Commenting on Rom 5:12, New Testament scholar John Ziesler wrote the following:
Even if Paul is saying that all people sinned in Adam, it does not follow that they were seminally in him or sinned when he did. In the light of contemporary and near-contemporary Jewish thought, it is more likely that Adam is Everyman (and Everywoman), so that to say that Adam sinned is a way of saying that everybody sins. Everyone is his or her own Adam (cf. II Apoc. Bar. 5419) and cannot put the blame on the historical Adam. The suggestion has often been made in Christian history that sin and guilt can be inherited, much as blue eyes can be inherited, but this is implausible. It does not seem to have been a Jewish belief up to Paul’s time, and if he is now propounding it for the first time, he fails to make his point clearly. What is hereditary in this passage is death, and while death is the consequence of sin, each person after Adam (or even in Adam) deserves that consequence. Death comes not because of Adam’s sin, seeing Adam as an individual only, but because of their own. Moreover, Paul is drawing a parallel between Adam and Christ and their respective effects, and he certainly does not say that righteousness passes automatically or genetically from Christ to his people. It is therefore unlikely that he is saying that sin passes from Adam, seen as an individual, to all people automatically, or genetically, or by sexual transmission . . . In this verse, then, Paul is saying that death did indeed spread to all people, in so far as they, like Adam (or even in Adam, if Adam is Everyman), sinned. In fact they do all sin, and naturally therefore they all die. Adam started the infection in the human race, and with it the penalty of death; to that extent there is an element of transmission and even determinism. On the other hand men and women are not absolved of responsibility, for they too have voluntarily embraced sinfulness. In short we have here a mixture of fate and guilty. (John Ziesler, Paul’s Letter to the Romans [London: SCM Press, 1989], 147)
For those curious, 2 Baruch 54:19 reads as follows:
Adam is, therefore, not the cause, except only for himself, but each of us has become our own Adam.
For those familiar with the theology of the Temple Endowment, such is rather striking.