I am not aware how the Bible explains it, but I do know what the concept of original sin refers to.
When God first created humankind, they were completely in line with God’s plans and purposes. There was no sickness or death or sin. But then humanity disobeyed God, rebelled against Him as it were, a consequence of which was original sin: sin entered humanity and thereby introduced sickness, death, desire to rebel against God. This sundered the relationship between humanity and God as humanity strayed by a large margin from God’s plans and purposes. Because of sin, we became imperfect and separated from God. Also, because of sin we were under the danger of dying in sin and thus never returning to God.
The answer to this dilemma is the Second Person of the Trinity: God the Son, Jesus Christ.
How Jesus overcame original sin for humanity differs between Protestant/Catholic Christians and Orthodox Christians. According to Protestant and Catholic Christians, Jesus chose to suffer for whatever punishments we deserved. He took upon Himself our sins and sacrificed Himself to God to atone for those sins. All who would seek him would be guaranteed, basically, of forgiveness of their sins (as long as they repented).
Orthodox Christians believe that by becoming human and suffering and offering Himself on the cross, atoning for our sins just as Protestant and Catholic Chrisians believe, He additionally healed the corruption within humanity: humanity could, to some degree, become perfect. The sin that prevented humanity from reaching its original natural destiny is removed. Of course, residues of it remain, in that sickness and death remain and the temptation to sin exists, but humanity can unite itself sipritually with God once again.
Original sin is natural to every human being born since the Fall of Adam and Eve. Only two people in the history of the world were born without original sin: the Blessed Virgin Mary (through the immaculate conception, wherein when she was conceived she did not contract, as it were, original sin as a special grace from God in preparation for the birth of Jesus) and Jesus (through the miraculous conception).
Original sin may be removed by baptism. Confirmation and its bestowal of the gift of the Holy Spirit help to keep the person free from sin and prompted to good by the Holy Spirit.
I should repeat what I have heard many Catholics say: “We know where salvation is found; we do not know where salvation is not found. Whereas humanity is bound to and by the sacraments, God is not bound to them: He may save whomever He wishes.” Although we have been told by God that this - baptism, confirmation, etc. - is the way out of original sin and to salvation, it may not be the exclusive way. It all depends on one’s theology and/or denomination. Some are more strict than others.
And religion, in the end, is about rationalization and faith. Facts, science, etc., are irrelevant.
WRS