How is original sin conveyed from our first parents unto their posterity?
Original sin is conveyed from our first parents unto their posterity by natural generation, so as all that proceed from them in that way are conceived and born in sin.1
Scripture proofs
The Westminster Assembly's proof texts (KJV). The bracketed numbers in the answer above mark the clause each set of references supports; expand a row to read the verses.
1 Ps. 51:5; Job 14:4; Job 15:14; John 3:6
Behold, I was shapen in iniquity; and in sin did my mother conceive me.
Who can bring a clean thing out of an unclean? not one.
What is man, that he should be clean? and he which is born of a woman, that he should be righteous?
That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
This doctrine across the Standards
Where the Confession and the Westminster Shorter Catechism treat the same matter, so the question can be studied alongside its parallel statements.
In the Westminster Confession
VI.1 Our first parents, being seduced by the subtlety and temptation of Satan, sinned in eating the forbidden fruit. …
Our first parents, being seduced by the subtlety and temptation of Satan, sinned in eating the forbidden fruit. This their sin God was pleased, according to his wise and holy counsel, to permit, having purposed to order it to his own glory.
→ VI.1 · Of the Fall of Man, of Sin, and of the Punishment ThereofVI.2 By this sin they fell from their original righteousness and communion with God, and so became dead in …
By this sin they fell from their original righteousness and communion with God, and so became dead in sin, and wholly defiled in all the faculties and parts of soul and body.
→ VI.2 · Of the Fall of Man, of Sin, and of the Punishment ThereofVI.3 They being the root of all mankind, the guilt of this sin was imputed, and the same death …
They being the root of all mankind, the guilt of this sin was imputed, and the same death in sin and corrupted nature conveyed to all their posterity descending from them by ordinary generation.
→ VI.3 · Of the Fall of Man, of Sin, and of the Punishment ThereofVI.4 From this original corruption, whereby we are utterly indisposed, disabled, and made opposite to all good, and wholly …
From this original corruption, whereby we are utterly indisposed, disabled, and made opposite to all good, and wholly inclined to all evil, do proceed all actual transgressions.
→ VI.4 · Of the Fall of Man, of Sin, and of the Punishment ThereofVI.5 This corruption of nature, during this life, doth remain in those that are regenerated; and although it be …
This corruption of nature, during this life, doth remain in those that are regenerated; and although it be through Christ pardoned and mortified, yet both itself and all the motions thereof are truly and properly sin.
→ VI.5 · Of the Fall of Man, of Sin, and of the Punishment ThereofVI.6 Every sin, both original and actual, being a transgression of the righteous law of God, and contrary thereunto, …
Every sin, both original and actual, being a transgression of the righteous law of God, and contrary thereunto, doth, in its own nature, bring guilt upon the sinner, whereby he is bound over to the wrath of God and curse of the law, and so made subject to death, with all miseries spiritual, temporal, and eternal.
→ VI.6 · Of the Fall of Man, of Sin, and of the Punishment ThereofIX.3 Man, by his fall into a state of sin, hath wholly lost all ability of will to any …
Man, by his fall into a state of sin, hath wholly lost all ability of will to any spiritual good accompanying salvation; so as a natural man, being altogether averse from that good, and dead in sin, is not able, by his own strength, to convert himself, or to prepare himself thereunto.
→ IX.3 · Of Free WillIn the Westminster Shorter Catechism
Q.13 Did our first parents continue in the estate wherein they were created?
Our first parents, being left to the freedom of their own will, fell from the estate wherein they were created, by sinning against God.
→ Open Q.13Q.14 What is sin?
Sin is any want of conformity unto, or transgression of, the law of God.
→ Open Q.14Q.15 What was the sin whereby our first parents fell from the estate wherein they were created?
The sin whereby our first parents fell from the estate wherein they were created, was their eating the forbidden fruit.
→ Open Q.15Q.16 Did all mankind fall in Adam's first transgression?
The covenant being made with Adam, not only for himself, but for his posterity; all mankind, descending from him by ordinary generation, sinned in him, and fell with him, in his first transgression.
→ Open Q.16Q.17 Into what estate did the fall bring mankind?
The fall brought mankind into an estate of sin and misery.
→ Open Q.17Q.18 Wherein consists the sinfulness of that estate whereinto man fell?
The sinfulness of that estate whereinto man fell, consists in the guilt of Adam's first sin, the want of original righteousness, and the corruption of his whole nature, which is commonly called original sin; together with all actual transgressions which proceed from it.
→ Open Q.18Q.19 What is the misery of that estate whereinto man fell?
All mankind by their fall lost communion with God, are under his wrath and curse, and so made liable to all miseries in this life, to death itself, and to the pains of hell for ever.
→ Open Q.19