"They say faith is their evidence."
Faith is belief without evidence, never stop pointing out that they admit this.
"...think that it's crazy to believe we "came from monkies".
It is crazy, it's a misrepresentation of "common ancestry". Aside from this, evolution isn't a belief, it's a scientific fact. Point out that they aren't "disbelieving evolution", they're refusing to accept a fact backed by evidence; because it conflicts with their "belief without evidence".
My favorite counter-apologetics argument has nothing to do with science, it has to do with the theist concept of "free will".
Atheist's Question: Why did god punish Adam and Eve?
Theist's Answer: Because they ate from the tree of knowledge of good and evil.
Atheist's Question: Why is knowledge of good and evil bad?
Theist's Answer: Because god forbade them to eat from that tree!
Atheist's Question: How could they know it was wrong to defy god if they had no knowledge of good and evil?
Theist's Answer: Free will!
Atheist's Question: If they had no knowledge of good and evil, how could they have free will?
Explaining evolution to creationists is tough, even when you have a firm grasp of it. Most of the possible counter-arguments to creationists are listed here at Talk.Origins. A lot of the "basics" are in the FAQ
If monkeys get involved just say "Well, studies have shown that 4 out of 5 primates don't want to be related to you either."
Keeps 'em quiet for a bit anyways.
The Bible says modern man has been here for only 6,000 years (we have an exact accounting from Adam to Abraham). Science has proven that modern man (emphasis-MODERN- just like us)- has been here for at least 200,000 years (we have the bones to prove it). I have also read that apes have 24 chromosomes- while we have 23- wait! there's the difference!-not so fast, it turns out that that 24th chromosome is actually fused into ours (again, we have the evidence to prove it).And how did that happen? It EVOLVED- and made us- well, us. Now ask them to: A.) Fill in the 194,000 year gap and B.) explain who Adam's son's were having kids with (unmentioned sister's??). It amazes me that people still want to hold on to a silly childish fairy tale just because they don't want to study the evidence because they don't like what the truth suggests (we're related to monkeys! gasp!). We have to go where the truth takes us, whether we like the answer or not.
I think in conversations like this its important to ask yourself what you want to get out of it.
That is: Do you just want them to know you better as a person? Do you want them to at least respect your views? To "agree to disagree"? Do you want them to reconsider their own views?
In this case, what advice i'd give on both if and how i'd explain evolution would depend on your goals with your parents.
As an aside, i just noticed someone posted this timely cartoon on your dilemma in the Atheist Humor group!
Thanks for taking a step back in this debate and getting to the heart of the matter. You are right, in that Tyler needs to first consider the bigger questions that this debate raises between he and the parents. Where does he want the debate to go, indeed? I am having the same struggles with my Christian wife on this same subject, from time to time, and I realize that I do not respect her beliefs, because they seem based solely on her desire to believe in Creationism, on faith alone, and reject evolution only because it contradicts her beliefs. It is very frustrating to deal with someone who you know is being irrational, but at the same time,I also know that we simply have to "agree to disagree" in order to make the marriage work. But how does one respect the person and at the same time, not that person's beliefs? That, at least for me, is the hard part. I hope this does not cause a wedge in Tyler's relationship with his parents. Sometimes i think you just have to let it go.
The problem is, (I think), that people who believe via faith, fear that without it life is meaningless, and would be chaotic. People of faith need to be helped to understand that a godless universe is OK - they can have values, and be moral people. They need to know that atheists are generally good people. It may also help, if they realise that "God" is a god of the gaps - that in days gone by, so much was attributed to the active intervention of "God". Now we have science which shows that in many, many, many cases, the god hypothesis has been shown to be redundant. Yet all of this does not make humans any less human or any less special to one another. Probably most of the values which people of faith hold, are also held by people without faith or belief in any god(s).
Of course the key values which will be lost, if a person were to lose their faith, and become atheist, is that "God" must be the centre of all living, and that Jesus is the way the truth and the life, and the sole soul redeemer, who will get you entry into heaven.
Since heaven is a non-entity for atheists, a deconvert would also have to accept that they will not have everlasting life, so they would be wise to make good use of the life they have. What we do in this life can have positive benefits on the world, even after we die, so such a finite life need not be pointless.