢や足を蹴り出していたことが判明
- 恐竜は実は鳥だったいう説を巡る論争に拍車
- 骨をさらに肉付けする:
- CAD の活用によって3D映像を再構成。 そのために薄紙をはがすように化石をそぎ取りつつ撮影。そして完全な動物体として、立体画像をモニター上に再現することができた。
- その道具をもってカンブリア紀へ:
- ダーウィンの時代以降、発見された化石の量は100倍以上に達している。だが、現生動物で特徴的な外部形態の痕跡は、先カンブリア時代からは発見されていない。
- "化石の研究によってすでに絶滅した動物の生活様式を解明することができる" (John. M. Smithの進化理論)
- 光と進化:
- 光は動物の行動を支配する主要な力である。過去いおいて光はずっと進化の重要な要因だった。
- カムフラージュと影:
- 葉の上に住んでいる甲虫は半円形をしている。これは光に対する帝王である。球形は影を生ずるが、反映型はほとんどの角度からの影は生じない。
- 構造色
- 古代ローマのメタリック色のガラス製造技術。薄膜のコーティングがしてある。
- 薄膜はその上端と下端で光を各々4%ずつ反射し、92%は透過する。
- 色素は通常1%以下しか反射しない。
- 液晶は、中に微小のバネが列をなして螺旋状の分子がはめ込まれている。その構造は、光の波長の大半を反射する。
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>Top 3. The infusion of LIght:
- Victorians of 19C:
- Thomas Young: any color could be obtained by combining only three different colors - blue, green and red.
- Light is a transverse wave.
- Speed of light: calculated by rotating mirror: its velocity is 299,853 km.
- James Clerk Maxwell:
- Light is in fact electromagnetic waves.
- Pigments:
- Pigments are molecules that absorb certain wavelengths in white light. These wavelengths are no longer available to vision, but the remaining wavelengths in the sun's spectrum are reflected from, or transmitted through, the pigment system. These are the wavelengths we see.
- The skin of the chameleon or cuttlefish is packed with chromato-phores - color cells. Each color cell contains just one type of pigment that causes one color.
- Adaptation to the sunlight:
- Animals have to adapt to the sunlight that strikes them. There are two routes: the path to camouflage (=indirect protection) or the path to conspicuousness (=direct protection or attraction between sexes).
- Sometimes repetitive patterns are less noticeable than a continuous color against a busy, varied background.
- Different colors absorbed:
- Red, ultraviolet and violet are the first to fade away, and at 200 m sunlight is exclusively blue.
- Diving beyond about 10 m, the world appears blue-green.
- Below 200 m, many animals are re. The lack of red light means that red pigments have no chance to reflect. red is a good camouflage color in the deep.
- Structural colors:
- Thin layer: about 4% of the rays in the original beam reflect from each surface of the thin film, and 92% pass through the film.
- Remember pigments appear as less than 1% reflection became their reflection covers a hemisphere, and we see only a tiny segment of that hemisphere.
- Liquid crystal:
- liquid crystals contain helical molecules, slotting together like a row of tiny springs. Half the wavelength of the light that is reflected from the structure.
- 92% of light that pass through a single layer meets with another layer, and another 4% reflects. Eventually, with enough turns of the helical molecules, all the light will be reflected: 100% reflection.
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3. 光の投入:
- 19C ビクトリア朝
- J.C.マックスウェル:
- 色素:
- 色素は、白色光の中の特定の波長だけを吸収する。吸収された光は眼に届かない。それ以外の波長の光が、色素から反射さえたり、透過したりして、我々の眼に入る。
- カメレオンやコウイカの皮膚には色素胞と呼ばれる色素細胞が並んでいる。個々の色素細胞は１種類の色素しか含まない。
- 光への適応:
- ２つの選択の岐路：カムフラージュ (間接的防御)または自己主張 (直接的防御なし異性誘因)
- 一様でない背景の場合は、反復模様の方が目立たない。
- 構造色:
- 薄膜：薄膜の上面と下面とでそれぞれ4%ずつ反射し、残る92%が膜を通過する。
- 色素色の場合、反射光の1%も眼に入らない。
- 液晶:
- 液晶の中には、らせん状の分子が並んで埋め込まれている。
- 92％の光が２層目に到達し、その表面でさらに4%が反射される。これが繰り返され100%の反射率となる。
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>Top 4.
When Darkness Descends
- Caves:
- Below waters the beam formation is broken, and sunlight is scattered in every direction. So here objects are illuminated equally from all directions, and no shadows are cast. A mirror in these waters vanishes from sight because in the mirror one sees only a weak reflection of the environment.
- structural colors:
Now imagine a stack of thin films of different thickness. As sunlight strikes this structure, its blue rays would be reflect from the lop layers; green rays are reflected from the middle layers, and finally the red rays from the lower layers. And the combined effect to form white, or silver (silver is a strongly directional form of white). This is how the fish skin appears silver
- Precambrian environment:
- Was the Precambrian environment similar to the modern cave environment?
- Darkness is the most obvious characteristic in the caves. It excludes photosynthetic organism, thereby reducing the amount of locally produced food to zero. Most cave predators have adapted to go without a meal for weeks, even months
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4. 光の減衰する時:
- 洞窟
- 水中では太陽光はあらゆる方向に散乱し、影は生じない。水中の鏡は、背景がぼんやり映るだけなので、鏡の存在は見えない。
- 構造色:
厚さの異なる薄膜を重ねたものを想像する。太陽光がこれに当たると、青色は最上層で、緑色は中間層で、赤色は最下層で反射される。これが混ざり合うと白色または銀色になる。太陽光の方向性が強いと銀色になる。魚の体色は銀色に見える。
- 先カンブリア紀の環境:
- 暗闇は洞窟の特徴。光合成生物がいないので、洞窟内での一次生産がゼロになる。洞窟内の捕食者は、何週間も何ヶ月も食物なしでやっていける。
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>Top
5. Light, Time and Evolution:
- Ostracod crustaceans, or seed-shrimps:
- They are abundant today and were equally common throughout the past, right back to the Cambrian period.
- Around 40,000 species of seed-shrimp have been described; we know only 8,700 species of birds and 4,100 of mammals.
- Seed-shrimps, like scallops, possess a two-part shell that can enclose the entire body (heavyweight seed-shrimp).
- The White cliffs of Dover in England are essentially heavy weight seed-shrimp fossils.
- Myodocopa; with less robust shells (lightweight group)
- 1818: another type of physical structure with reflective properties: the diffraction grating.
- Tiny corrugated sheet, where the spacing of the grooves are fairly constant and approximate to the wavelength of light.
- Now are used on stamps and banknotes since they are difficult to forge. But they wee unknown in nature and the subject of animal structural colors until 1993.
- >Top Bioluminescence:
- Two chemicals - luciferin and a luciferase - react with the oxygen in water, and light is emitted as a byproduct.
- They are employed for mating purposes.
- if mutation is somehow advantageous, it can be retained within the future evolutionary line. Considering we are talking about a code for courtship, the ancestral forms can no longer mate with the contemporary signalers. A new species has evolved.
- The new species would appear as the most derive on the evolutionary tree, at the tip of the branches.
- Humans adorn themselves with clothes, scent, jeweler or body art to attract the opposite sex.
- Light and environment:
- Light is an exception among the stimuli because in most environments it i always there.
- It is one thing to know what happens during the course of evolution, or the design of the evolutionary tree, but something altogether different to explain why it happens.
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5. 光と時間と進化:
- 甲虫
- カンブリア紀から今日まで繁栄
- 甲虫は４万種。鳥類は8,700種、哺乳類は4,100種確認
- 甲虫は、ほたて貝のような二枚貝を持つ (ヘビー級甲虫)
- 英国ドーバーにある白い崖は甲虫の化石
- ウミホタル目: あまり丈夫でない殻を持つ甲虫 (ライト級甲虫)
- 1818: 回折格子発見
- 光の波長にほぼ等しい溝が刻まれた小さな波形板。
- 回折格子は偽造が難しいので証書や紙幣に利用。
- 1993: 自然界にも回折格子が存在し、動物の構造色に関係していることを発見
- バイオルミネッセンス:
- ルシフェリンとルシフェラーズの２つの化学物質が水中の酸素と反応すると発光
- 求愛信号として利用
- 系統進化の過程での突然変異。祖先種はもはや新型信号の発信者と交尾できなくなる。新種への進化
- 新種は系統樹の枝の先端で出現する。
- 人間の場合も同様。衣服、香水、宝石等装飾で異性を引きつける。
- 光と進化:
- 光は刺激としては例外でいつも存在
- 進化の過程で何が起きたか、その進化の系統樹を描くことと、なぜそのような進化が起きたのかを説明することとは別。
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>Top 6.
Color in the Cambrian?:
- Egyptian god Osiris:
- Osiris has a blue-green face and wears a red skirt.
- Blue-green was the color used to represent the afterlife and red for festivity.
- Gold leaf:
- It lies between a pigment and a structural color. It is a thin layer of metal that reflects all the wavelengths in sunlight except blue, all of which add up to gold.
- Color in the Cambrian:
- We have learnt not simply to predict color based on animals today.
- Structure can be preserved in the fossil record.
- Opal:
- a form of silica dioxide, made up of tiny spheres, around half the wavelength of light in diameter.
- Opal produces structural colors, similar to that of the seed-shrimp diffraction gratings.
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6.
カンブリア紀の色彩は？:
- 古代エジプトのオシリス神:
- 顔は青緑色で、赤色のスカート
- 青緑色は来世を表す色で、赤色は祭礼の色。
- 金箔:
- 色素色と構造色の中間。青色以外のすべてを反射することで金色に見える
- カンブリア紀の色:
- 現生種の色で推測すべきでない。
- 構造は化石の記録に残る可能性がある。
- オパール:
- 成分は二酸化ケイ素で、直径は光の波長の半分ほどの微粒子から成る。
- オパールは構造色で、貝虫の回折格子の虹色に似ている。
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>Top 7. The Making of a Sense:.
- Detector:
- Eyes are the detectors that convert the light waves traveling through the atmosphere into visual images.
- Electromagnetic radiation of different wavelengths exists in the environment; color exist on in the mind.
- Two further clues remain to be found; the final pieces of the Cambrian puzzle. "When did eyes invent vision?"
- Darwin referred to the eye as an 'organ of extreme perfection and complication.'
- >Top Light perception:
- It takes place in many monocellular animals: they use light to orientate themselves - to distinguish up from down.
- Multicelled animals: independent light-sensitive cells perform the task of light perception; called ocelli. Light -sensitive surface backed by dark pigment. Sometimes they are capped by a rudimentary lens. (like jellyfish)
- The elementary light detectors cannot be called eyes because they don't form images.
- It is important that an image is first focused sharply on to the retina by some additional apparatus. a camera loaded with highly sensitive film would be useless without a lens.
- Simple eyes:
- There are three forms of simple eyes known in animals, and all can be found in molluscs.
- Pinhole eye:
- Mirror eye:
- Camera-type eye:
- Sharp image:
- So to keep central light rays snchronised with those from the periphery of the lens, the lens material in the center is optically very different from water and causes light to bend more, but also to slow down more.
- All the light rays striking the eye at one instant will be focused on the same point on the retina at the same time.
- >Top Compound eyes are divided into two basic types:
- Apposition type:
- like bees: Optically isolated from each other The tiny images formed within each facet are pieced together to produce the complete picture.
- Superposition type:
- like moths and lobsters: Cooperate optically so that they superimpose their light to form a single image at a common point on the retina.
- 430 ma:
- Eyes have been found in fossils up to 430 ma and their vision has been extrapolated with those of today.
- 543 - 538 ma:
The Cambrian explosion took place.
- 515 ma: The Burgess Shale community lived.
- >Top Eyes in the Cambrian:
- The list is reduced to just the arthropods and chordates.
- Pikaia of the Burgess Shale:
- The earliest Haikouella from Chengjiang:
- the front end is too small to be eyes. They could not see.
- Phylum with the first eye was the Arthropod.
- >Top Trilobites with compound eyes:
- Trilobites are found all over the world in the Paleozoic.
- The compound eyes of trilobites were made of the mineral calcite.
- Two types of compound eyes in trilobites - holochroal and schizochroal.
- 543 ma: the very first trilobites evolved and were equipped with holochroal compound eyes. Before this date there were neither trilobites nor eyes on Earth.
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7. 感覚の制作:
- 検出器
- 眼は、大気中を通ってきた光を映像に変換する検知器
- 環境中にはさまざまな電磁波の放射があるが、色は脳の中にある。
- ２つの鍵がまだ解けていない。カンブリア紀の最後のパズルである。眼が視覚を発明したのはいつか？
- ダーウィン曰く"眼とは完璧で複雑な器官"
- 光感知:
- 単細胞動物：上下を区別する光感受性
- 多細胞動物：独立した感光細胞がある。基本的な光感知器は眼点。
- 基本的な光受容器は像を結ばないので眼とは呼べない。
- 網膜上に鮮明な像を結ぶことが重要。カメラに高感度フィルムを装填してもレンズがなければ役立たない。
- 単眼:
- 動物には３種類の単眼があり、すべてが軟体動物にある。
- ピンホール型眼
- 反射型眼
- カメラ型眼
- くっきりした映像:
- レンズの中心部を通る光線と周縁部を通る光線とが網膜に同時に届くためには、レンズの中心部は屈折率の大きな材質からできており、網膜までの解く着時間を遅らせている。
- ある瞬間に眼に入った光線は、同じに網膜上の同じ位置に焦点を結ぶ。
- 複眼: 以下の２つに分類される。
- 連立像眼：
- ミツハチ：光学的には分離しており、個眼内で結ばれた小さな像が集められて像を形成する
- 重複像眼：
- 蛾やロブスター：光学的に統合されて網膜上に一つの像を結ぶ
- 430 ma:
- 543-538 ma:
カンブリア紀の爆発
- カンブリア紀の眼:
- 候補は、節足動物と脊索動物のみ
- ピカイア：バージェス頁岩動物群
- ハイコウエルラ (澄江)
- 三葉虫の複眼:
- 三葉虫は古生代を通じて、世界中から発見されている。
- 複眼は方解石からできている。
- 三葉虫の複眼は２種類：完全複眼と集合複眼
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>Top Important question:
- "How quickly can en eye evolve from its forebears?" Fossil evidence implies that eyes existed 543 ma but not before. Not, say, 544 ma. But surely an eye cannot simply evolve overnight? Surely it has to pass through a sequence of intermediate stages
- Nilsson and Pelger made their assumption about the slowest rate of evolution - 0.005 % modification from one generation to the next.
- >Top They found that the eye of a fish could evolve from its rudimentary beginnings in less than 400,000 generations. Assuming each generation is completed within a year, this result suggests that an efficient, image-forming eye can evolve in less than half a million years; really a blink of an eye on the geological timescale.
- It is conceivable that nerves used by one sense can be upgraded for use by two senses. Part of the brain may be capable of converting from touch to vision.
- Between 544 and 543 ma a revolution took place. During this one million year period, vision was born.
- Important point: Light-sensitive patches and other stages of rudimentary light receptors are not eyes.
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重要な質問:
- "眼の進化にはどの位時間がかかるか？" 化石の証拠によれば、543 maには眼が存在し、544 maには存在しなかった。
- NilssonとPelgerの推定によれば、進化速度を0.005%と想定した。各世代１年とすると、40万年足らずで達成されることになる。これは地質的なタイムスケールでは一瞬の出来事である。
- 一種類の感覚が利用している神経は、他の感覚が利用するためにアップグレードできるらしい。脳の一部を触覚担当から視覚担当へ変更することができるかも知れない。
- 544 -543 maの間に視覚が誕生した。
- 但し、感光性斑点など未発達な光受容器は眼ではない。
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>Top 8. The Killer Instinct:
- The law of life: for the survival of animals everywhere:
- Basic Rules:
- every man for himself; stay alive!
- For the good of one's kind
- Breed
- Find a niche and protect it
- Adapt to changes in the environment
- Lifecycle:
- predator
- Prey
- Tactics:
- Conspicuousness
- Crypsis/illusiveness
- Genuine strength/ability
- Vision is a major tactic:
- Genuine strength or ability is actually a rare attribute in animals; rarely does an animal dominate an ecosystem without considerable employment of warnings or illusions.
- Lioness is the main predator, but she cannot outrun her prey over short and long distances, so she must rely on camouflage colors and stalking behavior to take up a competitive position in her race for food.
- For a prey species:
- staying alive first means keeping off the dinner plate and then eating becomes important. Eyes positioned at the sides of the head are good for spotting predators. 360 degrees view of the terrain is possible.
- >Top For a predator:
staying alive usually means eating first and worrying about their predators and competitors after that.
Two eyes at the front of the head are needed - an accurate assessment of distances is the difference between a meal and hunger.
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8. 殺し屋の本能:
- 生命の法則:
- 基本原則
- 誰もが己のために生き続けよ
- 自分の種のために
- 繁殖せよ
- ニッチを見つけそれを守れ
- 環境変化に適応せよ
- ライフサイクル
- 捕食者
- 餌食
- 戦術
- 視覚は重要な戦術:
- 生態系の支配的な動物は、視覚的に相手を警告したり欺いたりする。
- ライオンの雌は捕食者の頂点にいるが、短距離でも長距離でも獲物の足にはかなわない。従って、隠蔽色でこっそり忍び寄る戦法をとる。
- 被食者にとって:
- 生き延びるためにはまず餌食にならぬこと。自分が食べるのは二の次。360度の視野が可能
- 捕食者にとって:
- 自分が食うことが先決で、他の捕食者や競合相手を危惧するのは二の次。頭部前面の２つの眼は距離を正確に測定するには必要。
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>Top Dragonfly:
- The compound eyes of dragon flies contain several hundred or thousand facets, not all of which are equal. There are one or two regions of the eye that contain larger facets known as the acute ones, the sights.
- One acute zone is positioned at the tope of the eye and identify prey insects against the sky. When a prey insect has been spotted, the dragonfly moves into its horizontal plane and tracks it with a forward facing acute zone. The prey is now locked into a line of fire.
- Swords, shields, and scars:
- Anomalocaris:
- widespread between 525 and 515 ma. It was up to 2m long, the largest animal of its time.
- circular mouth, a collection of hard plates that open and close like the iris of a camera, with a circular array of teeth inside.
- The fact that all Burgess arthropods possessed protective spines, or some form of protection against attack (except Anomalocaris), means they were not only predators, they were also prey. We found in the Burgess eyes - adaptation for 360 degrees of vision, with minor directional qualities.
- Gamble on different aspects of the laws of life:
- Shrimp-like crustacean Canadaspis and the tiny trilobite Ptychagnostus. Canadaspis has eyes whereas Ptychagnostus does not. Canadaspis placed its chips on eating, Ptychagnostus on breeding.
- >Top Ediacaran fauna: 565 ma:
- there was no Anomalocaris with its advanced detection system and search-and-destroy capabilities. All that patrolled the Precambrian water were the stinging nets of jellies. But in the jelly's favor, the prey could not sense them coming either. This was a kitten-and-mouse game, in comparison with the cat-and-mouse Cambrian.
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トンボ:
- 数百、数千の複眼があるがすべて同じではない。１〜２カ所個眼が大きな箇所があり、より分解能が高い。
- １つは眼の最上部にあり、上空の獲物を見つけるのに使う。トンボはその虫の高度まで上昇し、複眼の前方に位置する照準器に捕らえて追跡する。餌となる虫は、ミサイルのロックオンされたような状況となる。
- 剣と盾と刀傷:
- アノマロカリス：
- 524 - 515 maに繁栄。体長２mもあり、最大の動物
- 円形の口。何枚もの硬い顎板で、カメラの絞りのように開閉し、内側に歯が環状に並ぶ。
- バージェスのすべての節足動物は、防御用のとげを装備 (アノマロカリスにはない) これは、カンブリア紀の大半の動物は、捕食者であり獲物であり、360度の視野を持っていた。
- 生命の法則の賭け:
- 甲殻類のカナダスピスと小型三葉虫のプティチャグノストゥス。前者は食う方に投資し、後者は殖やす方に投資した。
- エディアカラ生物群：565 ma
- 刺胞の網を張ったクラゲくらい。獲物の方もクラゲの接近を探知できない。子猫とネズミの追跡のようで、カンブリア紀のネコとネズミの追跡とは異なる。
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>Top Beginning of predators on Earth:
- 'Inactive predation' was common in the Precambrian. Although, based on the lack of armour worn in the Precambrian, this type of predation obviously did not present a strong selection pressure for counter-predatory measures.
- >Top The first predator:
- The first animal with eyes was a trilobite.
- The first true trilobite was also a predator. Their spiny shields affirm that they were also prey. They probably attacked each other.
- They were bad news for Precambrian-style, soft-bodied forms everywhere. Life was about to be stirred up.
- 'Did a few species of predatory trilobites evolve from proto-trilobites and kick-start a chain reaction?' That chain reaction was the acquisition of hard parts and other external characteristics in all animal phyla - the Cambrian explosion.
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捕食者の始まり:
- スローな捕食者が一般的。装甲をまとった動物がいなかったことから言って、この様式は、捕食への対抗手段をとるような強い淘汰圧とはならなかった。
- 最初の捕食者:
- 最初に眼をもったのは三葉虫である。
- 最初の真の三葉虫は捕食者でもある。またトゲのある装甲は、同時に食べられる側でもあった。恐らく共食いをしていたのだろう。
- トゲだらけの頑丈な付属肢をもつ捕食動物の登場は、先カンブリア時代の軟体動物にとっては一大事であった。生命は騒乱の時を迎えた。
- 原始三葉虫から数種の捕食性の三葉虫が進化し、それが進化の連鎖反応を引き起こしたのだろうか？その連鎖反応とは、すべてにの動物門における硬組織とその外部の特徴のことであり、それがカンブリア紀の爆発なのだ。
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>Top 9. The solution:
- Wonderful colors:
- All those wonderful colors we see around us, whenever we are, do not actually exist. In the environment there is no color, only objects that happen to deflect different types of electromagnetic radiation.
- Roses are not beaming out reds, nor do leaves generate greens.
- Light is a major selection pressure acting on everyone.
- Share of vision:
- Dragonflies have big heads, with eyes occupying 3/4 of the area, and some seed-shrimps have eyes which monopolize a third of their body volume.
- Large portion of the brain of eyed animals is always devoted to vision.
- Search and destroy:
- 'Search' precedes 'destroy'｡Before destroying, one must search, identify and capture. Active predators would be useless without eyes or a comparable detector for another sense.
- >Top Light Switch theory:
- Divide geological time into two parts: pre-vision and post-vision. The boundary stands 543 ma.
- The most powerful sense of all had been launched on Earth. Suddenly an animal could detect everything in its environment. We can see food from some distance.
- The first eyed proto-trilobites must have been frustrated individuals. They saw their soft-bodied neighbors. But they had neither the mobility nor the jaws to capture and kill all of them.
- The selective pressures for hard parts were massive. And hard parts and active predation would follow, very quickly. Soon, proto-trilobites would become trilobites.
- There was a new selection pressure acting on them - to avoid becoming prey. It became dog eat dog, or, rather, trilobite eat trilobite.
 Evolution of receptors for different stimuli throughout geological time. Vision is the only sense that can divide geological time into two district phases. - Near-final thoughts:
- >Top There was never really a race waiting to begin in the Precambrian, a race to attain eyes. that's not the way evolution works, and would represent a teleological view.
- Rather, something happed in the environment one day that changed the rules. Then selective pressures changed either in their direction or size. Evolution works by adaptive radiation, usually caused by a change of some description in the environment.
- Although vision can be found in only 6 of 38 phyla today, over 95% of all animal species, taking account of all phyla, have eyes. Eyes certainly proved a significant method of exploiting en environment.
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9. 問題の解決:
- すばらしい色彩:
- 我々の周囲のすばらしい色彩は実は存在していない。各々の電磁波を屈折偏向させている物体があるだけ。
- バラは赤い色、葉は緑色を出している訳ではない。
- 光は全ての動物に作用する淘汰圧である。
- 索敵掃討:
- まず目標を捜索し、相手を識別してから、これを補足する。
- 捕食者は、眼あるいはそれに相当する認識装置を備えている。
- 光スイッチ説:
- 地史は視覚の登場前と後との二分される。
- 突如として視覚を持った動物が出現した。
- 最初の視覚を持った三葉虫は欲求不満だった。餌が周囲にあるが、それを捕まえる機動性も顎もなかったから。
- 硬組織形成への選択圧は強力だった。
- さらに新たな選択圧が生じた。今度は自分が餌にならないようにと。三葉虫同士の共食いの世界が始まった。
- さまざまな刺激受容器の進化。視覚だけが２つのフェーズに分かれている <左図>
- ほぼ最後の考察:
- 先カンブリア時代に、眼の獲得レースが開始の時を待っていたわけではない。目的論的な見方は間違い。
- ある日ルールを変えるような何かが環境中にもたらされ、淘汰圧の方向や規模が変わった。進化は適応放射によって進行する。その原因は、環境におけるある仕様の変更である
- 視覚を備えているのは38の動物門の内６門に過ぎないが、全動物門の種としては95%以上の動物種が眼を備えている。眼は環境を利用するには重要な方法であることがわかる。
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>Top 10. End of Story?:
- Question:
- "What triggered the evolution of the eye?"
- The first eye must have evolved in response to an increase in sunlight. Geologists have revealed an increase in sunlight levels at the very end of the Precambrian.
- >Top Ultraviolet light:
- Although the sea is not particularly transparent to ultraviolet light today, there are some shrimps and other animals which have the ability to see these wavelengths.
- An increase in ultraviolet transparency in seas at the end of the Precambrian could have been due to a change in mineral content, but also to a reduction in particles that scatter light.
- >Top Snow Ball Earth:
- the last Snowball Earth event ended 573 ma. So there is a difference of at least 32 million years between Snowball Earth and Cambrian explosion.
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10. 物語の結末？:
- 質問:
- "何が眼の進化の引き金となったのか？"
- 先カンブリア時代の日光の量の増大か。
- 紫外線:
- 現在の海は紫外線をよく透過することはない。しかし紫外線の光を感知する能力のエビが次々と発見されている。
- 先カンブリア時代に、海の紫外線透過率が高まった可能性は、海水中のミネラル含有量の変化と光を散乱させる粒子の減少か。
- スノーボール地球との関係:
- 最後のスノーボール地球は 575maで終わっており、カンブリア紀の爆発の543-538maとの間に3200万年の開きがある。
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