《達爾文所未知的》解說詞
撰寫（Written）：阿爾芒·馬裏耶（The Animal Mother）
翻譯（Translation）：趙永安（Zhao Yongan）
解說人：倫敦帝國學院阿爾芒·馬裏耶·利萊教授（Prof Armand Marie Lerol, Imprial College, London） ：
我們生活在一個精致多樣的世界裏，物種數量超過我們可能統計清楚的數量。例如，在馬拉維湖（Lake Malawi），有在其他地方找不到的成百上千種不同的魚。為什麼那麼多？為什麼如此不同？一百五十年前，查爾斯·達爾文發表了《物種起源》。在那本偉大的書中他提出了同樣的問題...，..並給出了正確答案...
達爾文問道，所有這些多樣性都來自哪裏？並回答說，它們一定是進化的產物。他認為，物種會產生其他物種，而且它們也會改變。這些每時每刻的變化都是細微而微妙的，但如果有足夠的時間，其結果將是驚人的。所以它們就是現在的樣子。
達爾文對地球生命如此誘人的解釋，如此簡單，以致於今天看起來很明顯。然而，達爾文對進化論如何運作的解釋充滿了漏洞，他的邏輯基礎並不穩固，他的證據也很無力。還有很多他並不知道東西。但達爾文相信，未來幾代科學家們將會完成他的工作，並證明他遠見卓識的基本真理。一百五十年來，這就是我們一直在做的事情。
在這部影片中，我將講述達爾文理論出現的衰落，描述如何終結和他的理論最終獲取勝利的。我將展示進化理論是如何演變的，因此，展現比他以往想象的更加廣闊和微妙情況。
片頭：達爾文所未知的
第一部分：生存競爭
1835年9月，達爾文抵達加拉帕戈斯群島...，..當他到達一個新的地方時，他總是這樣做——他放下自己的護身武器槍開始收集標本。在加拉帕戈斯群島居住著許多居民，幫助達爾文用牽制、醃制、射擊或填充物填充這四只鳥。它們看起來不太像，但需要你仔細地看看。看著它們，就像達爾文看著它們，你可以看到進化的開始。他們好似反舌鳥（Mockingbird）。每一只鳥都來自不同的島嶼，每個島嶼都與其他島嶼之間的鳥都有細微的差別。它們外觀的形狀、身體的大小和羽毛的顏色全都各不相同。正是這些差異使得達爾文開始思考物種是否會隨著時間推移而發生變異。
[反舌鳥，它們是一組來自嘲鶇科家族的新世界雀形目鳥類。它們以模仿某些其他鳥類的聲音以及昆蟲和兩棲動物的聲音習慣而聞名，這些動物常常響亮的連續不斷地高唱。共有三屬十七種。反舌鳥體型略大（29厘米）的全深色鶇。雄鳥全黑色，嘴橘黃，眼圈略淺，腳黑。雌鳥上體黑褐，下體深褐，嘴暗綠黃色至黑色。此鳥與所熟悉的烏鶇為同一種類。與灰翅鶇的區別在翼全深色。分布於歐亞大陸、北非、印度至中國；越冬至印度支那。（譯者注）]
達爾文推測，鳥類很可能是同一物種的變種，由此它們必然從一個共同祖先開始——不知何故的反舌鳥，很多年前才找到飛往加拉帕戈斯的路。那正是達爾文的一種預感，但如何證明物種來自共同的祖先呢？他肯定不能產生這個假想的祖先——它迷失於這個關鍵的時刻。所以在當時沒有充足數據資料的前提下，達爾文做了一件科學家們應該做的事情——他只能訴諸於一種具有吸引力的類比。
達爾文曾經飼養鴿子。鴿子對他來說，它們是進化的一個縮影。他們展露了任何生物，只要有足夠的時間，將會被轉化成與祖先截然不同的東西。盡管看起來難以置信，這些華麗的、怪異的、天生的貴族的鳥類世界——這只是斯堪達隆信鴿（Scandaroon），這只是弗萊巴克（Frillback），還有雅各賓（Jacobin），不要忘了這只默克（Mookee）——它們都屬於——最普通的野鴿。所有的鴿子在出生時都有細微的差別。飼養的人都選擇具有理想特征的動物讓其生存和繁殖下去...，..然後他們就把剩下的都剔除掉。這些值得擁有的特性經過一代又一代的長期積累變得最為適合生存，但有可能被誇大了。因此，很快，鳥類就這樣進化了。
達爾文認為，大自然就是這樣一概如此運作的。它偏愛某些特性，有利於物種的延續以及向各個方向發展。他稱這個過程為自然選擇。所有這些都解釋了為什麼《物種起源》的第一章不是關於自然界的奇跡，而是關於鴿子的故事。理解鴿子的變化後，他這樣說，相信鴿子，剩下的他當然都相信了。或者是這樣的嗎？因為達爾文有一個問題。自然選擇是他理論的基石。對他來說，這是進化的動力。然而，自然選擇是否真的起作用還不清楚。他說，這是一場自然的競爭。饑荒、暴力和死亡隨處可見。物種和個人被鎖定在為生存而奮鬥的過程中。只有強者才能生存繁衍...，..而弱者只能被逼走向死亡之角。如果有足夠的演變時間，這種選擇的壓力就足以帶來緩慢的漸進的變化。這就是達爾文推出《物種起源》中揭示的自然選擇進化論的經過。雖然進化論本身並不新鮮，但沒有人更有力地論證它，也沒有更嚴格地證明它的證據。但它是正確的嗎？達爾文真的提出了他的論點嗎？當然，許多宗教類型人士憎恨進化的想法。但達爾文的一些同行科學家也不太熱心。
值得注意的是理查德·歐文（Richard Owen），他寫了第一篇關於起源的批評評論。理查德·歐文最早的古生物學家，創造了“恐龍”這個詞，幫助設計這些東西。在南倫敦的公園裏充滿了橫沖直撞的恐龍，這些奇妙的重建是在十九世紀五十年代建造的。它們是基於歐文研究的恐龍生活場景。歐文有著曖昧的進化傾向。他認為物種在某種神聖法則的影響下，會出現間歇性地周期變化，但它們被一些重大災難卷走了。他討厭達爾文的無神的進化論。歐文的評論是徹底令人厭惡的東西。他對起源的評論，充滿惡意，充滿諷刺意味，他在稱贊自己的同時詆毀達爾文。當然所有都是匿名。如：“達爾文先生輕率的臆測貶低了科學。”“他像糟糕的法國人一樣。”歐文繼續說，“而且他對化石一無所知。”“如果他知道，他就會了解。”“魚龍（ichthyosaurs）出現在侏羅紀的早期，它呆在那裏保持不變，然後消失——那裏沒有進化的跡象。”歐文的惡意可能是由於純粹的怨恨而生的。
[魚龍，大型海洋爬行動物。魚龍類屬於魚龍魚或魚鱗魚類（魚類鰭狀肢），這是1840年由理查德·歐文爵士介紹的一種稱謂，盡管這個術語現在更多地用於魚龍魚的親緣分支。魚龍在中生代的大部分時期都很繁盛，根據化石證據，它們最早出現在2.5億年前，至少有一個物種存活到大約9000萬年前，進入白堊紀晚期。在三疊紀早期，魚龍是由一群不知名的陸生爬行動物進化而來的，它們回到海中，與現代海豚和鯨魚的祖先平行發展，它們逐漸在趨同進化的情況下變得相似。它們在後來的三疊紀和早期侏羅紀時期尤為豐富，直到後來又被另一個海洋爬行動物組織——蛇頸龍（Plesiosauria）所取代，成為了侏羅紀和白堊紀時期的頂級水生食肉動物。在白堊紀晚期，魚龍因為未知的原因而滅絕。（譯者注）]
盡管如此，似乎在他身邊還有化石記錄。根據達爾文的理論，從化石中可以逐漸看出進化的痕跡。但事實並非如此。相反，物種似乎是突然到來和離開的，相互之間區別很小。這些化石記錄中的差距將困擾著達爾文的進化理論。自然選擇的證據根本就不存在，甚至他的朋友也有疑慮。
托馬斯·亨利·赫胥黎（Thomas Henry Huxley）在帝國理工學院工作，我現在也在那裏工作。一個煽動者和一個平民主義者，他們稱他為達爾文的鬥牛犬。赫胥黎也回顧了起源。“這是一個宏偉的工作。”“這說明了進化的必要性。”但後來他轉向自然選擇。“是的，這是合乎邏輯的，是的，這很簡單，但是達爾文先生真的看到了一個物種是由自然選擇產生的嗎？”“他能證明它真的存在嗎？”“嗯，沒有。這是一個假設，”也許是最好的一個，但是，我把它說成是朋友，“你明白，達爾文先生並沒有證明他的觀點。”赫胥黎說自然選擇是看不見的。其他人則說這行不通。他們聲稱這在邏輯上是有缺陷的。這與達爾文關於遺傳的說法不一致，即物種如何將它們的特性代代相傳。
[托馬斯·亨利·赫胥黎（1825年5月4日- 1895年6月29日）是一位專攻比較解剖學的英國生物學家。他被稱為“達爾文的牛頭犬”，因為他擁護查爾斯達爾文的進化論。赫胥黎在1860年與塞繆爾·威爾伯福斯（Samuel Wilberforce）的著名辯論，是他更廣泛接受進化論和自己職業生涯中的關鍵時刻。赫胥黎原計劃在前一天離開牛津，但在與研究人員羅伯特·錢伯斯（Robert Chambers）會面後，他改變了主意，決定加入這場辯論。威爾伯福斯是理查德·歐文的學生，赫胥黎加入人類是否與猿類有密切的關系大辯論。（譯者注）]
這就是達爾文遺傳思想的繼承工作。假設一對父母其中一人有深色的羽毛、毛皮或皮膚、黑咖啡色的顏色，而另一個則是乳白色的，他們的後代將是兩者的混合體。它們是混合的。這似乎是一個無傷大雅的想法。也相當合理。畢竟，這難道不是人類的膚色是如何遺傳的過程嗎？
難道，達爾文的理論已走進了陷阱，一個名叫“弗雷明·詹金（Fleeming Jenkin）”的蘇格蘭工程師發展了這個理論。這是詹金如何措辭的論點：“設想一下，一個白人來到了黑人居住的島嶼，他將毫無疑問讓自己成為國王。他將擁有許多黑人妻子和許多混血的孩子。”“然而不管多麼成功，是我們的英雄，不管他多麼高貴，他的咖啡色後代都會變得越來越黑。”“在幾代人之內，他們存在的所有痕跡都會消失。”如果可以的話，讓我們忽略那些隨意的種族歧視。這是十九世紀六十年代的蘇格蘭，和詹金在站在了同一觀點。變異是進化的東西，如果混合變異，它就會消失。正如它消失了，那麼自然選擇的力量也會消退。
[亨利·查爾斯·弗萊明·詹金教授（Prof Henry Charles Fleeming Jenkin 1833年3月25日—1885年6月12日）他是愛丁堡大學工程學教授，因其具有多功能性而引人注目。他是世界聞名的纜車和電報的發明者，他是一名電工和電纜工程師，經濟學家，講師，語言學家，評論家，演員，戲劇家和藝術家。（譯者注）]
詹金面臨的挑戰是嚴重的，和達爾文沒有回應。他怎麼可以這樣呢？他的理論需要一些制度，一些遺傳法律，但其中並沒有混合法，但依然在幾代人之間保持穩定。然而，沒有人真正知道這樣一個系統是如何運作的。關鍵是，達爾文知道所有這些。我們知道的他都知道，因為他告訴了我們。也許《物種起源》最精彩的章節是第六章。這就是所謂的“困境理論”。查爾斯·達爾文以難以忍受的坦率、毀滅性的誠實和他的理論上所有弱點暴露了自己。他告訴我們他可能錯的所有原因，他的批評者指出的原因很多，但之後，他呼籲未來的科學家從他的書中汲取靈感，解決他的理論所面臨的困難。
人們很容易忘記，達爾文並不是第一個提出進化論的人。在五十年之前物種起源被一名法國人提出了進化論，雖然不如達爾文的連貫性和全面性。他的名字叫讓-巴蒂斯特·拉馬克（Jean-Baptiste Lamarck）。拉馬克是科特迪瓦自然博物館（Natural Museum of Cote d'Ivoire）動物學教授。在達爾文出生的那一年，他發表了關於進化論的觀點。然而，他們卻截然不同。拉馬克認為，當動物、任何動物都使用一些器官時，它就會變得更強壯、更大。這是相當明顯的。我們都知道鍛煉會改變我們身體的形狀。對其他生物也是如此。但拉馬克更進一步。他認為，這些在一個人的一生中獲得的變化，已經被傳承下去了。正因為如此，獲得性特征的繼承，因為它是眾所周知的，它是進化的引擎。拉馬克崇拜對象是長頸鹿。根據拉馬克的說法，一些祖傳的長頸鹿伸長了脖子，伸向最高的樹枝上。它那伸長的脖子已經傳給了它的後代，而它們又把脖子伸得更長了，所以現在所有長頸鹿都有長長的脖子。拉馬克的邏輯有一種誘人的、直觀的邏輯，達爾文在面對自己理論的不足之處時，發現越來越難以抗拒。長頸鹿的脖子是陳詞濫調。每一本教科書都解釋了達爾文進化論和拉馬克進化論的區別。但如果你真的讀過達爾文在起源最後一版的第六版中關於長頸鹿的說法，你會發現一些非常不同的東西。首先，他談到了自然選擇。這就是長頸鹿的脖子。但隨後他又補充了另一條關於增加遺傳效應如何利用的部分。兩方面的結合才會有長頸鹿的長脖子。“增加了如何利用部分”？這裏發生了什麼事？這是純粹的拉馬克觀點。難道那還是達爾文嗎，在他的溺愛中變得不那麼達爾文主義了嗎？嗯，是的。也許自然選擇並沒有他想象的那麼強大。取消主張嗎？不。這是一個老人的坦率，他一生都在試圖解讀這個世界。
達爾文於1882年4月去世。他本想在肯特郡自己的房子附近安靜地安葬，但他的支持者們卻在威斯敏斯特教堂舉行了葬禮。他們把不可知論者變成了新世俗唯物主義時代的聖人。這是查爾斯·羅伯特·達爾文的典範。他成為了一位偉大的英國人。但頌詞聽起來很空洞。達爾文證明了地球上的生命是自然法則的產物。但是這些定律是什麼呢？每個人，每個人，也就是重要人物，都同意進化是事實。但是自然選擇呢？不，謝謝。
就在達爾文躺在那裏的時候，一些達爾文主義者卻在打破常規。其中包括荷蘭植物學家雨果·德·弗裏斯（Hugo De Vries）。受到達爾文的啟發，他正在尋找一種合適的有機體來研究遺傳的工作原理...，發現了一個。他選擇了一種叫月見草（Oenothera lamarckiana）的植物。園丁們會知道它是月見草，因為它在黃昏時開花。它遍布整個沙丘，保護著荷蘭遠離的海洋。它真的只是一種野草。盡管如此的可愛。德弗裏斯發現了另一種月見草，偶爾會生長出與自己看起來非常不同的後代，它們的莖、葉、花各不相同。他發現的這些新變種並不混合，而是穩定的，像新物種一樣穩定。創造一個術語，德弗裏斯稱這些戲劇性的變化，叫“突變（Mutations）”。在他發現之後，德弗裏斯被任命為阿姆斯特丹植物園的負責人。他培育和雜交了更多的月見草屬，達到五萬三千多種。看起來很多，但話說回來，他畢竟是荷蘭人。
[雨果·馬利·德·弗裏斯（Hugo Marie de Vries 1848年2月16日- 1935年5月21日）荷蘭植物學家，也是最早的遺傳學家之一。他主要貢獻是提出基因的概念，在十九世紀九十年代重新發現遺傳規律，但那時不知道格雷戈爾·孟德爾的著作，因為引入了“突變”一詞，並發展了進化的突變理論。（譯者注）]
這是由棕櫚搭建的溫室，由阿姆斯特丹市為德弗裏斯建蓋的。這些都是他培育形形色色的一些開花植物的子孫後裔。它們顯得古老而幹燥，但你仍能看到生長和形態上的差異。突變似乎可以產生全新的植物。甚至可以說德弗裏斯創造了新的物種。這些都是不符合達爾文主義的。什麼是那些令人眩暈的時間尺度，無限的漸進步驟，達爾文又是如何看待宏大的生活的呢？無關緊要，德弗裏斯說。物種起源只需要一件事：突變。他稱之為這是他的“突變理論（Mutation Theory）”。這使他揚名。對於拉馬克，他說，物種的起源只是一種自然現象。對於達爾文來說科學調查是他研究的對象，對於德弗裏斯來說他喜歡用第三人稱談論自己，科學實驗是他研究的對象。
[突變理論，在查爾斯·達爾文1859年出版的《物種起源》一書出版之前和之後都存在著多種自然選擇，而突變理論是進化的幾種選擇之一。在理論中，突變是新奇性的來源，在突然的跳躍中創造出新的形式和新的物種。這被設想為推動進化，還被認為受到突變的提供的限制。在達爾文之前，生物學家普遍認為，在進化中有大跳躍的可能性，包括直接物種形成。達爾文反對突變，堅持漸進式的進化，就像在地質學中一樣。（譯者注）]
拉馬克、達爾文和德弗裏斯，毫無疑問，他們處在萬神殿的地位。德弗裏斯或其他人當時就意識到，這種月見草就是一個基因怪胎。很少有其他生物變得如此壯觀。他把他的整個理論建立在一個非常奇特的物種上。然而，這並沒有阻止突變的興起。其他人開始研究自然界的奇異之處。
在英國，劍橋大學的生物學家威廉·貝特森（William Bateson）發表了他所研究變異材料的著作。采集到雙頭烏龜的樣本，女孩有四個耳朵和長有八個指手。這是一本中世紀充滿怪物和講述令人驚奇的事物書，為進化時代而重新編制。突變是進化和自然選擇背後的真正創造力，突變論者說，但這並不是必需的。
[威廉·貝特森（1861年8月8日至1926年2月8日）英國生物學家，第一個提出遺傳學術語，描述遺傳研究的人。他1894年出版的《變異研究材料》是最早的遺傳學新方法之一。（譯者注）]
1909年倫敦。達爾文早已仙逝，但他的理論已有五十年曆史。在英國自然曆史博物館舉行慶館的時刻舉辦了一個達爾文主義的展覽：展品有標本、書信和手稿。這是一個盛大的慶典，一個值得紀念的人給了我們進化的思想。但是其中缺少一些東西，舉辦者放棄一些有吸引力的展品——自然選擇論。你可能已經預料到，南肯辛頓博物館（South Kensington Museum）現在是進化論的殿堂，它本來想要向公眾宣傳達爾文的理論。但是，對那些展覽中的管理員和策展人來說，這些都太有爭議了，更不願在大眾面前對進化辯論中做出承諾。不勇敢，但可以理解。到1909年，科學共識已經轉向達爾文的理論。自然選擇的進化幾乎滅絕了。
第二部分：達爾文的複興
就像達爾文主義處於最低點一樣，複興對於達爾文的批評者來說，他們自己正受到攻擊。先鋒和領導者是一位德國科學家，奧古斯特·魏斯曼（August Weismann）。魏斯曼既是醫生，又是一位生物學家，最重要的還是一個偉大的達爾文主義者。他將重振自然選擇的理由。他的主要展示是一種叫鳳蝶當納斯（Papilio dardanus）的昆蟲。鳳蝶當納斯是一種生活在非洲的蝴蝶，其物種的雌性是模仿的。這只雌性鳳蝶當納斯在這裏，模仿這裏所有的不相關的物種。這裏的這個模仿的是完全不同的東西。它在每一個細節上都是如此。經過許多代，雌性鳳蝶當納斯已經進化了。它們翅膀的形狀和顏色已經發生了改變...，..而原因是很明顯的。鳥類會吃掉蝴蝶，所以很多蝴蝶會進化出攻擊性的化學物質，讓它們看起來很討厭。鳳蝶當納斯不會這樣作，但通過模仿那些進化了的蝴蝶，它們可以愚弄了鳥。它們是自然界戰爭中的硬紙板坦克。
[奧古斯特·弗裏德裏希·利奧波德·魏斯曼（August Friedrich Leopold Weismann 1834年1月17日- 1914年11月5日）德國進化生物學家。恩斯特·邁爾（Ernst Mayr）將他列為十九世紀最著名的進化理論學家，僅次於查爾斯·達爾文。魏斯曼擔任動物研究所的所長，同時也是弗萊堡大學的動物學教授。他的主要貢獻是建立了“種質理論（Germ plasm theory）”，同時也被稱為魏斯曼學說。（譯者注）]
這裏，魏斯曼說道，證據表明達爾文是對的。只有自然選擇，那種緩慢而微妙的工匠，在無限微小的步驟中工作，可以使兩個無關的蝴蝶品種非常相似。
雨果·德·弗裏斯和他的同伴們認為，物種的起源是由單一的戲劇性突變產生的。
“不，”魏斯曼說，“它們是通過大量微小的突變積聚而逐漸進化的。”
自然選擇是一種微妙的力量，就像蝴蝶翅膀上的花紋一樣潛移默化的。
不過，魏斯曼保留了真實的憤怒情緒，對於另一個偉大的反達爾文主義理論拉馬克主義。他知道精子和卵子攜帶著遺傳物質。但是，他問道，它們是從哪裏來的呢？通過追蹤胚胎中細胞的起源和命運，魏斯曼意識到產生精子和卵子的細胞很快就從身體其他細胞中分離出來。它們形成了一個獨立的譜系。魏斯曼說，這就是為什麼人們不能把獲得的特性遺傳給後代，為什麼拉馬克是錯的，為什麼長頸鹿的脖子是徒勞無功的。
一個有機體可以爭取，受苦，伸展和犧牲，但是不能存在問題。所有的生命體都必須死亡，這是魏斯曼的觀點，只有你的卵子和精子傳遞的信息才能獲得永生。但是魏斯曼做了更多的事情。他推論遺傳的材料是每個精子和卵細胞核中的物理物質。他稱這種物質為種質材料。仔細觀察，他的同時代人在生殖質細胞內發現了不同的顆粒-染色體。隨著繁殖，染色體組合、交融和重組，但它們從不混合。它們總是完好無損地傳遞著。這對染色體的舞蹈證實了奧古斯丁牧師（Augustinian monk）早在三十年前所設想過的。
格裏格·孟德爾（Gregor Mendel），他是一個典型的科學英雄：他在摩拉維亞修道院工作，在離開了宗教工作後，在摩拉維亞進行豌豆育種工程，在一個默默無聞的刊物上發表兩篇論文，沒有人閱讀著兩份重要的文件，他們放棄了科學，就像許多偉大的科學家一樣，成為一名管理者。孟德爾被任命為布爾諾修道院院長。他放棄了他的實驗；他的出版物被遺忘了三十四年，當他去世時，他的文件被燒毀了。1900年，當他的實驗被重新發現並重新出版時，它們成為了科學傳奇的素材。想一想，你正在培育豌豆，青豆，黃豌豆，起皺的豌豆，光滑的豌豆。你計算每一代豌豆的數量，計算一些比率，然後你發現有別於其他人的一些東西，你就知道達爾文自己錯過了什麼。世間所有的生物遺傳法則。在孟德爾的“豌豆”中，利用數學法則解釋了性狀是如何代代相傳的。而且，非常奇妙的是，這些法則，僅僅是統計抽象，是自然選擇所需的繼承體系。他們給自然選擇提供了所需的可遺傳變異。
位於英國赫特福德郡的羅森斯特農業實驗站是進化生物學史上是一座不可思議的裏程碑。真正使它出名的是一個旨在估計肥料對農作物產量產生直接影響的實驗。這個實驗是在十九世紀四十年代開始的。每年都要收集和儲存樣品，並存放在那裏。直到1919年，他們聘請了一位年輕的劍橋數學家來幫助他們分析這些數據。他的名字叫羅納德·艾爾默·費舍爾（Ronald Aylmer Fisher）。費舍爾是一個天才。他極度近視，他已學會了在頭腦中可視化數學問題。你不會認為這樣聰明的人會願意從事農業產量的計算。但他喜歡這樣做。
有很多數據需要處理，沒有人知道他是怎樣做的。費舍爾說，沒有什麼問題，還發明了一些新的統計數據的辦法。一些新的統計數字？費舍爾發明了幾乎所有我曾經使用過的統計測試。而不僅僅是測試。當費雪想要解決一個問題時，他會發明一個全新的數學分支。但費舍爾感興趣的不僅僅是農作物的產量的提升。他也非常熱衷於優生學。
[羅納德·艾爾默·費舍爾（1890年2月17日- 1962年7月29日）英國統計學家和遺傳學家。由於他在統計學方面作出優異的貢獻，他被描述為“幾乎是一手創造了現代統計科學基礎的天才”和“二十世紀統計中最重要的人物”。在遺傳學方面，他的研究運用數學方法將孟德爾遺傳和自然選擇結合起來，這促成了二十世紀早期達爾文進化論的複興，即現代綜合理論的修正。費舍爾還做了農業實驗研究，使數百萬人免於饑餓。在接下來的幾年裏，他作為一名生物統計學家建立了自己的聲譽。他被認為是人口遺傳學的三個主要創始人之一。（譯者注）]
旁白：
在全國各地這樣的機構中，精神缺陷得到關注。
但如果他們從未出生，對他們和其他社區來說，這將會更好。費舍爾擔心英國人會變得越來越胖。窮人、不負責任的和愚蠢的人的繁殖，要遠比富人、節儉和聰明的人要多得多。所以你看，在短短四代人的時間裏，個人低於平均水平以下的人已經比富有的人多出五倍了。因此，如果我們想要維持一個高品質的人種，每個人都應該身心健康地嫁娶結婚，並且有足夠的孩子來延續他們的高貴血統。費舍爾自己是八個孩子的父親——這是他自己的優生學方案。這當然的和荒謬的。沒有證據表明這個國家的集體智商正在下降。然而，費舍爾的執著有了美妙的發現，出現了一些精彩的東西。對於計算之間的相關系數和養育後代，他考慮了自然選擇。對於費舍爾來說，自然選擇是一種力量，就像海浪拍打在沙灘上一樣。就像他們有時會毫不留情地拍打海岸，但有時也會輕輕回旋一下，所以自然的選擇可能是狂風或耳語，但它永遠不會消失。
就像海浪卷起來一樣，在海灘上篩選和排序鵝卵石，自然選擇同樣是篩選和排序物種內部的變化。這種排序就是進化本身。費舍爾形容這一切都可以用一個方程來描述。他稱之為這是自然選擇的基本定理，並且說它在生物科學中是至高無上的定律。他甚至認為自然選擇定律就像熱力學第二定律一樣具有普遍性。費舍爾把自然選擇變成了一個公式。但是一個沒有數據的公式並不是很好。你必須證明它確實有效——它說了一些非常有價值的東西，關於生存、呼吸和繁殖有用的東西。這使我們看到一種相當遲鈍的蛾子。一個自然選擇的故事正在發生。樺尺蠖（Biston betularia）的故事——善於偽裝的椒花蛾。曾幾何時，它是帶有象牙顏色的斑點。這種顏色非常適應周圍顏色，偽裝在林地彩色蝴蝶，利用林地地衣保護自己免受鳥類的捕食。但隨後發生了工業革命。煙灰殺死了地衣，把樹木也變黑了。飛蛾失去了偽裝，它們被暴露，容易受到攻擊。於是，他們開始快速進化。一種全新的黑色品種的蛾子蔓延開來。到二十世紀五十年代，它在英國各地被發現。
在森林裏，生物學家伯納德·凱特威爾（Bernard Kettlewell）進行了實驗，計算出變化的速度和自然選擇的強度，他發現這個了這個“方程”是成立的。凱特威爾：“每一個角色，每一種昆蟲，植物和人類本身，總是生存在集體的壓力之下。我們已經證明了在五十代內壓力是否足夠高。一個角色幾乎可以完全替代另一個角色。正是由於許多性狀的這種變化，才會引起新物種的逐漸進化。”而飛蛾也在繼續進化。
[亨利·伯納德·戴維斯·凱特威爾（Henry Bernard Davis Kettlewell 1907年2月24日- 1979年5月11日）是英國的遺傳學家，鱗翅類學者和醫學博士。世衛組織研究了工業黑變病對樺尺蠖(Biston betularia)汙染的影響，說明了在汙染地區為什麼樺尺蠖的顏色變得較深。這個實驗被認為是自然選擇在實踐中的經典應用。在與尼科爾·廷博根（Niko Tinbergen）的實驗視頻記錄後，休厄爾·賴特（Sewall Wright）稱這項研究為“一個明顯的進化過程已經被觀察到的最明顯的例子”。（譯者注）]
1956年，《清潔空氣法》（Clean Air Act）出臺，控制了來自全國天空的煙塵，樹木恢複了原貌。黑色的蝴蝶開始消失，白色的蝴蝶又回來了。進入了反向進化。自然選擇不僅存在，而且更加強大，進化比達爾文想象的要快得多。
但如果有一個地方能夠體現達爾文主義夢想的話，那就是馬拉維湖（Lake Malawi）。這是非洲三大湖泊之一，由大衛·利文斯通（David Livingstone）發現的，正如《物種起源》即將出版的那個時間。但在我們意識到這些水域的魚類有多了不起之前，我們花了一個世紀的時間尋找到它。很簡單，它們是達爾文理論最極好的證明。潛入其中，你注意到的第一件事是這些魚有多麼驚人的多樣性。它們彼此不同，它們的身體結構，嘴巴和牙齒的形狀都不一樣——它們的顏色和繁殖習性也不一樣，然而他們都是同一個家庭的成員。他們都是慈鯛科魚類的幼兒。兩百萬年以前，慈鯛科魚肯定進入這個湖泊並繁殖了。隨著時間的推移，湖泊水位上升和下降，創造了它們特殊的生存環境，充分利用每個棲息地的資源，不斷增強自己的身體機能終於進化成慈鯛。現在這裏有四五百種，甚至達到六百種魚類——比歐洲和美洲所有湖泊和河流裏的所有魚的種類都要多。
旁白：
“這不僅僅是因為這個湖有這麼多的麗魚物種，到底是怎樣就造成這種多樣化的呢，它們又有多少種不同的謀生方式呢，這裏被稱為長體擬麗魚（Pseudotropheus elongatus）呢，它靠岩石上的海藻梳理出來，以此為生。”
就是這樣的飲食方式造就了它有一張尖尖的嘴。它的牙齒排列很獨特，很像銼刀。帶著許多小牙齒，把它銼掉。可以刮掉了岩石上的海藻。這個...這裏的魚會把頭埋在泥沙中，張開嘴巴。然後吃掉生活在那裏的搖蚊蠓。這是它最引人注目的特點，在鉤嘴麗魚屬（Rhamphochromis）中最明顯。它是尤伯捕食者（uber-predator），食肉魚類，湖中的暴龍，啃噬，它有鋒利的牙齒，狼吞虎咽地吃任何東西。有什麼可驚訝的，這些魚就是他們所有的後裔，它們就是兩百萬年前進入這個湖泊的慈鯛後裔。有0到600條魚在大約200萬年前進入這個湖泊。這是地球上發生的最驚人的進化事件之一。
到二十世紀五十年代末，進化論有了一個新的公式。自然選擇的結合，隔離，孟德爾遺傳，和數學理論相互結合。這被稱為新達爾文合成理論。該公式和達爾文沒有關系，但並不影響他的理論。《物種起源》已經一百周年了，大家一致認為，達爾文的思想獲得了勝利。每個人都成為達爾文式論者。他們甚至比達爾文本人更達爾文。然而，當達爾文主義進入第二個世紀時，一些問題依然存在。自然選擇可能勝利了，但一些動物的行為仍難以解釋，在自然選擇的條件下是不行的。如利他主義，在一個由競爭驅動的世界裏，為什麼有些動物產生有利於其他動物的傾向呢？例如白蟻，在非洲草原上合作不懈地建造巨大的土丘。白蟻丘充滿了數百萬計的利他主義者，兵蟻和工蟻，他們的生活不是為了自己而是致力於維護和喂養女王。
他們是朝廷太監的白蟻，他們的存在是令人驚訝地難以解釋。根據達爾文的邏輯，生物是被設計出來的，通過自然選擇增加繁殖的機會。然而大多數白蟻都是不育的，它們根本不會繁殖。他們為殖民地工作，顯然沒有報酬。為什麼？1964年，動物學家比爾·漢密爾頓（Bill Hamilton），提出了解決利他主義問題的方法。一種解釋社會性昆蟲的存在。這一高度管制的行動由成千上萬的個人發起，是一種典型的社會昆蟲了不起的成就。漢密爾頓意識到任何殖民地的成員，有非常密切關系。因此，它們共享基因。僅僅是女王就代表殖民地複制了殖民地的基因。漢密爾頓說，這才是關鍵。如果你的利他行為有益於一個親戚，那麼你可能要付出代價。但至少你的一些基因會從中受益。自然選擇不計算個體的命運，它計算了基因的命運。白蟻戰士為他們的女王犧牲自己。因為她有很多種族基因，並傳遞基因。通過保護蟻，她的基因也就越多，因此它們的基因，這樣的傳遞比自己傳遞更可靠，才可能實現自己的個體基因。
[威廉·唐納德·漢密爾頓（William Donald Hamilton 1936年8月1日- 2000年3月7日）英國進化生物學家。漢密爾頓被認為是二十世紀最重要的進化理論家之一。他最為人所知的是他的理論著作，闡述了利他主義存在的嚴格遺傳基礎，利他主義是一種以基因為中心的進化觀點的發展的關鍵部分，被認為是社會生物學的先驅之一。（譯者注）]
這個思路不新鮮，早在六十年前就由著名的英國進化生物學家比爾·漢密爾頓（Bill Hamilton）首先提出來了。當年他正是在倫敦帝國學院舉辦的一次演講會上提出這一設想的，他通過數學計算證明這個方法可以讓某個物種滅絕，只要有足夠的時間就行。但因為基因技術本身的限制，這個設想一直無法付諸實踐，直到今年才終於獲得了成功。
這是達爾文主義的激進延伸，它催生了一門新的科學。在哈佛大學，E.O威爾遜給了它一個名字——社會生物學。在牛津大學，理查德·道金斯給了它一個口號——自私的基因。只要社會生物學家研究，他們解釋說，所有奇怪的動物都是自然選擇的產物，不是對個體，而是對他們的基因。每個個體都只是服從自己的基因。他們說，人類也一樣。我們的行為也可以用基因方案來解釋。通過自然選擇來塑造。這是社會生物學的基本原理。特定社會行為的基因存在。應用於人類，社會生物學似乎過於簡化。但毫無疑問，作為對動物行為的解釋，它勝利了。社會生物學的勝利就是自然選擇的勝利。在達爾文的時代，這股力量似乎是微弱而短暫的，現在則是無所不能，無所不在的。然而達爾文給我們的比自然選擇更多的東西，不僅僅是進化的機制。他也給了我們一個新的敘述，或者至少是一個承諾。他告訴我們，生命的曆史是史詩般力量和規模的故事，這是我們過去的發現。
第三部分：生命之樹
如果有達爾文理論的圖標，那就是這個。這是對所有進化史的一個隱喻。一棵樹——進化之樹。達爾文說，樹枝是種。通過樹枝它們與祖先相連。與他們的祖先們，深入到他們的過去。使生命的整個曆史可以表示為一棵宏大的樹。1837年，達爾文第一次構想了這樣的形象圖片。他畫了一個簡單的樹狀圖來，以顯示譜系也可來自於單一的來源，然後分枝和蔓延。在上面，他潦草地寫下了“我認為”。二十二年後，在《起源》中，他自信地斷言，就是這樣一棵樹。可以建造任何生物群。說起來容易，做起來難，達爾文甚至也沒有嘗試。
為什麼達爾文，如此大膽，如此有遠見，沒有告訴我們他的理論所暗示的生命的曆史？也許是因為他敏銳的意識到化石記錄的不足之處。這些岩石應該能對巨大的沖突作無聲的見證超過億萬年的時間。但是，正如理查德·歐文殘酷地揭露的那樣，現實情況卻大不相同。動物化石很豐富，但也存在巨大的差距。在寒武紀石層中看不出區別。這是，動物生命大爆炸時期發生了。新物種，整個動物群的出現，猶如天上掉下，他們沒有祖先。在那邊，這些是寒武紀岩石。這些岩石大約擁有5.25億年的曆史。它們包含動物生活的信息，諸如此類腕足類、介形蟲和三葉蟲的奇妙生物。這些岩石是前寒武紀，它們只有大約3000萬年的曆史。但它們的化石是空的。它們身上沒有動物遺骸。但這怎麼可能呢？如果這些前寒武紀岩石中沒有任何化石，這些動物是從哪裏來的？達爾文沒有回避這個問題。他寫道：“在這遼闊而時間未知的時期”，“這個世界一定擠滿了活生生的生物。”他承認，他不能生產這些生物，這是一個嚴重的困難時期。達爾文對能夠重建生命的曆史感到絕望。然而，他並不懷疑他的繼任者會這麼做。而他們卻做到了。
達爾文最忠實的門徒之一—— 一位年輕的德國科學家，恩斯特·海克爾（Ernst Haeckel）。在所有跟隨達爾文的科學家中，海克爾是最多變的。一位天才藝術家，他能揭示大自然優美的幾何圖形。除了他的筆，他也是一位傑出的解剖學家，花了幾個月的時間研究那些鮮為人知的海洋生物。他是個浪漫主義者，這是一個多愁善感、熱愛大自然哥德式崇拜的德國人。因為海克爾愛他的表妹安娜。她有金色的頭發和藍色的眼睛。他形容她是“森林裏一個真正的德國姑娘”。海克爾被她迷住了，娶了她。什麼是幸福！但僅僅過了幾個月，然後她就去世了。安娜的死讓海克爾精神失常。他考慮自殺。但後來他發現了宗教。不是基督教的虛假安慰，他們是苛刻的達爾文主義無神論者。他將成為它最大的使徒。他會把這本好書帶給德國大眾，他會宣揚真理，他會做達爾文所做的一切事。顯然，他沒能做到——他將改寫生命的曆史。
[恩斯特·海因裏希·菲利普·奧古斯特·海克爾（Ernst Heinrich Philipp August Haeckel 1834年2月16日 - 1919年8月9日）是一位德國生物學家、博物學家、哲學家、內科醫生、海洋生物學家和藝術家。他發現、描述和命名了數千種新物種，繪制了一種與所有生命形態相關的系譜樹，並在生物學中創造了許多術語，包括人類起源、生態、門、系統發育、幹細胞和原生生物。（譯者注）]
但如何寫呢？海克爾需要一種方法來重建過去的進化方式。這並不依賴於化石。他說，答案是研究胚胎。動物的胚胎信息包括，記錄了它過去的進化史。你可以看到在早期的發展中，你可以看到更遠的過去。海克爾說：胚胎，是阿裏阿德涅的線。他開始比較脊椎動物胚胎。就像你想象的那樣，很多人認為它們在出生之前就是不同的。但通過胚胎可以認識他們的過去，很久很久以前，而還沒有成長之前，他們看起來非常相似。它們有相同的背神經索，相同的咽縫。緊接著海克爾進一步深入研究了胚胎，在其早期發展時期。在四肢出現之前，在出現頭和尾巴之前，甚至更早時期，此刻，它只是與一個腸道的開端細胞球的時候，這是一個叫做“原腸的發展階段（gastrulation）”。在這裏，他覺得他發現了一些奇妙的東西——我們所有人的祖先。這裏，海克爾說，是一種紀念，一種回憶，這是最早動物標志的再現。一種生物，不會比一團鞭毛細胞更多，那曾經在前寒武紀的海洋中旋轉。他稱之為“加斯特雷亞（The gastrea）”。他說這是他最重要的發現。還有人說這是他最無恥的發明。海克爾使用胚胎來完善了進化樹理論。其中內容很多。它們看起來有點像達爾文的樹位，但它們不是抽象的隱喻，他們是第一次嘗試把所有生物都放在一起放置其進化的地方。所有的動物都在那裏，或多或少是正確的順序，在靠近樹幹底部一些地方導致所有其他動物的是加斯特雷亞——海克爾的假想——祖先野獸。
毫無疑問，海克爾的揣測太過於大膽了。胚胎不是一個包含生命曆史的簡單圖畫。然而，毫無疑問，他的猜測是，更多時候，來自於靈感。從二十世紀五十年代開始，就出現了少量的動物化石，從之前寒武紀岩石中被發現。數量稀少，有些僅僅是印記，有些則時間很短僅有一分鐘。但是，通過使用計算機斷層掃描成像，甚至可以看到單個細胞。而且，更重要的是，這是一些原始生物和海克爾的加斯特雷亞沒有太大的區別。但還有另一個原因讓我們認為動物是活著的，DNA告訴我們早在寒武紀之前。當沃森和克裏克闡明DNA的結構時，他們就組成了生命的結構。DNA的故事是毫無疑問，是最成功的故事之一。在科學史上非常重要。因為一般它不可能同時在兩個科學領域這麼快就作出這樣的重大發現。幾乎所有生物都將DNA作為遺傳載體。所以它們所有信息都必須記載與相關，正如達爾文所認為的，都來自一個祖先。但現在我們可以走的更遠一些。我們現在可以對任何生物的基因組進行排序解讀它，就像我們平常看書一樣。基因組序列是由上億個字母信息寫成的文檔。它們不斷重複，擦除和永無止境地增強，由進化這只手不停地在寫。如果你能讀懂它，你可以閱讀生命的曆史。
通過測序基因組，我們現在可以測定日期，在生命之樹上動物的起源。其中一些變化是驚人的古代時期。也許是所有動物中最簡單的，是一種被稱為絲盤蟲（Trichoplax）的微生物。它沒有內髒，嘴巴，大腦，甚至感覺器官都沒有。它的基因組表明它的祖先分離了，從主幹上動物就已經進化了，可能經過十億年的曆史。正如達爾文所設想的那樣，在前寒武紀的海洋裏一定會有很多動物。測序儀器正在揭示新的分支，在生命之樹上開始出現了分類。他們是給我們一種新的曆史敘述。但是，我們也發現了新的化石。通常，這個故事告訴他們是相同的。
考慮到鯨魚。鯨魚顯然是從一些哺乳動物進化而來的，但如果是這樣的話，鯨魚前身的化石在哪裏？那些有腿的鯨魚在哪裏？按照達爾文的邏輯，它們一定是存在的，而且一定是很大的。那麼它們哪裏？多年來，鯨魚的起源一直籠罩在默默無聞之中。沒有多長時間。近幾十年來，化石記錄變得非常完整，很奇妙。正如達爾文所預言的，正如達爾文所希望的那樣，我們現在有了一系列驚人的化石，展示了生活在陸地哺乳動物是如何向生活在海洋中的動物轉變的。它們展示了前肢是如何進化成鰭狀肢的，以及後肢如何退化的，以及鯨魚如何來呼吸的不是通過它們鼻孔，而是在它的後腦勺氣孔。
他們還向我們展示了一件事。他們告訴我們關於鯨魚在生命之樹上所處的位置。確切地說，鉸鏈的證據取決於腳踝骨上。事實證明，對於原始鯨魚來說，它們有腳踝骨，這與現代的有蹄類動物非常相似，比如牛，羊和豬。但我們並沒有單純依靠骨骼化石告訴我們關於鯨魚祖先的信息。我們也可以使用DNA測定。為了做到這一點，我們必須前往非洲一趟。將鯨類動物的DNA與其他哺乳動物的DNA進行比較。令人驚訝的事情出現了。他們最親密的關系就是河馬。鯨魚不是從河馬進化而來的，或者河馬是從鯨魚進化而來的。更確切地說，河馬和鯨魚都屬於同一目動物，因為河馬和鯨類是近親關系。他們也許是生活在遠古時代同一物種的後裔，那是在大約5500萬年之前。正是這種協議在DNA和化石之間證據，這使此案件的進化理由如此完全令人信服。所以，對於一種物種的進化使我們比其他問題更加關心。
有人可能會想到達爾文會說一些關於人類進化的事情。隨著在《物種起源》中他談到了。在四百多頁描述螞蟻、刺鼠、蝙蝠和甲殼蟲等等之後，整個動物的寓言，實際上，一直到斑馬，他終於平息了下來，開始考慮人類了。他所述如下：“光與火將拋出的人與他的曆史起源。”就是這樣。好的，謝謝你，親愛的查爾斯。
達爾文當然知道我們是猿類的後裔，但他讓其他人把它講出來。其中，恩斯特·海克爾。蓬勃發展的具有特色，他想象人類就像波提切利（Botticelli）的維納斯，在她周圍圍繞著野獸，使得她更加光輝燦爛。當時，沒有化石將人類與猿類聯系起來。於是他開始想象在他兩的中間應該會有什麼。沒有人類化石，這不是問題。讓我們創造一個介於猿和人之間的東西。讓我們給它起個名字——類猿人。讓我們給它一個真實的，恰當的拉丁名稱，猿人（Pithecanthropus）。像加斯頓（gastrea）一樣，猿人是一項發明，一個假設的祖先。然而，海克爾的推理是正確的。如果我們是從猿類進化而來的，遲早就會發現中間體的產物。
1891年，一位荷蘭醫生，尤金· 杜布瓦（Eugene Dubois），在爪哇的梭羅河畔進行挖掘時候發現這個頭蓋骨。它不是人類，不是猿猴，而是猿人。為了向海克爾致敬，杜布瓦稱它為“猿人”。在此後的幾個世紀，猿人已經獲得了一個新的名字，直立人，並已加入了其他化石收藏，一些是象猿的人類，其他人類的猿類。人類的族譜現在可以充滿物種了，這裏有一條清晰明確的線，在最早的類人猿和我們之間，智人。但是現在活著的類人猿中哪一支與我們是最親密的關系呢？這個問題，自達爾文時代以來就一直爭論不休，因為還沒有得到化石給與佐證。它需要DNA檢測才能得知。通過比較每一個類人猿的DNA序列，下降的進化順序已經很清楚了。與我們在基因上最接近的是黑猩猩和倭黑猩猩。五至六億年以前，我們的祖先是他們。七百萬年前，我們和大猩猩共享一個祖先。1200萬年前，我們就是黑猩猩。就這樣，等回到生命的開始。“你以為你是誰？”海克爾問道。他同時回答了問題，“你是猿猴，哺乳動物，爬行動物，魚，一個蠕蟲，一個細胞球，最後是一個單細胞。”“漂浮在原始海洋的鹽水子宮裏。”
一百五十年前，達爾文談到了時間，當生命之樹不僅僅是一個比喻，這將是一個准確的曆史記錄。那個時代很快就要到來。生命之樹就佇立在我們面前，在化石和DNA序列證據下，它的枝丫會變得越來越清晰，我們人類只不過是樹枝上的一片葉子而已，埋在它的巨大的分枝樹冠之中。
第四部分：無盡形態
到那時我們看到的將和現在大大不同了，形態、顏色和行為都會發生驚人變化。然而，在這種多樣性之下，有一項深入而統一的計劃。因為大多數動物的幾何形狀都差不多，同樣的基本結構計劃。對於達爾文來說，這是多樣性中統一的悖論。是生命之樹的禮物，物種產生的後果，不斷地適應無數代人。但達爾文從來沒有想到過在每個細胞中都能發現這種多樣性，每個生物的每個分子，每個基因，每一個生命的東西。幹得好，在哪兒呢？你能看到光嗎？我的光在哪裏？它在哪裏？埃莉（Ellie）是倫敦摩菲（Moorfields）眼科醫院的一名患者。她生下來就沒有虹膜。她的瞳孔巨大，因為不能收縮，所以她看東西很困難。虹膜現在到哪裏去了？現在去哪裏？這種紊亂被稱為無虹膜症。這種病症是因為突變引起的，她從母親那裏繼承來的基因。做得好，你的眼睛很可愛。她真是個好女孩。好，做得好。在1992年，遺傳學家確定了突變基因。現在，一個...好，好，好，好。位於11號染色體上，叫做PAX6。做得好，做得好。你真是個好女孩。PAX6是一種非常特殊的基因。這是一種分子開關，一種能開啟和關閉其他基因的基因，這個特殊的分子開關是人類眼睛構造所需要的。
然而，真正有趣的是接下來會發生什麼。1994年，遺傳學家研究了果蠅（Drosophila），尋找制造不同器官的基因。他們篩選了數千只果蠅，尋找導致異常的突變。其中一些變異導致果蠅成為“瞎子”。他們有一種叫做“無眼”的突變。正常的蒼蠅有大的，紅色的，複合的眼睛。沒有盲目的蒼蠅。通過分析無眼蠅的DNA，他們發現了突變基因。這是PAX6——同樣的基因，或者至少有“眼睛”方面的因素，這導致了人類無虹膜的原因。我記得當我們聽到這個結果時，我們都很驚訝。每個人都只知道人類的眼睛和蒼蠅的眼睛由獨立進化而來的。不然怎麼可能有這樣的結果，他們看起來是那麼的不同？但是發現他們的共同基因告訴我們他們共享一個進化史。
遺傳學家開始研究其他動物的眼睛無論他們看起來很不一樣，但是它們都有相同的基因。PAX6的分子電路是其中的一部分。這就是普遍存在的。眼睛是如此無處不在，如此有用，如此多樣，所以設計了各種功能。在二十世紀的大部分時間裏，動物學家曾爭論說，他們肯定已經進化了很多次。然而，這肯定是錯誤的。眼睛一次就進化成功了，所有的眼睛，屬於地球上所有的動物，可以追溯其來源到一個非常簡單的眼睛嗎？那是一個很簡單的生物，也許，在十億年前。
這是另一種變異體果蠅。它的眼睛很正常，但是它的腿多長了一雙，那應該是它長觸角的地方。這裏還有一個不同的突變體。它不是通常的兩個翅膀，而是四個。沒錯，它們有點畸形，但它們絕對是一組額外的翅膀。這些果蠅的Hox基因存在著突變。就像PAX6一樣，Hox基因也是分子開關。這樣就可以打開或關閉其他基因。它們決定了蒼蠅翅膀的基本幾何形狀、數量和位置。它的四肢和翅膀的部分。和PAX6一樣，Hox基因是普遍存在的。它們可以在包括我們在內的所有動物身上找到。各種動物的身體看起來是如此的不同。然而它們不是這麼簡單。蒼蠅有翅膀和細分的腳，我們有胳膊和脊椎骨。在你直看到胚胎之前，你可能認為只是一個簡單的比較。這是一個果蠅胚胎。這裏，一個接一個，Hox基因正在被表達著。他們確保每一個環節，從頭到尾，知道要做什麼結構。他們是精湛的邏輯，使用計算機程序，將細胞導向它們的命運。
這是一個人類胚胎。再一次，Hox基因沿著頭部到尾部被激活。確保我們的零件按正確的順序排列最後到正確的地方。更多的電路比果蠅更複雜得多，但邏輯是一樣的。發現了許多重要的基因在各種生物之間聯系讓人感到震驚。一門新的科學誕生了——進化發育生物學，演化發育生物學和短期科學。
像海克爾，我們將深入研究胚胎，以揭示我們的進化史。但是現在，我們不再研究我們的祖先是什麼樣子，我們會制定出它們遺傳基因計劃，使他們的樣子更加清晰。演化發育生物學（Evo-Devo）將解釋有機結構是如何同時發生的，如此相似，保守，卻又如此混亂。基因有一種矛盾的性質。看看任何動物，你都能看到許多相同的基因。做很多相同的事情。但是，仔細觀察它們，看看它們在胚胎中的作用，你可以看到所有多樣性的起源。這是四足動物的胚胎。隨著它的生長，Hox基因在一種萬花筒狀的模式下開啟和關閉。分子信號掃過肢體的胚芽，告訴每一個細胞。它是什麼，它必須變成什麼。四肢的細胞凝結成骨骼的輪廓。於是，鼴鼠長出了一只爪子。另一個胚胎，同樣的事情發生了...，..至少一開始是這樣。但是在這個胚胎中有更多的骨骼生長信號。四肢的骨骼變長了，手指間的細胞也長了沒有死亡，他們變成了織帶。因此，蝙蝠長出翅膀。兩個胚胎通過不同的方式開始了他們的生活，但僅僅是基因活性微妙的變化，就成為兩種完全不同的生物。
和海克爾一樣，我們也會深入研究胚胎，以揭示我們的進化史。但是現在，我們不去研究我們的祖先是什麼樣子，而是制定出他們的基因計劃。演化發育生物學將會解釋有機結構是如何同時具有相似和保守性的，然而，又是如此的混亂。基因有一種矛盾的性質。看看任何動物，你可以看到許多相同的基因在做同樣的事情。但是，仔細觀察它們，看看它們在胚胎中的作用，你可以看到所有多樣性的起源。這是四足動物的胚胎。隨著它的生長，Hox基因在一種萬花筒狀的模式下開啟和關閉。分子信號掃過四肢的芽，告訴每個細胞它是什麼以及它必須變成什麼。四肢的細胞凝集成骨骼的輪廓，所以鼴鼠長出了爪子。另一個胚胎，同樣的事情發生了...,..至少一開始是這樣。但是在這個胚胎中有更多的骨骼生長信號。四肢的骨頭長得更長，手指間的細胞不會死亡，它們變成了織網。蝙蝠長出翅膀。兩個胚胎在很大程度上開始了他們的生活，但隨著基因活動的微妙變化，它們變成了兩種完全不同的生物。
我可以講很多這樣的故事，關於嘴和羽毛的演變，鱗片，斑點和鼻子。但這是足夠的嗎？當然，科學的意義不僅僅在於講故事，更在於揭示自然規律。海克爾認為生物的對稱性是由簡單的定律引起的，與解釋晶體對稱性的定律沒有太大的區別。當然，生物比晶體複雜得多，但它們確實有幾何學。一種由巨大而複雜的基因、蛋白質和分子網絡組成的內部結構，它們共同工作以賦予生命。也許那時，自然界的戰爭不僅僅是個體之間的鬥爭，甚至是基因的鬥爭，而是在不同的組織生活方式之間的鬥爭。系統之間的鬥爭。在短期內，成功取決於是否強健。能夠經受住生存的變遷，然後繁衍。然而，從長遠來看，在進化的長期過程中，成功需要其他的東西，它需要靈活性。能夠對一個可變的或偶然的世界作出反應。讓我換種說法——在短期內，生物會進化。從長遠來看，它們在演變進化能力。
第五部分：進化的演變
大約十億年前，一種生物，像類似絲盤蟲，爬出了前寒武紀的淤泥。從表面上看，這可能並不引人注目。但似乎有一些新的、相當特別的東西。有關其基因網絡。它有一個足夠堅固的結構，靈活的足以改變。隨著時間的推移，這種組織生活的方式被複制了。經過無數次的修改。部分可以添加，甚至重新排列，然而，整個系統將繼續運轉。它是創新的引擎。它繼續征服世界。
自然選擇的進化理論是最美麗的科學產品之一。它提供了一個答案，唯一理性的答案，為生物承擔設計的標志。它如此簡單，如此有力，如此明顯的真實，人們很容易忘記這是多麼的不充分。有那麼多的問題我們無法回答...，為什麼這個湖上有六百種慈鯛，而不是六十或六千種呢？為什麼沒有麗魚科琵琶魚或麗魚科飛魚？或者，麗魚科鯊魚嗎？簡而言之，進化的極限是什麼？這個理論不夠充分，因為它不能預測。它解釋了演變的過程，但是不知道將要發生什麼樣子。有很多簡單的可能性，而且也沒有說哪一個選擇。我們只能沿著這條路走，重建路線。一旦它被完成了。但它必須一直如此嗎？
比較達爾文的進化論，根據牛頓對行星運動理論的描述和比較。畢竟，牛頓給了我們天體力學——這是一個數學理論。使我們可以對未來進行預測。這是達爾文沒有做過的，但是，我們能否做出進化的預測理論呢？我們是否可以計算出未來的生命嗎？很多人認為不可能。他們說，生命的進化是由法則和偶然性控制的。也許進化就像天氣一樣。只要有足夠的數據和計算能力，天氣預報員可以告訴我們周末是否會下雨。但是詢問他們一個月或一周之內的天氣情況，看看他們的預測，他們就會被不完美的數據打敗，而混亂隱藏在他們自己的方程式中。
然而，我仍然認為進化的預測理論是可能的。我之所以這麼做是因為對馬拉維湖的魚所做的研究。二百萬年的進化在這裏產生了六百種麗魚科的魚，以及驚人的多樣性形式。但更值得注意的是這一偉大的進化實驗並不是唯一的。沿著非洲大裂穀往西北走一百多英裏，你來到坦噶尼喀湖（Lake Tanganyika）。在那裏，也有在幾百萬年前到達的麗魚科魚。在那裏，它也在不斷地演變和成倍增長，不斷進化成數百萬計不同的種類。這兩個湖中的魚都只是和它們有遠程聯系，但是它們有相似的顏色，鰭，牙齒，飲食，習慣和棲息地。除了DNA不同之外，你很難說出它們的不同之處。換句話說，麗魚科進化已經運行了兩個時代，這兩個時代的結果是一樣的。正是這種重複性讓我思考，進化的大部分是可以預測的。
也許，對於我們的氣候，進化並不像天氣預報那樣簡單。在最壯觀的空間和時間規模上，大氣並不混亂。我們的地球物理學強加秩序和規定，因此，有一定的可預測性。所以，盡管我們幾乎無法告訴你明天會是什麼天氣，三周後，我們至少可以預測，三個百年後的氣候從概率上講還是可以預測的。
我認為進化是這樣的。當我們探索生物的內部幾何眾生時，我想我們會發現有確定性法則，該設計強加於反複無常的秩序。自然選擇和極限進化的路徑。當我們發現這些定律的時候，我們就可以建構進化的預測理論。我們將能夠完成達爾文的偉大工程。我們將解釋生活本身。“這種人生觀是偉大的，其中幾個權力最初已被吸收為幾種形式，或者變成了一種形式。”從如此簡單的開始，無盡的最美麗形式。“最奇妙的是，它們正在形成。”那這就起源的終點。也就是我們現代科學的起點。
英文版本（English version）：
Prof Armand Marie Lerol (Imprial College, London) ：
We live in a world of exquisite diversity, with more species than we can possibly count. Here in Lake Malawi, for instance, there are hundreds of different fish that are found nowhere else. Why so many? Why so different? 150 years ago Charles Darwin published On The Origin Of Species. And in that one great book he asked the right question..., ..and gave the right answer...
Where, asked Darwin, does all this diversity come from? And answered that it must be the product of evolution. Species, he argued, give rise to other species and as they do so, they change. The changes are minute and subtle, but given enough time the results could be spectacular. And so they are.
Darwin's explanation for life on earth was so seductive and so simple that it seems obvious today. And yet, Darwin's explanation of how evolution works Its logical foundations were shaky. His evidence was weak. There was so much he did not, could not, know. Darwin trusted that future generations of scientists would complete his work and prove the essential truth of his vision. And for 150 years that is what we have been doing.
In this film, I'll chart the decline, fall and ultimate triumph of Darwin's ideas. And I'll show how evolutionary theory has itself evolved, so that it is now far more vast and subtle than ever he imagined.
What Darwin Didn't Know
1 THE STRUGGLE FOR EXISTENCE
In September 1835 Charles Darwin arrived in the Galapagos Archipelago..., ..and did what he always did when arriving in a new place - he got out his gun and began to collect. Among the many inhabitants of the Galapagos that Darwin pinned, pickled, shot, or stuffed are these four birds. They don't look like much, but look at them closely. Look at them as Darwin looked at them, and you can see the beginnings of evolution. They are mocking birds. Each comes from a different island, and each is subtly different from the others. They differ in the shape of their bills and the size of their bodies, and the colour of their plumage. It was these differences that first caused Darwin to wonder whether species might transform over time.
Darwin surmised that the birds were variants of the same species and must therefore descend from a common ancestor - a mocking bird which had somehow found its way to the Galapagos many years earlier.That was Darwin's hunch, but how to prove it? He certainly couldn't produce the hypothetical ancestor - it was lost in time. So he did what scientists do when they don't have the data - he appealed to an analogy.
Darwin raised pigeons. Pigeons, for him, are a microcosm of evolution. They showed how any creature could, given enough time, be transformed into something very different from its ancestor. For, implausible though it may seem, these gorgeous, monstrous, inbred aristocrats of the avian world - the Scandaroon, the Frillback, the Jacobin, not to forget the Mookee - are all descended from this - the plebeian rock pigeon. All pigeons are, at birth, subtly different from each other. Breeders select those with desirable features to survive and reproduce..., ..and they cull the rest. The desirable features accumulate from generation to generation and become exaggerated. And so, remarkably quickly, the birds evolve.
Nature, Darwin said, works like that. It favours some features and permits others to whither away. He called this process natural selection. All this explains why the first chapter of The Origin Of Species is not about the wonders of the natural world, but rather about pigeons. Understand the pigeon, he is saying, believe the pigeon, and all the rest follows. Or does it? For Darwin had a problem. Natural selection was the cornerstone of his theory. It was, for him, the engine of evolution. And yet it was by no means clear that natural selection really worked. There is, he said, a war of nature. Famine, violence and death are everywhere. Species and individuals are locked in a struggle for existence. The strong survive and reproduce..., ..while the weak go to the wall. Given enough variation, this selective pressure is enough to bring about slow, incremental change. This was the theory of evolution by natural selection that Darwin unveiled in The Origin Of Species. While the idea of evolution was not in itself new, no-one had argued it more forcefully, or documented the evidence for it, with greater rigour. But was it right? Had Darwin really made his case? Of course, many religious types hated the very idea of evolution. But some of Darwin's fellow scientists weren't too keen either.
Notably Richard Owen, who wrote one of the first reviews of The Origin. Richard Owen, premier palaeontologist, coined the term 'dinosaur', helped design these things. Rampaging through a South London park, these marvellous reconstructions were built in the 1850s. They are a tableau of dinosaur life based on Owen's research. Owen had vague evolutionary leanings. He thought that species change intermittently, under the influence of some divine law and that periodically, they are swept away in some great catastrophe. He loathed Darwin's godless evolutionism. Owen was a thoroughly nasty piece of work. His review of The Origin, rich in malice, dripping with sarcasm, damns Darwin even as he praises himself. "Mr Darwin's rash speculations degrade science." "He's as bad as the French." "And", continues Owen, "he doesn't know anything about fossils." "If he did, he would know that" "ichthyosaurs appear in the lower Jurassic," stay there pretty much unchanged, and then just disappear - "no sign of evolution there."Owen's venom was probably born from mere spite.
Still, he did seem to have the fossil record on his side. According to Darwin's theory, gradual change should be visible in the rocks. But it wasn't. Instead, species seemed to arrive and depart, leaving little in between. Such gaps in the fossil record would haunt Darwin's theory. The evidence for natural selection simply wasn't there. Even his friends had their doubts.
Thomas Henry Huxley worked here at Imperial College London, where I now work. A firebrand and a populist, they called him Darwin's bulldog. Huxley also reviewed The Origin. "It's a magnificent work." "It makes the case for evolution." But then he turns to natural selection. "Yes, it's logical, yes, it's simple, but has Mr Darwin actually seen a species originate by natural selection?" "Can he even prove that it really exists?" "Well, no. It's a hypothesis," perhaps even the best one going, but, and I say this as a friend, "you understand, Mr Darwin really hasn't proved his point." Huxley said natural selection can't be seen. Others said it doesn't work. They claimed that it was logically flawed. That it was inconsistent with Darwin's account of inheritance, of how species transmit their features from one generation to the next.
This is how Darwin thought inheritance works. Suppose one parent has dark feathers, fur or skin, the colour of black coffee, while the other is milky white, their progeny would be a mix of the two. They would be a blend. It seems like an innocuous idea. Quite a reasonable one, too. After all, isn't this how human skin colour is inherited?
But Darwin had walked into a theoretical trap, and a Scottish engineer called Fleeming Jenkin sprang it. This is how Jenkin phrased the argument. "Imagine that a white man arrives on an island of negroes." He would, no doubt make himself king. "He would take many negro wives and father many mulatto children." "Yet no matter how successful our hero is, no matter how superior, his coffee-coloured descendants would become progressively darker." "Within a few generations, all trace of his presence would disappear." Let's ignore, if we can, the casual racism. This is Scotland in the 1860s, and Jenkin had a point. Variation is the stuff of evolution, and if variation blends then it disappears. And as it disappears, so the power of natural selection ebbs away.
Jenkin's challenge was serious, and Darwin had no response. How could he? His theory required some system, some law of inheritance in which variation did not blend, but remained stable over the generations. And yet no-one really knew how such a system could work. The thing is, Darwin knew all this. And we know that he knew because he told us so. Perhaps the most wonderful chapter of The Origin Of Species is Chapter VI. It's called Difficulties Of The Theory. Charles Darwin exposes, with unbearable candour, devastating honesty, all the weaknesses of his theory. He tells us all the reasons he may be wrong, the reasons that his critics pointed out, and more, but then, appeals to future generations of scientists to draw inspiration from his book, solve the difficulties with which his theory is riddled.
It's easy to forget that Darwin was not the first evolutionist. 50 years before The Origin Of Species, a Frenchman had proposed a theory of evolution, albeit less coherent and comprehensive than Darwin's. His name - Jean-Baptiste Lamarck. Lamarck was Professor of Zoology at the Museum d'Histoire Naturelle. They were, however, very different. When an animal, any animal, uses an organ, Lamarck argued, it becomes strengthened and enlarged. That's fairly obvious. We all know that exercise modifies the shape of our body. It's the same for other creatures as well. But Lamarck went further. He argued that these changes, acquired in one's lifetime, were passed on. And it is this, the inheritance of acquired characteristics, as it came to be known, that's the engine of evolution. The icon of Lamarckism is the giraffe. According to Lamarck, some ancestral giraffe had stretched its neck reaching for leaves on the highest branches. That stretched neck had been passed on to its offspring, who, in turn, had stretched their necks even further, so that now all giraffes have long necks. There is a seductive, intuitive, quality to Lamarck's logic, one that Darwin, confronting the inadequacies of his own theory, found increasingly hard to resist. The giraffe's neck is a cliche. It's in every textbook that explains the difference between Darwinian and Lamarckian evolution. But if you actually read what Darwin says about the giraffe in the sixth and final edition of The Origin, what you find is something rather different. First he talks about natural selection. That's what gives you the giraffe's neck. But then he adds another line about the inherited effects of the increased use of parts. Together, they give you the giraffe's neck. "Increased use of parts"? What's going on here? That's pure Lamarck. Can it be that Darwin, in his dotage, is becoming less Darwinian? Well, yes. Perhaps natural selection is not as powerful as once he had thought. A recantation? No. Just the candour of an old man who had spent his life trying to understand the world.
Darwin died in April 1882. He had wanted to be buried quietly near his house in Kent, but his supporters arranged a funeral here at Westminster Abbey. They turned the agnostic into a saint of the new secular materialist age. It was the apotheosis of Charles Robert Darwin. He had become a great Briton. But the eulogies rang hollow. Darwin had shown that life on earth was the result of natural laws. But what were those laws? Everyone - everyone, that is, who mattered - agreed that evolution was a fact. But natural selection? No thanks.
Even as Darwin lay in state, some Darwinians were breaking ranks. Chief among them, Dutch botanist, Hugo De Vries. Inspired by Darwin, he was searching for a suitable organism with which to investigate the workings of inheritance..., and found one. He chose a plant called Oenothera lamarckiana. Gardeners will know it as the evening primrose for it blooms at dusk. It is found throughout the dunes that protect Holland from the sea. And it's really just a weed. Though lovely for all that. De Vries discovered that Oenothera lamarckiana occasionally produces progeny that looked very different from itself, that have different stems, leaves, flowers. These new variants he found did not blend but were stable, as stable as new species. Coining a term, De Vries called these dramatic variations mutations. Following his discovery, De Vries was made director of the botanical gardens in Amsterdam. He bred and crossbred more Oenotheras, 53,000 of them. It seems like a lot, but then again, he was Dutch.
This is the palm house that Amsterdam built for De Vries. And these are some of his flowers pressed for posterity. They are ancient and desiccated but you can still see the differences in growth and form. Mutation, it seemed, could produce radically new plants. It could even, said De Vries, produce new species. This was all very unDarwinian. What of the vertiginous time scales, the infinity of incremental steps, the grandeur of Darwin's view of life? Irrelevant, said De Vries. The origin of species requires only one thing: mutation. He called it his Mutation Theory. It made him famous. For Lamarck, he said, the origin of species was a natural phenomenon.For Darwin, the object of scientific investigation, for De Vries, he liked to talk of himself in the third person, it was the object of experimental enquiry.
Lamarck, Darwin, De Vries. No doubts about HIS place in the pantheon, then. What De Vries or no-one else realised at the time was that Oenothera lamarckiana was a genetic freak. Few other organisms mutate so spectacularly. He has based his entire theory on one, very peculiar, species. That, however, didn't stop the rise of mutationism. Others began to investigate the oddities of nature.
In Britain, a Cambridge biologist, William Bateson, published materials for the study of variation. A collection of two-headed turtles, girls with four ears, and eight-fingered hands. It was a medieval monsters and marvels book, reworked for the evolutionary age. Mutation was the real creative force behind evolution and natural selection, said the mutationists, just wasn't needed.
London 1909. Darwin is long dead, and his theory is 50 years old. The British Museum of Natural History celebrates with an exhibition of Darwiniana: specimens, letters, manuscripts. It's a magnificent celebration, a worthy commemoration of the man who gave us evolution. But something is missing, something upon which the organisers refuse to be drawn. Natural selection. You might have expected that the South Kensington museum, now a temple of evolutionism, would have wanted to tell the public about Darwin's theory. But no, that's all too controversial for the keepers and curators who'd much rather not commit themselves in the great evolution debate. Hardly courageous, but understandable. By 1909 scientific consensus had shifted against Darwin's theory. Evolution by natural selection was almost extinct.
2 DARWIN RESURGENT
Just as Darwinism was at its nadir, a revival was underway. For Darwin's critics were, themselves, coming under attack. And leading the vanguard was a German scientist, August Weismann. And leading the vanguard was a German scientist, August Weismann. Weismann was a doctor, a biologist and above all a great Darwinian. He would revive the case for natural selection. His key exhibit, an insect called Papilio dardanus. Papilo dardanus is a butterfly that lives throughout Africa, and the females of the species are mimics.This female Papilio dardanus here mimicry this all together unrelated species. And this one over here mimics something completely different. And it does so in every detail. Over many generations, Papilio dardanus females have evolved. The shapes and colours of their wings have transformed..., ..and the reason why is very obvious. Birds eat butterflies, so many butterflies have evolved offensive chemicals that make them taste repugnant. Papilio dardanus doesn't, but by mimicking those that do, they can fool the birds. They are the cardboard tanks in the battle of nature.
Here, said Weismann, is evidence that Darwin was right. Only natural selection, that slow and subtle craftsman, working in infinitesimally small steps, could make two unrelated butterfly species so very much alike.
Hugo De Vries and his fellow mutationists had argued that species originate instantaneously by single dramatic mutations.
No, said Weismann, they evolve gradually by the accumulation of a great many tiny mutations.
Natural selection is a subtle force - as subtle as the markings on the wings of a butterfly.
But Weissman's real ire was reserved for that other great anti-Darwinian theory, Lamarckism. He knew that sperm and eggs carry the material of inheritance. But where, he asked, do they come from? By tracing the origin and fate of the cells in the embryo, Weismann realised that the cells that give rise to sperm and eggs were quickly isolated from the rest of the body's cells. That they formed a separate lineage. That, said Weissman, is why acquired characteristics could not be passed on to future generations, why Lamarck was wrong, and why the giraffe stretches its neck in vain.
A body would strive, suffer, stretch and sacrifice and none of it would matter. All bodies must die was Weismann's message, only your eggs and sperm have even a shot at immortality. But Weissman did more.He reasoned that the material of inheritance was something physical in the nucleus of each sperm and egg cell. He called this material germplasm. Looking closer, his contemporaries saw distinct particles within the germ plasm - chromosomes. With reproduction, chromosomes mix, mingle, and recombine, but they never blend. They are always passed on intact. This dance of the chromosomes confirmed what an Augustinian monk has supposed three decades earlier.
Gregor Mendel, he's the archetypal scientific hero: works away breeding peas in a Moravian monastery, publishes two luminous papers in an obscure journal that no-one reads, give up science and becomes, like so many great scientists, an administrator. Mendel was appointed abbot of Brno monastery. He abandoned his experiments; his publications were forgotten for 34 years, and when he died his papers were burned. When, in 1900, his experiments were rediscovered and republished, they became, however, the stuff of scientific legend. Think about it, you're breeding peas, green peas, yellow peas, wrinkled peas, smooth peas. You count the numbers of peas in each generation, calculate a few ratios, and you discover what everyone else, what Darwin himself had missed. The laws that rule the inheritance of nearly every living thing. Here, among Mendel's peas, were mathematical laws that explained how traits are passed down the generations. And, rather wonderfully, these laws, mere statistical abstractions, were the very system of inheritance that natural selection needed. They gave natural selection the supply of heritable variation that it needed to work.
Rothamsted Agricultural Station in Hertfordshire is an unlikely landmark in the history of evolutionary biology. What it's really famous for is an experiment aimed at estimating the effects of fertilizers on crop yields. The experiment had begun in the 1840s. Every year, samples had been collected and stored and there they lay. Until 1919 when they hired a young Cambridge mathematician to analyse them. His name was Ronald Aylmer Fisher. Fisher was a prodigy. Profoundly myopic, he had learnt to visualize mathematical problems in his head. You wouldn't think that such a clever man would be happy calculating agricultural yields. But he liked it. There were lots of numbers to crunch, and no-one knew how to do it. No problem, said Fisher, and invented some new statistics. Some new statistics? Fisher invented just about every statistical test I've ever used. And not just the tests. When Fisher wanted to solve a problem, he would invent a whole new branch of mathematics. But Fisher was interested in more than crop yields.He was also rather keen on eugenics.
NARRATOR:
In institutions such as this all over the country, mental defectives are cared for.
But it would have been better by far, for them and for the rest of the community, if they had never been born. Fisher was worried that the British were becoming thick. That the poor, feckless and stupid were outbreeding the rich, thrifty and smart. So you see, that in a mere matter of four generations individuals below the average have become more than five times as abundant as those above it. And so if we want to maintain the race at a high level, everybody sound in body and mind should marry and have enough children to perpetuate their stock and carry on the race. Fisher fathered eight children himself - his own personal eugenics programme. It was, of course, absurd. There's no evidence that the nation's collective IQ was in terminal decline. Yet out of Fisher's eugenical obsessions came something wonderful. For in the evenings between calculating correlation coefficients and fathering children, he thought about natural selection. For Fisher, natural selection was a force rather like the waves that beat against a beach. Just as they may at times pound the shore without relent and at other times lap gently, so too natural selection may gust or whisper, but it never disappears.
And just as the waves winnow, sift and sort the pebbles on this beach, so natural selection winnows, sifts and sorts the variation within species. And it is this sorting that is evolution itself. All this Fisher described with a single equation. He called it his Fundamental Theorem of Natural Selection, and said that it was supreme among the laws of biological science. He even compared it in its scope and power and generality to the Second Law of Thermodynamics. Fisher turned natural selection into a formula. But a formula without data isn't much good. You have to show that it actually works - that it says something useful about living, breathing, copulating creatures. Which brings us to a rather dull-looking moth. Here is a story of natural selection in action. The story of Biston bestularia - the peppered moth. Once upon a time, it was the colour of speckled ivory. This colour was an adaptation, camouflaging the moth as it rested on woodland lichens, protecting it from the birds that would prey on it. But then came the Industrial Revolution.Soot killed the lichens and turned the trees black. The moths were no longer camouflaged, they were exposed and vulnerable to attack. So they began to evolve - fast. A new, dark, form of the moth spread. By the 1950s it was found across Britain.
In the woods, biologist Bernard Kettlewell conducted experiments, calculated the rate of change and the strength of natural selection, and he found that the equations worked. Kettlewell: "Every character, in every species of insects, plant and man himself, is constantly under collective pressure. We have shown if the pressure is high enough within 50 generations one character can nearly entirely substitute another. It is due to such changes in many characters that new species are gradually evolving."And the moths have continued to evolve.
In 1956 the Clean Air Act scrubbed the soot from the nation's skies, and from the bark of the nation's trees. The dark moths began to disappear, and the light moths returned. Evolution went into reverse. Natural selection not only existed, it was far more powerful, and evolution far swifter, than Darwin had ever imagined.
But if there is a place of which Darwinians dream, it is Lake Malawi. One of the three great lakes of Africa, it was discovered by David Livingstone just as The Origin of Species was going to press. But it took the best part of a century before we realise just how remarkable are the fish in these waters. They are, quite simply, the most beautiful vindication of Darwin's theory. Dive among them, and the first thing you notice is how astonishingly various are these fish. They differ from each other in the shapes of their bodies, their mouth and teeth - in their colours and their breeding habits, and yet they are all members of the same family. They are all cichlids. Two million years ago a cichlid must have entered the lake and multiplied. Over time it seems the lake levels rose and fell, creating a universe of different habitats, each with its own resources to exploit, and each evolving its own set of cichlids. And now there are 400, 500, maybe 600 species here - more than all the species of fish in all the lakes and rivers of Europe or America.
NARRATOR:
"It's not just that this lake has so many species of cichlids, it's how diverse they, how many different ways in which they make a living.This fish over here is Pseudotropheus elongatus andit makes a living by scraping algae off rocks and combing through it."
This one does the same except it has an even more elaborate mouth. It has its teeth arranged rather like a rasp with lots of little teeth with which it files away and scrapes the algae off the rocks. This...this fish here buries it head in the sand, opens its mouth and gobbles up little Chironomid midges that are living there. And this thing is the most remarkable cichlid of all, Rhamphochromis. It is the uber-predator, the Tyrannosaurus of the lake, gobbling anything that it can with those formidable sharp teeth. What's so most amazing about these fish is that they're all descended from one cichlid that entered this lake about two million years ago. 0 to 600 fish in about two million years. It is one of the most astonishing evolutionary events that has ever happened on this planet.
By the end of the 1950s evolution had a new formula. A combination of natural selection, isolation, Mendelian inheritance, and mathematical theory. It was called the neo-Darwinian synthesis. The formula wasn't entirely Darwinian, but that didn't matter. On the centenary of The Origin of Species, everyone agreed that Darwin's vision had triumphed. Everyone was a Darwinian.You could almost say that they were more Darwinian than Darwin himself. And yet, as Darwinism entered its second century, some anomalies remained. Natural selection may have triumphed,yet some animal behaviours were still hard to explain in terms of natural selection. Such as altruism. In a world driven by competition, why are some animals altruistic? Termites, for instance, cooperate relentlessly building vast mounds on the African plain. A termite mound is filled with millions of altruists, the soldiers and workers whose lives are devoted to defending and feeding the queen.
They are the eunuchs of the termite state and their existence is surprisingly hard to explain. According to Darwinian logic, creatures are engineered by natural selection to increase their chances of reproduction. Yet most termites are sterile, they don't reproduce at all. They work for the colony, apparently without reward. Why? In 1964 zoologist, Bill Hamilton, proposed a solution to the problem of altruism. One that explained the existence of social insects. This highly regimented move by hundreds of thousands of individuals is a typically impressive achievement of the social insects. Hamilton realised that the members of any colony are very closely related. And, as such, they share genes. The queen alone is replicating the genes of the colony on its behalf. That, said Hamilton, is the key. If your altruistic act benefits a relative then you may pay a cost. But at least some of your genes will reap the benefit. Natural selection does not count the fates of individuals, it counts the fates of genes. Termite soldiers sacrifice themselves for their queen because she shares many of their genes. And by devoting their lives to her, are passed on than they could possibly achieve by themselves.
This was a radical extension of Darwinism and it spawned a new science. At Harvard E O Wilson gave it a name - sociobiology. At Oxford, Richard Dawkins gave it a slogan - The Selfish Gene. Wherever sociobiologists looked, they explained all the strange things animals do as the product of natural selection, not on individuals, but on their genes. Each individual is just obeying its own genes. And humans, they said, are no different. Our behaviours too, can be explained by genetic programmes shaped by natural selection. This is the fundamental principle of sociobiology. The genes for particular social behaviour exist. Applied to humans, sociobiology seems excessively reductive. But there's no doubt that as an explanation of animal behaviour, it triumphed. And sociobiology's triumph was the triumph of natural selection. A force, that in Darwin's time, seemed weak and ephemeral, was now omnipotent and omnipresent. Yet Darwin gave us more than natural selection, more than a mechanism of evolution. He also gave us a new narrative, or at least the promise of one. He told us that the history of life was a tale of epic forces and scales and that it was ours to discover.
3 TREE OF LIFE
If there is an icon of Darwin's theory, it is this. A metaphor for all evolutionary history. A tree. The twigs, Darwin said, were species. And they were connected to their ancestors by branches, and those ancestors to theirs, reaching deep into the past. So that the whole history of life could be represented as a great tree. Darwin first conceived this image in 1837. He sketched a simple tree-like diagram to show how lineages could originate from a single source and then diverge and proliferate. Above it he scribbled the words, "I think". 22 years later, in The Origin, he confidently asserts that just such a tree could be constructed for any group of creatures. Easy to say, hard to do, and Darwin didn't even try.
Why did Darwin, so bold and so visionary, not give us the history of life that his theory implied? Perhaps because he was so acutely aware of the deficiencies of the fossil record. The rocks ought to bear mute testimony to titanic conflicts playing out over eons of time. But, as Richard Owen had so cruelly exposed, the reality was rather different. Animal fossils were abundant, but there were also huge gaps. And nowhere was the gap greater than at the base of the Cambrian. That's when an explosion of animal life seems to have occurred. New species, entire faunas emerged as if from nowhere, their ancestors absent. Those rocks over there are Cambrian. That makes them around 525 million years old. And they contain animal life, wonderful creatures such as brachiopods, ostracods and trilobites. These rocks are Precambrian, they're only about 30 million years older. And yet they are empty. There are no animal remains in them whatsoever. But how could this be? If these Precambrian rocks didn't have any fossils in them, where did the animals come from? Characteristically, Darwin did not shirk the problem. "During these vast, and unknown periods of time", he wrote, "the world must have swarmed with living creatures." That he couldn't produce them was, he admitted, a grave difficulty. Darwin despaired of being able to reconstruct the history of life. Yet he did not doubt that his successors would do just that. And so they have.
Enter one of Darwin's most ardent disciples - a young German scientist, Ernst Haeckel. Of all the scientists who followed Darwin, Haeckel was the most protean. A gifted artist who could reveal nature's exquisite geometries with the stroke of a pen, he was also a brilliant anatomist, devoting months to the study of obscure sea creatures. And he was a romantic, of the sentimental, nature-loving Goethe - worshipping German kind. For Haeckel loved his cousin, Anna. She had golden hair and blue eyes. He described her as "a true German child of the forest." Haeckel was besotted with her and married her. What bliss! But for only a few months, and then she died. Anna's death left Haeckel unhinged. He contemplated suicide. But then he found religion. Not the false consolations of Christianity, but the harsh, godless clarity of Der Darwinismus. He would become its greatest apostle. He would take the good book to the German masses, he would preach the truth and he would do what Darwin had so conspicuously failed to do - he would re-write the history of life.
But how? Haeckel needed a way of reconstructing the evolutionary past that did not rely on fossils. The answer, he said, was to look at the embryo. The embryo of an animal contains, is, a record of its evolutionary past. The earlier in development you look, the further back into their past you can see. The embryo, Haeckel said, is Ariadne's thread. He began by comparing vertebrate embryos. Just before birth they seem very different, as you'd expect. But follow the embryos back in time, to when they are younger, and less developed, they look remarkably alike. They have the same dorsal nerve cords, the same pharyngeal slits. But Haeckel looked further, deeper into the embryo, earlier into its development. Before the limbs appear, before there's a head or a tail, and further yet, to when it is but a ball of cells with the beginnings of a gut. This is a stage of development called "gastrulation". And here he thought he found something wonderful - the ancestor of us all. Here, said Haeckel, is a remembrance, a recollection, a recapitulation of the very first animal. A creature, no more than a ball of flagellated cells, that had once whirled through the Precambrian seas. He called it the gastrea and said that it was his most important discovery. Others said it was his most outrageous invention. Haeckel used embryos to produce evolutionary trees. Lots of them. They look a bit like Darwin's tree, but they are not abstract metaphors, they are the first attempt to put every living thing in its evolutionary place. All the animals are there, in more or less the right order, and somewhere near the base of the trunk leading to all the other animals is the gastrea - Haeckel's hypothetical ancestral beast.
Haeckel's speculations were, no doubt, too bold. The embryo does not contain a simple picture of the history of life. And yet, there's no doubt that his guesses were, more often than not, inspired. Since the 1950s, a trickle of animal fossils has been emerging from Precambrian rocks. Some are little more than imprints, others are minute. But by using Computed Tomography Imaging, even individual cells can be seen. And, what's more, some of these proto-creatures are not so very different from Haeckel's gastrea. But there's another reason to think that animals lived long before the Cambrian and that's because DNA tells us so. When Watson and Crick elucidated the structure of DNA they unified life. The DNA story is without doubt one of the greatest success stories in the history of science. Because it can't be often that two newcomers to a field make such a major discovery so quickly. Nearly all living things use DNA as the stuff of inheritance. So they must all be related, and descend, much as Darwin had supposed, from a single ancestor. But now we can go further. We can sequence the genome of any living thing and read it as if we were reading a book. Genomes are documents written in billion of letters. They are palimpsests, endlessly augmented, erased, and rewritten by the hand of evolution. And if you can read them you can read the history of life.
By sequencing genomes we can now date the origin of animals in the tree of life. Some of them turn out to be astonishingly ancient. Perhaps the simplest of all animals is a microscopic creature called Trichoplax. It doesn't have a gut, a mouth, a brain, or even sense organs. Its genome suggests that its ancestors departed from the main trunk of animal evolution, perhaps a billion years old. Just as Darwin had supposed, there must have been animals in the Precambrian seas. The sequencing machines are revealing new branches on the tree of life. They are giving us a new historical narrative. But, we are also discovering new fossils.
And often, the story they tell is the same. Consider the whale. Whales obviously evolved from some land mammal but, if so, where were the fossil half-whales? Where were the whales with legs? By Darwin's logic, they must have existed and they must have been big. So where were they? For years, the origin of whales was shrouded in obscurity. Not any more. In recent decades, the fossil record has become wonderfully complete. Just as Darwin had predicted, just as Darwin had hoped, we now have an astonishing array of fossils that show how a land mammal makes a transition to one that lives in the sea. They show how front limbs evolved into flippers, and how hind limbs just wither away, and how a whale comes to breathe not through their nostrils in the tips of its snout but rather a blowhole in the back of its head.
And they show us one more thing. They tell us about the place of whales in the tree of life. The evidence hinges, literally, on an ankle bone. For primitive whales, it turns out, have ankle bones that are remarkably similar to those of modern ungulates, such as cows, sheep and pigs. Yet we don't have to rely on fossilised bones to tell us about the ancestry of whales. We can use DNA too. And to do that we have to go to Africa. Compare the DNA of a cetacean to that of any other mammal and something surprising emerges. Their closest living relation is this, a hippo. It's not that whales evolved from hippos, or that hippos evolved from whales. Rather, it is simply that hippos and cetaceans are, as it were, cousins. They are descended from a common ancestor that lived, perhaps, 55 million years ago. It is precisely this sort of agreement between DNA and fossil evidence that makes the case for evolution so utterly compelling. And so, to the evolution of the one species we care about more than any other.
One might have expected Darwin to say something about human evolution. And, in The Origin Of Species, he does. After 400 pages of ants and agoutis, bats and barnacles, the whole bestiary, in fact, right through to zebras, he settles down to consider humanity. And what he says is this. "Light will be thrown on the origin of Man and his history." And that's it. Well, thanks for that, Charles.
Darwin, of course, knew we were descended from apes, but left others to spell it out. Among them, Ernst Haeckel. With a characteristic flourish, he imagined humanity like Botticelli's Venus, rising gloriously from the brutes that surround her. At the time, there were no fossils linking man to apes. And so he set to imagining what lay between. No human fossils, no problem. Let's just invent one. Something between an ape and a man. Let's give it a name. Ape man. Let's give it a real, proper, Latin name, Pithecanthropus. Like the gastrea, Pithecanthropus was an invention, a hypothetical ancestor. Yet Haeckel's reasoning was sound. If we were descended from apes, then sooner or later intermediates would be found.
In 1891, a Dutch physician, Eugene Dubois, digging in the banks of the Solo River in Java discovered this skullcap. It wasn't human, it wasn't ape, it was an ape man. In homage to Haeckel, Dubois called it Pithecanthropus. In the centuries since, Pithecanthropus has acquired a new name, Homo erectus, and has been joined by a collection of other fossils, some, apish humans, others, human apes.
150 years ago, Darwin spoke of a time when the tree of life would be more than a metaphor, when it would be an accurate historical record. That time has come. The tree of life stands before us, its branches becoming clearer with every fossil and DNA sequence, and our species is but a leaf on a twig, buried within in its vast and ramifying canopy.
4 ENDLESS FORMS
When we look at living things it is the differences that we first see, the astonishing variety of form, colour and behaviour. And yet, beneath this diversity runs a deep, unifying plan. For most animals have much the same geometry, the same basic body plan. For Darwin, this paradox of unity within diversity was the gift of the tree of life, the consequence of species giving rise to species, endlessly adapting over countless generations. But what Darwin could never have imagined is that such unity within diversity can be found in every cell, every molecule and every gene of every living thing. Well done, where's that? Can you look at the light? Where's my light? Where's that? Ellie is a patient at Moorfields Hospital in London. She was born without irises. Her pupils are enormous for they cannot contract, and she can barely see. Where's it gone now? Where's it gone now? The disorder is called Aniridia and it's caused by a mutation that she inherited from her mother. Well done, oh, you get a lovely view of your eye. She's such a good girl. Good, well done. In 1992, geneticists identified the mutant gene. Now that one... Good, good, good, good. Located on chromosome 11, it's called PAX6. Well done, well done. You're such a good girl. PAX6 is a very special kind of gene. It's a molecular switch, a gene that turns other genes on and off, and this particular molecular switch is needed in the construction of the human eye.
The really interesting bit, however, is what happens next. In 1994, geneticists were studying fruit flies, searching for the genes that make its different organs. They screened thousands of flies for mutations that cause abnormality. Some of the mutant flies were blind. They had a mutation called eyeless. Normal flies have large, red, compound eyes. Eyeless flies have none. Analysing the DNA of eyeless flies, they identified the mutant gene. It was PAX6 - the same gene, or at least its fly version, that causes aniridia in humans. I remember how amazed we all were when we heard about this result. Everyone just knew that human eyes and fly eyes had evolved independently. How could it be otherwise - they just looked so very different? But the discovery that they shared a gene told us that they shared an evolutionary history.
Geneticists started looking into the eyes of other animals and wherever they looked, they found the same thing. The molecular circuit of which PAX6 is a part is universal. Eyes are so ubiquitous, so useful and so various in their design, that for most of the 20th century, zoologists had argued that they must have evolved many times. This, however, must be wrong. Eyes have evolved only once. All the eyes, belonging to all the animals on earth, can trace their origin to one very simple eye that belonged to one, doubtless, very simple creature that lived, perhaps, one billion years ago.
Here is another mutant fruit fly. Its eyes are quite normal, but it has an extra pair of legs where its antennae should be. And here's a different mutant. Instead of the usual two wings, it has four. True, they're a little deformed, but they're definitely an extra set of wings. These flies have mutations in their Hox genes. Like PAX6, Hox genes are molecular switches that turn other genes on and off. They determine a fly's basic geometry, the number and position of its segments, limbs and wings. And like PAX6, Hox genes are universal. They can be found in all animals, including us. Animal bodies seem so very different from each other. And yet they are not. A fly has wings and segments, we have arms and vertebrae. A facile comparison, you may think, until you look at the embryo. This is a fruit fly embryo. And here, one by one, the Hox genes are being expressed. They ensure that every segment, head to tail, knows what structure to make. They work with the exquisite Boolean logic of a computer programme, directing cells to their fates.
This is a human embryo. Once again, Hox genes are activated from head to tail. Make sure our parts are arranged in the correct order and get to the right place. More circuits are much more complicated than Drosophila, but the logic is the same. It was shocking to discover that many important genes are linked between various creatures. A new science was born - evolutionary developmental biology, evolutionary developmental biology, and short-term.
Like Haeckel, we would delve into the embryo to unravel our evolutionary past. But now, instead of working out what our ancestors looked like, we'd work out the genetic programmes that made them. Evo-Devo would explain how organic structures can be, at once, so similar and conservative and, yet, so promiscuously different. There is a paradoxical quality to genes. Look at any animal and you can see many of the same genes doing much the same thing. And yet, look at them closely, look at them working in the embryo, and you can see the origins of all diversity. This is the embryo of a tetrapod. As it grows, Hox genes switch on and off in a kaleidoscopic pattern. Molecular signals sweep across the limb buds, telling each cell what it is and what it must become. The cells of the limb condense into the outline of bones and so a mole grows a paw. Another embryo and the same thing happens..., ..at least to begin with. But there's far more bone growth signal in this embryo. The bones of the limb grow longer and the cells between the fingers do not die, they become webbing. And so a bat grows a wing. Two embryos that start their lives in much the way, but with just a subtle shift in gene activity, become two very different creatures.
I could tell many such stories about the evolution of beaks and feathers, scales and spots and snouts. But is it enough? Surely the point of science is not merely to tell stories, but rather to reveal the laws of nature. Haeckel believed that the symmetries shown by living things were caused by simple laws, not very different from those that explained the symmetries of crystals. Living things are, of course, much more complex than crystals, yet they do have a geometry. An internal one composed of vast and intricate networks of genes, proteins and molecules, all working together to give life. Perhaps then, the war of nature is not simply a struggle among individuals, or even genes, but a struggle among different ways of organising life. A struggle among systems. In the short run, success depends on being robust. On being able to weather the vicissitudes of existence and then reproduce. In the long run, however, in the evolutionary long run, success needs something else, it needs flexibility. On being able to respond to a mutable and contingent world. Let me put it another way - in the short run, creatures evolve. In the long run, they evolve evolvability.
5 THE EVOLUTION OF EVOLUTION
About a billion years ago, a creature, something like Trichoplax, crawled out of the pre - Cambrian ooze. Superficially, it may have been unremarkable. But it seems that there was something new and rather special about its genetic network. It had a structure that was robust enough to be strong, yet flexible enough to change. Over time, this way of organising life was copied and modified countless times. Parts could added, even rearranged, and yet the system as a whole would continue to work. It was an engine of innovation and it went on to conquer the world.
The theory of evolution by natural selection is one of the most beautiful products of science. It provided an answer, the only rational one we have, as to why living things bear the hallmarks of design. It is so beguilingly simple, so powerful and so manifestly true, that it is easy to forget just how inadequate it is. There are so many questions that we can't answer...，Why are there 600 species of cichlid in this lake and not 60 or 6,000? Why are there no anglerfish cichlids, or flying fish cichlids? Or, cichlid sharks? What, in short, are the limits to evolution? The theory is inadequate because it is not predictive. It explains what has evolved, but not what will. There are simply too many possible streams and there's no saying which one will be chosen. We can only follow the journey and reconstruct the route once it is done. But must it always be so?
Compare Darwin's theory of evolution to Newton's account of the planetary motions. Newton, after all, gave us celestial mechanics - a mathematical theory that enables us to make predictions far into the future. Darwin did nothing of the kind, but can we, perhaps, make a predictive theory of evolution? Can we compute the future of life? Many would say no. The evolution of life, they say, is ruled by chaos and contingency. Perhaps evolution is like the weather. Given enough data and computing power, forecasters can tell us whether or not it will rain at the weekend. But ask them about a month of Sundays and their predictions fall apart - defeated by imperfect data and the chaos concealed in their own equations.
And yet, I still think a predictive theory of evolution might be possible. And the reason I do is because of the fish in Lake Malawi. Two million years of evolution have produced 600 species of cichlid here and an astonishing diversity of form. But what's even more remarkable is that this great evolutionary experiment is not unique. Follow the African rift north-west for just a few hundred miles and you come to Lake Tanganyika. There, too, a cichlid arrived a few million years ago and there, too, it multiplied and evolved into hundreds of different species. The fish in both lakes are only remotely related, but they have similar colours, fins, teeth, diets, habits and habitats. You can hardly tell some of them apart without DNA. In other words, the tape of cichlid evolution has been run twice and both times the outcome has been much the same. It's this repeatability that makes me think that much of evolution is indeed predictable. Perhaps then evolution does not so much resemble the weather as it does our climate. At the grandest scales of space and time, the atmosphere is not chaotic. The physics of our planet imposes order and, thus, predictability upon it. So, although we can scarcely tell what the weather will be three weeks from now, we can predict, at least probabilistically, what the climate will be three centuries hence.
I think evolution is like that. As we explore the internal geometry of living things, I think we'll discover that there are deterministic laws that impose order upon the capricious designs of natural selection and that limit the paths of evolution. And when we discover those laws, we'll be able to construct a predictive theory of evolution. We'll be able to complete Darwin's great project. We'll explain life itself. "There is grandeur in this view of life, with its several powers having been originally breathed into a few forms, or into one." From so simple a beginning, endless forms most beautiful "and most wonderful have and are being evolved." That is how The Origin ends. And it is how our science begins.
文字：《傑特遜工作室》(JENTSON STUDIO) 制作
視頻：《傑特遜工作室》(JENTSON STUDIO) 紀錄片數據庫BBC-014號
翻譯：趙永安
