Augustine’s answer (that we are literally descended from Adam and Eve) anticipated a very important technical question: “Why Baptism?”.

The imputation of “descent” (with all those seamy and twisted details that never can be fully dissociated from the idea) suggested that Baptism “washed clean” this connection to Adam’s transgression plus all that dirty stuff in between.

Thus, to change metaphors, the person’s body became a temple capable of housing sanctifying grace.