Answer:
The Apostolic Fathers and the Apologists mostly dealt with topics other than original sin. The doctrine of original sin was first developed in second-century Bishop of Lyon Irenaeus's struggle against Gnosticism. The Greek Fathers emphasized the cosmic dimension of the Fall, namely that since Adam human beings are born into a fallen world, but held fast to belief that man, though fallen, is free. It was in the West that precise definition of the doctrine arose. Augustine of Hippo taught that original sin was physically transmitted from parent to child through the concupiscence (roughly, lust) that accompanied sexual reproduction, weakening the will and making humanity a massa damnata (mass of perdition, condemned crowd). In Augustine's view (termed "Realism"), all of humanity was really present in Adam when he sinned, and therefore all have sinned. Original sin, according to Augustine, consists of the guilt of Adam which all human beings inherit. As sinners, human beings are utterly depraved in nature, lack the freedom to do good, and cannot respond to the will of God without divine grace.
As defined by Augustine, original sin is inherited. Not every Christian accepts that it is true. The concept of original sin was never accepted in the Greek-speaking east, and it has been largely abandoned by many of the Protestant Churches. Even in the Roman Catholic Church, whether it is an actual sin depends on the reality of the story of Adam and Eve, from whom we must inherit it. The Catholic Church is gradually moving away from a literal reading of the story of Adam and Eve as the first two, historical people on earth. Cardinal George Pell recently stated that the story of Adam and Eve is a myth, describing it as a religious story told for religious purposes.
It is too early to predict that the Catholic Church will soon officially abandon the doctrine of original sin, but if the story of Adam and Eve is only a myth, any grounds for believing that original sin is actually true are being undermined.