Creationism is yet another indicator of the pathological narcissism inherent in religion. Much of the driving force behind creationism is the need to believe that mankind is not just another animal--that we are, in fact, godlike ("made in his image"). The rest comes from a deep seated inability to admit error, which is also a sign of pathological narcissism.
Creationists want to believe that they and their "group" (parents, family, church members) simply can't be wrong and that simply being human makes them extremely special--you can't get much more special than "godlike".
If a person reveals to you that he or she is a creationist, especially a young earth creationist, then it is probably pointless to discuss anything relating to religion with that person. Only religious fanaticism can explain creationism--a fanatical determination to keep up the pretense of believing that the bible is literally true. The science behind evolution is overwhelming, and any objective examination of life on this Earth confirms it.
If you debate with creationists, it quickly becomes obvious that they know nothing about science at all--not even the rudiments that should be learned by any modern citizen of the Earth with a high school education and a television or computer. Again, only fanatical determination can explain this level of ignorance. How else could someone fail to learn anything at all about a subject that permeates even our popular culture?
Every time any information about it comes up, these people turn their brains off. I can draw no other conclusion that fits the facts and there is research supporting it. But, in spite of the fact that they know nothing about science, they feel perfectly confident to expound on the subject. This can only be a symptom of pathological hubris.
I say that they know nothing about science, in part, because it is clear that they really don't know what evolution is. All they know is that it stands for the proposition that the bible is wrong and that their invisible magic friend didn't "magic" all the animals into existence for our use in one day.
If you do choose to debate with creationists, don't expect any success. The advice I gave before about simply planting your little "thought barbs" and walking away applies with special emphasis in this situation.
You can break down any discussion with a creationist into three parts: 1. Correcting their erroneous notions about evolution. 2. Correcting the false statements they make about the evidence. 3. Presenting the actual evidence. I suggest trying to do just a little of each, perhaps adding a suggestion that they do research somewhere other than a creationist website, such as the National Center for Science Education's website or the Why Evolution Is True site.
The first part is usually the best place to start because creationists generally have no clue what evolution means, and it is easy to pull the rug out from under them on that most basic point. They don't know that the word "theory" when used in regard to science does not mean the same thing when used by laymen. To a scientist, a theory is the currently accepted formulation of a scientific idea that has been established by suitable evidence resulting in its acceptance by the scientific community. It is not a mere hypothesis. When a layman uses the word "theory", he means what a scientist means by the word hypothesis.
You can drive this point home by saying:
"Gravity and electricity are just theories, too. You don't know that scientists mean something different from the rest of us when they use the word 'theory'?"
You can then add,
"You do know that words have different meanings depending on how and where they are used, don't you?"
(One of the believers' favorite tactics is this seeming deliberate obtuseness where they confuse and conflate the different definitions applicable to a word so that it means what they want it to mean in order to support their argument. You will see it often. Always pull them up short and correct them when you do.)
It's a good idea to be prepared for the arguments they will make, which means doing a bit of research on creationist arguments yourself. One of the best places to start is to search for such arguments on Wikipedia. Although Wikipedia is not authoritative, because so many can edit it, it is often a good place to find abbreviated information with references for further research. This will relieve you of having to go through the painful process of actually reading creationist websites or watching some of their horrid videos.
The creationists would have us believe that all the species on the Earth were deposited here magically a few thousand years ago.
The evidence to the contrary, however, is overwhelming. All around us are species that are clearly related but which have evolved to have different characteristics and fit into different ecological niches, where they were able to carve out a living with less competition than they might have had before and all because they discovered a "fit" between some characteristic they had and the environment of that niche.
One of the best questions to ask is:
"Why is Australia home to so many widely varied marsupial species while other continents have virtually none?"
The almost unavoidable answer is that Australia has been separated from the other continents for so long that evolution has taken paths that are quite different from those taken elsewhere. The creationist will probably duck the question in some fashion, however, because he knows he can't answer it.
One of the creationists' current favorite arguments is that there is no evidence of any transitional species. This one is ludicrous because everywhere you look today you can see examples of transitional species. (But, just in case you are interested, here is a link to list of transitional fossils.)
Just look at sea birds. There is a clear sequence of changes between birds that survive almost solely on land and those that spend more time in the water. From shore birds to those that fish more exclusively to cormorants and anhingas, which can barely fly, and finally penguins, which can't fly, can barely walk, and hardly resemble birds at all anymore.
When a creationist tells you that there have never been any transitional species discovered, you can say:
"Scientists have discovered a transitional species; they decided to call it the 'penguin'."
You can also use the ostrich, the emu, or the kiwi. A bird that has lost the ability to fly is obviously an example of a species in the middle of an evolutionary transition.
One of the ways to work into their thinking is to work with things they accept such as selective breeding, which is a fact that not even creationists deny. Because another thing they don't understand about evolution is its relationship with selective breeding
You can also ask:
"How is it that different breeds of dogs exist?"
If they respond by pointing out that dog breeding isn't an example of evolution, you can say they are correct but that it does show what can happen when certain traits are used to determine which animals reproduce.
In just a few thousand years humans have bred varieties of dogs that are nearly different species. Compare the Great Dane with the Dachshund. One crucial measure of speciation is whether the two related species can interbreed. In the case of a Great Dane and a Dachshund it is clear that successful interbreeding would be impossible without massive human help. The two species could not mate normally, and if the female were the Dachshund, then it is doubtful whether she could successfully carry such large puppies to term.
At the appropriate point, you can add:
"Evolution is just selective breeding done by nature in a radically brutal manner over a long time."
Whether you use that last suggested argument or not, at some point in this discussion, you will want to make the point that over millions of years the accretion of such changes can result in animals that are completely different species. At this point, the creationist will usually drag out the young Earth nonsense. Their usual gambit is to point out that carbon dating can't date items more than 60,000 or 70,000 years old.
This is an example of their gross dishonesty. First, even 60,000 year old objects belie their holy writings, which allege that only 6,000 years have elapsed since the dawn of time. Second, they probably know, or should know, that there are several other methods of radiometric dating that are not limited by the decay of carbon. They will argue that those aren't known to be accurate because they can only be gauged by comparing them to each other. This, too, is another example of a half-truth pointing to complete dishonesty.
The reason these other methods were ever hypothesized and attempted was because of our knowledge of chemistry and physics and the known rates of radioactive decay in certain materials. And, if our knowledge of these rates is correct, then one would expect these other methods of radiometric dating to agree with each other. If they didn't, then there would be cause for alarm because that would indicate that our understanding of the underlying principles was wrong.
Another bit of clear evidence for evolution that creationists will have a hard time denying is the mule, or the Liger, or any other nonviable offspring of two related species. Members of the same species can and do have healthy offspring that can reproduce. Related species can sometimes interbreed but the offspring are not viable--cannot live normally or cannot reproduce themselves.
Such non-viable hybrid offspring would simply not be possible if the two species were not related. To be closely related enough to have offspring at all, the two species had to have a common ancestor. Yet, because they have different traits and cannot successfully reproduce, they are clearly different species. This means that different populations of those common ancestors diverged and evolved into two new species. All those farmers who were at the Scopes trial spent most of their days staring at the back end of proof of evolution as they plowed their fields behind a mule.
The human animal is one of the best arguments for evolution. We are very badly designed. We have only two legs, when everyone should know that a minimum of three legs is needed to keep anything, a stool or an animal, stable. For an animal, which needs to move, four legs is best because then the animal can move one leg at a time without sacrificing stability. Having only two legs makes us inherently unstable, even when standing still. Worse yet, having only two legs means we are in the shape of a tower with our most valuable asset, our brains, at the very top. As a result, we are just about the only animal that can die simply from falling down.
This is clearly a horrible design. Why don't humans have four legs like the other animals? The obvious answer is that we do, but we have converted two of them to other uses.
Here are a few other tidbits you can use:
"Did you know that there are fish that are capable of surviving on land, even moving purposefully from one point to another on land?"
"Why are some sea creatures mammals and others are not?"
"Why do some sea mammals and snakes have vestigal leg bones?"
"In fact, if evolution isn't true, then why would any animal have vestigal traits?"
"Why do bats, humans and seals all have similar structures in their wings, hands and flippers?"
"Why do different continents have different species filling the same environmental niche (or position on the food chain)?"
"Why are humans and chimps almost identical genetically?"
"Why does the human fetus take the shape of different types of creatures during its early development?"
They like to play up the Piltdown hoax, but actually the revelation of that hoax proves that science is not like faith. Scientific conclusions are always subject to revision. Scientists are constantly checking each other and rethinking each other's conclusions.
"The story of the Piltdown hoax is a good example of why science is reliable because science tries to discover when it's wrong and admits when it is."