Christians who believe in evolution: Where does original sin come from?

Thats a great question.

I don't think believing that evolution is true means you can't believe that Adam and Eve existed in some form.

I know a few Christians who believe that Adam was the first Homo Sapiens formed by God "from the dust" (i.e. formed from micro-organisms over the course of millions of years), and that God took Eve from Adam's "rib" (i.e. Adam's recent ancestral family, the Homo Erectus or equivalent). - personally I think this is most plausible.

Others believe that Adam and Eve were only given human bodies (God "weaving animal skins" for them) after the Fall, when they were cast out of Eden... and before that they were some kind of celestial being, explaining their direct confrontations with God and Satan.

Others believe that Adam and Eve were not individual people but rather groups or the first generations of homo sapiens, evolved from homo erectus... and that the story of Eden is a poetic description of what happened over a very long period of time - and that the Fall of Man happened in a sort of process, rather than a snapping instant of giving into temptation.

And finally another group of Christian evolutionists (myself included) find it all very interesting to look at these different theories, but ultimately everything doesn't hinge on these secondary issues and the important thing to understand is that we agree through science that evolution most probably is a real natural process that happened and continues to happen, and that it's not mutually exclusive that we also believe there is sufficient evidence to believe in the Fall of Man, Sin, Jesus' Salvation etc.

[By the way - original sin does not mean everyone is born a sinner, it means everyone is born with the temptation and tendency to sin. And no person in history has resisted that temptation in thought, word or deed, other than Jesus]

Obviously Adam...

Thats the thing atheists don't seem to be able to understand, even with Common Descent there is nothing that prevents the Creator from creating Adam and Eve as a special creation apart from whatever hominids may have 'evolved', or a literal reading of the Genesis creation account. It only creates issues for one of the four literal interpreations of Genesis Chapter 1 and that is the YEC interpretation.

My questioning Common Descent is 100% based on the science and has nothing to do with what the Bible may or may not say. I am an empiricist and when I see an entire model based entirely on inference with the excuse (it happens too slowly to be observed) to explain why there is no empirical evidence it raises red flags with me (and many other empiricists)

What if Original Sin is a ephemism for part of human nature?

As one of my professors--an ordain minister and the chair of the Religious Studies Department--used to point out to his classes, in proportion to how literally you read the Bible, you miss the point. The Garden of Eden myth is a good example.

Like any myth, its purpose is to convey an important truth about humanity and our relationship to the universe. Like any myth, it does so in the form of a story. The target audience is people who are capable of distinguishing the fictional details from the point of the story, and distinguishing storytelling from historical chronicles. That is, the target audience is people who are functionally literate--at least as literate as readers of Dr. Seuss. (It's not very demanding, really!)

The POINT of the story is, in fact, the concept we label "original sin." It's the observation, available to anyone who ever paid any attention to people at all, that we have an innate tendency to screw up. Original sin is the motivation for the story, not a consequence of it.

Original sin is simply observed fact. It is true, regardless of whether one of our screwups happens to be insisting that a fiction be treated as a fact.

If a Christian believed the evolution theory, then he/she would have to believe that life came from non life, and that doesn't make any sense at all. For Christians, God is the life giver, so life would have to originate from the living God, and not an inanimate thing.

Dave-

Did that first man and woman have dealings with a talking snake? Were they commanded to avoid the Tree of Knowledge?

No Christian who rightly understands the truth of God believes in the lies of Evolution.

Well, even animals "sin". For example there are evidences of apes that kill just for the sake of it, just for fun.