Christianity and Judaism
In contrast to the Jewish view of being morally balanced, Original Sin refers to the idea that the sin of Adam and Eve's disobedience (sin "at the origin") has passed on a spiritual heritage, so to speak. Christians teach that human beings inherit a corrupted or damaged human nature in which the tendency to do bad is greater than it would have been otherwise, so much so that human nature would not be capable now of participating in the afterlife with God. This is not a matter of being "guilty" of anything; each person is only personally guilty of their own actual sins. However, this understanding of original sin is what lies behind the Christian emphasis on the need for spiritual salvation from a spiritual Saviour, who can forgive and set aside sin even though humans are not inherently pure and worthy of such salvation. Paul the Apostle in Romans and I Corinthians placed special emphasis on this doctrine, and stressed that belief in Jesus would allow Christians to overcome death and attain salvation in the hereafter.
Adam
Christianity sees human nature as irrevocably stained by the sin of Adam. The idea is not found in Judaism (nor in Islam), and was introduced by the Apostle Paul, drawing on currents in Hellenistic Jewish thought which held that Adam's sin had introduced death and sin into the world. Sin, for Paul, was a power to which all humans are subject, but Christ's coming held out the means by which the righteous would be restored to the Paradise from which Adam's sin had banished mankind. He did not conceive of this original sin of Adam as being biologically transmitted or that later generations were to be punished for the deeds of a remote ancestor. It was Saint Augustine who took this step, locating sin itself in male semen: when Adam and Eve ate of the fruit they were ashamed and covered their genitals, identifying the place from which the first sin was passed on to all succeeding generations. Only Jesus Christ, who was not conceived by human semen, was free of the stain passed down from Adam. (Augustine's idea was based on the ancient world's ideas on biology, according to which male sperm contained the entire unborn baby, the mother's womb being no more than a nurturing chamber in which it grew.)