I have friends who are Creationists. If that sounds weird, imagine how it is from their side to have a friend who is a Buddhist and a science and math teacher. Neither of them really wants to talk about their Creationism with me, but once in a while I can draw them out a bit. I also read Creationist Web sites as a sort of hobby with professional applications in the study of delusion, as it bears on education, politics, and economics.
It is endlessly fascinating to me to see what Creationists think science is about, and where they draw the line between real science that they can believe in, and the "Darwinist" religion [sic], that they can't.
Some of this is clear.
Physics is generally OK, even the structure and fuel cycles of stars, except for cosmology and using radioactivity to date things. The problem with radioactivity is that it lets us date formerly living things up to about 60,000 years ago (carbon dating), and rocks over a range from thousands to billions of years, which the Creationists can't have. They also have to slide over the fact that nuclear fusion allows stars to shine for billions of years. The Big Bang is right out. Of course many other Christians see that as the moment of God's Creation, with the first few days in Genesis (light, stars, sun, moon, oceans, land...) lasting, oh, 13 billion years or so, right up to the point where plants and animals started to appear out of the soup of single-celled organisms in the Pre-Cambrian period. But that's biology.
Chemistry is fine with them, even organic chemistry, until you get into certain parts of molecular biochemistry that bear on genetics and abiogenesis (the theory of the evolution of life from non-life) But that's biology, too.
Biology of individual organisms is no problem. Similarities between life forms, from gross anatomy to DNA sequences, give no offense right up until the moment when you start to use the words "common ancestor" and "speciation". Creationists refuse to accept the existence, much less the findings, of experimental evolution, including experimental abiogenesis, the attempt at construction of life from non-life.
Nature builds all of the common kinds of small organic molecule, and starts chaining several kinds together, without any assistance. The hard part of the problem is figuring out how to encode proteins in RNA or DNA, and then have the proteins catalyze pretty much everything else. Since RNA can sometimes catalyze itself, biologists expect to work out the entire process in time, step by step.
The Creationists are, of course, predicting utter failure, on the hypothesis that it can't be done in small enough steps (Irreducible Complexity) to have high enough probability. This hypothesis has failed in the case of bird wings (useful for balance before flight), eyes (any ability to sense light, even without focus, is valuable), and several other important structures that Richard Dawkins would be delighted to tell you about. To maintain their hypothesis, Creationists also deny these facts.
With those sciences, we know pretty much where we stand. You can talk about anything that doesn't bear directly on evolution or the age of the Cosmos. The next step is the age of the Earth. How old are rocks and fossils? So we have the denial of radioactive dating in support of geology, and a proposed superfast Flood Geology instead. All of the layers were laid down, folded, metamorphosed into other kinds of rock, and ground up to make topsoil in less than a year during Noah's flood, and so on, ignoring glaciers and much more. Well, the last ice age was more than 10,000 years ago, and we can't have that.
It gets really weird in astronomy, where there is no way around the distance scale if you accept any of physics. The constant speed of light has been a given ever since Einstein's Special Relativity. The redshift of distant galaxies is simply a fact, with no viable explanation other than the expansion of the Cosmos. So we see galaxies with measured redshifts up into the range of 6-7 currently, with hints of objects at up to 10. The Cosmic Microwave Background is at a redshift of more than 1,000. No matter which you pick, you are talking about billions of light-years, hence light traveling for billions of years.
Now here is where it gets hairy. There are Young Earth Creationists (YEC) who agree that the stars and galaxies really are as far away as they appear in our telescopes. But they do not admit that light has been traveling from them for billions of years. The universe is no more than 10,000 years old according to all variations of YEC. So how did the light from the galaxies get here for us to see?
Answer: It didn't. Right at the start, less than 10,000 years ago, God created the light along the entire path from the galaxies to here so that it would look to us just as if it had traveled all that way, the same way He put the dinosaur fossils in the ground to make it look like they had lived long ago. It's all to test our faith, or rather our ability to believe absolutely any nonsense rather than ask a question.
The curious thing is that there was very little Young Earth Creationism before the 1960s, most of it in the Seventh Day Adventist church. Adventist George McCready Price wrote a book, The New Geology, in 1923, arguing against both evolution and scientific geology. Henry M. Morris and John C. Whitcomb, Jr. used it to write their own book The Genesis Flood in 1961, making no mention of Adventism, and that was when it caught on.
Now the real question is why they believe this guff. They, of course, claim that they believe it because God said so in the Bible. I don't think so. That ignores the question why they believe that the Bible is a history and science textbook. None of the non-Creationist Christian churches can find where God told them anything like that, and Jews agree with them.
Well, why does anybody believe anything? Somebody told them, certainly, but that isn't enough. Somebody told them quite forcefully that they would go to Hell if they didn't believe. That works to a degree, but that wasn't the reason the idea caught on.
Nobody is going to admit to this, but I have a notion. Young-Earth Creationism caught on in the Godless, immoral 1960s, as some of the Churches would have it, right after the Civil Rights movement took hold, culminating in the Voting Rights Act. Gays started to come out of the closet. Abortion became legal. In reaction, we got the "Impeach Earl Warren" movement and the Republican Southern strategy of signaling support for racism in ways that they could deny in the North. Creationism caught on at the same time. Coincidence? Ha!
Here's the deal. Ever since Darwin came out with The Origin of Species, and even more with The Descent of Man, opponents have been deriding "Darwinism" as the theory (sometimes "religion") that man is descended from monkeys. Not apes, monkeys. The Scopes Monkey Trial, for example. Chimpanzees are apes, and the last common ancestor of humans and chimpanzees would also be an ape. So why monkeys?
I've been collecting Republican Code Words and a range of ethnic insults, and I finally got to "monkey" as an insult to Blacks. And here is where the penny dropped and I could see the whole picture. When they say monkey, they don't mean monkey. It's a code word, like States' Rights (the right to oppress their own people). "Monkey" is one of the uncounted insults applied to Blacks/African-Americans, whether slaves, ex-slaves, or descendants of slaves, and of course to Africans. "Ape" is an insult, but not specific to Blacks. "Gorilla" likewise. You don't hear those when people deride Evolution. Always monkeys. You see?
Now this code has been laid on so thick that many of those who use it probably have never been told in so many words what it means, and no doubt some do not even know. But that's what Creationism is: the claim that Southern White Christians are not descended from Black Africans.