God in the details: The Biochemical Challenge to Evolution
Jerry A. Coyne reviews Dr. Michael Behe's new book Darwin's Black Box:
細節里的上帝
——評《達爾文的黑匣子》
The goal of creationists has always been to replace the teaching of evolution with the narrative given in the first eleven chapters of Genesis. When the courts stymied this effort, creationists tried a new strategy: cloaking themselves in the mantle of science. This produced the oxymoronic 'scientific creationism', arguing that the very facts of biology and geology show that the Earth is young, all species were created suddenly and simultaneously, and mass extinctions were caused by a great world-wide flood. The resemblance between this theory and the book of Genesis was, of course, purely coincidental. Scientific creationism, however, also came to grief. Virtually all creation 'scientists' were religious fundamentalists without biological expertise, and American courts clearly spied clerical collars beneath the lab coats.
In Darwin's Black Box, Michael Behe offers a new and more sophisticated version of scientific creationism. Unlike his predecessors, Behe is a genuine scientist, a biochemist from Lehigh University in Pennsylvania. The book jacket asserts that he is not a creationist, but believes in the scientific method. His argument, however, is a recycled version of the creationist notion that 'complex design' implies an intelligent designer. But where William Paley illustrated this logic with a watch, Behe uses biochemistry. His intended audience of lay readers may be impressed by the elaborate descriptions of molecular biology and long lists of references, but Behe's 'scientific' alternative to evolution ultimately becomes a confusing and untestable farrago of contradictory ideas.
Behe's thesis is that organisms harbour molecular pathways so elaborate and interconnected that they cannot be explained by gradual evolution from simpler precursors. His examples of such pathways, described with admirable clarity, include blood- clotting, the immune system and intracellular transport. These share what he calls "irreducible complexity": they would not function if any single component were removed. Because Darwinism requires that a pathway be useful at every stage of its evolution, Behe claims that such irreducibly complex pathways could not evolve in steps. Their existence therefore implies conscious design and an intelligent designer. (Like all scientific creationists, Behe keeps quiet about the identity of the Great Designer, but the author's professed Roman Catholicism offers one clue.) Evolutionists are said to resist this idea of design because of our dogged but unreasonable dislike of supernatural explanations. Behe, however, is free from this constraint. With paternal pride, he declares that his discovery of biochemical design "must be ranked as one of the greatest achievements in the history of science", rivalling "those of Newton and Einstein, Lavoisier and Schrodinger, Pasteur, and Darwin".
There is no doubt that the pathways described by Behe are dauntingly complex, and their evolution will be hard to unravel. Unlike anatomical structures, the evolution of which can be traced with fossils, biochemical evolution must be reconstructed from highly evolved living organisms, and we may forever be unable to envisage the first proto-pathways. It is not valid, however, to assume that, because one man cannot imagine such pathways, they could not have existed. Moreover, a J.B.S. Haklane pointed out: "My own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose." We face not only the absence of data, but also the awful fact that we ourselves are evolved creatures with limited cognition and imagination.
The answer to Behe's argument lies in realizing that biochemical pathways did not evolve by the sequential addition of steps to pathways that became functional only at the end. Instead, they have been rigged up with pieces co-opted from other pathways, duplicated genes and early multifunctional enzymes. Thrombin, for example, is one of the key proteins in blood- clotting, but also acts in cell division, and is related to the digestive enzyme trypsin. Who knows which function came first? Behe makes a few half-hearted attempts to build up such pathways, but quickly abandons the enterprise and cries "design".
Evolutionists will find two other problems with Behe's arguments. First, there is ample evidence for the evolution of morphology and anatomy from studies of palaeontology, embryology, biogeography and vestigial organs. Such evolution must, of course, be based on the evolution of molecules and biochemical pathways. Second, we have plenty of direct evidence for the evolution of molecules. This includes the remarkable congruence between phylogenies based on anatomy and those based on DNA or protein sequence (bat haemoglobin, for example, is far more similar to that of whales than of birds), the relatedness of genes through gene duplication (including those involved in the immune system and blood-clotting), and the existence of vestigial 'pseudogenes' that were useful in ancestors. (Unlike most mammals, humans cannot synthesize vitamin C, we still carry the gene for the final step in this pathway, but deletions have rendered it non-functional.)
進化論者會發現在Behe的論證中還有兩個問題。首先，古生物學、胚胎學、生物地理學和退化器官的研究為形態和結構的進化提供了大量的證據。形態和結構的進化理所當然地必須以分子和生化途徑的進化為基礎。其次，我們也有有關分子進化的充分的直接證據。這包括，根據解剖結構構建的種系發生樹和根據ＤＮＡ或蛋白質系列構建的種系發生樹具有顯著的一致性（比如，蝙蝠的血紅蛋白質與鯨的形似性遠遠高於與鳥的），通過基因重複導致的基因的親緣性（包括那些參與免疫系統和血液凝固的基因），以及存在那些在祖先中有過作用而現在已喪失功能的退化的「假基因」（與大多數哺乳動物不同，人類不能合成維生素Ｃ，但是我們具有在此路徑的最後步驟起作用的基因，只不過刪除突變使它不起功能）。
Behe's response to these problems constitutes the major weakness of his theory. He chews on the idea of morphological evolution, but cannot bring himself to swallow it. He finds the idea of common descent of all organisms "fairly convincing", and admits that microevolution occurs within species, but sees no evidence for transitions between major forms. (How one can admit common descent but deny macroevolution is one of the fascinating questions Behe leaves unanswered.) Finally, in a tactic unique in the creationist literature, he admits that both evolution and creation might occur at the molecular level. Such a hybrid theory, however, yields sterile offspring, such as Behe's idea that the first 'designed' cell could include the DNA for all future evolutionary change, including that producing eyes and the immune system.
Responding to observations of non-functional genes and inefficient molecular processes, Behe theorizes that he Great Designer, like his counterparts in Paris and Milan, has goals beyond functionality: "Features that strike us as odd in a design might have been placed there by the designer for a reason -- for artistic reasons, for variety, to show off, for some as-yet-undetectable practical purpose, or for some unguessable reason -- or they might not." One should add the "puckish reason": to confuse future biologists by making things look as though they evolved.
我們已發現無功能的基因和效率低下的分子過程，對此Behe建立了一個理論，認為大設計者，就象他在巴黎和米蘭的同僚，懷有功能性之外的目的：「那些讓我們覺得奇怪的特徵之所以被設計者放在那裡，可能有一個原因－－為了藝術的原因，為了多樣化，為了炫耀，為了還未被發覺的實用目的，或者為了無法猜測的原因－－或者根本就沒有原因。」我們還可以再加一個「惡作劇的原因」：讓後來的生物學家誤以為生物是進化來的。
If one accepts Behe's idea that both evolution and creation can operate together, and that the Designer's goals are unfathomable, then one confronts an airtight theory that can't be proved wrong. I can imagine evidence that would falsify evolution (a hominid fossil in the Precambrian would do nicely), but none that could falsify Behe's composite theory. Even if, after immense effort, we are able to understand the evolution of a complex biochemical pathway, Behe could simply claim that evidence for design resides in the other unexplained pathways. Because we will never explain everything, there will always be evidence for design. This regressive ad hoc creationism may seem clever, but it is certainly not science. As the theologian Dietrich Bonhoeffer pointed out, it is also bad religion: "If in fact the frontiers of knowledge are being pushed farther and farther back (and that is bound to be the case), then God is being pushed back with them, and is therefore continually in retreat."
如果接受Behe的觀念，認為進化和神創能夠同時存在以及設計者的目的是深不可測的，那麼人們就遇到了一個無法被證明是錯誤的密不透風的理論。我能夠想象否證進化論的證據（在前寒武紀發現一具猿人化石將會成功地否征它），但是沒有人能夠否證Behe的雜合理論。即使在巨大的努力之後我們能夠明了一個複雜的生化途徑的進化，Behe也能夠簡單地聲明設計的證據存在於其它未解釋的途徑之中。因為我們將永遠無法解釋所有的事情，就總會有設計的證據存在。這種退化的特定神創論看上去似乎很聰明，但是毫無疑問不是科學。正如神學家Dietrich Bonhoeffer所指出的，它也是很糟糕的宗教：「如果在事實上知識的前沿一直在不斷地越來越遠地推進（而這是肯定的），然後上帝也跟著一直不斷地被推開，這是在持續後退。」
In the end, Darwin's Black Box is a work of advocacy whose creationist ancestry is revealed by both its rhetoric and its failure to deal honestly with the evidence for evolution. There is the usual selective quotation of evolutionists (including, to my horror, a remark of my own, both altered and taken out of context), ridicule of scientists, and a folksy 'us-against-them' style reflecting the populist roots of creationism. The book will no doubt be widely cited by Biblical creationists who will tout its message of design wile ignoring its timid acceptance of evolution and its view of the creator as Cosmic Prankster.
最後，《達爾文的黑匣子》是一部詭辯性的著作，它同時展示了前神創論者的花言巧語和不能誠實地對待進化的證據。在其中，有精心挑選出來的進化論者語錄（我有幸也被經篡改和斷章取義地選了一條評論），有對科學家們的奚落，以及隨意的神創論大眾「逆反」基礎。這本書毫無疑問將被神創論者們所廣泛引用，這些人將會兜售它的宣揚設計的詞句，而忽視它對進化論羞羞答答的接納和把造物主視為宇宙惡作劇者的看法。
If the history of science shows us anything, it is that we get nowhere by labelling our ignorance 'God'. Lord Kelvin declared that the primaeval Earth had cooled down too quickly to permit the great age required by Darwinism. How could he imagine that radioactivity would be discovered four decades later and prove the missing source of heat? Duane Gish, the doyen of American creationists, once argued for the separate creation of mammals and reptiles, based on their jaw structure. Each has a jaw joint made from a different pair of bones, and Gish could not imagine how the transitional form could chew while its jaw was being unhinged and rearticulated. In 1958, however, Fuzz Crompton described a mammal-like reptile with a double jaw joint that included both pairs of bones. The evolution of biochemical pathways is certainly queerer than Professor Behe can suppose.