One of the simplest ways of describing the evidence for evolution can be demonstrated with a small bit of logic (borrowed and modified from my colleague at UW-Madison - who teaches a history of paleontology course):
- Throughout all of recorded history, the only way people have ever seen one living organism appear on Earth is from the body of another organism. This could be a seed dropped by a plant, a fungal spore, an egg, or even a live baby.
- It follows then, that if organisms come into existence via reproduction of other organisms, all the organisms that we see today are the descendants of older organisms (some of which are dead and preserved as fossils).
- We can observe (often without much difficulty) that offspring are not 100% exactly the same as their parents (I'm willing to make a simplified philosophical exception in rare, individual cases of asexual reproduction, but even that's not exactly correct).
- If it is also true the organisms in the past were different, then it must be true that organisms have changed over time.
I like this argument for several reasons. First, it's simple. It is also relatively easy for most rational people to agree with each step. It forces any anti-evolution arguments to also be simple or easily tossed aside as irrelevant to the premise (e.g. the mechanism for change may be natural selection, but it doesn't have to be). So what if a former child actor claims evolution is false because some unspecified transitional "Crocoduck" hasn't been found. At its basic level, evolution does not require any transitional form. All it needs is that past organisms are not the same. And to refute that claim, one needs to either deny fossils outright, or invoke pseudo evolutionary mechanisms and double-talk to claim that these fossils are "different" but not different enough (e.g. Kurt Wise and his "forms" argument).
To this, I would ask what level of "difference" would be sufficient? And this definition must be applied evenly and fairly to all past organisms. Because if somehow Noah's diaspora managed to change into the animals we see today, why are some of them spread across vast distances, why are some now unable to interbreed (or if they do, produce infertile offspring)? It also uses (correctly) the same rhetorical trick that creationists use incorrectly. The folks at AiG love to use the "were you there?" argument.
The answer is obviously, no. We weren't there. But neither were they. If the creationist is going to require someone to be present for a moment of evolution in order for it to be accepted as fact, they must also have someone present for the moment of creation (or multiple moments of creation, depending on the brand of creationism). Since the creationist is trying to make a counterclaim that is rather extraordinary, one would need extraordinary evidence for falsifying the assertion that the only way for a living organism to appear on Earth is from the body of another. And no, the book of Genesis is not such a document - in part because it is not internally consistent (it also relies on the assertion that reproduction is the primary way in which living organisms appear on Earth). Think about this: if reproduction weren't absolutely necessary, why bother with the Ark in the first place? Why not boot up Eden v2.0?
What this argument does not do is directly address Intelligent Design. ID is the creationist attempt at rebranding "Creationism" so that they might weasel around the basic premise of evolution - attacking the internal mechanisms of change by some kind of magical hand-waving. The judge in the Dover ID case did an excellent job of spelling out why ID is a load of crap.
When it gets down to it, the way in which creationists make arguments against evolution is contradictory. They attempt to falsify a factual statement or conclusion with a different statement that is neither factual nor falsifiable itself. If the statement cannot be tested, doesn't allow for falsification (testing, fact-checking, comparison to other evidence, etc.) it is not science. In the case of AiG, their claims point to a specific religious source. There are non-christian creationists out there, but none are any more scientific.
UPDATE: Some commenter named "David" offered links to some rather interesting sites. Not worth publishing as they are: being devoid of context, I'm not sure if David was trying to be ironic or not. But the links were fascinating (not in a good way). I'll have to talk about them at some point.