From the working definition of “apocalypse” we have developed in class gives me a starting point for separating the “causes” and “symptoms” of apocalypse.   Within the novels Oryx and Crake and The Children of Men the cause of apocalypse is broad and encompasses all of humanity.
The cause of an apocalypse presages the symptoms, like a pathogen infecting the body.   In The Children of Men Theo relates how the degradation of society predated the Omega generation and the loss of fertility.  The loss of passion in “humanity” began the sequence that led to the apocalyptic events and is thus the cause of the apocalypse in The Children of Men. 
The loss of fertility in humanity was the greatest empiric symptom of the apocalypse.  Theo also talks about the riots, mass suicides like the quietus, and madness such as treating dolls like they are their biological children.  These are symptoms of the apocalypse in The Children of Men. 

In Oryx and Crake the biological plague that wipes out humanity differs from the loss of fertility in The Children of Men in that one is deliberately created by Man and the other is an anomaly.  This creates a tremendous difference in the way we can look at the cause and effect of the Crakian apocalypse. 
The apocalypse of Oryx and Crake is caused by the rampant indulgence of vices in society.   The corruption causes the reaction in Crake that leads him to destroy humanity.  Another contributing cause is the biological engineering that humanity indulged in.  It contributed to humanities self serving instincts and enabled Crake to so effectively destroy humanity.  
The symptoms of the Crakian apocalypse were violent and relatively brief compared to The Children of Men.   The Red Plague was not the only element in the extinction of humanity.  Crake was aware that humanity in its fear would tear itself to pieces.   The panic would be as effective as the Red Plague to drive humanity into extinction.  The symptoms provided the opening for a re-birth of humanity through the Children of Crake.