Vestiges of Creation: A Pivotal Work in the History of Evolutionary Thought, Slides of Science education

Download Vestiges of Creation: A Pivotal Work in the History of Evolutionary Thought and more Slides Science education in PDF only on Docsity! C EVIDENCE OF EVOLUTION MARY NICOLE G. MATA 10-SINAI > EVIDENCE FROM VESTIGES > EVIDENCE FROM BIOCHEMISTRY > EVIDENCE FROM BIOGEOGRAPHY   The most common example of a vestige is the presents of small, internal hind leg bones in modern whales, passed on to them by their land- dwelling mammalian ancestors. The response by many creationists—most notably of which; Kent Hovind, in his series, Lies in the Textbooks—is that if a proposed vestige has any function at all, it isn’t really a vestige, and that this applies to whales since their leg bones play a roll in reproduction. What these creationists fail to understand is that the definition of a vestige has never been an evolutionary remnant with no function—it’s always been an evolutionary remnant that has lost or nearly lost its original primary function. If it has any current function, it’s either a persisting secondary function, or a function gained sometime after the lost of its primary one—a process called exaptation, or co-opting. • . •       This concept was known even as far back as Charles Darwin. Now, in Darwin’s day, the term ‘vestigial organ’ didn’t exist; but the idea the term describes was something Darwin wrote on in both his publication, The Descent of Man, and in this very publication. He used the terms ‘rudiments’ and ‘rudimentary,’ rather than ‘vestiges’ and ‘vestigial.’ On pages 451-452 of the original publication of On the Origin of Species, Darwin wrote: • An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose; and remain perfectly efficient for the other … Again, an organ may become rudimentary for its proper purpose, and be used for a distinct object: in certain fish the swim-bladder seems to be rudimentary for its proper function of giving buoyancy, but has become converted into a nascent breathing organ or lung. Other similar instances could be given ( Darwin, 1859, p.451-452).    Now that the basic idea has been explained, here are six ways exaptation can occur—with examples of each—as explained by Dr. Gregory on pages 361 through 363 of his publication on complex organ evolution:       There are several possible routes by which an organ, components of an organ, or genes can become exaptations (Gould and Vrba 1982; Arnold 1994; Gould 2002; McLennan 2008): the middle ear bones of mammals are derived from former jaw bones (Shubin 2007).1. One organ (or gene) has an existing function but takes on or switches to a new function as a result of selective pressures experienced after the organism moves into a new environment or adopts a new ecological lifestyle... Example: 2. One organ (or gene) has an existing function but at some stage modification of the feature for the initial function makes it amenable to modification in a new role and this allows the organism to move into a new environment or adopt a new ecological lifestyle. Example: early tetrapod limbs were modified from lobe- fins and probably functioned in pushing through aquatic vegetation; at some point, they became sufficiently modified to allow movement on to land (Shubin et al. 2006). 5. A feature that had become vestigial in terms of its original function takes on a new function in its reduced state. Example: the vestigial hind limbs of boid snakes are now used in mating (Hall 2003). 6. A feature that formerly had no function and was present for non- adaptive reasons (a "spandrel"; Gould and Lewontin 1979; Gould 1997, 2002) takes on a function and may become specialized for that function. This, too, can occur at both the genetic level and the organ level. Example 1: the sutures in infant mammal skulls are useful in assisting live birth but were already present in non-mammalian ancestors where they were simply byproducts of skull development (Darwin 1859). Example 2: some formerly parasitic transposable elements in the genome, which had no function at the organism level, have been co-opted into a variety of other roles, such as in the vertebrate adaptive immune system (e.g., Zhou et al. 2004). The important point regarding exaptations, then, is that the current function of a feature may not reflect the reasons for its origin. Rather, the feature may only have come to occupy its current role comparatively recently.        Now that it’s been established what vestiges are, how they form, how they provide evidence for common ancestry, and how the creationist objection from functionality is invalid, let's take a look at some specific examples of structural, anatomical, and reflexive vestiges. First Sere (ad Fish beeench = bEearech Gill shit 1 Mental saorta Embryological Development 7 ue oe Ob) Miaaniads: Eustacthian rurtie- Bortal aorta 5 uc aos ie. Aivlerbcer here - ~ Pgthrerkaany nearer ej (“Left Vagus Right Vagus Li Right iV =\ | tine? SS) fl Left Recurrent Recurrent Af ee ets Be Laryngeal Nerve Laryngeal & ' : Nerve CS LS }.Left ; | oh MAS ubclavian Rig ht _<J racked, Subclavians}—_/ Artery : • 2. The gonads of sharks, other fish, and even humans develop in same place—the chest. This works well for sharks, since they stay there, but in human males, the gonads need to travel all the way down into the scrotum to keep cool. This causes an unnecessary looping of the spermatic cord, which causes a weakness in there body wall, leaving them prone to developing a hernia (Shubin, 2009, p.64-66). This is consistent with decent, with modification, from an ancestor we share with modern fish. » Hiccups The hic of hiccups can at times be caused by blockages or lesions that crimp ane of the phrenic nerves, which control breathing and are an evolutionary hand-me-down from fish. These nerves relay brain signals that induce aspasm of muscles in the throat and chest, causing the epiglottis to shut the windpipe. The sharp inspiration and blocking of the throat, the hic, are a legacy of a tadpole’s pumping of water into its mouth when breathing through its gills. As it ingests water, its glottis clases to prevent fluid from entering its lungs, which are used for breathing on land. Windpipe © 2008 SCIENTIFIC AMERICAN, INC. Closed Phrenic nerve •    Vestigial reflexes •    1. Signals are sent from the human brain, through the phrenic nerves, that induce synchronous spasms of the diaphragm. The subsequent sharp inhalation of air closes the epiglottis. This is commonly known as the hiccups. The evidence, as laid out by Dr. Straus (2003), that it is a vestigial reflex is as follows: sor aE a eee — Sa Pare Pigneent layer —————_ sirakawn germninatiwu9n {stratum Spios un, str.sihorm basake —— armnechor pili mauesche sebaceous gland ——S hair Follicle —— papillae of heir — meee File bho ad lynne wees eels Peacmian corpuscile dere! papell j Sono ere eoadliirey Fear erect 4 — EPIDERMIS. DERMIS if SUBCUTIES he pod erieis) • 2. In many particularly hairy vertebrates, such as apes, dogs, and rats, the involuntary erection of hairs via the contraction of muscles, called Arrectores pilorum, act as an efficient means of thermoregulation. This is achieved by trapping insulating air against the skin. Humans, however, are not hairy enough for this reflex to have any significant effect in regulating their temperature. The involuntary erection of hair is also an emotive reflex in many vertebrates, increasing their apparent size to intimidate predators when afraid, to intimidate rivals when angry, or to convey various other emotions (Darwin, 1872, p.95-102). The only secondary purpose Arrectores pilorum serve is in aiding the sebaceous gland in secreting sebum (Song et. al., 2007). • Vestiges of the Natural History of Creation is an 1844 work of speculative natural history and philosophy by Robert Chambers. Published anonymously in England, it brought together various ideas of stellar evolution with the progressive transmutation of species in an accessible narrative which tied together numerous scientific theories of the age. • Vestiges was initially well received by polite Victorian society and became an international bestseller, but its unorthodox themes contradicted the natural theology fashionable at the time and were reviled by clergymen – and subsequently by scientists who readily found fault with its amateurish deficiencies. The ideas in the book were favoured by Radicals, but its presentation remained popular with a much wider public. Prince Albert read it aloud to Queen Victoria in 1845. Vestiges caused a shift in popular opinion which – Charles Darwin believed – prepared the public mind for the scientific theories of evolution by natural selection which followed from the publication of On the Origin of Species in 1859. • For decades there was speculation about its authorship. The 12th edition, published in 1884, revealed officially that the author was Robert Chambers, a Scottish journalist, who had written the book in St Andrews between 1841 and 1844 while recovering from a psychiatric illness.[1] Initially, Chambers had proposed the title The Natural History of Creation, but friends persuaded him to revise the title in deference to the Scottish geologist James Hutton, who had remarked of the timeless aspect of geology: "no vestige of a beginning, no prospect of an end". Some of the inspiration for the work derived from the Edinburgh Phrenological Society whose materialist influence reached a climax between 1825 and 1840. George Combe, the leading proponent of phrenological thinking, had published his influential The Constitution of Man in 1828. Chambers was closely involved with Combe's associates William A.F. Browne and Hewett Cottrell Watson who did much to spell out the materialist theory of the mind. Chambers died in 1871 and is buried in the grounds of St Andrews Cathedral, within the ancient chapel of St Regulus. Now it is possible that wants and the exercise of faculties have entered in some manner into the production of the phenomena which we have been considering; but certainly not in the way suggested by Lamarck, whose whole notion is obviously so inadequate to account for the rise of the organic kingdoms, that we only can place it with pity among the follies of the wise. (p.231) In an (anonymous) autobiographical preface written in the third person that only appeared in the 10th edition, Chambers remarked that "He had heard of the hypothesis of Lamarck; but it seemed to him to proceed upon a vicious circle, and he dismissed it as wholly inadequate to account for the existence of animated species."[4] • RECEPTION • The book quickly became a best-seller, and a sensation which was eagerly read in royal circles. Every afternoon for a period early in 1845, Prince Albert read it aloud to Queen Victoria as a suitable popular science book explaining the latest ideas from the continent.[5] Abraham Lincoln is reported to have read the book and been "deeply impressed with the notion of the so-called 'universal law' – evolution."[6] It was well received by middle class readers and unorthodox clergymen, particularly of Nonconformist church groups such as Unitarians. At first scientists ignored the book and it took time before hostile reviews were published, but the book was then publicly denounced by scientists, preachers, and statesmen. Notably, Sir David Brewster, wrote a very critical review of the work in the North British Review, where he stated: Robert Chambers, the anonymous author of Vestiges • The establishment might have tolerated a predesigned law of creation, but Vestiges presented a progressive law with humanity as its goal, and thus continuity which treated the human race as the last step in the ascent of animal life. It included arguments that mental and moral faculties were not unique to humans, but resulted from expansion of brain size during this ascent. This materialism was rejected by the religious and scientific establishment, and scientists were incensed that Chambers had bypassed their authority by appealing directly to the reading public and reaching a wide audience.[9] • Early praise[edit] The publisher John Churchill had, as instructed, distributed free review copies to numerous daily and weekly newspapers, and many carried advertisements giving one line quotations or ran excerpts from the book, with even the Scottish evangelical Witness giving it publicity and credence in this way. Several carried substantial reviews, one of the first appearing in mid November 1844 in the weekly reform newspaper the Examiner:[10] In this small and unpretending volume, we have found so many great results of knowledge and reflection, that we cannot too earnestly recommend it to the attention of thoughtful men. It is the first attempt that has been made to connect the natural sciences into a history of creation. An attempt which presupposed learning, extensive and various; but not the large and liberal wisdom, the profound philosophical suggestion, the lofty spirit of beneficence, and the exquisite grace of manner which make up the charm of this extraordinary book.[11] • As a result of this publicity the first edition of 1,750 copies sold out in a few days. Among those fortunate enough to have ordered their copy promptly, Tennyson commented to his bookseller that the review suggested it "seems to contain many speculations with which I have been familiar for years, and on which I have written more than one poem." Having read the book, he concluded "There was nothing degrading in the theory." Benjamin Disraeli told his sister that the book was "convulsing the world, anonymous" and his wife told her that "Dizzy says it does and will cause the greatest sensation and confusion."[11][12] • The limited number of copies available at first were targeted at a select fashionable readership. The late Autumn literary season was just getting under way as the first reviews appeared, and by early January the book was the subject of conversations at elite literary gatherings. At venues such as Buckingham Palace and Lady Byron's parties, cosmic evolution became a topic of discussion for the first time in many years.[12] Reforming medical journals including The Lancet for 23 November 1844 carried favourable reviews, while criticising specific points.[13] In January the Unitarian quarterly Prospective gave powerful support, but the influential prestige quarterlies which could determine the long term success of books were still looking for reviewers.[14][15] • Anglican clergymen were usually quick to publish pamphlets on any theological controversy, but tended to excuse themselves from responding to Vestiges as they lacked expertise: men of science were expected to lead the counterattack. The universities of Oxford and Cambridge were part of the Anglican establishment, intended to educate Christian gentlemen with half of the students becoming clergymen. Science subjects were optional lectures. The professors were scientific clergymen with strong reputations, and at Cambridge science had developed as natural theology, but there was no unified scientific establishment. The quarterly review magazines turned to them for commentary on the book, but demonstrating that it was superficial was difficult when its range of topics meant experts being drawn into superficial responses outside their own area of intensive expertise. William Whewell refused all requests for a review to avoid dignifying the "bold, speculative and false" work, but was the first to give a response, publishing Indications of a Creator in mid February 1845 as a slim and elegant volume of "theological extracts" from his writings. His aim was to inform superficial London society used to skimming books as conversation pieces and lacking properly prepared minds to deal with real philosophy and real science, and he avoided mentioning Vestiges by name. During the crucial early months of the debate this and Hume's lecture distributed as a pamphlet were the only responses to Vestiges published by the established clergy, and there were just two other short works opposing it: a published lecture by the Anabaptist preacher John Sheppard, and an unorthodox anti-science piece by Samuel Richard Bosanquet.[17][18] • There was a wide range of readings of the book among the aristocracy interested in science, who assessed it independently without dismissing it out of hand. Sir John Cam Hobhouse wrote his thoughts down in his diary: "In spite of the allusions to the creative will of God the cosmogony is atheistic—at least the introduction of an author of all things seems very like a formality for the sake of saving appearances—it is not a necessary part of the scheme". While disquieted by its information on embryology implying human origins from animals, he thought its tone was good. He concluded that "It does not meddle with revealed religion—but unless I am mistaken the leaders of revealed religion will meddle with it." Lord Morpeth thought it had "much that is able, startling, striking" and progressive development did not conflict with Genesis more than then current geology, but did "not care much for the notion that we are engendered by monkeys" and objected strongly to the idea that the Earth was "a member of a democracy" of similar planets.[19] • Vestiges was published in New York, and in response the April 1845 issue of the North American Review published a long review,[20] the start of which was scathing about its reliance on speculative scientific theories: "The writer has taken up almost every questionable fact and startling hypothesis, that have been promulgated by proficients and pretenders in science during the present century...The nebular hypothesis... spontaneous generation...the Macleay system, dogs playing dominoes, negroes born of white parents, materialism, phrenology, - he adopts them all, and makes them play an important part in his own magnificent theory, to the exclusion, to a great degree, of the well-accredited facts and established doctrines of science."[21] • Sedgwick's long, rambling and scathing article was published in the July 1845 edition of the Edinburgh Review.[26] Articles were anonymous, but he ensured that his authorship was well known. He had disregarded William Whewell's caution about attempting a point by point refutation, and the body of his review followed the structure of Vestiges, packed with current evidence to undermine the supposition of continuous transitions underlying the progressive development hypothesis which he scorned as mere speculation, and pointing out errors showing the inadequate expertise of the author. Vestiges crucially undermined the separation between man and beast, and endangered hopes for the afterlife. Sedgwick expressed concern for "our glorious maidens and matrons .... listening to the seductions of this author; who comes before them with a bright, polished, and many-coloured surface, and the serpent coils of a false philosophy, and asks them again to stretch out their hands and pluck forbidden fruit", who tells them "that their Bible is a fable when it teaches them that they were made in the image of God—that they are the children of apes and breeders of monsters—that he has annulled all distinction between physical and moral", which in Sedgwick's view would lead to "a rank, unbending and degrading materialism" lacking the proper reading of nature as analogy to draw moral lessons from physical truths. That needed the use of reason by great men who believed that "moral truth is the ennobled form of material truth" and that "all nature, both material and moral, has been framed and supported by one creative mind" so that one truth could never be in conflict with another. In presenting natural law as explaining the soul, Vestiges threatened the fine balance between faith and science.[27][28] • Journals that had already opposed the book welcomed Sedgwick's article, with the Literary Gazette calling it a "scourging and irrefragable review", as did sections of the church which were suspicious of science and geology. However, its crude vehemence was ill suited to fashionable society, and Whewell wrote "To me the material appears excellent, but the workmanship bad, and I doubt if it will do its work." Aristocrats found its "lengthy inefficiency" heavy going, and John Gibson Lockhart of the Tory Quarterly Review suspected that "The savants are all sore at the vestige man because they are likely to be in the same boat as him." The extreme liberal press also thought "a mere anonymous bookmaker might well be sacrificed to evidence the orthodoxy of a Cambridge divine", in the hope of "immunity to their own speculations, by a cheap display of eloquent zeal against all who dare to go beyond their measure."[29] • Explanations: A Sequel[edit] • There was renewed debate in correspondence in newspapers. The publisher Churchill advised the anonymous author against meeting attacks by going to the people with a cheap edition, and was told that the author was "writing a defence of the book, with particular reference to the coarse attack of Mr. Sedgfield", with the intention of publishing it as letters to The Times followed by a pamphlet. On Churchill's advice the response was broadened into a 206-page book bound to match the original work, which was published at the end of 1845 at a price of five shillings under the title of Explanations: A Sequel to the Vestiges of the Natural History of Creation, a "forcible and argumentative work" aimed at "convincing open-minded men", published anonymously "By the author of that work". The revised fifth edition of Vestiges was ready in January 1846, and the two were commonly sold together, catching the publicity from reviews of Explanations.[30] • Sedgwick added a 400+ page preface to the 5th edition of his Discourse on the Studies of the University of Cambridge (1850), including a lengthy attack on Vestiges and theories of development in general. • Among religious criticisms, some maintained that Chambers' use of "natural law" to explain the creation of the planets and the successive creation of new species, including man, excluded the possibility of miracles and providential control. In other words, under this scheme, God did not personally interact with His creation after bringing forth these initial Laws. For these critics, this was akin to denying the central miracle of Christianity and, therefore, Christianity itself.[35] • Darwin and Vestiges[edit] • Among the early readers of Vestiges, Charles Darwin had conceived his own theory of natural selection to explain evolution six years earlier, and in July 1844 had written down his ideas in an '"Essay". For a year he had been tentatively discussing his evolutionary ideas in correspondence with Joseph Dalton Hooker, who wrote to Darwin on 30 December 1844 that he had "been delighted with Vestiges, from the multiplicity of facts he brings together, though I do [not] agree with his conclusions at all, he must be a funny fellow: somehow the books looks more like a 9 days wonder than a lasting work: it certainly is “filling at the price”.— I mean the price its reading costs, for it is dear enough otherwise; he has lots of errors."[36] Darwin had read the book in November, finding that it drew on some of the lines of evidence he had been putting together, and introduced questions that had to be dealt with.[37] He responded that he had been "somewhat less amused at it .... the writing & arrangement are certainly admirable, but his geology strikes me as bad, & his zoology far worse.[38] Darwin had learnt geology from Adam Sedgwick, and was particularly interested in what his former mentor had to say about evolution. In October 1845 he wrote to his friend Charles Lyell that Sedgwick's review was a "grand piece of argument against mutability of species" which he had read with "fear & trembling," but had been "well pleased to find" that he had anticipated Sedgwick's objections and "had not overlooked any of the arguments". [39] • He read Explanations early in 1846 and thought "the spirit of [it], though not the facts, ought to shame Sedgwick", while noting speculation and evidence suggesting that Chambers had written the books.[40] In April 1847, after meeting Chambers then subsequently receiving a presentation of Vestiges, Darwin became convinced that Chambers must have been the author.[41] • In his introduction to On the Origin of Species, published in 1859, Darwin assumed that his readers were aware of Vestiges, and wrote identifying what he felt was one of its gravest deficiencies with regards to its theory of biological evolution: • It is probable that Darwin read Chambers's comments, because he removed the offending passage from the 3rd edition of the Origin (1861) and all subsequent editions.[44] In a historical sketch, newly added to the 3rd edition, Darwin softened his language a bit: • The author apparently believes that organisation progresses by sudden leaps, but that the effects produced by the conditions of life are gradual. He argues with much force on general grounds that species are not immutable productions. But I cannot see how the two supposed "impulses" account in a scientific sense for the numerous and beautiful co- adaptations which we see throughout nature; I cannot see that we thus gain any insight how, for instance, a woodpecker has become adapted to its peculiar habits of life. The work, from its powerful and brilliant style, though displaying in the earlier editions little accurate knowledge and a great want of scientific caution, immediately had a very wide circulation.[45] • Darwin even suggested that Chambers' book helped pave the way for the publication of his theory of evolution by natural selection. "In my opinion it has done excellent service in this country in calling attention to the subject, in removing prejudice, and in thus preparing the ground for the reception of analogous views."[45] • The harsh reception that Vestiges received, and the mockery which was made of its evolutionary ideas, has been cited by some historians as a factor leading to Darwin's caution in publishing his own theory of evolution. In a letter to Thomas Henry Huxley in 1854 (five years before his own book on evolution was published but twelve years after its ideas had first been sketched out in an unpublished essay), Darwin expressed sympathy for the (still anonymous) author of Vestiges in the face of a savage review by Huxley: "I must think that such a book, if it does no other good, spreads the taste for Natural Science. But I am perhaps no fair judge, for I am almost as unorthodox about species as the Vestiges itself, though I hope not quite so unphilosophical."[46] However, later the same year, in a letter to Hooker, Darwin mentioned Vestiges in a more sober tone: "I should have less scruple in troubling you if I had any confidence what my work would turn out. Sometimes I think it will be good, at other times I really feel as much ashamed of myself as the author of the Vestiges ought to be of himself."[47] • According to the historian James A. Secord, Vestiges outsold The Origin of Species up until the early 20th century • Robert Chambers became a prominent suspect as early as the spring of 1845. In 1854, following the publication of the 10th edition of Vestiges along with its anonymous biographical sketch, a former assistant named David Page accused Chambers directly. The accusation was printed in the Athenaeum, but because Page was an embittered former employee of the Chambers's firm, his testimony was not taken very seriously. Vyvyan finally denied that he was the author outright and the British Museum listed the book under George Combe's name as late as 1877.[56] • After Robert's death in 1871 his brother, William, penned a biography for Robert but refused to reveal the secret.[57] He only mentioned the Vestiges to note that Robert's suspected authorship was used as a means to discredit him when he ran for the office of Lord Provost of Edinburgh in 1848. The secret was finally revealed at last in 1884 when Alexander Ireland issued a new 12th edition with Robert's name and an introduction explaining the circumstances behind its publication. •EVIDENCE FROM BIOCHEMISTRY •Evidence for Intelligent Design from Biochemistry • He succeeded brilliantly. Cleverly, Darwin didn't try to discover a real pathway that evolution might have used to make the eye. Instead, he pointed to modern animals with different kinds of eyes, ranging from the simple to the complex, and suggested that the evolution of the human eye might have involved similar organs as intermediates. •Here is a paraphrase of Darwin's argument. Although humans have complex camera-type eyes, many animals get by with less. Some tiny creatures have just a simple group of pigmented cells, or not much more than a light sensitive spot. That simple arrangement can hardly be said to confer vision, but it can sense light and dark, and so it meets the creature's needs. The light-sensing organ of some starfishes is somewhat more sophisticated. Their eye is located in a depressed region. This allows the animal to sense which direction the light is coming from, since the curvature of the depression blocks off light from some directions. If the curvature becomes more pronounced, the directional sense of the eye improves. But more curvature lessens the amount of light that enters the eye, decreasing its sensitivity. The sensitivity can be increased by placement of gelatinous material in the cavity to act as a lens. Some modern animals have eyes with such crude lenses. Gradual improvements in the lens could then provide an image of increasing sharpness, as the requirements of the animal's environment dictated. • Using reasoning like this, Darwin convinced many of his readers that an evolutionary pathway leads from the simplest light sensitive spot to the sophisticated camera-eye of man. But the question remains, how did vision begin? Darwin persuaded much of the world that a modern eye evolved gradually from a simpler structure, but he did not even try to explain where his starting point for the simple light sensitive spot came from. On the contrary, Darwin dismissed the question of the eye's ultimate origin: • GTP-transducin-activated rhodopsin now binds to a protein called phosphodiesterase, located in the inner membrane of the cell. When attached to activated rhodopsin and its entourage, the phosphodiesterase acquires the ability to chemically cut a molecule called cGMP (a chemical relative of both GDP and GTP). Initially there are a lot of cGMP molecules in the cell, but the phosphodiesterase lowers its concentration, like a pulled plug lowers the water level in a bathtub. • Another membrane protein that binds cGMP is called an ion channel. It acts as a gateway that regulates the number of sodium ions in the cell. Normally the ion channel allows sodium ions to flow into the cell, while a separate protein actively pumps them out again. The dual action of the ion channel and pump keeps the level of sodium ions in the cell within a narrow range. When the amount of cGMP is reduced because of cleavage by the phosphodiesterase, the ion channel closes, causing the cellular concentration of positively charged sodium ions to be reduced. This causes an imbalance of charge across the cell membrane which, finally, causes a current to be transmitted down the optic nerve to the brain. The result, when interpreted by the brain, is vision. • My explanation is just a sketchy overview of the biochemistry of vision. Ultimately, though, this is what it means to "explain" vision. This is the level of explanation for which biological science must aim. In order to truly understand a function, one must understand in detail every relevant step in the process. The relevant steps in biological processes occur ultimately at the molecular level, so a satisfactory explanation of a biological phenomenon such as vision, or digestion, or immunity must include its molecular explanation. •Well, for starters, a system that is irreducibly complex. Irreducible complexity is just a fancy phrase I use to mean a single system which is composed of several interacting parts, and where the removal of any one of the parts causes the system to cease functioning. • Let's consider an everyday example of irreducible complexity: the humble mousetrap. The mousetraps that my family uses consist of a number of parts. There are: 1) a flat wooden platform to act as a base; 2) a metal hammer, which does the actual job of crushing the little mouse; 3) a spring with extended ends to press against the platform and the hammer when the trap is charged; 4) a sensitive catch which releases when slight pressure is applied, and 5) a metal bar which connects to the catch and holds the hammer back when the trap is charged. Now you can't catch a few mice with just a platform, add a spring and catch a few more mice, add a holding bar and catch a few more. All the pieces of the mousetrap have to be in place before you catch any mice. Therefore the mousetrap is irreducibly complex. • An irreducibly complex system cannot be produced directly by numerous, successive, slight modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. Since natural selection can only choose systems that are already working, then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on. • But how does a cilium work? Experiments have shown that ciliary motion results from the chemically- powered "walking" of the dynein arms on one microtubule up a second microtubule so that the two microtubules slide past each other. The protein cross- links between microtubules in a cilium prevent neighboring microtubules from sliding past each other by more than a short distance. These cross-links, therefore, convert the dynein-induced sliding motion to a bending motion of the entire axoneme. • Now, let us consider what this implies. What components are needed for a cilium to work? Ciliary motion certainly requires microtubules; otherwise, there would be no strands to slide. Additionally we require a motor, or else the microtubules of the cilium would lie stiff and motionless. Furthermore, we require linkers to tug on neighboring strands, converting the sliding motion into a bending motion, and preventing the structure from falling apart. All of these parts are required to perform one function: ciliary motion. Just as a mousetrap does not work unless all of its constituent parts are present, ciliary motion simply does not exist in the absence of microtubules, connectors, and motors. Therefore, we can conclude that the cilium is irreducibly complex; an enormous monkey wrench thrown into its presumed gradual, Darwinian evolution. • Blood Clotting Now let's talk about a different biochemical system of blood clotting. Amusingly, the way in which the blood clotting system works is reminiscent of a Rube Goldberg machine. The name of Rube Goldberg; the great cartoonist who entertained America with his silly machines, lives on in our culture, but the man himself has pretty much faded from view. Here's a typical example of his humor. In this cartoon Goldberg imagined a system where water from a drain-pipe fills a flask, causing a cork with attached needle to rise and puncture a paper cup containing beer, which sprinkles on a bird. The intoxicated bird falls onto a spring, bounces up to a platform, and pulls a string thinking it's a worm. The string triggers a cannon which frightens a dog. The dog flips over, and his rapid breathing raises and lowers a scratcher over a mosquito bite, causing no embarrassment while talking to a lady. • When an animal is cut a protein called Hageman factor sticks to the surface of cells near the wound. Bound Hageman factor is then cleaved by a protein called HMK to yield activated Hageman factor. Immediately the activated Hageman factor converts another protein, called prekallikrein, to its active form, kallikrein. Kallikrein helps HMK speed up the conversion of more Hageman factor to its active form. Activated Hageman factor and HMK then together transform another protein, called PTA, to its active form. Activated PTA in turn, together with the activated form of another protein (discussed below) called convertin, switch a protein called Christmas factor to its active form. Activated Christmas factor, together with antihemophilic factor (which is itself activated by thrombin in a manner similar to that of proaccelerin) changes Stuart factor to its active form. Stuart factor,working with accelerin, converts prothrombin to thrombin. Finally thrombin cuts fibrinogen to give fibrin, which aggregates with other fibrin molecules to form the meshwork clot you saw in the last picture. • Blood clotting requires extreme precision. When a pressurized blood circulation system is punctured, a clot must form quickly or the animal will bleed to death. On the other hand, if blood congeals at the wrong time or place, then the clot may block circulation as it does in heart attacks and strokes. Furthermore, a clot has to stop bleeding all along the length of the cut, sealing it completely. Yet blood clotting must be confined to the cut or the entire blood system of the animal might solidify, killing it. Consequently, clotting requires this enormously complex system so that the clot forms only when and only where it is required. Blood clotting is the ultimate Rube Goldberg machine. • The Professional Literature Other examples of irreducible complexity abound in the cell, including aspects of protein transport, the bacterial flagellum, electron transport, telomeres, photosynthesis, transcription regulation, and much more. Examples of irreducible complexity can be found on virtually every page of a biochemistry textbook. But if these things cannot be explained by Darwinian evolution, how has the scientific community regarded these phenomena of the past forty years? A good place to look for an answer to that question is in the Journal of Molecular Evolution. JME is a journal that was begun specifically to deal with the topic of how evolution occurs on the molecular level. It has high scientific standards, and is edited by prominent figures in the field. In a recent issue of JME there were published eleven articles; of these, all eleven were concerned simply with the comparison of protein or DNA sequences. A sequence comparison is an amino acid-by-amino acid comparison of two different proteins, or a nucleotide-by-nucleotide comparison of two different pieces of DNA, noting the positions at which they are identical or similar, and the places where they are not. Although useful for determining possible lines of descent, which is an interesting question in its own right, comparing sequences cannot show how a complex biochemical system achieved its function; the question that most concerns us here. By way of analogy, the instruction manuals for two different models of computer putout by the same company might have many identical words, sentences, and even paragraphs, suggesting a common ancestry (perhaps the same author wrote both manuals), but comparing the sequences of letters in the instruction manuals will never tell us if a computer can be produced step by step starting from a typewriter. • Detection of Design What's going on? Imagine a room in which a body lies crushed, flat as a pancake. A dozen detectives crawl around, examining the floor with magnifying glasses for any clue to the identity of the perpetrator. In the middle of the room next to the body stands a large, gray elephant. The detectives carefully avoid bumping into the pachyderm's legs as they crawl, and never even glance at it. Over time the detectives get frustrated with their lack of progress but resolutely press on, looking even more closely at the floor. You see, textbooks say detectives must "get their man," so they never consider elephants. • There is an elephant in the roomful of scientists who are trying to explain the development of life. The elephant is labeled "intelligent design." To a person who does not feel obliged to restrict his search to unintelligent causes, the straightforward conclusion is that many biochemical systems were designed. They were designed not by the laws of nature, not by chance and necessity. Rather, they were planned. The designer knew what the systems would look like when they were completed; the designer took steps to bring the systems about. Life on earth at its most fundamental level, in its most critical components, is the product of intelligent activity. • The conclusion of intelligent design flows naturally from the data itself, not from sacred books or sectarian beliefs. Inferring that biochemical systems were designed by an intelligent agent is a humdrum process that requires no new principles of logic or science. It comes simply from the hard work that biochemistry has done over the past forty years, combined with consideration of the way in which we reach conclusions of design every day.