Ana səhifə

Evolution Alone Explains Life on Earth

Yüklə 31.47 Kb.
ölçüsü31.47 Kb.
"Evolution Alone Explains Life on Earth."At Issue: Creationism Versus Evolution.  Eric Braun. San Diego: Greenhaven Press, 2005. Opposing Viewpoints Resource Center. Gale. Lane Tech. 10 Mar. 2008 

Table of Contents:Further Readings

Massimo Pigliucci is associate professor of ecology and evolution at the University of Tennessee, Knoxville. He holds a master's degree in biological sciences and doctorates in genetics and botany. Pigliucci was the recipient of the 1997 Dobzhansky Award from the Society for the Study of Evolution.

Any credible theory of life on Earth must withstand scientific scrutiny based on asking a specific question, answering it with a hypothesis based on observation and experimentation, and then testing that hypothesis to try to disprove it. There is only one theory of evolution, answering the question "How do species originate and change?" The theory has survived more than one hundred years of such scrutiny. In contrast, although creationists try to present a unified front, there is a wide range of creationist positions—from flat-earth literalists to more liberal creationist positions that graft evolution onto theistic origins, or try to equate biblical "days" and geological ages and then claim their theory is scientific. No creationist theory holds up to the scientific method, but creationists are interested in winning an ideological war, not in scientific evidence. Creationists start with a preferred conclusion (God created life) and then make observations about the natural world that fit that theory, ignoring or discounting contradictory evidence. Human progress depends on a scientific, not theological, understanding of life on Earth, and only evolution provides that.

There is one theory of evolution, just as there is one theory of general relativity in physics. True, there are different schools of evolutionary thought that emphasize distinct mechanisms to explain organic evolution, and creationists have tried to capitalize on these differences to show that the whole field is in disarray. Yet differences among scientists are the bread and butter of scientific progress. It is through the empirically driven resolution of theoretical disagreements [the resolution of disagreements through testing and observation] that science at its best progresses and yields a better understanding of the natural world.... But the realities of scientific practice and discourse are far from what creationist propaganda claims. Furthermore, the idea of a monolithic and unchangeable science is a dangerous myth—one that scientists and science educators should work toward eradicating.
On the other hand, even a superficial look at creationism itself clearly shows that creationists have gone to a great deal of trouble to construct what looks deceptively like a unified front to naïve outsiders. As we shall see, the difference between proponents of intelligent design theory such as [American mathematician] William Dembski and young-Earth creationists like [American biochemist] Duane Gish spans a theological and scientific abyss. One of the few things that these people have in common is their hatred for what they perceive as a materialistic, scientific worldview that leaves no space for God and spirituality. Intelligent design defender Phillip Johnson has proposed the idea that creationists can win by driving a wedge into what he thinks is a small but crucial crack in the edifice of science.... I would like to suggest to scientists and educators that the crack in the creationist camp is much wider and easier to exploit, if only we stop being on the defensive and initiate a counterattack.... I will first briefly discuss the astounding variety of creationist positions, focusing in particular on the two most popular ones as embodied by the Institute for Creation Research and by the Discovery Institute and its Center for the Renewal of Science and Culture. As a counterpoint, I will then explain what evolutionary theory is really about....

The Many Forms of Creationism

Perhaps the best classification of positions on the question of origins, as the broader conception of evolution is often referred to, has been proposed by [American biologist] Eugenie Scott of the National Center for Science Education and is summarized in the figure below. As Scott points out, there [are many] ideas to choose from, and they differ in degree as to what they accept from science on the one hand and from the Bible on the other.

At one extreme we find people believing that Earth is actually flat. While these are certainly a minority even among creationists, their thoroughly literalist position is arguably the most biblical of them all: In addition to rejecting evolution, they believe not only that Earth is 6,000 years old, but that it is flat and is the center of the universe, precisely as the Bible says.
A slightly different position is the geocentric one, which accepts the idea of a spherical Earth but squarely rejects astronomy after Copernicus and Galilei. This is also a minority view, but it is instructive—together with the flat-Earth position—because it is indicative of an interesting aspect of mainstream creationist thinking. On many occasions I have had conversations or have exchanged letters with young-Earth creationists (the next group in Scott's classification) who vehemently deny being gullible, antiscience individuals. They claim that the scientific evidence is definitely against evolution and in favor of a young Earth. I usually politely point out that the only reason they think so is that they believe ... the Bible [to be error free] in scientific as well as spiritual matters. I then occasionally ask why they don't believe that Earth stands still while the sun moves around it and that our planet is flat, since both notions are also present in the Bible. In fact, one could argue that these two positions are much more clearly defined in the Christian scriptures than the age of Earth, which has to be calculated on the basis of assumptions concerning the life span of the lines of descent mentioned in the book. The astonishing creationist response is to deny that the Bible makes claims either about a flat Earth or in defense of geocentrism. But this goes clearly against not only the existence of creationists who see and defend both claims, but also against the historical evidence: For most of Western history, Christians have espoused both views precisely on biblical grounds! It is not for nothing that both Copernicus and Galilei got into trouble with the Church of Rome.
Young-Earth creationists, however, seem to be able to live with this internal contradiction; they actually represent the majority of creationists in the United States (according to a 1999 Gallup poll, 45 percent of Americans believe that God created human beings "pretty much in (their) present form at one time or another within the last 10,000 years"). For them the story in Genesis is to be taken literally: The world was created 6,000 years ago, and most humans and animals died in a worldwide flood that occurred about 4,000 years ago.... Several interesting fallacies underlie this position, and young-Earth creationists are the epitome of what happens when science education fails completely. It simply makes no sense—given the evidence that we have today from a variety of fields, such as geology, paleontology, ecology, physics, and astronomy—to deny that Earth is billions of years old and that while mass extinctions certainly occurred, they were not due to floods and no such event happened on a worldwide basis so recently in Earth's history.

Old-Earth Creationism

The next category in Scott's classification of theories of origins marks a fundamental theological, if not yet scientific, divide from the positions discussed so far: We are now entering the realm of old-Earth creationism, which therefore at least acknowledges modern geology.... It is also in agreement with the scientific research in this field conducted throughout the twentieth century. Within old-Earth creationism, the idea often referred to as gap theory is by far the most peculiar. Supporters maintain that there is a large temporal [time] gap between the first and second chapters of Genesis in the Hebrew Bible, suggesting the existence of a pre-Adamic Earth that was destroyed and replaced by a second creation, when God started over and (re?)made Adam and Eve. This interpretation obviously solves the well-known problem posed by the discrepancy between the two accounts of creation in Genesis, but literalists are clearly less than happy with such a solution because it is obtained at the theologically costly price of introducing a scenario (two successive creations) of which there is no hint in the Bible itself. This is the much-dreaded "slippery slope" of interpretation of the sacred Scripture that, even though it is adopted in one fashion or another by most practicing Christians, is seen as very dangerous by fundamentalists, who believe that the word of God should be a clear and universal message, not subject to the whims and fashions of human explanations.

An even more liberal interpretation of the Bible is adopted by people espousing the next category of old-Earth creationism in Scott's taxonomy: the day-age system. According to this idea, each "day" referred to in the traditional six-day account of creation is comparable to a geological age, so it literally took tens of millions of years to create stars, planets, and life on Earth—in convenient agreement with the evidence from astronomy and geology. This solution still suffers some obvious shortcomings from a scientific standpoint, most egregiously the incompatibility between the chronology of events in Genesis (e.g., whales before land animals) and the data from the fossil record. But it also makes religious fundamentalists very unhappy because it proceeds further down the slippery slope of arbitrary interpretation of the Bible: What is there to stop the believer from even accepting a substantial amount of evolution?
Not much, as is clear from a cursory examination of the next position: so-called progressive creationism. A typical proponent of this version of old-Earthism is Hugh Ross of Reasons To Believe ministries, which, as the name implies is based on the idea that someone can accept Christianity on the basis of reason not just on faith. Progressive creationism is a peculiar and idiosyncratic blend of creationism and science that accepts, for example, the Big Bang and many other scientific conclusions, even within the biological sciences, but limits the power of evolution. For example, evolution is said to occur, but only within the basic "kinds" of organisms originally created by God. Although many young-Earth creationists, such as Duane Gish, also allow what they refer to as microevolution within kinds, progressive creationists—because they accept long spans of geological time—at least don't find themselves in the awkward position of having to concede more evolution than even the most ardent evolutionist would feel comfortable with (the number of "kinds" was limited by the size of Noah's Ark for a young-Earth creationist, so tens of millions of species had to evolve from a few thousand in as little as 4,000 years: an astronomic evolutionary rate by any standard!).
Working our way through Scott's useful classification, we finally arrive at intelligent design (ID) theory.... This is the idea—originally formulated in some detail by the ancient Greeks—that the universe is the result of some kind of supernatural plan evidently constrained by forces that even the gods cannot entirely control. Plato, in the Timaeus, presents us with the idea of a god (later called the demiurge, literally "the craftsman") which makes the universe "as best as it can be" made within the constraints imposed by contingency....
The last step in this long series of creationist positions is usually referred to as theistic evolution. This is the position more or less implicitly accepted by the majority of Christians, especially in western European countries: Simply put, God works through the natural laws and processes that He created, and there is no reason to think that natural selection is an exception. This is also essentially the official position of the Catholic Church after two writings of Pope John Paul II. Previous popes, such as Pius XII had taken a stern position against evolutionary theory: "Some imprudently and indiscreetly hold that evolution ... explains the origin of all things.... Communists gladly subscribe to this opinion so that when the souls of man have been deprived of every idea of a personal God, they may the more efficaciously defend and propagate their dialectical materialism." John Paul II (the pope who, without being a paragon of liberalism, still managed to pardon Galilei, albeit after a few centuries of delay), on the contrary, wrote a much more sober letter in 1997 to the Pontifical Academy of Sciences stating that "new knowledge has led to the recognition of the theory of evolution as more than a hypothesis."...

Materialistic Evolution

The last entry in Scott's classification is the only one that does not involve any creationist component at all, even of the mild type accepted by the Catholic Church and most mainstream Protestant denominations: the much-dreaded (by all creationists) materialistic evolution. This is a philosophical (as opposed to scientific) position maintaining that there is no reason whatsoever to invoke supramaterial causes for any natural law or process, including evolution. Not even the most ardent Christian would submit that God works directly through the law of gravity by supervising the motion of every single object; analogously, biologists tend to think that natural selection is just that—a natural process with no need of supervision.

Two things are important to realize in connection with materialistic evolution. First, and perhaps most importantly for our discussion and for the creation-evolution controversy, even materialistic evolution does not automatically imply atheism. There are several more possibilities that permit acceptance of both materialistic evolution and belief in a god. This is true both in theory and in practice. In theory, for example, one can be a deist—that is, somebody who believes that God created the universe and its laws but then refrained from any further direct intervention in His creation. In practice, Theodosius Dobzhansky, the evolutionist responsible for one of the sentences most hated by creationists ("nothing in biology makes sense if not in the light of evolution") was himself a devout Christian. Second, it has always been commonly accepted that most scientists are materialists and do not believe in a personal god. This turns out to be quantitatively accurate.... Surveys show that such is the belief (or more properly lack thereof) of a majority of "average" scientists and of almost every "top" scientist (as measured by their membership in the National Academy of Sciences)....
Given the [huge variety] of opinion regarding important conceptual issues within the creationist camp, ... it is amazing that creationists can present such a unified front.... Or is this unified front just a matter of appearances, thinly disguising the vat of trouble that is brewing among creationists? ...

An Ideological War

Scientists and educators are involved in this debate because they care about science education, not about winning an ideological war. In this, I can safely say, they are different from creationists. Even though most creationists are sincerely convinced of their positions, they are interested only in winning the ideological war. If evolutionary theory had no theological implications (say, like atomic theory), there would be no debate. This point is strangely missed by scientists, who continue to behave as if creationists were either lunatics (which by and large they are not) or as if they needed to be rebutted on solid scientific grounds, after which they would go away.

The reason it is important to explain science to the general public is that it is important for our society that people have a scientific understanding of the world. Without it, as a recent report of the National Science Foundation remarked, people are likely to make bad decisions in the voting booth, as members of a jury, or in their private lives when considering an insurance policy or a moneymaking scheme. But to refuse to accept that this particular debate is about ideology rather than science is foolish and largely accounts for the lack of progress we have made since the Scopes trial.1 It is therefore urgent that scientists and educators be in a position to counterattack and to point out the internal inconsistencies in the creationist camp. As uncomfortable as this may be, this is bound to make much more of an immediate impact than any esoteric explanation of the second principle of thermodynamics....

What Evolution Really Is

Having attempted to explain the basic tenets of the major forms of creationism, it is only fair—and most urgent, judging from my experiences at debates against creationists—to briefly explain what evolutionary theory really is, and even a few things that it is thought to be but isn't.... The evolution-creation debate is marred by many misunderstandings and a lot of ideological posturing, often on both sides. One major thing that creationists seem reluctant to acknowledge, however, is the distinction between what evolutionary theory actually is and what they think it is. And the difference is both huge and crucial. No matter what one's ideological position, it seems to me necessary to understand what biologists claim evolution to be and not to build straw men just to be able to demonize the opposition....

If one asks an evolutionary biologist—by definition the only person qualified to answer the question—she will tell you that evolution is simply a change of gene frequencies over time. This may sound rather simple and philosophically uninteresting, but it is in line with what science is all about: seeking answers to specific questions, not to questions of ultimate meaning. The theory of genetic changes in natural populations is very well understood by a branch of biology called population genetics, and modern molecular biology provides direct evidence that gene frequencies do indeed change under our very nose. Examples are abundant and are found in all classes of living organisms (humans included, of course)....
Yet most people think of evolution in terms of descent with modification, to use Darwin's term, of large organisms, and in particular animals.... Let's look at evolution seen at the level of macroscopic creatures and long timescales. This is the realm of comparative anatomy and paleontology, and the evidence for evolution of plants and animals comes from studies of their genetics, physiology, morphology, and development. Additional evidence comes from the much maligned fossil record....
There are many great examples of morphological evolution in plants and animals, but perhaps one of the most spectacular is the evolution of modern whales, which has recently been largely elucidated by a series of paleontological findings and molecular studies....
The story of whales started about 55 million years ago, although the exact group of ancestors is currently unknown. They were terrestrial animals belonging to the Artiodactyla (the modern group that includes hippopotami, sheep, camels, and pigs). That group was itself closely related to the now extinct Mesonychia, which until recently were considered a better candidate for the direct ancestors of whales, but are now regarded as their cousins. The earliest animals belonging to the Cetacea (of which modern whales and dolphins are also members) were closely related to Pakicetus and Ambulocetus.... The early relatives of these two were terrestrial artiodactyls, occupying an ecological niche similar to the one filled today by bears (i.e., they were probably scavengers and fish eaters), although whales and bears themselves are not closely related to each other. Between 53 and 45 million years ago (MYA) a variety of intermediate forms appeared to connect the artiodactyl ancestors to modern whales. Some of these forms have been found in the fossil record, though there probably were many more that did not survive the fossilization process. Fifty MYA the already mentioned Pakicetus appeared, sporting a lifestyle that included both land and water hunting (judging from its skeleton and skull). A little after that, Ambulocetus showed advanced features adapted to a marine life, with a skeleton very similar to that of modern otters, sea lions, and other pinnipeds that are still today in an intermediate stage of their aquatic evolution. Between 40 and 35 MYA other forms arose, in particular Basilosaurus. This animal was truly almost like a whale except for the still apparent limbs, which, however, were reduced enough to make it impossible for it to walk on land.

What Evolution Is Not

So much for what evolution is. Now there are a couple of important things that evolution is not, misleading claims by creationists notwithstanding. For example, evolution is not a theory of the origin of life, for the simple reason that evolution deals with changes in living organisms induced by a combination of random (mutation) and nonrandom (natural selection) forces. By definition, before life originated there were no mutations, and therefore there was no variation; hence, natural selection could not possibly have acted. This means that the origin of life is a (rather tough) problem for physics and chemistry to deal with, but not a proper area of inquiry for evolutionary biology. It would be like asking a geologist to explain the origin of planets: The geologist's work starts after planets come into existence, and it is the cosmologist who deals with the question of planetary origins....

Evolution is also most definitely not a theory of the origin of the universe. As interesting as this question is, it is rather the realm of physics and cosmology. Mutation and natural selection, the mechanisms of evolution, do not have anything to do with stars and galaxies. It is true that some people, even astronomers, refer to the "evolution" of the universe, but this is meant in the general sense of change through time, not the technical sense of the Darwinian theory. That the universe does "evolve" in this larger sense is clear from the fact that powerful telescopes like the Hubble can actually peer into the distant past (thanks to the fact that light travels at a finite speed) and show us firsthand what primordial galaxies looked like....
Is the fact that evolutionary theory can explain neither the origin of life nor the formation of the universe a "failure" of Darwinian evolution? Of course not. To apply evolutionary biology to those problems is like mixing apples and oranges, or like trying to understand a basketball play by applying the rules of baseball. Creationists often do this, but their doing so betrays either a fundamental misunderstanding of science or a good dose of intellectual dishonesty—neither of which should be condoned.
Creationists and scientists think along vastly different lines.... Creationist decisions are based on beliefs and preferences, not on any attempt to objectively assess the problem. As I said earlier, creationists—contrary to all principles of sound science and critical thinking—start out with a preferred conclusion and then try to find evidence to back it up.... This is exactly the modus operandi of pseudoscience and what, in the words of philosopher of science Karl Popper, distinguishes it from actual science.

1. the 1925 trial of John T. Scopes, who was found guilty of violating Tennessee law that prohibited the teaching of evolution in public schools

Gale Document Number: EJ3010182213

© 2008 Gale, Cengage Learning.

Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur © 2016
rəhbərliyinə müraciət