This study examined the associations between a high-K fitness strategy (i.e., a Darwinian reproductive strategy where the individual invests significantly in a smaller number of offspring) and PTSD on a sample of 1400 disaster workers who had exposure to a singular traumatic event (the 9/11 attack on the World Trade Center in New York City). The participants underwent psychological evaluations consisting of 1) Clinician-Administered PTSD Scale (CAPS) and 2) PTSD Checklist (PCL).

The participants were also administered the 3) High-K Strategy Scale (HKSS) (Giosan, 2006). Other factors, such as demographics, prior trauma, prior psychiatric history, and the severity of exposure to 9/11 were also captured. The results showed that HKSS score was an important negative predictor of PTSD, accounting for 10% of the variance in the PCL and 5% of the variance in the CAPS, after controlling for demographics, prior trauma, prior psychiatric history and the severity of exposure to 9/11. The findings speak against the evolutionary view that PTSD symptoms are adaptive while strengthening the evolutionary view that PTSD is the expression of an overlearned survival response in vulnerable individuals (Silove, 1998), which, when activated, can have significant negative effects on fitness.