Irreducible complexity is the key component of most of the arguments put forth by the ID camp. Proponents of ID argue that extremely complicated structures, such as the eye, could not have evolved through a series of small steps because an eye is so complicated that it won't work without all its parts. When something can't work without all its parts, they conclude that it could not have been assembled one part at a time.
To bolster their argument, ID proponents quote Darwin himself, claiming that his very words support their argument against evolution. Well, here's what Darwin actually said about the structure of the eye, an organ he considered "of extreme perfection complication" (Note: The italics are mine and they highlight the part of this quote that ID proponents don't share):
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.
Time and again, for pretty much whatever the ID camp claims couldn't have evolved incrementally, evolutionary biologists have identified the intermediate steps that led to the complex structure. Two classic examples of highly complex structures that evolved precisely through intermediate steps are the eye and blood-clotting factors.
Just because a system is made up of a series of parts doesn't mean that those parts evolved to perform the functions they now perform. Take, for example, bacteria that have evolved to break down polychlorinated biphenyls (PCBs), which are new to the environment. Until humans made them, these very nasty chemicals didn't exist. But some bacteria have evolved very complicated biochemical mechanisms for breaking down these compounds. As it turns out, the biochemistry that allows these bacteria to degrade PCBs is kludged together from a series of other biochemical pathways that serve other functions. Such PCB-busting biochemical mechanisms seem irreducibly complex, but the individual parts are advantageous in ways that are not related to PCB degradation.
ID proponents argue that the theory of evolution isn't the only theory explaining how life on Earth came to be; therefore, in the interest of fairness and balance, ID should be taught along with evolution in the science classroom.
The issue isn't what should be included in the school curriculum, but what should be included in a science class. This statement may sound like hairsplitting, but science instruction isn't about a simple accumulation of facts and data (even though facts and data are accumulated in the process of doing science).
¿jtjW^ Science is a way of asking questions by coming up with ideas and then trying hard to shoot them down. The ideas that scientists can't shoot down even after lots of trying become theories about how things work. And if at some point, other scientists come up with evidence that refutes these theories, they shoot the theories down.
Although the ID argument is compelling to many people, it isn't science. In fact, it turns the entire scientific process on its head. Instead of trying to shoot down their own premise that a designer is responsible for the complexity of the universe, ID proponents use the very complexity that they claim requires a designer to prove the existence of the designer. This reasoning is circular (and an error in logic); it's not science.
jjiJABEft The ID argument relies on a particular world view that demands a designer. In essence, it promotes the religious viewpoint that something beyond natural processes created the world and the creatures in it. Evolution, on the other hand, is a scientific discipline; it doesn't concern itself with anything beyond what can be seen or observed in the natural world. That one deals with the supernatural and the other with the natural is the key difference between science and religion and why they don't have to be at odds.
It's a Fringe Topic
Evolution is a central part of modern biology. In fact, making sense of most of biology concepts in the absence of an evolutionary perspective is difficult. One of the most important things that an understanding of the evolutionary process provides to the study of biology is a way to understand the effect of history.
This historical perspective is important for fields as diverse as agriculture, conservation biology, and medicine. Doctors, for example, don't worry about removing an appendix, because they have a framework in which to understand that it's a vestigial organ — that is, it may have served a purpose once, but that purpose is long gone, even though the organ isn't. And understanding how organisms evolve continues to be vital in the fight against infectious diseases (see Chapters 18 and 19 to find out why).
Conservationists seeking to save species also need to preserve biological diversity. Without genetic diversity, endangered species — even those that are making headway in the numbers game — remain vulnerable to extinction. By understanding natural variation in the evolutionary process, conservationists better understand what their conservation goals should be and how to meet them. It's probably better to save a few spotted owls from a bunch of different forests than all the spotted owls from one isolated forest, for example.
It's at Odds with Biblical Creation
Quite a few people see discrepancies between the biblical creation story as they understand it and the idea of evolution. Young Earth creationism, for example, states that the Earth is only a few thousand years old and that all living organisms were created by God exactly as you see them today. Right there, you can see the areas of disagreement. This theory's creation date is at odds with most of what humans know from other fields of science — specifically, from physics and astronomy, which indicate that the Earth is about 4 billion years old. If the Earth were only a few thousand years old, the evolutionary process as scientists understand it wouldn't have had sufficient time to generate the diversity of the planet.
Old Earth creationism differs from Young Earth creationism in that it accepts that the Earth is as old as physicists and astronomers say, but it disagrees that any evolutionary processes would have occurred over that time. According to this theory, species were formed by God and did not change subsequently.
Other groups make other distinctions:
1 Some allow for the possibility of small evolutionary changes that may have happened within a species over time but not for the origin of new species.
1 Others allow for the possibility that speciation could have occurred within specific groups but say that larger taxonomic groups could not have arisen.
i Still others, recognizing that the Ark was only so big, have come up with a clever workaround that melds both biblical and evolutionary theory: Noah loaded the Ark with all the animals that existed on Earth at the time. Then somehow, in the few short years that followed the grounding of the Ark, the species diversified to produce the variety we see today.
In all these regards, evolution is at odds with a literal interpretation of biblical creation story. There's just no way around it. Many denominations of Christianity (as well as other religions), of course, have no problem with the theory of evolution or with the age of the Earth being a little over 4 billion years. Maybe, they say, that's just the way God did things.
Evolution is a fact that scientists can measure and test. As we further our understanding of the underlying processes responsible for evolution, we refine our theories about the details. If these theories ever seem at odds with particular aspects of religious belief, be assured that that was merely a consequence of following the data and never an intentional goal. The process of science has no mechanisms for addressing questions of a spiritual nature; it concerns itself solely with the natural world.
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