ABSTRACT
Having proposed an evolutionary basis for PTSD and examined it from a clinical perspective let us now revisit the mammalian defences and see what flows from these considerations. For many millions of years defence has been fundamental for survival. Despite interspecies diversity of defences, there is a great deal of uniformity when it comes to overall behavioural strategies. In mammals defensive behavioural strategies can be conceptualized as sixfold and loosely in the following sequence: avoidance, followed by flight and then aggressive defence, with attentive immobility diffusely crossing boundaries,
appeasement, and finally tonic immobility. I further suggest that vigilance and risk assessment are precursors to all these defences. The next four chapters will proceed on this basis.
