How is it that someone who lived thousands of years ago can "represent" me?

Adam got his spirit from God, so his spirit was perfect. When Adam sinned, he made his spirit faulty, and thus passed on his imperfect spirit to all of his offspring. That is why everybody has a tendency to sin....because Adam passed on his imperfect spirit to all. Jesus however had a perfect spirit, since His spirit did not come from Adam, only his body.

I don't think anything in the Bible or Christian theology says that Adam "represents" us in the sense that you are using the word, that is, that we are held responsible for Adam's actions. Rather, it says that Adam's actions brought sin and death into the world, and everyone since then has sufferred because of it. 1 Cor 15:21-22 "For since by man came death, by Man also came the resurrection of the dead. For as in Adam all die, even so in Christ all shall be made alive." It is not like a judge saying, "Your father robbed a bank, so I sentence you to jail." Rather, it is like your father moved to a crime-ridden area, you grew up among drug dealers and gangsters, you ended up joining a gang and becoming a criminal yourself, and now the judge says, "You have turned out to be as bad a criminal as your father was, and because of the crimes you committed I sentence you to jail."

I think this is what Warren was trying to say with his "European ancestors" analogy. I didn't choose to have ancestors who emmigrated to the United States. I had no control over their actions as I wasn't even born yet. But their decisions and actions have affected my life, for good or ill.

Surely you don't claim that God is unfairly accusing you of being a sinner, blaming you for something that Adam did! I don't know you, of course, but unless you are unique among human beings, you have broken many of God's laws in the course of your life. I can pretty fairly guess that you have been guilty of lying, greed, lust, egotism, etc etc. Don't get me wrong -- I've done these and plenty more too. We all have. That's the point. Adam brought sin into the world. But you are not held accountable for Adam's sinsh; you are held accountable for your own.

The Orthodox have a different perspective on Adam which makes a lot of sense, at the cost of being a tad "mystical".
http://web.archive.org/web/20091011031949/http://www.zephyr.gr/stjohn/sixdawn2.htm

Put simply, Adam is not the biological ancestor of all humans, but God chose him as the representative of all creation, not just all humans, to be the first to receive divine life (a living soul).

In essence, we do not inherit responsibility or culpability for his actions, but we do share the same nature as all the rest of Creation.

Something which I believe nobody has mentioned, in Genesis 5 Adam - either figuratively or not - passes on the broken image of God through the bloodline.

Genesis 5:3 (emphasis added) When Adam had lived 130 years, he had a son in his own likeness, in his own image; and he named him Seth.

Which is opposed to Adam being made in God's image and likeness.

Oh, and I hope someone who lived thousands of years ago can "represent" me... I need Jesus to represent me.

Paul outlines this a bit in Romans 5 in constrasting the role of Adam as representative vs. Christ as representative (emphasis mine).

Romans 5:12-21

12Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned— 13for sin indeed was in the world before the law was given, but sin is not counted where there is no law. 14Yet death reigned from Adam to Moses, even over those whose sinning was not like the transgression of Adam, who was a type of the one who was to come.

15But the free gift is not like the trespass. For if many died through one man’s trespass, much more have the grace of God and the free gift by the grace of that one man Jesus Christ abounded for many. 16And the free gift is not like the result of that one man’s sin. For the judgment following one trespass brought condemnation, but the free gift following many trespasses brought justification. 17For if, because of one man’s trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ.

18Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. 19For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous. 20Now the law came in to increase the trespass, but where sin increased, grace abounded all the more, 21so that, as sin reigned in death, grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord.

As far as fairness goes, the short answer, I think, is that it's just as fair counting (presumably, sinless?) men as sinners under the representation of Adam as is it counting (presumably, sinful) men righteous under the represenation of Christ :) For a long answer, I think there's a bit of a clever twist in there, in that Adam's representation seems to be the very embodiment of the attitude that God's design is not just or fair and the presumption that man knows of a better way...IOW, the irony is that even if we weren't represented collectively by Adam; the representation he represents actually seems pretty fair and accurate.

The even longer answer is related to covenental therology which includes the notion of "federal headship" (FH). I think an important key to the idea of FH is a distinction between an intrinsic "is" and a forensic (or legal) one. The FH view is that humanity is forensically linked to Adam (note that the curse in Genesis was applied to all of creation; not just him),

** As a bit of an aside, doctrine of "original sin" deals more with intrinsic inheritence whereas "federal headship" deals more with forensic inheritence....it's a somewhat subtle difference, and many folks hold to both, but it's not logically necessary to hold to (or reject) them in tandem. **

Convental theologians would argue that the theme of covenent and federal headship permeates the entire narrative of Scripture: Adam, Noah, Abraham, Moses, priests, kings (esp. David), Christ...and maybe even more generally husbands/fathers...all of these were, in some ways identified as particular representative "heads" of a larger community. As the head of the community rose/fell, so, too, did the community itself.

I think the clearest example for Christians is probably found in an analysis of the double imputation of Christ--our (intrinsic) sins were imputed (forensically) to him, and his (intrinsic) obedience is imputed (forensically) to us.

Christ was intrinsically righteous (he was perfectly obedient), and through his headship, his people are declared (forensically) righteous. Even though we're not obedient by our own right, we are deemed as such by virtue of being found "in Christ." It's important to note that our justification is not found in our personal obedience or works (lest any man should boast); the mechanism for this is the federal headship of Christ--i.e. he's our representative; we are his people.

Likewise, our sins are still atoned through that same mechanism, but in reverse; Christ is not intrinsically sinful ("He who knew no sin..."), but by being our representative, he is forensically cursed through the sins of his people ("...became sin"). In a very real sense the sins of the redeemed have carried with them the penalty of death in the same way the sins of the condemened have...it's just that Jesus--as head of the redeemed/as our represenative-- paid the price of his people. We are his sinful people; he's our represenative.

Adam, as a type of Christ played a similar role. As first man, he was a representative who specifically and instrinsically broke the original commandment. Through his disobedience, we're all (forensically) condemned.

A modern day parallel would be something like a diplomat/ambassador and/or national leader, who, though he is an individual, speaks on behalf of his nation. The corporate nation is bound to the promises and treaties that its leaders make even if, as individuals, we would never make some of those promises to begin with.

I found this link which explains this "federal headship" in relation to covenant theology. It's an interesting read, and summarizes thusly:

The Importance of Covenant

Covenant is the fabric of the whole Bible. Once this fundamental schema of covenant in the Scriptures comes clear, all the patterns of God's relations with the sons and daughters of Adam unfolds into a rich tapestry unifying the Scriptures.

We have seen that Adam in Romans 5:12-21 was the federal representative of his race under the covenant of works. Some theologians reject this understanding of Paul's teaching outright, because it "violates all sense of justice."20 But if we are to use our "sense of justice" as an ultimate criterion for judging the truths of Scripture, then shouldn't we deny all covenant imputation as well? If sin cannot be imputed from one to many, conversely it cannot be imputed from many to one. Under this method, how can we maintain that "He himself bore our sins in his body on the tree" "the righteous for the unrighteous" (1 Pet. 2:24; 3:18; cf. Isa. 53)? Shouldn't this violate our sense of justice, too? And if our sins were not imputed to Christ, neither can his righteousness become ours (e.g., 1 Cor. 1:30; 2 Cor. 5:21). Then we would all be cut off from Christ and personally obligated (as was Adam), to keep all of God's holy law ourselves (Gal. 5:2-3 again).

In contrast to this grim prospect, Covenant theology offers a fresh restatement of classic Protestant insights into the essential truths of justification as the imputed righteousness of Christ by grace alone and received by faith alone. What makes imputation work is covenant, for covenant is the forensic instrument by which God faithfully extends his blessings to the heirs of the covenant of grace. The curse on Adam was not the last word on covenant in the Bible. This is what excites Paul in Romans 5:12-21 and what excites covenant theologians as well:

God's grace and the gift that came by the grace of the one man, Jesus Christ, overflow to the many (v. 15) ... the gift followed many trespasses and brought justification (v. 16) ... those who receive God's abundant provision of grace and of the gift of righteousness reign in life through the one man, Jesus Christ (v. 17) ... the result of one act of righteousness was justification that brings life for all men (v. 18) ... through the obedience of the one man the many will be made righteous (v. 19) ... grace might reign through righteousness to bring eternal life through Jesus Christ our Lord (v. 21; NIV).

I didn't get to vote or have any say in my forebears leaving their homelands and emigrating to the United States (or, The New World, as it was then known in Europe); nor did I have any say in whether or not to participate in their bloodline. Yet they represented me when they did it.

If we take the Bible to be God's word, and we believe that God cannot lie, then we also have to believe that Adam and Eve were the first people on earth, and that they had the choice to not sin - but of their own free will chose to disobey God.

It is not "Christianity" which says we are sinners because of Adam's sin, it is the Bible that says such:

Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned

& here:

For since by a man came death, by a man also came the resurrection of the dead.

& here:

all have sinned and fall short of the glory of God