In Chapter 11, Zimmerman dealt with the question of how Original Sin was propagated.  He started by admitting that even the Catechism of the Catholic Church has not figured this question out.

There seems to be a material substrate that depends on genetic traits: the triune brain.  Then there are phenotypic expressions with innate biases: concupiscence.  Finally there is an acquired aspect: whatever is necessary to interpellate pride, to define one’s own “reality” independent of connectedness, to enter into the madness described above.

Consequently, one cannot say that transmission is exclusively through generation (genetic & phenotypic) or contagion (acquired).