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Dawkins on Darwin
« on: 2009-02-16 16:44:28 » |
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source: TimesOnline
Why we really do need to know the amazing truth about evolution, and the equally amazing intellectual dishonesty of its enemies
Richard Dawkins
How can you say that evolution is “true”? Isn’t that just your opinion, of no more value than anybody else’s? Isn’t every view entitled to equal “respect”? Maybe so where the issue is one of, say, musical taste or political judgement. But when it is a matter of scientific fact? Unfortunately, scientists do receive such relativistic protests when they dare to claim that something is factually true in the real world. Given the title of Jerry Coyne’s book, this is a distraction that I must deal with.
A scientist arrogantly asserts that thunder is not the triumphal sound of God’s balls banging together, nor is it Thor’s hammer. It is, instead, the reverberating echoes from the electrical discharges that we see as lightning. Poetic (or at least stirring) as those tribal myths may be, they are not actually true.
But now a certain kind of anthropologist can be relied on to jump up and say something like the following: Who are you to elevate scientific “truth” so? The tribal beliefs are true in the sense that they hang together in a meshwork of consistency with the rest of the tribe’s world view. Scientific “truth” is only one kind (“Western” truth, the anthropologist may call it, or even “patriarchal”). Like tribal truths, yours merely hang together with the world view that you happen to hold, which you call scientific. An extreme version of this viewpoint (I have actually encountered this) goes so far as to say that logic and evidence themselves are nothing more than instruments of masculine oppression over the “intuitive mind”.
Listen, anthropologist. Just as you entrust your travel to a Boeing 747 rather than a magic carpet or a broomstick; just as you take your tumour to the best surgeon available, rather than a shaman or a mundu mugu, so you will find that the scientific version of truth works. You can use it to navigate through the real world. Science predicts, with complete certainty unless the end of the world intervenes, that the city of Shanghai will experience a total eclipse of the sun on July 22, 2009. Theories about the moon god devouring the sun god may be poetic, and they may cohere with other aspects of a tribe’s world view, but they won’t predict the date, time and place of an eclipse. Science will, and with an accuracy you could set your watch by. Science gets you to the moon and back. Even if we bend over backwards to concede that scientific truth is no more than that which enables you to pilot your way reliably, safely and predictably around the real universe, it is in exactly this sense that – at the very least – evolution is true. Evolutionary theory pilots us around biology reliably and predictively, with a detailed and unblemished success that rivals anything in science. The least you can say about evolutionary theory is that it works. All but pedants would go further and assert that it is true.
Whence, then, comes the oft-parroted canard, “Evolution is only a theory”? Perhaps from a misunderstanding of philosophers who assert that science can never demonstrate truth. All it can do is fail to disprove a hypothesis. Evolution is an unfalsified hypothesis – one that was vulnerable to falsification but has so far survived. Scientists generally don’t mind this kind of philosopher and even thank him for taking care of such matters, thereby freeing them to get on with advancing knowledge. They might, however, venture that what is sauce for the goose of science is sauce for the gander of everyday experience. If evolution is an unfalsified hypothesis, then so is every fact about the real world; so is the very existence of a real world.
This kind of conversation is swiftly and rightly sidelined. Evolution is true in whatever sense you accept it as true that New Zealand is in the Southern Hemisphere. If we refused ever to use a word like “true”, how could we conduct our day-to-day conversations? Or fill in a census form: “What is your sex?” “The hypothesis that I am male has not so far been falsified, but let me just check again”. As Douglas Adams might have said, it doesn’t read well. Yet the philosophy that imposes such scruples on science has no basis for absolving everyday facts from the same circumlocution. It is in this sense that evolution is true – provided, of course, that the scientific evidence for it is strong. It is very strong, and Professor Coyne displays it for us in a way that no objective reader could fail to find compelling.
Here I must anticipate another favourite accusation that will, as I know from personal experience, be plonkingly levelled against Coyne and his book: “Why bother? You are tilting at a dead horse, flogging windmills. Nobody takes creationism seriously, nowadays”. (Translation: “The Regius Professor of Theology at my University is no creationist, the Archbishop of Canterbury accepts evolution, therefore you are wasting your time arguing the case”.) The melancholy facts are these. Polls in both Britain and the United States show a majority wanting “intelligent design” to be taught in science classes. In Britain, according to MORI, only 69 per cent want evolution to be taught at all. In America, more than 40 per cent believe that “life on Earth has existed in its present form since the beginning of time” (Pew) and that “God created human beings pretty much in their present form at one time within the last 10,000 years or so” (Gallup).
Science teachers, especially in America but increasingly in Britain, feel beleaguered, and it is small comfort to them if a handful of theologians and bishops occasionally murmur a word of support for evolutionary science. Occasional murmurs are not enough. In October 2008, a group of about sixty American science teachers met to compare notes, at the Center for Science Education at Emory University in Atlanta, and they had some revealing experiences to relate. One teacher reported that students “burst into tears” when told they would be studying evolution. Another teacher described how students repeatedly screamed, “No!” when he began talking about evolution in class.
Such experiences are common throughout the United States, but also, I am loath to admit, in Britain. The Guardian reported that, in February 2006, “Muslim medical students in London distributed leaflets that dismissed Darwin’s theories as false”. The Muslim leaflets were produced by the Al-Nasr Trust, a registered charity with tax-free status. The British taxpayer, that is to say, is subsidizing the systematic distribution of scientific falsehood to educational institutions. Science teachers across Britain will confirm that they are coming under slight, but growing, pressure from creationist lobbies, usually inspired by American or Islamic sources.
So, let nobody have the gall to deny that Coyne’s book is necessary. Not just his book, and here I must declare an interest. February 12, 2009, was Charles Darwin’s 200th birthday, and the 150th anniversary of The Origin of Species falls this autumn. Publishers being as anniversary-minded as they are, Darwin-related books were obviously to be expected this year. Nevertheless, it is true to say that neither Jerry Coyne nor I was aware of the other’s book on the evidence for evolution when we began our own – his published now, mine in the autumn. And our two books may not be the only ones. Bring them on, I say. The more the merrier. The evidence is massive, the modern version of the story would surprise and inspire even Darwin, and it cannot be told too often. Evolution is, after all, the true story of why we all exist, and an exhilaratingly powerful and satisfying explanation. It supersedes – and devastates – all predecessors, no matter how devoutly and sincerely believed.
Why Evolution Is True is outstandingly good. Coyne’s knowledge of evolutionary biology is prodigious, his deployment of it as masterful as his touch is light. His coverage is enviably comprehensive, yet he simultaneously manages to keep the book compact and readable. His nine chapters include “Written in the Rocks”, laced with examples that make short work of the most popular of all creationist lies, the one about unbridgeable “gaps” in the fossil record: “Show me your intermediates!”, say the creationists. Jerry Coyne shows them, and very numerous and convincing they are. Not just fossils of large charismatic animals like whales and birds, and the coelacanth-cousins that made the transition from water to land, but also microfossils. These have the advantage of sheer numbers: some kinds of sedimentary rock are almost entirely made of the tiny fossilized skeletons of foraminiferans, radiolarians and other calcareous or siliceous protozoa. This means you can plot a sensitive graph of some chosen measurement, as a continuous function of geological time, while you systematically work your way through a core of sediments. One of Coyne’s graphs shows a genus of radiolarians (beautiful protozoans with minute, lantern-like shells) caught in the act, two million years ago, of “speciating” – splitting into two species.
Such splitting of one species into two is what Darwin’s title actually means, and it is one of the few weak areas in that great book. Jerry Coyne is probably today’s leading authority on speciation, and it is not surprising that his chapter called “The Origin of Species” is so good. So also is “The Geography of Life”. Possibly the most immediately convincing evidence against creationism is to be found in the geographical distribution of animals and plants, on continents and islands (in the broad sense, “islands” include lakes, mountain tops, oases – from an animal’s point of view any small area where it can live, surrounded by a larger area where it can’t). After setting out the voluminous evidence on the subject, Coyne concludes:
"Now try to think of a theory that explains the patterns we’ve discussed by invoking the special creation of species on oceanic islands and continents . . . . There are no good answers – unless, of course, you presume that the goal of a creator was to make species look as though they evolved on islands. Nobody is keen to embrace that answer, which explains why creationists simply shy away from island biogeography."
Such dishonesty by omission is lamentably characteristic of creationists. They love fossils because they have been schooled, wrongly as Coyne shows, to believe that “gaps” in the fossil record are an embarrassment to evolutionary theorists. The geographical distribution of species really is an embarrassment to creationists – and they conspicuously ignore it.
The book includes a lucid exposition of natural selection at the level of the gene (knowing nothing of genes, Darwin expressed it at the level of the individual organism). Coyne describes how a parasitic worm changes the appearance and behaviour of its ant host, turning the ant’s abdomen into a simulacrum of a red berry, angled temptingly up in the air with carefully weakened stalk joining it to the thorax. You’ve guessed the sequel. The “berry”, full of worm eggs, is eaten by a bird, which is the definitive host of the worm. In Coyne’s own words:
"All of these changes are caused by the genes of the parasitic worm as an ingenious ploy to reproduce themselves . . . . It is staggering adaptations like this – the many ways that parasites control their carriers, just to pass on the parasites’ genes – that gets an evolutionist’s juices running."
Very true. That kind of gene-centred “adaptationist” language has become all but universal among evolutionary biologists working in the field. It is amusing, therefore, to recall the overbearing hostility with which it was attacked thirty years ago by the dedicatee of Coyne’s book, his old teacher, the distinguished geneticist Richard Lewontin. It is not irrelevant that Coyne also has a very necessary clarification of the idea of the “selfish gene”, in which he correctly explains that it has no connection with spurious claims that we are deterministically hardwired to be selfish. Thirty years on, how things have changed.
Coyne’s chapter on “The Engine of Evolution” begins with a splendidly macabre example. Giant Japanese hornets raid the nests of honeybees to feed their larvae. A single hornet scout discovers a beehive and marks it “for doom” with a sort of chemical black spot.
"Alerted by the mark, the scout’s nestmates descend on the spot, a group of twenty or thirty hornets arrayed against a colony of up to 30,000 honeybees. But it’s no contest. Wading into the hive with jaws slashing, the hornets decapitate the bees one by one. With each hornet making heads roll at a rate of forty per minute, the battle is over in a few hours: every bee is dead, and body parts litter the hive. Then the hornets stock their larder."
Coyne’s purpose in telling the story is to contrast the terrible fate of European bees, introduced into Japan, with native Japanese bees that have had time to evolve a defence.
"And their defense is stunning – another marvel of adaptive behavior. When the hornet scout first arrives at the hive, the honeybees near the entrance rush into the hive, calling nestmates to arms while luring the hornet inside. In the meantime, hundreds of worker bees assemble inside the entrance. Once the hornet is inside, it is mobbed and covered by a tight ball of bees. Vibrating their abdomens, the bees quickly raise the temperature inside the ball to about 117 degrees Fahrenheit. In twenty minutes the hornet scout is cooked to death, and – usually – the nest is saved."
Coyne adds that the bees can survive the high temperature, but it is another insight of the “gene’s eye view” that this would not be necessary in order for natural selection to favour the adaptation. Worker bees are sterile: their genes survive, not in the workers themselves but as copies in the bodies of the minority of hive members destined for reproduction. If the workers in the centre of the ball were cooked alongside the hornet, it would be well worth the sacrifice. Copies of their genes “for cooking” live on.
There’s a good chapter on “Remnants, Vestiges, Embryos and Bad Design”, topics that Darwin himself treated well, and also on “How Sex Drives Evolution”, and on human evolution. But Coyne really comes into his own with another strand of powerful evidence that was not available to Darwin. The molecular genetics revolution, which began in 1953, would have taken Darwin’s breath away and filled him with exultation. Every living creature carries within each of its cells a voluminous textual recipe for making itself. Nowadays, we can read these messages, accurately and with a completeness that is limited only by (rapidly shrinking) costs and time. Because the DNA texts of all animals and plants use the identical four-letter code, we have a gold mine of opportunity for comparison. In his own time, Darwin could compare, say, the wing of a bat, the flipper of a whale and the spade of a mole, and spot the relationships among a handful of bones. Today – and more cheaply in the near tomorrows – we can do it on an altogether grander scale, lining up billion-letter DNA texts from bat, whale and mole, and literally counting the single-letter discrepancies and resemblances. Moreover, we don’t have to limit our comparisons to one group, such as the mammals. The universal genetic code allows us to make letter-for-letter textual comparisons across plants, snails and bacteria, as well as vertebrates. This not only provides evidence for the fact of evolution that is orders of magnitude more solid even than the powerful evidence Darwin could muster. We can also construct, finally and definitively, the complete tree of all life, the universal pedigree. And we can find, in huge numbers, the molecular equivalents of vestigial evolutionary relics like the human appendix and the kiwi’s wings.
For the genome is littered with dead genes. Huge wastes of DNA territory comprise a graveyard of discarded, superseded old genes (plus meaningless sequences of nonsense DNA that never functioned) with occasional islands of current, extant genes that are actually read by the translating machinery and turned into action. Dead, untranslated genes are called pseudogenes. The reason our sense of smell is poor, compared with, say, that of dogs, is that most of our ancestral genes for smelling have been rendered inactive. We still have them, but they are dead. Molecular biologists can still read them – serried ranks of molecular “fossils” – but the body does not.
It is wonderful enough that we can construct a tree of life based on active genes, and find that different genes agree on the same pedigree. It is even more convincing that we get the same pedigree with dead genes, whose DNA sequences represent nothing, and must be regarded only as the inert legacy of history. How would creationists explain that? How would they explain the very existence of pseudogenes? Why would the creator litter the genome with useless, untranslated variants of genes, and locate them, moreover, in exactly the right pattern around the animal and plant kingdoms to give the impression – the deceptive impression, as a creationist would presumably have to admit – that they evolved and were not created?
Coyne is right to identify the most widespread misunderstanding about Darwinism as the idea that, in evolution, “everything happens by chance”. This common claim is flat wrong – obviously wrong, transparently wrong, even to the meanest intelligence (a phrase that has me actively restraining myself). If evolution worked by chance, it obviously couldn’t work at all. Unfortunately, instead of working out that they have probably misunderstood evolution, creationists conclude, instead, that evolution must be false. This one misunderstanding, single-handed, accounts for much of the uncomprehending opposition to evolution that made it necessary for Jerry Coyne to write his book in the first place. The need was great; the execution is superb. Please read it.
Jerry Coyne
WHY EVOLUTION IS TRUE
309pp. Oxford University Press. £14.99 (US $27.95).
978 0 19 923084 6
Richard Dawkins has just retired as Professor of the Public Understanding of Science at the University of Oxford. His most recent books are The Ancestor’s Tale, 2005, and The God Delusion, 2007.
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