Chapter 5 — Part I — Article III (Of the Incarnation)
Section 168. Q. Why did not the first man only die, and not all, as now? A. Because all have come of Adam since his infection by sin, and all sin themselves. As from an infected source there naturally flows an infected stream, so from a father infected with sin, and consequently mortal, there naturally proceeds a posterity infected like him with sin, and like him mortal.