It is disturbing indeed to feel it necessary to explain the basics of Evolution and Creationism in North America in the year 2010. This should not be necessary. Every high school graduate should know enough about the natural sciences to understand the validity of Evolution. But in spite of 150 years of increasingly thorough refutation of the Creationist perspective, this fallacy persists. Creationist rhetoric has become quite clever, altering the public's understanding of what Evolution itself is about, as well as what the debate is about.What Evolution claims is that lifeforms change from generation to generation, and that some of those changes contribute to or detract from an individual's ability to survive and to produce offspring that also survive and reproduce. What Charles Darwin didn't know about when he developed the theory was that these changes in body shapes and body functions are based in inheritable genes, segments of the DNA molecule that specify most of what a cell does. The main mechanism of Evolution, as it is now understood, is a change over time in the assortment of genes available in a population. The technical details are complex, but this is a reasonably complete summary.
Evolution makes the adherents of some religions uncomfortable for exactly one reason: it challenges the idea that human beings are a special creation of God and are therefore outside of nature. Evolution says nothing directly about God or gods, but it does say that human beings (or at least human bodies) are a product of the same natural processes that produced all the other lifeforms on Earth today.
The creationist critique of Evolution usually goes much further than this one issue, however, and in so doing most creationists are working with a fanciful, and scientifically inaccurate, idea of what Evolution is and is not. One part of that scientific inaccuracy has to do with the idea of an old Earth, meaning an earth that is thousands of millions of years old, as opposed to a young Earth that is just 6,000 (or some other low number) years old. It is a common misconception to believe that the Theory of Evolution is the source of the idea of an old Earth. The fact is that the evidence of an old Earth comes from other sciences entirely, from Astronomy, Geology, and Physics. An old Earth is an assumption of (input to) the Theory of Evolution, not an assertion of (output from) that theory. If one could prove that the Earth is young, that would automatically disprove Evolution, because the validity of Evolution depends on the slow accumulation of many small changes over millions of years. But creationists try to claim the reverse, that by undermining Evolution they are saving their idea of a young Earth. That is not a valid line of reasoning, because even if Evolution is a false theory, Astronomy, Geology, and Physics still say the Earth is old.
It is common for Creationists to take their critique even further away from what Evolution is really about. Creationists often claim that Evolution is an inadequate explanation for the appearance of life from non-organic chemistry, but this is an issue Evolution makes no attempt to address. Evolution depends on genes, genes are dependent on DNA (and therefore RNA), and these are organic molecules caught up in life processes. The explanation of how life comes from lifelessness -- if it ever did -- must come from some other theory. Similarly, Creationists often berate the "evolution" of gas clouds into stars and galaxies, the "evolution" of heavier elements out of hydrogen and helium, or the "evolution" of those heavier elements into rocky planets like our Earth. These processes might all be called "evolution" in some general sense, but they have nothing to do with the neo-Darwinian Theory of Evolution that explains how modern humans descended from now-extinct apes and, if we go back far enough, from primitive bacteria.
What Creationists attack, then, is much more than Evolution. Creationists attack Science itself, the reliance upon logic, evidence, and experimental testing as means of arriving at an understanding of the observable universe. This they must do, since the religions they adhere to don't just make claims about the realm of the spirit or the meaning of life. With some variation from creationist to creationist, they claim that there was light in the universe before there was a sun, moon, or stars; that there were plants growing on dry land before there was a sun, moon, or stars;that the Earth (perhaps the universe itself) it 6,000 years old, certainly less than 10,000 years old; that a flood submerged the entire surface of our planet some 4,000 years ago; that major geological features, including fossils and canyons, were produced by that flood; that dinosaurs were still living at the time of that flood (and maybe even after); that the light from distant stars was created in transit, making it appear much older than it really is; that the laboratory-verified rates of radioactive decay of various elements have changed over time, making rocks appear much older than they really are;that there are no "transitional" forms in the fossil record; etc., etc. These are not claims about morality, meaning, or the immaterial; they are claims about the physical universe. Claims about the physical universe are testable by science, and that is something Creationists cannot abide.
Claiming to attack Evolution, then, is no more and no less than a marketing gimmick. What creationists want is to subordinate all science and reason to their particular version of revealed truth. They'll get far less support if they're honest about that though. They claim their assault is limited to Evolution to make themselves appear more reasonable than they really are, and to give the false impression that their goal is smaller than it really is. But to make that assertion, they have to lie about what Evolution does and does not claim.