What is the biblical evidence for original sin?

From Gospel Translations

There are several lines of biblical evidence for the historic Christian doctrine that we are all born into the world with sinful natures, due to the sin of Adam.

Scripture says that we are born sinners and that we are by nature sinners
Psalm 51:5 states that we all come into the world as sinners: "Behold, I was brought forth in iniquity, and in sin my mother conceived me." Ephesians 2:2 says that all people who are not in Christ are "sons of disobedience." Ephesians 2:3 also establishes this, saying that we are all "by nature children of wrath." If we are all "by nature children of wrath," it can only be because we are all by nature sinners--for God does not direct His wrath towards those who are not guilty. God did not create the human race sinful, but upright. But we fell into sin and became sinful due to the sin of Adam.

Scripture speaks of humans as unrighteous from infancy
There are also verses which declare that we are all unrighteous from the time that we are born. Proverbs 22:15 says "Foolishness is bound up in the heart of a child." Genesis 8:21 declares, "...the intent of man's heart is evil from his youth." Jonathon Edwards, in his classic work The Great Christian Doctrine of Original Sin Defended, remarks that on this verse: "The word translated youth, signifies the whole of the former part of the age of man, which commences from the beginning of life. The word in its derivation, has reference to the birth or beginning of existence...so that the word here translated youth, comprehends not only what we in English most commonly call the time of youth, but also childhood and infancy."

Humanity is Often Described in General Terms as Unrighteous
Unrighteousness is often spoken of in Scripture as something belonging to the human race as a whole.This implies that it is the property of our species. In other words, sinfulness is considered a property of human nature after the fall. Thus, it must be concluded that we are all born sinners, since we are all born human and sin is regarded as a property of humanity. In this vein, consider Ephesians 2:1-3:

And you were dead in your trespasses and sins, in which you formerly walked according to the course of this world, according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience. Among them we too all formerly lived in the lusts of our flesh, indulging the desires of the flesh and of the mind, and were by nature children of wrath, even as the rest.

Paul is here reminding Christians of what they were like before their conversion to Christ ("you were dead in your trespasses...in which you formerly walked"). Thus, all people, until and unless they are converted, are sinners. Paul goes on to make it absolutely clear that all Christians came from this state ("...we to all formerly lived in the lusts of our flesh") and that all non-Christians are still in this state ("...and were by nature children of wrath, even as the rest.") Thus, Scripture regards all people before they are saved by Christ as sinners and thus deserving of punishment from God. Which is to say that from the inception of our existence, we are sinful.

In Psalm 14:2, 3 we read: "The Lord has looked down from heaven upon the sons of men, to see if there are any who understand, who seek after God. They have all turned aside; together they have become corrupt; there is no one who does good, not even one." Here again we see unrighteousness as a property of the human race: "they have all turned aside...there is no one who does good."

Job 15:14 similarly declares that sinfulness is a property of humanity: "What is man, that he should be pure, or he who is born of a woman, that he should be righteous?" Verses 15-16 then speaks of the human race as a whole in shocking terms expressing our general corruption: "Behold, He puts no trust in His holy ones, And the heavens are not pure in His sight; How much less one who is detestable and corrupt, Man, who drinks iniquity like water!"

Jeremiah 17:9 says that "the heart is more deceitful than all else and is desperately sick; who can understand it." This seems to assume original sin--wickedness is a property of the human heart. Ecclesiastes 9:3 declares a similar truth: "...the hearts of the sons of men are full of evil, and insanity is in their hearts through their lives." Again, the human heart is sinful, and therefore all humans are sinful.

These texts indicate, then, that human nature is corrupt. Therefore, even infants are corrupt because they are human. And if infants are corrupt, then this is the same as saying that we are born corrupt--which means we are born with original sin. One may, however, object that these texts speak nothing of infants, only those who are old enough to make moral decisions. All of those people are sinful, but this doesn't mean that infants are.

This is an ingenious objection, but it does not succeed. First, the texts do not seem to restrict themselves to people who are old enough to make intelligent decisions. They seem to speak of human nature as a whole, a classification under which infants certainly fall. Second, as Jonathan Edwards pointed out, "..this would not alter the case...For if all mankind, as soon as ever they are capable of reflecting, and knowing their own moral state, find themselves wicked, this proves that they are wicked by nature."

In other words, even if these verses were only speaking of people old enough to mentally understand sin, they would still be teaching original sin. For on that view, these verses would be saying that all people, as soon as they know good from evil, find themselves sinners. But if all people, as soon as they are capable of moral decisions, find themselves sinners, this proves that they are that way by nature.

Third, Edwards also says, "why should man be so continually spoken of as evil, carnal, perverse, deceitful, and desperately wicked, if all men are by nature as perfectly innocent, and free form any propensity to evil, as Adam was the first moment of his creation?" (Edwards, The Great Christian Doctrine of Original Sin, 188).

Infants die, therefore they are not innocent
Death--both physical and spiritual--is a result of sin (Romans 5:12; 6:23). Thus, death only comes upon those who have sinned. Since infants die, they therefore must be sinners. It could be objected that Christ was sinless, and yet He died. But He willingly gave up His life, and He did it to conquer the curse of death that we were under. In fact, God imputed to Christ our sins on the cross, and Christ died in punishment of those sins.

If humanity is not born in sin, wouldn't we expect there to be some people who have "beaten the odds" and never sinned?
If we are born innocent and good, why aren't there at least some people who have continued in this state and remained sinless? The fact that everybody sins needs some explanation. The best explanation is that we are sinners by nature. Someone might argue that the reason all people sin is because society is sinful, and thus society renders it impossible for anybody to keep themselves entirely pure. But that only pushes the question back one step. How did society get sinful in the first place? If people are born morally good, then how did it come about that they congregated into socities that influence all people to sin?

Further Resources

Jonathan Edwards, The Great Christian Doctrine of Original Sin Defended in The Works of Jonathan Edwards Volume I, pp. 143-233.

Wayne Grudem, Systematic Theology, chapter 24, "Sin."